Chapter 12: DNA

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Chapter 12 DNA RNA

• What do you already know about DNA?

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12.1 Contributors to the Genetic Code

• Griffith and Transformation
• Worked with bacteria causing pneumonia
• Two Strains
• S strain (smooth) DEADLY
• R strain (rough) - HARMLESS

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12.1. Contributors to the Genetic Code

• Griffith Experiment
• The Experiment
• Mouse R Life
• Mouse S Death
• Mouse heat-killed S Life
• Mouse heat-killed S and R Death

Transformation changing one strain of bacteria
into another using genes. Pointed to some type
of transforming factor.
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12.1. Contributors to the Genetic Code

• Griffith
• Conclusion something transformed the living
  R-strain (harmless) into the S-strain (deadly)
  Transformation
• Oswald Avery repeated Griffiths work
• Destroyed all the organic compounds in heat
  killed bacteria except DNA Result
  transformation occurred.
• Destroyed all the organic compounds and DNA
  Result transformation did not occur.
• Conclusion DNA was the transforming factor that
  caused the change in the R-strain

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12.1 Contributors to the Genetic Code

• Alfred Hershey Martha Chase
• Question Are genes made of DNA or Proteins
• What they know viruses use other organisms to
  reproduce

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12.1. Contributors to the Genetic Code

• Alfred Hershey and Martha Chase
• Experiment
• They tagged the virus DNA with blue radioactive
  phosphorous
• They tagged the protein coat with radioactive
  sulfur

Conclusion Virus only injects DNA (DNA is the
genetic material)
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Bacteriophage Images
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12.1 Three important functions of DNA

• Store genetic information stores genes
• Copy information copy genes prior to cell
  division
• Transmit the information pass genetic
  information along to next generation

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12.2 Structure of DNA

• DNA Deoxyribonucleic Acid
• A nucleotide is composed of
• Sugar (deoxyribose)
• Phosphate group
• Nitrogenous Base
• A nucleotide is the monomer of a DNA strand
  (polynucleotide)

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12.2 Structure of DNA

• Nitrogenous Bases
• Purines Adenine Guanine (two rings in
  structure)
• Pyrimidines Cytosine Thymine (one ring)

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12.2 Structure of DNA

• DNA is a double-stranded helix
• James Watson and Francis Crick
• Worked out the three-dimensional structure of
  DNA, based on work (photos taken using x-ray
  crystallography) by Rosalind Franklin

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12.2 Structure of DNA

• The structure of DNA
• Consists of two polynucleotide strands wrapped
  around each other in a double helix (twisted
  ladder)

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12.2 Structure of DNA

• Hydrogen bonds (weak) between bases
• Hold the strands together
• Each base pairs with a complementary partner
• A with T, and G with C

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• Chromosome structure
• Chromatin DNA that is tightly packed around
  proteins called histones
• - during cell division, chromatin form packed
  chromosomes

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12-3 DNA Replication

• When does DNA replicate?
• DNA must copy before cell division (mitosis)
• How does it replicate?
• DNA is separated
• Nucleotides are added according to base pairing
  rules, using DNA polymerase (enzyme).

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12-3 DNA Replication

• DNA replication is semi-conservative
• The parent strand gives rise to two daughter
  strands.
• Each daughter strand is composed of one half the
  parent (old strand) and one half new.

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12.3 DNA Replication

• DNA replication is a complex process
• The helical DNA molecule must untwist
• Each strand of the double helix is oriented in
  the opposite direction (antiparallel)

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DNA Replication

• Replication process of copying DNA
• - occurs during S phase of Interphase
• - process
• 1. DNA is separated into two strands by an
  enzyme
• 2. Free nucleotides are added by DNA polymerase
  according to base pairing rule

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DNA Replication
Nitrogenous bases
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Chapter 13 Protein Synthesis
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Central Dogma of Cell Biology

• DNA codes for DNA REPLICATION
• DNA codes for RNA TRANSCRIPTION
• RNA codes for protein TRANSLATION

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Chapter 13 Protein Synthesis - Overview

• The DNA of the gene is transcribed into RNA
• Which is translated into protein
• The flow of genetic information from DNA to RNA
  to Protein is called the CENTRAL DOGMA

DNA
Transcription
RNA
Translation
Protein
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FLOW IS FROM DNA TO RNA TO PROTEIN
Chapter 13 Protein Synthesis (Overview)

• Genes on DNA are expressed through proteins,
  which provide the molecular basis for inherited
  traits
• A particular gene, is a linear sequence of many
  nucleotides
• Specifies a polypeptide (long protein made of
  amino acids)

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13-1 Messenger (mRNA)

• Monomer nucleotide
• Parts of a mRNA Nucleotide
• Ribose Sugar
• Phosphate
• Nitrogenous Base
• Three main differences between mRNA and DNA
• Ribose instead of deoxyribose
• mRNA is generally single stranded
• mRNA has uracil in place of thymine (U instead of
  T)

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13.1 RNA

• Three Types of RNA
• Messenger RNA (mRNA) carries copies of genes
  (DNA) to the rest of the cell.
• Ribosomal RNA (rRNA) make up the ribosomes.
• Transfer RNA (tRNA) transfers the amino acids
  to the ribosomes as specified by the mRNA

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• 13.1 TRANSCRIPTION The process of making mRNA
  from DNA
• Why do you need this process?
• Location of DNA? Nucleus
• Location of Ribosome? Cytoplasm
• mRNA takes code from DNA in the nucleus to the
  cytoplasm

Strand to be transcribed
DNA
Transcription
G
U
U
U
A
G
A
U
A
A
G
U
RNA
Startcondon
Stopcondon
Translation
Met
Lys
Phe
Polypeptide
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• 13.1 Transcription produces genetic messages in
  the form of mRNA
• During transcription, segments of DNA serve as
  templates to produce complementary RNA molecules.

