2.1.4 enzymes Flashcards
What are enzymes
proteins that act as biological catalysts for intra and extracellular reactions to determine structure and function. Therefore they affect metabolism of cells and whole organisms
specific tertiary structure determines shape of active site, complimentary to a specific substrate
Formation of enzyme substrate complex is lower activation energy of metabolic reactions
What are the differences between catabolic and anabolic Reactions
catabolic: bonds are broken, breaks molecules apart, exergonic (releases energy), E.g. hydrolysis and cellular respiration
anabolic: bonds are made, molecules are joined, endergonic (take in energy) E.g. protein synthesis and photosynthesis
What is the activation energy
Activation energy is the minimum energy required before a reaction can occur.
a reaction will not occur unless the particles involved collide with a certain minimum energy called the activation energy of the reaction
Activation energy is often provided as heat,
an enzyme catalysed reaction lowers the amount of activation energy required to allow a reaction to proceed.
It allows stable molecules to be broken down at a fast enough rate for life processes
and substrate and product level stay the same even after an enzyme catalysing
Give an example of an enzyme that catalyse intracellular reactions
Catalase: catalyses decomposition of hydrogen peroxide into water and oxygen
Give two examples of enzymes that catalyse extracellular reactions
amylase: carbohydrates catalyses digestion of starch to maltose and saliva
trypsin: pancreatic endopeptidase Catalyses hydrolysis of peptide bonds in small intestine lumen
Explain the induced fit model of enzyme action
shape of active site is not directly complimentary to substrate and is flexible
conformational changes enable ES complexes to form when substrate adsorbs
This put strain on substrate bonds, lowering activation energy. Bonds in enzyme-product complexes our week, so products desorbs
Explain the lock and key model of enzyme action
Suggests that active site has a rigid shape determined by tertiary structure so it’s only complimentary to 1 substrate. Formation of enzyme substrate complex lower activation energy. Bonds in enzyme product complex a week so product desorbs
Name five factors that affect the rate of enzyme controlled reactions
enzyme concentration
substrate concentration
concentration of inhibitors
PH
Temperature
How does substrate concentration affect rate of reaction
Given that enzyme concentration is fixed, rate increases proportionally to substrate concentration. The rate levels off when maximum number of enzyme substrate complexes form at any given time
effects of temperature: What happens when you increase the temperature
More random collisions between enzyme and substrate occur, at a greater force. More enzyme substrate complexes are formed and more products are formed
effects of temperature: What happens during the optimum temperature
Maximum rate of successful collisions between enzyme and substrate occurs, maximum rate of enzyme substrate complex formation and the maximum rate of reaction occurs
effects of temperature: What happens if you increase the temperature above the optimum
molecule starts to vibrate, a strain is put on bonds in the molecules, weaker hydrogen and ionic bonds are broken, tertiary structure changes, active site is affected, enzyme denatured and the enzyme substrate complexes Can no longer be formed and this is irreversible
How does enzyme concentration affect rate of reaction
Given that substrate is in excess, rate increases proportionally to enzyme concentration. rate levels off when maximum number of enzyme substrate complex is formed at any given time
How does temperature affect the rate of enzyme controlled reactions
rate increases as kinetic energy increases and peaks at optimum temperature. Above optimum, ionic and hydrogen bonds break and active site no longer is complimentary to substrate (denature)
ph: What are buffers
To resist changes to PH, buffers are used. Buffers are certain chemicals that can donate or except protons and they are therefore able to maintain a pH within fairly narrow limits. Hydrogen carbonate ions act as an important buffer in biological systems
What is the temperature, coefficient
Q10 measures the change in rate of reaction per 10°C temperature increases
Q10 = R2 divided by R1 ( where r represents rate)
How does PH affect rate of reaction
enzymes have a narrow optimum pH range. Outside range, hydrogen ions interact with hydrogen bonds and ionic bonds in 3 degree structure = denature
How do competitive inhibitors work
bind to active site since they have similar shape to substrate. Temporarily prevent enzyme substrate complexes from forming until released. Increasing substrate concentration decreases their affect
How do non-competitive inhibitors work
bind at allosteric binding site. Trigger confirmational change of active site. Increasing substrate concentration has no impact on their affect
What is endproduct inhibition
One of the products of a reaction acts as a competitive or non-competitive inhibitor for an enzyme involved in the pathway. Prevents further formation of products
What are irreversible inhibitors
permanently prevent formation of enzyme substrate complexes
Heavy metal ions e.g. mercury, silver cause disulphide bonds in tertiary structure to break.
