Lecture 8

Question 1

Plasma membrane is different on the inside and outside of cell

Answer 1

-outer and inner leaflets differ in composition (lipids, proteins, and carbohydrates)

• in other words. The cells outer surface is way different than the inner surface

-referred to as membrane asymmetry

Question 2

Phospholipid bilayers

Answer 2

Hydrophilic head

Hydrophobic tail

Question 3

Self assembly of phospholipids in water

Answer 3

• happens spontaneously when add free phospholipids to water
• hydrophobic tails avoid water. Hydrophilic heads love the water
• influenced by lipid type and concentration

Question 4

Why does membrane fluidity matter

Answer 4

1- proper functions, adaptability, and homeostasis

Examples:

-during exocytosis, after a vesicle membrane is incorporated into plasma membrane, things need to spread out since the membrane region is different composition

-during cell division needs to be flexible to be remodelled

• enable proper function of membrane proteins(get where they need to go, interact with other membranes proteins)

Question 5

Major factors influencing membrane fluidity

Answer 5

-Temp: higher increase fluidity

-Structure and composition of phospholipids

-cholesterol levels

Question 6

Amphipathic

Answer 6

One end hydrophilic. One end hydrophobic

Question 7

Membranes vary in phospholipid concentration example

Answer 7

Ex. Phospholipid tail desaturation

Saturated hydrocarbon tails (straight)

Unsaturated tails have kinks

Question 8

Phospholipid composition influences membrane fluidity

Answer 8

A. Degree of unsaturation (double bonds) in tail (more= more fluid)

B. Also the length of fatty acid tail (longer= more viscous)

Question 9

What causes lipid tail to kink

Answer 9

Double bonds. When unsaturated it makes it bend

Question 10

What enzyme makes double bonds

Answer 10

Desaturase enzyme

Question 11

Levels of desaturase in the cell change with temperature

Answer 11

-heat makes membranes more fluid so don’t need as much desaturase enzyme

• desaturase levels determined by measuring mRNA for desaturase

Question 12

Cholesterol is a major component of membranes

Answer 12

• helps maintain proper membrane fluidity in response to temperature changes
• in essence, cholesterol acts as a fluidity buffer

Question 13

Summary of factors influencing membrane fluidity

Answer 13

• temperature (higher temp. Higher fluidity)
• structure and composition of phospholipids (tail length and degree of saturation)
• cholesterol levels (buffers temperature fluctuations)

Question 14

How is membrane fluidity affected when phospholipid tail length increases

Answer 14

Decreases fluidity

Question 15

How is membrane fluidity affected when temperature increased

Answer 15

Membrane fluidity increased

Question 16

How is membrane fluidity affected when

At higher temperatures cholesterol does what to make fluidity do what

Answer 16

At ^ temp, cholesterol down membrane fluidity

Question 17

How is membrane fluidity affected when at lower temperature cholesterol what

Answer 17

Cholesterol ^ membrane fluidity ^

Question 18

How is membrane fluidity affected when saturated fatty acid content increased

Answer 18

Membrane fluidity decreased

Question 19

Major functions of membrane proteins

Answer 19

• transporters
• enzymes
• signal transduction
• cell surface attachment/ recognition

Question 20

2 membrane protein locations

Answer 20

Integral membrane proteins

Peripheral proteins

Question 21

Peripheral proteins where and what

Answer 21

Sit on the surface and form noncovalent bonds with lipids and membrane proteins

Question 22

Integral membrane proteins (transmembrane)

Answer 22

Contain hydrophobic domains that cross the bilayer

Question 23

Trans membrane proteins can be identified based on amino acid sequences how?

Answer 23

-stretches of NON POLAR amino acids indicate trans membrane domains

-non polar = hydrophobic like the inside of the membrane bilayer

Question 24

Is non polar amino acids hydrophobic or hydrophilic

Answer 24

Hydrophobic

Question 25

Types of movement across membranes Membrane transport

Answer 25

Passive transport - no energy required Active transport- energy required Exo/endocytosis

Question 26

Passive vs active transport

Answer 26

Passive is like pushing a boulder down a hill Active is like pushing a boulder up a hill

Question 27

Types of passive transport

Answer 27

Diffusion Facilitated diffusion

Question 28

Diffusion explained

Answer 28

Passive transport Things move from high to low concentration Like food colouring in water

Question 29

Passive diffusion across semi permeable membrane

Answer 29

Non polar molecules and small uncharged polar molecules move through Large uncharged polar molecules and ions can’t move through

Question 30

Facilitated diffusion

Answer 30

Passive Membrane proteins form channels to facilitate diffusion of stuff across the membrane

Question 31

Facilitated diffusion types of proteins

Answer 31

Channel proteins Gated channel proteins Carrier proteins

Question 32

Carrier proteins responsible for

Answer 32

Facilitated diffusion of sugars (uptake of glucose), amino acids, and nucleosides

Question 33

Active transport types

Answer 33

Primary Secondary

Question 34

Primary active transport

Answer 34

Uses ATP

Question 35

Secondary active transport

Answer 35

Uses electrochemical gradients