Biological Membrane :) Flashcards
1
Q
What are plasma membrane?
A
A barrier between the cell and its environment controlling which substances enter and leave the cell
2
Q
Can substances move across the cell membrane?
A
Some molecules can but not others because they are partially permeable
3
Q
How can substances move across a plasma membrane?
A
By diffusion, osmosis or active transport
4
Q
What do plasma membranes allow?
A
Recognition by other cells e.g. The cells of the immune system Cell communication (cell signalling)
5
Q
What do the membranes around organelles do?
A
Divide the cell into different compartments and act as a barrier between organelles and the cytoplasm making different functions more efficient e.g. Substances needed for respiration kept together in mitochondria
6
Q
What can membranes within cells form?
A
Vesicles to transport substances between different areas of the cell
7
Q
What are cells and many organelles surrounded by?
A
Many membranes which have a range of functions
8
Q
What do membranes within cells control?
A
Which substances enter and leave the organelles e.g. RNA leaves the nucleus via nuclear membrane. (It’s partially permeable)
9
Q
Where else can you get membranes?
A
Within organelles
10
Q
What do membranes within organelles act as?
A
Barriers between membrane contents and the rest of the organelle e.g. Thylakoid membranes in chloroplasts
11
Q
What can membranes be site of?
A
Chemical reactions
E.g. Inner membrane of mitchrondrion contains enzymes needed for respiration
12
Q
How does the structure of all membranes differ?
A
Not a lot because they are basically the same
13
Q
What are membranes composed of?
A
Lipids (phospholipids mainly)
Proteins
Carbohydrates (proteins or lipids)
14
Q
What happened in 1972?
A
Fluid mosiac model was suggested to describe the arrangement of molecules in the membrane
15
Q
What do phospholipids molecules do?
A
Form a continuous bilayer
16
Q
What is this bilayer and why?
A
Fluid because the phospholipids are constantly moving
17
Q
What are within the bilayer?
A
Cholesterol molecules
Protein molecules scattered through bilayer like tiles in a mosiac
18
Q
Fluid mosiac model
Carbohydrates
A
Some proteins have polysaccharide (carbohydrate) chain attached (glycoproteins)
Some lipids have polysaccharide chain attached (glycolipids)
19
Q
Phospholipid bilayer size?
A
About 7nm thick
20
Q
What do phospholipids do in the membrane?
A
Form a barrier to dissolved substances
But not to fat-soluble substances e.g. Fat-soluble vitamins, can dissolve and pass directly through
21
Q
Explain phospholipids?
A
They have a hydrophilic head and a hydrophobic tail
Automatically arranges itself into bilayer heads face out, tails face inwards either side of membrane
Centre of bilayer is hydrophilic so membrane doesn’t allow water-soluble substances through it
22
Q
Cholestral
A
Type of lipid
Present in all cell membranes except bacterial cell membranes
Fit between phospholipids. They hung to hydrophobic tails of phospholipids causing them to pack more closely together making membrane less fluid and more rigid
23
Q
What’s does protein do?
A
Control what enters and what leaves the cell
24
Q
Proteins
A
Form channels in membrane allowing small or charged particles through
Act as receptors for molecules in cell signalling when a molecule binds to the protein a chemical reaction is triggered inside the cell
25
What do carrier proteins?
Transport molecules and ions across the membrane by active transport and facilitated diffusion
26
Glycoproteins and glycolipids
Stabilise membrane by forming hydrogen bonds with surrounding water molecules
Sites where drugs, hormones and antibodies bind
Act as receptors for cell signalling
Antigens- cell surface molecules involved in immune response
27
Why do cell need to be able to communicate with each other?
To control processes inside the body and to respond to changes in their environment
28
How do cell communicate with each other?
Using messenger molecules
1) one cell releases a messenger molecule (hormone)
2) molecule travels (in blood) to another cell
3) messenger molecule is detected by the cell because it binds to a receptor on its cell membrane
29
How do cell receptors play an important role in cell signalling?
