Flashcards in CELL-SURFACE MEMBRANE STRUCTURE Deck (27)
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1
What is the function of membrane
control what passes through them and allows different conditions to be established inside and outside the cell
2
What are the molecules that form the structure of the cell-surface membrane (5 points)
1) phospholipids
2) proteins
3) cholesterol
4) glycolipids
5) glycoproteins
3
What do phosholipids form
bi-layer
4
What characteristics of phospholipids mean it is an important component of cell-surface membranes (2 points)
1) hydrophilic head - attracts water
2) hydrophobic tail - repels water
5
Which part of the phospholipid points outwards on the cell membrane
head
6
What are the functions of the phospholipids in the membrane (3 points)
1) allow lipid soluble substances to enter and leave the cell
2) prevent water soluble substances entering and leaving the cell
3) make the membrane flexible and self-sealing
7
How are proteins embedded in the phospholipid bilayer (2 ways)
1) in the surface - to give mechanical support or act as cell receptors
2) span the layer - protein channels or carrier proteins
8
What do protein channels do
allow water-soluble ions to diffuse across the membrane
9
What do carrier proteins do
bind to ions or molecules (like glucose and amino acids) and change shape in order to move the molecules across the membrane
10
What are the functions of the proteins in the membrane
1) provide structural support
2) act as channels transporting water-soluble substances across membrane
3) allow active transport across the membrane through carrier proteins
4) form cell-surface receptors for identifying cells
5) help cells adhere together
6) act as receptors (e.g hormones)
11
What does cholesterol do to the membrane
adds strength to the membrane
12
What is the function of cholesterol in the membrane (3 points)
1) reduce lateral movement of other molecules
2) make the membrane less fluid at high temperatures
3) prevent leakage of warer and dissolved ions from the cell
13
What are glycolipids made up of
carbohydrate covalently bonded with a lipid
14
What is the function of glycolipids in the membrane (3 points)
1) act as recognition sites for specific chemicals
2) help maintain the stability of the membrane
3) help cells to attach to one another & so form tissues
15
What are glycoproteins
carbohydrate chains attached to extrinsic proteins
16
What is the function of glycoproteins in the membrane (3 points)
1) act as recognition sites for hormones and neurotransmitters
2) help cells attach to one another and so form tissues
3) allows cells to recognise one another (e.g. lymphocytes)
17
Are membrames permeable
yes, partially permeable
18
How can substances move across cell-surface membranes
1) diffusion
2) osmosis
3) active transport
19
What structure does the cell membrane have
fluid-mosaic
20
Why is the bilayer described as 'fluid'
the phospholipids are constantly moving relative to one another
21
What are glycolipids
lipids with a polysaccharide chain attached
22
Why is the bilayer described as 'mosaic'
the proteins that are embedded in the phospholipid bilayer vary in shape, size and pattern (same as tiles)
23
Why do most molecules not move across the membrane? (4 points)
they are either:
1) not soluble in lipids and therefore cannot pass through the phospholipid bilayer
2) too large to pass through the channels in the membrane
3) of the same charge as the charge on the protein channels and so are repelled
4) polar (electrically charged) so have difficulty passing through the non-polar hydrophobic tails in the bilayer
24
How does temperature affect membrane permeability
higher/lower temperature = higher permeability
25
What is the permeability when temperatures are below 0 and why
high permeability, because the phospholipids don't have much energy so they are packed closely together & membrane is rigid, but channel and carrier proteins deform, which increases permeability and ice crystals may form that pierce the membrane
26
What is the permeability of the membrane when temperatures are between 0 and 45, and why
high, low, increasing, because the phospholipids aren't packed as tightly together so the membrane is partially permeable. As temperatures increase the phospholipids have more energy so move more, which increases the permeability
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