General Biology Study Notes: Genetics, Evolution, Immunity, and Molecular Biology

IMMUNE SYSTEM

Overview of the Immune System

The immune system is a complex network of cells, tissues, and organs that defend the body against pathogens such as viruses, bacteria, and parasites. It consists of innate and adaptive components that work together to recognize and eliminate foreign invaders.

• Pathogen: A foreign organism (e.g., virus, bacteria, parasite) that causes disease.

• Immune System: Cells, tissues, and organs that protect the body from pathogens.

• Innate Immunity: Rapid, non-specific immune defense present at birth.

• Adaptive Immunity: Specific immune defense that develops over time and provides long-lasting protection.

• Antigen: A molecule that triggers an immune response.

• Antibody: A protein made by B cells that binds to antigens and helps neutralize pathogens.

• Phagocytosis: The process by which immune cells engulf and destroy pathogens.

• Phagocyte: Immune cell that performs phagocytosis (e.g., macrophages, neutrophils).

• Inflammation: Immune response causing redness, swelling, heat, and pain; increases blood vessel permeability to allow immune cells to reach infection sites.

• Cytokine: Signaling molecule that attracts and activates immune cells.

• B Cell: Immune cell that produces antibodies.

• Plasma Cell: Activated B cell that secretes antibodies.

• Helper T Cell: Activates B cells and cytotoxic T cells.

• Cytotoxic T Cell: Kills infected or abnormal cells.

• Memory Immune Response: Faster and stronger response upon re-exposure to the same pathogen.

• Vaccine: Triggers immunity without causing disease.

MENDELIAN GENETICS

Basic Principles of Inheritance

Mendelian genetics explains how traits are inherited through discrete units called genes. Gregor Mendel's experiments with pea plants established foundational laws of inheritance.

• Gene: A segment of DNA that codes for a trait.

• Allele: Different forms of a gene.

• Dominant Allele: Masks a recessive allele; expressed when present.

• Recessive Allele: Expressed only when two copies are present.

• Genotype: Genetic makeup of an organism (e.g., AA, Aa, aa).

• Phenotype: Observable physical expression of a trait.

• Homozygous: Two identical alleles for a gene (e.g., AA or aa).

• Heterozygous: Two different alleles for a gene (e.g., Aa).

• Punnett Square: Tool to predict genetic outcomes of crosses.

• Monohybrid Cross: Cross involving one trait.

• Law of Segregation: Alleles separate during meiosis, so each gamete receives one allele.

EVOLUTION

Mechanisms and Evidence of Evolution

Evolution is the process by which populations change over time through genetic variation and natural selection. It explains the diversity of life and adaptation to environments.

• Evolution: Change in allele frequencies in a population over time.

• Natural Selection: Individuals with favorable traits survive and reproduce more successfully.

• Variation: Differences among individuals in a population.

• Selection Pressure: Environmental factor that affects survival and reproduction.

• Fitness: Ability to survive and reproduce in a given environment.

• Antibiotic Resistance: Bacteria evolving to survive antibiotics (example of rapid evolution).

• MRSA: Methicillin-resistant Staphylococcus aureus, a bacterium resistant to many antibiotics.

DNA, RNA, & PROTEINS

Central Dogma and Molecular Biology

Genetic information flows from DNA to RNA to protein, a concept known as the central dogma of molecular biology. This process involves transcription and translation, resulting in the synthesis of proteins that perform cellular functions.

• DNA: Stores genetic information.

• RNA: Helps make proteins; several types include mRNA, tRNA, and rRNA.

• Central Dogma: DNA → RNA → Protein.

• Transcription: DNA is used to make RNA.

• Translation: RNA is used to make proteins.

• mRNA: Carries genetic instructions from DNA to ribosomes.

• tRNA: Transfers amino acids to ribosomes during protein synthesis.

• rRNA: Forms ribosomes, the site of protein synthesis.

• Codon: Three-base sequence on mRNA that codes for an amino acid.

• Anticodon: Complementary sequence on tRNA.

• Start Codon: AUG; signals the start of translation.

• Stop Codon: Ends translation (UAA, UAG, UGA).

• Amino Acid: Building block of proteins.

• Peptide Bond: Bond linking amino acids in a protein chain.

MUTATIONS

Types and Effects of Mutations

Mutations are permanent changes in DNA sequence that can affect protein function and lead to genetic diversity or disease. They can be classified based on their effects on the protein product.

• Mutation: Permanent change in DNA sequence.

• Silent Mutation: No change in amino acid sequence (due to redundancy in the genetic code).

• Missense Mutation: Changes one amino acid in the protein sequence.

• Nonsense Mutation: Creates a stop codon, leading to a truncated protein.

• Frameshift Mutation: Shifts the reading frame, altering all downstream amino acids.