B: Movement Across Membranes (16)

Question 1

How can lipid composition of membranes be changed

Answer 1

Lipid composition of membranes can be changed by desaturating the fatty acid chains or exchanging them

Question 2

What are the 3 membrane proteins

Answer 2

1) Transmembrane protein domain
2) Helice (alpha-helices)
3) Tetraspanins (TM4SFs)

Question 3

Transmembrane protein domain: structure

Answer 3

Peptide sequence that is largely hydrophobic and spans across plasma membrane

Predominantly attaches integral proteins into the BM

Question 4

Helice (alpha-helices): Structure

Answer 4

9 AAs that have hydrophobic side chains

Question 5

Tetraspanins (TM4SFs): Structure

Answer 5

Family of membrane proteins found in all multicellular eukaryotes

4 transmembrane alpha-helices, and 2 extracellular domains (one short - EC1, one longer- EC2)

Question 6

What is the most abundant membrane protein

Answer 6

Helice (alpha-helices)

Question 7

What are the roles of membrane proteins

Answer 7

Cell adhesion, mobility and proliferation

Question 8

Can everything pass through the cell membrane?

Answer 8

No, lipid bilayer does not allow most molecules or compounds to pass through freely

Question 9

What can pass through the lipid bilayer with ease

Answer 9

Small uncharged molecules can cross membrane easily (O2, CO2, NO)

Question 10

What can’t pass through the lipid bilayer with ease

Answer 10

Large, polar, and charged compounds cannot easily cross lipid bilayer (Ca+, Na+, K+, glucose)

Question 11

What are the 4 basic mechanisms of moving molecules across membranes

Answer 11

1) Simple diffusion
2) Diffusion through a channel
3) Facilitiation diffusion
4) Active transport

Question 12

Explain passive transport

Answer 12

Passive transport: does not require energy, relies on molecular concentrations

Question 13

Explain active transport

Answer 13

Active transport: requires energy

Question 14

How do protein channels work

Answer 14

Protein channels: effective for small charged molecules (Na+, Cl-)

• Ions move down concentration gradient, flow is downhill
• Only lets certain types of ions to pass through
• Formed by integral membrane proteins that line aqueous pore

Question 15

How do ion channels work

Answer 15

Ion channels: type of protein channel

• Can be opened or closed via a gate
• Provides the channel the ability to respond to different stimuli (neurotransmitters)

Question 16

How does facilitated diffusion work

Answer 16

• Compounds bind specifically to integral membrane protein called facilitative transporter, change in transporter allows compound to be released to other side of membrane
• Most animal cells use facilitated diffusion to move glucose from blood into cells

Question 17

What is the integral membrane protein used in facilitated diffusion called

Answer 17

Facilitative transporter

Question 18

What are the 2 types of protein channels

Answer 18

1) Voltage-gated channels
2) Ligand-gated channels

Question 19

How do Voltage-gated channels work

Answer 19

Responds to changes in charge across membranes
Eg. neurons and action potential

Question 20

How do Ligand-gated channels work

Answer 20

• Responds to binding of specific molecule (ligand) on its surface
• Binding of ligand produces a conformational change
• Only a ligand that matches the binding site can produce a change

Question 21

What is tetrodotoxin (TTX)

Answer 21

Very potent toxin
Discovered in pufferfish but also other aquatic animals

Question 22

What does TTX do

Answer 22

Blocks Na+ channel parenting nervous system from sending messages to muscles
Causes respiratory failure and then death

Question 23

What is curare

Answer 23

Mixture of organic compounds found in different Central and South American plants

Used as paralyzing poison and hunting tool