Lecture 11: Transport Across Membranes

Question 1

What are the two types of transport?

Answer 1

Passive Transport (does not require ATP)
- Simple Diffusion & Osmosis (H2O)
- Facilitated Diffusion (via channel and carrier proteins)

Active Transport (requires ATP)
- Primary active transport
- Secondary active transport

Question 2

What does the rate of diffusion depend on?

Answer 2

• The size and mass of the moelcule or ions (the bigger the slower)
• The temperature (the hotter the faster)
• The density (the more dense the slower)
• The concentration gradient (larger difference the faster)
• The area & distance (the larger the distance the slower)

Question 2

What can go through the membrane without issue?

Answer 2

Small nonpolar molecules (O2, CO2, N2) or small uncharged polar molecules (H2O, glycerol)

Question 3

Osmosis, how does it work?

Answer 3

• Water diffuses from hypotonic enviroment to hypertonic enviroment (low amt of water to high amt of water)
• Water moves down the concentration gradient

Question 4

What are some example of channels utilzied in facilitated diffusion?

Answer 4

• Ligand gated channel: ligand binding causes conformational change that allows substance to pass (acetylcholine receptor)
• Voltage gated channel: respond to change in membrane potential
• Mechanically gated channels - respond to mechanical stimuli, distorted membrane (stereocillia causes potassium channels to open)
• Aquaporins : specialized channels for water (faster diffusion)
• Carrier proteins: aid passive diffusion by binding substances, transport polar or larger molecules, such as sugars and amino acids (glucose transporter)

Question 5

Active Transport

Answer 5

moves substances against their concentration gradient, occurs via a transporter protein, and requires energy

• uniporter (Calcium ATPase)
• symporter (Sodium-Glucose linked transport SGLT)
• antiporter (Sodium-Calcium exchanger)

Question 6

Primary vs Secondary active transport

Answer 6

Primary: involves direct hydrolysis of ATP
Secondary: indirectly uses ATP via ion concentration gradient established by primary active transport

Question 7

What is Vesicular transport and the different kinds?

Answer 7

• Transport of large substances

Endocytosis
- Phagocytosis
- Pinocytosis
- Receptor-Mediated Endocytosis (coated pits & clathrin)

Exocytosis
- Secretion (digestive enzymes)
- Removal of Waste