Cell and Molecular Biology Exam 1

How is E. coli useful as an experimental model?

• Prokaryote

• Provided understanding of DNA replication, gene expression, and protein synthesis

• Why use them?

  • Easy to keep

  • Short life cycle (divide every 20 min)

  • Simpler genome (4.6 million)

How are yeasts useful as an experimental model?

• Single Cell Eukaryotes

• Shared characteristics w/ E. coli

  • Easy to keep

  • Short life cycle

  • Larger genome than E. coli, but simpler than human

• Shared characteristics w/ humans

  • Distinct nucleus

  • Genome is organized in 16 linear chromosomes

  • Organelles

How are C. elegans useful experimental models?

• multicellular eukaryotes

• Nematode

• Are transparent during early development, allowing for easy observation of cellular processes (animal development and cell differentiation)

• Small # of genes and cell (have been mapped)

• Use mutations to study developmental abnormalities

  • Similar genes in humans

How is drosophila melanogaster a useful experimental model?

• Fruit fly

  • Larger genome than C. elegans

  • Easy to maintain

  • Short reproductive cycle (~2 weeks)

• Good to study molecular mechanisms of development

• Similar genes and mechanisms exist in humans

How is arabidopsis thaliana a useful experimental model?

• Simple plant

  • Small genome

  • Easy to grow/maintain

• Methods for molecular gene manipulations are available

  • ID of genes involved in plant development

How are zebrafish useful experimental models?

• Vertebrates

• Easy to maintain

• Reproduce rapidly (3-4 months)

• Embryos develop outside the mother and are transparent

• Several molecular techniques available to map mutations

How are mice useful experimental models?

• Vertebrates

• More complex than other models

  • Many mutations identified

  • Several mutant mice available

• More applicable to medicine

  • Similar genomes

  • Mutations in homologous genes result in similar phenotypes

How is cell culture a useful experimental model?

• Controlled manipulations

• Makes it easier to study signaling mechanisms

• Primary cultures vs immortal cell lines

• HeLa cell line (Henrietta Lacks)

How are viruses useful experimental models?

• Intracellular parasites that cannot replicate on their own

• Similar and simpler genomes

• Can be studied in cultured cells

• Discovered that some cancers are caused by viruses

How were biomolecules able to form on Earth given its hot environment?

• The Earth started to cool down which led to:

  • Reduced environment → not much O2, plenty of nitrogen, methane, H2S, NH3

  • Liquid water → oceans/small pools start to form which allows area for molecules to interact

  • Energy → right amt of heat, lightning, UV radiation interact with volcanic clouds

Explain the experimental done by Stanley Miller.

Miller's experiment simulated early Earth conditions by combining water, methane, ammonia, and hydrogen, then applying electrical sparks to mimic lightning. This resulted in the formation of amino acids, demonstrating how organic molecules could form abiotically.

How did molecules lead to the formation of cells?

Small molecules formed macromolecules which are the building blocks for cells

What was the RNA world hypothesis and what observations supported it?

First cell was an enclosed bit of self-replicating RNA in a phospholipid bilayer

• Support for RNA:

  • 1) RNA forms spontaneously

  • 2) RNA can self-replicate

  • 3) RNA can form enzymes (rRNA, tRNA)

How did metabolism evolve?

First cells obtained direct energy

1. Glycolysis → 2 ATP

2. Photosynthesis

3. Oxidative phosphorylation → 36-38 ATP

   • This was possible because of the O2 accumulating as a byproduct of photosynthesis

How did cells go from prokaryotic to eukaryotic?

Endosymbiosis

• Mitochondria and chloroplast are similar size to prokaryotes so it is likely that an Archaea, through endocytosis, took in a bacteria and the genes of bacteria transferred

What are covalent bonds and their use in biology?

