a natural substance in the cell or a fluorescent dye that binds to a specific cell material is stimulates of a beam of light, and the longer-wavelength fluorescent light is observed directly from the dye.
uses fluorescent materials but adds a system of focusing both the stimulating and emitted light so that a single plane through the cell is seen. The result is a sharper two-dimensional image than with standard fluorescense microscopy.
Stained Bright-Field Microscopy
a stain added to preserve cells enhances contrast and reveals details not otherwise visible. Stains differ greatly in their chemistry and their capacity to bind to cell materials, so many choices are available.
Schleiden and Schwann Cell Theory 1838
All living organisms are composed of cells: Cells are the smallest units that can sustain life, cells are the main structural and functional units of life, and all cells arise by division of pre-existing life (life cannot arise spontaneously).
Louis Pasteur Experiment
Hypothesis- microorganisms come only from other microorganisms and cannot arise by spontaneous generation.
Method- Have 2 flasks with plastic tubing on the top. Break the tubing off one of the flasks, and keep the tube on the other flask. Dust enters into the flask without the tube, And the tube prevents dust from entering the second flask.
Results- Microbial life grows only in the flasks exposed to microorganisms. There is no spontaneous generation of life in the sterile flask.
Conclusion- All life comes from pre-existing life. An environment without life remains lifeless.
limited by diffusion (process is responsible for the movement of molecules through the cytoplasm and in and out of cells)
Prokaryotes and Eukaryotes
both have DNA as their genetic material, are membrane bound, have ribosomes, similar basic metabolism, amazingly diverse forms.
Major Characteristics of Prokaryotes
Unicellular, DNA floats freely in the cytoplasm--in a localized region calles nucleoid, plasma membrane is encased in a rigid peptidoglycan cell wall, outer membrane are absent in some, or a second outer membrane, or a carbohydrate capsule. Have internal membrane folds, flagellae, and pili.
long, whip-like projections that spin. Clockwise= tumbling, Counter Clockwise= swimming.
thread-like structure projecting from the surface that help bacteria adhere to each other and various surfaces.
discovered penicillin in 1928. Penicillin kills bacteria by inhibiting the synthesis of the bacterial cell wall. Antibiotic drugs to treat bacterial infections take advantage of the difference between eukaryotes and prokaryotes.
Eukaryotic Organisms-Defining Characteristics
are unicellular or multicellular, have a nucleus, larger cells, complex cytoplasm containing internal organelles-compartamentalized by membranes, localized, many reactions can take place at once-cytoplasm contains a dynamic skeleton, contains endo-membrane system.
power house of the cell, help synthesize ATP, mediates programmed cell death, ~ 1. 5 μm in diameter; 2-4 μm long (~ size of a bacterial cell) but can have different shapes and constantly changes shape, May be only a few per cell or many per cell, encased by a double membrane- (outer is smooth serves as a barrier and inner is folded inward to produce cristae and has ATP synthesizing enzymes, causes H+ gradient), innermost compartment is the matrix-contains ribosomes and DNA
in plant cells only, Storage of toxic waste materials (may be distasteful or poisonous for predators)
• Storage of food and nutrients
• Provides the stiffness (called "turgor" ) of the plant cells for support (controlling its internal water content) so that stems and leaves retain their structure
rigid, maintains structural, limits size of plant cell, acts as a barrier and it contributes to the plant form and growth
contains most of the cell's DNA, largest organelle, important for DNA replication, bounded by a double membrane, fairly rigid, location of the genes for making ribosomal RNA, has one or more distinct non-membrane bound regions
DNA in the bacterial cell is generally confined to this central region. Though it isn't bounded by a membrane, it is visibly distinct (by transmission microscopy) from the rest of the cell interior.
The nuclear envelope is a double-layered membrane that encloses the contents of the nucleus during most of the cell's lifecycle. The outer nuclear membrane is continuous with the membrane of the rough endoplasmic reticulum (ER), and like that structure, features numerous ribosomes attached to the surface. The outer membrane is also continuous with the inner nuclear membrane since the two layers are fused together at numerous tiny holes called nuclear pores that perforate the nuclear envelope. These pores regulate the passage of molecules between the nucleus and cytoplasm, permitting some to pass through the membrane, but not others.
The nucleolus is a prominent sub-nuclear structure that is not bound by a membrane and resides within the nuclear matrix.
Nuclear Pore Complexes
nuclear envelope contains hundreds, the are channels, enable the passage of selective macromolecules into and out of the nucleus-controlled.
