Lect. 8 Membrane Transport - Energy and Metabolism

Question 1

Definition of something that is “selectively permeable”

Answer 1

It allows some substances to cross it more easily than others.

Question 2

Generally, biological membranes are permeable to:

Answer 2

small molecules (H2O, O2, CO2) and lipid-soluble substances

they can penetrate the hydrophobic interior of the bilayer

Question 3

A selectively permeable bilayer is permeable to:

Answer 3

• small uncharged molecules (O2)
• very small polar molecules (H2O, CO2)
• large non-polar molecules

urea, glycerol

Question 4

A selectively permeable bilayer is impermeable to:

Answer 4

• large polar molecules (glucose)
• charged particles (ions: H+, Na+, Cl-, HCO-)

glucose, sucrose

Question 5

Molecules enter/leave cells by: (5)

Answer 5

1. diffusion
2. osmosis (for water)
3. facilitated diffusion
4. active transport
5. bulk transport: endocytosis & exocytosis

DOFAB

Question 6

Water’s role in cells

Answer 6

• essential for survival
• prevents drying
• all chemicals that enter a cell can only do so if dissolved in water

all cells must live in a moist env

Question 7

Diffusion is a ____ process. Does the cell have to expend energy to make it happen?

Answer 7

Diffusion is a passive process: the cell does not have to expend energy to make it happen.

Question 8

Diffusion occurs when there exists a ____ until ____ .

Answer 8

Diffusion occurs when there exists a concentration gradient (CG) until equilibrium is reached.

Question 9

What is a concentration gradient?

Answer 9

The difference in concentration b/w the high concentration vs the area of low concentration.

ex: - campfire: heat source; warm when close, cool when far; diff in temp represents a gradient
- perfume spray at one end of room; high fragrance next to spray, low at opp side of room; diff in fragrance represents a gradient

Question 10

Concentration Gradient in a Cell

ex: A lipid-soluble substance moves through the lipid bilayer from ____ to ____ concentration.

Answer 10

A lipid-soluble substance moves through the lipid bilayer from high to low concentration.

Question 11

As long as CG exists, net movement of molecules will be:

Answer 11

in direction of gradient.

Question 12

Once equilibrium is reached, net movement stops but:

Answer 12

exchange still occurs on a molecule for molecule basis.

Question 13

Diffusion: a physical process based on random motion

All atoms and molecules possess ____ above absolute 0.

Answer 13

All atoms and molecules possess kinetic energy above absolute 0. This is why there is random molecular motion in diffusion.

Question 14

Factors that influence diffusion rate: (3)

Answer 14

1. Concentration gradient
2. Size and shape (small=more free mov, globular moves easier)
3. Temp (kinetic E of the particles)

Question 15

What are the 2 general principles that apply to diffusion and osmosis?

Answer 15

1. concentration gradient
2. equilibrium

Question 16

Osmosis = fluid diffusion

Water’s net mov is from the side of ____ solute concentration to side of ____ solute concentration.

Answer 16

Water’s net mov is from the side of low solute concentration to side of high solute concentration.

Question 17

Osmosis = fluid diffusion

Water’s net mov is from the side of ____ solvent concentration to side of ____ solvent concentration.

Answer 17

Water’s net mov is from the side of high solvent concentration to side of low solvent concentration.

Question 18

An animal cell in a hypotonic solution will be:
While a plant cell is:

Answer 18

• lysed (pop)
• turgid (normal)

Question 19

When an animal cell is normal in an isotonic solution, a plant cell is:

Answer 19

flacid.

Question 20

In a hypertonic solution, an animal cell is:
and a plant cell is:

Answer 20

• shriveled/crenated
• plasmolyzed

Question 21

tonicity in plant cells

ex: When water seeks to exit cell, solution surrounding cells is:

plant looks sad

Answer 21

hypertonic

no turgor pressure on cell wall

Question 22

osmoregulation: control water balance

Paramecium is ____ to the pond in which it lives. To solve this problem, paramecium cells have a specialized organelle, the contractile vacuole, which functions as a pump to force water ____ the cell.

Answer 22

hypertonic, out of

Question 23

Definition of “tonicity”

Answer 23

Tonicity is a measure of osmotic pressure related to the concentration of impermeable solutes in a particular solution.

hypotonic / hypertonic / isotonic

Question 24

Definition of “osmolarity”

Answer 24

Osmolarity is a measure of molarity of all solutes (permeable + impermeable) dissolved in a particular solution.

hyperosmotic / hypo-osmotic / isosmotic

Question 25

In facilitated diffusion, molecules that are too big (glucose or AA) and polar/charged molecules require ____ to get them through the cell membrane.

Answer 25

In facilitated diffusion, molecules that are too big (glucose or AA) and polar/charged molecules require **protein molecules** to get them through the cell membrane.

Question 26

Types of transport proteins facilitate movement of molecules/ions across membranes: (2)

Answer 26

1. channel proteins (tunnel like gap junctions) 2. carrier proteins | down a concentration gradient ## Footnote w/out carrier proteins, many molecules would not move across the membrane or would do so in such a slow fashion as to be useless to the cell

Question 27

# Channel proteins Channel proteins provide ____ corridors for the passage of specific charge/polar molecules/ions.

Answer 27

Channel proteins provide **hydrophilic** corridors for the passage of specific charge/polar molecules/ions.

