ch7: inside the cell
Terms in this set (52)
Molecular zip codes
Aid material transport and organization of intracellulare components within a cell
What are the Major Tenets of Cell Theory?
1.All organisms are composed of one or more cells, within which all the processes of life occur.
2.Cells are the smallest living things. Nothing smaller and less complicated than a cell is considered alive.
3.Cells arise only by the division of a previously existing cell.
Properties of Cells
- acquire and utilize energy from their environment
- are highly complex and organized
- can grow.
- can repair themselves
- can reproduce
- carry out a variety of chemical reactions
- perform mechanical work
- sense and respond to stimuli
- can regulate themselves
According to MORPHOLOGY species fall into what two categories.
Prokaryotes and Eukaryotes
-eukaryotic cells have a membrane-bound compartment called a nucleus & -prokaryotic cells do not
organisms are divided into three broad domains called 1) Bacteria, 2) Archaea, & 3) Eukarya
-(bacteria & archaea are prokaryotes & Eukarya are eukaryotes)
what do prokaryotic and eukaryotic cells have in common?
- DNA as genetic material.
-ribosomes synthesize proteins
-enzymes that catalyse metabolic reactions
-similar metabolic pathways
-membreabes with similar or identical components and organization.
-vary in size and shape
-they have similar structures:- plasma membrane
-a single chromosomes
-stiff cell walls
Prokaryotic Cells - Internal Structure
- All prokaryotic cells contain ribosomes, consisting of RNA molecules and protein, for protein synthesis.
- Many prokaryotes have internal photosynthetic membranes.
- Some prokaryotes have membrane-enclosed organelles.
- The inside of many prokaryotic cells is supported by a
cytoskeleton of long, thin protein filaments.
Eukaryotes and Prokaryotes Compared
-eukaryotic chromosomes are found inside a membrane bound copartment called a nucleus.
-eukariyotics cells are often much larger
- eukaryotic cells contian extensive amounts of internal membrane.
- eukaryotic cells feature a deverse and dynamic cytoskeleton.
The Nucleus structure
- The nucleus is surrounded by a double-membrane nuclear envelope.
- The nucleus has a distinct region called the nucleolus.
the nucleus function
- Information storage and processing
- Contains the cell's chromosomes
- Ribosomal RNA synthesis (in the nucleolus)
A complex double membrane that encloses the nucleus.
Pores in the nuclear envelope that allow or disallow molecules entrance into the nucleus.
A lattice-like sheet made of fibrous proteins that stiffen the structure and maintain the shape of the nucleus.
- Ribosomes are non-membranous (they are not considered organelles).
- Have large and small subunits, both containing RNA molecules and protein
- Ribosomes can be attached to the rough ER or free in the cytosol, the fluid part of the cytoplasm.
- Protein synthesis
endoplasmic reticulum (ER) This membrane is continuous with the nuclear envelope and is labeled with 2 distinct regions (smooth and rough)
Rough Endoplasmic Reticulum
- The rough endoplasmic reticulum(rough ER, RER) is a network of membrane-bound tubes and sacs studded with ribosomes.
- The interior is called the lumen.
- The rough ER is continuous with the nuclear envelope
Rough Endoplasmic Reticulum
- Ribosomes associated with the rough ER synthesize proteins.
- New proteins are folded and processed in the rough ER lumen
Smooth Endoplasmic Reticulum structure
- The smooth endoplasmic reticulum (smooth ER, SER) lacks the ribosomes associated with the rough ER
Smooth Endoplasmic Reticulum function
- Enzymes within the smooth ER may synthesize fatty acids and phospholipids, or break down poisonous lipids.
- Reservoir for Ca2+ ions
Golgi Apparatus STRUCTURE:
- The Golgi apparatus is formed by a series of stacked flat membranous sacs called cisternae.
Golgi Apparatus function
- The Golgi apparatus processes, sorts, and ships proteins synthesized in the rough ER.
