Topic 4 membranes

Question 1

What is a membrane or plasma membrane

Answer 1

A selectively permeable lipid bilayer that separates the cell from its surroundings.

Question 2

list some functions of the membrane

Answer 2

Selective uptake of ions/molecules 
Energy production (e.g. ATP in mitochondria)
Cell compartmentalization 
Cell Signalling
Protein sorting 
Cytoskeleton anchoring
Nuclear Division 
Adhesion to other cells/extracellular matrix

Question 3

What 3 components are membranes made up of?

Answer 3

Lipids, proteins and carbohydrates (sometimes)

Question 4

membrane lipids include…?

Answer 4

Phospholipids, Gylcolpids, Sphingolipids, and steroids

Question 5

Phospholipids are what type of molecules…?

Answer 5

Amphipathic

Question 6

what does amphipathic mean?

Answer 6

Containing hydrophobic and hydrophilic regions.

Question 7

steroids like cholesterol are important for what?

Answer 7

membrane fluidity

Question 8

importance of membrane proteins

Answer 8

proteins determine most of the membranes specific functions

Question 9

what is a peripheral protein

Answer 9

are bound to the surface of the membrane

Question 10

what are integral proteins

Answer 10

penetrates the hydrophobic core

Question 11

6 major functions of membrane proteins

Answer 11

• Transport of cell; into cell; within cell
• Enzymatic activity
• Signal transduction
• Cell‐cell recognition
• Intercellular joining
• Attachment to the cytoskeleton and extracellular matrix (ECM)

Question 12

importance of membrane carbohydrates

Answer 12

Carbohydrates of the surface of the membrane act as identity tags, different cell types and different tissues display unique carbohydrates.

Question 13

how do cells recognize each other?

Answer 13

By binding to surface molecules, often carbohydrates, on the plasma membrane

Question 14

Type of membrane carbohydrates

Answer 14

glycolipids, Gylcoproteins

Question 15

Glycolipids are?

Answer 15

carbohydrates convalently bonded to lipids

Question 16

Glycoproteins are?

Answer 16

carbohydrates covanlently bonded to proteins

Question 17

Carbohydrates have distinct inside and outside faces which do what…?

Answer 17

The asymmetrical distribution of proteins, lipids, and carbohydrates on the plasma
membrane is determined when the membrane is built by the ER and Golgi apparatus
• This asymmetry is important for the biological functions of many of the proteins and
carbohydrates

Question 18

Who proposed the fluid mosaic model and give an explanation

Answer 18

J.Singer and G.Nicolson proposed the fluid mosaic model in 1972, that a cell membrane is a mosaic of proteins dispersed withing the bilayer, with only the hydrophilic regions exposed to water

Question 19

what evidence supports the fluid mosaic model

Answer 19

freeze fracture studies, Hybrid cell experiments, photo bleaching

Question 20

explain some membrane fluid movements

Answer 20

Phospholipids are able to move within the bilayer, most of the lipids are able to move laterally, rarely does a molecule flip-flop across the membrane

Question 21

membranes must be….. to work properly

Answer 21

fluid

Question 22

fluidity depends on what?

Answer 22

temperature and lipid composition of the membrane

Question 23

Membranes become for solid/fluid when temperatures become cooler?

Answer 23

Solid

Question 24

membranes rich in unsaturated fatty acids are more or less fluid than those rich in saturated fatty acids?

Answer 24

more fluid

Question 25

the steroid cholesterol has different effects of membrane fluidity at different temperatures what are they?

Answer 25

at warm temperatures cholesterol restrains membrane fluidity, while cooler temperatures allows more fluidity because the cholesterol prevents tight packing

Question 26

membrane structure results in selective permeability what does the membrane allow to pass through be specific

Answer 26

O2 and H2O are small molecules and are readily passing through the membrane, Hydophobic (non poplar) molecules such as hydrocarbons can dissolve in lipid bilayer and pass through the membrane readily aswell

Question 27

what does the membrane not allow to penetrate through

Answer 27

Polar molecules such as sugars do not pass readily as well as large molecules.

Question 28

What is passive transport?

Answer 28

the diffusion of substances across a membrane with no energy investment

Question 29

what is osmosis

Answer 29

the diffusion of water across a semi-permeable membrane

Question 30

isotonic solution

Answer 30

solute concentration is the same as inside the cell; no net water movement across membrane

Question 31

Hypertonic

Answer 31

solute concentration is higher than inside the cell ; water lost from cell

Question 32

Hypotonic

Answer 32

cell concentration is less than inside the cell ; water gained in the cell

Question 33

whatdoes the cell wall help with the plant cell?

Answer 33

helps maintain water balance inside the cell.

Question 34

a plant cell in hypotonic solution swell until the cell becomes?

Answer 34

Turgid

Question 35

what is Facilitated transport

Answer 35

transport proteins speed the movement of molecules across a membrane

Question 36

what do channel proteins do

Answer 36

provide corridors that allow specific molecule or ions to cross the plasma membrane

Question 37

what do carrier proteins do?

Answer 37

undergo a subtle change in shape that translocates the solute binding site across the membrane

Question 38

what is active transport what is an example of one

Answer 38

substances are moved against their concentration gradient

example potassium- sodium pump

Question 39

explain exocytosis give example

Answer 39

transport vesicles migrate to the membrane, fuse wit it, and release their content, secretion of insulin

Question 40

explain endocytosis

Answer 40

cell takes in macromolecules by forming vesicles from the plasma membrane

Question 41

types of exocytosis

Answer 41

phagocytosis, pinocytosis, receptor mediated endocytosis

Question 42

what is phagocytosis

Answer 42

cell engulfs a particle in vacuole. the vacuole fuses with a lysosome to digest the particle.

Question 43

what is pinocytosis

Answer 43

molecules are taken up when extracellular fluid is “gulped” into tiny vesicles

Question 44

explain receptor-mediated endocytosis

Answer 44

binding of ligands to receptors triggers vesicles formations

Question 45

what is a ligand

Answer 45

is any molecule that binds specifically to receptor site of another molecule