Enzymes in Physiology Flashcards
Define Enzyme
Enzymes are protein catalysts that speed up the rate of biochemical reactions without being changed or used up.
Enzymes provide..
A reaction surface (active site)
A suitable environment.
What do enzymes actually do?
They decrease the activation energy. More molecules meet this energy leading to an increased rate of reaction.
Every chemical energy is accompanied by…
a change in free energy, (Gibbs free energy)
Gibbs free energy equation
(free energy of initial state) - (free energy of final state)
What is active site?
A region within an enzyme that fits the shape of substrate molecules.
How do substrates bind?
Amino acid side-chains align to bind the substrate through H-bonding and hydrophobic interactions.
When are products released?
When the reaction is complete as they no longer fit well in the active site.
2 Binding Hypothesises:
Lock and key (rigid structure)
Induced Fit (more flexible and changes shape upon a drug.)
Enzymes optimum pH
7.4
What happens at low or high pH?
Activity as lost as tertiary structure is disrupted.
Changing the pH alters.. (3)
the ionization state of amino acid side chains
ionic bonding, structural stability, shape and functionality of enzyme
overall 3D structure of all enzymes
Enzymes optimum temperature
37 degrees
What are cofactors?
Non-organic molecules that bind to the active site and facilitate the reaction by maintaining correct configuration of active site.
Polypeptide proportion of the enzyme is called..
Apoenzyme
What are coenzymes?
Organic molecules bound to the enzyme by weak interactions or H bonds - many have modified vitamins in their structure and carry electrons.
All enzymes end in …
-ase
sucrase
catalyses the hydrolysis of sucrose
Describe Oxido-reductases
Catalyse transfer of electrons from donors to acceptors (oxidation and reduction reactions)
Oxido-reductases
Dehydrogenases
Accept and donate electrons as hydride ions or hydrogen atoms often using cofactors such as NAD+/NADH as an electron donor to acceptor.
Describe Transferases
Catalyse transfer of a specific functional group between molecules.
Transferases
1- What do Kinases do?
2 - What do Aminotransferases do?
3 - Glycosyltransferases?
4 -Acyltransferases?
1- kinases - transfer phosphate groups
2 - transfer amino groups
3 - transfer carbohydrate residues
4 - transfer fatty acyl groups
Describe Hydrolases
Catalyse cleavage of bonds by the addition of a water molecule
Hydrolases
1- What do phosphates do?
2 - Lipases?
3 - Peptidases?
1 - hydrolyse phosphoric ester bonds
2- hydrolyse ester bonds in lipids
3 - hydrolyse peptide bonds to form 2 products.
Describe Lysases
Catalyse the addition of water, ammonia or CO2 to double bonds or remove them to create double bonds
Lysases
1- Decarboxylases?
2 - Dehydrases?
3- Deaminases?
1- remove CO2
2- remove H2O
3 - remove NH3
Describe Isomerases
Catalyse the interconversion of isomeric forms of a molecule by transferring groups within the same molecule
e. g. Cis and Trans molecules
e. g. D and L isomers
Describe Ligases
Catalyse the synthesis of new covalent bonds using ATP energy
Enzymes may recognise and catalyse…. (3)
Absolute - one type of reaction for a single substrate
Group - one type of reaction for similar substrates
Linkage - one of type of reaction for a specific type of bond
Example of Absolute catalysis
Urease catalyses only hydrolysis of urea
Example of Group catalysis
Hexokinase adds phosphate groups to hexoses
Example of Linkage
Trypsin catalyses hydrolysis of peptide bonds
Active site conformation drives selectivity
Chymotrypsin prefers…
aromatic side chains adjacent to scissile bond
Active site conformation drives selectivity
Trypsin prefers…
positively charged side chains that can interact with Asp189
Active site conformation drives selectivity
Elastase prefers…
small uncharged side chains, as pocket is blocked
What are isoenzymes?
Different forms of an enzyme catalysing same reaction in different tissues.
Are there any differences between isoenzymes?
Slight variations in quaternary structure - different physical attributes and optimal conditions.
Give an example of isoenzymes
LDH1 - in heart muscle converts lactate to pyruvate, and then to Acetyl coA
LDH5 - in skeletal muscle converts lactate to pyruvate.
Positive allosterism is when…
Some effectors speed up enzyme action
Negative allosterism is when…
Some effectors slow enzyme action.
Structure of allosteric enzyme
Quaternary structure with two different sites of attachment - the active site and the effector binding sit
How does Allosteric regulation of enzyme action work (3)
Enzyme complex attaches to the substrate at the active site - releases product.
One product functions as a negative feedback effector by fitting into the effector binding site.
Binding of the effector in the effector binding site causes a conformational shift of the enzyme that closes the active site and inactivates the enzyme.
Allosteric enzymes are basis for…
feedback inhibition.
What happens in feedback inhibition?
A product serves as an inhibitor for a previous allosteric enzyme earlier in the series.
