CELL-SURFACE MEMBRANE STRUCTURE Flashcards Preview

BIOLOGY - CELL STRUCTURE AND DIVISION > CELL-SURFACE MEMBRANE STRUCTURE > Flashcards

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

27

What is the permability when temperatures are above 45, and why

increasing and at increasing rate, because the phospholipid bilayer starts to break down & the membrane becomes more permeable, channel and carrier proteins deform so they can't control what enters or leaves the cell which also increases permeability