Forces Across Membranes 2

Question 1

Why does a difference of charge occur across the membrane?

Answer 1

The ions creating the concentration gradient are charged particles, causing an electric gradient

Question 2

What is an electrochemical gradient?

Answer 2

Net effect of the chemical and electrical gradients

Question 3

What defines the movement of ions across the membrane?

Answer 3

The electrochemical gradient

Question 4

What does movement against the electrochemical gradient require?

Answer 4

Energy (active transport)

Question 5

What is the resting membrane potential?

Answer 5

-70mV inside compared to outside

Question 6

What are the 5 mechanisms of movement across the membrane?

Answer 6

Endocytosis and exocytosis

Diffusion

Mediated transport

Osmosis

Filtration

Question 7

What is endocytosis/exocytosis?

Answer 7

Mechanism for moving macro molecules across the membrane without disrupting them

Question 8

What are the steps of endocytosis?

Answer 8

1. Invigination of the membrane to form a vesicle
2. Disintegration on the cytoplasmic surface of the membrane
3. Releasing the contents

Question 9

What is the process of exocytosis?

Answer 9

The reverse process of endocytosis (leaving the cell)

Question 10

What is diffusion?

Answer 10

Process where gas or a substance in solution expands to fill all available space

Question 11

What does diffusion means in terms of the movement of molecules?

Answer 11

Molecules spread from regions of high concentration to regions of low concentration

Question 12

During diffusion what direction to molecules move?

Answer 12

From high concentration to low, although some do randomly go from low to high - but the net movement is from high concentration to low concentration

Question 13

What must the barrier be to allow diffusion to occur?

Answer 13

Permeable to the substance

Question 14

What expression describes the size of diffusion?

Answer 14

F = kpA(C₂-C₁)

kp is the permeability coefficient

A is the surface area

F is the magnitude of diffusion

Question 15

What are the two ways diffusion through the membrane can occur?

Answer 15

Through the phospholipid bilayer or protein channels

Question 16

What must molecules be to pass through the phospholipid bilayer?

Answer 16

Small

Lipophillic

Uncharged

Question 17

Do any lipophobic molecules pass through the lipid bilayer by diffusion?

Answer 17

Yes, small uncharged ones such as CO₂ and urea

Question 18

What are the two ways that ions cross the membrane?

Answer 18

Through protein channels or mediated transport proteins

Question 19

What are protein channels?

Answer 19

Transmembrane proteins that act as an aqueous route though the membrane

Question 20

Why can molecules like glucose not use protein channels?

Answer 20

The molecules are too large

Question 21

What forms of protein channels are there?

Answer 21

Open

Closed

Question 22

What are closed protein channels controlled by?

Answer 22

Gates

Question 23

What are the two types of closed protein channels?

Answer 23

Voltage gated protein channel

Ligand gated protein channel

Question 24

What are voltage gated protein channels?

Answer 24

Open/close in response to alternations of the membrane electrical potential

Question 25

What are ligand gated protein channels?

Answer 25

Open/close in response to a chemical such as a neurotransmitter or a hormone

Question 26

What do ligand gated protein channels act as?

Answer 26

A receptor and a transporter

Question 27

How do gated protein channels work?

Answer 27

Stimuli causes a conformational change of the protein which opens or closes the channel

Question 28

When is electrochemical equilbrium reached?

Answer 28

When the electrical and chemical gradients are in balance

Question 29

What is carrier mediated transport?

Answer 29

Proteins that are only open on one side of the membrane at any time that move molecules across

Question 30

What are the two forms of carrier mediated transport?

Answer 30

Facilitated diffusion

Active transport

Question 31

What is facilitated diffusion?

Answer 31

Movement of molecules through transport proteins down their electrochemical gradient

Question 32

What is active transport?

Answer 32

Movement of molecules through transport proteins against their electrochemical gradients using energy (ATP)

Question 33

How does carrier mediated transport switch the side of the membrane that it is open on?

Answer 33

A molecule binds to it and causes a conformational change which exposes the binding site on the other side

Question 34

What do carrier mediated transport proteins act as (other than a transporter)

Answer 34

An enzyme as it hydrolysis ATP to release energy

Question 35

What are active transporters otherwise known as?

Answer 35

Pumps

Question 36

What do active transporters maintain?

Answer 36

The concentration gradient

Question 37

What does each molecule of ATP allow to pass through a pump?

Answer 37

3 molecules of Na⁺ and 2 molecules of K⁺

Question 38

How much of the bodies resting energy is used to pumps?

Answer 38

40%