CHAPTER 10 Molecular Biology of the Gene

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CHAPTER 10Molecular Biology of the Gene

• DNA serves as the molecular basis of heredity

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THE STRUCTURE OF THE GENETIC MATERIAL
Experiments showed that DNA is the genetic
material

• The Hershey-Chase experiment showed that certain
  viruses reprogram host cells to produce more
  viruses by injecting their DNA

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The Hershey-Chase Experiment
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DNA and RNA are polymers of nucleotides

• DNA is a nucleic acid, made of long chains of
  nucleotides

Nitrogenous base(A, G, C, or T)
Phosphategroup
Thymine (T)
Nucleotide
Sugar(deoxyribose)
Polynucleotide
Sugar-phosphate backbone
DNA nucleotide
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DNA has four kinds of bases, A, T, C, and G
Thymine (T)
Cytosine (C)
Adenine (A)
Guanine (G)
Pyrimidines
Purines
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DNA and RNA are polymers of nucleotides

• RNA has a slightly different sugar
• RNA has U instead of T

Nitrogenous base(A, G, C, or U)
Phosphategroup
Uracil (U)
Sugar(ribose)
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DNA is a double-stranded helix

• James Watson and Francis Crick worked out the
  three-dimensional structure of DNA, based on work
  by Rosalind Franklin

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DNA Structure I

• The structure of DNA consists of two
  polynucleotide strands wrapped around each other
  in a double helix

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DNA Structure II

• Hydrogen bonds between bases hold the strands
  together
• Each base pairs with a complementary partner
• A pairs with T
• G pairs with C

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DNA Structure III

• Three representations of DNA

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DNA REPLICATION

• DNA replication depends on specific base pairing
• In DNA replication, the strands separate
• Enzymes use each strand as a template to assemble
  the new strands

Nucleotides
Parental moleculeof DNA
Both parental strands serveas templates
Two identical daughtermolecules of DNA
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DNA REPLICATION II

• Untwisting and replication of DNA

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DNA REPLICATION III
DNA

• Without DNA replication, new cells would have
  only half the DNA of their parents.
• DNA is copied during interphase prior to mitosis
  and meiosis
• It is important that the new copies are exactly
  like the original molecules.

Replication
Replication
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THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA
TO PROTEIN

• The DNA genotype is expressed as proteins, which
  provide the molecular basis for phenotypic traits
  (Genes provide the instructions for making
  specific proteins.)
• The information constituting an organisms
  genotype is carried in its sequence of bases
• The DNA is transcribed into RNA, which is
  translated into the polypeptide
• DNA -gt RNA -gt protein.

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10.7 Genetic information written in codons is
translated into amino acid sequences

• Transfer of DNA to mRNA uses language of
  nucleotides
• Letters nitrogen bases of nucleotides
  (A,T,G,C)
• Words codons triplets of bases
• ( ex. AGC)
• Sentences polypeptide chain
• The codons in a gene specify the amino acid
  sequence of a polypeptide

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10.8 The genetic code is the Rosetta stone of life

• Virtually all organisms share the same genetic
  code

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Process of protein synthesis
Transcribed strand
DNA
Transcription
RNA
Stopcodon
Startcodon
Translation
Polypeptide
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Protein Synthesis 2 step process

• 1. TRANSCRIPTION
• In nucleus DNA -gt mRNA
• 2. TRANSLATION
• in cytoplasm mRNA -gt Protein
• Involves 3 types of RNA
• 1. Messenger RNA (mRNA) carries
• the blueprint for construction of a protein
• 2. Ribosomal RNA (rRNA)
• the construction site where the protein is
  made
• 3. Transfer RNA (tRNA)
• the truck delivering the proper amino acid
  to the site at the right time

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10.9 Transcription produces genetic messages in
the form of RNA

• In transcription, the DNA helix unzips
• RNA nucleotides line up along one strand of the
  DNA following the base-pairing rules
• The single-stranded messenger RNA peels away and
  the DNA strands rejoin

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10.10 Eukaryotic RNA is processed before leaving
the nucleus

• Noncoding segments called introns are spliced out
  ( coding segment exons)
• A cap and a tail are added to the ends

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10.11 Transfer RNA molecules serve as
interpreters during translation

• In the cytoplasm, a ribosome attaches to the mRNA
  and translates its message into a polypeptide
• The process is aided by transfer RNAs
• Each tRNA molecule has a triplet anticodon on one
  end and an amino acid attachment site on the
  other
• Anticodon base pairs with codon of mRNA

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10.12 Ribosomes build polypeptides
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10.15 Review The flow of genetic information in
the cell is DNA?RNA?protein

• The sequence of codons in DNA spells out the
  primary structure of a polypeptide
• Polypeptides form proteins that cells and
  organisms use

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10.16 Mutations can change the meaning of genes

• Mutations are changes in the DNA base sequence
• These are caused by errors in DNA replication or
  by mutagens
• The change of a single DNA nucleotide causes
  sickle-cell disease

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Types of mutations

• Point mutation base sustitution
• Frameshift mutation base deletion

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Types of mutations
NORMAL GENE
mRNA
Protein
BASE SUBSTITUTION
Missing
BASE DELETION