Download Chapter 9 DNA: The Genetic Material

Chapter 9 DNA: The Genetic Material
Section 1: Identifying Genetic Material
Frederick Griffith (1928) – hoped to prepare a vaccine against pneumonia, caused by Streptococcus
pneumoniae.
Strain R (rough)
(had no protective capsule)
Strain S (smooth)
(had protective capsule)
Heat-killed S
Heat-killed S
+ R
Blood contained
live bacteria with
capsules!
Griffith discovered transformation.
Some chemical must have been absorbed into the live strain R bacteria to transform, or change them.
Transformation – a change in genotype when cells take up foreign genetic material.
Oswald Avery (1944)
 Repeated transformation experiment using enzymes that destroyed proteins and enzymes that
destroyed DNA in separate trials.
 When protein-destroying enzymes were used transformation still occurred.
 When DNA-destroying enzymes were used transformation did not occur.
 This indicated that DNA is the chemical responsible for transformation.
Hershey & Chase (1952) Finally proved DNA is the genetic material!
 Knew viruses are made of DNA or RNA surrounded by a protein capsule.
 Did an experiment with a bacteriophage (virus that only infects bacteria)
 Grew bacteriophages in radioactive P and radioactive S and allowed them to infect E. coli
bacteria. (Phosphorus is found in DNA, and sulfur is found in protein).
 Radioactive P, not S was found inside the bacteria.
 This indicates that DNA was invading the host bacteria. DNA was the genetic material!
Section 2: The Structure of DNA (deoxyribonucleic acid)
Watson and Crick (early 1950s)
 Credited with discovering the double helix structure of DNA.
 Made of subunits (monomers) called nucleotides.
 Nucleotides are made of 3 parts:
1. Phosphate group
2. Sugar (deoxyribose)
3. Nitrogen base (4 different ones)
 Adenine
 Guanine
 Cytosine
 Guanine
How did Watson & Crick figure it out?
They used information from other scientists!
 Wilkins & Franklin used X-ray diffraction.
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Watson & Crick figured out the double helix shape would produce this image.
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Chargaff- measured amounts of the four bases in different species.
Chagaff’s Rule – amounts of A & T are always the same in a species, & amounts of G & C are
always the same in a species. (Indicated that these bases must pair together.)
A & T are complementary base pairs.
C & G are complementary base pairs.
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Section 3 The Replication of DNA
DNA Replication- the process of making a copy of DNA; occurs in S phase of cell cycle, before a cell
divides.
1. Original DNA strands separate after DNA helicases unzip the helix.
2. DNA polymerases add complementary nucleotides to each strand.
3. Two DNA molecules form that are identical to the original DNA molecule.
DNA polymerases also “proofread” the strand and change incorrect pairs if mistakes are made.
Chapter 10 How Proteins Are Made
Section 1 From Genes to Proteins
DNA (deoxyribonucleic acid) – coded instructions for making proteins. (Proteins determine genetic
traits.)
RNA (ribonucleic acid) – DNA helper molecule.
Three structural differences:
1. Single stranded molecule. (DNA is double)
2. Ribose sugar (DNA has deoxyribose sugar.)
3. Uracil (U) instead of thymine (T).
Protein Synthesis / Gene Expression (steps involved in making a protein).
1. Transcription - instructions are transferred (rewritten) from DNA to a molecule of
mRNA (messenger RNA). (occurs in the nucleus)
 RNA polymerase binds to genes promoter (sequence that signals process to start.)
 DNA strands unwind and separate.
 Complementary RNA nucleotides are added to make mRNA strand.
 Codon - sequence of 3 nucleotides on mRNA; stands for one amino acid in a protein.
2. Translation – tRNA (transfer RNA) molecules transport amino acids to the ribosome
where they are linked together to make a protein.
 mRNA leaves nucleus and attaches to a ribosome.
 tRNA has a folded shape.
 Its 3 nucleotides are called an anticodon. The anticodon is complementary to the
mRNA codon.
 Ribosome has two binding sites. Two tRNA molecules can pair up at one time.
 Process of adding amino acids to the protein stops when a “STOP” codon is read.
Mutation – any change in DNA (may be good; may cause no problem; but most are harmful!)
Caused by mutagens (chemicals, radiation, pollution, smoke, etc.)
1. Point mutation – a single nucleotide (one letter) is changed.
 Insertion – one nucleotide is added.
 Deletion – one nucleotide is lost.
 These are called frameshift mutations since they change the grouping of 3.
 Substitutions- one nucleotide is substituted for another.
2. Chromosomal mutations – change a large section of a chromosome; many
nucleotides.
 Addition – extra genes added
 Deletion – genes are lost
 Inversion – broken section is turned upside down
 Translocation – two nonhomologous chromosomes break & exchange genes.