Biochem Lecture 5&6

Question 1

What kinds of molecules have a hard time getting through plasma membranes?

Answer 1

Because the core of the membrane is non-polar, ionic and polar substances have a hard time getting through.

Question 2

What is glycocalyx?

Answer 2

Carbohydrate in the cell membrane.

Question 3

What are the two main types of membrane transport and any subcategories under them?

Answer 3

Non-mediated: no transport proteins required.
Mediated: carriers and channels required.
-Passive-mediated: channels and carriers
-Active transport: Primary and secondary

Question 4

What is the difference between primary and secondary active transport?

Answer 4

Primary is ATP driven and secondary is driven by ion gradients.

Question 5

What are glycerolphospholipids?

Answer 5

These are a membrane lipid. They have a non-polar head group attached to a phosphate group on a glycerol group attached to two fatty acid tails.

Question 6

What are sphingolipids?

Answer 6

A single fatty acid chain in the sphingosine molecule attaches to ceramide and either becomes sphingomyelin or a glycolipid depending on what binds next.

Question 7

What are the components of sphingomyelin?

Answer 7

Sphingosine, ceramide, phosphate, choline

Question 8

What are the components of glycolipids?

Answer 8

Sphingosine, ceramide, sugars

Question 9

What are cerebrosides and gangliosides?

Answer 9

Both are types of glycolipids.
Cerebrosides: contain a single glucose or galactose molecule attached to ceramide.
Gangliosides: have glycans as their head groups.

Question 10

What causes multiple sclerosis?

Answer 10

The myelin around axons degrades. This sheath is made of sphingomyelin and galactocerebrosides. The nerve cells lose their ability to transmit signals.

Question 11

What causes Niemann-Pick disease?

Answer 11

A deficiensy in sphingomyelinase causes sphingomyelin to build up in various organs causing enlarged cells.

Question 12

How does cholesterol affect cell membranes?

Answer 12

Cholesterol has a non-polar body, but often a polar head group. This allows it to be positioned in the membrane wall. It restricts movement of the phospholipids within the bilayer. It reduces fluidity of the membrane and permeability to small molecules.

Question 13

Explain asymmetric membrane distribution of lipids.

Answer 13

Most membrane lipids are prevalently located on one side of the membrane. Glycerolphospholipids and sphingolipids do not naturally flip flop between two monolayers. It requires flipases to transfer sides of the membrane. Only cholesterol is hypothesized to naturally flip flop.

Question 14

What increases and decreases membrane fluidity?

Answer 14

Decrease fluidity: Long chain FAs, Saturated FAs, low temp, high cholesterol
Increase fluidity: Short FAs, Unsaturated FAs, High temp

Question 15

What are the three classes of membrane proteins in regard to how they bind to the membrane?

Answer 15

Transmembrane: Contain spans of hydrophobic amino acids that interact well with the interior of the membrane and allow the protein to span it. These are bound by non-covalent interactions.
Lipid-like: Attached through covalent interactions between lipid-like structures on the protein and the membrane.
Peripheral: These proteins attach to the membrane by electrostatic or hydrogen bonds that non-covalently link them to integral membrane proteins or phospholipid head groups.

Question 16

What are glycoproteins?

Answer 16

Glycosylated proteins.

Question 17

What are the roles of glycocalyx?

Answer 17

Cell recognition
Protect against mechanical stress, slimy surface (water adsorption quality of carbohydrates)
Involved in blood clotting, egg-sperm interaction

Question 18

What can cross membranes through simple diffusion?

Answer 18

Small, uncharged and non-polar: gases, steroid hormones

Small, uncharged and polar: water, ethanol, glycerol, urea

Question 19

What molecules cannot cross membranes unaided?

Answer 19

Large uncharged polar: glucose, galactose, fructose

Ions, Large polar and charged: H+, Na+, K+, HCO3-, Ca2+, Cl-, amino acids

Question 20

What is the difference between passive and active transport?

Answer 20

Passive does not require energy because the substance is going down its concentration gradient. Active requires energy.

Question 21

What are the two types of active transport?

Answer 21

Primary: requires ATP
Secondary: uses another means of energy, often another molecule going down its concentration gradient, such as Na+

Question 22

Do channels bind to the solute?

Answer 22

No. But they are specific to which molecules they allow to pass through. Because they do not bind, they are much faster than carriers.

Question 23

What is the difference between paracellular and transcellular transport?

Answer 23

Para goes between cells and trans goes through them.

Question 24

What are the four steps of transport?

Answer 24

Binding, transport, dissociation, recovery

Question 25

What are the differences in the GLUT transporters 1-4 in the body and where are they located?

Answer 25

All GLUT proteins mediate passive glucose transport. They each have a different affinity to glucose to make them more or less active depending on the concentration of glucose in the blood.
The brain has GLUT-1&3 so it takes up glucose at all concentrations.
The liver has GLUT-2 and only takes up glucose at higher concentrations.
Muscle and adipose tissue have GLUT-4 and uptake glucose at high concentrations. These are regulated by insulin levels.

Question 26

How is glucose transported for the intestinal lumen into the blood and what three transports are necessary?

Answer 26

Intestine->epithelial cells through secondary active transport using Na+gradient to drive transport. In apical membrane.
Epithelial cells->blood through passive mediated transport with GLUT-2. In basal and lateral membranes.
Na+ is pumped back out through the Na+ K+ ATPase pump which is primary active transport. Located in basal and lateral membranes. 3Na+ and 2K+ are pumped each time.

Question 27

How does the Na+K+ pump contribute to cell volume control?

Answer 27

It pumps more solutes out of the cell than into it so water is drawn out of the cell to follow the solutes and decrease the osmotic pressure in the cell.

Question 28

How does the acetylcholine-gated Na+ ion channel work?

Answer 28

When the neurotransmitter acetylcholine binds to the channel, it changes conformation and opens to allow Na+ to rush through down its electrochemical gradient.