Proteins in cell membrane act as receptors for messenger molecules (membrane- bound receptors)
Receptor proteins have specific shapes
Different cells have different types of receptors
30
Receptor proteins have specific shape?
Only messenger molecules with complementary shapes can bind to then
31
Different cells have different types of receptors?
Respond to different messenger molecules
| Cell responds to particular messenger molecule (target cell)
32
What is glucagon?
A hormone that's released when there isn't enough glucose in the blood. It binds to receptors on liver cells causing liver cells to break down stores of glycogen to glucose
33
How do many drugs work?
By binding to receptors in cell membranes
| Either trigger a response in the cell or block the receptors and prevent it from working
34
Antihistamines
Cell damage causes the release of histamine. Histamine binds to the receptors on the surface of other cells and causes inflammation. Antihistamines work by blocking histamine receptors on cell surface preventing histamine from binding to the cell membrane
35
What is the permeability of cell membrane affected by?
Different conditions e.g. Temperature, solvent type and solvent concentration
36
How can you investigate how things affect permeability?
By doing an experiment using beetroot. Beetroot cells contain a coloured pigment that leaks out- the higher the permeability of the membrane the more pigment leaks out of the cell
37
Investigate how temperature affects beetroot membrane permeability? Step 1
Cut give equal sized pieces of beetroot and rinse them to remove any pigment released during cutting
38
Investigate how temperature affects beetroot membrane permeability? Step 2
Place five equal sized pieces in five different test tubes each with 5cm3 of water
39
Investigate how temperature affects beetroot membrane permeability? Step 3
Place each test tube in a water bath at different temperatures e.g. 10, 20, 30,40,50 degrees for the same length of time
40
Investigate how temperature affects beetroot membrane permeability? Step 4
Remove pieces of beetroot from the tubes, leaving just coloured liquid
41
Investigate how temperature affects beetroot membrane permeability? Step 5
Use colorimeter
Machine that passes light through liquid and measures how much water of the light is absorbed the higher the permeability of the membrane the more pigment released so the higher the absorbance of the liquid is
42
Temperature below 0 degrees membrane permeability?
Phospholipids don't have much energy so can't move very much. Packed closely together and the membrane is rigid. But the channel orotund and carrier proteins in the membrane deform increasing permeability of the membrane. Ice crystals may form and pierce the membrane making it highly permable when it thaws
43
Temperature between 0 and 45 membrane permeability?
Phospholipids can move around and aren't packed as tightly together- the membrane is partially permeable. As the temperature increases the phospholipids move more because they have more energy increasing permeability of the membrane
44
Temperature above 45 degrees?
Phospholipids bilayer starts to melt and the membrane becomes more permeable. Water inside the cell expands, putting pressure on the membrane. Channel proteins and carrier proteins deform so they can't control what enters or leaves the cell increasing permeability of the membrane
45
What else can affect the permeability of the membrane?
Different solvents and their concentrations
46
What does surrounding a cell in a solvent like ethanol do?
Increases permeability of their cell membrane because solvent dissolve the lipid in a cell membrane so the membrane loses its structure
47
How much do solvent increase cell permeability?
Some more than others
48
What will increasing the concentration of the solvent also do?
Increase membrane permeability
49
What is diffusion?
The net movement of particles (molecules or ions) from an area of higher
Passive process so no energy needed for it to happen
50
What way will diffusion happen?
Both ways but the net movement will be to the area of lower concentration. This continues until particles are evenly distributed throughout the liquid or gas
51
What is the concentration gradient?
The path from an area of higher concentration to an area of lower concentration. Particle diffuse down a concentration gradient.
52
How do small non-polar molecules such as oxygen and carbon dioxide get through the cell membrane?
Diffusion easily between phospholipids
53
How come osmosis happens?