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Transcription

• Transcription requires an enzyme, known as RNA
  polymerase, that is similar to DNA polymerase.
• RNA polymerase binds to DNA during transcription
  and separates the DNA strands.

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Promoters

• RNA polymerase binds only to promoters, regions
  of DNA that have specific base sequences.
• Promoters are signals in the DNA molecule that
  show RNA polymerase exactly where to begin making
  RNA.
• Similar signals in DNA cause transcription to
  stop when a new RNA molecule is completed.

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• 13.1 In the nucleus, the DNA helix unzips
• And RNA nucleotides line up along one strand of
  the DNA, following the base pairing rules
• As the single-stranded messenger RNA (mRNA) is
  released away from the gene
• The DNA strands rejoin

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• 13.1 Eukaryotic mRNA is processed before leaving
  the nucleus
• Noncoding segments called introns are spliced out
  leaving only the coding exons
• A 5 cap and a poly A tail are added to the ends
  of mRNA
• Cap and tail protect mRNA

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The Genetic Code

• Proteins are made by joining amino acids
  together into long chains, called polypeptides.
• As many as 20 different amino acids are commonly
  found in polypeptides.

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The Genetic Code

• The specific amino acids in a polypeptide, and
  the order in which they are joined, determine the
  properties of different proteins.
• The sequence of amino acids influences the shape
  of the protein, which in turn determines its
  function.

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The Genetic Code

• RNA contains four different bases adenine,
  cytosine, guanine, and uracil.
• These bases form a language, or genetic code,
  Each three-letter word in mRNA is known as a
  codon.
• A codon consists of three consecutive bases that
  specify a single amino acid to be added to the
  polypeptide chain.

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How to Read Codons

• Because there are four different bases in RNA,
  there are 64 possible three-base codons (4 4
  4 64) in the genetic code.

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How to Read Codons

• Most amino acids can be specified by more than
  one codon.
• For example, six different codonsUUA, UUG, CUU,
  CUC, CUA, and CUGspecify leucine. But only one
  codonUGGspecifies the amino acid tryptophan.

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Start and Stop Codons

• The methionine codon AUG serves as the
  initiation, or start, codon for protein
  synthesis.
• Following the start codon, mRNA is read, three
  bases at a time, until it reaches one of three
  different stop codons, which end translation.

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• DNACCGTCATGTTCGCGCTACAAATGAAATGAGGCAGTACAAGCGCGAT
  GTACTTTACT
• mRNA
• Polypeptide

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13-2 Protein Synthesis - Translation

• Translation is defined as going from mRNA to
  protein
• tRNA which have amino acids attached are going to
  the ribosome.
• What are amino acids? monomers of proteins
• Does the order of amino acids matter? Yes, they
  must be in order for the protein to fold
  correctly.
• How does the correct tRNA (with amino acid
  attached) bind to the mRNA? The tRNA contains an
  anticodon which matches up with the mRNA sequence
  (codon).

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• Transfer RNA (tRNA) molecules serve as
  interpreters during translation
• Translation
• Takes place in the cytoplasm

• A ribosome attaches to the mRNA and translates
  its message into a specific polypeptide aided by
  transfer RNAs (tRNAs)
• tRNAs can be represented in several ways

Amino acid attachment site
0
Amino acid attachment site
Hydrogen bond
RNA polynucleotide chain
Anticodon
Anticodon
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13.2 Translation

• Each tRNA molecule
• Is a folded molecule bearing a base triplet
  called an anticodon on one end
• A specific amino acid
• Is attached to the other end

Amino acid attachment site
Anticodon
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13.2 Translation

• Ribosomes build polypeptides (proteins)
• A ribosome consists of two subunits
• Each made up of proteins and a kind of RNA called
  ribosomal RNA

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13.2 Translation

• The subunits of a ribosome
• Hold the tRNA and mRNA close together during
  translation

tRNA-binding sites
Largesubunit
Next amino acid to be added to polypeptide
Growing polypeptide
tRNA
mRNA-binding site
mRNA
Smallsubunit
Codons
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• An initiation codon marks the start of an mRNA
  message
• mRNA, a specific tRNA, and the ribosome subunits
  assemble during initiation

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• Elongation adds amino acids to the polypeptide
  chain until a stop codon terminates translation
• Once initiation is complete amino acids are added
  one by one to the first amino acid
• The mRNA moves a codon at a time
• A tRNA with a complementary anticodon pairs with
  each codon, adding its amino acid to the peptide
  chain

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• Each addition of an amino acid
• Occurs in a three-step elongation process

Aminoacid
Polypeptide
P site
A site
Anticodon
mRNA
Codons
mRNAmovement
Stopcodon
New Peptidebond
Figure 10.14
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13.3 Mutations

• Mutations heritable changes in genetic
  information (changes to the DNA sequence)
• Two types - gene and chromosomal mutations
• Mutations can be caused by chemical or physical
  agents (mutagens)
• Chemical pesticides, tobacco smoke,
  environmental pollutants
• Physical X-rays and ultraviolet light

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13.3 Mutations

• Gene mutations
• Point Mutation mutations that affect a single
  nucleotide
• Frameshift mutation shift the reading frame of
  the genetic message.
• Can change the entire protein so it doesnt work
• Gene Mutations Explained

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13.3 Mutations
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13.3 Chromosomal Mutations

• Chromosomal mutation mutation that changes the
  number or structure of chromosomes.

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13.3 Chromosomal Mutations

• Types of chromosomal mutations
• Deletion The loss of all or part of a
  chromosome
• Duplication A segment is repeated
• Inversion part of the chromosome is reverse
  from its usual direction.
• Translocation one chromosome breaks off an
  attaches to another chromosome.