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MBB 231 Lecture Notes - Lecture 19: Microfilament, Monomer, Cytoskeleton

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School
Simon Fraser University
Department
Molec Biol & Biochem
Course
MBB 231
Professor
Ingrid Northwood

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Document Summary

There are three types of filaments that are common in eukaryotic cytoskeleton: microtubules (subunit tubulin dimer, microfilaments (subunit actin, intermediate filaments (subunit varies) All three types of filaments are composed up of polymers of subunits that undergo assembly and disassembly. Cell polarity: the ability of cells to generate functionally distinct regions. Cell signaling regulates cytoskeletal function of providing shape and polarity. Microfilaments: two stranded helical polymers of the protein actin which are organized into a variety of bundles and. They are concentrated beneath the plasma membrane and can easily change the cells morphology by assembling and. Humans have 6 isoforms of actin which differ in ~25 amino acids and have various distinct functions. There are 4 types of -actin in muscle (involved in contraction) and a -actin and . The atp binding cleft in actin monomers is oriented in the same direction in all actin monomers in the filament.

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Related Questions

1/ G-proteins are a commonly found in cell signaling pathways, which of the following events normally activates a GTP-binding protein?

(a) GTP hydrolysis by the protein

(b)Activation of an upstream GTPase-activating protein

(c)Exchange GDP for GTP by the activation of an upstream guanine nucleotide exchange factor(GEF)

(d)Pi release after GTP hydrolysis

2/ Which of the following inactivates a G-protein?

(a) The β subunit exchanges its bound GDP for GTP.

(b) The GDT bound to the α subunit is hydrolyzed and forms GDP

(c)The α subunit exchanges its bound GDP for GTP.

(d) Theβγ complex inactivates the G-protein

3/ Olfactory receptors where first hypothesized to be numerous receptor types that were able to recognize specific odorants. We now know that olfactory receptors are made up of ONE receptor family, which is one of the largest gene families know in the human genome. Which of the receptors below comprise the olfactory receptor family?

(a)RTK

(b) Delta-Notch

(c) GPCR-cAMP family

(d) Ion Channel Receptors

4/ Which of the following are possible responses a cell may have as a result of activation of a cell signaling pathway?

(a) Change in gene expression

(b) Alteration of activity of metabolic enzymes

(c) Reconfiguration of cytoskeleton

(d) All of these

5/ Which of the following statements about the cytoskeleton is false?

(a) The cytoskeleton is made up of three types of protein filaments.

(b) The cytoskeleton controls the location of organelles in eukaryotic cells.

(c) Microtubules are polymers made up of monomeric subunits, but other two cytoskeletal filaments are not.

(d) The cytoskeleton of a cell can change in response to the environment.

1. Kinesin-1 motors can move long distances on microtubule tracks without dissociating. By contrast, myosin II motors in skeletal muscle take only one or a few steps before letting go. What is most likely the difference between these two motors that allow two different types of movement?

A. Differences in length of the stalk of each respective motor allow for differences in step size

B. Differences in ATP versus GTP hydrolysis alter the motor head movement along filaments

C. Actin filaments are smaller in diameter and have less space for movement

D. Binding affinity of the Kinesin-1 motor head to microtubules is high, whereas binding affinity of the myosin II motor head to actin filaments is low

E. Microtubules are larger in diameter and have more space for movement

2. Dynamic instability causes microtubules either to grow or to shrink rapidly. What is the most likely reason for a microtubule to undergo rapid growth?

A. GTP hydrolysis exceeds the rate of heterodimer addition

B. GTP hydrolysis of alpha tubulin causes an outward bend in the heterodimer conformation

C. A low concentration of tubulin heterodimers are in solution

D. Heterodimer addition exceeds the rate of GTP hydrolysis

E. Increased trafficking of microtubule motor proteins favors stability

3. There are no known motor proteins that move on intermediate filaments (IFs). What property of intermediate filaments would most likely explain the lack of motor proteins?

A. Tissue specific expression of IFs prevent a single type of motor protein to evolve over time

B. Lateral bundling of IFs prevent motor movement

C. IFs are less dynamic than microtubules and actin filaments

D. IFs are unpolarized

E. IFs do not bind a nucleotide

4. You discover a mutation that results in less rapid hydrolysis of GTP by the beta-tubulin subunit. What would most likely occur?

A. There would be no change in filament assembly

B. There would be enhanced instability of the microtubule

C. There would be enhanced stability of the microtubule

D. Microtubules would not form

E. There would be enhanced treadmilling

5. Which of the following statements describes common features of cadherins and integrins?

A. They can link to microtubules using specific adapter proteins

B. They mediate heterophillic interactions

C. They achieve high binding affinity through clustering

D. They are responsible for interactions of a cell with the extracellular matrix

E. They are found in the apical plasma membrane of an epithelial cell

6. Intermediate filaments are uniquely non-polar and built by lateral bundling in five steps: 1) synthesis of an alpha-helical monomer, 2) formation of a coiled-coil dimer, 3) formation of a staggered tetramer of two coiled-coil dimers, 4) lateral association of 8 tetramers, and 5) addition of 8 tetramers to a growing filament. At what step is polarity lost?

