Transport Across Membranes Flashcards
1
Q
What are lipids made up of?
A
C, H, O
2
Q
What can lipids exist as?
A
Fats, waxes, oils
3
Q
How are triglycerides formed?
A
By esterification three times
4
Q
What is esterification?
A
A condensation reaction between 3 fatty acids and 1 glycerol
5
Q
Functions of lipids? (6)
A
- protection of vital organs
- to prevent evaporation in plants and animals
- insulation on the body
- as a water source
- they form the myelin sheath around some neurones
- as a component of cell membranes
6
Q
What two chemicals combine to form a lipid?
A
A
7
Q
What elements are found in lipids?
A
C, H, O
8
Q
What is the chemical difference between saturated and unsaturated fats?
A
A
9
Q
What is the biological importance of unsaturated fats?
A
A
10
Q
Name one unsaturated fat
A
A
11
Q
Why could a fat free diet kill you?
A
A
12
Q
What do omega 3 oils do for you?
A
A
13
Q
Name a good source of omega 3 oils
A
Fish
14
Q
Functions of a membrane? (6)
A
- selectively permeable barrier
- structural, keeping the cell contents together
- allows communication with other cells
- allows recognition of other external substances
- allows mobility of some substances (eg amoeba)
- the site of various chemical reactions
15
Q
Are lipids soluble or insoluble in water?
A
Insoluble
16
Q
How do substances cross the concentration gradient in diffusion?
A
Down the concentration gradient
17
Q
Why do organisms need energy?
A
-
18
Q
Define diffusion
A
The net movement of particles from an area of high concentration to low concentration - down a concentration gradient.
19
Q
Does diffusion require energy?
A
No
20
Q
What is simple diffusion?
A
Where molecules move directly through a cell membrane
21
Q
How would big molecules such as glucose, amino acid affect diffusion?
A
They would diffuse very slowly through the phospholipid belayer because they’re so big
22
Q
Why would charged molecules (eg ions / polar molecules) diffuse slowly?
A
Because they’re water soluble and the centre of the bilayer is hydrophobic
23
Q
Does facilitated diffusion require energy?
A
No, it’s a passive process.
24
Q
What do carrier proteins do?
A
They move large molecules across the membrane, down their concentration gradient.
25
Why are there so many carrier proteins?
Because different carrier proteins facilitate the diffusion of different molecules
26
Explain how a carrier protein works. (3)
1. A large molecule attaches to a carrier protein in the membrane.
2. Then, the protein changes shape.
3. This releases the molecule on the opposite side of the membrane.
27
What do channel proteins do?
They form pores in the membrane for charged molecules to diffuse (down the concentration gradient)
28
What 3 things affect simple diffusion?
- concentration gradient
- thickness of the exchange surface
- surface area
29
How does the concentration gradient affect simple diffusion?
The greater the convent ration gradient, the greater the rate of diffusion.
However, this slows over time when the difference in concentration between the two sides of the membrane reaches an equilibrium.
30
How does the thickness of the surface affect simple diffusion?
The thinner the exchange surface, the faster the rate of diffusion.
Thinner exchange surface = the shorter the distance the particles have to travel
31
Why would the surface area affect simple diffusion?
The larger the surface area, the faster the rate of diffusion
32
What does facilitated diffusion depend on?
- the concentration gradient
| - the number of channel or carrier proteins
33
At what point might facilitated diffusion stop happening any faster?
When all of the carrier and channel proteins are in use
34
What does water potential mean?
The likelihood of water to diffuse into or out of a solution.
35
What has the highest water potential?
Pure water
36
If two solutions have the same waste potential, what is it called?
Isotonic
37
What are the two differences between active transport and facilitated diffusion?
1. Active transport requires energy unlike facilitated diffusion
2. Active transponer moves solutes from low to high, whereas facilitated diffusion is high to low concentration
38
Co-transporters are a type of...
Carrier protein
39
What factors affect the rate of active transport?
- the speed of individual carrier proteins
- the number of carrier proteins present
- rate of respiration in the cell (and the availability of ATP)
40
By which process do sodium ions move into the blood?
Active transport
41
Sodium ions are moved from the (where)? into the blood?
