Topic 4: Chapter 5

Enzymes Enzymes – – Part 1Part 1

Biological

Biological

CatalystsCatalysts

What are Catalysts?

• Substances which can alter or speed up a chemical reaction,

• without itself being chemically changed at the end of the reaction.

• Substances which can alter or speed up a chemical reaction,

• without itself being chemically changed at the end of the reaction.

CatalystsCatalysts

(A) Inorganic

• Iron – Haber process• Vanadium (v) Oxide – production of sulphuric acid• Manganese (IV) Oxide

(A) Inorganic

• Iron – Haber process• Vanadium (v) Oxide – production of sulphuric acid• Manganese (IV) Oxide

(B) Organic

• Digestive enzymes• Metabolic enzymes

(B) Organic

• Digestive enzymes• Metabolic enzymes

• Enzymes are biological catalysts

• which are mainly proteins that are produced by living cells.

• Enzymes can be DENATURED by heating or by changes in the pH of the solution

• E.g. Digestive enzymes,

Metabolic enzymes

(B) Organic Catalysts(B) Organic Catalysts

The function of enzymes

• How is energy released from sugar (glucose)?

• But how can our cells provide such high temperatures during cellular respiration to release energy from glucose??

Glucose + Oxygen Carbon dioxide + Water + Energy

Strong Heat

The function of enzymes

Lower Activation EnergyLower Activation Energy• Activation Energy: Energy required to start a

chemical reaction.

Activation Energy with enzyme

Activation Energy without enzyme

Reactants (Substrate):(Glucose + Oxygen)

Products:(Carbon dioxide + water)

Energy

Time

Enzyme-Catalyzed ReactionsEnzyme-Catalyzed Reactions

(A) Synthesis of complex substances

Anabolic Reactions• Protein synthesis• Photosynthesis• Conversion of glucose to glycogen• etc…

(A) Synthesis of complex substances

Anabolic Reactions• Protein synthesis• Photosynthesis• Conversion of glucose to glycogen• etc…

(B) Breaking down of complex substances

Catabolic Reactions• Digestion• Cellular Respiration• Detoxification in the liver and blood by catalase• etc…

(B) Breaking down of complex substances

Catabolic Reactions• Digestion• Cellular Respiration• Detoxification in the liver and blood by catalase• etc…

Enzyme-Catalyzed Anabolic ReactionsEnzyme-Catalyzed Anabolic Reactions

Protein SynthesisProtein Synthesis

• Synthesis of proteins from amino acids in the cytoplasm

PhotosynthesisPhotosynthesis

• Synthesis of sugar from carbon dioxide and water

Glycogen formationGlycogen formation

• Conversion of glucose to glycogen for storage.

Enzyme-Catalyzed Catabolic ReactionsEnzyme-Catalyzed Catabolic Reactions

DigestionDigestion

• Breakdown of complex food substances to smaller, simpler, more soluble and diffusible substances.

• So that food can pass through the cell membrane and be absorbed into the bloodstream.

• Enzymes involved – Hydrolases (e.g Carbohydrases, Proteases and Lipases)

Enzyme-Catalyzed Catabolic ReactionsEnzyme-Catalyzed Catabolic Reactions

Cellular RespirationCellular Respiration

• Oxidation of glucose by cells to release energy.

• Many enzymes involved

Enzyme-Catalyzed Catabolic ReactionsEnzyme-Catalyzed Catabolic Reactions

Detoxification in the liver and bloodDetoxification in the liver and blood

• Conversion of toxic to non-toxic substances

• Example: Conversion of toxic Hydrogen peroxide, H2O2 (a by-product of cellular respiration) to non-toxic water and oxygen by enzyme CATALASE

Classification of enzymesHydrolasesHydrolases

• Enzymes that catalyzes hydrolytic reactions which involves the addition of water molecules to breakdown a complex molecule

• Examples of hydrolytic reactions: Digestion of carbohydrates,

proteins & fats

Classification of enzymesHydrolasesHydrolases

Types of Hydrolases

Example(s) Substrate

Carbohydrases Salivary and pancreatic amylase Starch

Cellulase produced by some bacteria

Cellulose

Proteases Pepsin produced in the stomach Proteins

Trypsin produced as an inactive form (trypsinogen) by the pancreas

Proteins

Erepsin produced by intestinal glands

Polypeptides

Lipases Pancreatic and Intestinal lipases Fats

Classification of enzymesOxidation-Reduction EnzymesOxidation-Reduction Enzymes

• Enzymes that are involved in cellular respiration.

• Breaks down glucose to release energy, carbon dioxide and water

15

Test yourself

With questions in Textbook Page 75

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Test yourself – pg 75 - answers

1 An enzyme is a biological catalyst made of protein. It alters the rate of a chemical reaction without itself being chemically changed at the end of the reaction.

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Test yourself – pg 75 - answers

2 Yes, the statement is valid. Large, insoluble molecules such as carbohydrates, fats and proteins cannot diffuse through the cell surface membrane. They must first be converted into simpler, smaller substances, which are soluble and diffusible.

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Test yourself – pg 75 - answers

3 Meat contains mostly proteins, hence we can infer that this enzyme acts on proteins. The enzyme could soften meat by breaking down the proteins into peptides or amino acids.

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Test yourself – pg 75 - answers

4 A very rapid, violent chemical reaction would take place, with a thick layer of foam produced. Water and oxygen are produced when catalase in the red blood cells breaks down hydrogen peroxide.