Pores are composed of 8 protein complexes arranged in a circle, with protein fibrils on the nuclear side;a region of the nuclear pore complex suspended from the nuclear ring and extends into the nucleoplasm; attached to distal ring
nuclear localization signal (or NLS)
Signals on the proteins destined for the nucleus (like an address) target the proteins to the nucleus
make up the contents of the nucleus of a cell. The primary functions are; to package DNA into a smaller volume to fit in the cell (chromosomes), to strengthen the DNA to allow mitosis and meiosis and prevent DNA damage, and to control gene expression and DNA replication.
double membrane organelles, found in some plants and protists, main functions: photosynthesis and storage
Which organelle does not have a double membrane?
Nucleus, Chloroplast, Mitochondria
all of them have a double membrane
• Organelles that carry out photosynthesis • 2-10 micrometers long and 2-3 micrometers thick-can be 100-200 chloroplasts per cell
• Are bounded by two membranes, a smooth outer membrane and a highly folded inner membrane
• grana, thylakoids, stroma.
• About 60-100 genes are present, which code for proteins involved in photosynthesis
chloroplast-The individual sacks, membranes contain chlorophyll and other light-absorbing pigments for photosynthesis.
The most inside region which contains DNA and ribosomes (like bacterial DNA and ribosomes).
Why are some sea anemone green?
they eat algae, which is green. sea anemone are not able to photosynthesize.
Organelles filled with pigments (red, orange, yellow)- they synthesize and store the pigments - attractant for pollinating insects—pollenation and seed dispersal-is a plastid
Depots for synthesis and storage of starch and fats-- located in roots and non- photosynthetic tissues- is a plastid
Theory for the Origin of Double-Membrane Bound Organelles:
• Mitochondria and chloroplasts are believed to have originated when larger prokaryotes engulfed, but did not digest, smaller ones. For example, chloroplasts are believed to be endosymbiotic cyanobacteria (blue-green algae).
• Mutual benefits permitted this symbiotic relationship to evolve into eukaryotic organelles of today.
(small; ~ 0.5 μm), single membrane vesicles- part of the endomembrane system
• Contain digestive enzymes - "the intracellular digestive system"
• Function- to breakdown macromolecules (proteins, polysaccharides, nucleic acids, lipids, and even bacteria)
A common genetic disease of lysosomes:
• The lysosomes cannot break down certain membrane glycolipids (complexes of sugars and lipids) caused by mutations in the gene for hexose-aminidase A
• The glycolipids accumulate abnormally in the lysosomes within brain cells
• Blindness, dementia, death by 3-4 years of age
• 1:1000 in Eastern European Jews and French Canadians (genetic testing is readily available)
(very tiny - 0.2 - 1.7 μm in diameter)
• granular or crystalline interiors
• contain enzymes for destroying toxic peroxides, such as hydrogen peroxide-hydrogen peroxides can destroy cells and organelles
What is the name of the network that is composed of three different types of skeletal fibers?
What are the three different types of skeletal fibers in the cytoskeleton?
actin fibers/microfilaments, microtubules, and intermediate filaments
•made up of strands of the protein actin; often interact with strands of other proteins.
•Looks like two strings of pearls
•Have a negative and a positive end (not charges)
• They assemble and disassemble by noncovalent, reversible, addition/loss of actin monomers at the ends of the filaments
• ATP is hydrolyzed to ADP and Pi, releasing energy to the filaments, creating a type of dynamic activity-treadmilling
•ACTIN FILAMENTS (assembly at one end of the filament (the plus end) and disassembly at the opposite end (the minus end)
•MICROTUBULES undergo a process where tubulin subunits preferentially add to the microtubule plus end and preferentially come off at the minus end. (Minus end shortens and plus end has a net growth). It is a major pathway of microtubule turnover in plant cells.
•Continuously changing- but the cell shape is maintained
Actin Filament Functions
1. Determining cell shape - can either shorten or lengthen
2. Cell movement (cell motility)- aemeba movement, movement of cytoplasm with in the cell. Active filaments shorten when muscles contract
actin filaments in cell shape, (bundles of actin filaments) help keep cells elongated
•made up of strands of the protein actin and other proteins.
•They change cell shape and drive cellular motion, including contraction, cytoplasmic streaming, and the "pinched" shape changes that occur during cell division.
•Microfilaments and myosin strands together drive muscle action.
( stable actin bundles projecting from the cell surface)
•protein cap, actin microfilaments, cross-linking actin-binding proteins, plasma membrane and intermediate filaments.
helps with structural support
What are the projections of the plasma membrane that increase the surface area of the cell?
