2.3.2 Fundamental Biological Molecules

The four biological molecules including carbohydrates, proteins, lipids, and nucleic acids are of fundamental nature in protoplasm because they are essentially present in each cell.

• They are found in the simplest prokaryotic cell as well as in the most advanced mammalian cell.
• These fundamental biomolecules are important for the maintenance of cell structure and their specific metabolic activities.

Roles of Fundamental Biomolecules:

Proportions of Biomolecules in Bacterial and Mammalian Cells

Important Observations:

• Water is the most abundant molecule in both bacterial and mammalian cells (70%).
• Proteins are the second most abundant (15–18%).
• RNA is more abundant in bacterial cells (6%) than in mammalian cells (1.1%).
• DNA is more abundant in bacterial cells (1%) than in mammalian cells (0.25%).
• Inorganic ions are present in small amounts (1%) in both.

Intermediate Level

Bioelements in Detail

Major Bioelements (99% of protoplasm):

Minor Bioelements (less than 1%):

Fundamental Biomolecules in Detail

• Made of C, H, O.
• Function: Fuel for metabolic activities.
• Examples: Glucose, starch, glycogen, cellulose.

• Made of C, H, O, N (sometimes S).
• Function: Structural (membranes, ribosomes, cytoskeleton) and functional (enzymes).
• Examples: Collagen, hemoglobin, enzymes.

• Made of C, H, O (less oxygen than carbohydrates).
• Function: Energy storage, insulation, protection, membrane structure.
• Examples: Fats, oils, phospholipids, steroids.

• Made of C, H, O, N, P.
• Function: Storage and transmission of genetic information.
• Examples: DNA, RNA.

Proportions of Biomolecules

• Water is the solvent for all biochemical reactions.
• It is essential for the structure and function of the cell.

• Proteins are involved in almost all cell functions.
• They are structural components and enzymes.

• Bacteria have a high metabolic rate and need many ribosomes for protein synthesis.
• rRNA is a major component of ribosomes.

• Bacterial cells have a higher DNA-to-mass ratio compared to mammalian cells.
• Mammalian cells are larger and have more cytoplasm.

Important Points

• 1. Protoplasm is the living mass of the cell specifically, and of organisms generally.
• 2. All biochemical reactions and activities essential for a cell to sustain take place in protoplasm.
• 3. Protoplasm is chiefly composed of bioelements and biomolecules.
• 4. Out of 92 naturally occurring elements on earth, approximately 25 elements are found in living organisms and are called bioelements.
• 5. The human body is composed of only 16 of these bioelements.
• 6. Only six bioelements constitute about 99% of the protoplasm and are called major bioelements.
• 7. The six major bioelements are:
• - Oxygen (65%)
• - Carbon (18%)
• - Hydrogen (10%)
• - Nitrogen (3%)
• - Calcium (2%)
• - Phosphorus (1%)
• 8. Those bioelements which are less than 1% of protoplasm are called minor bioelements.
• 9. The bioelements combine with each other to form thousands of different biomolecules.
• 10. Biomolecules may be:
• - Inorganic – Water and minerals
• - Organic – Carbohydrates, lipids, proteins, and nucleic acids
• 11. The four fundamental biological molecules are:
• - Carbohydrates – Act as fuel for metabolic activities
• - Proteins – Present in membranes, ribosomes, cytoskeleton, and enzymes
• - Lipids – Provide reserve energy source; shape, protect, and insulate cells
• - Nucleic acids – DNA controls cell activity; RNA takes genetic information from DNA and plays role in protein synthesis
• 12. Proportions of biomolecules in bacterial and mammalian cells:
• - Water: 70% (both)
• - Protein: 15% (bacterial), 18% (mammalian)
• - Carbohydrates: 3% (bacterial), 4% (mammalian)
• - Lipids: 2% (bacterial), 3% (mammalian)
• - DNA: 1% (bacterial), 0.25% (mammalian)
• - RNA: 6% (bacterial), 1.1% (mammalian)
• - Other organic molecules: 2% (both)
• - Inorganic ions: 1% (both)

