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CU DENVER / Biology / BIOL 3611 / What is the function of the axonemal?

What is the function of the axonemal?

What is the function of the axonemal?


UNIT 3 EXAM – study guide I

What is the function of the axonemal?

Chapter 13 – Cytoskeletal systems

1. Compare and contrast microtubules, microfilaments and intermediate  filaments;








I – Acidic cytokeratins II – Basic cytokeratins III – Vimentin,  

Desmin, GFA protein IV – Neurofilament  protein

V – Nuclear lamins VI - Nestin


25 nm

7 nm

8 – 12 nm



∙ Organization  



of animal cell

shape and  


∙ Chromosome  


∙ Intracellular  

transport and

movement of  



∙ Cell motility

∙ Muscle  


∙ Cell  


∙ Cytoplasmic  


∙ Cytokinesis

∙ Maintenance  of animal  


∙ Intracellular  


∙ Structural  


∙ Maintenance of animal cell  


∙ Formation of  

nuclear lamina  

and scaffolding

∙ Strengthening  

of nerve cell  




∙ Keeping muscle fibers in  



Polymerizati on




What is the function of cytoplasmic?

Don't forget about the age old question of Can mutations in sex cells be inherited?


Drugs affecting microtubules (MT)



Colchicine, colcemid

Binds tubulin monomers,  

Inhibits assembly


Binds β-tubulin

Inhibits polymerization

Vinblastine, vincristine

Aggregates tubulin heterodimers


Stabilizes microtubules

Drugs affecting Microfilaments (MF)



Cytochalasin D

Prevents monomer addition to plus ends

Latrunculin A

Sequesters actin monomers


Binds and stabilizes assembled  


What are the effects of nocodazole?

Don't forget about the age old question of Explain torah's opinion about god.

2. How does ftsZ support the theory of endosymbiosis?

ftsZ proteins have been found to be produced by certain organelles in in  some eukaryotes, such as chloroplasts and mitochondria, and localizes to  sites where these organelles divide. The overall structure of ftsZ protein in  eukaryotes are strikingly similar to the counterparts in bacterial cells and  even bind to the same phosphonucleotides.

3. Explain the following terms:

∙ Nucleation:  

This is the process in the formation of microtubules where oligomers serve as nuclei from which new microtubules can grow.  

∙ Elongation:  Don't forget about the age old question of Why is pareto efficiency important?

This is the growing of the microtubule by the addition of subunits at either  end

∙ Treadmilling

This is the simultaneous assembly and disassembly at either the plus or  minus ends of microtubules.

∙ GTP/ATP hydrolysis

This is the process by which energy stored in ATP/GTP is released. If you want to learn more check out How do you tell if an allocation is pareto efficient?

Microtubules form primarily by addition of GTP-bound beta-tubulin at the (+)  end, but after being added, the beta-tubulin molecules later hydrolyze their  GTP, leaving them GDP-bound.

4. Explain the following terms:

∙ Catastrophe:  

This is the event in which when microtubule switches from growth to  shrinkage, the microtubules disappear completely

∙ Rescue:  

This is the event in which when microtubule switches from growth to  shrinkage, the microtubules abruptly switch back to growth phase.

∙ GTP cap:  

This stabilizes the plus end of growing microtubules.

5. What is the dynamic instability model of microtubules

∙ This is the growth of microtubules in which there are periods of slow growth  and rapid shrinkage.  

6. Explain the functions of these parts of the cell Don't forget about the age old question of What is the configuration of an electron?
Don't forget about the age old question of What are the two functions of the respiratory system?

∙ MTOC:  

This serves as a site at which MT assembly is initiated and acts as an anchor  for one end of the microtubules.

∙ Centrosome:

A centrosome is an MTOC near the nucleus of a cell containing centrioles  from which spindle fibers develop in cell division.

∙ Centriole:

Centrioles are organelles which help cell division in animal cells by the  forming of spindle fibers which separate the chromosomes during cell division

∙ Basal bodies:

These are MT associated structures found at the base of the cilia

∙ Gamma tubulin:

These nucleate the assembly of new microtubules away from the centrosome

7. Describe the role of the following proteins  

∙ MAPs (microtubule associated proteins)

MAPs bind at regular intervals along the wall of a microtubule, to increase MT  stability and affects density of MT bundles

∙ +TIPS ( plus end tubulin interacting proteins)

These capture and protect the growing plus ends of microtubules, stabilizing  them.

∙ Stathmin/OPv18

These bind to tubulin heterodimers preventing them from polymerizing

∙ Catastrophins

These act at the ends of microtubules once they have been polymerized to  promote the peeling of subunits at the end.

∙ Katanins

Katanins sever microtubules

8. What is tau and how does it link to disease?

Tau is a MAP that causes microtubules to form tight bundles in axons. Large  amounts of hyperphosphorylated tau protein cause neurofibrillary tangles  which can lead to alzheimer’s disease, pick’s disease and several types of  palsy.

