2.3 membranes

Question 1

Why is the structure of the cell-surface membrane called the fluid-mosaic model

Answer 1

Fluid-because the phospholipid molecules can move around within each layer so membrane is flexible and can change shape
mosaic-The membrane is studded with protein molecules and the arrangement of these proteins vary like tiles of a mosaic

Question 2

Structure of the cell-surface membrane?

Answer 2

A phospholipid bi-layer

Question 3

Function of phospholipids?

Answer 3

Acts as a barrier to most molecules

Question 4

Function of Glycoproteins and glycolipids?

Answer 4

Involved in cell recognition, cell signalling and cell attachment

Question 5

Function of intrinsic proteins?

Answer 5

Transports molecules across the membrane, or catalyses reactions

Question 6

Function of cholesterol?

Answer 6

Helps control membrane fluidity

Question 7

Where are intrinsic proteins?

Answer 7

Fully embedded in the membrane from one side to the other

Question 8

What are the two types of intrinsic proteins?

Answer 8

-Channel proteins
-Carrier proteins

Question 9

Structure of channel proteins

Answer 9

-Channel running through centre which is lined with hydrophilic amino acids and filled with water molecules

Question 10

Function of channel proteins

Answer 10

-Allow water-soluble molecules and ions to diffuse through

Question 11

Function of carrier proteins

Answer 11

-Can change their shape or position to transfer molecules or ions from one side of the membrane to the other

Question 12

Where are extrinsic proteins found?

Answer 12

-Do not span the membrane
-are found on one side of membrane or the other
-can be attached to intrinsic proteins

Question 13

Functions of extrinsic proteins

Answer 13

-Some play structural role within membrane
-Can act as enzymes
-Can be receptors for other molecules such as hormones

Question 14

Definition of diffusion

Answer 14

-The net movement of molecules from a high concentration to a low concentration down a concentration gradient until an equilibrium is reached

Question 15

What are the two types of diffusion?

Answer 15

-Simple
-Facilitated

Question 16

Differences in structure between the two types of diffusion

Answer 16

Simple- Non-polar, lipid soluble, gases, (small)
Facilitated- Polar, water soluble, Through intrinsic proteins, (large)

Question 17

What affects diffusion rate?

Answer 17

-temperature
-membrane fluidity
-concentration gradient
-diffusion difference

Question 18

Why is diffusion a passive process?

Answer 18

-It does not require metabolic energy to take place

Question 19

Why can water molecules pass through the cell membrane?

Answer 19

Even though they are charged, they are small

Question 20

What takes place in facilitated diffusion?

Answer 20

Hydrophilic substances diffuse across the cell membrane via protein molecules which allow the hydrophilic substances to cross without interacting with hydrophobic centre

Question 21

What is active transport?

Answer 21

The net movement of ions moved from a lower concentration to a higher concentration against the concentration gradient