Lesson 2. Critical Reading Name___________________ Class______________ Date________ Read these passages from the text and answer the questions that...

Lesson 2.2: Critical Reading

Name___________________ Class______________ Date________

Read these passages from the text and answer the questions that follow.

Biochemical Reactions and Enzymes

Biochemical reactions are chemical reactions that take place inside the cells of living things. Biochem-

istry is a relatively new field that emerged at the interface of biology and chemistry. Its emergence shows

that knowledge of chemistry as well as biology is needed to understand fully the life processes of organisms

at the level of the cell. The sum of all the biochemical reactions in an organism is called metabolism. It

includes both exothermic and endothermic reactions.

Types of Biochemical Reactions

Exothermic reactions in organisms are called catabolic reactions. These reactions break down molecules

into smaller units and release energy. An example of a catabolic reaction is the breakdown of glucose,

which releases energy that cells need to carry out life processes. Endothermic reactions in organisms are

called anabolic reactions. These reactions build up bigger molecules from smaller ones. An example of

an anabolic reaction is the joining of amino acids to form a protein. Which type of reactions — catabolic

or anabolic — do you think occur when your body digests food?

Enzymes

Most biochemical reactions in organisms need help in order to take place. Why is this the case? For

one thing, temperatures are usually too low inside living things for biochemical reactions to occur quickly

enough to maintain life. The concentrations of reactants may also be too low for them to come together

and react. Where do the biochemical reactions get the help they need to proceed? The help comes from

enzymes.

An enzyme is a protein that speeds up a biochemical reaction. An enzyme works by reducing the amount

of activation energy needed to start the reaction. Less activation energy is needed when the correct enzyme

is present than when it is not present.

Enzymes are involved in most biochemical reactions, and they do their job extremely well. A typical

biochemical reaction could take several days to occur without an enzyme. With the proper enzyme, the

same reaction can occur in just a split second! Without enzymes to speed up biochemical reactions, most

organisms could not survive. The activities of enzymes depend on the temperature, ionic conditions, and

the pH of the surroundings. Some enzymes work best at an acidic pH, while others work best in neutral

environments.

Questions

1. What is an enzyme?

2. How are biochemistry and metabolism related?

3. Which type of reactions — catabolic or anabolic — do you think occur when your body digests food?