Attributes

• Strong bonds formed by sharing of electrons b/n atoms (# of bonds dependent on unpaired e- in valance shell)

• Polar or non-polar

• Single, double, or triple bonds

Uses

• Form backbone of organic molecules in living matter (structural stability)

• Enzyme activity regulation via covalent modifications

• High energy bonds in ATP store energy

What are ionic bonds and their uses in biology?

Attributes

• “Give and take” of electrons (form cations and anions)

• Ions held together by attraction of opposite charges (salts)

Uses

• Stabilize protein folding and enzyme active sites

• Nerve signaling: Ion gradients (e.g., Na⁺/K⁺ pump) are essential for nerve impulse transmission.

• Buffer systems rely on ionic interactions to regulate cellular pH

What are hydrogen bonds and their uses in biology?

Attributes

• Weak bonds formed between a hydrogen atom covalently bonded to an electronegative atom (O, N, or F) and another electronegative atom

Uses

• Bonds b/n base pairs (A-T, G-C) stabilize the double helix.

• Contribute to secondary and tertiary protein structures.

• Gives water its high cohesion, adhesion, and solvent capabilities

What are hydrophobic interactions and their uses in biology?

Attributes

• Non-polar molecules or regions cluster together to minimize contact with water

Uses

• Drive the formation of lipid bilayers in cell membranes.

• Protein folding: nonpolar amino acid side chains cluster in the protein’s interior to maintain stability in aqueous environments

• Many signaling molecules (e.g., steroid hormones) rely on hydrophobic interactions for proper function

What are the laws of physics useful to biology?

• 1st Law: Conservation of Energy

  • The total energy of a system and its surroundings is constant

• 2nd Law: Entropy increase over time

  • A system will change spontaneously to a state of greater disorder

What types of physical reactions can occur in a cell?

Catabolic: Breakdown of complex molecules into simpler ones and release energy that was used to form them

Anabolic: Link simple molecules to complex molecules. Require energy to form bonds within the smaller molecules

How do macromolecules form and break down?

• Form by dehydration reactions (condensation) occurs when two monomer bond together through the loss of a water molecule

• Broken down by hydrolysis, a rxn that is essentially the reverse rxn of condensation; requires water

What is the general formula for a simple sugar? What do simple sugars provide?

Cn(H2O)n

Simple sugars provide energy

What are the four categories for carbohydrates?

Monosaccharide: smallest form of carbohydrate

Disaccharides: two monosaccharides trung together via dehydration rxn forming a glycosidic linkage

Oligosaccharides: 2-10 monomers

Polysaccharide: >10 monomers

What are the three major jobs that complex sugars have and what do they entail?

1. Energy storage

   • Starch and glycogen are readily hydrolyzed by enzymes

   • Residues at branch points connected via alpha 1-6 bonds, other bonds use alpha 1-4

2. Structure

   • Cellulose is not readily hydrolyzed, but bacteria can break it down. Chitin is the animal equivalent

   • Connected with alpha 1-4 bonds

     • Alpha → –OH facing down

     • Beta → –OH facing up

3. Signaling

   • Attach to proteins to act as address

What lipids are involved with energy storage and what are their attributes?

Fatty acids

• Long hydrocarbon chains

  • Can be saturated (max amount of hydrogens/no double bonds) or unsaturated (double bonds present)

• Carboxyl group is polar

• Non-polar C-H group

Triglycerides

• 3 fatty acids linked by a glycerol

• Insoluble in water (clump together)

• Efficient energy storage

What lipids are involved with the cell membrane and what are their attributes?

Phospholipids

• 2 acyl (C-H) chains instead of 3

• 3rd chain replaced by polar head group

• Acyl chains can either be held together by glycerol OR AA serine (sphingomyelin)

• Amphipathic 

  • Tail = hydrophobic

  • Head = hydrophilic

What lipids are involved with signaling and what are their attributes?

Glycolipids

• Similar to phospholipids

• Head contains carbohydrate

• No phosphate, instead a sugar

• Cellular recognition

Cholesterol

• C-H chain is formed into a multi-ring structure

• Also used as hormones (signaling)

• Hydroxyl group is polar

What are the two types of nucleic acids, their components, and their biological roles?

