MTM WK 1 - PROTEINS & CELL SURFACE

Question 1

PROTEIN STRUCTURE

Answer 1

PRIMARY - amino acid sequence
SECONDARY - a-helix or B-pleated sheet (held by H bonds)
TERTIARY - proteins folded into 3D shape & has lowest energy (no -ve + -ve)
QUATERNARY - more than one polypeptide chain

Question 2

FIBROUS PROTEIN

Answer 2

• form elongated sheets for structural rigidity

- e.g. actin, collagen

Question 3

GLOBULAR PROTEINS

Answer 3

• soluble, may be secreted, often enzymes

- e.g. insulin, haemoglobin

Question 4

MEMBRANE PROTEINS

Answer 4

• form pores for passage of solutes (e.g. NA/K channels) & contain separated hydrophobic & hydrophilic region

Question 5

PROTEINS USED AS DRUGS

Answer 5

e.g. HIV protease (study AS of HIV enzyme & make a protein to block it)

Question 6

PROTEIN PHOSPHORYLATION

Answer 6

• phosphate group attached covalently to amino acid side chains which leads to inhibition or activation or protein (catalysed by KINASE protein)
• dephosphorylation catalysed by PHOSPHATASE protein

Question 7

PROTEIN SECRETORY PATHWAY

Answer 7

1. proteins made on ribosome in cytosol & has sorting signal to take it to correct site in cell
2. proteins transported from cytosol to organelles by vesicles (transport vesicles = move proteins to lysosomes for degradation)(secretory vesicles = store hormones waiting for a signal to start fuse & release)

Question 8

FLUID MOSAIC CELL MEMBRANE

Answer 8

• dynamic structure (protein move within structure)

- made of proteins & lipids (each lipid has hydrophilic head & hydrophobic tail)

Question 9

PHOSPHOLIPID STRUCTURE

Answer 9

2 fatty acids, 1 glycerol, 1 phosphate group

Question 10

JOB OF CHOLESTEROL IN MEMBRANES (in eukaryotic cells)

Answer 10

adds rigidity so regulates membrane fluidity (less permeable at 37)

Question 11

WHY MEMBRANES MUST BE FLUID

Answer 11

• allows them to fuse with other membranes e.g. exo/endo cytosis
• ensures membranes equally shared between daughters in cell division

Question 12

WHY WE NEED ELECTROCHEMICAL GRADIENTS

Answer 12

• drive transport across membranes

- maintain osmotic balance

Question 13

HOW NA+/K+ ELECTROCHEMICAL GRADIENT MAINTAINED

Answer 13

NA+ bind to ATPase (hydrolyses ATP to ADP + Pi) = Pi phosphorylates ATPase to change shape so 3 NA+ out & 2 K+ in (both against electrochem gradient) = change in ATPase shape to original

Question 14

SYMPORTER

Answer 14

• both solutes move inside in the same direction
• in NA+/glucose symporter there is more of NA & less of glucose outside but we need glucose inside so both bind to symporter carrier protein & NA+ moves in (down gradient) & glucose moves out (against gradient)

Question 15

ANTIPORTER

Answer 15

• each solute travels in an opposite direction
• in NA+/CA2+ antiporter in cardiac muscle, rise in [CA2+] = contraction so antiporter takes CA2+ out & 3NA+ in to reduce [CA2+] for weaker contraction

Question 16

PROTEIN

Answer 16

• structural
• catalytic
• binding
• switching (signalling pathways)

Question 17

ELECTROCHEMICAL GRADIENT

Answer 17

net force driving charged solute across membrane due to conc. Grad & voltage across membrane e.g. more positive outside would make it easy to go over membrane (+ve to -ve)