Cell Shape

Question 1

What is the cytoskeleton involved in and its 3 main components?

Answer 1

Involved in structural support, cell-cell interactions, cell division, cell polarity and motility. It has a dynamic structure.
Microfilaments
Microtubules
Intermediate filaments

Question 2

How are actin filaments formed

Answer 2

Actin filaments are built by polymerization of globular actin proteins.
Actin filaments are 7 nm thick
Every actin filament has a minus end and a plus end so they are polarized filaments. At the plus end, the polymerization, addition of new actin proteins, is more frequent, whereas at the minus end depolymerization is more frequent.
G-actin +ATP = actin undergoes a tiny conformational change and it nucleates so forms long filaments (protofilament) when ATP is bound its then called f-actin. It has a twist in its structure giving mechanical strength so helps cells stay in shape.
actin has an ATPase activity, ATP can be hydrolyzed by actin to ADP and Pi and the time it takes for hydrolysis of each ATP is 6 min. These then monomers start falling off the other end.

Question 3

Velcro principle

Answer 3

Many weak interactions = strong interaction

Question 4

Examples of heteropolymers for structural support intermediate filaments

Answer 4

Lamins (all cells)
Keratins (acidic/basic)
Vimentin
Desmin
NF proteins (neuronal)

Question 5

Adherens junction

Answer 5

Sticks cells together
proteins that go across the plasma membrane are called cadherins which are calcium dependent

Question 6

Microtubules

Answer 6

An a, b-tubulin heterodimer is the basic structural unit of microtubules.
a & b tubulins, homologous but not identical.
a-Tubulin can bind GTP
b-Tubulin can hydrolyze its bound GTP to GDP plus Pi, release Pi (causing kinks), and exchange the GDP for GTP.
Grow from the centrosome/mitotic spindle (important in cell division)
Tracks/chromosome segregation
they have a plus and minus end
when these microtubules fall apart and shed from the minus end they break off parts as curled peelings

Question 7

dynein and kinesin are motor proteins

Answer 7

Transporting substances from plasma membrane to inside of the cell as these proteins walk along microtubules. It is an ATP-dependent process.
microtubules have two ends and so kinesin goes from minus to plus end and dynein goes vice versa this is important for direction of cargo transportation.

Question 8

In a flagellum (microtubules)

Answer 8

9 doublet microtubules around and a pair of microtubules in the middle. Waves of contractions/relaxation of microtubules for snake-like movement of flagellum.