Cell Membrane Flashcards
What do proteins do in the cell membrane?
- provide structural support
- act as carrier transporting water-soluble substances
- function as enzymes
- form ion channels for sodium, potassium etc.
- act as energy transducers
- form recognition sites by identifying cells
- help cells adhere together
- act as receptors (e.g. for hormones)
What do phospholipids do in the cell membrane?
- allow lipid-soluble substances to enter and leave the cell
- prevent water-soluble substances entering and leaving the cell
- give the membrane fluidity
What does cholesterol do in the cell membrane?
- reduces lateral movement of phospholipids
- makes membrane less fluid at high temperatures
- prevents leakage of water and dissolved ions from the cell
- regulates membrane fluidity
What do glycolipids do in the cell membrane?
- act as recognition sites (e.g. ABO blood system)
- help maintain stability of the membrane
- help cells attach to one another and so form tissues
- cell signalling
What do glycoproteins do in the cell membrane:
- acts as recognition sites for hormones and neurotransmitters
- help cells attach to one another and so form tissues
- act as antigens allow mint cells to recognise one another (e.g. lymphocytes can recognise an organism’s own cells)
- cell signalling
Describe a channel protein
- protein with a specific shape that complements the shape of a substance to be transported across the membrane
- used in facilitated diffusion
Describe a carrier protein
- protein with specific shape that complements the shape of a substance to be transported across a membrane
- used in active transport and facilitated diffusion
Describe cell signalling
• receptors on cells bind to hormones, drugs and other cells, leading to a series of reactions within the cell
Describe osmosis
water molecules are small enough to pass between phospholipid molecules down a water potential gradient until a dynamic equilibrium is reached
Describe the relationship between temperature and permeability
- high temperature boosts kinetic energy of the component molecules of the membrane and the transported substance, making the membrane more permeable
- very high temperatures will denature the protein molecules, changing their shape and making the membrane more permeable, eventually the membrane will be destroyed
Describe facilitated diffusion
- large, water-soluble substances cannot pass between lipid molecules and so are carried through the membrane by carrier proteins down a concentration gradient by facilitated diffusion
- polar, water-soluble substances that cannot pass through the membrane between lipid molecules can be transported via specific channel proteins down a concentration gradient
Describe diffusion
Small, lipid-soluble substances can pass through the lipid bilayer between the phospholipid molecules, down a concentration gradient
Describe active transport
Water-soluble substances that must be moved against a concentration gradient require a carrier protein and ATP
Describe the glycocalyx
- the layer of carbohydrates on the outside of the bilayer
- glycolipids and glycoproteins
- thickens membrane to 7.5nm
Why do phospholipids work well in a membrane?
- lipids are insoluble in water
- break up FWPs and watery cytoplasm
- hydrophilic heads give stability
