cytoskeliton

Question 1

size and function of microfillaments

Answer 1

5-7nm
Actin Determine cell shape
Allow cell movement

Question 2

size and function of intermediate filaments

Answer 2

10-12nm
Intermediate filament proteins: large family of proteins
Mechanical strength and structure

Question 3

size and function of micro-tubules

Answer 3

25 nm in diameter
Organelle and chromosome movement:
Determine position of membrane -bound organelles
Direct transport in the cell
Separate sister chromatids during cell division

Question 4

actin micro-filaments are used to

Answer 4

1) alow dynamic movement e.g. chemo attraction fillapodia
2) define shape of cell e.g. growth cones fillapodia
3) pinching off of cell in cell division

Question 5

explain how actin filament polarity contributes to function

Answer 5

G actin can polymerize at both - & + end but polymerizes faster at + end this is used to move actin in a controlled direction

Question 6

Capping proteins can be used to create unidirectionality in actin explain:
Cap-z
Tropomodulin

Answer 6

Cap-Z blocks + end (normal growth end) limits growth to - end.
Tropomodulin blocks - end where it usually depolymerises stabilizing it for growth.

Question 7

microtubule composition:

Answer 7

• Polymers of Α and β tubulin forming dimers
• dimers organised in protofilament chains (thermaly unstable)
• multiple protofilaments organised round into 13 subunit tubes which are stable
• can be connected into singlet dublets or triplets

Question 8

microtubule assembly involes addition of

Answer 8

GTP bound beta tubulin

while GDp bound tubulin is removed

Question 9

Cytoplasmic kinesin family members walk cargo along microtubules in which diection

Answer 9

towards + end away from centromere

Question 10

dyenin members walk cargo along microtubules in which diection

Answer 10

towards - end towards centromere

Question 11

properties of intermidiate fillaments

Answer 11

No intrinsic polarity
No nucleotide binding
No known motors
High stability
Unique to metazoans
Many different types: -Nuclear lamins -Keratin -Vimentin

Question 12

keratin structure

Answer 12

Conserved alpha-helical rod domain that forms a coiled -coil motif.
then form protofillaments -pairs of coiled coils (simetric no polarity
these coil together to form microfibrils

Question 13

Actin cytoskeleton basis of cellular movement in 3 main ways

Answer 13

Chemotaxis = movent response to chemical signal
Muscles
Flagelum

Question 14

Actin also enables cells to crawl by:

Answer 14

assembling in growth direction and disassembling at other end.

Question 15

Actin polymerisation drives envagination and phagocytosis by:

Answer 15

by ARP2/3 dependent actin polymerization around nucleation factors on cell surface

Question 16

there are 3 main classes of myosin explain differences:

Answer 16

class 1 with a singular motor head. 
Class II and class v are diners class two often conjoining more= less flexibility often used in muscle
Class v can walk along an actin filament due to the splay of its motor head enabling e.g. vesicle transport

Question 17

eukaryotic flagellum consist of:

Answer 17

circular arrangement of micro-tubules with ATP dependent dyenin cross links that bend the flagellum

Question 18

structure and variation of actin filaments alpha beta and gama

Answer 18

Two stranded helical polymers of G-actin monomers

Alpha form in muscle, beta and gamma in other cells

Question 19

microtubules convert between growth and shrinkage GTP favours growth GDP favours shrinkage what is this called

Answer 19

dynamic instability

Question 20

Microtubules often radiate from organising centers (often centrosome) - stable minus end is embedded to prevent breakdown. examples include

Answer 20

Fibroblast: All microtubules head out from MTOC
Neuron axon: microtubule plus end at synapse; minus end in cell body
Transport down long axons; degeneration: starvation of axon terminals
Vesicles transported along microtubules at synapse

Question 21

(micro-tubules) tubulin mutations:

Answer 21

a-tubulin mutations cause impaired neuronal migration in mice and lissencephaly in humans (a brain development abnormality)
b-tubulin mutations cause cortical malformations in the brain

Question 22

intermediate filaments- Neurofilament proteins:

Answer 22

light, medium and heavy (NF-L, NF-M, NF-H) NF proteins form cross-links to provide axons with tensile strength The Level of NF gene expression controls axon diameter (structure), hence rate of electrical signal (function)

Question 23

intermediate filaments- Nuclear lamin proteins

Answer 23

Nuclear lamin proteins A, B and C Form nuclear lamina: meshwork of intermediate filaments lining inside of inner nuclear membrane Determines nuclear shape and provides anchoring point for chromosomes and proteins of nuclear pore complex. Lamin genes are the ancestral intermediate filament. Regulates nuclear reassembly after mitosis

Question 24

what are the 3 types of cell junction

Answer 24

adherant juctions- hold cells together
occluding junctions- seal the gap
gap junctions- alow transport/comunication
synapses

Question 25

adherent/anchoring junctions types

Answer 25

Desmosomes: cell to cell
Hemidesmosome: cell to basal lamia
adherins junction connects actin bundeles of two cells
desmosomes connect intermidiate fillaments of once cell to the next

Question 26

what family of protines hold two desmosomes together

Answer 26

cadherin family

Question 27

tight occlusion junctions
function:
Examples:

Answer 27

Control permeability between cells paracellular transport
Prevent proteins leaking into the interstitial fluid from capillaries or into bladder from glomerulous.
Barrier to ‘harmful’ luminal contents but allows uptake of nutrients/drugs
Permeability changes dependant on type of tissue small intestine vs blood brain barrier

Question 28

occlusion junction pathology

Answer 28

Pathologies affect tight junction permeability e.g. Crohn’s disease tight junctions more permeable

Question 29

gap junction structure/ example

Answer 29

Hexamers of conexin subunit connected end to end

Used for synchronized electrical conductance in brain and cardiac muscle.