Cell Membraines (Chapter 4) Flashcards
What do membranes do?
Control what passed through them
Are membranes partially permeable?
Yes
List the three SIMPLE ways substances can move across a membrane?
Osmosis
Diffusion
Active transport
What molecules form a continuous bilayer?
Phospholipids
Why is the cell membrane model called a fluid mosaic model?
Phospholipids are constantly moving and it looks like a bit like a mosaic
What is cholesterols role in the bilayer?
Binds to the phospholipid tails causing them to pack more closely- restricting movement making it more rigid
Helps keep animal cell walls more rigid/ and support eg. Red blood cells
What types of proteins are present in the bilayer?
Channel proteins
Carrier proteins
Receptor proteins
What are glycoproteins?
Proteins which have a polysaccharide chain attached to it
What are glycolipids?
Lipids which have a polysaccharide chain attached to it
Can proteins move sideways and also be fixed in position in the bilayer?
Yes
In a phospholipid what is the head?
Hydrophilic
In a phospholipid what is the tail?
Hydrophobic
How is the phospholipid bilayer arranged?
Phospholipid heads face outwards and tails inwards
Centre of the bilayer is hydrophobic- membrane does not allow water soluble substances in
Which required practical investigates the permeability of cell membranes?
Beetroot cylinders- pigment leakage
Investigate temperature, concentration etc ………
What happens to the permeability of the cell membrane in temperatures below 0°c?
HIGHLY PERMEABLE
Phospholipids do not have much energy so don’t move much
Phospholipids packed closer together
Channel and carrier proteins deform
Ice crystals can pierce membrane
Increases permeability
What happens to the permeability of the cell membrane between 0°c & 45°c?
Phospholipids can move around and aren’t tightly packed together
MEMBRANE IS PARTIALLY PERMEABLE
As temperature increases phospholipids move more which increases permeability
What happens to the permeability of the membrane at temperatures above 45°c?
Phospholipids start to melt
BECOMES MORE PERMEABLE
Water inside cell expands putting pressure on membrane
Channel and carrier proteins deform- cannot control entry and exit
Define diffusion
Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration.
Can molecules diffuse in both directions?
Yes
But the net movement will be to the area of lower concentration. This continues until particles are evenly distributed throughout the liquid or gas.
Is diffusion passive?
Yes it does not require metabolic energy
(Requires kinetic energy)
What is simple diffusion?
When molecules diffuse directly through a cell membrane
What is facilitated diffusion?
Where large or charged molecules, diffuse through carrier or channel proteins in the membrane.
Is facilitated diffusion passive?
Yes it does not require metabolic energy
(Requires kinetic energy)
What do carrier proteins do?
Move large molecules across membranes
How do carrier proteins work?
Large molecule attaches
Protein changes shape
Releases the molecule on the other side of the
What do channel proteins do?
Allows charged particles to diffuse through the membrane
What are the three factors that affect the rate of simple diffusion.
The concentration gradient
Thickness of the exchange surface
The surface area
How do microvilli increase the surface area for faster diffusion?
Large surface area- can increase it by 600 times
What are the two factors that affect the rate of facilitated diffusion?
Concentration gradient
Number of channel or carrier proteins
Define osmosis
Osmosis is the diffusion of water molecules across a partially permeable membrane, from an area of higher water potential to an area of lower water potential
What is water potential?
Water potential is the likelihood of water molecules to diffuse in and out of a solution
Does pure water have a high water potential?
Yes the highest
All solutions have a lower one than water
Define isotonic
When two solutions have the same water potential
List the three factors which effect the rate of osmosis
Water potential gradient
Thickness of exchange surface
Surface area of the exchange surface
What is the required practical linked to water potential.
Using potato cylinders
5 serial dilutions using sucrose and water
Measure mass change %
What is active transport?
Active transport uses energy to move molecules and ions across membranes usually against a concentration gradient
Which protein is usually involved in active transport?
Carrier proteins
What are the two main differences between active transport and facilitated diffusion?
Active transport usually moves molecules form a low to high concentration, in facilitated diffusion they move from a high to low concentration
Active transport requires metabolic energy (ATP) facilitated diffusion does not
How does ATP release energy?
Undergoes hydrolysis splitting it into ADP and Pi (inorganic phosphate)
This releases energy
What is a co-transporter?
A type of carrier proteins which binds to two molecules at a time
How does co transport work?
Concentration gradient of one of the molecules is used to move the other molecule against its own concentration gradient
Explain the 4 steps of co-transport of glucose in the ileum of the small intestine?
Sodium ions actively transported out of the epithelial cell into the blood via sodium-potassium pump, this creates a concentration gradient of sodium ions.
This causes sodium ions to diffuse from the lumen of ileum into epithelial cell, down their concentration gradient. Via sodium-glucose co-transporter proteins.
The co-transporter carries glucose into the cell with sodium- glucose concentration inside cell increases.
Glucose diffuses out of the cell into the blood, down its concentration gradient through a protein channel via facilitated diffusion .
