Genetic Transformation and DNA Evidence

Bacterial Transformation and Genetic Material

• Griffith (1927) identified bacterial transformation, where bacteria can change their genetic makeup by taking in foreign DNA from other bacteria.
• Avery's team provided experimental support that DNA is the genetic material.

DNA and Inheritance Studies

• Hershey and Chase (1952) demonstrated that DNA, not proteins, serves as the molecule of inheritance by tagging bacteriophages with radioactive isotopes 32P (DNA) and 35S (proteins).
• Rosalind Franklin utilized X-ray diffraction to show that DNA has a double helix structure.
• Meselson and Stahl (1953) confirmed that DNA replicates in a semiconservative manner, supporting Watson and Crick's model.

Types and Functions of RNA

• Messenger RNA (mRNA): synthesized from DNA during transcription, carries genetic information.
• Transfer RNA (tRNA): transports specific amino acids to the ribosome for polypeptide formation during translation.
• Ribosomal RNA (rRNA): structural component of ribosomes.

Chromosomes and Their Characteristics

• Chromosomes: Coiled DNA associated with histone proteins.
• Haploid (N): Contains one set of chromosomes found in sex cells (e.g., sperm and egg).
  • Example: Sperm has 22 autosomes + X or Y chromosome; egg has 22 autosomes + X chromosome.
• Diploid (2N): Contains two sets of chromosomes in somatic (body) cells.
  • Common examples: kidney, liver, brain, and skin cells.
• Humans have 46 chromosomes in somatic cells, arranged as follows:
  • Females: 44 autosomes + XX sex chromosomes.
  • Males: 44 autosomes + XY sex chromosomes.
• Karyotype: A visual representation of chromosomes arranged by size during metaphase.

Watson-Crick DNA Model

• DNA structure: Resembles a twisted ladder (double helix).
• Nitrogen bases pair through weak hydrogen bonds:
  • Adenine (A) pairs with Thymine (T) through double hydrogen bonds.
  • Cytosine (C) pairs with Guanine (G) through triple hydrogen bonds.
• The two DNA strands are complementary and anti-parallel.

DNA Replication

• Process of DNA duplication involves several enzymes:
  • DNA Helicase: Unwinds DNA by breaking hydrogen bonds between strands.
  • DNA Polymerase: Synthesizes new DNA strands by adding nucleotides in a 5' to 3' direction; also repairs DNA.
  • DNA Ligase: Joins nucleotides together to form a continuous DNA strand.

Protein Synthesis

• Transcription: Process where DNA is transcribed into RNA.
  • RNA polymerase binds to a promoter, assembling nucleotides to form mRNA.
• Codons: Three-nucleotide sequences in mRNA that code for specific amino acids; the start codon is AUG.
• Stop codons: UAA, UAG, UGA signal termination of protein synthesis.
• Splicing: Involves removing introns (non-coding regions) from pre-mRNA to produce mature mRNA.

Bacterial Transformation and Genetic Material

• Griffith (1927) identified bacterial transformation, where bacteria can change their genetic makeup by taking in foreign DNA from other bacteria.
• Avery's team provided experimental support that DNA is the genetic material.

DNA and Inheritance Studies

• Hershey and Chase (1952) demonstrated that DNA, not proteins, serves as the molecule of inheritance by tagging bacteriophages with radioactive isotopes 32P (DNA) and 35S (proteins).
• Rosalind Franklin utilized X-ray diffraction to show that DNA has a double helix structure.
• Meselson and Stahl (1953) confirmed that DNA replicates in a semiconservative manner, supporting Watson and Crick's model.

Types and Functions of RNA

• Messenger RNA (mRNA): synthesized from DNA during transcription, carries genetic information.
• Transfer RNA (tRNA): transports specific amino acids to the ribosome for polypeptide formation during translation.
• Ribosomal RNA (rRNA): structural component of ribosomes.

Chromosomes and Their Characteristics

• Chromosomes: Coiled DNA associated with histone proteins.
• Haploid (N): Contains one set of chromosomes found in sex cells (e.g., sperm and egg).
  • Example: Sperm has 22 autosomes + X or Y chromosome; egg has 22 autosomes + X chromosome.
• Diploid (2N): Contains two sets of chromosomes in somatic (body) cells.
  • Common examples: kidney, liver, brain, and skin cells.
• Humans have 46 chromosomes in somatic cells, arranged as follows:
  • Females: 44 autosomes + XX sex chromosomes.
  • Males: 44 autosomes + XY sex chromosomes.
• Karyotype: A visual representation of chromosomes arranged by size during metaphase.

Watson-Crick DNA Model

• DNA structure: Resembles a twisted ladder (double helix).
• Nitrogen bases pair through weak hydrogen bonds:
  • Adenine (A) pairs with Thymine (T) through double hydrogen bonds.
  • Cytosine (C) pairs with Guanine (G) through triple hydrogen bonds.
• The two DNA strands are complementary and anti-parallel.

DNA Replication

• Process of DNA duplication involves several enzymes:
  • DNA Helicase: Unwinds DNA by breaking hydrogen bonds between strands.
  • DNA Polymerase: Synthesizes new DNA strands by adding nucleotides in a 5' to 3' direction; also repairs DNA.
  • DNA Ligase: Joins nucleotides together to form a continuous DNA strand.

Protein Synthesis

• Transcription: Process where DNA is transcribed into RNA.
  • RNA polymerase binds to a promoter, assembling nucleotides to form mRNA.
• Codons: Three-nucleotide sequences in mRNA that code for specific amino acids; the start codon is AUG.
• Stop codons: UAA, UAG, UGA signal termination of protein synthesis.
• Splicing: Involves removing introns (non-coding regions) from pre-mRNA to produce mature mRNA.

Explore the pivotal discoveries in genetics from Griffith's bacterial transformation to Avery's evidence of DNA as the genetic material and Hershey and Chase's experiments determining DNA's role in inheritance. This quiz tests your knowledge of these foundational experiments in molecular biology.