2: CELLS - MEMBRANES Flashcards
What is the function of cell-surface membranes?
- act as a barrier between cell and environment
- control what substances enter/leave the cell
- partially permeable
What is the function of membranes within cells?
- divide cell into compartments (compartmentalisation)
- act as a barrier between organelle and cytoplasm
- control what substances enter/leave organelle
- partially permeable
What does partially permeable mean?
only allows particular substances to move across it but not others
Describe the fluid mosaic model
- phospholipids form a continuous bilayer in which phospholipids are constantly moving (fluid)
- proteins are scattered throughout the bilayer (mosaic)
What are the components of a membrane?
- phospholipids
- proteins
- cholesterol
What is the role of phospholipids in a membrane?
- form a bilayer which acts as a barrier to water soluble substances
- heads (phosphate group) are hydrophilic and tails (fatty acids) are hydrophobic so they line up with the heads facing out towards water on either side of the membrane and the tails facing inwards
- this makes the centre of the bilayer hydrophobic so water-soluble substances can’t pass through
What is the role of cholesterol in a membrane?
- gives membrane stability
- fits between phospholipids
- bids to fatty acid tails causing phospholipids to pack more tightly together which restricts movement of phospholipids making the membrane less fluid
- hydrophobic regions allow cholesterol to create a further barrier to polar substances moving through the membrane
- helps to maintain shape of animal cells (this is important for cells that aren’t supported by other cells)
What is the role of proteins in a membrane?
- transport proteins - allow large/charged molecules to diffuse across membrane
- receptor proteins - allow cell to detect chemicals released from other cells which signal the cell to respond in some way
What are glycoproteins?
proteins with a carbohydrate chain attached
What are glycolipids?
lipids with a carbohydrate chain attached
What are the functions of glycoproteins and glycolipids/why do they have a carbohydrate attached?
- involved in cell signalling
- cell recognition
- antigens/markers
- attachment receptors for hormones
- adhesion (cells binding together)
How do temps below 0°C affect membranes?
- phospholipids don’t have much energy so they can’t move very much. they’re packed closely together making the membrane rigid
- channel proteins and carrier proteins denature causing membrane permeability to increase
- ice crystals may form and pierce the membrane making it highly permeable when the ice thaws
How do temps between 0°C and 45°C affect membranes?
-phospholipids can move around and aren’t packed as tightly together
- membrane is partially permeable
- as temp increases phospholipids gain energy so they move more which increases membrane permeability
How do temps above 45°C affect membranes?
- phospholipid bilayer starts to melt (break down) and membrane becomes more permeable
- water inside the cell expands, putting pressure on the membrane
- channel proteins and carrier proteins denature which increases the permeability of the membrane