Membranes

Question 1

What types of lipids are most abundant in animal cell membranes?

Answer 1

Glycerophospholipids.

Question 2

What are the 4 types of glycerophospholipids and their properties?

Answer 2

Phosphatidylethanolamine: Electrically neutral at physiological pH
Phosphatidylserine: Electrically negative
Phosphatidylcholine: electrically neutral at physiological pH

Question 3

What is the difference between sphingolipid and glycerophospholipid?

Answer 3

made from sphingomyelin rather than glycerol.

Question 4

Are sphingomyelin and Sphingosine electrically neutral at physiological pH?

Answer 4

yes.

Question 5

What are the key properties of a sterol?

Answer 5

Rigid ring structures: single polar group (OH-), single short non-polar chain.

Question 6

What is an example of a sterol?

Answer 6

Cholesterol: OH bit orients to polar part/heads of phospholipids. This intercalates with acyl chains and reduces motility. The higher the temperature, the less fluid the membrane. At low temps, it disrupts the ordered packing of the acyl chains.

Question 7

Which is more energetically favourable? Micelles or Planar bilayer with edges exposed to water?

Answer 7

Micelles.

Question 8

What do flippases and floppases do?

Answer 8

They use ATP to move specific phospholipids from one leaflet to another.

Question 9

What is an integral membrane protein?

Answer 9

Proteins that are embedded in the membrane, alpha helix (recognition, receptors),

Question 10

What are the properties/uses of Intermediate filaments?

Answer 10

Uses: for cells that have to undergo pressure (not movement). Great strength, enables cells to withstand mechanical stress that occurs when stretched. Strengthens nuclear membrane, producing nuclear lamina. Forms desosomes between cells (bits that hold the cells together).
Structure: Alpha monomeric strands twist with other strands to produce a DIMER and binding is non-covalent. Structure is rope-like. Diameter is 10nm. Plectin (accessory protein) required to reinforce filaments.

Question 11

What three main filaments is the cytoskeleton made of? How are they distributed across the cell?

Answer 11

Intermediate filaments- from nucleus to rest of the cell
Microtubules-spider out from nucleus to the rest of the cell
Actin filaments- around the cell and microvilli.

Question 12

What are the properties/uses of Intermediate filaments?

Answer 12

Uses: for cells that have to undergo pressure (not movement). Great strength, enables cells to withstand mechanical stress that occurs when stretched. Strengthens nuclear membrane, producing nuclear lamina. Forms desosomes between cells (bits that hold the cells together).
Structure: Alpha monomeric strands twist with other strands to produce a DIMER and binding is non-covalent. Structure is rope-like. Diameter is 10nm. Plectin (accessory protein) required to reinforce filaments.

Question 13

What is the structure and function of the microtubule?

Answer 13

Structure: Microtubules are polarised throughout the cell. They are long. hollow and stiff. They are made of alpha and beta tubulin by non covalent bonds and 25nm diameter. They rupture when stretched. They are polar (alpha is minus end, beta is plus end)
Function: Provides motorway system for vesicles and other stuff. Allows mitotic division. Has dynamic instability- microtubule strands grow out of centromeres in different directions, so if the direction is not required, the microtubule quickly falls apart and a new strand in a different direction is made.

Question 14

What three main filaments is the cytoskeleton made of? How are they distributed across the cell?

Answer 14

Intermediate filaments- from nucleus to rest of the cell
Microtubules-spider out from nucleus to the rest of the cell
Actin filaments- around the cell and microvilli.

Question 15

What are the different transporters and what do they transport?

Answer 15

P type pump: ions
F-type pump: H+
ABC transporter: small molecules
These all rely on ATP

Question 16

What can easily pass membranes—> what can’t easily pass a membrane?

Answer 16

Gases (o2, co2), non polar (hydrophobic) molecules (benzene), Small polar molecules (H20, ethanol), large polar molecules and charged molecules and transporters.

Question 17

Microfilaments

Answer 17

F-actin, G-actin

Question 18

Intermediate filaments

Answer 18

4 major types, they extend across the cell cytoplasm, rope like structure.

Question 19

Microtubules

Answer 19

alpha, beta tubulin.

Question 20

In microtubules, how do they assemble?

Answer 20

Heterodimer of alpha and beta tubulin built into 13 protofilaments.
GTP is bound to alpha tubulin is trapped in the heterodimer, therefore never hydrolysed.

Question 21

Actin filaments, how are they assembled?

Answer 21

Neg to pos- have Mg2+ ions in their dimers.

Question 22

How is actin assembled: processes?

Answer 22

Nucleation: where a few molecules G-actin with ATP bind together in the nucleus.
Elongation: where the rest of the G acting molecules start binding and they produce an F-actin filament.
Steady pahse: Where G actin molecules come on and off off the F-acting filament.

Question 23

How are intermediate filaments assembled: process?

Answer 23

They all have N-terminal segments, helical egments and Linker segments.
Alpha helical region adds onto each other to produce a staggered dimer. Then 8 come together to produce a rope-like structure.
They are anchored in cell junctions like in keratin and desmosomes.

Question 24

How does cholesterol change the fluidity of the membrane at different temperatures?

Answer 24

When temp is high, cholesterol decreases the fluidity
When temp is low, cholesterol increases fluidity.
Cholesterol is ampipathic and sticks to acyl chain of phospholipid.

Question 25

What is the surface of many cells covered in?

Answer 25

Glycocalyx. (poly sugar side chains)

Question 26

How do peripheral membrane proteins stop themselves from interacting with the hydrophobic core?

Answer 26

Ampipathic alpha helix, hydrophobic loop, lipidation. electrostatics.

Question 27

Where is phosphatidylserine mostly found in cells?

Answer 27

On the cytosolic side. It is negative and inside is more negative that outside.

Question 28

What does nucleus do?

Answer 28

Stores DNA
DNA, RNA synthesis

Question 29

What does nucleolus do?

Answer 29

Ribosome production, rRNA synthesis.

Question 30

What does the nuclear envelope do?

Answer 30

QC check, only mature mRNA can leave.