2.5 Biological membranes Flashcards
What is the fluid mosaic model?
The theory of cell membrane structure with proteins embedded in a sea of phospholipids.
What is a glycolipid?
Lipid/ phospholipid with a certain chain of carbohydrate molecules attached.
What is a glycoprotein?
A protein with a chain of carbohydrate molecules attached.
Why do cell membranes need to be partially permeable?
They need to allow some molecules through, into or out of the cell.
How are cell membranes partially permeable?
Permeability refers to the ability to let substances pass through.
- Some, very small molecules simply diffuse through the cell membrane, in between structural molecules.
- Some substances dissolve in the lipid layer and pass through.
- Other substances pass through special protein channels or are carried by carrier proteins.
Why are cell membranes described as partially permeable?
They do not let all types of molecules pass through them.
What is the role of membranes at the surface of cells?
- Separates the cell’s components from external environment. e.g. tissue fluid.
- Regulates transport of materials into and out of the cell.
- May contain enzymes involved specific metabolic pathways.
- has antigens, so that the organism’s immune system can recognise the cell as being ‘self’ and not attack it.
- Releases chemicals that signal to other cells.
- Contains receptors, so is a site for cell communication or signalling; hormones and drugs may bind to these receptors.
- Site for chemical reactions.
What is another word for cell surface membrane?
Plasma membrane.
What is the role for membranes within cells?
- Mitochondria have folded inner membranes (cristae) , these give a large surface area for some reactions of aerobic respiration and localise some of the enzymes needed for respiration to occur.
- The inner membranes of chloroplasts, called thylakoid membranes, house chlorophyll. On these membranes some of the reactions of photosynthesis occur.
- There are some digestive enzymes on the plasma membrane of epithelial cells that line the small intestine, these enzymes catalyse some of the final stages int he break down of certain sugars.
What are the two types of plasma membranes?
- Cell membranes at the surface of cells
- Cell membranes within cells.
Describe the fluid mosaic model?
In 1972, Singer and Nicolson proposed a model that allowed the passage of molecules through a membrane. Their structure explained how cell membranes could be more dynamic and interact the the cells environment.
It proposed that the fabric of the membrane consisted of a phospholipid bilayer with proteins floating in it, making up a mosaic pattern.
What are the folded inner membranes of mitochondria called?
Cristae
