Chapter 4 - Enzymes Flashcards
What are enzymes?
Biological catalysts that interact with substrate molecules to facilitate chemical reactions, without being used up
What are anabolic reactions?
Chemical reactions required for growth (building up) -catalysed by enzymes - energy is required
What are catabolic reactions?
Chemical reactions that involve the breaking down of large organic molecules - this process releases energy
Metabolism
The sum of all the different reactions and reaction pathways happening in a cell or an organism
What is Vmax?
Is the maximum initial velocity or rate at which the enzyme catalysed a reaction
Happens when all active sites are saturated by substrates
What is the specificity of an enzyme ?
The ability of an enzyme to bind with a specific substrate or catalyse a specific set of chemical reactions
Activation energy
The minimum amount of energy required to start a reaction
The two enzyme hypothesis :
The lock and key hypothesis
Induced fit hypothesis
Lock and key hypothesis
- an area within the tertiary structure of the enzyme has a complementary shape to the substrate which is called the active site
- the enzyme and substrate bind to form an enzyme-substrate complex
- the substrate is held so that the right atom groups are close enough to react
- r groups in the active site interact with the substrate forming temporary bonds
- these put strain on the bonds within the substrate - helps réaction along
- enzyme-product complex is formed
- products released
Induced fit hypothesis
- active site slightly changes shape as substrate enters it
- initial reaction between the enzyme and substrate is weak, however these interactions cause changes in the enzymes tertiary structure that strengthen binding , putting strain on the substrates molecule
- this can weaken bonds in the substrate - lowering the activation energy
- forms enzyme-product complex
- products leave the active site
What are intracellulaire enzymes?
Enzymes that act within cells
E.g catalase - breaks down hydrogen peroxide which is a toxic product of many metabolic pathways
What are extracellular enzymes ?
Enzymes that work outside the cell that made them
- enzymes are released to break down polymer nutrients into smaller molecules in the process of digestion, so they can become able to pass through the cell surface membrane (can be absorbed in bloodstream) to provide cells with components necessary for survival and growth
Amylase , trypsin
Why is amylase and maltase needed to digest starch
- Amylase partially breaks down starch polymers into maltose
Amylase is produced by salivary glands and pancreas - released as salivai and pancreatic juice (in small intestine) - maltase is then used to break down maltose into glucose
- maltase is present in the small intestine
What is protease
Type of enzyme that catalysés the digestion of proteins into smaller peptides, further broken down into amino acids
The digestion of protein
- trypsin is produces in the pancreas and released with pancreatic into small intestine juice
- it acts on proteins , breaking it down
- amino acids are absorbed by cells lining the digestive system
- then absorbed into bloodstream
Temperature affecting the enzyme rate of reaction
- increase temperature = more kinetic energy = more frequent collisions = more successful collisions - increase in rate of reaction
Température coefficient q10
Measure of how much the ror increases with a 10C rise in temperature
Is usually 2
Dénaturation from temperature
- bonds holding the protein together vibrate
- vibrations increase until the bonds strain and then break
- results in a change in the tertiary structure
- changes shape of active site - no longer function as a catalyst
- no longer complementary
- denatured
Optimum temperature
Temperature at which enzymes has the highest rate of activity
40c in human body
Temperature extremes
Cold environments
Thermophiles
Cold
- enzymes have more flexible structures
- less stable
- smaller temperature changes will denature
Thermophiles
- more stable
because of hydrogen bonds and sulphur bridges in tertiary structure
- more resistance to change as the temperature rises
How does ph affect enzymes
- hydrogen ions interact with polar and charged rgroups, changing ph changes this interaction.
