Chapter 4 Chemical Composition of The Cell

  • The following elements can be found in a cell:

carbon, hydrogen, oxygen, nitrogen, sulphur,

phosphorus, calcium, potassium, magnesium,

chlorine, sodium and ferum.

  • Chemical compounds in the cell include carbohydrates, lipids, proteins, nucleic acids and water. Chemical compounds can be classified into organic compounds and inorganic compounds.
  • Organic compounds originate from living things and contain carbon. Inorganic compounds originate from non living things and do not contain the carbon element except the carbonates and oxides as well as sulphides of carbon.
  • Water is a molecule composed of two atoms of hydrogen and one atom of oxygen. It is an important component of cells and makes up more than 75% of the cell weight.
  • Water has many uses in an organism. These

- as
a universal solvent

- essential in photosynthesis

- as a transport medium for organisms

- regulates body temperature in organisms

-provides support to the plants

- as a lubricant in the digestive system and

in the joints between skeletal bones

  • Protein is composed of carbon, hydrogen, oxygen, nitrogen, sulphur and phosphorus.
  • The proteins are the most fundamental constituents of protoplasm.
  • The enzymes and chromosomes framework are also of protein nature.
  • The basic unit that forms the protein is amino acid. About twenty-five amino acids form various proteins.
  • Proteins are nitrogenous compounds formed by the condensation of large numbers of amino acids. On complete hydrolysis the amino acids are separated again.
  • Carbohydrates are made up of the elements carbon, hydrogen and oxygen, the latter two elements being in the proportion of two is to one.
  • Carbohydrates include simple sugars and compounds formed by a combination of these.
  • Carbohydrates form important food storage compounds (like starch, glycogen, sucrose) structural materials (cellulose, lignin) and respiratory substrates (hexose sugars -glucose).
  • Lipids include the oils and fats (also known as glycerides)
  • Lipids are made up of the elements hydrogen, carbon and oxygen.
  • All the lipids are insoluble in water but soluble in some organic solvents.
  • The main concentrations of lipid material are found in the adipose tissues of animals and in oily seeds. Lipids also form an important part of the protoplasm being present in every living cell.
  • Lipid provides energy to the cells.
  • Nucleic acids are made up of the elements carbon, oxygen, hydrogen, phosphorus and nitrogen.
  • The two types of nucleic acids are ribonucleic acid (RNA) and deoxyribonucleic acid. (DNA).
  • The nucleic acids, are the fundamental constituents of chromosomes.
  • The DNA molecule plays an important role in genetic inheritance.
  • The RNA molecule is important in the synthesis of protein.
  • Enzymes are biological catalysts which are synthesised within cells and accelerates the rate of biochemical reactions.
  • Enzymes are protein in nature. This ensures that the catalytic function is highly specific.
  • An enzyme allows a reaction to proceed rapidly under suitable physiological conditions of temperature and pH.
  • The general characteristics of enzymes are as


- required in small quantity only

- enzyme actions are reversible

- enzymes are easily denatured by extreme pH

and temperature conditions

  • Intracellular enzymes are synthesized within the cell and functions within the cell, whereas extra cellular secreted by the cells are channeled to where they are required.
  • Enzymes are sensitive to various factors in the environment and the rate at which an enzyme-catalysed reaction proceeds depends on

- the temperature (optimum temperature for enzyme is between 35CC- 40°C

- the pH (sensitive to change pH)

- the concentration of the enzyme.

- the concentration of the substrate

  • Uses of enzymes in daily life and in industry include the following: tenderising meat, food processing and detergent manufacturing.


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