Molec Cell: Ch. 2 pt. 3

Chapter 2 part 3

Where does the substrate bind to?

To the active site

Active sites

Active sites are clefts or grooves on the surface of an enzyme, which are where the substrate binds to

Substrates are initially bound by ____ *,* ____ , and ____ ___.

Substrates are initially bind by hydrogen bonds, ionic bonds, and hydrophobic interacyions.

Most biochemical reactions involve reactions between how many different substrates?

Most biochemical reactions involve reactions with two or more different substrates.

What happens to the reaction where there is a binding of substrates to an active site?

The binding of substrates to the active site in the proper position and orientation accelerates the reaction.

Enzymes also accelerate reactions by…

Enzymes also accelerate reactions by altering the conformation of their substrates.

Induced fit

conformation of both enzyme and substrate is modified

Many enzymes participate ___ in the ____ process.

Many enzymes participate directly in the catalytic process.

Specific side chains in the --- --- may react with the --- and form bonds with reaction ---.

Specific side chains in the active site may react with the substrate and form bonds with reaction intermediates.

What is a serine protease? Example, and what does it do?

Enzymes that cleave peptide bonds adjacent to specific types of amino acids. An example is chymotryosin and it digests bonds adjacent to hydrophobic amino acids

What does trypsin so?

Trypsin digests bonds next to basic amino acids.

The active sites of serine proteases contain ---, ---, and ---.

The active sites of serine proteases contain serine, histidine, and aspartate.

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How do substrates bind?

Substrates bind by insertion of the amino acid adjacent to the cleavage site into a pocket at the active site.

What are some features of enzymatic catalysis?

* Specificity of enzyme-substrate interaction
* Positioning of substrate molecules in the active site
* Involvement of active-site residues in formation and stabilization of the transition state

What are coenzymes? Are they altered by a reaction?

small organic molecules that participate in specific types of enzymatic reactions

Coenzymes are not altered by the reaction.

Nicotinamide adenine dinucleotide (NAD+)

a coenzyme that carries electrons in oxidation-reduction reactions

\--- can accept --- and --- electrons from one substrate, forming NADH.

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\--- can then donate the --- to a second substrate, reforming NAD+.

NAD+ can accept H+ and two electrons from one substrate, forming NADH.

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NADH can then donate the electrons to the second substrate, re-forming NAD+.

Other coenzymes…

1. Act as electron carriers


1. are involved in the transfer of a variety of chemical groups

Many coenzymes are closely related to ---, which…

Many coenzymes are closely related to vitamins, which contribute part or all of the structure of the coenzyme.

Enzyme activity can be regulated to meet…

Enzyme activity can be regulated to meet various physiological needs that may arise during the life of the cell

In feedback inhibition…

In feedback inhibition, the product of a metabolic pathway inhibits an enzyme involved in its synthesis.

What is feedback inhibition?

A type of allosteric regualtion.

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Enzyme activity is controlled by the binding of small molecules to regulatory sites on the enzyme

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This changes the conformation of the enzyme and alters the active site.

Phosphorylation

* A common mechanism of enzyme regulation
* Phosphate groups are added to the side-chain OH groups of serine, threonine, or tyrosine residues.
* Can either stimulate or inhibit the activities of many enzymes