Membranes (wk 5 and 6)

Question 1

T/F:

Different compartments of the cells all have the same environments of the cytosol

Answer 1

False

They can have different environments than the cytosol

Question 2

List some organelles that may have two membranes rather than one

Answer 2

Nucleus
Mitochondria
Chloroplast

Question 3

In organelles that have two membranes, the inter-membrane is topologically equivalent to the ______ of the cell

Answer 3

Exterior

Question 4

In organelles that have two membranes, the internal aqueous space is topologically equivalent to the _____ of the cell

Answer 4

Cytoplasm

Question 5

List some functions of lipids

Answer 5

Store energy
Insulation from the environment
Water repellent
Membrane structure
Cofactors for enzymes
Signalling molecules
Pigments
Antioxidants

Question 6

What is the most important function of membranes?

Answer 6

Allows cells to exist and be unique

Allows differentiation of different cell types/organs

Question 7

T/F:

Unsaturated fatty acids pack in a fairly orderly way because of favourable reactions

Answer 7

False

Saturated fatty acids

Question 8

T/F:
Unsaturated cis fatty acids have a lower melting point resulting in less thermal energy to disrupt disordered packing of unsaturated fatty acids

Answer 8

True

Question 9

Why do unsaturated fatty acids pack badly?

Answer 9

Double bonds cause kinks

Question 10

What’s the benefit of having more saturated fats compared to unsaturated fats in the blood stream?

Answer 10

More thermostable, can survive heat better

Question 11

How do trans fatty acids form?

Answer 11

Partial dehydrogenation of unsaturated fatty acids

Question 12

T/F:

Trans fatty acids pack more regularly and show higher melting points than cis forms

Answer 12

True

Question 13

T/F:

Consuming trans fatty acids decreases risk of cardiovascular disease

Answer 13

False

Increases

Question 14

T/F:

The properties of the tail group in a lipid determines the surface properties of membranes

Answer 14

False

properties of the head groups will determine the surface properties of the membranes

Question 15

Describe the net charge of the inner and outer side of the membrane and what this allows

Answer 15

The charges will be different
Allows polarization and depolarization
Allows for synapses
Life without this would not exist

Question 16

Which lipid is the major constituent of eukaryotic cell membranes?

Answer 16

Phosphatidylcholine

Question 17

T/F:

Bacterial cells can synthesise phosphatidylcholine

Answer 17

False

Therefore our immune system can recognise bacterial cells and remove them

Question 18

T/F:

The backbone of sphingolipid is glycerol

Answer 18

False

Question 19

T/F:

The backbone of sphingolipids is a long-chain amino alcohol sphingosine

Answer 19

True

Question 20

Which phospholipid constitutes myelin that surrounds nerves?

Answer 20

Sphingomyelin

Question 21

What confers flexibility to phosphatidylcholine rather than sphingomyelin?

Answer 21

Phosphatidylcholine has two saturated bones (double bonds)

Question 22

What is the physiological role of sterols in the cell?

Answer 22

Modulate fluidity and permeability
Thicken the plasma membrane
Most bacteria lack sterols

Question 23

How can you obtain cholesterol?

Answer 23

In food

Synthesize in the liver

Question 24

When do micelles form?

Answer 24

When in the presence of a solution of amphipatic molecules that have larger heads than tails

Question 25

T/F: | A vesicle has a single layer

Answer 25

False | Double layer

Question 26

How does sterol affect membranes?

Answer 26

Planar so makes the membranes rigid

Question 27

What type of components can the central aqueous cavity of a vesicle contain?

Answer 27

Dissolved molecules

Question 28

What shape are the individual units of the lipid monolayer

Answer 28

Cylindrical

Question 29

List some of the roles of membranes

Answer 29

• Define the boundaries of the cell • Allow import and export o Selective import of nutrients (e.g., lactose) o Selective export of waste and toxins (e.g., antibiotics) • Retain metabolites and ions within the cell • Sense external signals and transmit information into the cell • Provide compartmentalization within the cell o separate energy-producing reactions from energy-consuming ones o keep proteolytic enzymes away from important cellular proteins • Produce and transmit nerve signals • Store energy as a proton gradient • Support synthesis of ATP

Question 30

What type of forces stabilise membranes?

Answer 30

Non-covalent forces | Especially the hydrophobic effect

Question 31

T/F: | Lipid bi layers in cells are symmetric

Answer 31

False | asymmetric

Question 32

T/F: | Carbohydrates are always intracellular to the membrane

Answer 32

False | always extracellular

Question 33

Are integrins firmly or weakly attached to the membrane?

Answer 33

Firmly attached

Question 34

Are proteins firmly or weakly attached to the membrane?

Answer 34

Weakly attached | Can be removed easily

Question 35

T/F: | Fatty acids can diffuse laterally in membranes

Answer 35

True

Question 36

T/F: | Glycolipids are mostly found on the inside of membranes

Answer 36

False mostly on the outside they are used as secondary markers for our immune response

Question 37

T/F: | Prokaryotes lack sterols

Answer 37

True

Question 38

T/F: | Plasma membranes have lots of cholesterol that confer flexibility

Answer 38

False | lots of cholesterol that confer rigidity

Question 39

Which side of the bilayer is more positively charged?

Answer 39

Outside leaflet

Question 40

T/F: | Membranes are permeable to polar molecules

Answer 40

False | non-polar

Question 41

Which part of the membrane does CO2 interact with when it passes easily through

Answer 41

Interacts with the fatty part

Question 42

What two phases can the membrane be in?

Answer 42

Gel phase= molecules do not move around | Fluid phase= molecules can move around

Question 43

Which phase are membranes most likely to be found in physiological conditions?

Answer 43

Fluid phase

Question 44

What mostly determines membrane fluidity?

Answer 44

Fatty acid composition

Question 45

What types of fatty acids are required for a membrane to maintain their fluidity?

Answer 45

Unsaturated fats These have lower melting points Need them to maintain the fluidity

Question 46

T/F: | Proteins move faster than lipids

Answer 46

False

Question 47

T/F: | Lateral diffusion of individual lipids is fast

Answer 47

True

Question 48

T/F: | 'flip flop' rarely occurs

Answer 48

True

Question 49

Why are spontaneous flips from one leaflet to another rare (transverse diffusion)

Answer 49

The charged polar head must traverse the hydrophobic tail region of the membrane

Question 50

Floppases move individual lipids from the ___ to the ____

Answer 50

inside to outside

Question 51

Flippases move individual lipids from the outside to the inside

Answer 51

outside to the inside

Question 52

Scramblases move lipids in ____

Answer 52

either direction, towards equilibrium