Biological Membranes

?
  • Created by: Carly2289
  • Created on: 19-11-16 12:31
What is the definition of the fluid mosaic model?
Theory of cell membrane structure with proteins embedded in a sea of phospholipids
1 of 49
What is the definition of a glycolipid?
A lipid/phospholipid with a chain of carbohydrate molecules attached
2 of 49
What is the definition of a glycoprotein?
A protein with a chain of carbohydrate molecules attatched
3 of 49
What is the definition of a plasma membrane?
Cell surface membrane
4 of 49
What are cell membranes?
Partially permeable barriers
5 of 49
What do cell membranes do?
Form a barrier and separate the cell contents from the cell's exterior environment or separate organelles fro cytoplasm and allow some molecules in or out of the cell
6 of 49
What is permeability?
The ability to let substances pass through
7 of 49
How do molecules pass through?
Some very small molecules diffuse through the cell membrane in between its structural molecules, some substances dissolve in the lipid layer and pass through, some substances pass through protein channels or are carried by carrier proteins
8 of 49
Why are these membranes known as partially permeable barriers?
Because they don't let all types of molecule through
9 of 49
What determines the membranes permeability?
The properties of the component molecules of the cell membrane
10 of 49
What are the (7) roles of membranes at the surface of cells (plasma membrane/cell surface membrane) Part1
Separates cell components from its external environment (external surroundings or tissue fluid/cells surrounding it), regulates transport of materials in and out of cell, may contain enzymes for specific metabolic pathways
11 of 49
What are the (7) roles of membranes at the surface of cells (plasma membrane/cell surface membrane) Part2
Has antigens so organisms immune systems recognises the cell as its self and doesn't attack, may release chemicals that signal to other cells, contains receptors for chemical signals (site for cell communication) and may be site of chemical reactions
12 of 49
Why is it important that there are membranes around many organelles?
It separates them allowing them to be able to perform it's function
13 of 49
What are the roles of membranes within cells? (mitochondria)
Mitochondria have folded inner membranes (cristae) giving a large surface area for some reactions of aerobic respiration and locate some of the enzymes needed for respiration to occur
14 of 49
What are the roles of membranes within cells? (Chloroplasts)
The inner membrane of chloroplasts called thylakoid membranes, house chlorophyll. On these membranes some of the reactions for photosynthesis occur
15 of 49
What are the roles of membranes within cells? (Digestive enzymes)
There are some digestive enzymes on the plasma membrane of epithelial cells that line the small intestine and these enzymes catalyse some of the final stages in the breakdown of certain types of sugars
16 of 49
Who created the fluid mosaic model of cell membrane structure and when?
Singer and Nicolson in 1972
17 of 49
What does the fluid mosaic model explain?
How cell membranes could me more dynamic and interact more with the cell's environment. Also shows the passage of molecules through membranes
18 of 49
What does the model propose the fabric of the membrane consisted of?
A phospholipid bilayer (double layer) with proteins floating in it, making up a mosaic pattern
19 of 49
What gives the model more fluidity?
The lipid molecules can change places with each other and some of the proteins can move
20 of 49
What is the lipid bilayer made up of?
Two layers of phospholipid molecules. Hydrophilic heads are in contact with the watery exterior or interior (cytoplasm) and the hydrophobic tail are in the centre of the membrane, away from water
21 of 49
What proteins span the membrane?
Some have pores and act as channels allowing ions to pass through, some are carriers and change shape to carry specific molecules across the membrane, and others may be attached to the carriers as enzymes, antigens or receptor sites
22 of 49
Eukaryotic cell membranes contain cholesterol, why is it important?
It helps regulate the fluidity of the membrane, maintains mechanical stability and resists the effects of temperature changes on the structure of the membrane
23 of 49
What is the total thickness of a cell membrane?
Between 5 and 10 mm
24 of 49
What is glycocalyx?
It is outside the membrane and formed from the carbohydrate chains attached to either glycolipids of glycoproteins in the membrane
25 of 49
To learn the fluid mosaic model practice drawing it out and labelling it with the functions
Example is on page 129 of the OCR AS/A level biology A text book
26 of 49
