Bio Chemistry - Enzymes

Enzyme

Enzyme

A biological catalyst.

proteins.

all enzymes are

10^9 to 10^20

Enzymes can increase the rate of a reaction by a factor of ______ over an uncatalyzed reaction.

reaction or reactions

Enzymes are commonly named after the _______________ they catalyze.

Oxidoreductases

six major groups of enzymes: Oxidation-reduction reactions

Transferases

six major groups of enzymes: Group transfer reactions.

Hydrolases

six major groups of enzymes: Hydrolysis reactions

Lyases

six major groups of enzymes: Addition of two groups to a C–C double bond, or removal of two groups to create a C–C double bond.

Isomerases

six major groups of enzymes: Isomerization reactions

Ligases (or synthetases)

six major groups of enzymes: The joining to two molecules.

Apoenzyme

The protein part of an enzyme

Cofactor

A nonprotein portion of an enzyme that is necessary for catalytic function;

Coenzyme

A nonprotein organic molecule, frequently a B vitamin, that acts as a cofactor.

Substrate

The compound or compounds whose reaction an enzyme catalyzes

Active site

The specific portion of the enzyme to which a substrate binds during reaction.

Enzyme activity

A measure of how much a reaction rate is increased.

• Enzyme concentration. • Substrate concentration. • Temperature. • pH.

We examine how the rate of an enzyme-catalyzed reaction is affected by:

rate increases coactively with enzyme concentration

The effect of enzyme concentration on the rate of an enzyme-catalyzed reaction. Substrate concentration, temperature, and pH are constant.

rate increases and decreases over a period of time [rainbow shape]

The effect of substrate concentration on the rate of an enzyme-catalyzed reaction. Enzyme concentration, temperature, and pH are constant.

rate increases as temperature increases, stabilizes beyond 50c

The effect of temperature on the rate of an enzyme-catalyzed reaction. Substrate and enzyme concentrations and pH are constant

rate increases as pH increases, stabilizes beyond pH 8

The effect of pH on the rate of an enzyme-catalyzed reaction. Substrate and enzyme concentrations and temperature are constant.

Activation

Any process that initiates or increases the activity of an enzyme.

Inhibition

Any process that makes an active enzyme less active or inactive.

Competitive inhibitor

A substance that binds to the active site of an enzyme thereby preventing binding of substrate.

Noncompetitive inhibitor

Any substance that binds to a portion of the enzyme other than the active site and thereby inhibits the activity of the enzyme.

Lock-and-key model

The enzyme is a rigid three-dimensional body. • The enzyme surface contains the active site.

Induced-fit model

The active site becomes modified to accommodate the substrate.

competitive inhibition.

When a competitive inhibitor enters the active site, the substrate cannot enter.

noncompetitive inhibition

The inhibitor binds itself to a site other than the active site (allosterism), thereby changing the conformation of the active site. The substrate still binds but there is no catalysis.

Feedback control

An enzyme-regulation process where the product of a series of enzyme-catalyzed reactions inhibits an earlier reaction in the sequence.

Proenzyme (zymogen)

An inactive form of an enzyme that must have part of its polypeptide chain hydrolyzed and removed before it becomes active.

Allosterism

Enzyme regulation based on an event occurring at a place other than the active site but that creates a change in the active site.

allosteric enzyme

An enzyme regulated by allosterism

polypeptide chains.

Allosteric enzymes often have multiple

Negative modulation

Inhibition of an allosteric enzyme.

Positive modulation

Stimulation of an allosteric enzyme.

Regulator

A substance that binds to an allosteric enzyme.

Protein modification

The process of affecting enzyme activity by covalently modifying it.

Isoenzyme (Isozymes)

An enzyme that occurs in multiple forms; each catalyzes the same reaction.

3–17 U/L

Alanine aminotransferase (ALT) normal activity

2.5–12 U/L

Acid phosphatase normal activity

13–38 U/L

Alkaline phospha- tase (ALP) normal activity

19–80 U/L

Amylase normal activity

7–19 U/L

SERUM Aspartate amino- transferase (AST) normal activity

7–49 U/L

CEREBROSPINAL FLUID Aspartate amino- transferase (AST) normal activity

100–350 WU/mL

Lactate dehydro- genase (LDH) normal activity

7–60 U/L

Creatine phospho- kinase (CPK) normal activity

15–75 U/L

Phosphohexose isomerase (PHI) normal activity

WU/mL

Wroblewski units per milliliter.

U/L

5 International units per liter

Hepatitis

an increased or abnormal activity of the enzyme: Alanine aminotransferase (ALT) indicates =

Prostate cancer

an increased or abnormal activity of the enzyme: Acid phosphatase indicates =

Liver or bone disease

an increased or abnormal activity of the enzyme: Alkaline phospha- tase (ALP) indicates =

Pancreatic disease or mumps

an increased or abnormal activity of the enzyme: Amylase indicates =

Heart attack or hepatitis

an increased or abnormal activity of the enzyme: Aspartate amino- transferase (AST) in SERUM indicates =

Heart attack or hepatitis

an increased or abnormal activity of the enzyme: Aspartate amino- transferase (AST) in CEREBROSPINAL FLUID indicates =

Heart attack

an increased or abnormal activity of the enzyme: Lactate dehydro- genase (LDH) indicates =

Heart attack

an increased or abnormal activity of the enzyme: Creatine phospho- kinase (CPK) indicates =

Heart attack

an increased or abnormal activity of the enzyme: Phosphohexose isomerase (PHI) indicates =

You! GOODLUCK!

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