Week 4

Question 1

Why is cholesterol important in a cell?

Answer 1

Cholesterol is important for merane integrity

Cholesterol sits next to an unsaturate fatty acid

A source for the production of hormones, bile acids and vitamin D

Question 2

How does fluidity effect a membrane?

Answer 2

Fluidity-Flexibilty maintained so that the membrane can fucniton properly

Question 3

What happens if a membrane is too fluid?

Answer 3

The membrane will be leaky

Question 4

What happens is a membrane is not fluid enough?

Answer 4

No movement or solute passage

Question 5

What effect does heat have on a membrane?

Answer 5

HEAT = lipids move more, arranging/rearranging; more fluid membrane

Question 6

How does cold effect membrane fluidity?

Answer 6

COLD = lipids laterally orders.organisaes, lipid chains pack togehter tightly

Question 7

What other factors effect a memrbanes fluidity?

Answer 7

• Fatty acid length
  
  • Long= stiff
  • Short = less stiff
• Double bonds
  
  • Satureated = more stiff
  • Unsaturated = less stiff
    *

Question 8

How does cholesterol dampen the effect of temperature?

Answer 8

• Cholesterol and heat = stabilizes the membrane and raises its melting point
• Cholestoer and cold = intercolated between phospholopids; prevents clusterind and stiffening

Question 9

What are teh different types of membrane transport?

Answer 9

1. Dissusion
2. Facilitated diffusion
3. Active transport
4. Secondary active transport

Question 10

What are the two different types of diffusion? And waht are their differences?

Answer 10

1. Simple diffusion through the phopholipid bilayer
   - E.g. O2 and CO2 and lipid-soluble substances cross membrane by simple diffusion
   - Molecules move b engaging in random collisions with other like molecules
   - From high conc to low conc
2. Factilitated diffusion through channel porteins or carrier proteins
   - Facilitated diffusion requires teh transported molecuels to bind to a specific carrier protein
   - Energy is not required

Question 11

How can water pass through into and out of a cells?

Answer 11

Aquaporins

• Aquaporins are channel proteins
• Water molecules move in a single file through a hydrophilic cahnnel
• Water passively pours through aquaporins by osmosis, moving from low to high concentrations
• This is facilitated diffusion (part of passive)

Question 12

What are symporters and antiporters?

Answer 12

They are ‘coupled transporters’ because tehy move two substances at once

Symporters = simultaneously transport a sugar (or amino acid) and an ion (usually Na+ of H+ ion) across a membrane. E.g.Na+/glucose symporter: couples transmembrane movement of 1 glucose molecule to teh transport of 2 Na+ ions.

Antiporters = Transport one solute in one direction while transporting a second solute in the opposite direction. Exchange of one solute for another, and one is expelled at the expense of the import of one. E.g. Na+/Ca+ antiporter.

Question 13

What is active transport? And what are the different types and example?

Answer 13

Transporters that use energy.

• Energy concentrates the compound on one sidde of the membrane
  1. [rimary active transport = energy applied to teh transporter (e.g. ATP hydrolysis by Na, K-ATPase; and Ca2+-ATPase) ATPase is an enzyme that catalyze hydrolysis of ATP to yield ADP and inorganic phosphate with release of free energy
  2. Secondary active transport = energy establishes ion gradient (e.g. teh Na+ gradient), ad the gradient is used to concentrate another compound

Question 14

How does the Sodium/potassium ATPase (Na/K-ATPase) pump work?

Answer 14

Energy from ATP hydrolysis phosphorylates an internal domaina nd cahnge the transporter’s conformation.

Na+ are released to the outsie, and two external K+ bind adn trigger hydrolysis of the bound phosphate group and a reture to teh original conforation, accompanied by release of K + inside the cell.

Cells can maintain a much lower intracellular [Na+] anc much higher intracellular [K+] than present in serum.

Question 15

How does secondary active transport work?