• DNA: long term info storage

• RNA: short term info storage

• Composed of nucleotides: sugar (ribose/deoxyribose), phosphate group, nitrogenous base (AT(U)GC)

• Roles in cell:

  • Energy (ATP)

  • Singaling (cAMP)

  • ATP → cAMP → AMP

How are nucleotides attached to form a nucleic acid strand?

Dehydration reactions for phosphodiester bonds between 5’ phosphate and 3’ hydroxyl

• Each new nucleotide is added to the 3’ carbon of the last sugar. Thus the NA grows in the 5’ to 3’ direction

Phosphate and sugars make the “backbone”

What are the functions of proteins?

1. Structure component

2. Transport

3. Enzymes

4. Transmitting information

5. Defense

How many AA are there, and what is the structure?

• 20 AA (different R groups)

• Alpha carbon, R group, carboxyl group, hydrogen, amino group

What are the major categories of AA, their structural attributes, and which AA belong in each group?

Non-polar

• Located on the inside of proteins, away from the aqueous environment

• Look for hydrocarbons

• Glycine, Alanine, Valine, Leucine, Isoleucine, Proline, Cysteine, Methionine, Phenylalanine, Tryptophan

Polar, uncharged

• Look for –OH groups

• Serine, Threonine, Tyrosine, Asparagine, Glutamine

Polar, charged

• Located on the outside of proteins, in contact with the aqueous environment, often participate in chemical reaction

• Two types:

  • Acidic

    • Look for a negative charge on the R group @ physiological pH

    • Aspartic acid, Glutamic acid

  • Basic

    • Look for positive charge on the R group @ physiological pH

    • Lysine, Arginine, Histidine

How are peptide chains formed?

• Dehydration rxn to form peptide bond—amino group of one and the carboxyl group of the other

  • Built N-terminus (amino) → C-terminus (carboxyl)

  • Does not change the properties of R groups

What are the structural levels of a protein?

1. Primary

2. Secondary

3. Tertiary

4. Quaternary (sometimes)

What does the primary structure of a protein consist of?

• AA sequence

• Big role in the end shape of protein

What does the secondary structure of a protein consist of?

Alpha helix

• CO and NH of different peptide bonds form a hydrogen bond

  • Helical formation → bond b/n AA located 4 residues downstream

• R groups project out from the central axis to determine the hydrophilic/hydrophobic/amphipathic character

Beta sheets

• CO and NH of different peptide bonds form a hydrogen bond

  • Sheet formation → bond b/n residues of chains lying side by side

    • 2+ chains either parallel or antiparallel

What does the tertiary structure of a protein consist of?

• Overall 3D shape

  • Determined by noncovalent interactions (hydrogen, ionic, van der Waals)

    • Hydrophobic R → middle

    • Hydrophilic R → surface

What does the quaternary structure of a protein consist of?

Type, number, and arrangement of the subunit polypeptides in a protein

• e.g. hemoglobin

How do proteins fold?

Spontaneously; driven by interactions b/n AA/AA and AA/water

What role do chaperones play in protein folding?

Prevent misfolding & increase speed

How do prions work, and why is this bad?

• Protein folding gone wrong (PrP = prion protein)

  • Normal random coil and alpha helices → misfold into beta sheet that noncovalently interact with other proteins (domino effect)

  • Beta-sheets line up to form insoluble structures (become sticky), which can kill cells and form plaques

    • e.g. Mad Cow Disease (BSE), Creutzfeldt-Jakob Disease, Fatal Familial Insomnia

Most proteins are stable, but what about those that are not?

Intrinsically disordered proteins (IDP) have entirely disordered structures

Intrinsically disordered regions (IDR) of proteins have disordered portions

• Regions are usually made of charged/polar AA and allow proteins to adapt their structure

What are enzymes and two properties associated with them?

