Lec 19 Flashcards Preview

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Flashcards in Lec 19 Deck (19):
1

What are the two types of transport?

Passive-no energy required
active-energy required

2

Passive Transport

-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

3

Active Transport

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

4

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

1) substrate concentration inside vs outside the membrane
2)membrane potential

5

For diffusion what determines the rate of transport?

-rate is unlimited
-depends only on the concentration gradient and charge

6

For protein-assisted transport (requiring energy or not)

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

7

What are 3 the types of channels

uniport
synport
antiport

8

uniport

passes one substrate at a time

9

synport

passes two different substrates

10

antiport

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

11

Potassium Channels

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

12

Bacterial K+ channel

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

13

Selectivity Filter

-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

14

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

-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

15

Primary Active transport

-- 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

16

Secondary Active Transport

-- 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

17

Na+-K+ ATPase transporter

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

18

ABC Transporters

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

19

MDR

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