- Membranous vesiclescarry materials to and from the organelle.
- Peroxisomes are globular organelles bound by a single membrane.
- Center of oxidation reactions
- Lysosomes are used for digestion and waste processing.
-are single membrane-bound structures containing approximately 40 different digestive enzymes.
- Lysosomes are found in animal cells.
How Are Materials Delivered to Lysosomes?
Materials are delivered to the lysosomes by three processes:
- Receptor-mediated endocytosis
Endocytosis is a process by which the cell membrane can pinch off a vesicle to bring outside material into the cell.
- In addition to phagocytosis and receptor-mediated endocytosis, a third type of endocytosis called pinocytosis brings fluid into the cell.
- Some vacuoles are specialized for digestion.
- Most vacuoles are used for storage of water and/or ions to help the cell maintain its normal volume
vacuoles are large membrane-bound structures found in plants and fungi.
- Some contain digestive enzymes.
The Cell Wall
• Fungi, algae, and plants have a stiff outer cell wall that protects the cell.
- In plants and algae, the cell wall's primary component is cellulose.
- In fungi, the primary component is chitin.
• Woody plants have a secondary cell wall containing lignin.
• The cytoskeleton, composed of
protein fibers, gives the cell shape and structural stability, and aids cell movement and transport of materials within the
• In essence, the cytoskeleton organizesall of the organelles and other cellular structures into a cohesive whole.
Structure and Function at the Whole-Cell Level
An organelle's membrane and its enzymes correlate with its function, and cell structure (e.g., the type, size, and number of organelles) correlates with cell function.
• Cells are dynamic living things with interacting parts and constantly moving molecules.
How Dynamic Are Eukaryotic Cells?
• Your body's cells use, and synthesize, approximately 10 million ATP molecules per second.
• Cellular enzymes can catalyze >25,000 reactions per second.
• Each membrane phospholipid can travel the breadth of its organelle or cell in under a minute.
• The hundreds of trillions of mitochondria inside you are replaced about every 10 days, for as long as you live.
• The fluid plasma membrane's composition is constantly changing
The Signal Hypothesis
The signal hypothesis predicts that proteins and other macromolecules have a "zip code" or signal sequence that
directs the them to a particular location in the cell.
The Nuclear Envelope: A Transport Mechanism
•the nuclear envelope has two membranes, each consisting of a lipid bilayer, and is continous with the endoplasmic riticulum
•the inside surface is linked to fibrous proteins that form a lattice like sheet called the nuclear lamina.
- Stiffens the membrane's structure and maintains its shape
- Provides attachment points for each chromosome
• The envelope contains thousands of openings called nuclear pores.
- Function as doors into and out of the nucleus
How Are Molecules Imported into the Nucleus?
• Messenger RNAs and ribosomes are synthesized in the nucleus and exported to the cytoplasm. Materials such as proteins needed in the nucleus are imported into the nucleus.
• Movement of proteins and other large molecules into and out of the nucleus is an energy-demanding process.Proteins destined for the nucleus have a molecular "zip code"—a 17-amino-acid-long nuclear localization signal (NLS)—which allows them to enter the nucleus.
Imagine that you "bio-engineered" a large nuclear protein so that you removed the ribonucleotides that
coded for its nuclear localization signal. This protein would be
synthesized in the cytoplasm and remain in the cytoplasm.
The Endomembrane System
• The endomembrane system is composed of the smooth and rough
ER and the Golgi apparatus, and is the primary system for protein and lipid synthesis and membrane synthesis and turnover.
• Ions, ATP, amino acids, and other small molecules diffuse randomly throughout the cell, but the movement of proteins and
other large molecules is energy demanding and tightly regulated.
