4.1- STRUCTURE OF THE CELL-SURFACE MEMBRANE Flashcards Preview

B4- TRANSPORT ACROSS CELL MEMBRANES > 4.1- STRUCTURE OF THE CELL-SURFACE MEMBRANE > Flashcards

Flashcards in 4.1- STRUCTURE OF THE CELL-SURFACE MEMBRANE Deck (41)
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1

what is the term cell-surface membrane specifically given to?

plasma membrane that surrounds cells + forms boundary between cell cytoplasm + environment

2

What does the cell-surface membrane allow?

different conditions to be established inside + outside of cell

3

What is the function of the cell-surface membrane?

controls movement of substances in and out of cell

4

What do phospholipids form?

a bilayer

5

Where does the hydrophilic heads of both phospholipid layers point to?

outside of cell-surface membrane

6

Why does the hydrophilic heads point to outside of the cell surface membrane?

attracted by water on both sides

7

Where does the hydrophobic tails of both phospholipid layers point?

into the centre of the cell membrane

8

Why does the hydrophobic heads point into the centre of the cell membrane?

repelled by water on both sides

9

How do lipid-soluble materials move through the membrane?

via phospholipid portion

10

Functions of phospholipids in membrane? (3)

allow lipid-soluble substances to enter + leave cell

prevent water-soluble substances entering + leaving cell

make membrane flexible + self-sealing

11

Are proteins interspersed throughout the cell surface membrane?

yes

12

One way in which proteins embedded in phospholipid bilayer?

proteins occur in surface of bilayer + never extend completely across it

13

What do proteins that occur on the surface of the bilayer and not extend completely across it do?

give mechanical support to membrane or in conjunction with glycolipids, as cell receptors for molecules i.e. hormones

14

Another way in which proteins embedded into phospholipid bilayer?

proteins completely span phospholipid bilayer from one side to other

15

examples of proteins that completely span phospholipid bilayer from one side to other?

protein channels
carrier proteins

16

What do protein channels do?

form water-filled tubes to allow water-soluble ions to diffuse across membrane

17

What do carrier proteins do?

bind to ions or molecules like glucose and amino acids, then change shape to move these molecules across membrane

18

Function of proteins in membrane? (6)

provide structural support

act as channels transporting water-soluble substances across membrane

allow active transport across membrane through carrier proteins

form cell-surface receptors for identifying cells

help cells adhere together

act as receptors, i.e. for hormones

19

Where do cholesterol molecules occur within?

phospholipid bilayer of cell-surface membrane

20

What do the cholesterol molecules do?

add strength to membranes

21

Are cholesterol molecules hydrophobic or hydrophilic?q

very hydrophobic

22

As cholesterol molecules are very hydrophobic what important role do they play?

preventing loss of water + dissolved ions from cell

23

What other important role does cholesterol molecules carry out regarding fatty acid tails?

pull together fatty acid tails of phospholipid molecules, limiting their movement and that of other molecules but without making membrane as a whole too rigid

24

Function of cholesterol in membrane? (3)

reduce lateral movement of other molecules including phospholipids

make membrane less fluid at high temperatures

prevent leakage of water + dissolved ions from cell

25

What are glycolipids made up of?

a carbohydrate covalently bonded with a lipid

26

Where does the carbohydrate portion of the glycolipid extend from into?

from phospholipid bilayer into the watery environment outside cell where it acts as a cell-surface receptor for specific chemicals

27

An example where glycolipids act as a receptor for specific chemicals?

human ABO blood system operates as a result of glycolipids on the cell-surface membrane

28

Functions of glycolipids in the membrane? (3)

act as recognition sites

help maintain stability of membrane

help cells to attach to one another and so form tissues

29

What are glycoproteins made up of?

carbohydrate chain attached to many extrinsic proteins on the outer surface of the cell membrane

30

What do the glycoproteins act as?

cell-surface receptors

31

What do glycoproteins act as receptor for more specifically?

hormones and neurotransmitters

32

Function of glycoproteins in the membrane? (3)

act as recognition site

help cells attach to one another and so form tissues

allow cells to recognise one another, e.g. lymphocytes can recognise an organism's own cells

33

Why do most molecules not freely diffuse across the cell-surface membrane? (4)

not soluble in lipids

too large

of same charge as charge on protein channels

electrically charged

34

Why are molecules that are not soluble in lipids not able to diffuse across the cell-surface membrane?

they cannot pass through the phospholipid bilayer

35

Why are large molecules not able to diffuse across the cell-surface membrane?

cannot pass through the channels in the membrane

36

Why are molecules that have the same charge as the protein channels unable to diffuse across the cell-surface membrane?

they're repelled

37

Why are molecules that are electrically charged unable to diffuse across the cell-surface membrane?

have difficulty passing through the non-polar hydrophobic tails in the phospholipid bilayer

38

What is the arrangement of all the various molecules combined into the structure of the cell-surface membrane known as?

fluid-mosaic model

39

Why is the model known as 'fluid' in fluid-mosaic?

individual phospholipid molecules can move relative to one another

40

What does the fluidity of the phospholipid molecules give?

give membrane a flexible structure that's constantly changing in shape

41

Why is the model known as 'mosaic' in fluid-mosaic?

as proteins that are embedded in phospholipid bilayer vary in shape, size and pattern in same way as stones/tiles in mosaic