Intro to Molecular Biology: The Molecules of Life

Intro to Molecular Biology

• Molecular biology focuses on the molecules of life.

Biological Macromolecules

• Definition: Large molecules that perform many important biological functions.

• Key Types:

  • Carbohydrates

  • Lipids

  • Proteins

  • Nucleic Acids

• Polymers: Many biological macromolecules are polymers.

  • A polymer is a large molecule made of repeating units of identical or similar subunits.

  • Each subunit in a polymer is called a monomer.

  • Analogy: Think of a train, where the entire train is a polymer, and each car is a monomer. The connections between cars are like covalent bonds.

  • Nucleic acids, proteins, and complex carbohydrates are all polymers of smaller molecules (monomers).

Nucleic Acids

• Examples: Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

• Structure: They are polymers of nucleotides.

• Functions:

  • Store cellular information.

  • Are the molecules of inherited information, forming the basis for genetics.

  • Often large, very complex molecules.

  • Serve as templates for proteins.

  • Help control the regulation of cellular functions.

Proteins

• Proteins are considered the most versatile of the macromolecules, performing a wide array of functions:

  • Structural: Provide support; examples include collagen, keratin, silk, and tubulin.

  • Storage: Store amino acids; examples include casein and ovalbumin.

  • Transport: Carry substances; an example is hemoglobin (transports oxygen).

  • Hormones: Act as signaling molecules; an example is insulin.

  • Receptor: Receive signals; an example is ASGPR.

  • Contractile: Facilitate movement; an example is actin.

  • Defensive: Protect against disease; an example is antibodies.

  • Enzymatic: Catalyze biochemical reactions; examples include lysozyme and many others.

Carbohydrates

• Composition: Comprise sugars and polymers of sugars.

• Functions: Used for a variety of purposes:

  • Energy: Simple sugars (e.g., glucose).

  • Storage of Energy: Starches (in plants) and glycogen (in animals).

  • Structural Components: Examples include cellulose (plant cell walls) and chitin (fungal cell walls, insect exoskeletons).

Fats (Lipids)

• Primary Function: Used primarily as a long-term method of energy storage.

• Properties:

  • Fats are hydrophobic, meaning they avoid water.

  • Lipid-based molecules can be used as a barrier for water, forming biological membranes.

Useful Background: Chemical Bonds

• Definition: Chemical bonds are forces that keep atoms together in the same molecule.

• Types of Bonds Discussed:

  • Covalent bonds

  • Ionic bonds

  • Hydrogen bonds

Covalent Bonds

• Mechanism: Strong bonds formed when two atoms share electrons.

• Significance: Common in biologically relevant molecules.

• Examples with Molecular Formulas and Structures:

  • (a) Hydrogen ($ext{H}_2$)

  • (b) Oxygen ($ext{O}_2$)

  • (c) Water ($ext{H}_2 ext{O}$)

  • (d) Methane ($ext{CH}_4$)

Ionic Bonds

• Mechanism: Strong bonds that form between positively ($+$) and negatively ($-$) charged ions.

• Strength: Can be very strong.

• Behavior in Water: These bonds typically break in water.

• Example: Table salt (sodium chloride, $ext{NaCl}$) is held together by ionic bonds between a sodium ion ($ext{Na}^+$, a cation) and a chloride ion ($ext{Cl}^-$, an anion).

Hydrogen Bonds

• Strength: Much weaker than covalent or ionic bonds, approximately $1/20$th as strong as a covalent bond.

• Mechanism: Form between weak charges that arise on covalent molecules if electrons are not shared evenly (polarity).

• Dynamism: They form and break rapidly.

• Example: Water molecules can form up to four hydrogen bonds per molecule due to their polarity.

Central Dogma of Molecular Biology

• This fundamental principle describes the flow of genetic information within a biological system.

• Steps:

  1. Transcription: Information contained in DNA is used to encode an RNA molecule.

     • Unlike DNA, RNA can leave the cell nucleus.

  2. Translation: Information in RNA is used as a blueprint to build a specific protein.

  3. Protein Function: The assembled proteins then perform specific functions in the organism.