A. Step 1

B. Step 2

C. Step 3

D. Step 4

E. Step 5

7. Collagenase is an enzyme that breaks peptide bonds in collagen to help destroy extracellular structures. What would be the most likely reason to use collagenase in a cell biology laboratory?

A. Disrupt cadherin interaction with the extracellular matrix

B. Disrupt cell-cell contacts to passage cells in cell culture

C. Dissociate epithelial cells from the underlying basement membrane to separate tissues

D. All of the answers are likely uses for collagenase

E. Lyse cells to expose intracellular proteins and organelles

Hello everyone, i'm working on thesepractices multiple choices for my finals. If you know any of theseanswer, please help. i appreciate your time and your help. Thankyou!!!

1. ___ Which of thefollowing statements about the cytoskeleton is false?

(a) The cytoskeletonis made up of three types of protein filament.

(b) The bacterialcytoskeleton is important for cell division and DNAsegregation.

(c) Protein monomersthat are held together with covalent bonds form cytoskeletalfilaments.

(d) The cytoskeleton of acell can change in response to the environment.

2. ___ Which of thestatements below about intermediate filaments is false?

(a) They can stayintact in cells treated with concentrated salt solutions.

(b) They can befound in the cytoplasm and the nucleus.

(c) They can beanchored to the plasma membrane at cell-cell junction.

(d) Each filament is about10 ?m in diameter.

3. ___ Keratins,neurofilaments, and vimentins are all categories of intermediatefilaments. Which of the following properties below is nottrue of these types of intermediate filaments?

(a) They strengthencells against mechanical stress.

(b) Dimers associateby noncovalent bonding to form a tetramer.

(c) They are foundin the cytoplasm.

(d) Phosphorylation causesdisassembly during every mitotic cycle.

4. ___ Which of thefollowing statements about microtubules is true?

(a) Motor proteinsmove in a directional fashion along microtubules by using theinherent structural polarity of a protofilament.

(b) The centromerenucleates the microtubules of the mitotic spindle.

(c) Becausemicrotubules are subject to dynamic instability, they are used onlyfor transient structures in a cell.

(d) ATP hydrolysis by atubulin heterodimer is important for controlling the growth of amicrotubule.

5. ___ Thehydrolysis of GTP to GDP carried out by tubulin molecules________________.

(a) provides theenergy needed for tubulin to polymerize

(b) occurs becausethe pool of free GDP has run out

(c) tips the balancein favor of microtubule assembly

(d) allows the behavior ofmicrotubules called dynamic instability

6. ___ The microtubulesin a cell form a structural framework that can have all thefollowing functions except which of the following?

(a) holding internalorganelles such as the Golgi apparatus in particular positions inthe cell

(b) creating longthin cytoplasmic extensions that protrude from one side of thecell

(c) strengtheningthe plasma membrane

(d) moving materials fromone place to another inside a cell

7. ___ Which of thefollowing statements about organellar movement in the cell isfalse?

(a) Organellesundergo saltatory movement in the cell.

(b) Only themicrotubule cytoskeleton is involved in organellar movement.

(c) Motor proteinsinvolved in organellar movement use ATP hydrolysis for energy.

(d) Organelles areattached to the tail domain of motor proteins.

8. ___ Which of thefollowing statements is correct?

Kinesins and dyneins____________________.

(a) have tails thatbind to the filaments

(b) move along bothmicrotubules and actin filaments

(c) often move inopposite directions to each other

(d) derive their energyfrom GTP hydrolysis

9. ___ Cell movementinvolves the coordination of many events in the cell. Which of thefollowing phenomena are not required for cell motility?

(a) Myosin-mediatedcontraction at the rear of the moving cell.

(b) Integrinassociation with the extracellular environment.

(c) Nucleation ofnew actin filaments.

(d) Release ofCa2+ from the sarcoplasmic reticulum.

10. ___Which of the followingstructures shorten during muscle contraction?

(a) myosinfilaments

(b) flagella

(c) sarcomeres

(d) actin filaments

7. ___ Referring to Figure Q16-29,which of the following statements below is false?

(a) A constitutivelyactive mutant form of PKA in skeletal muscle cells would lead to adecrease in the amount of unphosphorylated phosphorylasekinase.

(b) A constitutivelyactive mutant form of PKA in skeletal muscle cells would notincrease the affinity of adrenaline for the adrenergicreceptor.

(c) A constitutivelyactive mutant form of PKA in skeletal muscle cells would lead to anexcess in the amount of glucose available.

(d) A constitutivelyactive mutant form of PKA in skeletal muscle cells would lead to anexcess in the amount of glycogen available.

8. ___ Match the targetof the G protein with the appropriate signaling outcome.

adenylyl cyclase________ A. cleavageof inositol phospholipids

ion channels_________ B.increase in cAMP levels

phospholipase C_________ C. changes in membranepotential