chapter 4 - cell membrane transport Flashcards
(32 cards)
1
Q
Where are plasma membranes found ?
A
- around cells and certain organelles
- in both prokaryotic and eukaryotic cells
2
Q
Where are the components of plasma membranes ?
A
- phospholipid bilayer
- peripheral and integral proteins
- cholesterol
- glycolipids
- glycoproteins
3
Q
What is the structure of the phospholipid bilayer and how does it affect the membrane
A
- has hydrophilic head ( because is has a negative charge so is attracted to water ) and hydrophobic tails ( because they have no charges they have repel water but attract other lipids )
- so allows lipid soluble, small molecules to pass through
- but not other molecules to pass through so is partially permeable
4
Q
What does cholesterol do to the plasma membrane ?
A
- they make the bilayer to be less fluid
- so that when we are hotter the membrane doesn’t become too fluid ( the pores being too big ) and allow water and dissolved ions to move out
5
Q
What are glycolipids and glycoproteins and what do they do ?
A
- glycolipids are carbohydrates attached directly to the membrane
- glycoproteins are carbohydrates attracted to integral proteins
- these both act as receptors for the cell to recognise other objects
6
Q
What are integral proteins and what do they do ?
A
- they are proteins that do not pass all the way through the membrane
- when attached to carbohydrates they act as receptors
7
Q
What are peripheral proteins and what do they do ?
A
- proteins that pass all the way through the bilayer
- there are 2 types: carrier and channel
- carrier = bind with a molecule that makes them change shaper so they can then release the molecule to the other side
- channel = are like tunnels that allow molecules to pass through
- channel proteins also fill with water to allow water soluble ions to pass through
8
Q
Why are plasma membranes partially permeable ?
A
- because only certain molecules can diffuse through by simple diffusion
- because the bilayer is a phospholipid only lipid soluble molecules and very smaller molecules can pass through simple diffusion
- water soluble molecules ( polar ) and large molecules (glucose) cannot pass through by simple diffusion
9
Q
What is simple diffusion ?
A
- the next movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached
10
Q
Is simple diffusion passive or active ?
A
- passive
- because it does not require ATP
11
Q
What is needed for simple diffusion to happen ?
A
- kinetic energy so the particle will move
- lipid soluble and small molecules
12
Q
What is facilitated diffusion
A
- the movement of ions and polar molecules to an area of high concentration to an area of lower concentration
- channel and carrier proteins are used to transport the molecules across membranes
13
Q
Is facilitated diffusion a passive or active process ?
A
- passive
- as it doesn’t use any ATP
14
Q
How do protein channels help with facilitated diffusion ?
A
- the tubes fill with water
- which enable water soluble ions to to pass through the membrane
15
Q
Ho do carrier proteins help with facilitated diffusion ?
A
- a molecule will bind to the carrier proteins which causes the protein to change shape
- which allows the molecule to be released on the other side
16
Q
What is osmosis ?
A
- the movement of water from an area higher water potential to an area lower water potential across a partially permeable membrane
17
Q
What is water potential and how does this differ for different solution
A
- water potential is the pressure exerted by water molecules on the membrane ( container ) surrounding a solution
- its measured in kpa
- pure water has a water potential of 0 kpa
- you cannot have a water potential higher than 0
- the lower the water potential the more concentrated with a solute the solution is
18
Q
How do we describe the water potential in animal and plant cells ?
A
- hypertonic, isotonic and hypotonic
19
Q
What happens in a hypotonic solution ?
A
- the water potential is higher outside of the cell
- so water moves into the cells
- animal cells swell and burst = lysed
- plant cells swell an become turgid
20
Q
What happens in a hypertonic solution ?
A
- the water potential is lower outside the cell
- so water movers out of the cell and into the solution
- animal cells shrink and shrivel
- plant cells become plasmolysed = cell membrane moves away from the cell wall
21
Q
What happens in an isotonic solution ?
A
- water potential is the same inside the cell than outside the cell
- so there’s no net movement into of out of the cell
- so the animal and plant cells will stay the same ( or plant cells become flaccid )
22
Q
What factors affect the rate of diffusion ?
A
- temperature: more kinetic energy = faster diffusion
- concentration gradient: steeper concentration gradient = faster rate of diffusion
- membrane thickness: thinner surface = shorter distance = particles diffuse faster
- surface area: larger surface area = more particles can cross membrane at once = faster diffusion
- number of carrier/ channel proteins: more proteins = faster rate of facilitated diffusion
23
Q
What factors affect the rate of osmosis ?
A
- temperature: higher temperature = more kinetic energy = faster diffusion
- water potential gradient: steeper gradient = faster rate of osmosis
- membrane thickness: thinner surface = shorter distance = water molecules diffuse faster
- surface area: larger surface area = more water molecules can cross the membrane at once = faster osmosis
24
Q
What is active transport ?
A
- the movement of particles from an area of lower concentration to an area of high concentration using energy from respiration in the form of ATP
25
Why is active transport an active process ?
- because is used energy
26
How does active transport work ?
- molecule that’s is complementary to the receptor on a carrier proteins binds to the protein
- on the other side, ATP binds to the carrier protein
- it is then hydrolysed into ADP + Pi
- the Pi binds to the carrier protein, and this causes the carrier protein to change shape
- so the molecule is released to the other side
- then the Pi is released and forms ATP again and the proteins returns into its original shape
27
What part of the carrier proteins changes shape ?
- the tertiary structure
28
What factors affect the rate of active transport ?
- temperature: higher temperature = particles have more kinetic energy an travel faster, respiration also increases with temperature BUT very high temperatures denature proteins which decreases the rate of active transport
- membrane thickness: thinner surface = shorter distance = particles travel faster
- number of carrier proteins: more proteins = faster rate of active transport
- rate of respiration: more respiration = more ATP available for active transport
29
What do we use co transport in the body
- to transport glucose from the ileum to the blood
30
How does the co transport process for glucose work ?
- sodium ions are transported out of the epithelial cell through a sodium potassium pump
- so now the concentration of sodium ions in the epithelial cell is lower than in the lumen
- sodium ion diffuse can now diffuse into the epithelial cell ( down their concentration gradient) through a co transporter protein
- glucose molecules ( and amino acids sometimes ) are transported into the epithelial cell through the co transporter protein
- now there is a higher concentration of glucose in the epithelial cell than in the blood
- so now glucose moves down it’s concentration gradient into the blood via facilitated diffusion (channel protein )
31
Why is the concentration of glucose never higher in the blood ?
- because there is no build up of glucose in the blood right outside the epithelial cells
- because the blood flows and carries the glucose with it
32
What do microvilli on the epithelial cells do ?
- increases the surface area for co transporter proteins
