Chapter 2

Section 4Energy and Chemical Reactions

Grade 10 BiologyFall 2010

Bell Ringer

1. What energy forms do each of these represent?

1. Tuning fork?2. Flashlight?3. Vinegar and baking soda?4. Explosion?

Objectives

• Evaluate the importance of energy to living things

• Relate energy and chemical reactions• Describe the role of enzymes in chemical

reactions• Identify the effect of enzymes on food

molecules

Energy for Life Processes

• Energy: is the ability to move or change matter

• Energy exists in many forms – Light, heat, chemical energy, mechanical energy,

and electrical energy

• It can be converted from one form to another • If you kick a ball, the energy of your kick

makes the ball move

Energy for Life Processes

• Energy can be stored or released by chemical reactions

• A chemical reaction is a process during which chemical bonds between atoms are broken and new ones are formed, producing one or more different substances

Energy for Life Processes

• Reactants: starting materials for chemical reactants

• Products: newly formed substances• Chemical equations: summarize chemical

reactions Reactants Products

• The arrow reads changes to or forms

Energy in Chemical Reactions

• In chemical rxn.’s, energy is absorbed or released when chemical bonds are broken and new ones are formed

Energy in Chemical Reactions

• This graph represents an energy releasing reaction • When water freezes, the process that leads to the

formation of ice crystals causes heat energy to be released

• When you fill an ice cube tray with water and place it in the freezer to make ice, heat is released from the water as the water freezes

Products

Reactants

Energy in Chemical Reactions

• This graph represents an energy absorbing graph• When you remove ice cubes from the freezer, the

ice cubes begin to melt • When ice melts, it absorbs heat from the

environment

Energy absorbed

Activation Energy

• Activation energy: the energy needed to start a chemical reaction – Ea

• Even in a chemical reaction that releases energy, activation energy must be supplied before the reaction can occur

Enzymes

• Chemical reactions in cells occur and at relatively low temperatures because of the action of many enzymes

• Enzymes: substances that increase the speed of chemical reactions

• Most enzymes are proteins • Enzymes are catalysts, which are substances

that reduce the activation energy of a chemical reaction

Enzymes

• An enzyme increases the speed of a chemical reaction by reducing the activation energy of the reaction

Enzymes

• Help organisms maintain homeostasis • Without enzymes chemical reactions wouldn’t

occur quick enough to sustain life • Ex. Pg 40, blood and carbon dioxide

Enzyme Specificity

• Substrate: a substance on which an enzyme acts during a chemical reaction

• Enzymes act only on specific substrates • Ex. Enzyme amylase assists in the breakdown

of starch to glucose in the following chemical rxn.

starch (amylase) glucose• Starch is amylase’s substrate

Enzyme Specificity

• An enzyme’s shape determines its activity • Typically, an enzyme is a large protein with

one or more folds on its surface • Active site: site on an enzyme that attaches to

a substrate • Enzyme acts only on one substrate because

only that substrate fits into its active site (lock and key model)

Enzyme Specificity

• Step 1: when an enzyme first attaches to a substrate during a chemical reaction, the enzyme’s shape changes slightly so that the substrate fits more tightly in the enzyme’s active site (page 41, figure 15)

Enzyme Specificity

• Step 2: at an active site, an enzyme and a substrate interact in a way that reduces the activation energy of the reaction, making the substrate more likely to react

• Step 3: the reaction is complete when products have formed. The enzyme is now free to catalyze further reactions.

Factors in Enzyme Activity

• Any factor that changes the shape of an enzyme can affect the enzyme’s activity

• Enzymes operate best within a specific temp. range, changing the temp. outside of this range will affect enzyme activity

• Enzymes operate best within a specific pH range, enzymes operating outside this range will loose effectivness

Review 1. _______________ energy is the energy required to start a

chemical reaction. 2. _______________ increase the speed of chemical

reactions by reducing the activation energy. 3. List 3 ways that organisms use energy. 4. Carboxypeptidase is an enzyme that catalyzes reactions in

the small intestines. The products of these reactions are amino acids. What are the substrates of carboxypeptidase?

1. Proteins2. Carbohydrates3. Lipids4. Nucleic acids

Answers

1. Activation2. Enzymes3. Organisms store energy, use energy to power

the chemical reactions of metabolism, and use energy to build cell structures.

4. Answers 1. Correct. Amino acids are the building blocks of

proteins 2. Incorrect. Carbohydrates are made up of sugars3. Incorrect. Lipids are not made up of amino acids4. Incorrect. Nucleic acids are made up of nucleotides