HBS - Cell Membranes - Topic 2

Question 1

List the components of the plasma membrane.

Answer 1

1. Phospholipids
2. Carbohydrates
3. Cholestrol
4. Proteins

Question 2

Describe the functions of the phospholipid.

Answer 2

It regulates the permeability of the membrane.

• Higher concentrations of UNsaturated acids promote membrane fluidity, larger gaps
• Higher concentration of saturated fatty acids reduce cell membrane fluidity, fewer gaps

Question 3

Describe the functions of Carbohydrates.

Answer 3

-Two main types:
Glycolipids
Glycoprotein

• Three main roles:
  1) Maintain membrane stability and cell protection (glycocalyx)

2) Aid cell-cell adhesion (cell adhesion molecules)
3) Facilitate cell recognition

Question 4

What is cholestrol?

Answer 4

• Is a lipid. Approximately 20% of membrane lipid is cholesterol.
• is amphiphilic
• Can migrate and even ‘flip’ between the membrane layers

Question 5

What is the function of a protein?

Answer 5

Serve different functions: enzymes, carrier proteins, channel proteins, receptors, cell adhesion, recognition

Question 6

What are the 2 main types of protein?

Answer 6

• Integral (firmly inserted into membrane)

- Peripheral (looslely attached to membrane)

Question 7

Membrane fluidity is affected by:

Answer 7

1. Extreme temperatures (hot or cold)
2. Concentration of unsaturated fatty acids
3. Cholesterol levels

Question 8

How does low temperature affect membrane fluidity?

Answer 8

• Less kinetic energy
• Phospholipids pack together
• Membrane less fluid

Question 9

How does high temperature affect membrane fluidity?

Answer 9

• More kinetic energy
• Phospholipids tend to move further away
• Membrane more fluid

Question 10

How does cholestrol affect membrane fluidity?

Answer 10

-Maintains fluidity by preventing lipids from getting too close or too far apart from each other

Question 11

Describe the differences between active and passive transport

Answer 11

Passive: Moves down a concentration (electrochemical) gradient
Active: against a concentration (electrochemical) gradient

Passive: Uses inherent K.E
Active: Needs external energy source

Active: Requires specific carrier protein, Has directionality

Question 12

Summarise the key parts of simple diffusion.

Answer 12

• Small, uncharged, non polar molecules
• O2, CO2, NO, urea
• Uses kinetic energy (natural motion)
• Rate of diffusion proportional to concentration gradient

Question 13

Summarise the key parts of Facilitated Diffusion.

Answer 13

• Small, polar molecules
• H2O, Glucose, Na+
• Uses specific integral proteins (carrier proteins)

Question 14

Summarise the key parts of Osmosis.

Answer 14

• Net movement of water down a concentration gradient
• Water highly polar, but small amounts can ‘sneak’ through the membrane unaided
• Water moves freely and reversibly through specific protein channels called Aquaporins- fac.diffusion

Question 15

Summarise the key parts of Primary Active Transport.

Answer 15

• Uses energy from Hydrolysis of ATP
• Movement of Na+ and K+ uses the Na+/K+ pump
• Maintaining ion concentration differences inside the cell are crucial

Question 16

Summarise the key parts of Secondary Active Transport ( Co-Transport)

Answer 16

• 2 substances move at SAME time, a substance moves against conc gradient, and ion moves down conc gradient.
• The energy comes from the electrochemical gradient across the membrane

Question 17

E.g of Secondary Active Transport?

Answer 17

Na+/Glucose transporter

Question 18

E.g of Primary Active Transport

Answer 18

• Na+/K+ pump, 3 Na+ out, 2 K+ in.

- Calcium and Hydrogen pumps

Question 19

What are the 2 types of secondary active transport?

Answer 19

Symport

Antiport

Question 20

What is symport?

Answer 20

• Transported substances move in the same direction

- Na+/Glucose transporter

Question 21

What is antiport?

Answer 21

• Transported substances move in opposite direction

- Na+/Ca2+ exchanger – uses the Na electrochemical gradient to transport Ca2+ out of the cell.

Question 22

Define transport vesicles

Answer 22

• Bubble-like, membranous sacs
• Made of a phospholipid bilayer containing fluid
• Transport bubble
• Protects substances being transported

Question 23

Define Endocytosis briefly.

Answer 23

Moves large molecules INTO the cell (ingestion / uptake)

Question 24

What are the 3 types of endocytosis?

Answer 24

Phagocytosis
Pinocytosis
Receptor-mediated

Question 25

Define Exocytosis briefly.

Answer 25

Moves large molecules OUT of the cell (excretion / secretion)

Question 26

What are the 3 types of exocytosis.

Answer 26

Hormone secretion
Neurotransmitter release
Mucous secretion

Question 27

Summarise Phagocytosis (endocytosis).

Answer 27

• cell eating
• Ingestion of large particles by specialised cells (phagocytes; in the immune system)

-Used for removing bacteria and debris

Question 28

Summarise Pinocytosis (Endocytosis).

Answer 28

• cell-drinking’
• Process used to take in extracellular fluid with dissolved substances

-Droplet enters the cell and fuses with an endosome (sorting vesicle)

Question 29

Summarise Receptor mediated endocytosis.

Answer 29

• Main mechanism for specific uptake of macromolecules
• Uptakes substances (hormones, cholesterol) found in small amounts
• Some viruses can hijack this route and enter our cells

Question 30

Summarise Key parts of exocytosis.

Answer 30

1. Process is stimulated by a cell-surface signal
2. Transported to plasma membrane
3. Fuses with membrane and ejects substance

Question 31

What type of substances move out of the cell by exocytosis?

Answer 31

• Hormones
• Waste Products
• Neurotransmitters