Lecture 3

Question 1

What factors affect membrane permeability

Answer 1

varies depending on size, charge and polarity

Question 2

How are ions and polar molecules transported?

Answer 2

must be assisted by proteins

Question 3

What is passive transport (diffusion)?

Answer 3

When molecules move from an area of high concentration to low concentration

Question 4

describe active transport

Answer 4

Requires input of energy and can move molecules against their concentration gradient

Question 5

What is passive diffusion affected by?

Answer 5

concentration and charge

Question 6

What is transport of uncharged vs. charged molecuels governed by?

Answer 6

concentration; concentration & voltage gradients

Question 7

What specialized channel proteins allow water to move more rapidly across a membrane

Answer 7

aquaporins

Question 8

What are gradient-driven pumps?

Answer 8

transporters that facilitate the movement of 2 different molecules

Question 9

Compare symport vs. antiport

Answer 9

molecules in same direction vs. molecules in opposite direction

Question 10

What is a uniport?

Answer 10

Moves a single type of molecule by concentration gradient, Not considered pumps - no external energy required

Question 11

Differentiate apical surface and basal domain:

Answer 11

Na+ is driven into the cell through electrochemical gradient, Glucose is actively transported into the cell; Na+ is actively transported out of the cell (Na+/K+ pump), Glucose passively diffuses out of the cell

Question 12

How is glucose able to go from lumen to cell?

Answer 12

Active transport

Question 13

What does the Na+/K+ pump do?

Answer 13

Maintains the sodium gradient, Used to regulate cell volume and sugar/amino acid transport

Question 14

True or false: Na+/K+ pump uses much of the energy in the body

Answer 14

True

Question 15

Describe the Na+/K+ pump activity (6)

Answer 15

1. Na+ binds
2. pump phosphorylates, ATP hydrolyzed
3. Na+ is ejected
4. K+ binds
5. pump dephosphorylates
6. K+ ejected, pump back to original form

Question 16

Describe function of channel rhodopsin

Answer 16

Allows sodium to pass through - opens because of blue light (creates aggression in mice)

Question 17

What are channel proteins

Answer 17

Aqueous pores that allow passive movement of small, water-soluble molecules (ions) across a membrane

Question 18

true or false: channel proteins are always open

Answer 18

false. not continuously open - require stimulus

Question 19

Describe stereocilia, what does it do?

Answer 19

move as basal membrane vibrates in response to sound, The movement causes the mechanically-gated ion channels to open - eliciting a response

Question 20

How are proteins transported and targeted to regions of the cell?

Answer 20

ions and small molecules are transported by diffusion, channels, and carrier proteins

Question 21

What are the three ways proteins are transported to organelles?

Answer 21

Pores, protein translocators, transport vesicles

Question 22

What do pores do in protein sorting?

Answer 22

selective gates that actively transport specific macromolecules and allow free diffusion of smaller molecules

Question 23

What do protein translocators do in protein sorting

Answer 23

transport proteins (typically unfolded) into organelles

Question 24

what do transport vesicles do in protein sorting

Answer 24

pinch off from the membrane of one compartment and then fuse with another

Question 25

What do signal peptides / signal patches do to proteins?

Answer 25

Target proteins to specific organelles by amino acid sequences

Question 26

Compare inner nuclear envelop with outer

Answer 26

Inner: interacts with nuclear lamina - stabilization, Outer: continuous with the ER

Question 27

What does the nuclear pore complex do?

Answer 27

forms a gate - Disordered and repeating regions of the proteins fill the channel - blocks large molecules, small water-soluble molecules pass freely

Question 28

What does the nuclear localization signal do?

Answer 28

interacts with nuclear import receptors - Subsequent interaction with cytosolic fibrils toward the pore (NIR disrupts repeating sequencing in the meshwork)

Question 29

What is GTPases

Answer 29

family of proteins that bind and hydrolyze the nucleotides guanosine triphosphate (GTP) to GDP and inorganic phosphate

Question 30

what is hydrolysis

Answer 30

chemical breakdown of a compound due to reaction with water

Question 31

What is GAP and what does it do?

Answer 31

GTPase activating protein, Hydrolyzes GTP (removes one phosphate)

Question 32

what is GEF and what does it do?

Answer 32

guanine nucleotide exchange factor, Causes Ran-GDP to release GDP and take up GTP

Question 33

How to import an NIR? (2)

Answer 33

Cytosolic Ran-GDP binds has a low affinity for NIR, Protein + NIR move through pore independently from GTPase

Question 34

How to selectively export a NIR? (4)

Answer 34

Ran-GTP in the nucleus has a high affinity for NIR, displaces cargo - This moves to the cytosol and GTP is hydrolyzed, Ran-GDP and NIR dissociate

Question 35

What does mitochondrial protein import rely on?

Answer 35

chaperone proteins within the mitochondrial membranes

Question 36

true or false: Proteins must enter unfolded and be folded when inside mitochondrial protein import

Answer 36

true

Question 37

Steps of protein sorting to the mitochondria (5)

Answer 37

1. A mitochondrial localization signal of an unfolded protein (with chaperone proteins) binds to an import receptor protein 2. The protein is moved through TOM 3. The protein is then shuttled through TIM within the inner membrane. Any protein in the cytosol or in the mitochondrial space interacts with chaperone proteins until folded 4. Once the whole peptide is within the mitochondrial matrix, it folds 5. The signal peptide is cleaved

Question 38

What is the endoplasmic reticulum involved in?

Answer 38

synthesis of proteins destined for other locations, proteins to be secreted, or proteins to function inside the ER

Question 39

Three step process of protein sorting to the ER

Answer 39

1. A signal recognition particle (SRP) binds to the hydrophobic signal sequence and ribosome slowing translation 2. The SRP binds to a receptor associated to the ER membrane (SRP) 3. The ribosome is passed to a protein translocator (transmembrane channel) and protein synthesis resumes at its normal rate

Question 40

what does peptidase do in protein sorting?

Answer 40

a peptidase cleaves the signal and moves it to the bilayer, later degrading

Question 41

What does the translocator do in protein sorting (single pass transmembrane proteins)?

Answer 41

holds onto both the stop transfer sequence and the ER signal sequence, then ejects both into the bilayer

Question 42

What do start & stop sequencs do in double pass transmembrane proteins?

Answer 42

help anchor the protein across the membrane