LECTURE 4: ENZYMES Flashcards by Miss Bambi

diverse group of water-insoluble
biological molecules; fats – energy stores;
phospholipids and sterols – major
components of membrane

Lipids

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What are the biological molecules?

-Lipids
-Proteins
-Carbohydrates
-Nucleic Acid

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energy stores

fats

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major components of membrane.

phospholipids and sterols

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polyhydroxyl aldehyde
and ketones with the
general formula of
(CH2O)n

Carbohydrates

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most complex and most abundant
organic molecules containing at least one
carboxyl group and one amino group

Proteins

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DNA carries coded information,
arranged into genes, that is passed from each
cell to its daughter cells and from one
generation to the next; RNA instrumental in
translating the coded message of DNA into
sequences of amino acids during synthesis of
protein molecules

Nucleic acid

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_____ carries coded information,
arranged into _______

-DNA
-Genes

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instrumental in
translating the coded message of DNA into
sequences of amino acids during synthesis of
protein molecules

RNA

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The process of increasing the rate of
reaction with the use of a catalyst.

Catalysis

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any substance that increases rate
of reaction upon addition to a certain
reaction

Catalyst

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➢catalyst of biochemical reactions (biological
catalysts)
➢neither used up in the reaction nor do they
appear as reaction products
➢are proteins of very specific amino acid
composition and sequence
➢ denatured and precipitated with salts,
solvents and other reagents
➢ catalyze all the synthetic and metabolic
reactions of the cell
➢ allows for a faster speed of reaction
➢ increases the reaction rates by means of
lowering the energy of activation

Enzymes

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➢the kinetic energy required to bring the
reactants into position to interact.
➢measured as the number of calories required
to bring all the molecules in a mole of reactant
at a given temperature to a reactive (or
activated) state

Activation energy/free energy of activation

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How do enzymes hasten the reaction?

➢ enzyme lowers
the activation
energy

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Write this in formula:
➢enzyme (E) binds with a substrate (S) to
form an activated enzyme-substrate
complex (ES).
➢ES state, the path to the product (P) has a
lower activation energy than the
nonenzymatic reaction.

S (substrate) + E (enzymes) ➢ ES (enzyme substrate complex) ➢ P (product) + E (enzyme)

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reactions catalyzed by enzymes are usually
_____________ times faster than uncatalyzed
reactions.

10^3 to 10^17

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each enzyme is specific for a certain
substrate (reactant molecule)
➢ specificity of enzymes varies
e.g. stereo-specific
single product
specific bonds

Enzyme Specificity

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where the substrate can fit
like a lock-and-key mechanism

active site

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side groups of certain amino acid
residues that are brought into proximity
by this tertiary structure, even though
they may be widely separated in the
amino acid sequence of the enzyme.

Enzyme Specificity

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catalytic potency
of an enzyme

enzyme activity

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number of
reactions catalyzed per second by the
enzyme

turnover number

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➢substrate interacts with the active site of the
enzyme
➢forming an enzyme-substrate complex (ES)
➢product separates from the enzyme
➢free enzyme can form an ES complex with a
new substrate molecule

Enzymatic Reaction

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Enzymatic Reaction

S (substrate) + E (enzymes) ➢ ES (enzyme substrate complex) ➢ P (product) + E (enzyme

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How enzymes accelerate reactions?

➢ holds substrates in close proximity to one
another in order to enhance the probability
of a reaction
➢ form an unstable intermediate that readily
undergoes second reaction
➢ presence of proton donors and acceptors in
the active site of the enzyme

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Factors affecting enzyme activity

1. Temperature and Reaction 2. Enzymes and Cofactors 3. Enzyme Kinetics 4. Enzyme Inhibition 5. Regulation of Metabolic Reactions

➢rate of chemical reaction depends on this. ➢ Increase temperature ➢ increase average of molecular velocity ➢ increase in number of molecular collisions per unit ➢ increase probability of successful interaction of the reactant molecules. ➢as their velocities increase, the molecules possess higher kinetic energies and thus are more likely to react upon collision

Temperature and Reaction Rates

➢as temperature ________, reaction rate initially increases (increased kinetic energy of the substrate molecule)

increases

➢as temperature increases further, reaction rate _________________

decreases (onset of denaturation)

➢reaction rate is maximal at the ___________

optimal temperature

➢drop in_____ exposes more positive sites on an enzyme for interaction with negative groups on a substrate molecule.

