MBS Lecture 3

Question 1

What does the plasma membrane act as?

Answer 1

A barrier, nutrients must get in, products and wastes must get out

Question 2

What does permeability determine?

Answer 2

It determines what moves in and out of a cell

Question 3

Types of permeability?

Answer 3

Lets nothing in or out is impermeable
Lets anything pass is freely permeable
Restricts movement is selectively permeable

Question 4

What is the permeability of plasma
membrane?

Answer 4

Selectively permeable
Allows some materials to move freely – Restricts other materials

Question 5

What does selective permeability restrict?

Answer 5

Size, Electrical charge, Molecular shape and Lipid solubility

Question 6

What are the types of transport through
plasma membrane?

Answer 6

Active (requiring energy and ATP)
Passive (no energy required)

Question 7

Define the types of transport through the
plasma membrane

Answer 7

Transport through a plasma membrane can be Active (requiring energy and ATP) – Passive (no energy required)
Diffusion (passive)
Carrier-mediated transport (passive or active)
Vesicular transport (active)

Question 8

What are the factors affecting diffusion?

Answer 8

Distance the particle has to move
Molecule size, Smaller is faster
Temperature, More heat, faster motion
Gradient size, The difference between high and low
concentrations
Electrical forces, Opposites attract, like charges repel

Question 9

What are the types of diffusion across the
plasma membranes?

Answer 9

It can be simple or channeled

Question 10

What are the materials that diffuse through the plasma membrane by simple diffusion?

Answer 10

Materials that diffuse through plasma membrane by simple diffusion: – lipid-soluble compounds(alcohols, fatty acids,
and steroids)
- dissolved gases (oxygen and carbon dioxide)

Question 11

What are the materials that diffuse through the
plasma membrane by transmembrane
proteins (channels)?

Answer 11

Materials that pass through transmembrane proteins
(channels):
- are water–soluble compounds and are ions

Question 12

What does channel mediated diffusion depend
on?

Answer 12

Passage depends on: size , charge and interaction with the channel

Question 13

What is diffusion?

Answer 13

The net movement of a substance from an area of higher concentration to an area of lower concentration

Question 14

What is concentration gradient?

Answer 14

The difference between the high and low concentrations.

Diffusion tends to eliminate that gradient.

Question 15

What is electrical gradient?

Answer 15

The difference in electrical charges between two
compartments is called an electrical gradient. The interior of the plasma membrane has a net negative charge relative to the exterior surface, due in part to the high concentration of proteins in the cell. This negative charge tends to pull positive ions into the cell, while opposing the entry of negative ions.

Question 16

What do concentration and electrical gradient reach?

Answer 16

Equilibrium

Question 17

What is osmosis?

Answer 17

A Special Case of Diffusion – Osmosis is the diffusion of water across the cell membrane

Question 18

What is diffusion-osmosis?

Answer 18

More solute molecules, lower concentration of water molecules
Membrane must be freely permeable to water, selectively permeable to solutes
Water molecules diffuse across membrane toward solution with more solutes
Volume increases on the side with more solutes

Question 19

What is osmotic pressure?

Answer 19

Is the force of a concentration gradient of water

Equals the force (hydrostatic pressure) needed to block osmosis

Question 20

Define Tonicity

Answer 20

The osmotic effect of a solute on a cell:

Two fluids may have equal osmolarity, but different tonicity

Question 21

Hypertonicity

Answer 21

Hypertonic (hyper- = above)

Has more solutes and gains water by osmosis

Question 22

Hypotonicity

Answer 22

Hypotonic (hypo- = below)

Has less solutes and loses water through osmosis

Question 23

Isotonic

Answer 23

A solution that does not cause osmotic flow of water in or

out of a cell

Question 24

What does a cell do in a hypotonic solution?

Answer 24

Gains water
Ruptures(hemolysis of red blood cells)

Question 25

What does a cell do in a hypertonic solution?

Answer 25

Loses water - Shrinks (crenation of red blood cells)

Question 26

What is carrier mediated transport?

Answer 26

Carrier-mediated transport of ions and organic substrates
Facilitated diffusion
Active transport

Question 27

Characteristics of carrier mediated transport

Answer 27

Specificity: – one transport protein, one set of substrates
Saturation limits: – rate depends on transport proteins, not substrate
Regulation: – cofactors such as hormones

Question 28

Explain cotransport

Answer 28

Two substances move in the same direction at the same time

Question 29

Explain countertransport

Answer 29

One substance moves in while another moves out

Question 30

What is facilitated diffusion?

Answer 30

Passive, Carrier proteins transport molecules too large to fit through channel proteins (glucose, amino acids):
- molecule binds to receptor site on carrier protein
- protein changes shape, molecules pass through
- receptor site is specific to certain molecules

Question 31

What is active transport?

Answer 31

Active transport proteins:
- move substrates against concentration gradient
- require energy, such as ATP
- ion pumps move ions (Na+ , K+ , Ca2+ , Mg2+ )
- exchange pump countertransports two ions at the
same time
Sodium-potassium exchange pump
- active transport, carrier mediated:
» sodium ions (Na+) out, potassium ions (K+) in
» 1 ATP moves 3 Na+ and 2 K+
Secondary active transport
- Na+ concentration gradient drives glucose transport
- ATP energy pumps Na+ back out

Question 32

Endocytosis

Answer 32

(endo- = inside) is active transport using ATP:
- receptor mediated
- Pinocytosis “cell drinking”-extracellular fluid
- Phagocytosis“cell eating”-solid objects