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Molecular Biology: Structure and Function of Biomolecules

February 20, 2025

Introduction to Molecular Biology: Exploring the Structure and Function of Biomolecules in Cellular Processes

1. Introduction to Molecular Biology

Molecular biology is a branch of science that focuses on the molecular underpinnings of biological activity. It seeks to understand how various biomolecules such as DNA, RNA, proteins, and enzymes contribute to the complex functions of cells and organisms.

Structure and Function of Biomolecules,
Introduction to molecular biology basics,
Structure and function of biomolecules,
Role of enzymes in metabolism,
DNA and RNA molecular structure,
Importance of lipids in cells.

Key Focus Areas:

Structure and function of biomolecules
Gene expression and regulation
DNA replication, transcription, and translation
Cellular signaling and enzymatic functions

2. The Central Dogma of Molecular Biology

The central dogma explains the flow of genetic information within a biological system:

DNA Replication – Copying genetic material for cell division
Transcription – Conversion of DNA into messenger RNA (mRNA)
Translation – Synthesis of proteins from mRNA

3. Structure and Function of Biomolecules

Molecular biology revolves around four major classes of biomolecules:

3.1 Nucleic Acids (DNA & RNA)

Deoxyribonucleic Acid (DNA):
- Double-stranded helix
- Stores genetic information
- Composed of nucleotide units: adenine (A), thymine (T), cytosine (C), guanine (G)
Ribonucleic Acid (RNA):
- Single-stranded
- Involved in protein synthesis and gene regulation
- Types of RNA: messenger RNA (mRNA), transfer RNA (tRNA), ribosomal RNA (rRNA)

3.2 Proteins

Composed of amino acids linked by peptide bonds
Function as enzymes, structural components, and signaling molecules
Levels of protein structure:
- Primary structure: Sequence of amino acids
- Secondary structure: Alpha-helices and beta-sheets
- Tertiary structure: Three-dimensional folding
- Quaternary structure: Multiple polypeptide chains forming a complex

3.3 Carbohydrates

Provide energy and structural support
Classified as:
- Monosaccharides: Glucose, fructose
- Disaccharides: Sucrose, lactose
- Polysaccharides: Starch, glycogen, cellulose

3.4 Lipids

Hydrophobic molecules including fats, oils, and phospholipids
Serve as energy storage, cell membrane components, and signaling molecules
Types:
- Triglycerides: Energy storage
- Phospholipids: Form cell membranes
- Steroids: Hormones such as cholesterol

4. Enzymes: Catalysts of Life

Biological catalysts that speed up chemical reactions
Specific to substrates and operate under optimal pH and temperature conditions
Types:
- Hydrolases: Break bonds using water
- Oxidoreductases: Catalyze oxidation-reduction reactions
- Ligases: Join two molecules together

5. DNA Replication and Gene Expression

5.1 DNA Replication

Semi-conservative process ensuring genetic continuity
Key enzymes involved:
- Helicase: Unzips the DNA double helix
- DNA Polymerase: Adds nucleotides to form a new strand
- Ligase: Joins Okazaki fragments on the lagging strand

5.2 Transcription (DNA to RNA)

Initiation: RNA polymerase binds to the promoter region
Elongation: RNA polymerase synthesizes complementary RNA
Termination: RNA synthesis stops, and the mRNA is released

5.3 Translation (RNA to Protein)

mRNA is decoded by ribosomes to synthesize proteins
Key molecules involved:
- Ribosomes: Protein synthesis machinery
- tRNA: Transfers amino acids to the ribosome
- mRNA: Contains codons that specify amino acids

6. Molecular Techniques in Biology

6.1 Polymerase Chain Reaction (PCR)

Amplifies DNA sequences for genetic testing and research

6.2 Gel Electrophoresis

Separates DNA, RNA, or proteins based on size and charge

6.3 CRISPR-Cas9 Technology

Gene editing tool for genetic modifications and disease treatment

7. Applications of Molecular Biology

Genetic engineering and biotechnology
Disease diagnostics and treatment
Drug development and personalized medicine
Agricultural advancements through GMOs

8. Conclusion

Molecular biology is fundamental to understanding life at a microscopic level. By studying biomolecules and their functions, scientists can develop new medical treatments, improve agricultural yields, and enhance biotechnology applications.

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MCQs on “Introduction to Molecular Biology: Structure and Function of Biomolecules”

1. Which of the following is the basic unit of a protein?

A) Monosaccharide
B) Fatty acid
C) Amino acid
D) Nucleotide

✅ Answer: C) Amino acid
Explanation: Proteins are composed of amino acids linked together by peptide bonds. Each amino acid consists of an amino group (-NH₂), a carboxyl group (-COOH), and a unique R group.

2. DNA and RNA are composed of repeating units called:

A) Monosaccharides
B) Nucleotides
C) Amino acids
D) Fatty acids

✅ Answer: B) Nucleotides
Explanation: DNA and RNA are nucleic acids made up of nucleotide units, which consist of a phosphate group, a sugar molecule (deoxyribose in DNA and ribose in RNA), and a nitrogenous base.