(25 nm diameter)
•long, hallow cylinders made up of many molecules of the protein tubulin (tubulin diskers). Tubulin consists of two subunits, alpha-tubulin and beta-tubulin-(tubulin dimers).
The two ends of microtubules have different properties-One end is called the plus end, the opposite end is called the minus end.
(10 nm diameter)
•made up of fibrous proteins organized into tough, ropelike assemblages that stabilize a cell's structure and help maintain its shape.
•Many different kinds of proteins all build similar cable-like filaments- strong ropelike- twist and twist together
•very stable- used for structural support- like the lamins that support the nuclear envelope, once they form they do not turn over
have monomers and twist together to form dimer, so they are very fibrous, they line up to form a tretramer. Tertramers link end to end in order to make a strand of intermediate filament. They stack (8 of them) in order to make an intermediate filament cable.
What are the two types of dynamics that are carried out by microtubules?
Dynamic Instability and Treadmilling
also called "centrosomes"
-found very close to the nucleus
-bright spot where microtubules emerge from
• are barrel shaped structures made of 9 sets of triplet microtubules
•Right angles to each other
•Bunch of proteins surrounding barrels
pull chromosomes apart so that each daughter cell will have equal Numbers of chromosomes
What are the Microtubule Machines in Eukaryotes?
Cilia and Flagellae (different from prokaryote flagellae)
•Long cell projections used for swimming movement and moving materials across the cell's surface
-cilia are short (~10 micrometers)- very numerous and all beat together, stiff and then flexible
-flagellae are long ( ~ 50 micrometers)- used for swimming
cilia-cause the microtubule doublets to slide over each other, causing shape change-cilia and flagella will bend
bottom of cilia-microtubule triplet-does not have the two singlets in the middle, 9 triplets
motor proteins do the work, they are enzymes that use ATP hydrolysis (energy released causes shape change/movement) and make microtubules slide past each other (called walking) - this causes bending→ reversible shape change.
•In isolated cilia without nexin cross links, movement of motor proteins causes microtubule doublets to slide past one another.
• is present to cross link the doublets, they cannot slide and the force generated by dynein movement causes the cilium to bend.
•They work by bending
Movement of Vesicles along Microtubules
•Dynein bridges microtubule doublets
•Dynein detaches from one microtubule
•Dynein reattaches, causing sliding
•Kinesin cross links the vesicle to the microtubule
•Detachment and reattachment of kinesin causes it to "walk" akong microtubule.
•Can cause transport of vesicles throughout the cell. Kinesin attaches to a microtubule and the legs will bind, drags vesicle along, attaches and reattaches, looks like walking.
•Dynein moves toward minus end
•Kinesin moves toward the plus end
•Vesicles can switch directions if they have both
•Requires ATP in order to move
Which of the following is not a cytoskeletal element?
Microtubules, Microfilament, Lamin, Actin Filament
All are in the cytoskeleton
1. The plasma membranes that encase all cells
2. The internal membrane system the endomembrane system
make up all membranes
the head group can change and they length and saturation of the hydrocarbon chain—causes property of membrane to change.
Membranes become less fluid when it is cold, so they can change their membrane composition so that it remains fluid and does not freeze. Larger the chains the more hydrophobic it will be and the more fluid it will become. Can control fluidity.
~ 10 nm thick→ very thin
-contains and holds the contents of the cell (keeps everything inside cell)- separates the contents from the outside world, allows the cells to have a different concentration gradient than the surroundings
-selectively blocks passage of some molecules from one side to the other, and permit passage of others, control what it wants in the cell
Selective permeability: only allowing certain molecules inside
four ring structure that embeds in the membrane, gives it rigidity, without it the membrane would be floppy. Like goldilocks--Not too hot, not too cold. Prevents membrane from becoming too fluid---keeps membrane "just right"
conformations can change, so they can recognize the cells are not right. Helps the cells of the same tissue to recognize each other
What are the three basic ways to transport materials across membranes?
Passive Diffusion, Carrier Mediated Diffusion (Facilitated Diffusion, and Active Transport
the simplest transportation mechanism; involves crossing of molecules tat can dissolve in the lipid portion of the membrane-must be lipid soluble
Important Rules for Passive Diffusion
the molecules do not become concentrated on either side- molecules will keep moving, it is random until equilibrium is reached
-the flow is with the concentration gradient, move from higher to lower concentration
-no energy (ATP) required
-no carrier proteins
- diffuse by themselves
What kinds of molecules can passively diffuse across cell membranes?
