1
Q
What are enzymes?
A
- biological catalysts
- globular proteins
- interact with substrate molecules increasing the rate of reaction without the need for harsh environments.
2
Q
What are the roles of enzymes?
A
- synthesis of large-polymer based components e.g. cellulose forms the walls of plant cells
- anabolic (building up) and catabolic (breaking down) reactions
- digestion
- metabolism
3
Q
What is meant by Vmax?
A
Maximum velocity or rate at which enzymes catalyse a reaction. Happens when all active sites are saturated with substrate.
4
Q
What is the specificity of the enzyme?
A
- when many different enzymes are produced by living organisms, as each enzyme catalyses one biochemical reaction, of which there are thousands in any given cell.
5
Q
How do enzymes work?
A
- molecules in a solution move and collide randomly. For a reaction to happen they need to collide in the right orientation.
- energy needs to be provided for the reaction to start. This is activation energy.
- enzymes help the molecules collide successfully and therefore reduce the amount of activation energy required.
6
Q
What is the lock and key hypothesis?
A
- area of enzyme complementary to specific substrate molecule. This area is called the active site.
- when substrate is bound to active site an enzyme-substrate complex is formed
- they then react and the products are formed in an enzyme product complex
- products released leaving enzyme unchanged and able to react again
7
Q
How does the enzyme help a reaction take place?
A
- substrate is held by the enzyme so atom-groups are close enough to react.
- R-groups within the active site will also interact with the substrate forming temporary bonds that put a strain on the bonds within the substrate which helps the reaction proceed.
8
Q
What is the induced fit hypothesis?
A
- active site of the enzyme changes shape slightly as the substrate enters
- initial interaction between enzyme and substrate is relatively weak
- but these interactions rapidly induce changes in the enzyme’s tertiary structure that strengthen binding, putting strain on the substrate
- can weaken bonds in the substrate therefore lowering the activation energy for the reaction
9
Q
What are intracellular enzymes?
A
enzymes that act within cells
10
Q
Describe the production and release of extracellular enzymes
A
- protein made on RER
- protein packaged into transport vesicles
- vesicles move to golgi apparatus via cytoskeleton
- vesicles fuse with cis face of golgi as protein enters
- protein modified into specific 3D enzyme shape
- released from golgi trans face in secretory vesicle
- fuse with cell surface membrane
- enzymes released by exocytosis
11
Q
What are extracellular enzymes?
A
- work outside the cell that made them
- break down large nutrient molecules into smaller molecules in the process of digestion
- e.g. in humans amylase and trypsin
12
Q
What is the first step of digesting starch?
A
- starch polymers are partially broken down into maltose, which is a disaccharide
- enzyme involved is amylase
- amylase is produced by the salivary glands (saliva in mouth) and the pancreas (pancreatic juice in small intestine)
13
Q
What is the second step of digesting starch?
A
- maltose is broken down into glucose, which is a monosaccharide
- enzyme involved is maltase
- maltase is present in the small intestine
- glucose small enough to be absorbed by cells lining digestive system and so absorbed into bloodstream
14
Q
How do we digest protein?
A
- pepsin (protease produced by stomach wall) breaks proteins down into shorter peptide chains
- trypsin (protease produced by pancreas and released with pancreatic juice into the small intestine) produces even smaller chains
- other proteases break these down into amino acids which are then absorbed into the bloodstream
15
Q
Explain how catabolism and anabolism are related to metabolism
A
- catabolism is the breaking down of molecules
- anabolism is the building of molecules
- reactions include both and metabolism is the sum of these reactions
16
Q
Why have the models of enzyme action changed over time?
A
- improved technology
- continually investigated
- more evidence, so more accurate representation
17
Q
How does temperature increase the rate of reaction?
A
- more heat more kinetic energy
- more successful collisions between enzymes and substrates
- more ESC/EPC/product produced
18
Q
How does temperature denature the enzyme?
A
- more vibrations within molecules
- breaking hydrophilic and hydrophobic interactions, hydrogen and ionic bonds
- tertiary structure changes
- enzyme then denatures after optimum temperature
- substrate no longer complementary to shape of active site
19
Q
What is meant by Q10 (temperature coefficient)?
A
- The amount the rate of reaction increases when temperature is raised by 10c
- enzymes have a Q10 of 2 (this means the rate of reaction doubles for every 10C rise in temperature)
20
Q
What is the equation for Q10?
A
Q10 = rate of reaction at (T + 10C) / rate of reaction at TC
21
Q
How would you expect thermophile enzyme structure to differ from ours?
A
- more disulphide bridges that are less likely to break under high temperatures
- more cysteine amino acids in primary structure to form more strong disulphide bridges
- means active site less likely to denature
22
Q
Why are there different enzymes in different parts of the digestive system?
A
- enzymes have different optimum pas
- conditions are changing as enzymes are needed
- molecules have changed shapes through digestive system also
23
Q
How can ph affect enzyme structure?
A
- deviation away from optimum ph (H ion concentration)
alters enzyme structure by interfering with the hydrogen bonds and ionic bonds between R-groups - proteins can renature when ph returns to optimum as long as deviation wasn’t too significant
24
Q
Enzymes with low optimum temperatures tend to have flexible structures. Why is this necessary?
A
- at low temperatures kinetic energy is low
- substrates/enzymes move slowly so fewer collisions
- collisions have less energy increasing flexibility of active site
- so increases chance of successful collision
25
How does increasing substrate concentration affect the rate of reaction?
