Topic 3 Enzymes

Enzymes

proteins that act as biological catalysts, speeding up chemical reactions within living organisms

10^6 - 10^11

Biological catalyst (increases rate) from ______-__________ [except: class of catalytic ribonucleic acid (RNA)]

Proteins
Ribozymes

-All enzymes are ______ except _______

biological Reactions
Slow

-In the absence of enzymes, __________ are ________

Oxidoreductases

-Transfer electrons from donors to acceptors (oxidation/reduction reactions);

Dehydrogenase

transfer electrons that remain attached to hydrogen atoms.

Tranferases

-Transfer functional groups between donors and acceptors;

Transaminases

transfer amino group

Kinases

transfer phosphoryl groups from a high-energy molecule (usually ATP) to a substrate.

Phosphorylases

add inorganic phosphate to a substance without using ATP.

Phophatases

remove the phosphate group from the substrate

Carboxylases

transfer CO2, groups with the help of biotin.

Hydrolases

catalyze cleavage of bonds by addition of water, producing two products (e.g., peptidases cleave peptide (C-N) bonds).

Lyases

catalyze the breaking (an "elimination" reaction) of various chemical bonds by means other than hydrolysis (a "substitution" reaction) and oxidation, often forming a new double bond or a new ring structure (e.g., ATP-citrate lyase produces acetyl-coenzyme A and oxaloacetate from citrate). Synthases - no ATP required for the new bond formation. -Happens in Krebs’ cycle

Isomerases

-interconvert isomeric forms by transferring groups within the same molecule (e.g., phosphoglucose isomerase interconverts hexose aldehyde [glucose 6-phosphate] and ketone [fructose 6-phosphate) forms.

Ligases

also called synthetases, use ATP to form new covalent bonds (e.g., DNA ligase creates a new phosphodiester bond in a gap between two adjacent nucleotides in the DNA helix). Synthetases join two molecules together using a source of energy.

synthetases

Ligases are also called _________

Translocases

Moves ions of molecules across membranes.

Transmembrane Protein

type of protein that passes across membranes.

Holoenzyme

The complete structure of apoenzyme and coenzyme (prosthetic group) is called as __________

Prothetic group or Co-enzyme

non-protein part of a haloenzyme

Apoenzyme

protein part of a haloenzyme

Holoenzyme

An enzyme without a bound factor

Apoenzyme

An inactive enzyme, without its cofactor.

Coenzyme

-are nonprotein organic molecules that bind loosely to an enzyme. -recycled and can participate in multiple enzymatic reactions

Vitamins

Vitamins
Nucleotides

Many (not all) are ________ or are derived from ________ or _________

Prosthetic Groups

are enzyme partner molecules that bind tightly or covalently to the enzyme (heme is the prosthetic group for hemoglobin and myoglobin.

Optical Specificity

There can be many optical isomers of a substrate. However, it is only one of the isomers which acts as a substrate for an enzyme action, (e.g. for the oxidation of Dand L-amino acids, there are two types of enzyme: D - AA oxidases and L- AA oxidases.) -some amino acids look the same but doesnt need the same enzyme.

Reaction Specificity

substrate can undergo many reactions but in a reaction specificity one enzyme can catalyze only one of the various reactions. -an enzyme is only for a specific pathway and not for other pathway.

Substrate Specificity

-There are two types of substrate specificity, viz, absolute specificity and relative specificity. -ex. Shape of substrate and enzyme.

Absolute Specificity

: is comparatively rare such as urease which catalyzes hydrolysis of urea.

Relative Specificity

Group dependent or bond dependent.

Consumed
Permanently Altered

Enzymes increase the rate of chemical reactions without themselves being ____________ or ____________ by the reaction.

Altering
Chemical Equilibrium

increase reaction rates without __________the _____________ between reactants and products.

Michaelis and Menten

have proposed a hypothesis for enzyme action, which is most acceptable.

Bisubstrate Reactions

Is called when two substrates can bind to an enzyme molecule and such reactions are called as

Active Site
Catalytic Site

The site to which a substrate can bind to the enzyme molecule is extremely specific.

Active Site

consists of amino acid residues that form temporary bonds with the substrate (binding site) and residues that catalyze a reaction of that substrate (catalytic site).

Energy

cells require ________- to perform all their necessary functions. (this energy is obtained through chemical reactions.)

Exorgenic Reaction

type of reaction in which G
G (product) < G (Substrate)
△G<0

Endogernic

Type of Reaction in which
G (product) > G (subtrate)
△G> 0 (positive

Endergoni Reaction

Type of Reaction in shic is require an input of free energy to occur

Rate

The __________ of the reaction is determined by the energy of activation (△G++ or Ea), which is the energy required to initiate the reaction

Activation Energy

The energy required to reach the transition state

lower
△G
Equilibrium Constant

Enzymes _________ the energy of activation of a reaction; they do not affect the value of _______ or the __________ reaction, Keq

Kinetic Analysis of Enzymes

was used for the characterization of enzyme-catalyzed reactions even before enzymes had been isolated in pure form.

Increases

The rate of an enzyme-catalyzed reaction __________ with substrate concentration

Directly

Velocity of the reaction is ________ proportional to the enzyme concentration, provided the substrate concentration is unlimited

Increase

Reaction velocity increases with an _________ in temperature till a peak is reached

isoenzymes

Also called isozyme

Isoenzymes

are alternative forms of the same enzyme activity that exist in different proportions in different tissues.

Biomarkers

is a biological molecule whose concentration in the blood changes in response to a specific disease.

Lactase Dehydrogenase

is a cytosolic enzyme which catalyzes the reversible oxidation of Lactate to Pyruvate using NAD+

Createnine Kinase

-transfers a phosphate from creatine phosphate to adenosine diphosphate

1. Substrate concentration
2. Enzyme concentration
3. Product concentration
4. Temperature
5. pH
6. Activators/Inhibitors

Factors affecting Ensyme Activity

Lineweaver-Burk Equation

is a reciprocal form of the Michaelis-Menten equation. The same data graphed in this way yield a straight line

Inhibitos

The chemical substances which inactivate the enzymes

Negative Modifiers

Inhibitors are sometimes referred to as________________

Reversible
Irreversible

2 Groups of Inhibitors

Reversible

Inhibitor binds to the enzyme - Non Covalent bonds

Irreversible

-Inhibitor binds to the enzyme - Covalent bonds

Allosteri Inhibition

Inhibition by metabolites, occurs by a gradual reduction in the enzyme activity.

Competitive Inhibition

-When the active site or catalytic site of an enzyme is occupied by a substance other than the substrate of that enzyme, its activity is inhibited.
-Structural similarity b/w substrate and inhibitor (Structural analogue)
-Inhibitor binds to the enzyme at the same site as the substrate (active site)
-Inhibitor competes with the substrate by occupying the active site

Non competitive Inhibition

-The inhibitor binds with a site on the enzyme other than the active site so that it changes the shape, therefore the substrate is not able to bind with the active site.

Allosteric Enzyme

Enzymes that usually have more than one subunit and more than one active site.