Proteins that increase rate of rxn by up to 10^6-10^8 fold

1. Not consumed or permanently altered in the process

2. Do not alter the chemical equilibrium between reactants and products

What is ΔG and why is it important?

Gibbs free energy

• Determines whether a reaction is spontaneous or not

What is a positive, negative, and zero value of ΔG indicative of?

ΔG < 0 → free energy is released (exergonic) = SPONTANEOUS (-)

ΔG > 0 → free energy is required (endergonic) = NONSPONTANEOUS (+)

ΔG = 0 → rxn is at equilibrium

When breaking and forming a chemical bond, what state usually occurs between these stages?

Transition state: contorting (stretching or straining) of 1+ bonds in starting molecule into an unstable state (more energetic) before the reaction can initiate

What role do enzymes play in the transition state?

Enzymes decrease the energy of the transition state, making it easier for the reaction to take place

How are enzymes specific to certain chemical reactions?

Enzymes create an environment that favors the reaction to occur

Substrates bind to “active sites” on enzyme

Provides template that favors an orientation for the substrates to interact

What are the two models for how enzymes and substrates interact?

1. Lock and key: Shape specific and substrates bind

2. Induced fit: When substrate binds, the shape of the protein may change to fit

What are cofactors? Types?

Enzyme’s “helpers” to help with catalysis

• Types:

  • Coenzymes

    • Low-weight organic molecules

    • Bind loosely to the enzyme

    • Recycled during catalysis

  • Prosthetic group

    • Bind tightly or covalently to enzymes

    • Can be organic or inorganic

    • E.g. heme in hemoglobin

  • Other cofactors

    • Metal ions (loosely bonded)

• Vitamins are required by animals who seem to have lost the ability to synthesis the vital molecules themselves

What are the major ways enzymes are regulated?

1. Competitive inhibition

2. Noncompetitive inhibition

3. Phosphorylation

How does competitive inhibition work?

Inhibitor binds to active site preventing the substrate from binding to AS

How does noncompetitive inhibition work? And what is allosteric regulation?

Inhibitor binds to allosteric site (allosteric regulation: small molecules non-covalently binding to sites other than the AS to regulate enzymes by altering enzyme shape)

• Can be inhibitory or stimulatory

• Feedback inhibition: the product inhibits an enzyme needed for its synthesis

How does phosphorylation work for enzyme regulation?

Activate or inhibit the activity

Phosphate added to serine, threonine, or tyrosine residue

• Kinases – phosphorylate other proteins

• Phosphatase – dephosphorylates other proteins

Why are red blood cells a good model to study membrane structure?

Mature RBS do not have nucleus or organelles, only the plasma membrane

What are the key functions of a cell membrane? And how is it capable of those functions?

Functions

• Acts as a selective barrier

  • Prevents cellular contents and environment from mixing

• Primary zone of interaction for the cell

• Maintains chemical concentration gradient b/n compartments → can participate in the production of cellular energy

• Scaffold for biochemical activities

Structure

• Lipids = barrier function

• Protein = control selectivity

How do membranes form?

Spontaneously

Amphipathic molecules in aqueous environment

• Micelles: hydrophobic tails in the center and the head groups forming the surface of a ball

• Bilayer: double sheet of lipid molecules with their hydrophobic tails facing each other

Why is it said that a membrane follows a “fluid mosaic” model?

2D mosaic of laterally mobile amphipathic lipid and protein molecules

• Fluid = lipid

  • Lipids are free to move around on their layer and spin. They cannot flip to the other side

• Mosaic = proteins

Why are some proteins unable to move in the membrane? Why can this be a good thing?

• Attachment to an underlying cytoskeleton

• Patchwork of large lipid rafts in which some membrane proteins are free to mix and interact

  • “Microdomains” of membrane material; mostly cholesterol, sphingolipids, and glycolipids

    • Move as a unit through the mosaic membrane

• Interconnected by channels where mobility is restricted/prohibited

• By limiting the mobility of some proteins we can create distinct non-mixable regions of the membrane (e.g. top (apical) vs. bottom (basal))

  • Create barriers called tight junctions so nothing can come between cells but have to come through the cell

    • Regions that can have separate, specific functions

Are membranes symmetric or asymmetric?