Water is small enough to fit between phospholipids so it's able to diffuse across plasma membrane even through it's polar. Diffusion of water molecules is osmosis
54
The correlation between rate of diffusion and concentration gradient?
The higher the concentration gradient, the faster the rate of diffusion
55
The correlation between rate of diffusion and thickness of exchange surface?
The thinner the exchange surface the faster the rate of diffusion
56
The correlation between rate of diffusion and surface area?
The larger the surface area the faster the rate of diffusion
57
The correlation between rate of diffusion and the temperature?
The warmer it is, the faster the rate of diffusion because particles have more kinetic energy so they move faster
58
What is phenolphthalein?
A pH indicator
Pink in alkaline solution
Colourless in acidic solution
59
How can you use it to investigate diffusion in agar jelly? Step 1
1) make up agar jelly with phenolphthalein and dilute sodium hydroxide. This will make the jelly a lovely shade of pink.
60
How can you use it to investigate diffusion in agar jelly? Step 2
Fill breaker with dilute HCl using scalpel cut out few cubes from jelly and put them in a beaker of acid
61
How can you use it to investigate diffusion in agar jelly? Step 3
If you leave cubes for a while they'll eventually turn colourless as acid diffuses into agar jelly and neutralises sodium hydroxide
62
What do the agar cubes represent?
Cells
63
How would you see how surface area affects diffusion?
Cut agar jelly into different sized cubes and work out surface area to volume ratio. Time how long it takes each cube to go colourless when placed in the same concentration of HCl. You would expect the cubes with the largest surface area to volume ratio to go colourless fastest
64
How would you see how concentration gradient affects diffusion?
Prepare test tubes containing different concentrations of HCl. Put an equal-sized cube of agar jelly in each test the and time how long it takes each one to turn colourless. You would expect cubes in the highest concentration of HCl to go colourless fastest
65
How would you see how temperature affects diffusion?
Prepare several boiling tubes containing same concentration of HCl acid and put tubes into water baths of varying temperatures. Put equal-sized cube of agar jelly into each boiling tube and time how long it takes each cube to go colourless. You would expect the cubes in the highest temperature to go colourless fastest.
66
What mustn't you do with the temperature one?
Increase it to above 65 degrees or the agar jelly will start to melt
67
Can all molecules diffuse directly through phospholipid bilayer of the cell membrane?
No some larger molecules e.g. Amino acids, glucose, ions and polar molecules don't diffuse directly though phospholipid bilayer of the cell membrane
68
How do larger molecules, ions and polar molecules get through then?
They diffuse through carrier proteins or channel proteins in the cell membrane (facilitated diffusion)
Like diffusion facilitated diffusion moves particles down a concentration gradient
Passive process so doesn't use energy
69
What do carrier proteins do?
Move large molecules into or out of the cell down their concentration gradient. Different carrier proteins facilitate diffusion of different molecules.
70
How does a carrier protein work?
Large molecule attached to a carrier protein the membrane
Then the protein changes shape
This releases the molecule on the opposite side of the membrane
71
What do channel proteins do?
Form pores in the membrane for charged particles to diffuses through (down the concentration gradient). Different channel proteins facilitate the diffusion of different charged particles
72
What does active transport do?
Uses energy to move molecules and ions across plasma membrane against a concentration gradient which involved a carrier protein
73
How is active transport and facilitated diffusion similar?
A molecule attaches to the carrier protein m, the protein changes shape and this moves the molecule across the membrane releasing it on the other side
74
What's the difference between active transport and facilitated diffusion?
Active transport uses energy from ATP to move the solute against its concentration gradient while facilitated diffusion doesn't require energy
75
What happens when a huge molecule needs to get in?
It can't be taken into a cell by carrier protein so endocytosis happens
76
Endocytosis?
Cell surrounds substance with a section of its plasma membrane
The membrane pinches off to form a vesicle inside the cell containing the ingested substance
77
What do some cells also do to do with endocytosis?
