Molecular DNA

Chapter 5: Molecular Genetics

Introduction to Molecular Genetics

• Focus on DNA, DNA replication, transcription, and translation.

Sex Chromosomes

• Human Chromosomes: Two types of sex chromosomes: X and Y.

  • Females: Have two X chromosomes (XX).

  • Males: Have one X and one Y chromosome (XY).

Chromosomes Structure

• Chromosomes: Coiled structures made of DNA and proteins that encode genetic information.

  • Homologous Chromosomes: Same size, shape, and contain the same genes.

  • Key Components:

    • Centromere

    • Sister chromatids

Autosomes

• Autosomes: Chromosomes that carry genes unrelated to sex.

Gene Linkage

• Linked Genes: Genes on the same chromosome tend to be inherited.

  • Example: Genes for hair color and eye color.

  • Sex-linked Genes: Most commonly found on the X chromosome.

Genes

• Definition: Basic units of heredity passed from parent to offspring, segments of DNA coding for RNA.

• Functions of RNA:

  • Building proteins

  • Regulating processes inside cells

Human Genes and Alleles

• Alleles: Different versions of a gene, contributing to genetic variation among individuals.

Notable Discoveries in Genetics

• Griffith's Experiment: Showed transformation in bacteria.

• Avery's Experiment: Identified DNA as the transformation agent.

• Hershey and Chase: Demonstrated DNA as genetic material using viruses.

• Chargaff's Rules: Equal concentration of adenine-thymine and guanine-cytosine in DNA.

• Watson and Crick: Discovered the double-helix structure of DNA.

Chargaff’s Rule

• Concentrations of adenine = thymine and guanine = cytosine.

Historical Timeline of Genetic Research

• 1860s: Mendel's experiments with pea plants.

• 1920s: Griffith showed transformation.

• 1940s: Avery confirmed DNA as genetic material.

• 1950s: Hershey and Chase confirmed DNA in viruses.

• 1953: Watson and Crick discovered DNA structure.

Importance of DNA

• DNA: Genetic material determining traits, passed from parent to offspring.

DNA Structure

• Components:

  • Nitrogen bases: Adenine (A), Guanine (G), Cytosine (C), Thymine (T).

  • Purines: A, G (two-ring structure).

  • Pyrimidines: C, T (one-ring structure).

• Double Helix: Discovered by Watson, Crick, and Franklin.

  • Comprised of nucleotides with a phosphate group, deoxyribose sugar, and nitrogen bases.

Central Dogma of Molecular Biology

• Overview: The flow of genetic information: DNA → RNA → Protein.

• DNA located in the nucleus, proteins synthesized in ribosomes in the cytoplasm.

DNA Replication

• Definition: The process of copying DNA during the S phase of the cell cycle.

• Key Enzymes:

  • DNA Helicase: Unwinds the DNA strand.

  • Primase: Synthesizes RNA primers.

  • DNA Polymerase: Adds nucleotides to the new strand.

  • DNA Ligase: Joins Okazaki fragments on the lagging strand.

• Semi-conservative Replication: Each new DNA molecule consists of one original and one new strand.

Protein Synthesis

• Processes:

  • Transcription: DNA to mRNA in the nucleus.

  • Translation: mRNA to protein in the cytoplasm at the ribosomes.

• Result: Central Dogma confirmed.

Transcription Steps

• Initiation: RNA polymerase binds to the promoter, unwinding DNA.

• Elongation: RNA polymerase adds complementary RNA nucleotides.

• Termination: RNA polymerase detaches upon reaching the stop sequence.

Types of RNA

• Messenger RNA (mRNA): Carries instructions from DNA.

• Ribosomal RNA (rRNA): Forms ribosomes for protein assembly.

• Transfer RNA (tRNA): Brings amino acids to ribosomes for protein synthesis.

Genetic Code

• Definition: Sequence of nitrogenous bases in RNA; codons are groups of three bases that code for amino acids.

• Types of Regions:

  • Introns: Non-coding regions.

  • Exons: Coding regions.

• Start Codon: Establish reading frame.

• Codon Examples:

  • UUU: Phenylalanine

  • AUG: Methionine (start codon)

  • UAA, UAG: Stop codons

Summary of Protein Synthesis Steps

• Transcription:

  1. Initiation

  2. Elongation

  3. Termination

• Translation: Reading mRNA codons to synthesize proteins.