LC

Unit 4: Genetics - DNA Structure

DNA Structure

  • Introduction to Unit 4: Genetics

    • Excitement about studying genetics.
    • Focus on DNA structure as the foundation, progressing to DNA replication.

  • Review of Prior Knowledge

    • Content was previously covered in year 10.
    • Recap of key components:
      • Nucleus: Location of DNA storage.
      • Chromosome: Coiled structure for DNA storage.
      • DNA: Deoxyribonucleic acid.
      • Nitrogenous base (A, T, C, G).

Macromolecules and Nucleic Acids

  • Revisiting Unit 1 concepts
    • Macromolecules, monomers, and polymers.
  • Focus on nucleic acids (nucleotides) in Unit 4.
  • Nucleotides: Monomers of DNA.
    • Importance of understanding their structure and function in DNA.

Nucleotide Structure and Types of Nucleic Acids

  • Basic Nucleotide Structure
    • Phosphate group.
    • Pentose sugar (pentagon shape).
    • Nitrogenous base.
    • Recognition and labeling of the structure are essential.
  • Two Main Types of Nucleic Acids
    • DNA (deoxyribonucleic acid).
    • RNA (ribonucleic acid).

Differences Between DNA and RNA

  • Structural Differences
    • Sugars: DNA has deoxyribose sugar; RNA has ribose sugar.
    • Slight chemical structure variation.
  • Sugar-Phosphate Backbone
    • Formation: Bonds between sugars and phosphates.
    • DNA: Two chains with sugar-phosphate backbones.
    • Hydrogen bonds between bases hold the chains together.
    • Double helix shape: Twisted ladder structure.
  • RNA Structure
    • Single-stranded: Bases are exposed.
    • Enables reading of the genetic code.

Nitrogenous Bases and Base Pairing

  • Common Bases
    • Adenine (A), Thymine (T), Cytosine (C), Guanine (G).
  • Base Pairing Rules
    • DNA: Adenine (A) pairs with Thymine (T); Cytosine (C) pairs with Guanine (G).
    • RNA: Adenine (A) pairs with Uracil (U).
  • Uracil (U)
    • Replaces Thymine (T) in RNA.
  • Purines and Pyrimidines
    • Purines: Double-ringed (Adenine, Guanine).
    • Pyrimidines: Single-ringed (Thymine, Cytosine, Uracil).
    • Purines always pair with pyrimidines.

Comparison Table: DNA vs. RNA

  • Key Differences summarized.
    • Sugars: Deoxyribose (DNA) vs. Ribose (RNA).
    • Bases: Thymine (DNA) vs. Uracil (RNA).
    • Strands: Double-stranded (DNA) vs. Single-stranded (RNA).

Detailed Explanation of DNA Structure

  • Phosphodiester Bonds
    • Link nucleotides.
    • Forms one half of the double-stranded DNA.
  • Complementary Base Pairing
    • A with T, C with G.
    • Held together by weak hydrogen bonds.
  • Twisting of DNA
    • Hydrogen bonding between phosphate groups causes the DNA to twist into a double helix.

Predicting Base Proportions

  • Using Base Pairing Rules
    • If a person has 20% Adenine (A), they also have 20% Thymine (T) because A pairs with T.
    • Remaining 60% is split equally between Cytosine (C) and Guanine (G), so 30% each.

Three Prime and Five Prime Ends

  • Numbering of Carbons in Sugar
    • Sugar has five carbons, numbered 1' to 5' from the oxygen.
    • Phosphate attached to the 5' carbon, base to the 1' carbon in a single nucleotide.
  • DNA Replication
    • Occurs in the 5' to 3' direction.
    • Strands run antiparallel, ensuring the same genetic information is read.

DNA Packaging and Histones

  • Amount of DNA
    • Each person has enough DNA to reach the sun and back over 300 times.
  • Histones
    • Proteins around which DNA is wrapped.
    • Histone proteins are used in evolutionary trees.
  • Nucleosomes
    • Formed when DNA is wrapped around eight histones.
  • Chromatin Fiber
    • Compacted nucleosomes.
    • Formed by electromagnetic charges between negative DNA and positive histones.
  • Chromosomes
    • Further compacted chromatin.
  • Role in Gene Regulation
    • Histones regulate chromosome movement and protein synthesis.

DNA Locations

  • Four Main Locations
    • Nucleus of eukaryotes.
    • Chromosomes and plasmids in prokaryotes.
    • Mitochondria.
    • Chloroplasts.
  • Eukaryotes
    • DNA is found in chromosomes in the nucleus.
  • Mitochondria and Chloroplasts
    • Have their own circular DNA, not bound by histones.
    • Supports endosymbiotic theory: Complex eukaryotic cells evolved from simpler prokaryotic cells.

Prokaryotic Cells

  • Bacterial DNA
    • Found in one large circular chromosome, not bound to histones (naked DNA).
    • Also found in small chromosomal structures called plasmids.
  • Plasmids
    • Replicate independently.
    • Can be exchanged between bacteria via conjugation.
    • Carry genes, such as antibiotic resistance.
    • Conjugation process: Transfer of valuable genes between bacteria.

Further Exploration

  • Atomy quiz to test understanding.
  • TED Ed video on the discovery of DNA, focusing on Rosalind Franklin's contribution.
  • Videos on DNA replication.
  • Practical activity: DNA extraction from strawberries.
    • Simple kitchen experiment.