Key Terms in Immunology and Molecular Genetics

Key Concepts in Immunology and Molecular Genetics

Immunology: Defense Mechanisms of the Body

The immune system protects organisms from pathogens through a variety of mechanisms. Understanding the types of immunity and the roles of different immune cells is essential for grasping how the body defends itself against disease.

• Pathogen: A foreign organism (such as a virus, bacterium, or parasite) that causes disease.

• Innate Immunity: The body's fast, non-specific, and immediate defense system present from birth. It includes barriers like skin and mucous membranes, as well as immune cells that attack invaders indiscriminately.

• Adaptive Immunity: A slower, highly specific immune response that develops after exposure to specific pathogens. It involves memory, allowing for a faster response upon re-exposure to the same pathogen.

• Antigen: Any molecule that triggers an immune response, typically found on the surface of pathogens.

• Antibody: A protein produced by B cells that specifically binds to antigens, marking them for destruction or neutralization.

• B Cell: A type of white blood cell (lymphocyte) that produces antibodies as part of the adaptive immune response.

• Cytotoxic T Cell: A T cell that directly kills infected or cancerous cells.

• Helper T Cell: A T cell that assists other immune cells by releasing signaling molecules called cytokines.

Genetics: The Molecular Basis of Inheritance

Genetics explores how information is stored, transmitted, and expressed in living organisms. Key molecules such as DNA and RNA play central roles in these processes.

• Genotype: The genetic makeup of an organism; the specific set of genes it carries.

• Phenotype: The observable characteristics or traits of an organism, resulting from the interaction of its genotype with the environment.

• Gene: A segment of DNA that codes for a specific protein or functional RNA.

• Allele: Different versions of a gene that may produce variations in a trait.

• Chromosome: A structure composed of DNA and proteins that contains many genes. Humans have 23 pairs of chromosomes.

• DNA (Deoxyribonucleic Acid): The molecule that stores genetic information in all living organisms. Its structure is a double helix.

• RNA (Ribonucleic Acid): A molecule involved in gene expression and regulation. Types include mRNA, tRNA, and rRNA.

• Transcription: The process by which a segment of DNA is copied into messenger RNA (mRNA).

• Translation: The process by which the sequence of an mRNA molecule is used to build a protein at the ribosome.

• Mutation: A permanent change in the DNA sequence, which can affect gene function and phenotype.

Summary Table: Key Terms and Definitions

Term	Definition
Pathogen	Foreign organism causing disease
Innate Immunity	Fast, non-specific defense present from birth
Adaptive Immunity	Slow, specific defense acquired after exposure
Antigen	Molecule that triggers immune response
Antibody	Protein that binds antigens
B Cell	White blood cell producing antibodies
Cytotoxic T Cell	Kills infected or cancerous cells
Helper T Cell	Assists other immune cells
Genotype	Genetic makeup of an organism
Phenotype	Observable traits of an organism
Gene	Segment of DNA coding for a trait
Allele	Variant form of a gene
Chromosome	DNA structure containing genes
DNA	Molecule storing genetic information
RNA	Molecule involved in gene expression
Transcription	DNA to mRNA process
Translation	mRNA to protein process
Mutation	Permanent change in DNA sequence

Example: Central Dogma of Molecular Biology

• Central Dogma: The flow of genetic information in cells is described as DNA → RNA → Protein.

$\text{DNA} \xrightarrow{\text{transcription}} \text{RNA} \xrightarrow{\text{translation}} \text{Protein}$