2.1.5 biological membranes
- Created by: strawberry cake
- Created on: 06-02-19 19:53
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- plasma membrane
- Roles within the cells and at the surface
- PM is partially permeable
- It only allows some substances to pass through not all
- small molecules diffuse through the PM
- some substances dissolve in the lipid layer to pass through
- larger substances pass through protein channels or are carried by carrier proteins
- Roles of the plasma membrane (PM) and outside the cells
- Separates cell content from the external environment
- regulate the transport of materials into and out of the cell
- can contain specific enzymes for metabolic reactions
- contains antigens so immune system can recognise it as itself and not attack it.
- can release chemicals which signal to other cells
- cells communicate with each other using messenger molecules ( MM) eg. hormones
- 1) cell releases a MM 2) the molec. travels to another cell 3)MM binds to a receptor on the cell membrane
- cells communicate with each other using messenger molecules ( MM) eg. hormones
- may be the site of chemical reactions
- Roles of membrane within the cell
- the cristae of the mitochondria provides a large surface area for aerobic respiration
- the thylakoid of the chloroplast is the house of chlorophyll . on these membranes some reactions of photosynthesis occur
- the small intestine the PM of epithelial cells which line ti contain digestive enzymes which break down some sugars
- PM is partially permeable
- fluid mosaic structure
- B y singer and Nikelson - the FMM consists of a phospholipid bilayer with proteins floating in it making it a mosaic pattern
- the bilayer is fluid as some lipids and proteins in the layer can change places with each other
- the proteins have a polsaccheride chain attached ( carbohydrates) these are called glyco proteins
- some lipids have polysaccheride chains attached and are called proteins
- phospholipids
- have a head and tail
- the head is hydrophilic - it attracts water ( has contact with the exterior and interior of the cytoplasm
- the tails are hydrophobic and are found in the centre of the bilayer ( they are in the interrior hidden from water )
- cholesterol
- is a type of lipid and it gives the PM stability
- present in all PM ( not bacteria )
- cholesterol molec . fit between phospholipids and they bind to the hydrophilic tails making them move closer. it makes the membrane less fluid and more rigid
- proteins
- control what enters and leaves the cell
- some proteins are channels - they allow ions with a charge or small particles to pass through
- some are protein carriers- they change shape to carry specific molec. across the membrane
- proteins can atttach to carrier proteins and function as - enzymes , antigens , receptor sites for chemical signalling
- Not all cells have the same composition
- neurons ( nerve cells )
- axon is covered in protein channels and carriers which allows transport of ions and allow electrical impulses along the axon
- they have a mylenial sheath of flattened cells which are wrapped around several time to give more membrane layer and insulates the electrical impulses - m.s- is 20% proteins and 76% lipid
- PM of white blood cells
- they have special protein receptor which enables antigens to detect invading pathogens
- the root hair cell
- it has many carrier proteins to transport nitrate ions from the soil and into the cell
- cristae in mitochondria
- inner membrane contains electron carriers made from proteins
- hydrogen ion channels which are associated with ATP synthesis
- neurons ( nerve cells )
- glycolipids and proteins
- they are the site where hormones , drugs and antigens bind
- they act as receptors for cell signalling
- in drugs they bind to a receptor and trigger a response or block the receptor and prevent it from working
- they stabilise the membrane by forming HB with water molecules
- Roles within the cells and at the surface
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