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Molecular Genetics. Biology Chapter 12. Mystery of the Hereditary Material. Experiments in the 1950s showed that DNA is the hereditary material Scientists raced to determine the structure of DNA 1953 - Watson and Crick proposed that DNA is a double helix. Griffith Discovers Transformation.

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molecular genetics

Molecular Genetics

Biology

Chapter 12

mystery of the hereditary material
Mystery of the Hereditary Material
  • Experiments in the 1950s showed that DNA is the hereditary material
  • Scientists raced to determine the structure of DNA
  • 1953 - Watson and Crick proposed that DNA is a double helix
griffith discovers transformation
Griffith Discovers Transformation
  • 1928
  • Attempting to develop a vaccine
  • Isolated two strains of Streptococcus pneumoniae
    • Rough strain was harmless
    • Smooth strain was pathogenic
hershey chase s experiments
Hershey & Chase’s Experiments
  • Created labeled bacteriophages
    • Radioactive sulfur
    • Radioactive phosphorus
  • Allowed labeled viruses to infect bacteria
  • Asked: Where are the radioactive labels after infection?
slide6

virus particle labeled with 35S

virus particle labeled with 32P

Hershey and Chase Results

bacterial cell (cutaway view)

label outside cell

label inside cell

slide7
DNA
  • Deoxyribonucleic acid
  • Nucleic acids are polymers that are the blueprints for proteins.
  • Nucleotides: The monomers that make up nucleic acids which consist of:
    • 5 carbon sugar
    • Phosphate group
    • nitrogenous base
nitrogenous bases
NITROGENOUS BASES
  • DNA
    • Adenine (A) Cytosine (C)
    • Thymine (T) Guanine (G)
  • RNA
    • In RNA uracil replaces thymine.
composition of dna
Composition of DNA
  • Chargaff showed:
    • Amount of adenine relative to guanine differs among species
    • Amount of adenine always equals amount of thymine and amount of guanine always equals amount of cytosine

A=T and G=C

rosalind franklin s work
Rosalind Franklin’s Work
  • Was an expert in X-ray crystallography
  • Used this technique to examine DNA fibers
  • Concluded that DNA was some sort of helix
watson crick model
Watson-Crick Model
  • DNA consists of two nucleotide strands
  • Strands run in opposite directions
  • Strands are held together by hydrogen bonds between bases
  • A binds with T and C with G
  • Molecule is a double helix
dna structure helps explain how it duplicates
DNA Structure Helps Explain How It Duplicates
  • DNA is two nucleotide strands held together by hydrogen bonds
  • Hydrogen bonds between two strands are easily broken
  • Each single strand then serves as template for new strand
dna replication
DNA Replication
  • Each parent strand remains intact
  • Every DNA molecule is half “old” and half “new”
enzymes in replication
Enzymes in Replication
  • Enzymes unwind the two strands
  • DNA polymerase attaches complementary nucleotides
  • DNA ligase fills in gaps
  • Enzymes wind two strands together
dna rna protein
DNA – RNA – Protein
  • Transcription: RNA copies the code of the DNA in the nucleus and leaves the nucleus (mRNA)
  • Translation: Converts the mRNA message into proteins using tRNA. Occurs in the ribosomes
  • Codon: A 3 nucleotide code for a specific amino acid
slide19

DNA

mRNA

tRNA

Protein

editing the rna
Editing the RNA
  • Introns: Noncoding region of RNA
  • Exons: Coded regions of RNA
  • RNA splicing: The removing of introns and rejoining exons
three classes of rna
Three Classes of RNA
  • Messenger RNA
    • Carries protein-building instruction
  • Ribosomal RNA
    • Major component of ribosomes
  • Transfer RNA
    • Delivers amino acids to ribosomes
genetic code
Genetic Code
  • Set of 64 base triplets
  • Codons
  • 61 specify amino acids
  • 3 stop translation
slide26

Base Pairing during Transcription

DNA

G C A U

G C A T

RNA

C G T A

C G T A

DNA

DNA

base pairing in DNA replication

base pairing in transcription

slide27

Gene Transcription

DNA to be

transcribed unwinds

transcribed DNA winds up again

mRNA

transcript

RNA polymerase

translation
Translation
  • Anticodon: A three nucleotide group on the tRNA that is complimentary to the codon of the mRNA
  • A specific amino acid is attached to the other end of the tRNA
slide32

Transcription

Overview

rRNA

tRNA

mRNA

Mature mRNA transcripts

ribosomal subunits

mature tRNA

Translation

gene mutations
Gene Mutations

Missense

Nonsense

Base-Pair Substitutions

Insertions

Deletions

slide34

Base-Pair Substitution

a base

substitution

within the triplet (red)

original base

triplet in a DNA strand

During replication, proofreading

enzymes make a substitution

possible outcomes:

or

original, unmutated sequence

a gene mutation

frameshift mutations
Frameshift Mutations
  • Insertion
    • Extra base added into gene region
  • Deletion
    • Base removed from gene region
  • Both shift the reading frame
  • Result in many wrong amino acids
slide36

Frameshift Mutation

mRNA

parental DNA

arginine

glycine

tyrosine

tryptophan

asparagine

amino acids

altered mRNA

DNA with

base insertion

arginine

glycine

leucine

leucine

glutamate

altered amino-

acid sequence

Figure 14.12Page 234