Heredity and Genetics Overview

Heredity, Genetics, and Genetic Material

• Heredity is genetic inheritance
• Genetics is the study of inheritable biological traits
• Genome: the complete set of genetic material (chromosomes and genes) in an organism
• Gene: a segment of DNA that codes for a specific cell function (protein or RNA)
• Phenotype: observable characteristics
• Genotype: genetic makeup inherited from parents

Comparing Genetic Material

• Eukaryotes:
  • Linear DNA organized into chromosomes
  • DNA located in the nucleus (with some in mitochondria/chloroplasts)
  • Chromosomes associated with histone proteins (chromatin)
  • Multiple chromosomes (e.g., humans have 46)
  • Larger, more complex DNA with introns (non-coding regions) and regulatory sequences
• Prokaryotes:
  • Single, circular chromosome
  • DNA located in the nucleoid region (no membrane-bound nucleus)
  • DNA not bound by histones, but associated with proteins
  • May contain plasmids (small, circular DNA)
  • Smaller genomes, lack introns, fewer regulatory sequences
• Viruses:
  • DNA or RNA (single-stranded or double-stranded)
  • No cellular structure, require a host to replicate
  • Viral genomes are usually linear or circular, packaged within a protein coat (capsid), sometimes with a lipid envelope
  • Very small genomes, encoding only essential replication genes

DNA Organization and Packaging

• Eukaryotes:
  • DNA wrapped around histone proteins to form nucleosomes, then folded into complex structures forming chromosomes
  • Highly condensed during cell division for accurate chromosome segregation
• Prokaryotes:
  • Single circular chromosome in the nucleoid region
  • May contain plasmids (independent DNA fragments)
  • DNA associated with proteins to maintain structure/replication
• Viruses:
  • DNA or RNA enclosed within a protein capsid, sometimes with a lipid envelope
  • Genomes may be circular or linear, vary in size

DNA Structure and Significance

• DNA is a polymer of nucleotides
  • Phosphate group
  • Deoxyribose sugar (DNA) or Ribose (RNA)
  • Nitrogenous base (adenine, thymine, cytosine, guanine)
• Double helix structure, anti-parallel strands
  • A pairs with T (2 H-bonds)
  • C pairs with G (3 H-bonds)
• Double-helix allows efficient information storage/transmission
• Base pairing ensures replication accuracy

Nitrogenous Bases

• Purines: Adenine (A), Guanine (G)
• Pyrimidines: Cytosine (C), Thymine (T), Uracil (U)
• A pairs with T (DNA) or U (RNA)
• C pairs with G

DNA Replication (Prokaryotes)

• Semi-conservative: Each new DNA molecule has one old and one new strand
• Location: Cytoplasm
• Steps:
  • Initiation: Replication starts at the origin of replication (oriC)
  • Elongation: DNA polymerase III synthesizes new strands (5' to 3')
    • Leading strand continuous
    • Lagging strand in Okazaki fragments
  • Termination: Replication ends at termination sites; DNA ligase seals gaps

Flow of Genetic Information

• Central Dogma: DNA → RNA → Protein
  • DNA transcribed into RNA (mRNA)
  • mRNA translated into protein (by ribosomes and tRNA)

DNA Structure and Genetic Expression

• DNA structure provides template for RNA synthesis through transcription
• Genes are DNA sequences coding for proteins
• Base sequence in gene determines amino acid sequence in protein
• Protein structure/function determined by amino acid sequence

Transcription

• Location: Nucleus (eukaryotes), cytoplasm (prokaryotes)
• Steps:
  • Initiation: RNA polymerase binds to promoter region
  • Elongation: RNA polymerase synthesizes mRNA, complementary to DNA
  • Termination: RNA polymerase reaches terminator sequence, mRNA released

Genetic Code, Codons, and Anticodons

• Genetic code: set of rules for mRNA to code for proteins
• Codons: 3-nucleotide sequences in mRNA that specify amino acids/stop
• Anticodons: 3-nucleotide sequences in tRNA, complementary to mRNA codons
• tRNA anticodon binds to mRNA codon, ensuring correct amino acid placement

Translation (Protein Synthesis)

• Location: Ribosome (cytoplasm)
• Participants: mRNA, tRNA, ribosome
• Steps:
  • Initiation: Ribosome binds to mRNA at start codon (AUG), first tRNA binds
  • Elongation: Ribosome moves along mRNA, tRNAs bring amino acids
  • Termination: Stop codon reached, polypeptide chain released

Bacterial Recombination

• Transformation: Uptake of free DNA by bacteria, incorporation into genome
• Conjugation: Direct transfer of DNA between cells via sex pilus
• Transduction: Transfer of DNA by bacteriophages (viruses infecting bacteria)

Conjugation

• Main features: Sex pilus, F plasmid transfer
• Outcomes: Gene transfer, increased genetic diversity, antibiotic resistance

Transformation

• Requirements: Bacterial competence (ability to take up DNA), naked DNA
• Outcome: Acquiring foreign genes, evolutionary advantage

Transduction

• Process: Bacteriophage infection, packaging of bacterial DNA, transfer to new cell
• Outcome: Gene transfer, genetic diversity, evolution

Transposons

• Features: Mobile genetic elements
• Importance: Genetic diversity, horizontal gene transfer, antibiotic resistance

Dive into the fascinating world of heredity and genetics. This quiz explores genetic inheritance, the structure of genetic material in eukaryotes and prokaryotes, and key concepts such as genotype and phenotype. Test your knowledge of the principles that govern biological traits and genomic structure.