2.5 Biological Membranes

Question 1

What is the fluid mosaic model?

Answer 1

Theory of cell membrane structure with proteins embedded in a sea of phospholipids

Question 2

What is a glycolipid?

Answer 2

A lipid /phospholipid with a chain of carbohydrate molecules attached.

Question 3

What is a glycoprotein?

Answer 3

A protein with a chain of carbohydrate molecules attached.

Question 4

What is the plasma membrane?

Answer 4

Cell surface membrane.

Question 5

How can substances get into the cell?

Answer 5

• small = diffuse
• some substances dissolve in lipid layer and pass through
• protein channels and carrier proteins.

Question 6

What are the roles of the plasma membrane?

Answer 6

• separates from external environment
• regulates transport of materials
• contain enzymes
• has antigens so immune system recognises as self
• chemical signals to other cells
• receptors for chemical signals
• site of chemical reactions

Question 7

What are the inner membranes of mitochondria called?

Answer 7

Cristae

Question 8

What are Cristae used for?

Answer 8

Large surface area for aerobic respiration and localise enzymes for respiration.

Question 9

What are the inner membranes of chloroplasts called?

Answer 9

Thylakoid membranes.

Question 10

What do thylakoid membranes do?

Answer 10

House chlorophyll and some photosynthesis.

Question 11

What are there on the plasma membranes of epithelial cells that line the small intestine?

Answer 11

Digestive enzymes that catalyse the final stages of the breakdown of certain sugars.

Question 12

What makes the fluid mosaic model fluid?

Answer 12

The lipid molecules can change places with each other.

Question 13

How thick is the phospholipid bilayer?

Answer 13

7nm

Question 14

What do carbohydrate molecules on the outside of the membrane do?

Answer 14

Attract water with dissolved solutes.

Question 15

What is another name for the outside of the membrane?

Answer 15

Glycocalyx

Question 16

What does cholesterol do?

Answer 16

Gives mechanical stability and flexibility and resist the effects of temperature changes.

Question 17

What are channel and carrier proteins?

Answer 17

Integral proteins.

Question 18

How is that glycocalyx formed?

Answer 18

From carbohydrate chains attached either to lipids or proteins on the membrane.

Question 19

How are the membranes of neurones specialised?

Answer 19

Protein channels and carriers in the long axon allow ions to bring the conduction of electrical impulses.

Question 20

How are the plasma membranes of white blood cells specialised?

Answer 20

Have special proteins receptors that enable them to recognise the antigens on foreign cells.

Question 21

Define diffusion.

Answer 21

The net movement of molecules from and area of high concentration of that molecule to an area of low concentration.
May or may not be across a membrane
Is passive

Question 22

Define facilitated diffusion.

Answer 22

The net movement of molecules from an area of high concentration of that molecule to an area of low concentration, across a partially permeable membrane via protein channels or carriers
Is passive

Question 23

Why is water a special case for diffusion?

Answer 23

Molecules are polar and insoluble in the lipid in the phospholipid bilayer.

Question 24

Why is water able to diffuse through cell membranes?

Answer 24

It is present in great concentrations.

Question 25

What are specific water channel proteins called?

Answer 25

Aquaporins

Question 26

How is the concentration gradient maintained?

Answer 26

The molecules that enter the cells are used for metabolic reactions.

Question 27

What factors affect the rate of simple diffusion?

Answer 27

- temperature - diffusion distance - surface area - size of diffusing molecule - concentration gradient

Question 28

What molecules undergo facilitated diffusion?

Answer 28

Small molecules that have polarity are insoluble in lipid as they cannot interact with the hydrophobic tails of the lipid bilayer.

Question 29

Define osmosis.

Answer 29

Passage of molecules down their water potential gradient, across a partially permeable membrane.

Question 30

Define water potential.

Answer 30

Measure of the tendency of water molecules to diffuse from one region to another.

Question 31

What is the unit of water potential.

Answer 31

KPa

Question 32

What is the water potential of pure water?

Answer 32

0kPa

Question 33

What is it called when a cell swells and bursts due to too much water?

Answer 33

Cytolysis

Question 34

What is it called when animal cells shrivel?

Answer 34

Crenated

Question 35

What is it called when the cytoplasm of plant cells shrinks and the membrane pulls away from the cell wall?

Answer 35

Plasmolysed

Question 36

What is plant tissue with Plasmolysed cells called?

Answer 36

Flaccid

Question 37

Define active transport.

Answer 37

The movement of substances against their concentration gradient across a cell membrane, using ATP and carrier proteins.

