Topic 2 - Cell Membranes Flashcards
What are three ways in which a substance can move across the cell membrane?
Diffusion, active transport and osmosis
What does the fluid mosaic model describe?
Arrangement of molecules in the membrane
Describe the fluid mosaic model
Phospholipids form a continuous bilayer which is fluid, proteins are scattered throughout
What do receptor proteins in the cell surface membrane do?
Allow the cell to detect chemicals released from other cells
What is a glycoprotein?
Protein and carbohydrate
What is a glycolipid?
A lipid and carbohydrate
What molecules form a barrier to dissolved substances in a cell membrane?
Phospholipids
The head of a phospholipid is…
The tail is…
Head = hydrophilic
Tail = hydrophobic
Describe the arrangement of phospholipids in the bilayer
Heads face towards the water on either side of the membrane
Explain the importance of cholesterol in cell membrane
Helps animal cells that have no cell wall, creates barrier for polar substances as it is hydrophobic.
Explain the importance of cholesterol in cell membrane
Helps animal cells that have no cell wall, creates barrier for polar substances as it is hydrophobic.
How does cholesterol give the membrane stability?
Binds to the hydrophobic tails of the phospholipids causing them to pack more closely together.
How does cholesterol give the membrane stability?
Binds to the hydrophobic tails of the phospholipids causing them to pack more closely together.
How does temperature affect cell membranes?
Affects how much the phospholipids move which affects membrane structure and permeability.
Define diffusion
The movement of particles from an area of high concentration to an area of low concentration across a partially permeable membrane
What is a concentration gradient?
The path from an area of high concentration to of an area of low concentration
What is a passive process?
No energy required
What is simple diffusion?
Diffusion across a partially permeable membrane without the assistance another of molecule
What 3 factors affect the rate of diffusion?
Distance, concentration gradient and surface area
What is facilitated diffusion?
Diffusion of specific molecules using channel proteins or carrier proteins,
2 types of protein in facilitated diffusion
Channel
Carrier
What do carrier proteins do?
Move large molecules across the membrane down the concentration gradient.
What do channel proteins do?
Form pores in the membrane for charged particles to diffuse through down the concentration gradient.
Which 2 factors affect facilitated diffusion?
Concentration gradient
Number of proteins
Define osmosis
The movement of water particles from an area water of high potential to an area of lower water potential through a partially permeable membrane.
What is water potential?
The likelihood of water molecules to diffuse out of or into a solution.
What does isotonic mean?
Water potential is identical across both solutions
What factors affect the rate of osmosis?
Gradient
Thickness
Surface area
What is active transport?
The movement of particles from an area of low concentration to an area of high concentration against the concentration gradient and requiring ATP.
Explain what co transporters are and what they do
A type of carrier protein that binds two molecules at a time, one is used to more the other against its concentration gradient.
Where is glucose absorbed into the bloodstream and why does it need to be co transported?
Absorbed through the ileum
Needs to be co transported because it is going against its concentration gradient.
Explain step 1 in the absorption of glucose
Sodium ions are actively transported out of the epithelial cells in the ileum into the blood by the sodium potassium pump.
Explain step 2 in the absorption of glucose
Sodium ions diffuse down their concentration gradient into the epithelial cell via the sodium - glucose co-transporter proteins.
Explain step 2 in the absorption of glucose
Sodium ions diffuse down their concentration gradient into the epithelial cell via the sodium - glucose co-transporter proteins.