-water because of its SMALL SIZE passes through imperfections even though it is slightly polar--osmosis
-lipid soluble UNCHARGED molecules (e.g. uncharged lipids, nucleosides)
What kinds of molecules cannot diffuse passively across cell membranes?
Most water-soluble molecules
Polar molecules usually do not pass through- need a pore in order to do so
Molecules carrying positive or negative charges(sugars, amino acids, proteins, peptides, nucleic acids)
--When such molecules need to cross membranes, they must have help
Carrier Mediated Diffusion/Facilitated Diffusion
•Transported molecules are helped by "receptor proteins" or "carriers" in the membrane that can bind to the molecule→ allows molecule to pass through
•This is still a type of diffusion- no energy required
•transport can occur in either direction with the concentration gradient-passage occurs in either direction—move from higher to lower concentration.
•outside of cell high glucose concentration; inside the cell low glucose concentration
not very permeable across the membrane, so it needs a carrier, so it uses an integral membrane. Protein carriers are extremely specific. As the molecule comes in the cell breaks it down and uses it, therefore, the concentration of the molecule is higher outside the cell than inside the cell.
Facilitated versus Simple Diffusion
rate of diffusion is linear in simple diffusion, in facilitated the rate goes up to a maximum, the number is fixed. All carriers are occupied at the maximum, fully loaded with a solute so it cannot go at a faster rate. At lower concentrations it is linear like the simple diffusion.
Which of the following is NOT true of passive and facilitates diffusion across a membrane?
Both occur without energy input
Movement of molecule is doen the concentration gradient
The rate is saturable
The Rate is Saturable
•carriers use ATP to "pump" molecules against their concentration gradients
• transport only goes one way (is unidirectional)- used by the cell to bring in/export in only one direction
transport one substance in one direction. Uni-One. Calcium pumps on the ER membranes-pump calcium into the lumen.
transport two different substances in the same direction. Coupled transport. Use a already established gradient to bring ions into the cell. Sodium ion concentration is higher outside, so they couple it and bring it into the cell.
Primary Active Transport
all of the energy-to pump ions across concentration gradient, comes from Hydrolysis of ATP, even when two molecules are transported
1. 3Na+ and 1 ATP bind to the protein "pump".
2. Hydrolysis of ATP phosphorylates the pup protein and changes its shape.
3. The shape change releases Na+ outside the cell and enables K+ to bind to the pump.
4. Release of Pi returns the pump to its original shape, releasing the K+ to the cell's interior and once again exposing Na+ binding sites. The cycle repeats.
•Establishes the gradient in our cells, 2K+ in, 3 Na+ out
•Higher K+ concentration inside the cell, higher Na+ concentration outside the cell.
In the Sodium-Potassium pump what is transported in the cell and what is transported out of the cell?
2K+ in the cell
3Na+ out of the cell
Secondary Active Transport
the gradient established by the ATP-dependent primary system powers the transport of the system.
Na+, moving with the concentration gradient established by the Na+-K+ pump, drives the transport of glucose against its concentration gradient.
•SYMPORT Active Transport
Active Transport Channels
can be "gated" either by chemical substances or voltage differences across the membrane
the cell can control it, can be controlled by a chemical substance,-ligand-gated channel, voltage difference-voltage-gated channel.
1. A polar substance is more concentrated on the outside than the inside of the cell.
2. Binding of a stimulus molecule-(ligand) causes the pore to open...
3....and the polar substance can diffuse across the membrane.
•Only allows specific molecules to pass through
•Electrochemical gradient that forces ions through the channel
Which does NOT require a concentration gradient for transport? What do they require?
Active Transport; driven by hydrolysis of ATP
The process by which complex molecules, large particles, polysaccharides, bacterial cells, and water can enter cells.They are too big or too polar to fit/move across membrane.
•A membrane vesicle -part of the plasma membrane it will change shape (invaginate) -forms around a particle or a bacterium, used by eukaryotic cells to bring in large particles.
•Membrane vesicle is brought into the cell
The plasma membrane surrounds a part of the exterior environment and buds off as a vesicle
large particles and small cells are engulfed inside vesicles, also called "cell eating", feeding mechanism. The engulifing of bacteria by a macrophage (a white blood cells that "eats" bacteria).
(or "cell drinking"): cells take up water into vesicles, bring in small substances or fluids. Process is relatively non-specific.
takes certain kinds of macromolecules into cells. It is very specific, it must be recognized by the receptor. Highly regulated.
How does Receptor-Mediated Endocytosis work?