Asymmetric: two faces of the membrane have different structural and functional characteristics

• Inside of membrane sees different things than outside → performing different functions

How are lipids categorized in the membrane? Percentages?

Sterols: cholesterol (30-50%)

5 kinds of phospholipids (30-50%)

• Phosphoglycerides (4 kinds)

• Sphingomyelin

Glycolipids (1-4%)

What are phosphoglycerides? What causes difficulty with packing together properly?

Primary structural backbone of the membrane

Unsaturated fatty acid kinks make it difficult to pack these together side by side

What are sphingolipids?

Structure utilizes serine instead of glycerol

If the head group is phosphate + choline, it is called sphingomyelin

Made inside golgi membrane → mostly found on the outside of cells

What are glycolipids?

If head group is a simple/complex sugar = glycosphingolipid

Functions in recognition and protein beyond the simple membrane structure role

Made inside golgi membrane → only on the outside of cell

What are sterols (cholesterol)? How do they impact the membrane's fluidity at high and low temperatures?

• Stuck b/n phospholipids tails due to kink from unsaturated fatty acids

  • Polar heads of the lipid and cholesterol interact to secure position

• The phospholipid to which it is most attached displays reduced mobility

• Considered to be a “fluidity buffers”

  • Resistant changes in the fluidity of the membrane

  • Tends to increase the “stiffness” of the membrane at high temperatures (limit lipid movement)

  • Membrane more fluid at lower temperatures (by preventing dense packing)

How are the different membrane lipids distributed throughout the membrane?

Outside: sphingomyelin and glycolipids are made in golgi

Inside or outside: the other four lipids and cholesterol

What two factors influence membrane fluidity?

Temperature

• Too cold → membrane could freeze up

• Too hot → membrane become permeable

Lipid composition

• Unsaturated fatty acid chains have double bonds resulting in kinks

  • Reduce packaging and increase fluidity

• Longer acyl-chains have stronger interactions

  • Longer fatty acids decrease fluidity

• Sterol content buffers fluidity

  • Increases stiffness at high temp

  • Decrease stiffness at low temp

What are the three classes of membrane proteins, where are they located, and what is their role?

Integral membrane proteins

• Embedded within the membrane bilayer

• Regions projecting out on one or both sides

• Receptors and transporters

• Extraction destroys membrane

Peripheral membrane proteins

• Stuck to one side of the membrane

• Ionic interactions with lipid head groups, don’t touch tails

• Non-covalent interactions with integral membrane proteins

Lipid-linked proteins

• “Hang” from the membrane by their lipid tail

• Covalently linked to a modified fatty acid like molecules

How are integral membrane proteins categorized?

Single-pass

• N and C terminus on opposite sides

• Major class: alpha-helix-anchored protein

• Helix consists of 20-25 consecutive AA that are all hydrophobic

• The cylinder will be just long enough (3-5nm) to span the hydrophobic portion of the bilayer

Multi-pass

• N and C terminus can be on same or opposite sides

• Many are also multi-subunit and bind specific lipids

• Subclasses:

  • G-protein coupled receptors

    • No pore (nothing going through the protein, only bind to outside and something occurring on the other), undergo conformational changes upon binding ligands on the extracellular side, leading to changes inside the cell

  • Amphipathic-tunnel transmembrane proteins

    • Multiple alpha-helices pass membrane, 4+ are amphipathic

    • One side of the cylinder is lipophilic and other other is hydrophilic

      • Hydrophilic sides create tunnel through membrane

      • Lipophilic sides interact with surrounding lipids

    • Often channels for ions or transporters

What are the three types of membrane transport?