Find the enzymes by strong covalent bonds
What are reversible inhibitors
Maybe competitive or non-competitive. bind to enzyme temporarily e.g. by hydrogen bonds and enzyme substrate complexes can form after the inhibitor is released
Define metabolic poison
Substance that damages cells by interfering with metabolic reactions. Usually an inhibitor
Give some examples of metabolic poisons
respiratory inhibitors include
cyanide: non-competitive, irreversible, inhibits cytochrome c oxidase
arsenic: competitive, inhibits pyruvate dehydrogenase
How do some medicinal drugs act as inhibitors
penicillin: non-competitive inhibitor of transpeptidase to prevent formation of peptidoglycan cross links in bacterial cell wall
Give examples of extracellular digestion
saprophyte digestion: saprophytes like fungi digest what they sit on, they secrete digestive enzymes onto the food source and the food source is broken down into its monomers e.g. amino acids.
Humans: food taken into organism, passes through digestive system, enzymes released out of cells to break food down to his monomers and passes into cells and is used
Give examples of intracellular digestion
amoeba
Food taken into sell and digestion takes place within the cell
What are in active pre-cursors in metabolic pathways
to prevent damage to cells, Some enzymes in metabolic pathways are synthesised as inactive precursors. One part of the precursor acts and inhibitor. Enzyme substrate complexes formed when it is removed
What are cofactors
non-protein compounds required for enzyme activity e.g. coenzymes, inorganic cofactors, prosthetic groups
What are coenzymes
Organic cofactors. Do not bind permanently. Often transport molecules or electrons between enzymes
Frequently derived from water-soluble vitamins
What are inorganic cofactors
Facilitate temporary binding between substrate and enzyme. Often metal ions
What are Prosthetic groups
Tightly bound cofactors act as a permanent part of enzymes binding site
ppq: To calculate the rate of starch breakdown, the student measured the concentration of the breakdown product. Stay the other variable the student needed to know in order to calculate the rate of this reaction
time taken
ppq: explain why it is important that pH is kept constant during an experiment
So charges in active site do not change, so hydrogen bonds are unaffected. So tertiary structure is on altered and so the enzymes do not denature
ppq: Suggest why the lock and key and induced fit explanations are termed models
To make the process easier to understand and because it is a visual representation
ppq: Suggest why most scientists now except the induced fit model rather than the lock and key model
Be induced fit model is supported by more evidence and the evidence links more closely to the induced fit model
ppq: Certain parts of the enzyme molecule from the Antarctic fish are more flexible than the equivalent parts of the molecule from the non-Antarctic fish. Suggest how a more flexible structure might help this enzyme work faster at lower temperatures
It is easier for the substrate to enter the active site and more bonds can form between the active site and substrate.
ppq: Enzymes are proteins. The enzymes in Antarctic fish have a different structure from those found in non-Antarctic fish. suggest how the structure of the enzymes may differ in Antarctic and non antarctic fish
They have different amino acids and different structures e.g. different tertiary structures
ppq: If species of Antarctic fish were to become extinct, their unique enzymes would be lost. Suggest why the loss of these enzymes might be undesirable
The enzyme could have potential future application e.g. medical use
ppq: Enzymes are biological catalysts, explain the term biological catalyst
Enzymes are used in metabolism and they speed up metabolic reactions
ppq: Explain the effect of increasing the concentration of substrate on the rate of reaction without an inhibitor
More successful collisions between substrate and active site, at high concentration all active sites occupied and cannot work any quicker
ppq: Explain the effect of increasing the concentration of substrate on the rate of reaction with and inhibitor
Inhibitor can bind to active site and occupies it for a short time. Substrate can’t access the active site and more substrate reduces chance of an inhibitor getting in
ppq: Describe how an enzyme such as pepsin breaks down a substrate
The substrate is nearly complimentary to the active site. The substrate enters the active site on the enzyme and induced fit occurs. This forms the enzyme substrate complex which destabilising of bonds then forms the enzyme product complex. And the products leave active site
ppq: Explain why different enzymes are involved in each stage of the digestion process
enzymes are specific and the substrate have different shapes. Active site and substrate are complimentary so that the substrate will fit and form enzyme substrate complexes = induced fit occurs
ppq: Explain what might happen to an enzyme’s activity if the gene encoding its production was altered by mutation
The specific substrate might not be able to bind with the active site as they don’t have a complimentary shape anymore because the mutation could potentially damage the shape of the active site
ppq: why is the enzyme amylase described as being extracellular
Works outside cells
PPQ: Suggest how a student could produce a desired concentration of a solution from a stock solution
volume of stock solution = required concentration X final volume needed divided by concentration of stock solution
volume of distilled water = Final volume needed - Volume of stock solution