•First- the macromolecule binds to a receptor on the cell surface forming a "coated pit". -coated with clathrin. Has to stick out of the plasma membrane
•A protein called clathrin coats the inside surface of the plasma membrane at the coated pit, inside of the plasma membane.
•Forms a cage-deforms the plasma membrane so that is will invaginate to form the vesicle.
•A clathrin-coated vesicle forms- forms cage around particles and moves into the cell cytoplasm
•The vesicle moves into the cell cytoplasm and then becomes uncoated— can fuse with a lysosome to digest the engulfed material into monomers, releasing its contents into the cytoplasm
Low Density Lipoprotein (LDL) Endocytosis and Atherosclerosis
1. LDL particle binds to the LDL receptor at the cell surface, leading to formation of a coated pit
2. LDL particle is taken up into the clathrin-coated vesicles
3. Once inside the cell, the vesicle uncoats
4. The vesicle then fuses with a lysosome, which digests the contents of the vesicle-releasing the cholesterol which then is inserted into the plasma membrane
•buildup of cholesterol in blood plasma
•deposition of cholesterol on artery walls (artherosclerosis), narrowing of the arteries
•One defect leading to disease is genetically determined -absence of the LDL receptor resukts in a higher cholesterol concentration.
Absence of a functional LDL receptor prevents cholesterol from entering the cells, and it accumulates in the blood.
Processes by which complex molecules packaged into vesicles inside cells fuse with the plasma membrane and are exported out of the cells.
full of particles that are needed for export, need to be used elsewhere in the body
The Endomembrane (Internal Membrane) System
•Dense network of closed membrane tubules, closed vesicles, and closed sacs- Divides the cytoplasm into two compartments- inside of the membranes sacs/tubes and outside.
Main systems are the ER and Golgi
Functions of the Endomembrane System
1. Sequestration of molecules/particles into the cysternal space of the vesicles or sacs
2. Transport of sequestered molecules/particles from place to place within the cytoplasm or to the nucleus or into and out of the cell
3. Chemical modification of the sequestered molecules (e.g. glycosylation of proteins) as they pass
Functions of the Rough ER
A pipeline to the nucleus, closer to nucleus, continuous with the nucleus. And is continuous with the smooth ER, but not the golgi→ needs a vesicle.
•Receives into its lumen newly synthesized proteins, segregating them away from the cytoplasm- transports them to other locations in the cell.
•Proteins are chemically modified to alter their function and "tag" them for delivery to specific destinations- need to make sure proteins get to the right place
•Where Most membrane-bound proteins are made
Smooth ER: functions
1. for detoxification of molecules—liver cells contain a lot of SER- modifies the molecules to make them more polar, so they are easily removed.
2. site for hydrolysis of gylocogen in animal cells- store sugar
3. synthesis of lipids and steroids
Functions of the Golgi Apparatus
•Chemical modifications of proteins or synthesis of carbohydrates destined either for secretion in vesicles or use inside the cell
•contains different enzymes in the sacs.
Golgi Apparatus-Cis Section
on the same side, closest to the nucleus, begins the modification
Golgi Apparatus-Trans Section
on the opposite side, closest to the plasma membrane, has a sorting function, ends the modification
Which of the following organelles is NOT part of the endomembrane system?
ER, Golgi, Lysosome, Peroxisome, Mitochondria
How are molecules transported between the different organelles of the endomembrane system?
What are some other functions of membranes?
•Some organelles membranes help transform energy
•Some membrane proteins organize chemical reactions
•Some membrane proteins process information
1. A pigment attached to a membrane protein absorbs energy
2. the protein transfers the energy ADP to form ATP, which the cell can use s an energy source.
Organizing Chemical Reactions
1. each protein carries out a single chemical reaction
2. the product of the first reaction must diffuse by random motion to reach the site of the second reaction.
3. The membrane organizes the two reaction so that they occur at the same time and place
1. signal binding induces a change in the receptor protein...
2....causing some effect inside the cell→ usually production of second messangers
•from outside→ inside cell
Connective Tissue in Animals
• Strong fibrous network between cells on the outside cell surface that holds cells together to form tissues and organs
• Made in the cells and then secreted to the outside
(e.g., collagen, found in animals, and is the main component of connective tissue- it supports the skin, bones, cartilage, and blood vessels)
Collagen is the most abundant human protein
Functions of the Extracellular Matrix
-Holds cells together in tissues (glue) involved in cell recognition & adhesion
-Contributes to physical properties of cartilage, skin & other tissues
-Helps filter material between different tissues
-Orient cell movements during embryonic development and during tissue repair
-Cell to cell signaling
Extracellular Structures in plants
Plant Cell Walls
• Strong and thick (usually several μm thick); complex structure and chemistries, external to plasma membrane
Functions of Plant Cell Walls
1)Gives rigidity and strength, protection against mechanical stress—protection
2)Allows organism to build and hold its shape—growth of plane
3)Glues cells together
4)Limits the entry of large molecules, toxic materials—barrier to infection, prevents diseases
5)Provides a stable osmotic environment by preventing osmotic lysis
line channels between adjacent plant cells, allows for exchange of proteins, communication, water, etc.
