Membranes

Question 1

Function is membranes

Answer 1

Separating cell components from outer environment
Unique compartments within cells
Site of cell signalling and recognition
Control and regulation of reaction sequences
Regulate transport of materials in and out

Question 2

Three formations of phospholipids

Answer 2

Bilayer- where tails point inwards away from water
Micelles - single layer of phospholipids forming sphere with tails pointing to centre
Liposomes

Question 3

Thickness of membrane

Answer 3

7-10nm

Question 4

Other components in membrane (list)

Answer 4

Cholesterol, glycolipids, integral and peripheral proteins

Question 5

Description of fluid mosaic model

Answer 5

Bilayer of phospholipids forms basic membrane structure
Various proteins floating in bilayer, some others are bound one one side within the cell
Extrinsic proteins are partially embedded, intrinsic span the bilayer

Question 6

Constant fluidity and lateral movement allows…

Answer 6

Protein movement

Question 7

Role of cholesterol in membrane

Answer 7

Small, flat molecule which fits between fatty acid tails
Increases hydrophobic tendencies making the barrier more solid.
Generally membrane stability and fluidity regulation.

Question 8

Channel proteins roles

Answer 8

allow movement of small polar substances across the membrane. Many are also gated so allow one way, or controllable transport, such as in neurons.

Question 9

Carrier proteins roles

Answer 9

Move substances across the membrane.ms

Edification shaped so a certain molecule fits at which point they change shape to allow the molecule through.

Question 10

Receptor site

Answer 10

Allow hormones to bind causing a cell response. Specifically shaped.

Question 11

Diffusion

Answer 11

The net movement of molecules or ions I’m a gas or liquid from an area of high concentration to an area of low concentration.

Question 12

Factors affecting the rate of diffusion

Answer 12

Thickness of exchange surface
Concentration gradient
Surface area to volume ratio
Size of molecules
Temperature

Question 13

Fick’s law

Answer 13

Rate of diffusion is proportional to (surface area X difference in concentration) / thickness of exchange surface

Question 14

Things which can diffuse straight across the membrane

Answer 14

Small, non-polar molecules.

Ie. Lipid based molecules as can pass straight through the bilayer or gases which can pass between phospholipids

Question 15

Molecules requiring channels or protein carriers

Answer 15

Small charged particles, eg. Sodium ions through protein channels
Larger molecules eg. Glucose through carrier proteins
Larger quantities of water, through aquaporins

Question 16

Active transport

Answer 16

The transport of molecules or ions from a region of their lower concentration to a region of their higher concentration requiring energy and carrier proteins.

Question 17

Differences between carrier proteins used in facilitated diffusion and those used in active transport.

Answer 17

In active transport:
Carry specific molecules one way across the membrane
Use ATP
Work against the concentration gradient
Can carry molecules at a faster rate than could be done using diffusion
Can accumulate molecules in one place.

Question 18

Bulk transport or cytosis

Answer 18

Another form of active transport, either in or out of a cell, where large quantities of material are enrolled in the membrane and then pinched off into a vesicle, requiring ATP to move membrane and vesicles on the cytoskeleton.

Question 19

Exocytosis

Answer 19

Movement out of the cell

Question 20

Difference between pinocytosis and phagocytosis

Answer 20

Pino = transport of liquid material
Phago = transport of solid material

Question 21

Osmosis

Answer 21

The movement of water molecules from an area of higher water potential to an area of lower concentration across a partially permeable membrane.

Question 22

Hypotonic solution

Answer 22

Concentration of solutes is less, hence concentration of water is greater

Question 23

Isotonic solution

Answer 23

Concentration of solutes is equal, therefore no net movement.

Question 24

Hypertonic solution

Answer 24

Concentration of solutes is greater in solution, hence concentration of water is less.

Question 25

What occurs when plant and animal cells are placed in hypotonic solution

Answer 25

Animal cell bursts, is haemolysed

Plant cell is supported by cell wall, becomes turgid.

Question 26

What occurs when plant and animal cells are placed in hypertonic solution

Answer 26

Animal cells crinkled up, become crenated.

Plant cell membranes pull away from the cell wall, cell is plasmolysed.

Question 27

Types of cell signalling

Answer 27

Paracrine, endocrine, neuronal and contact dependant

Question 28

Cell signalling

Answer 28

Communication between cells that allows effective coordination of a response.

Question 29

Basic steps of cell signalling

Answer 29

1. messenger molecule (ligand) released by sending cell
2. Travels and binds to complementary receptor glycoprotein
3. Signal transduction - enzyme produces secondary messenger molecule
4. Results in change in gene expression, different proteins or enzymes found and so behaviours of cell altered

Question 30

Substance is carried in a single direction by…

Answer 30

Uniport carriers

Question 31

Two different substances are carried in the same direction by…

Answer 31

Symport carriers

Question 32

Two substances are carried in opposite directions by…

Answer 32

Antiport carriers

Question 33

Cotransporter protein

Answer 33

Protein in a membrane that allows the movement of one molecule when linked with the movement of the molecule in the same direction by active transport.