2.3 Protoplasm and Biological Molecules | Molecular Biology | Biology 11

This section details the chemical makeup of living matter, focusing on the essential elements and molecules that form the basis of all cellular life.

Protoplasm

Protoplasm is the living mass of a cell. It is the site of all biochemical reactions and activities essential for life. It is composed of bioelements and biomolecules that build and operate cellular structures (organelles). Thomas Huxley described it as the "physical basis of life."

Chemical Composition of Protoplasm

Bioelements are the chemical elements found in living organisms. Out of 92 naturally occurring elements, about 25 are bioelements. The human body is composed of 16 bioelements.

Major Bioelements: Six elements that constitute about 99% of the protoplasm. These are Oxygen (65%), Carbon (18%), Hydrogen (10%), Nitrogen (3%), Calcium (2%), and Phosphorus (1%).
Minor Bioelements: Elements that constitute less than 1% of the protoplasm (e.g., Potassium, Sulfur, Chlorine, Sodium, Magnesium, Iron, etc.).

Biomolecules are molecules formed when bioelements combine. They are the building blocks of life.

Inorganic Biomolecules: Includes water and minerals.
Organic Biomolecules: Includes carbohydrates, lipids, proteins, and nucleic acids.

Figure 2.3: Proportions of various bioelements in the human body.

Metabolism

The sum of all chemical reactions occurring within the protoplasm is called metabolism. This includes:

Anabolism: The synthesis of complex molecules from simpler ones (requires energy).
Catabolism: The breakdown of complex molecules into simpler ones (releases energy).

Fundamental Biological Molecules

These four molecules are essential and present in all cells, from simple prokaryotes to complex mammals. They are crucial for maintaining cell structure and metabolic activities.

Carbohydrates: Act as the primary fuel for the metabolic activities of the cell. Found in the cytoplasm and cell walls.

Proteins: Structural and functional components. Found in cell membranes, ribosomes, the cytoskeleton, and as enzymes.

Lipids: Provide a reserved energy source. They also contribute to cell shape, protection, and insulation. Found in membranes and the cytoplasm.

Nucleic Acids: Carry and transmit genetic information.

DNA (Deoxyribonucleic acid): Located in chromosomes. It contains the genetic code that controls all cell activities.
RNA (Ribonucleic acid): Found in the nucleoplasm and cytoplasm. It transfers genetic information from DNA to be used in protein synthesis.

Proportions of Biomolecules in Cells

The relative amounts of these molecules can vary between different types of cells, as shown below.

Table 2.1: Proportions of various biomolecules in bacterial and mammalian cells	Bacterial cell	Mammalian cell
Water	70%	70%
Protein	15%	18%
Carbohydrates	3%	4%
Lipids	2%	3%
DNA	1%	0.25%
RNA	6%	1.1%
Other organic molecules (enzymes, hormones, metabolites)	2%	2%
Inorganic ions ( $N a^{+}$ , $K^{+}$ , $C a^{2 +}$ , $M g^{2 +}$ , $C l^{-}$ , $S O_{4}^{2 -}$ )	1%	1%

Cytoplasm and Organelles→

This section details the chemical makeup of living matter, focusing on the essential elements and molecules that form the basis of all cellular life.

Protoplasm

Chemical Composition of Protoplasm

Bioelements are the chemical elements found in living organisms. Out of 92 naturally occurring elements, about 25 are bioelements. The human body is composed of 16 bioelements.

Major Bioelements: Six elements that constitute about 99% of the protoplasm. These are Oxygen (65%), Carbon (18%), Hydrogen (10%), Nitrogen (3%), Calcium (2%), and Phosphorus (1%).
Minor Bioelements: Elements that constitute less than 1% of the protoplasm (e.g., Potassium, Sulfur, Chlorine, Sodium, Magnesium, Iron, etc.).

Biomolecules are molecules formed when bioelements combine. They are the building blocks of life.

Inorganic Biomolecules: Includes water and minerals.
Organic Biomolecules: Includes carbohydrates, lipids, proteins, and nucleic acids.

Metabolism

The sum of all chemical reactions occurring within the protoplasm is called metabolism. This includes:

Anabolism: The synthesis of complex molecules from simpler ones (requires energy).
Catabolism: The breakdown of complex molecules into simpler ones (releases energy).

Fundamental Biological Molecules

These four molecules are essential and present in all cells, from simple prokaryotes to complex mammals. They are crucial for maintaining cell structure and metabolic activities.

Carbohydrates: Act as the primary fuel for the metabolic activities of the cell. Found in the cytoplasm and cell walls.

Proteins: Structural and functional components. Found in cell membranes, ribosomes, the cytoskeleton, and as enzymes.

Lipids: Provide a reserved energy source. They also contribute to cell shape, protection, and insulation. Found in membranes and the cytoplasm.

Nucleic Acids: Carry and transmit genetic information.

DNA (Deoxyribonucleic acid): Located in chromosomes. It contains the genetic code that controls all cell activities.
RNA (Ribonucleic acid): Found in the nucleoplasm and cytoplasm. It transfers genetic information from DNA to be used in protein synthesis.

Proportions of Biomolecules in Cells

The relative amounts of these molecules can vary between different types of cells, as shown below.

Table 2.1: Proportions of various biomolecules in bacterial and mammalian cells	Bacterial cell	Mammalian cell
Water	70%	70%
Protein	15%	18%
Carbohydrates	3%	4%
Lipids	2%	3%
DNA	1%	0.25%
RNA	6%	1.1%
Other organic molecules (enzymes, hormones, metabolites)	2%	2%
Inorganic ions ( $N a^{+}$ , $K^{+}$ , $C a^{2 +}$ , $M g^{2 +}$ , $C l^{-}$ , $S O_{4}^{2 -}$ )	1%	1%

Cytoplasm and Organelles→