➢rise in pH facilitates the binding of ______ on a substrate to negative sites on the enzymes.

positive groups

enzymes require________ for activity

cofactors

small organic molecules that act as cofactors

coenzymes

enzyme minus its cofactor; cannot function without its cofactor/coenzyme

apoenzyme

covalently attached cofactors, part of the enzyme molecule metal ions

vitamins

Cofactor (coenzyme, prosthetic group or metal ion) + apoenzyme = ?

holoenzyme

Some Enzymes requiring Ca^2+

-Phosphodiesterase -Protein Kinase C

Some Enzymes requiring Cu^2+ (Cu+)

-Cytochrome -Tyrosinase

Some Enzymes requiring Fe^2+ or Fe^3+

-Catalase -Cytochromes -Ferredoxin -Peroxidase

Some Enzymes requiring K+

-Pyruvate Phosphokinase (also requires Mg^2+) -Plasma Membrane ATPase

Some Enzymes requiring Mg^2+

-Phosphohydrolases -Phosphotransferases -Pyruvate Phosphokinase -Plasma Membrante ATPase

Some Enzymes requiring Mn^2+

-Arginase -Phosphotransferases

Some Enzymes requiring Na+

-Plasma Membrane ATPase (also requires K+ and Mg^2+)

Some Enzymes requiring Zn^2+

-Alcohol dehydrogenases -Carbonic anhydrase -Carboxypeptidase

Metal Ions Functioning as cofactors

-Calcium (Ca^2+) -Cupric Ion (Cu2+ (Cu+) - Ferrous Cation (Fe2+) or Ferric Cation (Fe3+) -Potassium (K+) -Magnesium (Mg2+) -Manganese (Mn2+) -Sodium (Na+) -Zinc (Zn2+)

Oxidation reaction

Oxidoreductases

Group Transfer

Transferase

Hydrolysis Reaction (transfer of functional groups to water)

Hydrolases

Additional or removal of groups to form double bonds

Lyases

Isomerization (intramolecular group transfer)

Isomerases

Ligation of two substrate at the expense of ATP hydrolysis

Ligases

Six Major Classes of Enzymes

-Oxidoreductases -Transferase -Hydrolases -Lyases -Isomerase -ligases

Example of Oxidoreductases

Lactate Dehydrogenases

Example of Transferase

Nucleoside monophosphate kinase (NMP kinase)

Example of Hydrolases

Chymotrypsin

Example of Lyases

Fumarase

Example of Isomerases

Triose phosphate isomerase

Example of Ligases

Aminoacyl-tRNA synthetase

The rate at which an enzymatic reaction proceeds depends on the concentrations of substrate, product, and active enzymes

Enzymes Kinetics

➢used in the living cell as a means of controlling enzymatic reactions ➢discovered important features of the active sites and of the mechanisms of enzyme action ➢enzymes can be irreversibly (toxins) or reversibly inhibited

Enzyme Inhibition

Two types of enzyme inhibition

-Competitive -noncompetitive

➢caused by molecules that react directly with the active site of the enzyme ➢can be reversed by an increase in substrate concentration ➢most competitive inhibitors are substrate analogs

Competitive inhibition

➢caused by molecules that bind to a region(s) of the enzyme outside the active site ➢reversed by dilution or removal of the inhibitor ➢chemical structure of noncompetitive inhibitors typically differs from that of the substrate.

Noncompetitive inhibition

Regulation of Metabolic reactions

1. Control of Enzyme Synthesis 2. Control of Enzyme Activity

➢certain conditions that reduce protein synthesis generally ➢regulated at the molecular level by modulation of the rate of transcription of the gene encoding it (DNA is packaging; rate at which RNA is translated into proteins) ➢enzymes are only synthesized when needed

Control of Enzyme Synthesis

➢regulated by modulator molecules (interact with a part of the enzyme molecule – allosteric site - distinct from the active site) ➢allosteric site - alters the tertiary structure of the enzyme thus changing the conformation of the active site ➢the affinity of the enzyme for its substrate decreases or increases

Control of Enzyme Activity

alters the tertiary structure of the enzyme thus changing the conformation of the active site

allosteric site

➢ first enzyme of the sequence that acts as the regulatory enzyme ➢ end product of the pathway feeds back to inhibit the activity of this first enzyme ➢ limits the rate of accumulation of the end product by slowing the entire sequence from the beginning

End-product (Feedback) Inhibition

➢interaction of the end product occurs in the allosteric site, making the end product an ____________

allosteric inhibitor

several cat-ion cofactors act as allosteric activators for some enzymes

Enzyme Activation

Two kinds of energy-yielding metabolic pathways in animal tissues:

1. Aerobic metabolism 2. anerobic metabolism

food molecules are completely oxidized to carbon dioxide and water by molecular oxygen; energy yield is far greater

aerobic metabolism

food molecules are oxidized incompletely to lactic acid (lactate); absence of oxygen

Anaerobic Metabolism