Pulse - Chase Experiments
- Cells exposed to a brief "pulse" of radioactive amino acids
- Radioactive amino acids washed out and replaced with non-radioactive
- Cells processed for autoradiography at various times after that
The Secretory Pathway Hypothesis
• The secretory pathway hypothesis proposes that proteins intended
for secretion from the cell are synthesized and processed in a highly prescribed set of steps.
• Proteins are packaged into vesicles when they move from the RER to the Golgi apparatus and from the Golgi apparatus to the cell surface.
- The RER and Golgi apparatus function as an integrated endomembrane system.
From ER to Golgi
• Proteins are transported from the ER to the Golgi apparatus in vesicles that bud off the ER, then fuse with the Golgi apparatus
membrane and deposit their contents inside.
golgi protiens and vesicle
-Each protein that comes out of the Golgi apparatus has a molecular tag that places it in a particular type of transport vesicle.
-Each type of transport vesicle also has a tag that allows it to be transported to the correct destination.
• Some proteins are sent to the cell surface in vesicles that fuse with
the plasma membrane, releasing their contents to the exterior of the
cell in a process called exocytosis.
The Dynamic Cytoskeleton
The cytoskeleton is a complex network of fibers that helps maintain cell shape by providing structural support. The
cytoskeleton is dynamic; it changes to alter the cell's shape, to transport materials in the cell, or to move the cell itself.
• There are three types of cytoskeletal elements:
- Actin filaments (microfilaments)
- Intermediate filaments
• Actin filaments are the smallest cytoskeletal elements.
• Actin filaments form by polymerization of individual actinmolecules.
• Actin filaments are grouped together into long bundles or dense networks that are usually found just inside the plasma membrane and help define the cell's shape.
• Actin filaments can also be involved in movement by interacting with the motor protein myosin.
• Actin-myosin interactions can cause cell movements such as cell crawling, cytokinesis, and cytoplasmic streaming
• Intermediate filaments are defined by size rather than composition. Many types of intermediate filaments exist, each
consisting of a different protein.
• Intermediate filaments provide structural support for the cell. They are not involved in movement.
• Intermediate filaments form a flexible skeleton that helps shape the cell surface and hold the nucleus in place
• miscrotubules are large, hollow tubes made of tubulin dimers ( two part compounds)
• Microtubules have polarity, are dynamic, and usually grow at their plus ends.
• Microtubules originate from the microtubule organizing centerand grow outward, radiating throughout the cell
• Animal cells have just one microtubule organizing center called the centrosome. Centrosomes contain two bundles of microtubules called centrioles.
• Microtubules provide stability and are involved in movement; they may also provide a structural framework for organelles.
- Microtubules can act as "railroad tracks"; transport vesicles move through the cell along these microtubule tracks in an
• Microtubules require ATP and kinesin and dyneins for vesicle transport to occur. Kinesin and dynein are motor proteins that
convert chemical energy in ATP into mechanical work.
Eukaryotic cells manufacture cytoskeletal proteins that help to
maintain the cells' shapes and functions. You would predict these
would be manufactured on free ribosomes in the cytoplasm
Cilia and Flagella: Moving the Entire Cell
• Flagella are long, hairlike projections from the cell surface that move cells.
- Bacterial flagella are made of flagellin and rotate like a propeller.
- Eukaryotic flagella are made of microtubules and wave back and forth.
• Closely related to eukaryotic flagella are cilia, which are short, filament-like projections.
• Cells generally have just one or two flagella but may have many cilia.
Cilia and Flagella Structure
• The axoneme of cilia and
flagella is a complex "9 + 2"
arrangement of microtubules
connected by links and spokes.
• The axoneme attaches to the cell
at a structure called the basal
A Motor Protein in the Axoneme
• The motor protein dyneinforms the arms between doublets and changes
shape when ATP is hydrolyzed to "walk" up the microtubule.
• When the dynein arms on just one side of the axoneme move, cilia and flagella bend instead of elongating because the
links and bridges constrain movement of the microtubule doublets.
Cells are dynamic, highly integrated