Lecture 8 Flashcards
Plasma membrane is different on the inside and outside of cell
-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
Phospholipid bilayers
Hydrophilic head
Hydrophobic tail
Self assembly of phospholipids in water
- happens spontaneously when add free phospholipids to water
- hydrophobic tails avoid water. Hydrophilic heads love the water
- influenced by lipid type and concentration
Why does membrane fluidity matter
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)
Major factors influencing membrane fluidity
-Temp: higher increase fluidity
-Structure and composition of phospholipids
-cholesterol levels
Amphipathic
One end hydrophilic. One end hydrophobic
Membranes vary in phospholipid concentration example
Ex. Phospholipid tail desaturation
Saturated hydrocarbon tails (straight)
Unsaturated tails have kinks
Phospholipid composition influences membrane fluidity
A. Degree of unsaturation (double bonds) in tail (more= more fluid)
B. Also the length of fatty acid tail (longer= more viscous)
What causes lipid tail to kink
Double bonds. When unsaturated it makes it bend
What enzyme makes double bonds
Desaturase enzyme
Levels of desaturase in the cell change with temperature
-heat makes membranes more fluid so don’t need as much desaturase enzyme
- desaturase levels determined by measuring mRNA for desaturase
Cholesterol is a major component of membranes
- helps maintain proper membrane fluidity in response to temperature changes
- in essence, cholesterol acts as a fluidity buffer
Summary of factors influencing membrane fluidity
- temperature (higher temp. Higher fluidity)
- structure and composition of phospholipids (tail length and degree of saturation)
- cholesterol levels (buffers temperature fluctuations)
How is membrane fluidity affected when phospholipid tail length increases
Decreases fluidity
How is membrane fluidity affected when temperature increased
Membrane fluidity increased
How is membrane fluidity affected when
At higher temperatures cholesterol does what to make fluidity do what
At ^ temp, cholesterol down membrane fluidity
How is membrane fluidity affected when at lower temperature cholesterol what
Cholesterol ^ membrane fluidity ^
How is membrane fluidity affected when saturated fatty acid content increased
Membrane fluidity decreased
Major functions of membrane proteins
- transporters
- enzymes
- signal transduction
- cell surface attachment/ recognition
2 membrane protein locations
Integral membrane proteins
Peripheral proteins
Peripheral proteins where and what
Sit on the surface and form noncovalent bonds with lipids and membrane proteins
Integral membrane proteins (transmembrane)
Contain hydrophobic domains that cross the bilayer
Trans membrane proteins can be identified based on amino acid sequences how?
-stretches of NON POLAR amino acids indicate trans membrane domains
-non polar = hydrophobic like the inside of the membrane bilayer
Is non polar amino acids hydrophobic or hydrophilic
Hydrophobic
Types of movement across membranes
Membrane transport
Passive transport - no energy required
Active transport- energy required
Exo/endocytosis
Passive vs active transport
Passive is like pushing a boulder down a hill
Active is like pushing a boulder up a hill
Types of passive transport
Diffusion
Facilitated diffusion
Diffusion explained
Passive transport
Things move from high to low concentration
Like food colouring in water
Passive diffusion across semi permeable membrane
Non polar molecules and small uncharged polar molecules move through
Large uncharged polar molecules and ions can’t move through
Facilitated diffusion
Passive
Membrane proteins form channels to facilitate diffusion of stuff across the membrane
Facilitated diffusion types of proteins
Channel proteins
Gated channel proteins
Carrier proteins
Carrier proteins responsible for
Facilitated diffusion of sugars (uptake of glucose), amino acids, and nucleosides
Active transport types
Primary
Secondary
Primary active transport
Uses ATP
Secondary active transport
Uses electrochemical gradients