Ilium epithelial cells
42
If the concentration of some ions is measured inside cells, it is often found that they are 20-30 times more concentrated than outside the cell. What does this mean?
Cells cannot make ions, suggesting that they must be able to move against the concentration gradient.
This requires energy and therefore this process is active.
43
Why is energy required in active transport?
To allow the carrier proteins (in cell membrane) to act as molecular pumps to transport molecules into / out of cells
44
How is active transport inhibited?
Things that prevent respiration will therefore prevent active transport eg:
- lack of oxygen
- respiratory inhibitors
45
Why do organisms require energy?
- metabolism
- movement
- maintaining body temperature
- producing substances (eg enzymes / hormones)
- active transport
- maintenance, repair and division of cells
46
Diffusion is ______ the concentration gradient
Down
47
Define osmosis
The net movement of water molecules from a solution with a higher to lower water potential, through a selectively permeable membrane.
48
Active transport is a provees by which a cell takes up a substance ______ a concentration gradient
Against
49
In a plasma membrane what do phospholipids do?
Form a bilayer
50
What are the functions of the phospholipids in the plasma membrane?
- allow lipid soluble substances to enter and leave the cell
- prevent water soluble substances from entering / leaving
- make the membrane flexible and self healing
51
In the plasma membrane, where are proteins found?
They're embedded in the phosopholipid bilayer
52
What are protein channels?
They form water filled tubes to allow water soluble ions to diffuse across the membrane.
53
What are the the functions of proteins in the membrane?
- provide structural support
- act as channels transporting water soluble substances across the membrane
- allow active transport across the membrane through carrier proteins
- act as receptors
- help cells adhere together
54
Where are cholesterol molecules found in the plasma membrane?
Within the phospholipid bilayer of the cell surface membrane
55
Cholesterol molecules are very hydrophobic. What does this result in?
They play an important role in preventing water loss and dissolved ions from the cell.
56
What are the functions of cholesterol in the cell surface membrane?
- reduce lateral movement of other molecules including phospholipids
- make them membrane less fluid at high temperatures
- prevent leakage of water and dissolved ions from the cell
57
What are glycolipids made of?
A carbohydrate covalently bonded with a lipid.
58
What are the functions of glycolipids in a cell surface membrane?
- act as a recognition site
- helps maintain the stability of the membrane
- helps cells to attach to one another and so form tissues
59
What are glycoproteins?
Carbohydrate chains attached to many extrinsic proteins on the outer surface of the cell membrane
60
What are the functions of glycoproteins on the cell surface membrane?
- act as recognition sites
- help cells to attach to one another and so form tissues
- allow cells to recognise one another
61
Why does the fluid mosaic model contain the term 'fluid'?
Because the individual phospholipid molecules can move relative to one another.
This gives the membrane a flexible structure that is constantly changing shape.
62
Why does the fluid mosaic model contain the term 'mosaic'?
Because the proteins that are embedded on the phospholipid bilayer vary in size, shape and pattern in the same way as a mosaic.
63
How does osmosis pass the concentration gradient?
DOWN
64
How does active transport cross the concentration gradient?
AGAINST
65
Define osmosis
Water travels by osmosis from an area of high water potential to an area of low water potential, down the concentration gradient.
66
How many heads and tails does a phospholipid have?
1 head
| 2 tails
67
What do carrier proteins bind to?
Ions or molecules like glucose or amino acids
68
How do cholesterol molecules limit the movement of the phospholipids?
They pull together the fatty acid tails of the phospholipids
69
Give an example of the use of glycolipids.
The human ABO blood system operates as a result of glycolipids pm the cell surface membrane
70
In osmosis, the solute and water molecules move in random motion due to...
Kinetic energy
71
Define rate of diffusion.
The amount diffused through the surface
/
Divided by the time taken.
72
What does the ate of diffusion depend on?
- temperature
- SA
- concentration gradient on either side of the exchange surface
- thin exchange surface
73
Explain temperature as a factor that affects rate of diffusion.
Molecules move faster in higher temperatures.
So the higher the temperature, the faster the rate of diffusion.
74
Explain surface area as a factor that affects the rate of diffusion.
The greater the surface area of the exchange area, the faster the total rate of diffusion.
75
Explain the difference in concentration on either side of the exchange surface as a factor that affects rate of diffusion.
