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Chapter 9 DNA: THE Genetic Material. Section1 Identifying the Genetic Material. Transformation. Frederick Griffith, a bacteriologist, prepared a vaccine against pneumonia Vaccine – a substance that is prepared from killed or weakened disease-causing agents, including certain bacteria

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Chapter 9 DNA: THE Genetic Material

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chapter 9 dna the genetic material

Chapter 9DNA: THE Genetic Material


Identifying the Genetic Material

  • Frederick Griffith, a bacteriologist, prepared a vaccine against pneumonia
  • Vaccine – a substance that is prepared from killed or weakened disease-causing agents, including certain bacteria
  • To protect the body against future infections by the disease-causing agent
griffith s experiments
Griffith’s Experiments
  • Griffith worked with 2 strains of S. pneumoniae
  • 1st strain had a smooth capsule that protected the bacterium from body’s defense systems (S)
  • Virulent – (full of poison) able to cause disease
  • 2nd strain lacked capsule and didn’t cause disease (R)
  • Mice injected with (S) strain died; mice injected with (R) strain lived
Griffith injected mice with dead S bacteria – mice lived
  • Griffith injected mice with heat-killed S bacteria-mice still lived
  • Meaning the capsule was not involved with killing the mice
  • He mixed harmless live R bacteria with the harmless heat-killed S bacteria-mice died
  • Transformation- a change in genotype caused when cells take up foreign genetic material
avery s experiments
Avery’s Experiments
  • Oswald Avery & co-workers demonstrated that DNA is the material responsible for transformation
  • Almost 100 years after Mendel’s experiments
viral genes and dna
Viral Genes and DNA
  • Many scientists remained skeptical
  • Knew little about DNA, so they could not imagine how DNA could carry genetic information
dna s role revealed
DNA’s Role Revealed
  • Alfred Hershey and Martha Chase performed an experiment that settled the controversy
  • Viruses are composed of DNA or RNA surrounded by a protective protein coat
  • Bacteriophage (phage)– a virus that infects bacteria
Step 1 – grew E. coli contained radioactive sulfur (35S) protein coat incorporated the sulfur
  • Grew second batch E.coli with radioactive phosphorus (32P) would become part of the phages’ DNA
  • Step 2 Labeled phages used to infect two separate batches of E. coli
Step 3 Used centrifuge tubes to separate the bacteria (heavy) from the viral parts (lighter)
  • Concluded that the DNA of viruses is injected into the bacterial cells, while most of the viral proteins remain outside
  • Experiments have shown that DNA is the molecule that stores genetic information in living cells
Watson & Crick determined that a DNA molecule is a double helix – two strands twisted around each other
  • Nucleotides – the subunits that make up DNA
  • 3 parts: a phosphate group, a 5-carbon sugar, and a nitrogen-containing base
Deoxyribose – sugar molecule from which DNA gets its full name, deoxyribonucleic acid
  • Nitrogen base may be : adenine, guanine, thymine, and cytosine
  • Adenine (A) and guanine (G) are classified as purines –two rings of carbon & nitrogen atoms
  • Thymine (T) and cytosine (C) are classified as pyrimidines –single ring C & N atoms
discovering dna s structure
Discovering DNA’s Structure
  • Chargaff’s 1949 observations – the amount of adenine always equaled the amount of thymine; amount of guanine always equaled the amount of cytosine; but amount varied between different organisms
wilkins franklin s photographs
Wilkins & Franklin’s Photographs
  • X-ray diffraction to study the structures of molecules
  • 1952 Wilkins & Franklin developed high-quality X-ray diffraction photographs of strands of DNA which suggested that the DNA resembled a tightly coiled helix and was composed of two or three chains of nucleotides
rosalind franklin
Rosalind Franklin
  • was an English scientist who contributed to the discovery of the molecular structure of deoxyribonucleic acid (DNA), 1951
watson crick s dna model
Watson & Crick’s DNA Model
  • 1953 Watson & Crick used the information from Chargaff, Wilkins, & Franklin along with their knowledge of chemical bonding, to make the “spiral staircase” configuration of DNA
pairing between bases
Pairing Between Bases
  • Watson & Crick determined that a purine on one strand of DNA is always paired with a pyrimidine on the opposite strand
  • Base-pairing rule – cytosine pairs with guanine and adenine with thymine
  • Complementary base pairs – sequence of bases on strand determines the sequence of N bases on the other strand of DNA
  • Section 1 Review p. 193 3-6
  • Section 2 Review p. 197 1-6
Watson & Crick proposed that one DNA strand serves as a template, or pattern, on which the other strand is built
  • DNA replication – the process of making a copy of DNA, which occurs during the (S) phase of the cell cycle
Step 1 – The double helix needs to unwind before replication can begin
  • Accomplished by enzymes called DNAhelicases which open the double helix by breaking the hydrogen bonds between the two strands
Additional proteins prevent the strands from assuming their double-helical shape
  • Replication forks – areas where the double helix separates
  • Enzymes known as DNA polymerases add nucleotides to the exposed nitrogen bases, according to the base-pairing rules – forming two double helixes
Step 3 The process continues until all of the DNA has been copied & the polymerases are signaled to detach
  • Nucleotide sequences are identical in the two DNA molecules
  • Checking for errors – DNA polymerases are important in “proofreading” the nucleotides – can backtrack
  • Errors in DNA replication about one error per 1 billion nucleotides
rate of replication
Rate of Replication
  • Replication does not begin at one end & end at the other
  • Prokaryotes usually have two replication forks
  • Eukaryotic cells – length a problem – 33 days if done with a single point
  • Each human chromosome is replicated in about 100 sections – replicated in about 8 hours
  • Section 3 Review p. 200 1-5
  • Performance Zone p. 202 1-4, 6-12
  • STP p. 203 1-3
how proteins are made