Question 38

Define endocytosis.

Answer 38

Bulk transport of molecules, too large to pass through a cell membrane even via channel or carrier proteins, into a cell.

Question 39

Define exocytosis.

Answer 39

Bulk transport of molecules, too large to pass through a cell membrane even via channel or carrier proteins, out of a cell.

Question 40

What ions are actively transported?

Answer 40

Sodium and potassium ions.

Question 41

How many sodium ions bind to the site on active transport?

Answer 41

3

Question 42

What is ATP hydrolysed to form?

Answer 42

ADP + P

Question 43

How many potassium ions bind to their site with active transport?

Answer 43

2

Question 44

What is phagocytosis?

Answer 44

When one cell engulfs another.

Question 45

What is pino(endo)cytosis?

Answer 45

Cells ingesting liquids.

Question 46

Is ATP needed for endocytosis?

Answer 46

Yes, to move vesicles using molecular motor proteins along cytoskeleton threads.

Question 47

What determines membrane fluidity at cold temperatures?

Answer 47

The proportions of unsaturated and saturated fatty acids within a cell membrane.

Question 48

What also buffers the effect of lowered temperature?

Answer 48

Cholesterol prevents phospholipid molecules from packing together too closely.

Question 49

How do solvents, such as acetone and ethanol, damage membranes?

Answer 49

They dissolve lipids.

Question 50

What is broken by strong reducing agents?

Answer 50

Disulfide bonds.

Question 51

Roles of membranes

Answer 51

- partially permeable barriers between the cell and its environment, between organelles and the cytoplasm and within organelles - sites of chemical reactions - sites of cell communication (cell signalling).

Question 52

What is cell signalling?

Answer 52

communication between cells

Question 53

Why can't water soluble substance pass through the membrane?

Answer 53

The centre of the bilayer is hydrophobic

Question 54

Functions of membranes within cells

Answer 54

Forms vesicles Isolation of ontents from cytoplasm Site of processes/ reaction Surface for attachment (of enzymes/ribosomes) Control what substances enter and leave organelles- selective permeability Creation of concentration gradients

Question 55

Functions of membranes within cells

Answer 55

Forms vesicles Isolation of ontents from cytoplasm Site of processes/ reaction Surface for attachment (of enzymes/ribosomes) Control what substances enter and leave organelles- selective permeability Creation of concentration gradients

Question 56

What molecule can easily pass through the phospholipid bilayer?

Answer 56

fat-soluble substances

Question 57

What membranes do not have cholesterol?

Answer 57

Bacterial membranes

Question 58

What is the function of glycolipids and glycoproteins?

Answer 58

- stabilise the membrane by forming hydrogen bonds with surrounding water molecules - where drugs, hormones and antibodies bind - receptors for cell signalling - antigens

Question 59

Describe the role of membrane bound receptors

Answer 59

- proteins - specific shapes - drugs use them to trigger a response from the cell or block the receptor and prevent it from working

Question 60

How can you investigate factors affecting membrane fluidity?

Answer 60

BEETROOT - cut five pieces and rinse - place in test tubes containing water - different temperatures for known time - remove beetroot, leaving coloured water - colorimeter - higher permeability = more pigment released = more absorbance

Question 61

How does temperature affect membrane permeability?

Answer 61

- <0 degrees, packed together, proteins deform, memrbane more permable, ice crystals may form + pierce membrane - 0-45 degrees - can move around and arnt packed = partially permeable - >0 bilayer breaks down, water expands inside and puts pressure, proteins deform

Question 62

How does changing the solvent affect membrane permeability?

Answer 62

- ethanol dissolves lipids so increases

Question 63

How can you investigate diffusion in model cells?

Answer 63

1) make agar jelly with phenolphthalein and dilute sodium hydroxide (it will be a LOVELY shade of pink) 2) fill beaker with dilute HCl 3) Cut cubes of jelly and put them in the acid 4) the cubes will go colourless

Question 64

How can you investigate water potential in the lab?

Answer 64

POTATO - different conc sucrose solutions - put potato in and weigh - calculate % change in mass

Question 65

What molecules do facilitated diffusion?

Answer 65

polar and charged carbohydrates amino acids ions

Question 66

Examples of hydrophobic molecules that can enter membranes?

Answer 66

O2 CO2 N2 steroids

Question 67

Examples of small uncharged polar molecules that can enter membranes

Answer 67

H2O glycerol urea ethanol

Question 68

Examples of large uncharged polar molecules that cant enter membranes

Answer 68

glucose and sucrose