Section 1: Heredity Basics

Genotype vs. Phenotype

Understanding the distinction between genotype and phenotype is fundamental in genetics. The genotype refers to the genetic makeup of an organism, while the phenotype is the observable physical or biochemical characteristics.

• Genotype: The set of genes carried by an organism.

• Phenotype: The expression of the genotype as traits.

• Example: A bacterium may have a gene for antibiotic resistance (genotype), which results in survival in the presence of antibiotics (phenotype).

Prokaryotic vs. Eukaryotic Chromosomes

Chromosomes are structures that contain DNA. Prokaryotes typically have a single, circular chromosome, while eukaryotes have multiple, linear chromosomes.

• Prokaryotic Chromosomes: Usually circular, found in the nucleoid region.

• Eukaryotic Chromosomes: Linear, located in the nucleus.

• Additional info: Plasmids are extra-chromosomal DNA found in prokaryotes and some eukaryotes.

Section 2: DNA Replication

DNA Replication Process

DNA replication is the process by which a cell duplicates its DNA before cell division. It is semi-conservative, meaning each new DNA molecule contains one old and one new strand.

• Key Enzymes: DNA polymerase (synthesizes new DNA), helicase (unwinds DNA), primase (synthesizes RNA primers), ligase (joins DNA fragments).

• Replication Fork: The area where DNA unwinding and synthesis occur.

• Leading vs. Lagging Strand: Leading strand is synthesized continuously; lagging strand is synthesized in Okazaki fragments.

• Equation: (replication)

Section 3: Transcription

Transcription Overview

Transcription is the process of synthesizing RNA from a DNA template. It is the first step in gene expression.

• Key Enzyme: RNA polymerase.

• Types of RNA: mRNA (messenger), tRNA (transfer), rRNA (ribosomal).

• Location: Occurs in the cytoplasm for prokaryotes and nucleus for eukaryotes.

• Equation: (transcription)

• Reverse Transcription: The process by which RNA is converted back to DNA, as seen in retroviruses.

Section 4: Translation & Protein Synthesis

Translation Process

Translation is the process by which ribosomes synthesize proteins using mRNA as a template.

• Key Components: Ribosome, mRNA, tRNA, amino acids.

• Steps: Initiation, elongation, termination.

• Equation: (translation)

• Genetic Code: Codons in mRNA specify amino acids.

Section 5: Mutations

Types and Effects of Mutations

Mutations are changes in the DNA sequence that can affect gene function and phenotype.

• Types: Substitution, insertion, deletion, frameshift.

• Effects: Can be beneficial, neutral, or harmful.

• Example: Antibiotic resistance in bacteria often arises from mutations.

Section 6: Genetic Variation Without Sexual Reproduction

Horizontal Gene Transfer

Prokaryotes can exchange genetic material through horizontal gene transfer, increasing genetic diversity.

• Transformation: Uptake of naked DNA from the environment.

• Transduction: Transfer of DNA by bacteriophages.

• Conjugation: Direct transfer of DNA between cells via pili.

• Plasmids: Small, circular DNA molecules that can carry antibiotic resistance genes.

Section 7: Regulation of Gene Expression

Gene Regulation Mechanisms

Cells regulate gene expression to respond to environmental changes and maintain homeostasis.

• Operons: Groups of genes regulated together in prokaryotes (e.g., lac operon).

• Regulatory Proteins: Activators and repressors control transcription.

• Example: The lac operon is activated in the presence of lactose.

Section 8: Summary Table – Types of RNA

The following table summarizes the main types of RNA and their functions: