4.1 Structure of the cell-surface membrane Flashcards
What is made up of a cell membrane?
- phospholipid
- glycolipids
- protein
- glycoprotein
- channel protein
- cholesterol
How is the structure of a phospholipid?
1.hydrophilic phosphate head
2. hydrophobic fatty acid tails
Does the hydrophilic phosphate head point inwards or outwards?
Outwards
Does the hydrophobic hydrocarbon tails point inwards or outwards?
Inwards
how are the phospholipids arranged in a cell membrane?
Bilayer
What is the function of phospholipids?
- allow lipid-soluble substances to enter or leave the cell
- prevent water-soluble substances to enter or leave the cell
- make the membrane flexible and self-sealing
What are the two places that proteins are located?
- in the surface of the bilayer
- completely span (跨越) the bilayer
What is channel protein?
Channels that form water-filled tubes to allow water-soluble ions to diffuse and span (跨越) across the membrane.
What is carrier protein?
Proteins that bind to ions or molecules like glucose and amino acids, then change shape in order to move these molecules across the membrane.
What are the functions of protein?
- provide structural support
- as a channel 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 (黏在一起)
- acts as receptors
Where is cholesterol located?
Within the phospholipid bilayer
Are cholesterol hydrophobic or hydrophilic?
Hydrophobic
Why does cholesterol bind with fatty acid tails and pull them together?
To limit fatty acid tails’ movement without making the whole membrane rigid (死板) .
What are the functions of cholesterol?
- add strength to the membrane
- reduce lateral (橫向) movement of molecules
- make the membrane less fluid at high temperature
- prevent loss of water and dissolved ions
What are glycolipids?
Carbohydrate chains that are attached to the hydrophilic phosphate head from the phospholipid bilayer on the outer surface of membrane.
What are glycolipids made up?
Covalent bond between lipid and carbohydrate.
How do glycolipids act as a receptor for special chemicals?
The carbohydrate extends from the phospholipid bilayer into the watery environment outside the cell.
What are the functions of glycolipids?
- act as recognition sites
- help maintain the stability of membrane
- help cells to attach to each other to form tissues
What are glycoproteins?
Carbohydrate chains that are attached to the extrinsic (外在的) protein on the outer surface of membrane.
What are glycoproteins made up?
Covalent bond between protein and carbohydrate.
What are the functions of glycoproteins?
- acts as recognition sites
- helps cells to attach to each other to form tissues
- allow cells to recognise each other
- acts as receptors for hormones and neurotransmitters
What is the model that shows the structure of a cell membrane?
Fluid-mosaic model
Why is the model called ‘fluid-mosaic’ model?
- ‘fluid’ because individual phospholipids can move relatively to one other
- ‘mosaic’ because proteins that are embedded in the phospholipid bilayer vary in shape and size