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Flashcards for Midterm #2 from Dr. Low's Lecture Material

Fluorescense Microscopy

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.

Confocal Microscopy

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 1864

Can life arise spontaneously or must it come from previous life?

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.

Cell Size

limited by diffusion (process is responsible for the movement of molecules through the cytoplasm and in and out of cells)

Spheres: As Diameter increases

Surface Area-to-Volume ratio decreases

Three Domains of Living Organisms

Bacteria, Eukarya, Archaea

Prokaryote Group

Bateria and Archaea

Eukaryote Group

yeast, protists, plants, animals, etc.

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.

Prokaryotic Shapes

Helical Bacteria, Bacilli, Cocci

Alexander Fleming

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.

Mitochondria- (Eukaryotes)

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

Golgi Apparatus- (Eukaryotes)

make up endomembrane system, vesicles bud on and off of it


manufacture proteins

Cell Wall

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

Where else can DNA be found in the cell?

Nucleus, Mitochondria and Chloroplast

Name the round structure inside the cell?
Ribosome, Nucleiod, Nucleus, Mitochondria



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.

Nuclear Envelope

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.

Nuclear Lamina

give nucleus its shape


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.

Nuclear Basket

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

DNA + Protein



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.


programmed cell death, way for multicellular organisms to get rid of dead/dying cells


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-Arising from the inner membrane are stacks of membrane sacks


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)

Tay-Sachs Disease

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

Actin Filaments/Microfilaments

•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

Stress Fibers

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

Focal Adhesions

places where the actin cytoskeleton attaches to the plasma membrane

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.

Intermediate Filaments

(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 main functions of microtubules?

1. Cell Shape

What are the two types of dynamics that are carried out by microtubules?

Dynamic Instability and Treadmilling

Dynamic Instability

switching between growth and shortening at microtubule ends

Where are microtubules "organized" in cells?

at the "Microtubule Organizing Centers"


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

Pericentriolar Matrix

is ill-defined and surrounds the pair of centrioles

Mitotic Spindles

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)

Microtubule Machines

•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-made up of nine doublets, two singlets in the middle-"9 plus 2 organization"

Radial "Spokes"

cilia-connects the outside doublets with the center

Motor Protein

cilia-cause the microtubule doublets to slide over each other, causing shape change-cilia and flagella will bend

Linker Protein

cilia-the doublets are connected together by these

Basal Body

bottom of cilia-microtubule triplet-does not have the two singlets in the middle, 9 triplets

How do cilia and flagella move?

dynein and nexin and kinesin


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

Nuclear Lamin

(support the nucleus, attachment points for the DNA), gives nucleous its shape

Keratin Filaments

supports skin, hair, hooves, horns


support long processes in neurons

Cell Membranes

1. The plasma membranes that encase all cells
2. The internal membrane system the endomembrane system

Endomembrane System

Endoplasmic Reticulum and Golgi Apparatus

Phospholipid Bilayer

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

Plasma Membrane

-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

Fatty Acid chains with a higher degree of unsaturation are more "kinky"



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

Plasma Membrane Carbohydrates

are recognition sites

What are the three basic ways to transport materials across membranes?

Passive Diffusion, Carrier Mediated Diffusion (Facilitated Diffusion, and Active Transport

Passive Diffusion

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

Glucose Transport

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

Which mechanisms of transport do NOT require ATP?

Facilitated and Passive Diffusion

Active Transport

ATP-dependent Transport;

•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

Is active transport unidirectional or multidirectional?


What are the three classes of Active Transport?

Uniporters, Symporters, and Antiporters


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.


transport two different substances in opposite directions.

True/False. Active Transport can be primary or secondary.


Primary Active Transport

all of the energy-to pump ions across concentration gradient, comes from Hydrolysis of ATP, even when two molecules are transported

Sodium-Potassium Pump

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.

Is the Sodium-Potassium pump anitport, uniport or symport?


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.

Ligand-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

Whatever the cell loses in endocytosis, it gains back in...


What are the three kinds of endocytosis?

1. Phagocytosis
2. Pinocytosis
3. Receptor-Mediated


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).
relatively non-specific.


(or "cell drinking"): cells take up water into vesicles, bring in small substances or fluids. Process is relatively non-specific.

Receptor-Mediated Endocytosis

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

Defects in the regulated uptake of LDL particles can cause...



•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.

Familial hypercholesterolemia

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.

Secretory Vesicle

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

Four Major Forms of the Endomembrane System

Rough ER, Smooth ER, Golgi Complex, Vesicles

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.

What are the three sections of the Golgi Apparatus?

Cis, Medial and Trans

Golgi Apparatus-Cis Section

"in section"
on the same side, closest to the nucleus, begins the modification

Golgi Apparatus- Medial Section

"middle section"
continues the modification

Golgi Apparatus-Trans Section

"out 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?

Membrane Vesicles

What are some other functions of membranes?

•Some organelles membranes help transform energy
•Some membrane proteins organize chemical reactions
•Some membrane proteins process information

Energy Transformation

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

Signal Transduction

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

How is the plasma membrane involved in cell adhesion and recognition?

extracellular structure

Extracellular Matrix

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

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