•Similar to gap junction.
•Desmotubles that are derived from the SER from one cell to the SER of the other cell.
• allows for the transfer of larger molecules, viruses, ions, etc.
What are the three main kinds of animal cell junctions?
Tight junctions, desmosomes, and gap junctions
Functions of Cell Junctions
1) helps cells to adhere to each other- stick to each other
2) facilitates communication between cells and facilitates or blocks transport of molecules between cells- exchange of molecules
the proteins of tight junctions form a "quilted" seal, barring the movement of dissolved materials through the space between epithelial cells. Lots of proteins used. Prevents leaking of molecules between cells, ring the whole cell, prevent free diffuson between the two domains.
Functions of Tight Junctions
1) Link cells together very tightly
2) Do not allow passage of materials in the space between the two cells
3) Do not allow movement of membrane proteins inside the membrane bilayers themselves
1) Holds cells together, but allow wide space between the cells, molecules can move in between the cells.
does not limit movement in the space between the two cells, cannot pull them apart. Linked by cell adhesion molecules. Spans across intracellular space. Bound to keratin fibers(intermediate filament). Very strong fibers, can withstand a lot of pressure.
•Desmosomes link adjacent cells tightly but permit materials to move around them in the intercellular space.
•permits passage of molecules (up to 1000 daltons) between two cells, small molecules.
•facilitate communication between cells.
•made of special connecting protein channels called connexins, form hydrophilic channels.
•Coordinate activity between cells.
•Let adjacent cells communicate.
Which of the following cell junctions facilitate cell to cell communication?
-Tight junctions, Desmosomes, Gap junctions
Chromosomes in Prokaryotes
• have one chromosome
• It usually takes the form of a closed circle made of double stranded DNA with some proteins.
• The stretched out length of a prokaryotic chromosome is ~ 1500 μm (the cell is 1-2 μm) Means that it is highly folded, very compact in order to fit inside the cell.
• So, it must be tightly folded to fit inside the cell
cell division in a prokaryote
1. DNA replication begins at the origin of replication (ORI) at center of the cell.
2. The chromosomal DNA replicates as the cell grows.
3. The daughter DNAs separate, led by the region including ori. The cell begins to divide.
4. Cytokinesis is complete; two new cell are formed
Which processes occur when bacterial cells divide?
replication of DNA, segregation of replicated DNA, addition of new material to the cell wall
tightly controls the eukaryotic cell
-these enzymes place phosphate groups on various cell cycle control targets
always work together as complexes/pair
-are control points: each act at different stages of the cell cycle: they control progression through the cycle
protein is made only at a certain point in the cell cycle. Only made at a certain point, not always present.
1. binding changes Cdk, exposing its active site
2. A protein substrate and ATP bind to Cdk. The protein substrate is phosphorylated.
3. The phosphorylated protein regulates the cell cycle. Each Cdk has specific protein targets.
How many check points are in the cell cycle and where are they located?
-one located in each phase
What is the most important Check Point?
Restriction (R) is the most important check point because it is before replication
RB (retinoblastoma protein)
causes a specific type of cancer; cancer of the eye, childhood cancer
-it's normal function is to inhibit the cell cycle in G1 at the restriction point
-when it gets phosphorylated by the G1-S cyclin-Cdk, it becomes inactive and the cell can progress into S
-If cyclin dependent kinases is active when it is not supposed to be, it can lead to cancer
-P53 defect causes cancer
If all 46 chromosomes were stretched out the DNA would be
2 meters long- size of a basketball player
-showed how compact DNA is
keep DNA from getting tangled
are positive which are attracted to the negative DNA
have threads that interact with each other in order to become more compact
are bead-like structures consisting of the DNA double helix wound around a core of 8 histone molecules-come together and DNA wraps around it twice
Chromatin has many levels of "folding" in the nucleus during interphase
Next higher degree of folding- 30nm diameter fibers
Next higher- 300nm diameter fibers: LOOPS-scaffold associated chromatin
Still higher- 700nm diameter fibers: COIL-one chromatin
protect chromosome from deterioration
located at the end of the chromatids
are consumed during cell division but can be replaced by an enzyme
Is there a relationship between the size/complexity of an organism and the number of chromosomes?
