Enzymes Flashcards
(42 cards)
What are Enzymes?
A biological molecule that act to catalyze the wide range of reactions that take place with the cells. i.e. they speed up the rate of reactions.
They typically help transform one form of energy into a more useful form
What are enzymes made of?
Amino Acids linked together in one or more polypeptide chains
What is catalytic RNA?
Catalytic RNA is RNA molecules with enzyme activity- cats as an enzyme
Is it necessary to regulate enzyme activity? Why?
Yes, it is necessary. This is because these processes govern cell behaviour such as homeostasis. Also, the cell needs to change how much or product produced and reactants used up based on external and internal conditions! (operates only on a need basis)
How might enzymes be regulated?
What is Non- Covalent Regulation?
- Feedback Inhibition
- Allosterism
- Protein-protein interaction
What is Covalent Regulation?
- Reversible covalent modification (eg. phosphorylation)
- Zymogen activation by proteolysis
What is Allosteric control?
- Many enzymes contain sites- allosteric sites- (in addition to active sites) that are used for regulatory purposes. Such enzymes. Such enzymes are called allosteric enzymes.
- Allosteric enzymes and proteins display cooperativity by the binding of effector molecules to the allosteric site.
- eg. Haemoglobin
What is Reversible Covalent Modification?
- The activity of many enzymes can be controlled and regulated by creating covalent bonds/ modification of that specific enzyme
- Most common eg.- the attachment of a phosphoryl group onto the enzyme (using protein kinases) from ATP (phosphorylation).
protein kinase Enzyme + ATP ---------------------> Enzyme--P + ADP
What is Zymogen Activation by Proteolysis?
- Many enzymes are produced in an inactive form and these enzymes are called zymogens or proenzymes.
- In order to activate the, they are usually cleaved irreversibly by proteases at specific sites on the polypeptides.
- Once activated, they can eventually be inactivated by the binding of some irreversible inhibitor.
- eg. Digestive enzymes and the blood cascade enzymes typically use this form of regulation.
What is Enzyme Concentration?
- Regulating the transcription of specific genes, which can control how much enzyme is produced. This can in turn regulate the overall level of activity due to some enzyme.
What are Cofactors?
- A non-protein chemical compound that tightly and loosely binds with an enzyme or other protein molecules
- Many enzymes would be inactive w/o the presence of some non-protein component referred to as a cofactor.
- Apoenzyme + cofactor = haloenzyme
Types of Cofactors?
Two types:
1. An organic molecule referred to as a coenzyme (tightly bound cofactors are sometimes referred to as prosthetic groups like FAD (prosthetic group) vs NAD+ (coenzyme))
- A metal ion
(a) metalloenzymes- superoxide dismutase (2Cu2+ & 2Zn2+) and carboxypeptidase A (Zn2+)
(b) metal- activated enzyme- creatine kinase and enolase (Mg2+)
What are the Important “Must Know” coenzymes?
- Coenzyme A (chemical group- acyl group, found in pantothenic acid, have a high energy -S bond)
- Biocytin (chemical group- C02. found in Biotin, is a prosthetic group)
- Lipoic Acid (chemical group- electrons and acyl groups, not required in diet, functions in acyl transfers)
How do we Classify Enzymes?
Why are enzymes necessary for life?
Enzymes help facilitate biochemical reactions in our bodies. They aid in everything from breathing to digestion. Having too little or too much of a certain enzyme can lead to health problems.
Consider that biological systems are typified by:
- Neutral pH
- Mild temperature
- Aqueous environment
Under these conditions, most reactions would take place only very slowly if at all
Specificity of Enzymes?
Enzymes are very specific due to the shapes of their active sites. Therefore,
Lock and Key Model
- In the lock and key model, the substrate fits precisely and perfectly into the active site due to their exact complimentary shapes
Induced Fit Model
- In the induced fit model, the shape of the enzyme’s active site is not exactly complimentary. However, upon binding of the substrate to active sites, the binding cases the active site to become complementary to the substrate
- More accurate explanation and understanding of active site binding.
What types of active sites does an enzymes have?
Contains 2 distinct types of sites or regions
- Binding sites- link to specific groups in the substrate- ensure proper orientation
- Catalytic sites- promotes the rxn
NB: active sites are specific, small compared to the entire enzyme, contain microenvironments that only comprise of the substrates and resulting products
What is Substrate Channeling?
The process in which the intermediate produced by one enzyme is transferred to the next enzyme without complete mixing with the bulk phase
Eg. Biotin does not take part in catalyzing the reactions but shuttles the product of one rxn to be the substrate of another rxn
What are examples of Enzymes and their Active Sites?
*Serine Proteases
- all have an identical fold-> Beta barrels w the catalytic triad of Asp, His, Ser at the interface of the two domains
- three types- chymotrypsin (hydrophobic pocket), trypsin (salt bridge), Elastase (small hydrophobic pocket)
What is the Collision Theory?
Molecules can only react if they come into contact (bond- forming distance) w/ each other
What are the Factors that Affect the Collision Rate?
- Activation Energy- for a reaction to occur, colliding molecules must have sufficient energy to overcome a potential barrier- the energy of activation
- Transition State Theory (Eyring)- postulates the formation of an unstable intermediate
What is Strain Mechanism Theory?
Postulates that distorted binding occurs- active site s almost complementary/ rigid
What is Transition State Stabilization?
- By binding substrates to their active sites, enzymes stabilize the structure of the transition state
- Substrate bound undistorted
- Enzyme-Substrate complex possesses unfavourable interactions
- E-S complex -> Transition State -> Products
