Blake_Biochem_17_Membranes II

Question 1

How is membrane fluidity controlled?

Answer 1

Fatty acid composition

Cholesterol content

Question 2

How does fatty acid composition control membrane fluidity?

Answer 2

• Length of the fatty acid chain
• Saturation levels (T_m, rigidity)
• Position of double bonds
  
  • cis-position produces bends
  • effects T_m, provides more fluidity

Question 3

How is lateral movement of membrane proteins proven?

Answer 3

FRAP - fluorescence recovery after photo-bleaching

Rate of recovery of fluorescense depends on the lateral mobility of the fluorescent labled component

Question 4

How is lateral movement of phospholipids in a membrane different from transverse diffusion?

Answer 4

Lateral movement is very rapid, transverse is very slow

Question 5

What is significant about the asymetrical distribution of lipid molecules?

Answer 5

Explains many phenomena

Question 6

Why are carbohydrates placed on the cell membrane?

Types of membrane carbs

specific membrane carbs

functions of membrane carbs

Answer 6

• carbohydrates, glycoproteins, glycolipids
• Glycosylation occurs on extracellular surface of the plasma membrane
• Glycocalyx participates in cell adhesion, lymphocyte homing….
• Contributes to cell identification
• Antibodies target foreign carbohydrate molecules
  
  • antibodies recognize red blood cells’ blood types by extracellular carbohydrates

Question 7

How are Eukaryotic cells distinguished from prokaryotic cells?

Answer 7

• membranous internal compartments:
  
  • peroxisomes
  • mitochondria
  • endoplasmic reticulum
  • golgi apparatus
• Eukaryotic cells have no cell walls

Question 8

How are inner membranes of eukaryotic organelles different from outer membranes?

Answer 8

Inner membranes are not permeable

Question 9

How is the nuclear envelope different from other eukaryotic organelles?

Answer 9

Nuclear envelope is not continuous; consists of closed membranes that come togehter in nuclear pores

Question 10

Membranes must be able to: (3)

Answer 10

• separate and join together so that:
  
  • take-up
  • transport
  • release the molecules

Question 11

RME

Answer 11

Receptor-mediated endo/exocytosis

Question 12

Receptor-mediated endocytosis: “Budding”

process

Answer 12

“Budding”

• signal binds receptor
• membrane invaginates around ligand bound receptor
• Invaginated membrane breaks off and fuses to form a vesicle
• signal and receptor are disociated
• receptors are recycled

Question 13

RME “Fusion”

Answer 13

• eg: fusion of a vesicle to a membrane is key for neurotransmitter release into synaptic cleft
• SNARE: gathers appropriate membranes to initiate fusion process (many intermediates)

Question 14

Mitochondrial Fission

Answer 14

• Mitochondria “pinches” and divides into 2 mitochondria
• DRP1 oligomers facilitiate pinching and vessical scission

Question 15

How many genes in Mitochondrial genome?

Answer 15

13

Question 16

Where are most mitochondrial proteins encoded?

Answer 16

from Cellular DNA

Question 17

How does mitochondrial fusion occur?

Answer 17

• Collision in movement of organelles along microtubules
• dying mitochondria signal to healthy mitochondria so that fusion can salvage usable components

Question 18

Why does mitochondrial fission occur?

Answer 18

to prepair the cell for mitotic division

Question 19

Requirements for inner-membrane fusion:

Answer 19

• Sufficiently large electrochemical gradient must be present across inner membrane
• Elevated GTP levels must be available for hydrolysis

Question 20

Control of fusion/fission mechanisms in mitochondria

Answer 20

unknown

Question 21

Protein import into mitochondria (4)

Answer 21

• N-terminal signal sequence - matrix targeting
• proteins are unfolded and threaded through “import pores”
• Refolded inside the mitochondrial target
• Transient channels (both outer and inner membranes) are necessary for intra-matrix proteins