Unit 6 - Biological Membrane

Question 1

Membrane Functions

Answer 1

1. Provides selectively permeable barrier
2. Transports solutes
3. Responds to external signals
4. Energy Transduction
5. Compartmentalization
6. Scaffold for biochem. activities

Question 2

Membrane Phospholipids

Answer 2

• polar head group
• phosphate group
• glycerol
• fatty acid chains/tails

Question 3

Amphipathic

Answer 3

-molecule with both hydrophobic & hydrophilic parts

Question 4

Movement of Phospholipids within Membrane

Answer 4

• constantly moving
• spinning in place
• travelling laterally within leaflet
• occasionally ‘flipped’ to opposite leaflet during membrane synthesis

Question 5

Membrane Fluidity

Answer 5

-how easily lipid molecules move rotationally and laterally within a membrane leaflet

Question 6

Membrane Fluidity is affected by…

Answer 6

1. Temperature

2. Changes in lipid composition which affects alignment of phospholipid tails

Question 7

Transition Temperature (Tm)

Answer 7

• temp. at which membrane transitions between fluid and gel phase
• above Tm –> membrane ‘melts’
• below Tm –> membrane gels, incompatible with life

Question 8

Tm is affected by

Answer 8

1. altering length of fatty acid chains: longer chains –> less fluid
2. altering degree of saturation of fatty acids: more double bonds –> more fluid
3. altering amount of sterol: cholesterol acts as ‘buffer’, inhibits phase transitions when temp. changes

Question 9

Homeo-viscous Adaptation

Answer 9

-maintaining membrane fluidity at temps low enough to cause membrane to enter gel phase, through altering the membrane lipid composition

Question 10

Low Temperatures

Answer 10

-enzymes which cut fatty acid chain length

Question 11

Difference between Membrane phospholipids in eukaryotic cells & archaebacteria

Answer 11

1. Eukaryotic: fatty acid chains ester-linked to D-glycerol

2. Archaebacteria: fatty acid chains ether-linked to L-glycerol

Question 12

Role of ER in Membrane Assembly

Answer 12

1. Free fatty acids in cytosol are catalyzed by enzymes bound to cytosolic side of ER
2. new phospholipids added to cytosolic side
3. Scramblases transfers random phospholipids to other leaflet
4. membrans with ‘scrambled’ phospholipids emerge from ER

Question 13

Role of Golgi in MA

Answer 13

1. Membranes with evenly distributed phospholipids arrive from ER
2. Flippases move PS and PE to cytosolic leaftlet
3. membrane asymmetry maintained from this point on

Question 14

Why is the Human RBC a Model Organism for the plasma membrane?

Answer 14

• best understood plasma membrane
• cells inexpensive and available in large numbers
• already present in single-cell suspension
• simple, pure preps of plasma membrane

Question 15

Types of Membrane Proteins (TARE)

Answer 15

1. Transport
2. Anchors
3. Receptors
4. Enzymes

Question 16

polypeptide chains usually cross as…

Answer 16

alpha helices

Question 17

hydrophilic channels are formed via…

Answer 17

several alpha helices

Question 18

proteins folded into pleated sheets can form…

Answer 18

pores!!

Question 19

Diffusion

Answer 19

• dissolved solutes in constant, random motion
• solutes ‘spread out’ until conc. in all regions are equal
• water moves down concentration gradient, if solute cannot move, water will move to even out solute conc.

Question 20

Osmosis

Answer 20

• diffusion of water across semi-permeable membrane down conc. gradient
• once water conc. equal on both sides, no net movement of water

Question 21

Hypotonic Solution

Answer 21

• net water gain
• cell swells
• Animal: bursts (lyses)
• Plant: normal state, turgid

Question 22

Isotonic Solution

Answer 22

• no net loss or gain
• Animal: normal state
• Plant: shrivels

Question 23

Hypertonic Solution

Answer 23

• net water loss
• cell shrinks
• Animal: shrivels
• Plant: plasmolysis

Question 24

Osmoconformers

Answer 24

-adjustment of internal salt conc. to match seawater/outside environement

Question 25

Osmoregulators

Answer 25

-single-celled eukaryotes have contractile vacuoles that periodically pump out water

Question 26

Turgor

Answer 26

-water pulled into cell, presses membrane out to cell wall

Question 27

Order to Molecules' ability to pass directly through membranes?

Answer 27

1. O2,CO2,N2, steroid hormones 2. H20, ethanol, glycerol 3. amino acids, glucose, nucleosides 4. ions

Question 28

Ion Channel Functions

Answer 28

- allow movement of ions down conc. gradient | - critical in many cell activities

Question 29

Ion Channel Features

Answer 29

- discriminate on both charge and size - usually highly selective - much faster than carriers - bidirectional - electrochemical gradient

Question 30

What determines whether channels are open or closed?

Answer 30

1. Voltage 2. Ligand (extracellular/intracellular) 3. mechanical

Question 31

Carrier Proteins

Answer 31

- mediate facilitated diffusion - binding solute at specific site - solute moves down conc. gradient

Question 32

GLUT1

Answer 32

-gluose transporter on mammalian cells

Question 33

Features of Membrane Carrier Proteins

Answer 33

1. Specificity 2. Passive 3. Saturable 3. Can be inhibited/blocked

Question 34

Active Transport

Answer 34

- transport against a gradient - using energy (directly/indirectly) to move ions - transport closely coupled to hydrolysis of ATP, absorption of light, and movement of electrons

Question 35

Sodium-Potassium ATPase

Answer 35

- first pump discovered - only present in animal cells - move 3 NA+ out for every 2 K+ in - coupled to hydrolysis of ATP

Question 36

Hydrogen-Potassium ATPase

Answer 36

- on parietal cells lining stomach | - enables cells to secrete high conc. of H+

Question 37

Coupled Transport

Answer 37

- membrane carrier proteins use driving force of ion moving down conc. gradient to move a solute across membrane against solute gradient - indirect active transport