The greater the difference in concentration on either side of the exchange surface, the faster the rate of diffusion.
76
Example of the body affecting the concentration gradient on either side of the exchange surface?
In the intestine, the blood is continual,y transporting the products of digestion away from the intestine wall. This ensures a greater concentration gradient and a faster rate of diffusion.
77
Explain a think exchange surface as a factor affecting the rate of diffusion. Example?
Diffusion is only efficient over very short distances. Exchange surfaces such as the epithelium of the intestine are only one cell thick.
78
In diffusion, particles of the substance diffuse _____ a concentration gradient.
Down.
79
In diffusion, why do particles of a substance diffuse down a concentration gradient?
Because they molecules are moving from an area of high concentration to an area of low concentration.
80
What causes the movement of molecules in diffusion?
Kinetic energy that the molecules possess
81
Surfaces through which diffusion takes place are called...
Exchange surfaces.
82
What type of molecule cannot pass directly through the phospholipid bilayer of a cell surface membrane?
Large, water soluble molecules eg glucose.
83
How do larger, water soluble molecules e.g. glucose pass through the phospholipid bilayer of a cell surface membrane?
Through carrier protein in the membrane.
84
How do carrier proteins work in facilitated diffusion?
1. Carrier proteins have a binding site on their surface, which has a specific shape so only certain molecules can fit to it.
2. The diffusing molecules bind to a carrier protein, and the protein changes shape and takes the molecules through the membrane.
85
Why might a particular cell take up some substances but not others?
Because carrier proteins have binding sites which only certain molecules will fit into - other molecule cannot therefore enter the cell.
86
What are channel proteins in facilitated diffusion?
Proteins that have a water filled centre which water soluble materials and ions can diffuse through.
87
Why is facilitated diffusion described as a passive process?
Because it does not require hydrolysis of ATP from respiration.
88
In facilitated diffusion, what do channel proteins do?
Help with the diffusion of ions. Some ion channels have gates that open or close.
89
Does pure water have the highest or lowest water potential?
Pure water has the highest water potential.
This is because it has the greatest number of water molecules in a given volume present (as nothing else is present).
90
What does selectively permeable mean?
A cell surface membrane that allows small molecules (e.g. water to pass through, but not larger moe
Culés.
91
What happens if you put an animal cell into a solution with a lower water potential than the cell?
There will be a net movement of water out of the cell and it will shrink in size.
92
What happens if you were to place a plant cell in a solution of lower water potential than the cell?
The cell membrane and its contents will shrink away from the cell wall.
So, the gal between the cell membrane and cell wall will be filled with external solution.
93
What happens if an animal cell is placed in a solution with a higher water potential than the cell?
It will take in water by osmosis and swell up. Eventually it will burst.
94
What happens if you place a plant cell in a solution of higher water potential than the cell?
The plant cell will take in water by osmosis, and will swell up to become firm. However, it will not burst because ether cell wall acts as a protective cage around it - stopping it increasing in volume excessively.
95
Active transport takes up a substance _______ the concentration gradient.
Against
96
Difference between active transport and facilitated diffusion?
Active transport requires external energy in the form of ATP which is produced during respiration. But facilitated diffusion is a passive process.
Active transport is the process by which a cell takes up a substance AGAINST a concentration gradient, but facilitated diffusion is the process by which particles of a substance diffuse DOWN a concentration gradient.
97
Outline the co-transport of glucose from the ilium.
1. Sodium ions are actively transported out of the epithelial cells, by the S-P pump, and into the blood by a protein carrier molecule.
2. This maintains a higher conc. sodium ions in the lumens than inside the epithelial cells.
3. Sodium ions can then diffuse into epithelial cells down the conc. gradient through a co-transport protein. As the Na+ diffuses through, they carry amino acids / glucose with them.
4. The AA / glucose pass into the blood plasma by facilitated diffusion.
98
Similarities between glycolipids and glycoproteins?
They both act as recognition sites.
| They also help cells to attach to one another and so form tissues.
99
What is the basic structure of all cell membranes?
Composed of lipids (mainly phospholipids), proteins and carbohydrates.
100
Why is the fluid mosaic model called 'fluid'?