Take in larger objects by endocytosis e.g. Some white blood cell mainly phagocytes use endocytosis to take in things like microorganisms and dead cells so that they can destroy them.
78
What does endocytosis need?
ENERGY
79
Why is exocytosis needed?
Some substances prodded by the cell (e.g. Digestive enzymes, hormones, lipids) need to be released from the cell
80
How does exocytosis happen?
Vesicle containing these substances pinch off from the sacs of the Golgi appartus and move towards the plasma membrane.
The vesicles fuse with plasma membrane and release their contents outside the cell.
81
Do all the stuff from exocytosis get put outside the cell?
No some substances aren't released outside the cell instead they are inserted straight into the plasma membrane.
82
What does exocytosis need?
ATP for an energy source
83
What's osmosis?
Diffusion of water molecules across a partially permeable membrane down a water potential gradient meaning water molecules move from an area of higher water potential to an area of lower water potential
84
What is water potential?
The potential of water molecules to diffuse out of or into a solution
85
What has the highest water potential?
Pure water
| All solutions have a lower water potential than pure water
86
How does water move in and out of a cell and how is it determined how much moves in and out?
Water moves in and out of a cell via osmosis
How much it moves in or out depends on the water potential of the surrounding solution. Animal and plant cells behave differently in different solution
87
Hypotonic means?
Solution with high water potential than cell
88
Isotonic means?
Solution with the same water potential
89
Hypertonic means?
Solution with a lower water potential than the cell.
90
Animal cell in hypotonic solutions?
Net movement of water molecules is into the cell. Cell bursts.
Lysed
91
Animal cell in isotonic solution?
Water molecules pass into and out of the cell in equal amounts. The cell stays the same.
92
Animal in hypertonic solution?
Net movement of water molecules is out of the cell. The cell shrinks
93
Plant cell hypotonic solution?
Net movement of water is into the cell. Vacuole swells. Vacuole and cytoplasm push against the cell wall.
Turgid cell
94
Isotonic plant cell
Water molecules move into and out of the cell in equal amounts. The cell stays the same
95
Hypertonic solution
Net movement of water is out of the cell. Cell becomes flaccid. The cytoplasm and the membrane pulls away from the cell wall.
Plasmolysis
96
How can you find out the water potential of plant tissue?
Do a simple experiment using potato cylinders
97
Experiment to investigate water potential involves?
Putting potato cylinders into different concentrations of sucrose solution- the higher the sucrose concentration the lower the water potential
98
Step 1 of experiment to investigate water potential?
Prepare sucrose solutions of 0.0M, 0.2M,0.4M, 0.6M, 0.8M, 1.0M
M written as mol dm-3
99
Step 2 of experiment to investigate water potential?
Use cork borer or chip maker to cut potatoes into the same sized pieces (need to about 1cm in diameter)
100
Step 3 of experiment to investigate water potential?
Divide chips into groups of 3 and use mass balance to measure mass of each group
Place one group in each solution
101
Step 4 of experiment to investigate water potential?
Leave chips in solution for as long as possible (making sure that they all get the same amount of time). Try to leave them for at least 20 minutes
102
Step 5 of experiment to investigate water potential?
Remove chips and pat dry gently with a paper towel
Weigh each group again and record your result
Calculate % change in mass for each group
103
Step 6 of experiment to investigate water potential?
Plot your results on a graph
The point where water potential of sucrose is the same as the water potential is on the X-axises crossing with the best fit line
104
If you could see the potato cell under a microscope what would you see?
Them becoming turgid as chips gain mass and plasmolysed as chips loss mass
105
What can you do a similar experiment with?
Chicken eggs that have had their shells dissolved. The remaining membrane is partially permeable so a good model for showing the effects of osmosis in animal cells.🐥🐥🐥🐥🐥🐥🐥🐥🐥
🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥🐥
