Week 4 lectures

Question 1

What is a phosphatidyl lipid

Answer 1

A glycerol backbone with 2 ester bonds to fatty acid chains and 1 ester bond to a phosphate group which binds to a polar head group which can vary

Question 2

Which Phosphatidyl lipid is charged

Answer 2

Phosphatidylserine

All of them have charged parts of the head group but they cancel out overall except phosphatidylserine

Question 2

Name the 3 phosphatidyl lipids and their head groups

Answer 2

phosphatidylenthanolanime - ethanol amine head group
Phosphatidylserine - serine head group
Phosphatidylcholine - choline head group

Question 2

How are sphingosine lipids different to phosphatidyl lipids

Answer 2

Instead of the 3 carbon with 3 hydroxyl groups (glycerol), sphingosine has 3 carbon structure with 2 hydroxyl groups and 1 amine. 1 hydroxyl group and 1 amine group are used to bond to the fatty acid chains and 1 hydroxyl group is used to bond to the phosphate

Question 3

which group which is added to sphingosine based lipids causes them to be negatively charged

Answer 3

sialic acid

sialic acid is a sugar group which can be added to sphingosine based lipids (glycosylated)

Question 4

Structure of cholesterol

Answer 4

Has a polar head group which consists of a singular hydroxyl group

A 4 membered ring structure which is highly rigid, and a short flexible aliphatic side chain.

much smaller and more rigid than the other lipid groupsn

Question 5

What are the 3 key lipid types

Answer 5

Phosphatidyl lipids- phosphatidylenthanolanime, Phosphatidylserine, Phosphatidylcholine

Sphingosine-based lipids and glycolipids

cholesterol

Question 6

What are the 4 types of motion found in a lipid bilayer

Answer 6

Flextion (pretty useless)
rotation (pretty useless)
lateral diffusion
flip-flop

Question 7

How can changes in the lipid bilayer cause changes in the fluidity of the membrane

Answer 7

The closer and the more regular the packing of the tails the more viscous and less fluid the membrane will be

this is dependant on the length of the tails - shorter tails are packed less tightly.
number of double bonds- more double bonds means packed less tightly

Question 8

What is the effect of cholesterol on membrane fluidity and why

Answer 8

No effect. tighter packing close to the head group is counteracted by less order away from the head group

It does effect the permeability of the membrane

Question 9

Different ways a protein can associate with the membrane

Answer 9

QUESTION ASKED ON PADLET CHECK FOR ANSWER

Question 10

How is the movement of a membrane proteins limited

Answer 10

Movement of membrane proteins are limited by the cortical cytoskeleton, Proteins largely move within one membrane domain but can move between domains

Question 11

How are proteins on the basal and apical sections of epithelial cells kept apart

Answer 11

there are very tight junctions towards the apical side of the cell, this tight junction means that proteins from the apical side cannot move to the basal side maintaining the polarity of epithidiel cells

Question 12

What are the roles of the cytoskeleton

Answer 12

Structural integrity
Shape and movement of cell
Subcellular organisation of the cell

cytoskeleton is a highly dynamic assembly

Question 13

How does the structure of the cytoskeleton allow for dynamic behaviour

Answer 13

Its composed of fibres that are build from individual proteins. Allowing monomers to be added and removed as needed.
they can be added and removed form either end.

Question 14

What are the 3 types of filaments

Answer 14

Intermediate filaments
Microtubules
Actin filaments

Question 15

What is the basic unit of a microtubule

Answer 15

A heterodimer of tubulin (alpha and beta subunits)

Question 16

How is a microtubule structured

Answer 16

Made form heterodimers of tubulin and formed around an inner hollow core

Thickest of all filaments
Have plus and minus ends

Question 17

What is the difference between the plus and minus ends of a microtubule

Answer 17

Minus end has an alpha subunit on the end
plus end has a beta subunit
Minus end is anchored into the MTOC or centrosome

Question 18

How do microtubules grow/shrink

Answer 18

Tubluin can bind to GTP. When they are in the GTP bound state this promotes the addition of further monomers. tubulin is also a GTPases and slowly converts GTP into GDP.
The end of the polymer can be severed of exposing the GDP bound tubulin which promotes the rapid removal of the monomers

