General organic and biological chemistry structures off life CH 20 1 enzymes and enzyme action GOB structures 5th ed

Lecture Presentation

Chapter 20

Enzymes and Vitamins

Karen C. Timberlake

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Chapter 20 Enzymes and Vitamins

A physician assistant (PA) helps a doctor by
examining and treating patients as well as
prescribing medications.
His or her duties may include obtaining patient
medical records and histories, diagnosing
illnesses, educating and counseling patients, and
referring the patient, when needed, to a specialist.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Chapter 20 Readiness

Core Chemistry Skills

•
•

Interpreting Graphs (1.4E)
Identifying the Primary, Secondary, Tertiary, and Quaternary Structures of Proteins (19.4,
19.5)

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


20.1 Enzymes and Enzyme Action

Enzymes are biological catalysts that

•

increase the rate of a reaction by changing
the way a reaction
takes place.

•
•

are not changed in the process of the reaction.

lower the activation energy of the reaction.

Learning Goal Describe enzymes and their role in
enzyme-catalyzed reactions.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

The enzyme carbonic anhydrase lowers the activation energy for the
reversible reaction that converts CO2 and H2O to bicarbonate and
+
H .

© 2016 Pearson Education, Inc.


Enzymes Lower Activation Energy

Enzymes increase the rate of a chemical reaction by reducing the energy required to convert reactant
molecules to products.

An enzyme in the blood called carbonic anhydrase catalyzes

•
•

+
the rapid interconversion of carbon dioxide and water to bicarbonate and H .
+
the reverse reaction, converting bicarbonate and H to carbon dioxide and water.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Enzymes and Active Sites

Nearly all enzymes

•

are globular proteins with a unique three-dimensional shape that recognizes and binds a small
group of reacting molecules, called substrates.

•

have a tertiary structure that includes a region called the active site where one or more small
groups of substrates bind to create a chemical reaction.

•

have specific amino acid residues within the active site that interact with functional groups of the
substrate to form hydrogen bonds, salt bridges, and hydrophobic interactions.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.

Enzymes and Active Sites

Enzymes like lactase have an active site where the substrate
fits for catalysis to occur. The quaternary structure of lactase
consists of four subunits. The substrate, lactose (gray), is held
in place in the active site by hydrogen bonds with amino acid
side chains.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Specificity of Enzymes

•
•
•

Some enzymes show absolute specificity by catalyzing only one reaction for one specific substrate.
Other enzymes catalyze a reaction of two or more substrates.
Some enzymes catalyze a reaction for a specific type
of bond.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Enzyme-Catalyzed Reaction

•
•
•

The combination of an enzyme and a substrate forms an enzyme–substrate (ES) complex.
The ES provides an alternative pathway for the reaction with lower activation energy.
Within the active site, amino acid R groups catalyze the reaction to form an enzyme-product
(EP) complex.

Core Chemistry Skill Describing Enzyme Action

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Enzyme–Substrate Complex

A flexible active site in lactase and the
flexible substrate lactose adjust to provide
the best fit for the hydrolysis reaction. Once
the disaccharide is hydrolyzed, the
monosaccharide products are released from
the enzyme, which is ready

to bind another lactose.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Models of Enzyme Action

•

A lock-and-key model has a rigid substrate binding to a rigid enzyme, much like a key fitting
into a lock.

•

The induced-fit model, a more dynamic model of enzyme action, states that the active site
is flexible enough to adapt to the shape of the substrate.

•

The induced-fit model has the substrate and enzyme working together to acquire a
geometrical arrangement that lowers the activation energy.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.

Study Check

1. Which is the active site?
A. the entire enzyme
B. a section of the enzyme
C. the substrate

2. In the induced-fit model, what happens to the shape of the enzyme when the substrate
binds?
A. stays the same
B. adapts to the shape of the substrate

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Solution

1. Which is the active site?
B. a section of the enzyme

2. In the induced-fit model, what happens to the
shape of the enzyme when the substrate binds?
B. adapts to the shape of the substrate

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


20.2 Classification of Enzymes

Enzyme names describe the compound or the
reaction that is catalyzed.

The ribbon structure for alanine transaminase, an
aminotransferase, contains 495 amino acid
residues.

Learning Goal Classify enzymes and give their names.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Names of Enzymes

The name of an enzyme

•

usually ends in ase.

•

identifies the reacting substance; for example, sucrase catalyzes the reaction of
sucrose.

•

describes the function of the enzyme; for example, oxidases catalyze oxidation.

•

can be a common name, particularly for the digestive enzymes, such as pepsin and
trypsin.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Enzyme Class, Oxidoreductases

The Enzyme Commission of the International Union of Biochemistry and Molecular Biology systematically
classifies enzymes according to the six general types of reactions they catalyze (Table 20.2).

Core Chemistry Skill Classifying Enzymes

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Enzyme Classes, Transferases, Hydrolases

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Enzyme Classes, Lyases, Isomerases

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Enzyme Classes, Ligases

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.

Study Check

Match the type of reaction with an enzyme.
1) aminase

2) dehydrogenase

3) isomerase

4) synthetase

A. converts a cis fatty acid to a trans fatty acid
B. removes two H atoms to form a double bond
C. combines two molecules to make a new compound
D. adds NH3

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Solution

Match the type of reaction with an enzyme.
1) aminase

2) dehydrogenase

3) isomerase

4) synthetase

3 A. converts a cis fatty acid to a trans fatty acid
2 B. removes two H atoms to form a double bond
4 C. combines two molecules to make a new compound
1 D. adds NH3

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Chemistry Link to Health:
Isoenzymes As Diagnostic Tools

Isoenzymes

•

are different forms of an enzyme that catalyze the same reaction in different cells or tissues of the body.

•

have quaternary structures with slight variations in the amino acids in the polypeptide subunits.

There are five isoenzymes of lactate dehydrogenase (LDH) that catalyze the conversion between lactate

and pyruvate.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Chemistry Link to Health:
Isoenzymes As Diagnostic Tools

Myocardial infarction may be indicated by an
increase in the levels of creatine kinase (CK) and
lactate dehydrogenase (LDH).

The different forms of an enzyme allow a medical
diagnosis of damage or disease to a particular
organ or tissue.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Chemistry Link to Health:
Isoenzymes As Diagnostic Tools

The different isoenzymes of lactate
dehydrogenase (LDH) indicate damage to

different organs in the body.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.