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Chemistry. Session. BIOMOLECULES - 2. Session Objectives. Enzymes Cofactors Sucrase Mechanism Carboxypeptidase Metabolism DNA and RNA Lipids Hormones and Vitamins. Enzymes. An enzyme is a protein that acts as a catalyst for a biological reaction.

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Session objectives
Session Objectives

  • Enzymes

  • Cofactors

  • Sucrase Mechanism

  • Carboxypeptidase

  • Metabolism

  • DNA and RNA

  • Lipids

  • Hormones and Vitamins


An enzyme is a protein that acts as a catalyst for a biological reaction.

Most enzymes are specific for substrates while enzymes involved in digestion such as papain attack many substrates


In addition to the protein part, many enzymes also have a nonprotein part called a cofactor

The protein part in such an enzyme is called an apoenzyme, and the combination of apoenzyme plus cofactor is called a holoenzyme. Only holoenzymes have biological activity; neither cofactor nor apoenzyme can catalyze reactions by themselves

A cofactor can be either an inorganic ion or an organic molecule, called a coenzyme

Many coenzymes are derived from vitamins, organic molecules that are dietary requirements for metabolism and/or growth

Types of enzymes by function
Types of Enzymes by Function

Enzymes are usually grouped according to the kind of reaction they catalyze, not by their structures

How do enzymes work citrate synthase
How Do Enzymes Work? Citrate Synthase

Citrate synthase catalyzes a mixed Claisen condensation of acetyl CoA and oxaloacetate to give citrate

Normally Claisen condensation require a strong base in an alcohol solvent but citrate synthetase operates in neutral solution

Sucrase mechanism

Sucrase Mechanism

Sucrase mechanism1

Sucrase Mechanism

The structure of citrate synthase
The Structure of Citrate Synthase

Determined by X-ray crystallography

Enzyme is very large compared to substrates, creating a complete environment for the reaction

Aspects of metabolism
Aspects of Metabolism

  • Metabolism.

  • The life process.

  • Catabolism.

    • Substances are broken down.

  • Anabolism.

    • Substances are built up.


  • Lipid metabolism.

    • Uptake of fats through walls of intestine.

    • Glycerol converted to glyceraldehyde-3-phosphate.

    • Fatty acids are oxidized by –oxidation.

  • Protein metabolism.

    • Stomach:

      • HCl and pepsin hydrolize 10% of peptide bonds.

    • Intestine:

      • Trypsin and chymotrypsin cleave peptide fragments further.

Components of dna and rna
Components of DNA and RNA

DNA: Deoxyribonucleic acid.

Chromosomes: Double stranded DNA rod-like structures.

Genes: Specific locations on chromasomes that code for specific traits.

RNA: Ribonucleic acid

Contains ribose instead of deoxyribose.

Generally single stranded.

Focus on protein synthesis and the genetic code
Focus On Protein Synthesis and the Genetic Code

The genetic code

How triplets of the four nucleotides unambiguously specify 20 amino acids, making it possible to translate information from a nucleotide chain to a sequence of amino acids.


How RNA polymerase, guided by base pairing, synthesizes a single-stranded mRNA copy of a gene’s DNA template

Protein synthesis translation
Protein Synthesis(Translation)


How base pairing between mRNA and tRNAs directs the assembly of a polypeptide on the ribosome

Fats and oils
Fats and Oils

  • Both are triglycerides.

    • Differ in the nature of the acid components attached.

    • Both are colorless, odorless and tasteless

    • Flavors and aromas come from organic impurites.

  • Fats.

    • Predominantly saturated fatty acids.

    • Normally solid at room temperature

  • Oils.

    • Predominantly unsaturated fatty acids.

    • Liquids at room temperature.


Hormones are molecules that transfer information from one group of cells to a distant tissue or organ.

They are produced by various endocrine glands.

They are classified on the basis of their structure or site of activity in the cell.


  • They are essential dietary factors required by an organism in minute quantities.

  • They are essential for life and their absence causes deficiency diseases.

  • Vitamins catalyze biological reactions in very low concentration

  • Vitamins are designated A,B,C,D,etc. in order of their discovery. Subgroup vitamins are designated by number subscript e.g. B1,B2,B6,B12

  • Classification:

  • Fat soluble

  • Water soluble