membranes and membrane transport

Question 1

lipid is bilayer is …. + ….. …..

Answer 1

dynamic
selectively permeable

Question 2

what do the proteins in the lipid bilayer enable

Answer 2

signalling, communication + selective permeability

Question 3

what are the cell membranes a mix of

Answer 3

glycolipids
phospholipids
sphingolipids
cholesterol

Question 4

what are phospholipids made from

Answer 4

glycerol
phosphate
head group
hydrocarbon tail

Question 5

phospholipids are ……….

Answer 5

amphipathic

Question 6

why are phospholipids amphipathic

Answer 6

hydrophilic head = face towards fluid
hydrophobic tail = face each other

Question 7

where do the hydrophobic tails face

Answer 7

towards each other

Question 8

where do the hydrophilic heads face

Answer 8

towards fluid

Question 9

what are the tails described as

Answer 9

hydrophilic

Question 10

what are the heads described as

Answer 10

hydrophobic

Question 11

what determines the fluidity of the membrane

Answer 11

fatty acid chains

Question 12

what do fatty acid chains determine

Answer 12

the fluidity of the membrane

Question 13

what are phosphoglycerides derived from

Answer 13

glycerol

Question 14

what are sphingolipids derived from

Answer 14

sphingosine

Question 15

what is functionally important

Answer 15

lipid symmetry

Question 16

describe glycolipids

Answer 16

found in the non cytosolic layer only
contain sugar
made from sphingosine
glycosylation occurs in lumen of golgi

Question 17

what do the inner and outer monolayers have

Answer 17

different compositions

Question 18

describe cholesterol

Answer 18

modulates the properties of lipid bilayers
inserts between membrane phospholipids
tightens packing in bilayer
decreases membrane permeability to small molecules
increases rigidity
different cells have different lipid compositions

Question 19

what does the hydrophobic nature of fatty acids derive

Answer 19

the structure formed by phospholipids

Question 20

what do lipid bilayers spontaneously do

Answer 20

close to form sealed compartments

Question 21

describe biological membranes

Answer 21

fluid structures
allows lipids and membrane proteins to rapidly diffuse in lateral plane + interact with one another
ensures membranes are equally shared between daughter cells during cell division
allows cells to change shape (cell motility)allows membranes to fuse with other membranes - eg. in exocytosis or secretion of proteins

Question 22

what are the 4 types of integral and peripheral membrane proteins

Answer 22

single-pass
multipass transmembrane proteins
beta-barrel
lipid-linked
peripheral membrane protein

Question 23

what do both single-pass and multipass transmembrane proteins have

Answer 23

hydrophobic amino acids with side chains interacting with lipid monolayer

Question 24

describe membrane protein function

Answer 24

transport
enzymatic activity
signal transduction
cell-cell recognition
intracellular joining
attachment to the cytoskeleton + extra-cellular matrix

Question 25

what are the 2 types of membranes

Answer 25

active passive

Question 26

what does active transport require

Answer 26

c

Question 27

passive transport doesn't require ....

Answer 27

ATP

Question 28

describe simple diffusion

Answer 28

non membrane proteins involved driven by conc gradients down a conc gradient ability of a solute to cross membrane by simple diffusion depends on: -conc gradient - hydrophobicity/charge , size -membranes are highly impermeable to ions

Question 29

what relationship do membranes have with ions

Answer 29

highly impermeable

Question 30

what does the ability of a solute to cross the membrane by simple diffusion depend on

Answer 30

-conc gradient - hydrophobicity/charge , size -membranes are highly impermeable to ions

Question 31

describe facilitated diffusion

Answer 31

membrane proteins involved driven by conc gradients no energy input - ATP not needed

Question 32

describe the transport of inorganic ions + small molecules across the membrane

Answer 32

required for intracellular ion concs uptake of nutrients excretion of metabolic waste products - are different mechanisms for transport of large macromolecules across membranes

Question 33

what are the 2 classes of proteins involved in facilitated diffusion

Answer 33

channels uniporter or carrier proteins

Question 34

describe channel proteins

Answer 34

discrimates mainly on size and charge

Question 35

describe uniporter carrier proteins

Answer 35

involves binding site for solutes -transport inorganic ions/small molecules across the membrane passively along their conc gradient/electrochemical gradients

Question 36

what is another word for conc gradients

Answer 36

electrochemical gradients

Question 37

describe ion channels

Answer 37

- membranes are impermeable to ions - channels transport them across the membrane - exhibit ion selectivity - driven by conc/electrochemical gradient - fast : transport up to 10 molecules per sec - may be regulated - eg. open and close in response to a stimulus

Question 38

describe K+ channels

Answer 38

- most common ion channels - present in all cells - important subsrt (K+ leak channels) are continuously open (not gated) - selective: conduct K+ 10,000-fold more effectively than Na+

Question 39

describe uniporter carrier proteins

Answer 39

- glucose transporter (Glut2) in gut epithelia (solute=glucose) - highly selective - transported molecule bound to carrier - relatively slow (<1000 molecules per second)

Question 40

describe the transport of glucose into erythrocytes by GLUT 1

Answer 40

glucose = higher conc in blood than erythocte tasnported into cell by GLUT 1 along conc gradient GLUT 1 - works in both directions = conc gradient maintain -> converting glucose into glucose-6-phosphate glucose-6-phosphate isn't recognised by GLUT 1 = one-directional transport

Question 41

why is it important for GLUT 1 to work in both directions

Answer 41

conc gradient is maintained achieved by converting glucose to glucose-6-phosphate

Question 42

why is the transport 1 directional

Answer 42

as glucose-6-phosphate isn’t recognised by Glut1

Question 43

describe active transport

Answer 43

energy required - ATP solutes move against conc gradient

Question 44

what are the 3 ways that cells carry out active transport

Answer 44

ATP-driven pumps coupled transporters light driven pumps

Question 45

describe ATP-driven pumps

Answer 45

- couple the transport of solute against its gradient to the hydrolysis of ATP - primary active transport

Question 46

describe coupled transporters

Answer 46

- couple the transport of one solute with the gradient to another against the gradient - secondary active transport

Question 47

describe light driven pumps

Answer 47

couple the transport of a solute against its gradient to the input of energy from light

Question 48

what do ATP driven pumps do

Answer 48

- move solutes against the gradient by expending energy - eg. na+ / k+ gradient - in absence of na+ / k+ ATPase ions would flow down their gradients disturbing osmotic balance and preventing ‘secondary’ active transport

Question 49

what do couple transporters do

Answer 49

- move solutes against conc gradient by coupling transport to Na+ gradient created by Na+/K+ ATPase - don’t directly depend on the hydrolysis of ATP - eg. secondary active transport

Question 50

summary

Answer 50

- Membranes consist of lipids (mainly phospholipid) and protein. - Membranes are fluid (fluid mosaic model). - Transmembrane proteins are inserted into the membrane during synthesis. - Lipid nature of membrane prevents passage of ionised molecules - Therefore need channels/ carriers to allow ions and ionic substances to cross the membrane - Passive- diffusion, Active- against concentration gradient

Question 51

describe Na+ / K+ pump action

Answer 51

1. 3 x Na+ ions bind. Pump hydrolyses ATP and is phosphorylated 2. Na+ dependent phosphorylation causes pump to undergo conformational change, Na+ is transferred across the membrane and released 3. 2 K+ ions bind and pump is dephosphorylated 4. K+ dependent dephosphorylation causes the pump to return to its original conformation. K+ is transferred across the membrane and released