Cell Membranes Flashcards
To understand the structure of cell membranes and their function, and how substances are transported throughout it.
What is the fluid mosaic model and how does it work?
Fluid mosaic model was suggested to describe the arrangement of molecules in the membrane.
In the model, phospholipid molecules form a bilayer.
The bilayer is fluid because the phospholipids are constantly moving
Cholesterol molecules are present in the bilayer.
Channel proteins and carrier proteins present in the membrane. Receptor proteins allow the cell surface membrane to detect chemicals released from other cells.
What is the structure of phospholipids like and how do they contribute to the structure of the bilayer?
Phospholipid molecules have a head and a tail
The head is hydrophilic (attracts water)
The tail is hydrophobic (repels water)
The molecules automatically arrange themselves into a bilayer, the heads face out towards the water on either side of the membrane.
The centre of the bilayer is hydrophobic so the membrane doesn’t allow water soluble substances through it and acts as a barrier to these dissolved solutions.
What is the structure of cholesterol and how does it contribute to the structure of the bilayer?
Cholesterol- type of lipid
They fit between phospholipids. They bind to the hydrophobic tails of the phospholipids, causing them to pack more closely together. This restricts the movement of the phospholipids, making the membrane less fluid and more rigid
Cholesterol helps to maintain the shape of animal cells
What is diffusion?
Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration. Particles diffuse down a concentration gradient
Diffusion is a passive process
When molecules diffuse directly through a cell membrane it’s known as simple diffusion
What is facilitated diffusion?
Large or charged particles have to diffuse through carrier or channel proteins in the membrane- this is facilitated diffusion.
Facilitated diffusion moves particles down a concentration gradient from a higher to lower concentration.
Also a passive process
What are carrier proteins and what do they do?
Carrier proteins move large molecules across membranes, down their concentration gradient.
A large molecule attaches to a carrier protein in the membrane
Then the protein changes shape
This releases the molecule on the opposite side of the membrane
What is a channel protein and what does it do?
Channel proteins form pores in the membrane for charged particles to diffuse through, down their concentration gradient.
What are the factors affecting simple diffusion?
Concentration gradient- the higher it is, the faster the rate of diffusion.
Thickness of the exchange surface- the thicker the exchange surface (the short the distance the particles have to travel), the faster the rate of diffusion
Surface area- larger the surface area, faster the rate of diffusion.
What are the factors affecting facilitated diffusion?
Concentration gradient- the higher the concentration gradient, the faster the rate if facilitated diffusion.
Number of channel or carrier proteins- once all the proteins in a membrane are in use, facilitated diffusion can’t happen any faster, even if you increase the concentration gradient. Greater number of channel or carrier proteins, faster rate of facilitated diffusion
What is osmosis?
Osmosis is the diffusion of water molecules across a partially permeable membrane, from an area 0f higher water potential to an area of lower water potential
What is water potential?
Water potential is the potential likelihood of water molecules to diffuse out of or into a solution.
Pure water has the highest water potential and all solutions have a lower water potential than pure water.
If 2 solutions have the same water potential, they’re said to be isotonic.
What are the factors affecting the rate of osmosis?
Water potential gradient- the higher the water potential gradient, the faster the rate of osmosis. As osmosis takes place, the difference in water potential on either side of the membrane decreases, so the rate of osmosis levels off over time
Thickness of the exchange surface- thinner exchange surface, faster the rate of osmosis.
Surface area of exchange surface- larger surface area, faster the rate of diffusion.
What is active transport?
Active transport uses energy to move molecules across a membrane, usually against a concentration gradient. Active transport usually moves solutes from a low to a high concentration.
How are carrier proteins involved in active transport?
A molecule attaches to a carrier protein and the protein changes shape and this moves the molecule across the membrane, releasing it on the other side.
How does active transport receive the energy that is needed for it to occur?
ATP is a common source of energy in the cell
ATP undergoes a hydrolysis reaction, splitting into ADP and Pi. This releases energy so that solutes can be transported.
