Enzymes Flashcards
What is the activation energy?
The minimum amount of energy required for a reaction to occur
Why are enzymes better for increasing the rate of a reaction rather than temperature and concentration
You want to maintain the temperature and concentration at a set point
What are enzymes?
Biological catalysts that increase the rate of reaction by lowering the activation energy
Why don’t enzymes affect the reaction equilibrium
It catalysed the reaction equally forwards and backwards
What is the active site?
The place where substrates bind and the chemical reaction occurs
What is the lock and key hypothesis
Where active sites are complementary in shape to the substrate
What is the INDUCED fit hypothesis
Binding of substrates cause conformational changes in the enzyme
What type of bonds are formed between the active site and substrate?
Week hydrogen binds which hold the substrate in the correct orientation but also allows it to be released
What does the Michaelis-Menton model propose?
That a specific complex between the enzyme and the substrate is a necessary intermediate. Represents that the rate is related to concentration of substrate
What is Vmax
The maximal rate when all enzymes active sites are saturated with substrate
What is Km?
The substrate concentration that gives half maximal velocity
What does a low Km value tell you?
The enzyme has a high affinity for the substrate
What is the lineweaver-Burk plot
Reciprocal graph that gives -1/Km at the X intercept and 1/Vmax at the y intercept
What is an enzyme inhibitor?
Molecules that slow down or prevent an enzyme reaction
What are the 2 types of inhibitors?
- Irreversible - bind very tightly forming covalent bonds
2. Reversible - can freely dissociate as they don’t form covalent bonds
What are the 2 types of reversible inhibitors
1- competitive (binds to active site. Affects Km not Vmax)
2- Non-competitive (bind to another site in the enzyme. Affects Vmax not Km)
Why do competitive inhibitors not affect Vmax?
Adding enough substrate will overcome the affect of the inhibitor so the maximum rate can still be reached
Why do competitive inhibitors affect Km?
The inhibitor competes with the substrate for the active site so the affinity decreases
Why do competitive inhibitors lower Vmax?
They decrease the turnover rate of the enzyme
Why does the active site of an enzyme only occur a small area?
A large proportion of the enzyme is needed to hold the shape of the active site
What is the units of enzyme activity
Micromoles per minute per litre
What affect does doubling the enzyme concentration have on the rate
It doubles the rate of reaction
Why does enzyme activity stay the same despite changes the enzyme concentration
The enzymes always work to the same activity. The rate at which they work doesn’t not change.
What are the 2 long term regulation methods for enzymes
- Change in protein synthesis
2. Change in protein degradation
What are the 2 short term regulation methods for enzymes
- Changes in substate/product concentration
2. Change in enzyme conformation
State 3 ways in which enzyme conformation can be changed
- Allosteric regulation
- Covalent modification
- Proteolytic cleavage
What graph shape do allosteric enzymes show
Sigmoidal
Why do allosteric enzymes show a sigmoidal graph for rate vs substrate concentration.
As the enzyme can exist in 2 forms (T and R state)
What do allosteric activators do
Increase the proportion of enzyme in the R state
What direction do allosteric activators shift the binding curve
Left
What do allosteric inhibitors do?
Increase proportion of enzyme in the T state
Give an example of a Substance that allosteric ally activates phosphofructokinase
AMP
Give a name of a substance that allosterically inhibits phosphofructokinase
ATP, citrate, H+
Why can’t you work out Km from allosteric enzyme graphs
As it’s a sigmoidal relationship not Michaelis-Menton
What enzymes add phosphates onto substances
Kinases
What enzymes remove phosphate groups
Phosphatase
Why is protein phosphorylation effective
Phosphate group can make Hydrogen bonds and the 2 negative charges on the group can cause a conformational change.
What are zymogens
Inactive precursors of enzymes
Where are zymogens synthesised
Stomach and pancreas
What digestive enzyme activates lots of zymogens
Trypsin
What condition results from a deficiency in alpha 1 antitrypsin
Emphysema
What does alpha 1 antitrypsin do
Inhibits the actions of trypsin
Why does a deficiency of alpha 1 antitrypsin cause emphysema
The trypsin activates elastase which breaks down the alveolar walls
What are the 2 pathways of the blood clotting cascade
Intrinsic and extrinsic
What does factor Xa do in the blood clotting cascade
Activates the zymogens prothrombin into thrombin
What does thrombin do in the blood clotting cascade
Converts fibrotic into fibrin
What does fibrin do in th blood clotting cascade
Cross links to form the blood clot
What protein are Kringle domains found
Prothrombin
What is the role of Kringle domains
Keep prothrombin in the inactive form
How are Gla domains formed
The additions of COOH group to glutamate residues forming carboxyglutamate (Gla)
What is the role of Gla domains
The negative charge of th Gla domains allows them to bind to the calcium ions at the site of damage and bring clotting factors together
A defect in what factor causes haemophilia
8
What does factor VIII do in the blood clotting cascade
Stimulates the activity of other factors
What affect does protein C have in the blood clotting cascade
Degrades factors and so stops the clotting process
What 3 methods stop the clotting process
- Dilution of clotting factors
- Digestion by proteases
- inhibitors
What is fibrinolysis
Breaking down of a blood clot
Why is vitamin K important in the blood clotting cascade
Required for the carboxylation of glutamate residues to form Gla domains.
What inhibits the oxidisation of vitamin K
Warfarin
How do zymogens become activated in acidic conditions
The pH causes a conformational change which unfolds the zymogen exposing the active site