The addition and removal of GTP caps causes the growth and shrinkage

Question 19

What are motor proteins

Answer 19

Proteins which associate with and move along microtubules and actin. Binds to the proteins as well as the cargo and uses ATP to change conformations to move along the actin/microtubule

On microtubules they can move from the plus end to the minus end. On actin it can only move from - to + end

Question 20

Different types of mictrotubule motor proteins

Answer 20

Kinesins - Move cargo from minus end to plus end – away from MTOC

Dynesins - move cargo from plus end to minus end

Question 21

What are the functions of microtubules

Answer 21

Interphase:
Vesicular transport
Structural integrity
formation/support of specialised cell structures like cilium

Dividing cell:
chromosome segregation

Question 22

Name drugs that affect microtubules

Answer 22

Colchicine - destabilises microtubules, Anti inflammatory drug

Taxol- Stabilises microtubules - cancer drug

Question 23

Name the process by which actin polymerises and how it works

Answer 23

Nucleation - nucleation is a process in which you disfavor the assembly of a small number of identical building blocks (actin monomers here) into a complex, while the further addition of building blocks once this small complex is formed becomes favorable. The tipping point of the number of assembled building blocks where you can switch from disfavored to favored assembly varies for each complex, for actin filaments that is three actin monomers. This process achieves two conflicting objectives. You want to make spontaneous assembly of monomers inefficient so that protein complexes don’t form at random (1 to 3 assembled actin monomers). At the same time you want to make the generation of larger protein complexes efficient as it otherwise would be practically impossible to build complexes of hundreds to thousands of monomers (3 and more assembled actin monomers).

Question 24

How can nucleation of actin be overcome

Answer 24

Arp2/3 complex
this is a complex which uses other existing actin filaments to create more actin filament. It is a highly regulated complex and is only active and when a new actin filament needs to be formed. when its activated the backside of the complex binds to the pre existing actin filament. this making it a new site for actin growth.
The Arp2/3 complex contains to proteins, Arp2 and Arp 3 which are structurally similar to actin making it much easier for an actin filament to form.

this combination of multiple beached structures means that you form a sheet-like structure composed of actin filaments

Question 25

How can polymerisation of actin be sped up

Answer 25

A protein family called formins bind to the plus end and provide a location to effectively add new actin monomers - doesn’t overcome nucleation but speeds up the process of actin polymerisation generating very long actin structures which are point like unlike sheet like structures formed from Arp2/3 complexes

Question 26

Motor proteins and actin

Answer 26

Motor proteins associate with and move along actin filaments using hydrolysis of ATP as energy
The motor proteins associated with actin is called myosin and can move actin filaments against each other and protein complexes, commonly on the surface of vesicles.
myosins move from the - to + end only

Question 27

What are the roles of myosin-I and myosin-II

Answer 27

Myosin-I - 1 side of the protein binds to the F-actin and the cargo side binds to membrane- can be vesicle or plasma membrane
Myosin-II moves different actin filaments against each other - muscle function, muscles are just highly organised structures of actin and myosin filaments when you contract the myosin filament pulls together the actin filaments

Question 28

Name actin filament structure

Answer 28

Microvilli
contractile bundle
sheet-like and finger-like projections
contractile ring
Stabilisation of membrane cortex - cell membrane are very thin and fragile, actin filaments underpin the membrane providing strength and mechanical stability.

Question 29

What is change of cell shape in migration atory cells

Answer 29

Actin filament and dynamic of actin filaments

Question 30

What are intermediate filaments

Answer 30

Toughest and most durable cytoskeleton structures, provide mechanical stability to the cell and like the dynamic features of actin and myosin

Question 31

Where are intermediate filaments found

Answer 31

Nucleus - form the nuclear lamina which underlies and strengthens the nuclear envelope
cytoplasm- form a network throughout the cell and are liked to cell-cell junctions allowing them to provide mechanical strength across a large number of cell - very important fro epithelial cells.

Question 32

What are the intermediate filaments made of

Answer 32

Several different proteins
Need to know that intermediate filaments that make up the nuclear lamia are Lamins A,B and C

Question 33

DO VESICLES LECTURE