Lec 19

Question 1

What are the two types of transport?

Answer 1

Passive-no energy required

active-energy required

Question 2

Passive Transport

Answer 2

• can occur without or with protein mediation
• simple diffusion-the substrate getting through the membrane by itself (rare)
• Pores (bacteria) or channels (animals) are selective holes made in the membrane by transmembrane proteins
• involves a protein receptor that binds and carries substrate through the membrane

Question 3

Active Transport

Answer 3

• will always involve a protein
• Primary active transport
• secondary active trasnport

Question 4

For transport that doesn’t require energy, what determines the rate of transport?

Answer 4

1) substrate concentration inside vs outside the membrane

2) membrane potential

Question 5

For diffusion what determines the rate of transport?

Answer 5

• rate is unlimited

- depends only on the concentration gradient and charge

Question 6

For protein-assisted transport (requiring energy or not)

Answer 6

transporter protein has a certain capacity for binding and transporting the substrate

Question 7

What are 3 the types of channels

Answer 7

uniport
synport
antiport

Question 8

uniport

Answer 8

passes one substrate at a time

Question 9

synport

Answer 9

passes two different substrates

Question 10

antiport

Answer 10

passes one substrate while at the same time passing a substrate in the opposite direction

Question 11

Potassium Channels

Answer 11

• conduct specific ions at high rates
• selective-excludes Na+ ions
• conduction can be turned on and off

Question 12

Bacterial K+ channel

Answer 12

• TETRAMER

- selectively filter is lined with backbone carbonyl groups from “re-entrant loops”(NOT ALPHA HELICAL)

Question 13

Selectivity Filter

Answer 13

• found in bacterial K+ channels
• lined with backbone carbonyl groups from “re-entrant loops” NOT ALPHA HELICAL
• oxygen atoms can replace the hydration shell that normally surrounds a K+ ion in solution- but do not form a good mimic of the Na+ hydration shell thus the protein provides a low energy path through the membrane for K+ ion but NOT Na+ ions

Question 14

What are the type of energy that can be used for active transport?

Answer 14

• ATP to ADP + Pi (most common)
• Sunlight- in photosystems- electrons are moved by energy from the sunlight
• oxidation/reduction reaction

**all three of these are exergonic reactions (delta G

Question 15

Primary Active transport

Answer 15

• • moves up its concentration gradient and required a direct source of energy
• -the exergonic reaction generating the energy is directly coupled to the endergonic transport reaction

Question 16

Secondary Active Transport

Answer 16

• • move up its concentration gradient and gets its energy from an ion gradient
• -the endergonic reaction of one transported substrate is coupled to the exergonic reaction of some other substrate

Question 17

Na+-K+ ATPase transporter

Answer 17

1) 3 Na+ ions bind to specific sites on ATPase
2) energy is utilized (ATP->ADP) and ATPase is phosphorylated
- very exergonic
- changes the conformation of the channel and Na+ is released to the exterior (nothing else would happen without this step)
3) Na+ is released
4) 2 K+ bind
5) binding induces a conformational change and the 2K+ are released on the other side

** both Na+ and K+ ions are transported against the concentration gradient

Question 18

ABC Transporters

Answer 18

-use energy derived from ATP hydrolysis to transport a variety of small molecule including amino acids, sugars, inorganic ions, and peptides

Question 19

MDR

Answer 19

Multi drug Resistance Protein

• is a ABC transporter
• the over expression of this transporter in human cancer cells gives them resistance to cytotoxic drugs that are used for chemotherapy
• The transporter pump drugs out of cancer cells-reducing their toxicity and making them resistant to chemotherapy