Plasma Membranes/ Endomembrane system

Question 1

what is a glycerophospholipid

Answer 1

basic phospholipid molecule with glycerol molecule (3xhydrocarbon carbon chain) bonds to fatty acid chains below, bonds to phosphate molecule above, which bonds to interchangeable head group above e.g, choline each with diff charge/ function (none with net -ve charge)

Question 2

Lipids found in eukaryotic membranes

Answer 2

Phospholipids, Cholesterol, sphingolipids- serine (some contain phosphates)
- all have hydrophilic (polar/charges) heads w hydrophobic (non charged) tail(s)

Question 3

polar nature of H2O

Answer 3

O ion -ve charge, e- pulled towards O
H ions +ve charge, e- pulled away
- hydrophilic molecules - soluble- make bonds w h2o molecules
- Hydrophobic - insoluble- don’t chemically mix, no bonds
explanation: h2o molecules are like magnets/ jigsaw pieces so only ones fitting the polar shape (=ve/-ve end) can fit in

Question 4

saturated vs unsaturated fatty acids

Answer 4

saturated e.g, hard fat - highly packed, straight, stable - used in animals in hot environments
unsaturated e.g, oil - loosely packed, wiggly, in plasma membranes of cold blooded animals, more fluid

Question 5

effect of heat on saturated

Answer 5

heat melts hard fats (saturated fatty acids) bc higher temp = more movement, shakes fatty tails to be less aligned = more fluid

Question 6

effect of cholesterol

Answer 6

makes membranes more stiff and thick

Question 7

lipid bilayer shape

Answer 7

planar (flat) lipid bilayers are energetically unfavourable as the edges remain exposed, so bilayer often forms “sealed compartments”- spheres called liposomes like the plasma membrane.

Question 8

leaflets

Answer 8

name of each side/single layer of a lipid bilayer

Question 9

Peroxisomes

Answer 9

Peroxisomes contain enzymes that oxidize certain molecules normally found in the cell, notably fatty acids and amino acids. Those oxidation reactions produce hydrogen peroxide, which is the basis of the name peroxisome.

• organelle in animal &plant cells

Question 10

cytosol

Answer 10

name for cytoplasm

Question 11

is the nucleus topologically equivalent to the cytoplasm?

Answer 11

yes, proteins must not pass across membrane, can move through nuclear pores

Question 12

endomembrane system pathway

Answer 12

• newly synthesised protein cross membrane into ER through translocon
• to Golgi apparatus
• to secretary vesicles
• exit cell

Question 13

how do proteins travel through the endomembrane system

Answer 13

budding & fusion/ endo/exosytosis between organelles - no membranes are crossed

Question 14

glycosylation

Answer 14

proteins only in the lumen of ER get N-glycosylated/O-glycosylates - glucose added if asparagine aas sequence is present

Question 15

Processes in Endoplasmic Reticulum

Answer 15

• Newly synthesised proteins from cytoplasm cross the membrane into ER through translocon (channel)
• “Quality control” of proteins checks for correct folding: held in ER by chaperones until they are folded
• Disulphide bonds made (intramolecular disulphide bonds: polypeptide (protein chain) forms bonds w itself to fold, or intermolecular: between 2 protein subunits)

Question 16

Processes in Golgi apparatus

Answer 16

• comprised of Golgi stacks - each with own role
• from cis to medial, to trans Golgi
• sugar/ protein modifications take place
  outputs:
• either sorted into vesicle transported to lysosomes
• or to plasma membrane to be secreted (“constitutive secretion”)
• into secretory vesicles (only fuse with plasma membrane when signalled to) (“regulated secretion”)

Question 17

Lysosome processes

Answer 17

• Stores “acidic hydrolyses” - Proteins sent into lysosomes used to degrade other macromolecules (enzymes) under acidic conditions - pH 5, e.g, nucleases
• uses protein pumps to pump H+ to stay acidic (active transport) normal cytoplasmic pH- 7.2