biological membranes : the structure of cell membranes

Question 1

define fluid mosaic model

Answer 1

theory of cell membranes structure with proteins embedded in a sea of phospholipids

Question 2

what does the cell-membrane form and what for ?

Answer 2

a barrier
- to separate the cell contents from the cell’s exterior environment
AND
- separate organelles from cytoplasm
AND
- they need to allow some molecules through in and out of the cell

Question 3

what do some organelles have and what do they also form ?

Answer 3

cell membrane and a barrier

Question 4

what does permeability refer to ?

Answer 4

the ability to let substances pass through

Question 5

how does substances pass through the cell membrane ? (3 marks )

Answer 5

• some very small molecules simply diffuse through the cell membrane , in between its structural molecules
• some substances dissolve in the lipid layer and pass through
• other substances pass through special protein channels or are carried by carrier proteins

Question 6

what are the cell-membranes described as and why ?

Answer 6

partially permeable because these membranes do not let all types of molecules pass through them

Question 7

what does the component molecules of the cell membrane determine ?

Answer 7

• determines which molecules it allows through

Question 8

what is the cell membrane referred to as ?

Answer 8

plasma membrane / cell surface membrane

Question 9

what is external environment in terms of single-celled organisms ?

Answer 9

the environment is external surroundings

Question 10

what is external environment in terms of multicellular organisms ?

Answer 10

each cell’s environment is the tissue fluid or cells surrounding it

Question 11

what may the plasma membrane contain ?

Answer 11

enzymes involved in specific metabolic pathways

Question 12

what does plasma membrane contain and why ? (A)

Answer 12

has antigens so that the organism’s immune system can recognise the cell as being ‘self’ and not attack it

Question 13

what may the plasma membrane release and why ?

Answer 13

may release chemicals that signal to other cells

Question 14

what may the plasma membrane contain and why ? (R)

Answer 14

contains receptors for such chemical signals
–> so is a site for cell communication OR signalling
- hormones and drugs may bind to membrane bound receptors

Question 15

what may the plasma membrane be the site of ?

Answer 15

chemical reactions

Question 16

why are there membranes around the organelles ?

Answer 16

so that organelles are able to perform its function

Question 17

what happens in some organelles ?

Answer 17

metabolic processes occur on membranes

Question 18

how does this occur in mitochondria ?

Answer 18

• the mitochondria has folded inner membranes called cristae
• this gives a large surface areas for some of the reactions of aerobic respiration + localise some of the enzymes needed for respiration to occur

Question 19

how does this occur in chloroplasts ?

Answer 19

• the inner membrane is called thylakoid membranes - house chlorophyll
• on these membranes some of the reactions of photosynthesis occurs

Question 20

how does this occur on epithelial cells ?

Answer 20

• some digestive enzymes on the plasma membrane of the epithelial cells - lines the small intestine
  -these enzymes catalyse some of the final stages in the breakdown of certain types of sugars

Question 21

who + when proposed the fluid mosaic model ?

Answer 21

in 1972-Singer + Nicolson

Question 22

what did the model allow ?

Answer 22

the passage of molecules through the membrane

Question 23

what did their structure explain ?

Answer 23

how cell membranes could be more dynamic and interact more with the cells environment

Question 24

what did the fluid mosaic model propose ?

Answer 24

the fabric of the membrane consisted of a phopsholipid bilayer with proteins floating in it - making a mosaic pattern

Question 25

what can the lipid molecules do and the proteins do ?

Answer 25

the lipid molecules can change places with each other + some of the proteins may move giving fluidity

Question 26

what is the fabric of the membrane made up of ?

Answer 26

2 layers of phospholipid molecules
- their hydrophilic heads are in contact with the watery exterior or watery interior (cytoplasam)
- their hydrophobic tail regions are in the centre of the membrane away from water

Question 27

draw and label the cell membrane

Answer 27

find in textbook :)

Question 28

define glycolipid

Answer 28

lipid/phsopholipid with a chain of carbohydrate molecules attached

Question 29

define gylcoprotein

Answer 29

protein with a chain of carbohydrate molecules attached

Question 30

what are the types of protein channels within the membrane ?

Answer 30

channel , peripheral and carrier

Question 31

what do some channel proteins act as ?

Answer 31

• have pores and acts as channels to allow ions , which have an electrical charge and are surrounded by water molecules to pass through

Question 32

what do carrier proteins act as ?

Answer 32

• they are carriers and by changing the shape, carry specific molecules across the membrane

Question 33

what do peripheral proteins acts as ?

Answer 33

• attached to the carrier proteins and function as enzymes antigens or receptor sites for complementary-shaped signalling chemicals such as hormones

Question 34

why is cholesterol important for cell membranes ?

Answer 34

for helping regulate the fluidity of the membrane
- to maintain mechanical stability and resist the effects of temperature changes on the structure of the membrane

Question 35

what is the total thickness of the cell membrane roughly ?

Answer 35

between 5 and 10nm

Question 36

define glycocalyx

Answer 36

a sugary coating on the cell’s surface that protects the cell, helps it communicate, and allows it to be recognized by other cells

Question 37

what does the protein channels and carrier of the neurons allow ?

Answer 37

entry and exit of ions to bring about the conduction of electrical impulse along their length

Question 38

how is the myelin sheath formed ?

Answer 38

by flattened cells around them several times - giving several layers of cell membrane

Question 39

what is the membrane formed of ?

Answer 39

20 % protein
76 % lipid

Question 40

what does white blood cells contain and what does it enable them to do ?

Answer 40

contain special protein receptors that enable them to recognise antigens on foreign cells
-> usually from invading pathogens from tissue or organ plants

Question 41

what does root hair cells in plants have and why ?

Answer 41

many carrier proteins
–> to actively transport nitrate ions from the soil into the cells

Question 42

what is the inner membrane of the mitochondria formed and why ?

Answer 42

76 % protein
24 % lipid
–> their inner membrane contains many electron carriers that are made of protein , and hydrogen ion channels associated with ATP synthase enzymes

Question 43

define intrinsic

Answer 43

that is located inside or is a natural, essential part of something

Question 44

give an example of intrinsic in terms of bio ?

Answer 44

intrinsic proteins:
-are proteins that are embedded within the cell membrane
-span across the membrane or are firmly attached to it

Question 45

define extrinsic

Answer 45

means something that is located outside or comes from outside a system or structure

Question 46

give an example of extrinsic in terms of bio ?

Answer 46

extrinsic proteins:
- are proteins found on the outer or inner surface of the cell membrane but not embedded in it
- attach loosely to the membrane