Enzymes And Membranes Oops Flashcards
1
Q
What is a biological catalyst?
A
- A protein that speeds up a metabolic reaction without being used up in the reaction.
2
Q
What is an intercellular enzyme?
A
- An enzyme which works within cells.
- E.g catalase which catalyses the breakdown of hydrogen peroxide into oxygen and water.
3
Q
What is an extracellular enzyme?
A
- An enzyme which works outside cells.
- Eg Amylase works in the saliva and catalyses the hydrolysis of starch into maltose in the mouth
- Eg Trypsin is produced in the pancreas and deferred into the small intestine, it catalyses the hydrolysis of peptide bonds.
4
Q
How to enzymes speed up reactions?
A
- They reduce the amount of activation energy that’s needed meaning reaction can occur at lower temperatures speeding up the rate of reaction.
5
Q
‘The Lock and key’
A
- Substrates fit into tenedume in the same way a key fits into a lock.
- The active site and substrate have a complementary shape.
- However, scientists soon realised that the enzyme-substrate complex changed shape slightly to complete the fit.
6
Q
The ‘induced fit’ model.
A
- The substrate approaches he active site.
- The substrate binds to the active site is complementary to.
- This slightly changes the shape of the active site.
- Enzyme-substrate complex is formed.
- The substrate is then broken down into products.
- Enzyme-product complex is formed.
- The products then move away from the active site.
7
Q
How does enzyme concentration affect enzyme activity?
A
-the rate of reaction increases as enzyme concentration increase -
there are more active sites for substrates to bind to.-
however increasing the enzyme concentration beyond a certain point has no effect on the rate of reaction.
- there are more active sites than substrates so substrate concentration becomes the limiting factor
8
Q
How does substrate concentration affect enzyme activity?
A
- as concentration of substrate increases, rate of reaction increases
- more enzyme-substrate complexes are formed.
- However, beyond a certain point the rate of reaction no longer increases as enzyme concentration becomes the limiting factor
9
Q
How does temperature affect enzyme activity?
A
- rate of reaction increases up to the optimum temperature,
- which is the temperature at which enzymes work at their maximum rate.
- Rate of reaction decreases above the optimum temperature.
- Enzymes denature.
10
Q
How does PH affect enzyme activity?
A
- Each enzyme has an optimum pH range.
- Changing the pH outside of this range will slow enzyme activity.
- Extreme pH values can cause enzymes to denature.
11
Q
What does the temperature coefficient show?
A
- How much the rate of reaction changes when the temperature is raised by 10*c.
12
Q
How to draw a tangent to estimate the initial rate of reaction
A
- Draw a tangent at t=0.
- Calculate the gradient of the tangent (change in y/change in x).
- Workout the unit, units of y/units of x.
13
Q
What is a coenzyme?
A
- organic cofactors which do not bind permanently to the enzyme.
- They facilitate the binding of substrate to enzyme.
14
Q
What is a cofactor?
A
- a non-protein compound required for the enzyme’s activity to occur.
- There are three types of cofactors: coenzymes, activators and prosthetic groups.
15
Q
What is an activator?
A
- inorganic metal ions which temporarily binds to the enzyme
- This alters the shape of the active site.
- Which makes the reaction more feasible.
16
Q
Where are phosphetic groups?
A
A cofactor which permanently binds to the enzyme.
17
Q
What is an inhibitor and what are the two types?
A
a -substance which slows down or stops a reaction by affecting the binding of substrate to the enzymes.
- Inhibitors can either be reversible and irreversible.
18
Q
What does an irreversible inhibitor do?
A
- cause disulphide bonds within the protein structure to break
- causing the shape of the active site to change
- affecting protein activity.
19
Q
What do Reversible inhibitors do? And what’s are the two types?
A
- They bind to the active site through hydrogen bonds and weak ionic interactions therefore they do not bind permanently.
- Reversible inhibitors can either be competitive or non-competitive.
20
Q
What do competitive inhibitors do?
A
- They are similar in structure to the substrate molecule
- Therefore they bind to the active site of the enzyme,
- This decreases it’s activity as they compete with substrate for the enzyme.
- The amount of product formed remains the same.
However the rate at which product formation occurs decreases. - The higher the concentration of competitive inhibitor the lower the reaction rate.
- Increasing the substrate reverses the effect of competitive inhibitors by outcompeting them.
21
Q
What do Non-Competitive inhibitors do?
A
- They bind to a site on the enzyme known as the allosteric site.
- This changes the shape of the active site therefore preventing the binding of the substrate.
- Increasing the concentration of substrate has no effect on non-competitive inhibition.
22
Q
Which bond is required for the inhibition to be irreversible?
A
Covenant bonds
23
Q
Which bond is required for inhibitor to be reversible?
A
- hydrogen or weaken ionic bonds.
24
Q
Types of drugs which are enzyme inhibitors
A
- penicillin which is used to fight bacterial infections,
- it is an inhibitor of enzyme transpeptidase which plays an important role in cell wall formation.
