Enzymes

Chemical reactions either release or store energy (5.11)

Vocab:

  • Endergonic reaction: A reaction that absorbs energy.

    • Biology example: Photosynthesis.

  • Exergonic reaction: A reaction that releases energy.

    • Biology example: Cellular respiration.

  • Metabolic pathway: A series of linked chemical reactions in a cell.

    • Biology example: Glycolysis.

  • Metabolism: All chemical reactions in an organism.

    • Biology example: Digestion.

Relationship between catabolic and anabolic reactions:

  • Catabolic: Exergonic; breaks down molecules, releases energy.

  • Anabolic: Endergonic; builds molecules, requires energy.

How Enzymes function (5.13)

Vocab:

  • Activation energy: Energy needed to start a reaction.

    • Biology example: Energy to break glucose bonds in respiration.

  • Catalyst: Speeds up a reaction.

    • Biology example: Enzymes in the body.

  • Energy barrier: Activation energy that must be overcome.

    • Biology example: The initial input of energy in ATP production.

  • Enzyme: A protein that lowers activation energy.

    • Biology example: Amylase breaking down starch.

Why cells need enzymes: To speed up reactions that would otherwise be too slow.

Relationship between enzymes and activation energy: Enzymes lower activation energy, making reactions occur faster.

Enzyme graph interpretation: Be able to label activation energy, exergonic or endergonic reaction, reactants, and products.

A specific enzyme catalyzes each cellular reaction (5.14)

Vocab:

  • Active site: The region where the substrate binds.

    • Biology example: The active site of lactase.

  • Allosteric site: A site other than the active site that can regulate enzyme activity.

    • Biology example: Feedback inhibition in metabolic pathways.

  • Cofactors: Non-protein helpers for enzymes.

    • Biology example: Zinc in DNA polymerase.

  • Coenzymes: Organic molecules that assist enzymes.

    • Biology example: NAD+ in cellular respiration.

  • Induced fit: The enzyme changes shape to better fit the substrate.

    • Biology example: Hexokinase fitting around glucose.

  • Substrate: The molecule an enzyme acts on.

    • Biology example: Sucrose for the enzyme sucrase.

Protein structure and enzyme specificity: The shape of the enzyme determines which substrates can bind.

Steps of a catalyzed reaction (catalytic cycle):

  1. Substrate binds to the enzyme’s active site.

  2. Enzyme changes shape (induced fit).

  3. Reaction occurs and product is formed.

  4. Product is released.

  5. Enzyme is ready for a new substrate.

Factors influencing enzyme function: Temperature, pH, and substrate concentration.

Predicting effects of changes on enzyme activity:

  • Temperature increase: May increase activity until denaturation.

  • pH change: Can alter enzyme shape and reduce activity.

  • Substrate concentration: Higher levels may increase reaction rate until saturation.