-i.e. potato has 24 chromosomes
How many pairs of chromosomes do humans have? How many chromosomes do humans have total?
-23 pairs (one of each pair was donated by the mother, the second member of each pari was donated by the father.
-46 total chromosomes
All chromosome pairs have the same genes, but different alleles, except for?
sex chromosomes X and Y
-during mitosis chromosomes become condensed, so you can arrange/extract them so they come together with their corresponding pair. They are then stained and observed under a microscope
-can be used to diagnose diseases: such as down syndrome
How can we establish chromosome pairs for karyotypes?
Chromosome pairs have their centromeres located in the same area, but they vary between each pair
•The process used by eukaryotic cells to separate the chromosomes (genes) when they divide into 2 daughter cells (except for the special situation of meiosis in development of sperm and eggs)
•The two identical chromatids of each chromosome in the parent cell separate from each other; one goes to one of the daughter cells and the second goes to the other daughter cell
The process used by eukaryotic cells to separate the chromosomes (genes) when they divide into 2 daughter cells- full chromosome set
-shortest phase of the cell cycle
-asexual reproduction (vegetative reproduction)
-results in genetic constancy: offspring are clones of parents
oVariation by random mutation
oRapid and efficient means of reproduction
oCactus can reproduce by mitosis-mulitcellular organisms also use it for growth of tissues and asexual reproduction
o1 cell gives rise to 2 cells
What are the important preparations for mitosis?
1. The DNA is duplicated during S phase, o that each chromosome contains 2 identical copies of DNA (46→92)
2. The centrosome is duplicated during S to make 2 centrosomes (these become the spindle poles) decide how the cell will be divided into two.
1. The cytoskeleton breaks down, the endomembrane
system is dispersed- ER and Gogli and will reform later
2. The chromatin condenses to the mitotic chromosome form
3. The centrosomes move to opposite sides of the nucleus and become the 2 poles of the mitotic spindle (spindle poles)
• begins with the nuclear envelope break down
•A kinetochore forms at the centromere of each chromatid
•The microtubules attach to the chromosomes which can now move to build the spindle
•like fly fishing-keep casting until they catch a chromosome
•The chromosomes are aligned at the center of the spindle-the mitotic spindle looks static, but the microtubules are highly dynamic
•Building of the mitotic spindle is completed, every chromatid must be attached to a microtubule.
-Center of the spindle where the chromosomes align during Metaphase
This is a surveillance checkpoint- the cell is ensuring that the spindle is fully formed and is "set to go"
•Cohesin proteins holding the two sister chromatids of each chromosome together are destroyed-keep them from getting mixed up
•One of the chromatids of each duplicated chromosome moves to one pole, and the other chromatid moves to the opposite pole
•The cleavage furrow (animal cells) or cell plate (plant cells) forms- surrounded by plasma membranes in animal cells so you can pinch apart.
•The spindle microtubules disassemble, plants have a cell wall, so they do not pinch off.
•A nuclear envelope re-forms around the cluster of chromosomes at each pole
•The chromosomes de-condense to the interphase form of the DNA and nucleoli can start again
What are the three kinds of microtubules that compose the spindle?
Kinetochore Microtubules, Interpolar Microtubules, and Astral Microtubules
All _____ ends face the poles, ____ ends face the center of the spindle.
-polar microtubules extend from each pole of the spindle
-Plus ends meet at the center, centrosomes are negative
How is the Spindle built?
•Microtubules are cast-out from the poles with their plus ends leading (by dynamic instability) Like fishing !!
•The plus end of a microtubule from a pole "hooks" on to a chromosome at the kinetochore of one of its chromatids
•Then the sister kinetochore then gets "hooked" by a microtubule from the opposite pole
•Many more microtubules become attached and the highly dynamic microtubules and motor molecules move the chromosome to the metaphase plate
the chromosomes move to the poles (the distance between the poles and kinetochores decreases)
1) Microtubules disassemble at the poles and motors positioned at the poles "pull in" the microtubules
2) Microtubules also disassemble at the kinetochores, while remaining attached shortening the kinetochore microtubules
elongating microtubules push the poles apart
•The interpolar microtubules from the two half spindles are pushed apart by kinesin motors while they simultaneously elongate
Cell Cleavage in Animal Cells
-usually starts at the beginning of telophase
•A ribbon of contractile actin filaments is built between the daughter cells, called the contractile ring
•The ribbon contracts (like a purse string), pulling in the membrane and creating a cleavage furrow
It works by a combination of actin filament shortening and myosin-motor activity (as in muscle contraction)
Cytokinesis (In Plants)
•Because of their strong cell walls, plant cells do not "pinch" into 2 cells
So, a new cell wall is built between the 2 forming cells half-way between the spindle poles
Row of vesicles will fuse to form a cell plate between the cell and above the cell wall below.