Diffusion

Through the membrane down concentration gradient

Channel

Passage for chemical movement down concentration gradient (passive)

• Non-gated: always open

• Gated: open or closed

• Don’t bind to the molecule transported (FAST)

Carriers

Proteins must bind and release the transported molecule

• Facilitators (passive or indirect active): dont require energy (MED)

  • Uniporters: one substance down gradient

  • Symporters: moves molecules in similar directions

  • Antiporters: moves molecules in different directions

• Pumps (active): require energy (SLOW)

  • ATP-driven

How does diffusion work? Which molecules are able to diffuse across the membrane?

Selective permeability of the membrane

Small, nonpolar molecules can diffuse: CO2, O2, H2O

Ions and larger uncharged molecules cannot diffuse: glucose

Is the membrane potential of most cells positive or negative? Which ions are concentrated the most outside and inside the cell?

Negative membrane potential → uneven distribution of ions on either side (chemical gradient)

• High concentration of Na+ outside

• High concentration of K+ inside

What are the four types of channels?

1. Leak channels

2. Voltage-gated channels

3. Ligand-gated channels

4. Mechanically-gated channels

What is the characteristic of leak channels?

Always open

Poke hole in membrane and move down gradient

What is the characteristic of voltage-gated channels?

Open/close in response to a change in membrane potential

Voltage-gated Na+ and K+ channels

How does the structure of voltage-gated channels contribute to its function?

• Basic structure composed of 6 transmembrane alpha-helices

  • S5&S6 separated by a pore loop (p-loop)

    • P-loop is the selectivity filter: the size of the channel pore matches diameter of dehydrated ion

  • S4 helix is the voltage sensor (how negative or how positive the inside of the cell is)

    • S4 has a lot of positive AA which attractive to the negative environment and hold the conformation of the protein so the channel is closed, when cell is positive inside, S4 repels and the shape change causes the pore to open

• K+ channel is constructed from 4 polypeptides (quaternary), while Na+ and Ca2+ are composed of 4 domains in one polypeptide (tertiary)

What is the characteristic of ligand-gated channels?

Open/close when bound by a specific chemical

• Ex) Acetylcholine (ACh) channel: “nonspecific cation channel”

  • Made of five subunits, 2 ligands (ACh) can bind in order to cause confirmation change

What is the characteristic of mechanically-gated channels?

Open/close in response to physical force on the membrane

• How cells respond to pressure of movement in their environment

  • E.g. Sensory receptors in the skin and ear

    • When stereocilia in inner ear bend in on direction the gates pry open and when it swings back they close

What are two types of carrier facilitators?

1. Uniporter facilitators

   • Glucose transporters

   • Transport down gradient

   • Flickers b/n open/closed

   • Slower than channels → only transports one glucose at a time

2. Symporter facilitators

   • Na+/Glucose transporters

   • Allows the energy stored in the Na+ electrochemical gradient to drive the accumulation of glucose

   • Indirect active

What are the two types of ATP-driven pumps?

1. ABC pumps

   • Move mixed organic and ions

   • Function as an importer (bring nutrients in) or exporters (pumping toxic substance out)

   • Two transmembrane domains (T domains) and two ATP-binding domains (A domains)

   • Example: Cystic fibrosis

     • Results from a mutated CF transmembrane conductance regulator

2. Ion pumps

   • Three types: P-, V-, F-type pumps

What are the P-type ion pumps?

Na+/K+ pump

• Ubiquitous in mammal cells

• Can consume as much as 25% of ATP produced in cell

• [K+]intra roughly 20x greater than [K+]extra

• [Na+]extra roughly 10-20x greater than [Na+]intra

  • 3 Na+ out, 2 K+ in

What are the V-type ion pumps?

“Vacuum”

Found in vesicles

Use ATP moves H+ into vesicles and vacuoles > makes them acidic

What are the F-type ion pumps?

