Week 7 - Plasma Membrane and Transport across membranes

Question 1

What are 5 examples of membrane function?

Answer 1

• a physical and chemical barrier
• communication
• recognition
• energy conversion
• a plateform for cellular processes

Question 2

What is the structure of a membrane?

Answer 2

• a very thin film of lipids and proteins held together by non-covalent interaction
• double lipid layer = lipid bilayer
• forms an impermeable barrier to water soluble (polar molecules)

Question 3

What are membrane lipids?

Answer 3

• phospholipids
• amphipatic
• two hydrophobid fatty acid chains
• a phosphate containing hydrophilic head group

Question 4

What is the formation of a fatty acid?

Answer 4

long hydrocarbon chain with a carboxyl end and a methyl end

Question 5

What does the head of a membrane lipid contain?

Answer 5

polar, hydrophilic head containing choline (example head group) and phosphate and prefer to be in aqueous environment

Question 6

What does the tail of a membrane lipid contain?

Answer 6

non polar, hydrophobic tail made of fatty acid (hydrocarbon chain) and a glycerol

Question 7

How do major lipids work in cell membranes?

Answer 7

• phosphate groups replaces a fatty acid attched to central glycerol
• group always binds to 3rd apart from with sponge where its the 2nd

Question 8

How does the bilayer work?

Answer 8

Unsaturated fatty acids pack loosely which allows the bilayer to remain fluid. if no double bonds, bilayers would solidify

Question 9

What can form between phospholipids?

Answer 9

cholesterol, has a hydroxyl group, tiny polar head attached to a rigid tail, this fills gaps in the bilayer to stabilise it

Question 10

What does the layer look like?

Answer 10

Heads face outwards both sides, tails sandwiched in the middle. this means only the hydrophilic heads are exposed to regions of water
forms a continuous spheroid

Question 11

Are membrane dynamic? If so why?

Answer 11

they are dynamic structures due to the ability of phospholipids to move

Question 12

What are the ways phospholipids can move?

Answer 12

• lateral
• flexion
• rotation
• flip flop (rarely occurs)

Question 13

What does the cis bond in unsaturated chain mean?

Answer 13

it makes the phosplipids more difficult to pack together, making membrane thinner
the insertion of cholesterol regulates membrane fluidity

Question 14

What does the orientation of cholesterol mean for the eukaryotic membranes?

Answer 14

cholesterol is highly abundant in eukaryotic membranes
orientation means that the steroid ring region of the cholesterol stiffens the upper region of the fatty acid chain
= immobilise the phospholipid
= less able to move laterally
= less fluid

Question 15

What are lipid rafts? Where can they be found?

Answer 15

A lipid raft is a specialised, dynamic microdomain within the plasma membrane that is enriched in certain types of lipids, such as cholesterol, sphingolipids, and specific proteins. These rafts are thought to play key roles in membrane organisation, cell signalling, and protein sorting.

Question 16

what ae sphingolipids?

Answer 16

an amino alcohol sphintosine is their back bone rather then glycerol
they have long, saturated fatty acid chains and the attractive forces are strong enough to hold adjacent molecules together in lipid rafts

Question 17

Why do proteins congregate towards lipid raft regions?

Answer 17

In preparation for vesticular budding and trasnport

Question 18

What are glycoproteins?

Answer 18

proteins glycosylated in RER and golgi (bonded to carbohydrates)

Question 19

What are glycolipids?

Answer 19

lipids from SER glycosylated in golgi

Question 20

What is Glycocalyx?

Answer 20

the CHO coating to the termed, it is protective, name for the carbohydrates

Question 21

What are the 2 main membrane proteins?

Answer 21

1 - Integral/Transmembrane proteins (span membrane from outer to inner)
2 - Peripheral membrane proteins (embedded within one layer or just attached to membrane)

Question 22

What are the 2 types of phospholipids?

Answer 22

1 - glycerophospholipids (most abundant)
2 - sphingolipids (abundant in lipid rafts)

Question 23

What are the types of integral/transmembrane proteins?

Answer 23

• multi pass
• single pass

Question 24

What are the types of Peripheral proteins?

Answer 24

• embedded
• covalently bonded to lipids
• non covalently bonded to other proteins

Question 25

What is the lipid bilayer an impermeable barrier to?

Answer 25

polar, hydrophilic molecules this enable a cell or intracellular compartment to maintain a different environment to the outside to transport molecules across membranes, specialised proteins are required

Question 26

What can be easily transported across the membrane?

Answer 26

- hydrophobic, non polar molecules such as oxygen, co2, nitrogen, steroid hormones - small uncharged polar molecules such as water, urea, glycerol, NH3

Question 27

What will need a transport mechanism to go across the membrane?

Answer 27

- large uncharged polar molecules such as glucose, sucrose - ions - charged so need a specialised mechanism

Question 28

What are the transport proteins for the specialised mechanisms?

Answer 28

the transmembrane, multipass proteins - no contact with the hydrophobic core

Question 29

What are carrier proteins?

Answer 29

binds to a solute and undergo conformational change to trasnfer across membrane

Question 30

What are channel proteins?

Answer 30

interact only weakly with solute; form aqueous pore that solutes (normally ions) can pass through quickly - it is a continuous pore

Question 31

What do channel and carrier proteins do?

Answer 31

They enable facilitated diffusion (passive transport) the concentration gradient determines the direction of flow

Question 32

What is an electrochemical gradient?

Answer 32

If it is an ion, then concentration and charge determine the direction of flow

Question 33

What is active transport?

Answer 33

Where solutes are 'pumped' across a membrane against the concentration gradient mediated by carriers requires ENERGY

Question 34

What are the 3 ways you can get energy for active transport?

Answer 34

1 - Light energy (bacteria) 2 - Energy release from electron transfer 3 - ATP hydrolysis

Question 35

What are the two two main mechanisms eukaryotes use for active transport?

Answer 35

1 - coupled carriers (secondary active transport 2 - ATP driven pumps (primary active transport)

Question 36

What are the two types of coupled carriers?

Answer 36

1 - symport 2 - antiport

Question 37

What does the symport channel do?

Answer 37

Transports more then one molecule in the same direction electrochemical gradient = stored energy Transport = release of energy

Question 38

What does the antiport channel do?

Answer 38

Molecules in different directions

Question 39

What are channel proteins?

Answer 39

form pores across the membrane some are large and if they were on the plasma membrane then it would allow lots of thing in and out - poor regulation channels on the membrane are very narrow, highly selective pores that open and close as they are gated. specifically concerned with transport of ions only participate in facilited diffusion

Question 40

What are the 4 types of gated ion channels?

Answer 40

1 - voltage gated 2 - ligand gated (extracellular ligand) 3 - ligand gland (intracellular ligand) 4 - mechanically gated