Week 8 - Cytoskeleton

Question 1

What are the three roles of a cytoskeleton

Answer 1

Cell shape
Cell strength
Movement

Question 2

What are the three types of cytoskeleton filament

Answer 2

Actin filaments
Microtubules
Intermediate filaments

Question 3

What is the role of actin

Answer 3

Cell surface shape, whole cell locomotion and pinching one cell into two

Question 4

What is the role of microtubules

Answer 4

Position of organelles, intracellular transport and motitic spindle

Question 5

What is the role of intermediate filaments

Answer 5

Mechanical strength

Question 6

How does each filament get utilised in the small intestine

Answer 6

Actin - enables microvilli formation and connects to cell junctions
Intermediate - anchors across cell to provide structure and strength via desmosomes
Microtubules - run from basal to apical surfaces providing transport network

Question 7

What are filaments held together by and why are they strong

Answer 7

Non covalent interactions which when multiple filaments join together are very strong collectively

Question 8

Describe how actin forms

Answer 8

G actin monomers polymerise to form 2 protofilaments which twist to form F actin which is in a helix shape

Question 9

Describe F actin structure

Answer 9

Large clefts which bind to ATP and all G actin faces same way to make it polar

Question 10

Describe nucleation

Answer 10

The first step in formation of a new structure via self assembly

Question 11

What is the critical condition of actin determined by

Answer 11

Rate of addition of G actin (K on) and rate of dissociation of G actin (K off)

Question 12

Describe how G actin associates and dissociates

Answer 12

If [G actin]> critical condition then G actin added
If [G actin]< critical condition then G actin dissociated

Question 13

Define treadmilling

Answer 13

Where subunits are added at + end and removed from - end yet the length remains constant

Question 14

Explain how Microtubules are formed

Answer 14

Polymerisation of tubulin heterodimers to form subunits which form protofilaments. 13 protofilaments form a hollow cylinder with a central lumen

Question 15

Explain how Microtubules are polar

Answer 15

Alpha tubulin at the - end and beta tubulin at the + end creates polarity

Question 16

Why are Microtubules unstable

Answer 16

Dissociation of tubulin GDP is favourable at the plus end, so it tends to grow a cap and shrink.
Minus end is stable at the MTOC

Question 17

What is the MTOC

Answer 17

The centrosome

Question 18

What are two distinct features of centrosomes

Answer 18

A pair of centrioles and pericentriolar material (protein matrix)

Question 19

What is the site of nucleation for Microtubules

Answer 19

Gamma tubulin ring complex found on the pericentriolar material

Question 20

What are the two associated motor proteins for microtubules

Answer 20

Kinesin and dynein

Question 21

What does kinesin do

Answer 21

Moves towards the + end of the Microtubules (anterograde = away from centre)

Question 22

What does dynein do

Answer 22

Move towards the - end of the Microtubule (retrograde = towards centre)

Question 23

Describe intermediate filaments

Answer 23

Great tensile strength, non polar and no associated motors

Question 24

Give an example of intermediate filaments in a cell

Answer 24

Nuclear laminar

Question 25

Name the 4 types of tissue

Answer 25

Epithelial Muscle Nervous Connective

Question 26

What are the three types of cell junction

Answer 26

Anchoring junction Occluding junction Communicating junction

Question 27

Describe anchoring junctions

Answer 27

Anchor cytoskeleton between cells or between cells and Extracellular matrix

Question 28

Describe occluding junctions

Answer 28

Prevents passage of ions and small molecules between cells

Question 29

Describe communicating junctions

Answer 29

Direct connections between cytoplasm of two cells

Question 30

Anchoring junctions: what do adherens junctions do

Answer 30

Connects actin filament of one cell with actin filament of another cell

Question 31

Anchoring junctions: What do desmosomes do

Answer 31

Connects intermediate filaments from one cell to intermediate filaments of another cell

Question 32

Anchoring junctions: What do Actin linked cell matrix (FA) junctions do

Answer 32

Anchors actin filaments in cell to extracellular matrix

Question 33

Anchoring junctions: what do hemidesmosome do

Answer 33

Anchors intermediate filaments in a cell to the extracellular matrix

Question 34

What do gap junctions do

Answer 34

Allow passage of small water soluble molecules between cells

Question 35

What is the name for the transmembrane protein responsible for cell cell attachment in anchoring junctions

Answer 35

Cadherins

Question 36

What is the name for the transmembrane protein responsible for cell matrix attachment

Answer 36

Integrins

Question 37

What is the term for when Cadherins bind to the same type of cadherin

Answer 37

Homophilic adhesion (different type is heterophilic adhesion)

Question 38

What is cadherin binding dependant on

Answer 38

Extracellular Ca2+

Question 39

What is the extracellular matrix

Answer 39

Network of proteins carbohydrates and water which provide support for cells and tissues and secreted by fibroblasts

Question 40

Hat are the three types of macromolecule in the ECM

Answer 40

Glycosaminoglycans Fibrous proteins Glycoproteins