ATP synthase

Runs in reverse compared to V-type

Will use H+ gradient in order to make ATP

What are the three general areas of cytoskeleton w/n the cytoplasm and their features?

1. Cortical cytoplasm

   • Just beneath plasma membrane helps to maintain cell shape

   • Dominated by an interconnected meshwork of microfilaments (actin)

   • Large membranous organelles and other bulky structures are mostly excluded from this region

2. Subcortical cytoplasm/endoplasm

   • Major organelles of the cell reside in this reign and are spatially organized and often attached to cytoskeletal elements

   • All types of cytoskeletal proteins abundant there

3. Nuclear cytoskeleton

   • Important in mitosis, allows the nucleus to maintain and change shape

     • Nuclear lamins (intermediate filaments) give the nucleus form

What is the structure of actin?

• G actin: actin monomer

  • “Globular”

  • 42 kDa protein (375AA)

  • Nonsymmetrical

    • Pointed end (-)

    • Barbed end (+)

  • Binds ATP or ADP in cleft

    • Binding ATP promotes polymerization (sticky)

    • ATP eventually hydrolyzes

How are microfilaments formed?

Nucleation: the formation of trimers, followed by more rapid growth

F actin: actin polymers

• (-) end only add to the (+) ends, giving the chain polarity

  • Reversible, but depends on subunit availability

What is treadmilling relative to microfilaments?

• G-actin can be added to both ends, but addition is more favorable at the (+) end (barbed end).

• G-actin is typically ATP-bound when added to the filament.

• Over time, ATP hydrolyzes to ADP, leading to a conformational change.

• At the (-) end (pointed end), G-actin is mostly bound to ADP, making it less stable and more likely to dissociate.

• The barbed (+) end grows 5–10x faster than the pointed (-) end.

• Treadmilling occurs when new G-actin is continuously added to the (+) end while ADP-actin dissociates from the (-) end, maintaining a steady-state filament length

What does this actin binding protein do: Profilin?

Stimulates ADP exchange for ATP

What does this actin binding protein do: Formin?

Catalyzes nucleation and extension of a microfilament

What does this actin binding protein do: Arp 2/3 complex?

Initiates the formation of branches

What does this actin binding protein do: Capping proteins and tropomyosin?

stabilize filaments

What does this actin binding protein do: Cross-linking proteins?

Cross-link filaments into bundles and networks

What does this actin binding protein do: Cofilin?

Severs actin filaments

How does the organization of actin filaments contribute to the structure and function of the cell cortex, and what key proteins help anchor the cortical cytoskeleton?

Actin filaments are concentrated at the periphery of the cell, forming the cortical cytoskeleton with the help of spectrin, ankyrin, and protein 4.1

What are focal adhesions and what are they composed of?

Areas of the cell that makes connections with the extracellular matrix

Composed of actin attachments (stress fibers) → creates more strength and withstand more stress

What are two types of cellular protrusions and what is the difference between them?

Microvilli: fingerlike extensions formed by actin bundles; abundant on cells involved in absorption (e.g. intestinal epithelial cells)

Stereocilia: fingerlike extensions; involved with detecting extracellular changes (e.g. auditory hair cells)

What are the steps for locomotion in cells?

1. Protrusion: leading edge has filopodia and lamellipodia. These probe forward in search of new substratum contact site

2. Substrate adhesion: if and when the leading edge encounters an adhesive region, it will attach, stabilizing forward extension.

   • Mechanism of attachment involved integral membrane receptors and their coupling to internal cytoskeletal elements

3. Traction/cell body movement: once a new forward contact has been made, a mechanism must exist to move the bulk of the cell cytoplasm in that direction.

What does locomotion look like in a cell?

Mostly, cells move in response to cues from the environment

Rho family proteins are coupled to receptors and respond to environmental cues by activating actin binding proteins

Stimulates actin remodeling and cell movement

What are intermediate filaments?

Important for scaffolding and structural integrity

Not involved with cell movement

All IF proteins have similar structure: N and C terminus globular domains