9. Structures of microfilaments



Stress fibers

These are contractile bundles of actin  which stretch from the trailing end to the front end of the cell found in cells which  do not move well.

Cell cortex

These lie immediately beneath the  plasma and crosslinked into a gel. They  are found in rapidly moving cells.


These are thin, sheet-like membrane  protrusions found at the leading edge  (front) of motile cells. The actin in  lamellipodia are typically less well  organized than in filopodia.


These are thin, actin-rich plasma membrane protrusions that function as  antennae for cells to probe their  environment. Actin in filopodia are  typically more well organized than in  lamellipodia.

10.What is the relationship between actin fibers and myosin S1?

The polarity of actin fibers can be observed by decorating them with myosin  S1 (globular heads of myosin II cleaved by proteases).

11.Describe the competition between thymosin β4 and profilin in actin  polymerization

∙ Thymosin β4 and profilin both compete for binding to G-actin monomers.  They are involved in the dynamic turnover and restructuring of actin  filaments.

12.Describe the role of the following proteins in actin polymerization




These bind to ADP-G-actin and F-actin  and are thought to increase the rate of  turnover of ADP-actin at the minus ends  of microfilaments. They also sever  filaments creating new plus ends as they do.

Capping proteins (CapZ and  


Capping proteins prevent either further  addition or loss of subunits thereby  stabilizing them.

CapZ binds to the plus end of actin  filaments and prevents further addition  of subunits.  

Tropomodulins bind to the minus end  of actin filaments and prevents further  loss of subunits.


Gelsolin severs actin MFs and cap their  newly exposed plus ends, thereby  preventing further polymerization


Mediates the bundling of actin filaments  into tightly organized arrays.Very  prominent in focal contacts and focal  adhesions.


Fascin keeps actin within the core of a  filopodium tightly bundled, contributing  to the spike-like appearance of such  protrusions


Cross-linking protein important in the  formation of filopodia


Villins also binds tightly together ,  adjacent MFs

Myosin I

MFs in the actin bundle are connected to the plasma membrane by lateral  proteins consisting of Myosin I and  calmodulin.

Myosin II

Slides MFs in muscle


MFs in the actin bundle are connected to

the plasma membrane by lateral  proteins consisting of Myosin I and  calmodulin.


Spectrin connects microfilaments to  each other, to proteins with the plasma  membrane and to the network of  intermediate filaments beneath the  terminal web.


This helps branches to form nucleating  new branches on the sides of existing  filaments.


Formins are required to assemble certain unbranched F-actin structures


These promote the spatially regulated  actin polymerization required for  efficient chemotaxis in response to  attractive and repulsive guidance cues


Act as splices to join two MFs where they intersect

Classifications of actin proteins

Proteins that

a. Regulate polymerization

∙ Thymosin beta4

∙ Profiling

b. Cap actin filaments

∙ CapZ (+ ends)

∙ Tropomodulin (- ends)  

c. Crosslink actin filaments

∙ Filamin

d. Sever actin filaments

∙ Gelsolin

e. Bundle actin filaments

∙ Alpha-actinin

∙ Fascin  

∙ Myosin I

∙ Calmodulin

∙ Fimbrin

∙ villin

f. Link actin to membranes

∙ Band 4.1

∙ Ezrin

∙ Radixin

∙ Moesin

∙ Spectrin

∙ Ankyrin

g. Promote actin branching and growth

∙ Arp 2/3 complex

∙ Formins

13.What is the role of Rho family GTPases and growth factors for regulating MF  formation?

Rho GTPases are regulators of actin cytoskeleton . They perform functions  ranging from formation of protrusions to assembly and disassembly of the  cytokinetic furrow to the regulation of endo and exocytosis. They are  stimulated by;

guanine-nucleotide exchange factors (GEFs): Foster exchange of a bound  GDP for GTP.

GTPase activating proteins (GAPs): Stimulate Rho GTPases to hydrolyze their  bound GTP thereby inactivating them.

Guanine-nucleotide dissociation inhibitors (GDIs): Sequester or isolate  inactive Rho GTPases in the cytosol

14.How can immunofluorescence aid in the identification of cancer cell types  based on IF?

Intermediate filament typing is used to determine the type of IF present in  cancer cells as tumor cells are known to retain the IF proteins characteristic  of the origin.

15.Explain the dynamic nature of IF in the nuclear lamina

IFs are not static structures. The nuclear lamina contains proteins called  lamins which become phosphorylated and breakdown as part of the nuclear  envelope disassembly in mitosis.

16.What are plakins?

Plakins are specific linker proteins which are responsible for the mechanical  integration of intermediate filaments, microfilaments and microtubules.

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