General Biology: Cells and Biological Macromolecules (Nucleic Acids Focus)

Cells and Biological Macromolecules

Introduction to Biological Macromolecules

Biological macromolecules are large, complex molecules essential for life. They include carbohydrates, proteins, nucleic acids, and lipids. These molecules play critical roles in cell structure, function, and regulation.

• Macromolecule: A large molecule composed of smaller subunits (monomers).

• Polymer: A long molecule consisting of many similar or identical monomers linked together.

• Monomer: The basic building block of a polymer.

• Examples: Proteins (polymers of amino acids), nucleic acids (polymers of nucleotides), carbohydrates (polymers of monosaccharides).

Major Classes of Biological Molecules

There are four major classes of biological molecules, three of which are polymers:

• Carbohydrates: Provide energy and structural support.

• Proteins: Perform a wide range of functions, including catalysis, transport, and structural roles.

• Nucleic Acids: Store and transmit genetic information.

• Lipids: Not polymers; important for energy storage and membrane structure.

Formation and Breakdown of Polymers

Polymers are assembled and disassembled through specific chemical reactions:

• Dehydration Reaction: Monomers are joined together by removing a water molecule.

• Hydrolysis Reaction: Polymers are broken down into monomers by adding a water molecule.

• Enzymes: Biological catalysts (usually proteins) that speed up these reactions.

Nucleic Acids

Structure and Function

Nucleic acids are polymers made up of nucleotide monomers. They are responsible for storing and transmitting genetic information in cells.

• Nucleotide: The monomer of nucleic acids, consisting of a sugar, a phosphate group, and a nitrogenous base.

• Nucleic Acid: The polymer (DNA or RNA) formed by linking nucleotides via covalent bonds.

• Function: DNA stores genetic information; RNA acts as a messenger and is involved in protein synthesis.

Primary and Secondary Structure

Nucleic acids have different levels of structure that affect their function:

• Primary Structure: The linear sequence of nucleotides.

• Secondary Structure: The folding and hydrogen bonding between bases (e.g., double helix in DNA, stem-loop structures in RNA).

• DNA: Typically double-stranded, with complementary base pairing (A-T, G-C).

• RNA: Usually single-stranded, but can form secondary structures by folding back on itself.

Nitrogenous Bases and Chargaff's Rules

Nucleic acids contain four main nitrogenous bases:

• Adenine (A) and Guanine (G): Purines (two-ring structure).

• Cytosine (C) and Thymine (T): Pyrimidines (one-ring structure). In RNA, Uracil (U) replaces Thymine.

• Chargaff's Rules: In DNA, the amount of A equals T, and the amount of G equals C.

Central Dogma of Molecular Biology

The central dogma describes the flow of genetic information in cells:

• DNA: Stores genetic information (genes).

• RNA: Messenger (mRNA) that carries instructions from DNA to the cell's protein-making machinery.

• Protein: The functional molecules that perform cellular tasks.

Central Dogma Equation:

$\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$

Applications: Polymerase Chain Reaction (PCR)

PCR is a laboratory technique used to amplify DNA outside of living cells.

• Purpose: To increase the amount of DNA for analysis (e.g., forensic science, ancient DNA studies).

• Process: Uses DNA polymerase to replicate DNA in vitro.

Common Elements in Living Organisms

Survey Results

Most living organisms are composed primarily of the following elements:

• Carbon (C)

• Hydrogen (H)

• Oxygen (O)

• Nitrogen (N)

• Phosphorus (P)

• Sulfur (S)

These elements are fundamental to the structure and function of biological macromolecules.

Survey and Questionnaire Review

Key Concepts from Student Responses

• Enzymes: Proteins that act as biological catalysts, speeding up chemical reactions.

• ATP (Adenosine Triphosphate): The primary energy carrier in cells. When used, ATP is converted to ADP (Adenosine Diphosphate).

• Photosynthesis: Occurs in chloroplasts of plant cells.

• Polymers vs. Non-polymers: Lipids are not polymers; proteins, nucleic acids, and polysaccharides are polymers.

• Crossing Over: Genetic exchange occurs between homologous chromosomes during meiosis.

Student Motivation for Taking Biology

• Interest in biology as a subject

• Requirement for degree

• Desire to learn applicable knowledge

Summary Table: Biological Macromolecules

Macromolecule	Monomer	Polymer	Main Function	Polymerization Reaction
Carbohydrate	Monosaccharide	Polysaccharide	Energy, structure	Dehydration
Protein	Amino acid	Polypeptide	Catalysis, structure, transport	Dehydration
Nucleic Acid	Nucleotide	DNA/RNA	Genetic information	Dehydration
Lipid	Fatty acid, glycerol	Triglyceride, phospholipid	Energy storage, membranes	Not a true polymer

Additional info:

• Some context and definitions have been expanded for clarity and completeness.

• Survey results were interpreted to highlight key biological concepts relevant to the course.