Cellular Membranes and Communication Flashcards
1
Q
What are phospholipids?
A
- Amphipathic molecules
- Hydrophilic glycerol, phosphate group head
- Two hydrophobic fatty acid tails
- Spontaneously form structures to hide their hydrophobic tails from water, exposing their hydrophilic heads
- e.g. micelles, membranes and vesicles
2
Q
How and why are membranes fluid?
A
- Hydrophobic interactions keep the membrane together
- Membranes can self-heal
- Phospholipids move around: frequent lateral movement or rotation, rare to flip between faces
- Membrane fluidity is crucial to its function: too cold and the membrane solidifies, too hot and the membrane is too fluid
- Organisms have evolved ways to maintain the correct amount of membrane fluidity when exposed to temperature extremes
3
Q
What are membranes composed of?
A
- Different phospholipid forms have different combinations of unsaturated and saturated fatty acids
- Lipid with saturated fatty acids pack together tightly at cold temperatures
- Lipids with unsaturated fatty acids pack together less tightly: helps to maintain fluidity at cold temperatures
- Organisms can change lipid composition with temperature
4
Q
What is cholesterol and what does it do?
A
- Cholesterol is a fluidity buffer
- Largely non-polar but is amphipathic
- Can insert into membranes to help maintain correct fluidity
- At low temperatures is maintains fluidity while at high temperatures it limits fluidity
5
Q
Why are membranes mosaics?
A
- Many different proteins are embedded in or associated with the phospholipid bilayer
- Proteins can diffuse freely around the membrane (unless tethered)
6
Q
What are types of membrane proteins?
A
TPIG
- Transmembrane proteins
- Peripheral proteins
- Integral proteins
- Glycoproteins
7
Q
What are functions of membrane proteins?
A
SEAT
- Signalling
- Enzymatic functions
- Adhesion
- Transport
8
Q
How are membranes barriers?
A
- Phospholipid bilayers are semipermeable
- More permeable to: small hydrophobic molecules
- Other molecules move via membrane proteins
- In order from most to least able to pass through: small non polar, small polar, large polar, charged
9
Q
How do substances move across membranes?
A
- Substances want to diffuse down their own concentration gradient
- Passive transport: movement across a membrane down concentration gradient with no energy expenditure
- Active transport: movement across a membrane against concentration gradient with energy required
10
Q
What are some types of passive transport?
A
- Simple diffusion
- Facilitated diffusion
- Osmosis
11
Q
What is simple diffusion?
A
Simple diffusion:
- Movement of substances through the membrane with no energy expenditure by the cell
- Down their concentration gradient
- Gradient provides energy
12
Q
What is facilitated diffusion?
A
Facilitated diffusion:
- Involves membrane proteins e.g. channel and carrier proteins
- Substances move down concentration gradient
- Carrier proteins provide channel for movement
- Energy provided by concentration gradient
13
Q
What is osmosis?
A
Osmosis:
- Passive transport of water
- Water moving across a semi-permeable membrane down its own concentration gradient
- Tonicity is a measure of solute concentration around cells: hypertonic = more solute, hypotonic = less solute, isotonic = equal
- e.g red blood cells: hypertonic = shrivelled, isotonic: normal, hypotonic: swollen/lysed
- e.g. plant cells: hypertonic = plasmolysed, isotonic: flaccid, hypotonic: turgid (normal)
14
Q
What is active transport?
A
- Movement of substances through a membrane against their concentration gradients with energy expenditure by the cell
- Primary active transport: direct use of chemical energy (ATP) to pump a substance against its concentration gradient
- Secondary active transport: harnessing the diffusion of one substance down its concentration gradient to pump another substance against its concentration gradient
15
Q
What is an example of primary active transport?
A
Na/K ATPase pump
- Primary active antiporter
- Transmembrane protein in the plasma membrane that uses ATP to pump 3Na out of the cell and 2K into the cell
- Creates an electrochemical gradient
- Consumes up to 1/3 of an animal cell’s energy