In neurones (nerve cells) how do ions enter/exit the cell?
The protein channels and carriers in the plasma membrane covering the long axon allow entry/exit of ions to bring about the conduction of electrical impulses along their length
27 of 49
What is a myelin sheath?
Neurones have a myelin sheath formed by flattened cells wrapped around them several times giving several layers of cell membrane, the membrane making the myelin sheath is 20% protein and 76% lipid
28 of 49
What do the plasma membranes of white blood cells contain?
Special protein receptors that enable them to recognise the antigens on foreign cells, usually from invading pathogens but also from tissue or organ transplants
29 of 49
Why do root hair cells in plants have many carrier proteins?
To actively transport nitrate ions from the soil into the cells
30 of 49
Why is the inner membrane of mitochondria 76% protein and 24% lipid?
Because their inner membranes contain many electron carriers that are made of protein, and hydrogen ion channels associated with ATP synthase enzymes
31 of 49
What is the definition of diffusion?
The passive (no ATP needed-metabolic energy) movement of molecules from an area of high concentration of that molecule to an area of low concentration and it may or may not be across a membrane
32 of 49
What is the definition of facilitated diffusion?
The passive movement of molecules from an area of high concentration of that molecule to an area of low concentration, across a partially permeable membrane via protein channels or carriers
33 of 49
Why do cells need to receive raw material or reactants?
For the reactions and biochemical processes that sustain life, as these take place in cells
34 of 49
What do cells respire to make?
ATP, which provides cellular energy to drive the biochemical reactions
35 of 49
What do cells need to do this?
They need oxygen and glucose and also need to remove the toxic metabolic waste products such as carbon dioxide
36 of 49
What do cells also need to export?
Some of the molecules that they make such as enzymes, hormones or other signalling molecules
37 of 49
What are passive processes?
Ones that don't use ATP and instead rely on the kinetic energy of the molecules
38 of 49
What happens when molecules move down their concentration gradient in simple diffusion?
They are still moving randomly but remain evenly dispersed so there is no net diffusion-they have reached an equilibrium
39 of 49
What molecules can pass through cell membranes by simple diffusion?
Small ones such as oxygen and carbon dioxide
40 of 49
Why can fat-soluble molecules such as hormones diffuse through cell membranes, even if they are large?
Because they dissolve in the lipid bilayer, they still move down their concentration gradient
41 of 49
Why does it seem as though water would not be able to pass through?
Because they are polar and insoluble in lipid, the phospholipid bilayer would seem to be an impenetrable barrier
42 of 49
Why does water diffuse through?
Because it is present in such great concentration that direct diffusion does occur
43 of 49
What happens in membranes where a very high rate of water movement is required?
Specific water channel proteins known as aquaporins may be needed to allow water molecules to cross the membrane without the challenge of moving through a lipid environment
44 of 49
What happens in most cases after the molecules enter the cell?
They pass into organelles and are used for metabolic reactions; this maintains the concentration gradient and keeps more of the molecules entering the cell
45 of 49
What happens when oxygen diffuses into the cytoplasm of respiring cells?
It then diffuses into the mitochondria and is used for aerobic respiration
46 of 49
What happens when carbon dioxide diffuses into the palisade mesophyll cells of a plant leaf?
It then diffuses into chloroplasts and is used for phottosynthesis
47 of 49
What factors affect the rate of simple diffusion?
Temperature, diffusion distance, surface area, size of diffusing molecule and concentration gradient
48 of 49
How does temperature affect the rate of diffusion?
As temperature increases, molecules have more kinetic energy so their rate of diffusion will increase
49 of 49

Other cards in this set

Card 2

Front

What is the definition of a glycolipid?

Back

A lipid/phospholipid with a chain of carbohydrate molecules attached

Card 3

Front

What is the definition of a glycoprotein?

Back

Preview of the front of card 3

Card 4

Front

What is the definition of a plasma membrane?

Back

Preview of the front of card 4

Card 5

Front

What are cell membranes?

Back

Preview of the front of card 5
View more cards

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Biological molecules resources »