Topic 2B - Cell Membranes Flashcards
Why is it called the fluid-mosaic model
The bilayer is fluid because the phospholipids are constantly moving.
Proteins are scattered throughout the phospholipid bilayer.
What does the channel protein do
Span the membrane and make hydrophilic tunnels across it, allowing molecules to pass through via diffusion
What does a carrier protein do
Binds to specific solutes and transfer them across the lipid bilayer
What do receptor proteins on the cell membrane allow?
Cells to detect chemicals released from other cells, which trigger a response
What are glycoproteins?
Proteins that have a carbohydrate attached to it
What are glycolipids?
Lipids that have a carbohydrate attached
What is a phospholipid?
They have a hydrophilic head and a hydrophobic tail
Describe the phospholipid bilayer (3)
Heads face outside and tails face inwards, forming a bilayer
Centre of the bilayer is hydrophobic, so the membrane doesn’t allow water soluble substances to diffuse through
Small non polar substances and water can diffuse through
What does cholesterol give to the membrane?
Stability
How does cholesterol provide the membrane with stability?
Binds to the hydrophobic tails of the phospholipids, causing them to pack tightly together. This restricts movement and makes membrane less fluid and more rigid
How does temperature below 0 degrees affect the membrane? (Phospholipid) (4)
Phospholipids don’t have much energy so they dont move very much
Packed closely together and membrane is rigid
Channel proteins and carrier proteins denature, increasing permeability
Ice crystals may form and Pierce the membrane, making it highly permeable when it thaws
How does temperature between 0 and 45 degrees affect the cell membrane? (3)
Phospholipids can move around and aren’t as tightly packed together
Membrane is partially permeable
As temperature increases the energy of the phospholipids increase, making it more permeable
How does temperature above 45 degrees affect the cell membrane?
Phospholipid bilayer begins to break down and membrane becomes more permeable
Channel proteins and carrier proteins denature, so they cant control what enters or leaves the cell - increasing permeability
What is simple diffusion?
When molecules diffuse directly through a cell membrane
What factors affect the rate of diffusion? (3)
The concentration gradient
Thickness of exchange surface
The surface area
What is facilitated diffusion?
The use of carrier proteins and channel proteins to transport large or charged molecules across a membrane
How do carrier proteins work?
A large molecule attaches to the carrier protein in the membrane
The protein changes shape
This releases the molecule on the other side of the membrane
How do channel proteins work?
Form pores in the membrane for charged particles to diffuse through (down conc gradient)
What factors affect the rate of facilitated diffusion?
The concentration gradient
The number of channel proteins or carrier proteins
What is osmosis?
The movement of water across a partially permeable membrane from an area of high water potential to an area of lower water potential
What is the water potential of pure water?
0
How can you lower the water potential of pure water?
Adding solutes (makes it more negative)
What is isotonic solution?
If 2 solutions have the same water potential
(There is no net movement of water)
What is a hypotonic solution?
Solutions with a higher water potential compared to the inside of the cell
What is a hypotonic solution?
Solutions with a lower water potential than the cell
What factors affect the rate of osmosis?
Water potential gradient
Thickness of exchange surface
Surface area of the exchange surface
Briefly explain the osmosis practical?
- Cut potatoes into identical cubes, measure the mass, divide into 2 groups
- Place each group into sucrose solutions for equal time, 20 min
- Remove and gently pat dry, weight each group and record results
- Calculate percentage change
What is active transport?
Uses energy to move molecules and ions across plasma membrane, against a concentration gradient
What are the 2 main differences between active transport and diffusion
Active transport mainly moves solutes from an area of low to a high concentration
Active transport requires energy
Why is ATP important in active transport?
Active transport required energy
When ATP undergoes hydrolysis, it releases energy which allows the solutes to be transported
What are co transporters? (3)
Type of carrier protein
Bind to 2 molecules at a time
The concentration gradient of the other molecules is used against its own concentration gradient
What are 3 factors which affect the rate of active transport
Speed of individual carrier proteins
Number of carrier proteins available
Rate of respiration in the cell and the availability of ATP
Explain the 3 steps in which glucose is absorbed via co transport
- Na ions actively transported out of the epithelial cells in the ileum in the blood, by the NaK pump - this creates a conc gradient. More Na in ileum than in the cell
- This causes Na ions to diffuse from lumen of ileum into the epithelial cells, down the conc gradient, they do this via sodium-glucose co transporter proteins - carries glucose into cell aswell as Na - Glucose in cell increases
- Glucose diffuses out of cell into blood down the conc gradient via facilitated diffusion
