Week 3 - membranes

Question 1

phospholipids

Answer 1

• glycerol - 3 carbon molecule
• 2 fatty acid attach to glycerol- nonpolar
• phosphate group attached to gluycerol - polar
• lipids associate via NON-COVALENT interactions → free to move around bilayer

Question 2

phospholipids and bilayers

Answer 2

• phospholipids spontaneously form MICELLES or LIPID BILAYERS
• structures cluser the hydrophobic regions of phospholipid towards inside & hydrophilic exposed to water environment
• basis of biological membrane

Question 3

membrane fluidity

Answer 3

• must be fluid to work properly
• as temp cool, membranes switch to a solid state → this temp depends on type of lipid
• membranes rich in unsaturated fatty acids ar emore fluid than those rich in saturated fatty acids

Question 4

bulk transport - exocytosis

Answer 4

movement of substances out of cell

Question 5

bulk transport- edocytosis

Answer 5

movement of sunstances into cell

• phagocytosis: cells take in particular matter
• pinocytosis: cell takes in fluid
• receptor-mediated endocytosis →specific
• moleules take in after they bind to a receptor

Question 6

membrane protein

Answer 6

• proteins determine membranes specific functions. →cell membranes & organelle membranes have a unique collection of proteins
• peripheral: loosely bound to surface of membrane
• integral: penetrate lipid bilayer TRANSMEMBRANE PROTEIN
• transport proteins: cannels permeases

Question 7

permeability

Answer 7

• REPELS POLAR MOLECULESNOT NON-POLAR
• nonpolar molecules will move until conc. is equal on both sides
• limited permeability to small polar molecules

Question 8

membranes - steroids

Answer 8

• at cold temp reduces packing of phospholipids →maintaining FLUIDITY
• at high temps cholesterol restrains movement of phospholipids making it LESS FLUID

Question 9

CARRIER PROTEIN

Answer 9

tRANSPORT BOTH IONS & OTHER SOLUTES → SOME SUGARS AND aa

• conc. gradient across membrane
• carrier muse bind moleculwe
• saturation : rate limited by no. of transporters

Question 10

Na+ - K+ pump

Answer 10

• direct use of ATP for active transport
• antiporter →moves 3 Na+ out of cell & 2K+ into cell, against conc. gradient
• affinity of carrier protein for either Na+ or K+ changes so ions can be carried across membrane

Question 11

Na+ - K+ pump steps

Answer 11

1. carrier in membrane binds intracellular sodium
2. ATP phosphorylates protein w/ bound sodium
3. phosphorylation causes conformational change in protein, reducing its affinity for Na+ → diffuses out
4. conformation has high affinity for K+ extracellular. potassium bindsw/ exposed sites
5. binding of K causes dephosphorylation
6. dephosphorylation of protein triggers change to original conformation w/ low affinity to K →K diffuses into cell

Question 12

cell membrane

Answer 12

• SEPARATEs a living cell form surroundings
• controls traffic in & out of cell
  → selectively permeable
  →allows some substances to cross more easily than others

Question 13

coupled transport

Answer 13

• uses ATP indirectly
• uses energy released when a molecule moves by diffusion to supply energy to active transport of a diff molecule
• symporter
• glucose - Na+ captures energy & moves glucose against gradient

Question 14

facilitated diffusion

Answer 14

• molecules that cannot cross membrane easy move through proteins
• move from high to low conc.
• channel proteins: hydrophilic channel
• carrier proteins: bind specific to molecules