Proteins and Enzymes

Thermodynamics The study of energy in living systems

Two laws of thermodynamics 1 st law of thermodynamics: conservation of energy. Energy is neither lost nor gained but just changes from one form to another. 2 nd law of thermodynamics: entropy – Tendency to move from order to disorder.

Conservation of energy Energy can neither be created nor destroyed. Energy can only be changed from one form to another.

Entropy: disorder For living beings or just molecules to be organized, a lot of energy is required. Very little energy is needed to create disorder.

A  B + C Breaking down a reactant (A) into products (B and C) Requires little energy to start breaking down substances Exergonic reaction – releases energy

A + B  C Making a product (C) from reactants (A and B) Requires much energy to start this reaction – Why? Endergonic reaction – absorbs energy

Energy graphs

Activation energy Activation energy: how much energy is required to start a reaction

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Activation energy on two types of reactions Energy-Absorbing Reaction Energy-Releasing Reaction Products Activation energy Activation energy Reactants

Graph of Energy of a reaction Which graph is Endergonic? Which graph is Exergonic?

Enzyme action Enzymes: special proteins that help to reduce the activation energy (E a ) What will enzymes do to the speed (rate) of a reaction?

Effects of Enzymes Reaction pathway without enzyme Activation energy without enzyme Activation energy with enzyme Reaction pathway with enzyme Reactants Products

How do enzymes help with the activation energy required for metabolic processes?

DNA Polypeptide= protein Amino acids

Enzymes are Proteins (made of amino acids) Remember, All enzymes are Proteins

Glucose Substrates ATP Substrates bind to enzyme Substrates are converted into products Enzyme-substrate complex Enzyme (hexokinase) ADP Products Glucose-6- phosphate Products are released Section 2-4 Figure 2-21 Enzyme Action Active site Enzyme activity (1)

Glucose Substrates ATP Substrates bind to enzyme Substrates are converted into products Enzyme-substrate complex Enzyme (hexokinase) ADP Products Glucose-6- phosphate Products are released Section 2-4 Figure 2-21 Enzyme Action Active site Enzyme activity (2)

Glucose Substrates ATP Substrates bind to enzyme Substrates are converted into products Enzyme-substrate complex Enzyme (hexokinase) ADP Products Glucose-6- phosphate Products are released Section 2-4 Figure 2-21 Enzyme Action Active site Enzyme activity (3)

Glucose Substrates ATP Substrates bind to enzyme Substrates are converted into products Enzyme-substrate complex Enzyme (hexokinase) ADP Products Glucose-6- phosphate Products are released Section 2-4 Figure 2-21 Enzyme Action Active site Enzyme activity (4)

Proteins can be Denatured Denature – changes the Secondary, Tertiary or Quaternary structure of a protein. Heat and pH changes are the most common ways to denature a protein (polypeptide).

Enzymes and Metabolism Enzymes facilitate the metabolic processes (chemical reactions) to sustain life. Enzymes help to maintain homeostasis. Enzymes help to build cells. Enzymes help in reproduction.

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