- affects hydrogen and ionic bonds causing bonds to break and the shape of the enzyme to change
- alters active site
- RENATURATION = ph returns to optimum and resumes its normal shape
- DENATURED = ph changes significantly
Substrate and enzyme concentration
When substrate / enzyme concentration is increased
- higher collision rate with active site
- formation of more enzyme-substrate complexes
- reaction increases until Vmax
- at this point all of the active sites are occupied by substrate particles
- no more enzyme-substrate particles can be formed until products are release from active site
The concentration of … becomes the limiting factor
Denatured
R group interactions are interrupted
Change in tertiary structure
Change in 3D shape of active site
No longer complementary
What are inhibitors
Molecules that prevent enzymes from carrying out their function of catalysis - slow them down
Competitive inhibition
- molecule with a similar shape to the substrate fits into the active site
- this prevents the enzyme from binding to a substrate and forming an enzyme substrate complex
- the enzyme can not carry out its function
- molecule and substrate will compete to bind to the active site , and catalyse the reaction
- reduces the number of enzyme substrate complexes at any given time, therefore slows down the rate of reaction
Effects on rate of reaction - competitive inhibitors
Reduces the rate of reaction
Does not change the Vmax
Examples of competitive inhibitors
Statins
Used to help people reduce blood cholesterol concentration
Aspirin
Irreversibly inhibits the active site of COX, preventing the synthesis of chemicals responsible for pain and fever
Non competitive inhibitors
- the inhibitor binds to the enzyme at the ALLOSTERIC site
- the binding causes a change in the tertiary structure of the enzyme , causing active site to change
- active site is no longer complementary
- can’t carry out its function
Effect of rates or reaction - non competitive
Increasing enzyme concentration will not overcome the effect
Adding more inhibitor will further decreases the active sites
WHAt is End product inhibition
final Product of the metabolic pathway acts as the inhibitor to an enzyme that acts previously in the pathway - negative feedback
Example of end product inhibition
In the breakdown of glucose, ATP regulates its own production.
This is because the two phosphate groups that results in initial breakdown of glucose is catalysed by the enzyme PFK, which is competitively inhibited by ATP
- When ATP levels are high, more ATP binds to the PFK, preventing the addition of the second phosphate
- Glucose is not broken down, and ATP is neither made
-ATP is used, PFK catalyses the addition of the second phosphate leading to more production of ATP
What are cofactors
Non protein components necessary for the effective functioning of an enzyme , help transfer atoms and molecules between the reaction pathway and can form part of the active site to help bind together enzyme and substrate
What is the role of cofactors
They work by helping the enzyme and substrate bind together
They don’t directly participate
What is the role of coenzymes
They participate in the reaction and are changed by it
Carriers that move chemical groups between different enzymes
what is a Prosthetic group
Prosthetic groups are cofactors that are tightly bound to and enzyme to form a permanent feature of the protein
What is precursor activation used for
Enzymes are synthesised as inactive precursors to prevent them from causing damage to cells / whose actions need to be controlled and only activated under certain conditions - protease
To be activated they need to undergo a chemical change
Achieved by an additions of a cofactors
Adding a cofactors to a precursor protein
Apoenzyme inactive + cofactors activator —> haloenzyme active
Other ways precursor enzymes can be activated
A change in the tertiary structure brought about by the action of another enzyme, which breaks bonds
Change in conditions (ph and temperature)
E.g
Pepsinogen is released and activated in stomach by ph levels
How do enzymes affect activation energy
Help molecules collide successfully
And reduce activation energy
What are serial dilutions
And when are they useful
Repeated stepwise dilution of a solution
Even when solution is unknown
Gives relative concentrations
How to make serial solutions
Add 1ml of stock solution to 9ml of distilled water
Take 1ml of that made solution and add 9ml of water
Why do enzymes at low temperatures have flexible structures
Low kinetic energy Enzymes move slower Less frequent collisions Collisions have less energy Flexible active sites needed to Increase the number of successful collisions
How do drugs act as enzyme inhibitors
Penicillin
Drugs that stop hiv
Antibiotics
Inhibits enzyme that catalyses formation of protein in cell wall
- can’t regulate osmotic pressures
- bacteria bursts and dies
Antivirals
Inhibits enzyme that catalyses replication of viral DNA
- prevents virus from replicating
How do metabolic poissons interfere with metabolic reactions
Cyanide
Arsenic
Malonate
Inhibits enzyme that catalyses respiration
Cells die
What is the bonding in inhibitors that makes them non reversible
Covalent bonds
Can’t be removed easily
What is the bonding in inhibitors that makes them reversible
Weaker hydrogen bonds or ionic bonds
Inhibitor can be removed
What does end product inhibition do
Regulates the pathway
Controls the amount of product made
What is a coenzyme
Organic cofactors
Example of cofactor
Cl-
Example of coenzyme
Vitamin
Example of prosthetic group for carbonic anhydrase
Zn2+
