Enzymes Flashcards
What are enzymes?
Enzymes are protein catalysts for chemical reaction in biological systems. They increase the rate of chemical reactions taking place within living cells without changing themselves.
What are simple enzymes?
Enzymes that are made up of only protein molecules not bound to any non proteins.
Give an example of a simple enzyme
Pancreatic Ribonuclease.
What fare holoenzymes/
Enzymes that are made up of protein groups and non-protein component
The protein component of a holoenzyme is called …………while the non-protein component is called a ………
The protein component of a holoenzyme is called apoenzyme, while the non-protein component is called a coenzyme
Examples of coenzymes that may participate in forming an intermediate enzyme-substrate complex include;
NAD, FAD, Coenzyme A
Enzyme molecules contain a special pocket or cleft called the ………
Active site
Outline the features of the active site
- The active site contains amino acid chains that create a three-dimensional surface complementary to the substrate.
- The active site binds the substrate, forming an enzyme-substrate (ES) complex.
Describe the two parts of the active site
- Catalytic site. It is the part of the enzyme that is responsible for catalysis. It determines reaction specificity. Occasionally, catalytic site and active site are used synonomously.
- Binding site. It is the part of the enzyme that binds with substrate. It determines substrate specificity.
…… determines substrate specificity
Binding site
…….. determines reaction specificity
Catalytic site
What is meant by enzyme turn over number?
Enzyme turn over number refers to the amount of substrate converted per unit time
……….. is the fastest enzyme
Carbonic anhydrase
Describe absolute specificity
this is a form of enzyme specificity, whereby one enzyme catalyzes or acts on only one substrate.
example: Urease catalyzes hydrolysis of urea but not thiourea.
………. Is a form of enzyme specificity whereby an enzyme is specific to only one isomer even if the compound is one type of molecule
Stereo specificity
Give examples of enzymes that exhibit stereo specificity
- glucose oxidase catalyzes the oxidation of β-D-glucose but not α-Dglucose,
- arginase catalyzes the hydrolysis of L-arginine but not D-arginine.
- Maltase catalyzes the hydrolysis of α- but not β –glycosides.
Enzymes that are specific for a bond or linkage such as ester, peptide or glycosidic exhibit ……….. specificity
Bond Specificity
Examples of enzymes that exhibit bond specificity are;
- Esterases- acts on ester bonds
- Peptidases-acts on peptide bonds
- Glycosidases- acts on glycosidic
……… are enzymes produced in nature in an inactive form which can be activated when they are required.
Zymogen (proenzyme)
Outline some examples of zymogens
Pepsinogen - from gastric juice, when required Pepsinogen converts to Pepsin
Trypsinogen - This zymogen is found in the pancreatic juice, and when it is required gets converted to trypsin.
The activation is brought about by specific ions or by other enzymes that are proteolytic.
A note on isoenzymes
These are enzymes having similar catalytic activity, act on the same substrate and produce the same product but originated at different site and exhibiting different physical and chemical characteristics such as electrophoretic mobilities, amino acid composition and immunological behavior.
For instance LDH (Lactate dehydrogenase) exists in five different forms each having four polypeptide chains. H = Heart and M = Muscle.
CPK (Creatine phospho kinase) exists in three different forms each having two polypeptide chains. Characteristic sub units are B = Brain and M = Muscle.
The amount of energy needed to convert a substance from ground state to transition state is called ……..
Activation energy
