CELL SURFACE MEMBRANES Flashcards
What is another name for the cell-surface membrane?
Plasma membrane
Components of a cell surface membrane:
- phospholipid bilayer
- proteins
- cholesterol
- glycoproteins and glycolipids
Importance of phospholipids:
- hydrophilic heads point to the outside of the cell-surface membrane attracted by water on both sides
- hydrophobic tails point into the centre of the cell membrane, repelled by water on both sides
Function of phospholipids:
- allow lipid-soluble substances to enter and leave the cell
- prevent water-soluble substances entering and leaving the cell
- make the membrane flexible and self-sealing
How are proteins embedded into the cell surface membrane?
- intrinsic
- extrinsic
What does intrinsic mean?
Inside the bilayer
What does extrinsic mean?
Outside the bilayer
What do proteins help the cell to do?
Stick together
Function of membranes (FOM): permeable?
Controls what enters and leaves the cell
FOM: separate compartment from cytoplasm?
Specific metabolic reactions can take place within them
FOM: internal transport system?
E.g. endoplasmic reticulum
FOM: surface?
Provide a surface on which reactions can occur e.g. protein synthesis
What molecules can easily pass through the membrane?
Small, uncharged, non-polar molecules
Why are membranes referred to as a fluid mosaic model?
Fluid- not fixed movement
Mosaic- mixed pattern
What happens if there is too much/ too little cholesterol?
Too much= too rigid
Too little= too fluid
Structure of cholesterol:
Hydrophobic tails
Hydrophilic heads point
Where do cholesterol molecules fit?
Between the phospholipid bilayer- orientated in the same way- head out, tail in
Is cholesterol hydrophobic or hydrophilic?
Hydrophobic to prevent loss of water
Function of cholesterol:
- movement- reduce movement of other molecules
- fluidity- makes the membrane less fluid at high temps
- tissues- helps cells attach to one another and form tissues
- strength- add strength to molecule
What is a glycolipids?
A carbohydrate covalently bonded to a lipid
What does a glycolipid act as and what does it add?
A cell-surface receptor and adds stability
Are glycoproteins extrinsic or intrinsic and what are they?
Extrinsic- on the outer surface of the cell membrane with carbohydrate chains attached
- act as cell-surface receptors- specifically hormones and neurotransmitters
What are protein channels?
Form water-filled tubes to allow water-soluble ions to diffuse across the membrane
What are carrier proteins?
Bind to ions or molecules like glucose and amino acids, change shape in order to move these glucose molecules across the membrane
Functions of proteins:
- provide structural support
- act as channels transporting water-soluble substances across the membrane
- allow active transport across the membrane through carrier proteins
- form cell-surface receptors for identifying cells
- help cells adhere together
- act as receptors- e.g. hormones
Functions of glycolipids:
- act as recognition sites
- help maintain the stability of the membrane
- help cells to attach to one another and so form tissues
Functions of glycoproteins:
- act as recognition sites
- help cells to attach to one another and so form tissues
- allow cells to recognise one another, for example lymphocytes can recognise an organism’s own cells
Difference between facilitated and simple diffusion:
Facilitated diffusion uses protein channels and carrier proteins