Remember

• - Protoplasm = living mass of the cell
• - Bioelements = elements found in living organisms
• - 25 bioelements found in living organisms; 16 in human body
• - Major bioelements = 6 elements (O, C, H, N, Ca, P) = 99% of protoplasm
• - Minor bioelements = less than 1%
• - Biomolecules = inorganic (water, minerals) + organic (carbohydrates, proteins, lipids, nucleic acids)
• - Four fundamental biomolecules: Carbohydrates, proteins, lipids, nucleic acids
• - Water = 70% (most abundant)
• - Proteins = 15–18% (second most abundant)
• - RNA = more in bacteria (6%) than mammals (1.1%)
• - DNA = more in bacteria (1%) than mammals (0.25%)

Common Mistakes

• 1. Confusing bioelements and biomolecules – Bioelements are elements; biomolecules are molecules formed by bioelements.
• 2. Thinking all 25 bioelements are present in the human body – The human body has only 16 bioelements.
• 3. Confusing major and minor bioelements – Major = 99% of protoplasm (6 elements); Minor = less than 1%.
• 4. Forgetting the six major bioelements – Oxygen, Carbon, Hydrogen, Nitrogen, Calcium, Phosphorus.
• 5. Thinking water is an organic molecule – Water is an inorganic molecule.
• 6. Confusing the roles of DNA and RNA – DNA controls cell activity and stores genetic information; RNA takes genetic information from DNA and plays role in protein synthesis.
• 7. Thinking proteins are only structural – Proteins are also functional (enzymes, hormones, antibodies, etc.).
• 8. Forgetting that RNA is more abundant in bacteria – RNA is 6% in bacteria vs. 1.1% in mammals.
• 9. Thinking DNA is more abundant in mammals – DNA is 1% in bacteria vs. 0.25% in mammals.
• 10. Forgetting that water is 70% in both bacterial and mammalian cells – Water is the most abundant molecule in both.
• 11. Confusing carbohydrates and lipids as energy sources – Both are energy sources, but carbohydrates are the primary fuel; lipids are for long-term storage.
• 12. Thinking nucleic acids are only in the nucleus – DNA is in the nucleus (chromosome); RNA is in the nucleoplasm and cytoplasm.

Quick Revision

• The living mass of the cell specifically, and of organisms generally, is called protoplasm.
• All the biochemical reactions and activities essential for a cell to sustain take place in protoplasm.
• It is chiefly composed of bioelements and biomolecules which make and run the machinery of the cell, i.e., cellular organelles.
• Out of 92 naturally occurring elements on earth, approximately 25 elements are found in living organisms and are called bioelements.
• However, the human body is composed of only 16 of these bioelements.
• Only six bioelements constitute about 99% of the protoplasm so called major bioelements and those which are less than 1% of protoplasm are called minor bioelements.
• The bioelements combined with each other to form thousands of different biomolecules which may be inorganic (water and minerals) and organic (carbohydrates, lipids, proteins, and nucleic acids).
• The four biological molecules including carbohydrates, proteins, lipids, and nucleic acids are of fundamental nature in protoplasm because they are essentially present in each cell.
• They are found in the simplest prokaryotic cell as well as in the most advanced mammalian cell.
• These fundamental biomolecules are important for the maintenance of cell structure and their specific metabolic activities.
• Carbohydrates present in the cytoplasm of the cells act as fuel for the metabolic activities of the cell.
• Proteins are present in the membranes, ribosomes, cytoskeleton, and enzymes of the cell.
• Different types of lipids are present in the membranes and cytoplasm of the cell. Lipids provide a reserved energy source, shape, protect, and insulate the cells.
• The nucleic acid DNA is present in the chromosome. It controls the cell activity.
• The nucleic acid RNA is present in the nucleoplasm and cytoplasm. It takes genetic information from DNA and plays role in protein synthesis.
• The proportions of these biomolecules in bacterial and mammalian cells are given in the table 2.1.

60-Second Revision

• Protoplasm = living mass of the cell
• Bioelements = elements in living organisms
• Major bioelements = 6 elements (O, C, H, N, Ca, P) = 99%
• Minor bioelements = less than 1%
• Biomolecules = inorganic (water, minerals) + organic (carbohydrates, proteins, lipids, nucleic acids)
• Four fundamental biomolecules: Carbohydrates, proteins, lipids, nucleic acids
• Water = 70% (most abundant)
• Proteins = 15–18% (second most abundant)
• RNA = more in bacteria (6%) than mammals (1.1%)
• DNA = more in bacteria (1%) than mammals (0.25%)
• Warning: Bioelements are not the same as biomolecules. The human body has 16 bioelements, not 25. Water is inorganic. DNA and RNA have different roles. RNA and DNA are more abundant in bacteria than in mammals.