Because the individual phospholipid molecules can move relative to one another.
Thus giving the membrane a flexible structure that's constantly changing shape.
101
Why is the fluid mosaic model called mosaic?
Because the proteins embedded in the phospholipid bilayer vary in shape, size and pattern in the same way as the tiles in a mosaic.
102
Phospholipid molecules have a hydrophilic head. Outline this in the cell membrane.
The head attracts water.
| So both heads point to the outside of the cell surface membrane.
103
Phospholipid molecules have a hydrophobic tail. Outline this in the cell membrane.
The tail repels water.
So the tails point into the centre of the cell membrane. And doesn't allow water-soluble substances (e.g. ions) through it.
104
What are the three main functions of phospholipids in the membrane?
- prevent water soluble substances entering and leaving
- allow lipid soluble substances to enter and leave the cell
- make the membrane flexible and self sealing
105
In hat ways are proteins embedded in the phospholipid bilayer?
- some occur in the surface to act as mechanical support. Or, in conjunction with glycolipids, act as cell receptors for molecules eg hormones.
- other proteins span the phospholipid bilayer (one layer to the other). Some are protein channels (which form water filled tubes to allow water soluble substances to diffuse across membrane).
Others are carrier proteins (that bond to ions / molecules eg AA, then change shape in order to move these molecules across the membrane).
106
What are the functions of protein in the membrane? (6)
- provide structural support
- act as channels (transporting water soluble substances across membrane)
- form cell surface receptors for identifying cells
- act as receptors eg hormones
- help cells adhere together
- allow active transport across membrane through carrier proteins
107
Where are cholesterol molecules found in the cell surface membrane?
Within the phospholipid bilayer
108
What are the functions of cholesterol in the membrane?
- make membrane less fluid at high temps
- prevent leakage of water / dissolved ions from cells
- reduce lateral movement of other molecules including phospholipid
109
Glycolipids are found in the cell surface membrane. But what are they?
A carbohydrate covalently bonded with lipid.
110
Give an example of a glycolipid in action.
Human ABO system - the carb portion extends from phospholipid bilayer into the watery environment outside the cell where it acts as a cell surface receptor for specific chemicals.
111
Give the three functions of glycolipids.
- acts as recognition sites
- helps maintain the stability of the membrane
- helps cells attach to one another and so form tissues
112
Glycoproteins are found on the cell surface membrane. But what are they?
Carbohydrate chains attached to extrinsic proteins on the outer surface of the cell membrane.
113
What are the similarities between the functions of glycoproteins and glycolipids?
- both act as recognition sites
| - both help cells to attach to one another and so form tissues.
114
What are the differences in function of glycoproteins and glycolipids?
Glycolipids help maintain the stability of the membrane.
Glycoproteins Llow cells to recognise one another (eg lymphocytes can recognise an organism's own cells) because they're attached to extrinsic proteins on the outer surface of cell membrane.
115
What are the functions of membranes within cells?
* control entry / exit of materials in discrete organelles eg mitochondria
* separates organelle from cytoplasm so that specific metabolic reactions can take place within them.
* provides internal transport system.
* provides surfaces upon which reactions can occur e.g. protein synthesis using RER.
* isolates enzymes that might damage the cell eg lysosomes.
116
Why don't most molecules diffuse freely across the cell-surface membrane?
- too large to pass through channels in membrane
- no soluble in lipids, so can't pass through phospholipid bilayer
- of the same charge as the charge of protein channels, and so are repelled
- electrical charged (aka polar molecules), therefore have difficultly passing through the non-polar hydrophobic tails in bilayer.
117
Why isn't a cell surface face membrane very permeable at temps below 0*C?
Because phospholipids don't have much energy, so can't move much. They're packed close together so membrane is rigid.
118
Why is a cell surface membrane very permeable at temps above 45*C?
The phospholipid bilayer starts to melt (break down), so membrane becomes more permeable. Water inside the cell expands, putting pressure on the membrane - therefore channel and carrier proteins deform so can't control what enters or leaves the cell.
119
Define diffusion.
The net movement of molecules / ions from a region of high conc to low conc.
Down the conc gradient.
120
Is diffusion passive or active? Why?
Passive - it requires no energy. The particulars move by the kinetic they possess.