Question 28

# Channel proteins Name the specialized gated channel proteins that carry water rapidly across the membrane in response to osmolarity.

Answer 28

aquaporins | gated: responds to chemical or electrical stimulus

Question 29

# Carrier Proteins Describe how a solute travels through carrier proteins

Answer 29

Carrier protein in the membrane selectively binds a solute particle and changes shape, opening a channel through the membrane. The solute can be transported into or out of the cell, but net mov is always from a region of higher to lower concentration.

Question 30

# Carrier proteins The rate of transport depends on: (2)

Answer 30

1. the number of carrier proteins 2. how fast a solute travels through them

Question 31

What are ion channels?

Answer 31

A specific category of protein that allow specific ions through, they function as gated channels. | Many ion channels are gated channels

Question 32

Active transport requires: (2)

Answer 32

1. energy (ATP) since it's going away from equilibrium 2. carrier proteins | transporting molecules against the chemical gradient

Question 33

Active transport allows cell to maintain ____ internal conditions compared to external conditions.

Answer 33

Active transport allows cell to maintain **different** internal conditions compared to external conditions.

Question 34

How does ATP supply its energy for active transport?

Answer 34

By phosphorylating (giving phosphate) to the carrier protein. It triggers the conformational change required to transport ions across membrane.

Question 35

What is the sodium-potassium pump responsible for?

Answer 35

Creating/maintaining the membrane potential in neurons. It transports K+ in and Na+ out. | pump = active transport

Question 36

# sodium-potassium pump The exchange is unequal: 2 K+ imported in for 3 Na+ exported. This creates:

Answer 36

a membrane potential; negative interior relative to a positive exterior.

Question 37

Pumps that create membrane potentials are called:

Answer 37

electrogenic pumps | eletrically generating

Question 38

Creating membrane potentials stores energy that can be harnessed for other reactions. What are the main electrogenic pumps in animal cells and {plants, fungi, and bacteria}?

Answer 38

animal: sodium-potassium pump plants, fungi, and bacteria: proton pump to export H+ ions from cytoplasm

Question 39

As a result of the membrane potential created via active transport, the *passive transport* of cations ____ the cell and anions ____ the cell is favoured.

Answer 39

As a result of the membrane potential created via active transport, the passive transport of cations **into** the cell and anions **out of** the cell is favoured.

Question 40

The 2 forces (gradients) that drive ions towards equilibrium:

Answer 40

1. Concentration gradient (applies to all molecules on either side of membrane) 2. Electrical gradient (applies to charged particles) ## Footnote The 2 combined are collectively called the electrochemical gradient.

Question 41

# Cotransport ex: Plant cotransport proteins use the energy expended from H+ entering the cell (____ transport) to transport sucrose into the cell against its concentration gradient (____ transport).

Answer 41

Plant cotransport proteins use the energy expended from H+ entering the cell (**passive** transport) to transport sucrose into the cell against its concentration gradient (**active** transport).

Question 42

Macromolecules (polymers: proteins, polysaccharides) and larger particles need to use what to enter the cells?

Answer 42

vesicles

Question 43

# Bulk Transport Materials are transported out of the cell via:

Answer 43

exocytosis ## Footnote ex: exit of insulin from pancreatic cells - vesicle approaches plasma membrane - fuses with it - releases its contents outside

Question 44

# Bulk Transport Materials are transported into the cell via:

Answer 44

endocytosis

Question 45

Types of endocytosis:

Answer 45

1. Phagocytosis 2. Pinocytosis 3. Receptor-mediated endocytosis

Question 46

How does Phagocytosis work? | "cell eating"

Answer 46

- cell wraps pseudopodia around particle and forms vacuole (large vesicle) - vacuole then fuses with lysosome for digestion

Question 47

ex: White blood cells phagocytize microbes constantly to protect the body from possible infection. Microbial debris are released by:

Answer 47

exocytosis

Question 48

How does Pinocytosis work? | "cell drinking"

Answer 48

- cell takes in portions of extracellular fluid and all solutes dissolved in the solution - non-specific mechanism (in comparison with receptor-mediated endocytosis)

Question 49

How does Receptor-mediated Endocytosis work?

Answer 49

- A vesicle is formed when specific molecules attach to their respective surface receptors on the membrane - specific mechanism compared to pinocytosis - once the molecules exit the vesicle in the cell, the receptors are returned to the cell surface for reuse

Question 50

ex: What is the mechanism used for the intake of LDLs?

Answer 50

receptor-mediated endocytosis - blood cholesterol travels as lipoprotein - LDL destined for uptake in cells ## Footnote LDL's bind to specific surface receptors

Question 51

ex: What does influenza virus use for endocytosis?

Answer 51

Receptor-Mediated Endocytosis Haemagglutinin is the protein responsible for both receptor binding and membrane fusion