How Proteins Are Made

Chap. 10

Section 1

decoding the information in dna
Decoding the Information in DNA
  • Traits are determined by proteins that are built according to instruction coded in DNA
  • Ribonucleic acid is also involved
  • RNA differs from DNA 3 ways

a single strand

five-C sugar, ribose

Uracil (U) instead of thymine (T)

A gene’s instructions for making a protein are coded in the sequence of nucleotides in the gene
  • Transcription – a process were the instructions for making a protein are transferred from a gene to an RNA molecule
Translation – the protein synthesis that takes place at ribosomes & that uses the codons in mRNA molecules to specify the sequence of amino acids to make protein
  • Gene expression (protein synthesis) – the process by which proteins are made based on the information encoded in DNA
transfer of information from dna to rna
Transfer of information from DNA to RNA
  • RNA polymerase, an enzyme that adds and links complementary RNA nucleotides during transcription, is required
  • Step 1 RNA polymerase binds to the gene’s promoter-a specific sequence of DNA that acts as a “start” signal for transcription
Step 2 - RNA polymerase unwinds and separates the 2 strands of the double helix, exposing the DNA nucleotides
  • Step 3 – RNA polymerase adds & then links complementary RNA nucleotides as it “reads” the gene –transcription follows the base-pairing rules for DNA except that uracil pairs with adenine
The RNA polymerase eventually reaches a “stop” signal in the DNA
  • RNA nucleotides are linked together with covalent bonds during transcription
  • Behind the RNA polymerase, the DNA closes up reforming the double helix
  • In transcription, new molecule is RNA and only part of one of DNA strands serves as a template
Transcription in prokaryotic cells occurs in the cytoplasm; in eukaryotic cells, in the nucleus
  • Many identical RNA are made simultaneously from a single gene
  • Look at Figure 3 page 210
the genetic code three nucleotide words
The Genetic Code: Three-Nucleotide “Words”
  • Different types of RNA are made during transcription
  • Messenger RNA (mRNA) carries the instructions for making a protein from a gene and delivers it to the site of translation
  • Translated from the language of RNA (nucleotide) to language of proteins (amino acid)
Codons - a series of three-nucleotide sequences on the mRNA Marshall Nirenberg, American, deciphered the first codon by making artificial mRNA that contained only the base uracil (U)
  • mRNA was translated into a protein phenylalanine amino-acid subuntis
Genetic code – the amino acids and “start” and “stop” signals that coded for by each of the possible 64 mRNA codons
rna s roles in translation
RNA’S Roles in Translation
  • Translation takes place in the cytoplasm
  • Transfer RNA molecules and ribosomes help in the synthesis of proteins.
  • Transfer RNA (tRNA) are single strands of RNA that temporarily carry a specific amino acid on one end & an anticodon at the other
  • Anticodon – a three-nucleotide sequence on a tRNA that is complementary to an mRNA codon
Ribosomes are composed of both proteins & ribosomal RNA (rRNA)
  • Ribosomal RNA molecules are part of the structure of ribosomes
  • Each ribosome temporarily holds one mRNA and 2 tRNA molecules
Step 1 The mRNA and the tRNA carrying methionine bind together “start” codon AUG, signals the beginning of a protein chain
  • Step 2 – The tRNA carrying the amino acid specified by the codon in the A site arrives
  • Step 3 – A peptide bond forms between adjacent amino acids
  • S 4 – The tRNA in the P site detaches and leaves its amino acid behind
S 5 – The tRNA in the A site moves to the P site. The tRNA carrying the amino acid specified by the codon in the A site arrives.
  • S 6 – A peptide bond is formed. The tRNA in the P site detaches and leaves its amino acid behind.
  • S 7 – The process is repeated until a stop codon is reached. The ribosome complex falls apart. The newly made protein is released.
Another ribosome can find the AUG codon on the same mRNA and begin making a second copy of the same protein
  • The genetic code is the same in all organisms, but for a few exceptions

duplicating DNA at rates as high as 1000 nucleotides per seconBecause each of the two daughters of a dividing cell inherits a new DNA double helix containing one old and one new strand (Figure 5-5), the DNA double helix is said to be replicated “semiconservatively” by DNA polymerase.d.


Section 1 review p. 214 1-6

Chapter review p. 222 1,2,6,7,8,12

P. 223 STP 1-3