Lecture 7 - Lipids Part 2

Question 1

What are functions of a plasma membrane?

Answer 1

protection (cell shape), transport, communication (signaling/regulation), cell adhesion (movement)

Question 2

What features does a plasma membrane have with regard to permeabillity and why is that the case?

Answer 2

impermeable to hydrophilic molecules b/c lipid bilayers with hydrophobic tails and hydrophilic heads

Question 3

What are the 3 major transport types and do they require energy?

Answer 3

passive: no energy, uses concentration gradient (simple, osmosis, facilitated)
active: energy required to move against concentration gradient (primary and secondary)
bulk: energy required (endocytosis and exocytosis)

Question 4

What is uniport, symport, and antiport (with regard to energy required and molecules moved)?

Answer 4

primary active transport = UNIPORT uses ATP to move 1 molecule against concentration gradient
secondary active transport: uses conc gradient of one moelcule (not ATP) to move another molecule
-symport: both molecules move in same direction
-antiport: both molecules move in diff direction

Question 5

What are the 2 types of bulk transport and is energy required? What “vessel” is required?

Answer 5

vesicular transport of bulk materials - requiring membrane vesicles and energy
-endocytosis: phagocytosis
-exocytosis: neurons releasing NTs

Question 6

What is an example for an uniporter found in rods, transporting what?

Answer 6

GLUT1 - glucose transporter 1 found in rods
PMCA: calcium ATPase transport Ca2+

Question 7

What is an example for an antiporter found in rods, transporting what?

Answer 7

Na-K-Ca Exchanger (NCKX): antiporter found in retinal rods that uses conc gradient made from Na+/K+ ATPase to transport Ca2+ out of cell while Na+

Question 8

Which 4 types of multiprotein complexes are found in a membrane involved in transport, signaling, adhesion, and protection?

Answer 8

1. gap junctions: transport, signaling (within tissue/between cells)
2. tight junctions: seal cells
3. desmosomes: cell adhesion (hold neighboring cells together); allow molecule transport
4. adherens junctions: cell adhesion to ECM

Question 9

Which one is the membrane model that is still accepted today and what are the major features of that model?

Answer 9

fluid mosaic model - highly dynamic = fluid; diff molecule types = mosaic (phosphollipids, cholesterol, protein, carbs)

Question 10

Which lipid classes are the main types found in plasma membrane?

Answer 10

glycerides (contain glycerol)
non-glycerides (sphingolipids, steroids like cholesterol)

Question 11

Which lipid types are the most abundant?

Answer 11

1. glycerophospholilpids/phosphoglycerides = glycerol + 2 FA tails + phosphate head (inositol, choline, ethanolamine)
2. sphingolipids (raft) - non-glycerides
3. cholesterol (raft) - influence lipid fluidity

Question 12

Which 3 types of membrane protein exist (with regard to location and attachment features)?

Answer 12

1. integral proteins: permanently incorporated
2. peripheral proteins: temporarily attached to bilayer or integral proteins
3. lipid-anchored proteins: permanently attached

Question 13

What are the major features of the 3 membrane protein types?

Answer 13

integral proteins: in bilayer –> so hydrophobic parts interact with hydrophobic phospholipid tail
peripheral proteins: hydrophilic so not linked with hydrophobic bilayer interior
lipid-anchored proteins: hydrophillic; on surface of membrane; covalently attached

Question 14

Which protein structure of TM-proteins is the predominant form in our membranes - alpha helix or beta barrel?

Answer 14

alpha helix (ex: rhodopsin)

Question 15

What is an example for TM protein that’s required for enzymatic activity (type/kind, not specific molecule)?

Answer 15

integral receptor protein - required for enzymatic activity

Question 16

What is an example for a TM-protein that’s required for cell recognition (type/kind, not a specific molecule)?

Answer 16

T-cell receptors and foreign antigens

Question 17

What is an example for a TM-protein that’s required for signal transduction/signaling (type/kind, not a specific membrane)?

Answer 17

GPCR - transmembrane receptors - ligand binds and G-protein changes shape and downstream effect occurs

Question 18

Where in the rod photoreceptor (structure/formation) is rhodopsin predominantly found and where in this structure is it located?

Answer 18

rhodopsin (alpha helical GPCR transmembrane protein) found in discs of PR rod outer segment which is embedded in RPE (retinal pigmented epithelium)

Question 19

Of which 2 components is rhodopsin made of (type of molecule and specific name)?

Answer 19

rhodopsin = opsin + 11-cis-retinal (chromophore = light absorbing pigment)

Question 20

What happens to these 2 components when light hits rhodopsin?

Answer 20

when light hits rhodopsin, 11-cis-retinal becomes 11-trans-retinal = activated rhodopsin

Question 21

What is the name of the G-protein that interacts with activated rhodopsin?

Answer 21

transducin = GPCR that interacts with activated rhodopsin

Question 22

What is the name of the ligand that keeps a special channel open to allow sodium to enter the rod? What is the name of the channel?

Answer 22

cGMP keeps cGMP gated Na+ channels open –> depolarized rod in the dark

Question 23

What is the name of the enzyme generating GMP and what is the substrate?

Answer 23

PDE: phosphodiesterase makes GMP from cCMP when activated alpha unit of G-protein interacts

Question 24

In the dark, the rod sodium channels are ____ resulting in ____ resulting in ____ resulting in ____?

Answer 24

In the dark, rod’s cGMP gated Na+ channels are OPEN, resulting in DEPOLARIZATION (increase conc positively charged ions) resulting in EPSP (excitatory post synaptic potential), resulting in RECEPTOR POTENTIALS

Question 25

When light is present, rod sodium channels are ____ resulting in ____ resulting in _____ resulting in ____?

Answer 25

When light is present, rod cGMP gated Na+ channels are CLOSED, resulting in HYPERPOLARIZATION (decrease in positive ions inside cell), resulting in IPSP (inhibitory post synaptic potential), resulting in FEW RECEPTOR POTENTIAL

Question 26

What is the visual cycle?

Answer 26

biochemical reactions that regenerate visual pigment (11-cis-retinal)

Question 27

Which enzymes/enzyme complexes are required in the visual cycle?

Answer 27

1. light activates rhodopsin so (opsin + 11-cis-retinal –> opsin + all-trans-retinal)
2. RDH8/12 (retinol dehydrogenase) reduces all-trans-retinal to all-trans-retinol in presence of NADPH
3. LRAT (lecithein retinol-acyl-transferase): all-trans-retinol to all-trans-ertinyl esters
4. RPE65 (retinol isomerase): all-trans-retinyl esters to 11-cis-retinol (retinol is vitamin A)
5. RDH5/10/11 (11-cis-retinol dehydrogenase): 11-cis-retinol to 11-cis-retinal

Question 28

Starting with all 11-cis-retinal converted to all-trans retinal which products (3) are generated in the cycle until 11-cis-retinal is renewed (correct sequence)?

Answer 28

1. 11-cis-retinal –> all-trans-retinal (via light activation)
2. all-trans-retinal –> all-trans-retinol (via RDH8/12)
3. all-trans-retinol –> all-trans retinyl esters (via LRAT)
4. all-trans-retinyl esters –> 11-cis-retinol (via RPE65)
5. 11-cis-retinol –> 11-cis-retinal (via RDH5/10/11)

Question 29

If proteins or enzymes in a retinal cell are not built or functioning, what will be the outcome?

Answer 29

results in congenital blindness in kids if RPE65 missing