Each daughter cell contribute the building toward formation of cell wall
•Results in genetic diversity - genetic material from two parents, siblings are not the same
oOffspring are not identical to parents or each other
•2 parents each contributes 1 gamete to each offspring
•1 cell gives rise to 4 cells
- there are 2 cytoplasmic divisions in a row without an intervening S phase -leads to a reduction in the amount of DNA- have to synthesize DNA first
•In each final gamete only one homolog of each pair is retained (the gametes are haploid), and each of the 23 chromosomes has only 1 chromatid
throw out one set—which set you throw our is random
•= efficient way to use resources Sexual reproduction requires large expenditure of energy
•Energy required for mating,
oDetracts from other useful activities such as feeding and caring for existing offspring. Males of species have to woo the females. Females like to be courted. Males evolve elaborate ways to attract females-birds are brighter colors. Sometimes they fight other males for a mate.
•Requires that resources be used to maintain a large population of males that do not bear offspring
•Genetic variation allows natural selection and evolution
oStill choice- chose to reproduce sexually because it allows them to change and become more adapted to their environment
•Cells of organisms that have a sexual life cycle have cells that have two complete sets of chromosomes, one from each parent. Such cells are called diploid (2n).
•organisms that have cells that have only one complete set of chromosomes are called haploid (1n or simply n).
oOne set of chromosomes→gametes
oCome together to form a diploid
oSperm donates DNA to the egg during fertilization
•In human diploid cells one member of each pair was donated by one parent, the second was donated by other parent
1 pair for each chromosome
oThe two chromosomes of a homologous pair contain the same genes (but they are not identical)- can have different alleles
-22 homologous pairs
occurs during meiosis as egg cells and sperm cells are formed and when egg cells and sperm cells combine to form the new individual- why you have genetic variation-which half of set you lose is random-leads to genetic diversity
(protists, fungi, some green algae). The zygote is the only diploid cell in the life cycle, goes through meiosis to become haploid
(animals, brown algae, some fungi) the gametes are the only haploid cells in the life cycle, mature organism is diploid- undergo meiosis with haploid- then restore diploid state
oThe 2 homologs of each pair become attached to each other in a process called synapsis (they are called bivalents, or tetrads) come together and adhere along their lengths-tetrads-4 chromatids
-Homologous chromosomes, each with a pair of sister chromatids, line up to form a tetrad.
•Adjacent chromatids of different homologs break and rejoin. Because there is still sister chromatid cohesion, a chiasmata forms
•The chiasma is resolved. Recombinant Chromatids contain genetic material from different homologs.
(or genetic recombination) occurs between the chromatids of the two homologs, results in reciprocal exchange of DNA--causes the re-assortment of genes
How long does meiosis take in males?
cells in the testis that undergo meiosis takes about a week for prophase I and about a month for the entire meiotic cycle
How long does meiosis take in females?
egg cells, prophase I begins before a woman's birth.
oBegins during her early fetal development and ends decades later during the monthly ovarian cycle.
•The chromosomes line up at the metaphase(equatorial) plate with the tips of the homologs attached to each other
•The kinetochore of one homolog is attached to one pole, the kinetochore of the other homolog is attached to the opposite pole.
-chromosomes line up randomly--genetic variation
-occurs in Meiosis
•One entire homolog with its two chromatids goes to one daughter cell, the other homolog goes to the other daughter cell
•This is the stage in which the cells go from the diploid (2n) to the haploid (1n) state
•Usually follows immediately after meiosis I without DNA synthesis
•Very much like a normal mitotic division. The two chromatids of each remaining chromosome separate from each other and go to opposite poles(daughter cells).
•Result is 4 different haploid cells
•One chromosome lines up, the kinetochores attach to the centromere of one and pulls it into 2 chromatids that move toward opposite poles
How does genetic diversity occur?
1. Random distribution of the two homologs of a pair to the daughter cells during meiosis I; random assortment during meiosis II
2. Crossing over between homologs during meiosis I
a pair of homologous chromosomes fails to separate during meiosis I or sister chromatids fail to separate during meiosis II