2.4 Membranes

Question 0

State the function of the phospholipid bilayer and outline it’s structure

Answer 0

Acts as a barrier against all molecules except the smallest (O2, CO2). Made up of hydrophilic phosphate heads facing outwards, and the hydrophobic fatty tails (made of hydrocarbons) facing into the middle of the bilayer.

Question 1

State the function of integral proteins.

Answer 1

Within the bilayer. Usually span from one side of the phospholipid bilayer to the other. Are usually involved in transporting substances across the membrane.

Question 2

Name the two kinds of integral proteins

Answer 2

Carrier proteins and channel proteins

Question 3

State the function of carrier proteins

Answer 3

Transport specific substances across the cell membrane.

Question 4

State the function of channel proteins

Answer 4

Allow specific molecules/ions to pass through from one side of the membrane to another.

Question 5

Outline the function of peripheral proteins

Answer 5

External to the bilayer, and sit on its surfaces. The ones of the outside are often involved with cell communication and recognition. The ones on the inside are involved in maintaining the cell’s shape.

Question 6

State the function of cholesterol

Answer 6

Binds together lipids in the plasma, reducing its fluidity.

Question 7

State the function of glycoproteins

Answer 7

Usually involved in cell recognition (part of the immune system)

Question 8

List the functions of membrane proteins

Answer 8

Transport
Recognition
Adhesion
Communication 
Enzymes

(Trace)

Question 9

Define diffusion

Answer 9

Diffusion is the passive movement of particles from an area of high concentration to an area if low concentration.

Question 10

Define osmosis

Answer 10

Osmosis is the diffusion of water molecules across a partially permeable membrane from an area of low solute concentration to an area of high solute concentration.

Question 11

Define passive tranport

Answer 11

Passive transport is when no energy (ATP) is used for the movement of molecules from one side of the membrane to the other.

Question 12

Define simple diffusion

Answer 12

Involves small or non-polar molecules passively diffusing through the membrane.

Question 13

Define facilitated diffusion

Answer 13

Movement of large or polar molecules/ions across the plasma membrane. They must travel through channel or carrier proteins. Each channel allows only a specific substance through. There is no control over direction of movement.

Question 14

Define active transport

Answer 14

The movement of materials across a membrane against the concentration gradient (from low to high). Requires energy (ATP).

Question 15

Explain the role of protein pumps and ATP in active transport.

Answer 15

Active transport relies in specific protein pumps in the lipid bilayer. ATP triggers a conformational change in the pump, moving particles across the membrane.

Question 16

Explain how vesicles are used to transport secretory products from the RER to the plasma membrane

Answer 16

A vesicles containing synthesised proteins pinches off from the RER and transports the proteins yo the Golgi apparatus, where thy are modified to glycoproteins. A vesicles then pinches off the GA, and travels to the plasma membrane.

Question 17

Define exocytosis

Answer 17

When a vesicles travels to the plasma membrane and merges with it, secreting its products.

Question 18

Define endocytosis

Answer 18

When the plasma membrane envelops extra cellular fluid to form a vesicles within the cell.

Question 19

State the two main types of endocytosis

Answer 19

Phagocytosis and pinocytosis

Question 20

Define phagocytosis

Answer 20

The process by which large particles are engulfed by the cell via a vesicles. This allows quick entry for a large amount of substance.

Question 21

Define pinocytosis

Answer 21

The process by which fluid is engulfed into the cell via a vesicle.

Question 22

Describe how the membrane can change shape, break and reform during endocytosis and exocytosis

Answer 22

The membrane is principally held together by relatively weak hydrophobic associations between phospholipids. This allows for membrane fluidity and flexibility, as the phospholipids can move about to some extent.

Question 23

Outline the structure of a phospholipid

Answer 23

Polar head made of phosphate and glycerol.

Non-polar tail made if two fatty acid chains.