Answer 15

A sodium symporter brings molecules into cells

Sodium moves down its gradient and this drives teh uphill transport of a cotransporter substrate (glucose)

Does not hydrolyze ATP but depends on maintenace of the sodium gradient by the sodium/potassium pump.

Question 16

How does glucose get into cells?

Answer 16

Not sufficiently lipid soluble to enter cells by passive diffusion (from intesting to cell)

Dietary glucose enters the intestinal mucosal cells mainly by sodium co-transport

Uptake of glucose from blood or intersitital fluid into cells occurs by facilitated diffusion e.g. GLUT2

Question 17

What is the role of digoxin in heart disease?

Answer 17

Drugs digoxin increase the force of heart muscle contraction (ionotropy) and are used in teh treatment of congestive heart failure.

Digoxin inhibits the Na/K-ATPase; and raises teh intracellular [Na+] and lower intracellular [K+]

The Na+/Ca2+ antiporter functions less efficiently with a lower Na+ gradient, fewer Ca2+ ions are exported and the intracellular Ca2+ concentration increases

This increase causes the muscle to contract more strongly.

• Digoxim sensitizes Troponin-C (TN-C)

A cardiac muscle protein

More Ca2+ binds

Question 18

What occurs in cystic fibrosis?

Answer 18

Mutation causing the absence of a single phenylalanine in the portein. Many organs are affected. Lungs most often affected. Dilute fluids become viscus and form a mucus

Prone to infection.

CFTR:Cl- ion cnahhel is mutant. Does not move chloride ions ausing sticky mucus to build up on the outside of the cell

Question 19

What occurs in cholera?

Answer 19

CFTR has a role in cholera

Cholera is an acute diarrhoeal infection caused by bacterium vibrio cholera

Cholera bacteria produces toxins taht activate CFTR and pump Cl- ions inot the small intestine.

Accumulation of Cl- ions int he gut creates an electric potential that attracts sodium, pulling it into the lumen, apparently across tight functions

Creates an osmotic gradient across teh tight junction and water is drawn into the lumen

Osmosis cna pull up to 6 L of water/day, creating the massive amounts of disarohea

Dehydration and death can result

Oral and intravenous rehydration is the preferred treatment

Question 20

How do large molecule get into cells?

Answer 20

Macromolecules enter through 3 types of endocytosis:

1. Phagocytosis = cellular eating large particles: macrophages and neutrophils do this
2. Pinocytosis (cell drinking) = smaller dissolived substances e.g. proteins or fluids. Secreory cells use pinocytosis to retrieve the membrane material
3. Receptor-mediated endocytosis; mediated by cell surface molecules e.g. LDL
   - The palsma membrane invaginated (folds inward), forming a small pockt around materials from teh environemnt
   - THe pocket deepends, forming vesicle

This vesicle separates from the plasam membrane and migrates with its contents to teh cell’s interior

Question 21

What is phagocytosis?

Answer 21

• Particle binds to components of the cell surface
• Cytoplasm flows around the particle by a mechanism tha tinvolves the polymerization and depolymerization of actin myofilaments, forming a phagocytic vacuole
• Fusion with lysosomes and digestion of the engulfd partile by lysosomal enzymes
• IN the human body, these processes are limites to macrophages, neutrophls and dendritic cells
• These professional phagoctes protect the body by eating aberrant cells and microbial invaders

Question 22

What is endocytosis?

Answer 22

• Mechanism for the selective uptake of soluble proteins and other high-molecular0weight materials
• Binding followed by clustering of receptor-ligand complexrs ont he cell surface and the formation of an endocytic vessicle
• Depends on receptor proteins (integral) located on cell surface of the palsma membrane
• These membrane regions are called coated pits and their cytoplasmic surfaces are coated by toher proteins, such as clathrin
• THe coated pit invaginates and forms a coated vesicle around the bound macomolecule and carries the macromolecule away fromt the plasma membrane and into the cytoplasm
• The vessicle losses its clathrin coat and may fise with a lysosome, where the engulfed material is digested and the produts released into the cytoplasm

Question 23

Draw a cell membrane and label teh major components?

Answer 23