25
What is a metabolic poison?
- They interfere with metabolic reaction causing damage, Illness of death.
- There are often enzyme inhibitors.
26
Example of metabolic poison.
- Malonare is a competitive inhibitor of succumate dehydrogenase which catalyses the respiration reactions.
27
What is end-products inhibition?
- When the final product in a metabolic pathway inhibits an enzyme that acts earlier on the pathway.
28
What is product inhibition?
- When each reaction is catalysed by a different enzyme.
29
Phospholipids.
- Hydrophilic head and hydrophobic tail meaning they automatically arrange themselves into a bilayer.
- Centre of bilayer is hydrophobic so doesn’t allow water-soluble substances (ions) to pass through it.
30
Cholesterol
- A type of lipid.
- Binds to the hydrophobic tail of the phospholipids.
- This causes them to pack more closely together.
- This makes the membrane less fluid and more rigid.
31
Glycolipids and glycoproteins
- They stabilise the membrane by forming hydrogen bonds with surrounding water molecules.
- They act as receptors for cell signalling.
- They also act as antigens.
32
Factors affecting membrane permeability
- Temperature
| - Solvent
33
Membrane permeability when temp is below 0*c.
- Phospholipids don’t have much energy so they can’t move much.
- they’re pack closely together and the membranes is rigid.
-
34
Membrane permeability when temp is between 0 and 45*c
- phospholipids can move and aren’t packed as tightly together.
- Membrane is partially permeable.
- As the temperature increase, phospholipids move more because they have more energy.
- This increase the permeability of the membrane.
35
Membrane permeability when temperature is above 45*c
- Phospholipid nils her start to melt and the membrane becomes more permeable.
- Channel and carrier proteins deform so they can’t control what enter and leaves the cell this increase the permeability of the membrane.
36
How do solvents affect membrane permeability?
- Ethanol is a non-polar solvent so it is able to dissolve non-polar substances such as lipids.
- This means that if you place a cell in ethanol, its membrane will become permeable and allow substances to leak into and out of the cell.
- As the ethanol concentration increases, membrane permeability will increase.
- If the ethanol concentration is high enough, enough phospholipids will dissolve to cause the plasma membrane to disintegrate completely which will kill the cell.
37
How to investigate the permeability of a cell membrane
- Cut 5 equal sized pieces of beetroot and rinse them to remove any pigment released during cutting.
- Place pieces in separate test tubes each with 5cm3 of water.
- Place each test tube in a water bath at a different temperature for the same length of time.
- Remove the pieces of beetroot from the tubes leaving just the coloured liquid.
- Use a colorimeter to work out the permeability, the higher the permeability, the higher the absorbable of the liquid.
-
38
Diffusion
- passive movement (doesn’t require energy)
- small, non-polar lipid soluble molecules such as carbon dioxide and oxygen.
- from an area of high concentration to an area of low concentration.
- The molecules move directly through the phospholipid bilayer.
39
Facilitated diffusion
- Net movement of particles from an area of high concentration to an area of lower concentration.
- Uses carrier proteins to aid diffusion of larger molecules.
- Uses channel proteins to aid the diffusion of smaller ions.
- Passive procces (doesn’t require energy).
40
- Osmosis
- The net movement of water molecules
- from an area of high water potential to and area of low water potential.
- Through a partially permeable membrane.
- Passive process (doesn’t require energy).
41
Active transport
- Movement of molecules against a concentration gradient.
- Uses carrier proteins to transport molecules.
- Active process (It requires ATP.)
42
Exocytosis
- Movement of molecules out of a cell.
- Vesicles fuse with the plasma membrane and release their contents.
- Active process (requires ATP).
43
The rate of gas exchange by diffusion becomes more rapid as…
. Surface area of the surface increases
. Diffusion distance decreases
. Diffusion gradient becomes more steep
44
What are isotonic solutions?
- When two solutions have the same water potential.
- Means there will me no net movement of water.
- No cells in an isotonic solution will lose or gain any water
45
What are Hypotonic solutions?
- Solutions with a higher water potential than inside the cell.
- Means water will move into the cell
- Animal cell will swell and eventually burst, plant cell will become turgid.
46
Hypertonic solutions
- When the cell has a higher water potential than the solution.
- Water will move out of the cell by osmosis.
- Animal cell would shrink and plant cell would become flaccid.
47
How to investigate her effect of water potential on plant cells.
- Prepares sucrose solution with different concentrations.
- Use a cork borer to cut potatoes into identically sized cylinders.
- Divide the cylinders into groups of 3 and measure the mass of each group using a mass balance.
- Place on group into each of the sucrose solutions.
- Leave the cylinders in the solution for 20 minutes.
- Remove the cylinders and dry them with a paper towel.
- Weigh each group again and record the results.
- Calculate the percentage change in ms for each group.
48
Endocytosis
- Movement of large molecules into a cell.
| - Active process (requires ATP)
