Cell Membranes And Membrane Transport 2.2-2.4 and CP3 Flashcards
Describe the fluid mosaic model
- Phospholipid belayer is constantly moving, therefore it’s fluid
- Protein molecules are scattered through the bilayer , like tiles in a mosaic, which can also move
Describe a phospholipid molecule
- Phosphate head is hydrophilic so attracts water
- Fatty acid (x2) tail is hydrophobic
How is the bilayer orientated and what does this prevent?
- The hydrophilic heads face outwards towards the water
- The hydrophobic tails face the centre which prevents water-soluble substances, such as ions, from passing through
What does it mean that the membrane is ‘partially permeable’?
- Small molecules move through gaps between the phospholipids
- Large molecules and ions can only pass through channel proteins and carrier proteins
What did scientists think of the cell membrane pre-1970s?
Originally thought there were two protein layers with a phospholipid layer in the middle = 3 layers
What experiment did scientists do to prove the model is ‘fluid’?
Fused a mouse cell with a human cell = membrane proteins of both organisms had intermixed throughout the cell membrane
What types of molecule are found in a membrane?
- Glycoproteins
- Glycolipids
- Cholesterol
What are glycoproteins?
Proteins with a polysaccharide chain
What are glycolipids?
Lipids with a polysaccharide chain attached
Where does cholesterol attach? What does it provide?
Fits in between the phospholipids to form bonds with them
It allows the membrane to be more rigid
At lower temperatures cholesterol makes the membrane more fluid
What is osmosis?
The net movement of water molecules across a partially permeable membrane from an area of high water potential to low water potential.
(Water molecules diffuse both ways)
What kind of process is osmosis, diffusion and facilitated diffusion?
Passive process
When would facilitated diffusion be used?
When large molecules or ions that can’t diffuse through the phospholipid bilayer want to get across the membrane
What is facilitated diffusion?
The movement of molecules down a concentration gradient using carrier or channel proteins and not requiring energy
What size molecules do carrier proteins transport?
Large molecules
How do carrier proteins work in facilitated diffusion?
1) A large molecules attached to the carrier protein
2) The protein changes shape
3) The molecules is release on the opposite side of the membrane
What type of molecules do channel proteins allow through?
Charged particles
How do channel proteins work in facilitated diffusion?
They form pores in the membrane
What is active transport?
Uses energy and carrier proteins to move molecules and ions against a concentration gradient
What’s the difference between active transport and facilitated diffusion?
- Active transport requires energy from the hydrolysis of ATP
- Active transport only uses carrier proteins, not channel proteins
What size of molecules are transported by endocytosis?
Very large molecules eg. Proteins , lipids and carbohydrates
How does endocytosis work?
- Cell membrane surrounds the molecule(s)
- The membrane pinched off to form a vesicle containing the ingested substance
Do endocytosis and exocytosis require energy?
Yes, through the hydrolysis of ATP
Give an example of a cell that uses endocytosis
White blood cell (phagocytes) inject microorganisms and dead cells