Week 4- Membranes

Question 1

role of carbohydrates with proteins?

Answer 1

located on outer surface of plasma, serves as a recognition site for other molecules and stop degradation

Question 2

glycolipid?

glycoprotein?

Answer 2

lipid with a carbohydrate attached

protein with carbohydrate attached

Question 3

homotypic binding?

Answer 3

the same molecule on both ends
binding of one protein of another of a similar kind, as would be the formation of a homodimer
eg, cadherins

Question 4

heterotypic binding?

Answer 4

binding of one protein to another of a different kind, as would be the formation of a heterodimer.

Question 5

tight junctions?

Answer 5

link adjacent epithelial cells together, mutual binding of specific proteins in the plasma
substances pass through the epithelial cells and keep stuff in or out
eg, gut, bladder, oesophagus
eg, colon cancer= mutations in tight junctions

Question 6

desmosomes?

Answer 6

connect adjacent plasma membranes, has a plaque on the cytoplasmic side which have adhesion molecules attached to it that stretch from one side of the cell to the other
provide mechanical stability

Question 7

gap junctions?

Answer 7

connexins (channel proteins) interact to form connexons that span the plasma of adjacent cells and the intercellular space between them
- water, small molecules, ions can pass through these junctions from cell to cell.
eg, cardiomyocytes

Question 8

passive diffusion?

Answer 8

move from high to low concentrations, no ATP

eg, steroid hormones, drugs, o2, co2

Question 9

facilitated diffusion?

Answer 9

passive and doesn’t require ATP
through channel proteins and carrier proteins
requires transported molecule to bind to carrier protein
eg, RBC

Question 10

channel proteins?

Answer 10

interact weakly with the solute, specific solutes to pass only, faster than carrier proteins, no energy required
eg aquaporins

Question 11

carrier proteins?

Answer 11

bind to a specific solute, undergo conformational change to transfer the bound solute across the membrane
sensitive to temperature changes

Question 12

uniporter?

Answer 12

type of carrier protein
transport one solute at a time, involved in facilitated diffusion that involves the transport of a solute across a membrane down its concentration gradient.

Question 13

Symporters?

Answer 13

transport two solutes across a membrane in the same direction.
Eg, sugars and amino acids

Question 14

Antiporters?

Answer 14

transport one solute in one direction while transporting a second solute in the opposite direction.
eg,
the Na/K-ATPase operates to pump three sodium ions out of the cell in exchange for two potassium ions and a molecule of ATP supplies the energy needed to drive this transport of ions.

Question 15

GLUT1?

Answer 15

Present in all cells and responsible for endogenous
GLUT1 increases at low glucose concentration
Found in RBCs and in the blood brain barrier

Question 16

GLUT2?

Answer 16

main liver glucose transporter
passive transport of glucose across all membrane
low affinity for substrate
importnant for detecting elevated BG levels

Question 17

GLUT3?

Answer 17

high affinity glucose transporter in neurons

important for placenta

Question 18

GLUT4?

Answer 18

insulin dependant, regulated by insulin
in muscle, adipose tissue, heart
GLUT4 in vesicles and fuse into the cell membrane

Question 19

GLUT5?

Answer 19

fructose transporter expressed in intestine, hepatocytes, muscle, brain, adipose

Question 20

human diseases related to GLUT transporters?

Answer 20

type 2 diabetes (hyperglycaemia and cardiovascular problems)

deficiency in GLUT1, glucose to cross BBB= seizures in infancy

effects brain function by the lack of glucose going to the brain

Question 21

ligand gated channels?

Answer 21

NT binds, opens channel, ions flow across the member e

Question 22

antiporters: primary active transport?

Answer 22

energy directly applied to transporter
eg, ATP hydrolysis by Na+K+ATPase
eg, Ca2+ATPase, removes Ca2+ from the cytoplasm to the outside of the cell or inside organelles.

Question 23

what is ATPase?

Answer 23

catalyzes hydrolysis of ATP to yield AP and inorganic phosphate with release of free energy

Question 24

antiporter:secondary active transport?

Answer 24

energy is used to establish an ion gradient and the gradient is used to concentrate another compound
- does not hydrolyze ATP but depends on maintenance of sodium gradient by the NA+/K+ pump.
eg, Na+ gradient

Question 25

secondary active transport mechanism?

Answer 25

Na+ moving with the concentration gradient that was established by the Na+K+ pump, glucose moves against the concentration gradient and into the cell.
- symporter

Question 26

how does glucose enter the cell?

Answer 26

sodium co-transport because it is not lipid soluble, it enters the intestinal mucosal cells
also used for kidneys and intestines
and through facilitate diffusion, glucose it taken up from blood and into cells but GLUT2

Question 27

heart disease: digoxin?

Answer 27

increase the force of heart muscle contraction and used to treat congestive heart failure

• inhibits NA+K+ATPase which raises intracellular Na+ and lowers K+
• the Na+/Ca2+ antiporters work less efficiently when there is a lower concentration gradient of Na+
• few Ca2+ exported inside and the ICF increases
• causes muscles to contract more strongly

Question 28

CFTRs role in cholera?

Answer 28

bacteria causes extreme diarrhea
cholera bacteria produces toxins that activate CFTR to pump Cl- ions in the intestine, accumulation of this creates an electrical potential that attracts Na+ pulling it into the lumen across the tight junctions
so water follows across the tight junctions into the lumen
this causes diarrhea

Question 29

how do macromolecules enter the cell?

Answer 29

3 types of endocytosis:
- Phagocytosis: cellular eating large particles
eg, macrophages and neutrophils
- Pinocytosis: cell drinking, retrieve membrane material (secretory cells)
eg, proteins, fluid
- Receptor- mediated: mediated by cell surface molecules
eg, LDL (low density lipoproteins)

Question 30

familial hypercholesterolemia?

Answer 30

inherited disease, have a deficient LDL receptor in their livers this prevents receptor mediated endocytosis of LDLs
results in high levels of serum cholesterols

Question 31

what are cadherins?

Answer 31

“calcium-dependent adhesion” are a class of type-1 transmembrane proteins (integral protein). They play important roles in cell adhesion, forming adherens junctions to bind cells within tissues together.