- higher collision rate with the active site of enzymes and the formation of more enzyme substrate complexes.
- rate of reaction therefore increases.
26
What are inhibitors?
- molecules that prevent enzymes from carrying out their normal function of catalysis (or slow them down).
- two types of inhibition: competitive and non-competitive
27
How does competitive inhibition work?
- Competitive inhibitor interferes with active site of enzyme so substrate can’t bind
- The substrate and the competitive inhibitor compete for the active site, reducing the number of ESC’s made in a given time, slowing the rate of reaction.
- Binding is normally temporary, so effect is reversible (aspirin is an exception)
28
What will determine the degree of inhibiton?
- relative concentrations of enzyme, substrate and the inhibitor
29
How does a competitive inhibitor effect the rate of reaction?
- reduces it for a given concentration of substrate
- does not change the Vmax of the enzyme it inhibits
- if substrate concentration is increased enough there will be so much more substrate than inhibitor that the original Vmax can still be reached.
30
How do statins work as competitive inhibitors?
- inhibit enzyme used in the synthesis of cholesterol
| - statins prescribed to reduce blood cholesterol concentration as high concentration can result in heart disease.
31
How do aspirins work as competitive inhibitors?
- irreversibly inhibits the active site of COX enzymes, preventing the synthesis of prostaglandins and thromboxane, the chemicals responsible for producing pain and fever.
32
What is non-competitive inhibition?
- Inhibitor binds to a region other than the active site (an allosteric site)
- Causes tertiary shape of the enzyme to change shape, so active site changes shape
- Substrate no longer complementary to the active site
- Enzyme therefore inhibited
33
How does a non-competitive inhibitor effect the rate of reaction?
- increasing concentration of substrate or enzyme will not overcome effect of a non-competitive inhibitor.
- increasing concentration of the inhibitor will decrease the rate of reaction further as more active sites become unavailable.
34
What are examples of irreversible, non-competitive inhibitors?
- Usually toxic
- Organophosphates (insecticides and herbicides) inhibit acetyl cholinesterase, an enzyme necessary for nerve impulse transmission. Can lead to paralysis or death.
- Proton pump inhibitors (PPI’s), used to treat long term indigestion, block a system used to secrete H+ into the stomach. Makes PPIs effective in reducing production of excess acid, which if left untreated can lead to formation of stomach ulcers.
35
What is end-product inhibition?
- term used for enzyme inhibition that occurs when the product of a reaction acts as an inhibitor to the enzyme that produces it.
- serves as a negative feedback control mechanism for the reaction: excess products not made and resources not wasted.
36
What is an example of end-product inhibition?
- The ATP produced in respiration non-competitively inhibits an enzyme (PFK) involved in the activation of glucose at the beginning of the respiration reaction.
37
How does the body obtain cofactors?
- inorganic cofactors via the diet as minerals, including iron, calcium, chloride, and zinc ions.
38
How does the body obtain coenzymes?
- from vitamins, a class of organic molecules found in the diet.
39
How do coenzymes and cofactors work?
- transfer atoms or groups from one reaction to another in a multi-step pathway
- or form part of the active site of an enzyme
- only difference is coenzymes are organic molecules
40
What is an example of a cofactor?
- amylase, which catalyses the breakdown of starch contains a chloride ion that is necessary for the formation of a correctly shaped active site.
41
What are examples of coenzymes?
- vitamin B3 is used to synthesise NAD
- NADP, which plays a similar role in photosynthesis is also derived from vitamin B3.
- vitamin B5, which is used to make coenzyme A, which is essential in the breakdown of fatty acids and carbohydrates in respiration.
42
What are prosthetic groups?
- Sub set of cofactors, they are required by certain enzymes to carry out their catalytic function
- Tightly bound to the enzyme protein and form a permanent feature of it.
43
What is an example of a prosthetic group?
- zinc ions form an important part of the structure of carbonic anhydrase, an enzyme necessary for the metabolism of carbon dioxide.
44
What are inactive precursor enzymes?
- enzymes produced in inactive form particularly ones that: can cause damage within the cells producing them, or tissues where they are released, or enzymes whose action needs to be controlled and only activated under certain conditions
45
Why do precursor enzymes need to change shape (tertiary structure) and how does it happen?
- to be activated
- addition of a cofactor
- by action of another enzyme, such as protease, which cleaves certain bonds in the molecule.
- in some cases it’s a change of condition (zymogens or proenzymes)
46
What is a precursor enzyme called before and after the cofactor is added?
- before: apoenzyme
| - after: holoenzyme
47
What is an example where conditions changing cause the precursor enzyme's tertiary structure to change?
- when inactive pepsinogen is released into the stomach to digest proteins, the acid ph brings about the transformation into the active enzyme pepsin. This adaption protects the body tissues against the digestive action of pepsin.
Biology Module 2
flashcards
Decks in class (16)
# Cards
-
Water13
-
Carbohydrates21
-
Cells Structure27
-
Testing for Carbohydrates12
-
Types of Microscopes20
-
Lipids and Proteins72
-
Plasma Membrane21
-
Transports across membrane19
-
Nucleic Acids23
-
DNA Replication and the Genetic Code19
-
Protein Synthesis18
-
ATP8
-
The Cell Cycle49
-
The organisation and specialisation of cells16
-
Stem Cells26
-
Enzymes47
