Foundations of Evolution, Heredity, and Biodiversity: Molecules, Cells, and Inheritance

Course Overview

Housekeeping and Logistics

This section outlines essential course policies, communication protocols, and technology requirements for a hybrid General Biology course. Students are expected to engage with readings and lectures, as both will be assessed in exams.

• Course Policies: Homework and in-class assignments must be submitted via designated platforms.

• Hybrid Considerations: Readings and lecture materials are both essential for exam preparation.

• Communication: Announcements are made via Canvas; students are responsible for staying updated.

• Technology: Homework assignments utilize the Pearson interface.

Big Picture: The Role of DNA in Biology

Importance of DNA

DNA is the molecular foundation for all biological processes and heredity. Understanding DNA is crucial for every subfield of biology, as it stores biological information and determines traits passed from parent to offspring.

• Foundation of Heredity: DNA encodes genetic information that is inherited.

• Biological Information: DNA's sequence of nucleotides stores instructions for cellular function.

DNA in Medicine: Factor V and Genetic Mutations

Factor V Protein and the F5 Gene

Factor V is a protein essential for blood clotting, produced by transcribing and translating the F5 gene. Mutations in the F5 gene, such as Factor V Leiden, can lead to abnormal clotting behavior.

• Normal vs. Mutant Allele: The wildtype F5 gene has a guanine (G) at position 1691; the Factor V Leiden mutation replaces it with adenine (A).

• Clinical Impact: Overactive Factor V leads to excessive blood clotting, increasing risk for deep vein thrombosis and pregnancy loss.

Essential Biochemistry: Biological Macromolecules

Macromolecules and Polymers

Macromolecules are large molecules critical for biological structure and function. Many are polymers, composed of repeating monomer units.

• Types: Carbohydrates, lipids, proteins, and nucleic acids.

• Polymer Structure: Proteins, carbohydrates, and nucleic acids are true polymers; lipids are generally not.

General Principle: Structure Begets Function

The structure of macromolecules determines their biological function, illustrating a core principle in cell biology.

Carbohydrates

Structure and Function

Carbohydrates are composed of carbon, hydrogen, and oxygen, and are often referred to as sugars. They serve as primary energy sources and energy storage molecules.

• Monomers: Monosaccharides (e.g., glucose, fructose, ribose).

• Polymers: Polysaccharides (e.g., starch, cellulose) are chains of monosaccharides.

Lipids

Structure and Properties

Lipids are hydrophobic molecules, including phospholipids, triglycerides, and cholesterol. They are not true polymers and are characterized by their nonpolar nature.

• Function: Lipids form cell membranes and store energy.

Proteins

Structure and Diversity

Proteins are polymers of amino acids, joined by peptide bonds. There are 20 different amino acids, and the diversity of protein structures underlies their wide range of functions.

• Polypeptides: Chains of amino acids that fold into specific 3D structures.

• Functions: Enzymes, structural support, transport, signaling, and more.

Nucleic Acids

Structure and Types

Nucleic acids (DNA and RNA) are polymers of nucleotide monomers. DNA stores genetic information, while RNA has various roles in gene expression and regulation.

• DNA: Double-stranded, stabilized by hydrogen bonds between complementary bases.

• RNA: Single-stranded, with multiple functional types (mRNA, tRNA, rRNA).

DNA Structure and Replication

Double Helix and Base Pairing

DNA consists of two strands held together by hydrogen bonds between complementary nitrogenous bases (adenine-thymine, guanine-cytosine).

• Replication: DNA is 'unzipped' and each strand serves as a template for synthesis of a new complementary strand.

• Accuracy: DNA replication is highly accurate, with proofreading mechanisms reducing errors to 1 in 10 billion nucleotides.

• Mutations: Permanent changes in DNA sequence, important for genetic diversity.

Genetic Diversity and Mutations

Role in Evolution

Mutations introduce genetic variation, which is essential for evolution and adaptation. Each individual typically has around 70 new mutations.

DNA Organization in Cells

Genome, Chromosomes, and Genes

The human genome contains approximately 3 billion base pairs. DNA is organized into chromosomes, each containing multiple genes. A gene is a stretch of DNA that codes for a functional product, usually a protein.

• Alleles: Different versions of a gene.

• Karyotype: Visualization of all chromosomes in a cell, organized by homologous pairs.

Cell Division and Genetic Inheritance

Mitotic and Meiotic Division

Cell division ensures identical copies of DNA are passed to daughter cells. In sexual reproduction, homologous chromosomes are randomly allocated to gametes, and crossing over increases genetic diversity.

• Sexual Reproduction: Fusion of gametes from two individuals creates novel gene combinations.

• Cloning: Produces genetically identical offspring; advantageous in stable environments.

Central Dogma of Molecular Biology

Flow of Genetic Information

The central dogma describes the flow of genetic information: DNA is transcribed to mRNA, which is then translated into protein.

• Transcription: DNA is converted to mRNA by RNA polymerase.

• Translation: mRNA is decoded by ribosomes to synthesize polypeptides.

• Codons: Triplet nucleotide sequences in mRNA specify amino acids.

Gene Expression and Regulation

Plasticity and Epigenetics

Gene expression determines which genes are active in a cell, leading to cell specialization. Regulation occurs via mechanisms such as DNA methylation, which can silence genes. Environmental factors can influence gene expression, and some changes are heritable (epigenetics).

• Example: Melanin production in skin cells is upregulated by UV exposure.

• Case Study: Dutch Hunger Winter—famine led to heritable changes in gene expression affecting multiple generations.

Summary Table: Biological Macromolecules

Macromolecule	Monomer	Polymer Name	Main Functions
Carbohydrate	Monosaccharide	Polysaccharide	Energy source, energy storage, structural support
Lipid	Fatty acid, glycerol	Not true polymers	Membrane structure, energy storage, signaling
Protein	Amino acid	Polypeptide	Enzymes, structural support, transport, signaling
Nucleic Acid	Nucleotide	DNA/RNA	Genetic information storage and transfer

Key Equations

• Peptide Bond Formation: $ext{Amino acid 1} + ext{Amino acid 2} ightarrow ext{Dipeptide} + H_2O$

• DNA Replication (Semi-conservative Model): $ext{Original DNA} ightarrow ext{Two DNA molecules, each with one old and one new strand}$

Conclusion

This guide covers the foundational concepts of evolution, heredity, and biodiversity, focusing on the molecular basis of inheritance, the structure and function of biological macromolecules, and the mechanisms of gene expression and regulation.