3. The backbone of a DNA molecule is composed of:

A) Phospholipids and proteins
B) Sugar and phosphate
C) Amino acids and nitrogenous bases
D) Fatty acids and nucleotides

✅ Answer: B) Sugar and phosphate
Explanation: DNA has a sugar-phosphate backbone, where deoxyribose (sugar) is linked to phosphate groups through phosphodiester bonds.

4. Which nitrogenous base is found in RNA but not in DNA?

A) Adenine
B) Cytosine
C) Thymine
D) Uracil

✅ Answer: D) Uracil
Explanation: RNA contains uracil (U) instead of thymine (T), which is found in DNA. Uracil pairs with adenine (A) in RNA.

5. Enzymes belong to which class of biomolecules?

A) Proteins
B) Carbohydrates
C) Lipids
D) Nucleic acids

✅ Answer: A) Proteins
Explanation: Enzymes are biological catalysts that speed up chemical reactions and are primarily made of proteins.

6. The function of hemoglobin in the body is to:

A) Transport oxygen
B) Digest proteins
C) Store genetic information
D) Conduct nerve impulses

✅ Answer: A) Transport oxygen
Explanation: Hemoglobin is a protein in red blood cells responsible for carrying oxygen from the lungs to tissues.

7. The process by which DNA is copied before cell division is called:

A) Transcription
B) Translation
C) Replication
D) Mutation

✅ Answer: C) Replication
Explanation: DNA replication ensures that each daughter cell receives an exact copy of genetic information.

8. The primary function of carbohydrates in cells is to:

A) Store genetic information
B) Provide energy
C) Synthesize proteins
D) Maintain cell structure

✅ Answer: B) Provide energy
Explanation: Carbohydrates like glucose serve as an immediate energy source through glycolysis and cellular respiration.

9. Which of the following is a polysaccharide?

A) Glucose
B) Fructose
C) Starch
D) Galactose

✅ Answer: C) Starch
Explanation: Starch is a polysaccharide made of glucose units and serves as a storage form of energy in plants.

10. The monomer of nucleic acids is called:

A) Monosaccharide
B) Nucleotide
C) Amino acid
D) Fatty acid

✅ Answer: B) Nucleotide
Explanation: Nucleotides are the building blocks of DNA and RNA, consisting of a sugar, phosphate group, and nitrogenous base.

11. Which of the following is an essential fatty acid?

A) Palmitic acid
B) Stearic acid
C) Linoleic acid
D) Acetic acid

✅ Answer: C) Linoleic acid
Explanation: Essential fatty acids like linoleic acid must be obtained from the diet as the body cannot synthesize them.

12. The type of bond that joins amino acids in a protein is called:

A) Hydrogen bond
B) Ionic bond
C) Peptide bond
D) Glycosidic bond

✅ Answer: C) Peptide bond
Explanation: Peptide bonds form between the amino group of one amino acid and the carboxyl group of another.

13. Which vitamin is a coenzyme in carbohydrate metabolism?

A) Vitamin A
B) Vitamin C
C) Vitamin B1
D) Vitamin D

✅ Answer: C) Vitamin B1
Explanation: Vitamin B1 (thiamine) is essential for carbohydrate metabolism and energy production.

14. Which biomolecule is responsible for catalyzing biochemical reactions?

A) Lipids
B) Enzymes
C) DNA
D) Phospholipids

✅ Answer: B) Enzymes
Explanation: Enzymes are specialized proteins that speed up chemical reactions in the body.

15. The structure of DNA was first described by:

A) Watson and Crick
B) Mendel
C) Franklin and Wilkins
D) Griffith

✅ Answer: A) Watson and Crick
Explanation: James Watson and Francis Crick proposed the double-helix structure of DNA in 1953.

16. The energy currency of the cell is:

A) DNA
B) ATP
C) RNA
D) NADPH

✅ Answer: B) ATP
Explanation: ATP (Adenosine Triphosphate) stores and provides energy for cellular processes.

17. Lipids are insoluble in:

A) Alcohol
B) Ether
C) Water
D) Chloroform

✅ Answer: C) Water
Explanation: Lipids are hydrophobic and do not dissolve in water but are soluble in nonpolar solvents.

18. Which nucleic acid carries genetic information from DNA to ribosomes?

A) tRNA
B) mRNA
C) rRNA
D) miRNA

✅ Answer: B) mRNA
Explanation: Messenger RNA (mRNA) carries genetic instructions from DNA to ribosomes for protein synthesis.

19. The enzyme that unzips the DNA double helix during replication is:

A) DNA ligase
B) Helicase
C) DNA polymerase
D) RNA polymerase

✅ Answer: B) Helicase
Explanation: Helicase breaks hydrogen bonds between base pairs, unwinding the DNA strand for replication.

20. The main function of phospholipids in the cell membrane is to:

A) Store energy
B) Provide structure and permeability
C) Act as enzymes
D) Carry genetic information

✅ Answer: B) Provide structure and permeability
Explanation: Phospholipids form the lipid bilayer, regulating cell membrane fluidity and transport.