Chapter 10: DNA and RNA

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Chapter 10 DNA and RNA
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DNA

• Deoxyribonucleic acid
• Structure of DNA
• Made up of four subunits called nucleotides
• Each nucleotide is made up of a sugar, a
  phosphate and a base

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Four Bases

• Two Purines
• Adenine (A)
• Guanine (G)
• Two pyrimidines
• Cytosine (C)
• Thymine (T)

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DNA Double Helix

• DNA is made of two nucleotide strands that wrap
  around each other in the shape of a double helix.

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DNA Structure

• Bonds Hold DNA Together
• Nucleotides along each DNA strand are linked by
  covalent bonds.
• Complementary nitrogenous bases are bonded by
  hydrogen bonds.

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Chargaff

• Amount of adenine equals the amount of thymine
  and the amount of cytosine equals the amount of
  guanine
• AT
• CG

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But what does DNA look like?

• Rosalind Franklin
• Working in Wilkins lab created x-ray pictures of
  DNA
• Wilkins shared this information with another pair
  of scientists without Franklins consent

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Watson and Crick

• Watson and Crick discovered that DNA resembles a
  twisted ladder shape double helix

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DNA Structure

• Two side of the ladder are made up of alternating
  sugar and phosphate molecules
• The rungs of the ladder are pairs of bases (A
  with T, and G with C) Base pair rule
• Rungs are anti-parallel (5-gt3 and 3 -gt5)

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Drawing DNA

• Draw one side of the rung 5 -gt 3
• Start with the sugar
• Add the phosphate and the base to form your
  nucleotide
• Continue adding bases to the 3 end
• Determine the matching base for next side
• When finishing each nucleotide, be sure to draw
  in the 3 -gt 5 direction

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Making copies Replication

• DNA can unzip when it needs to replicate
  (helicase)
• Occurs prior to cell division so each new cell
  gets the correct information

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Replication

• DNA molecule separates into two strands
• Complementary strands form on the template of
  each of the original sides of the DNA
• Each new DNA has one old and one new strand
  (semiconservative replication)

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Replication enzymes

• Helicase
• Unwinds DNA
• Primase
• Adds an RNA primer on unzipped DNA
• DNA polymerase
• Add new bases to the 3 end of previous base
• Ligase
• Seals fragments after RNA primer removed

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Steps of DNA Replication

• Replication begins with the separation of the DNA
  strands by helicases.
• Then, primase adds an RNA primer where
  replication will occur
• DNA polymerases form new strands by adding
  complementary nucleotides to each of the original
  strands.
• The new segments of DNA are sealed by ligase

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http//www.dnareplication.info/images/dnareplicati
on.jpg
See it in action
http//www.johnkyrk.com/DNAreplication.html
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DNA Replication
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DNA Replication

• Each new DNA molecule is made of one strand of
  nucleotides from the original DNA molecule and
  one new strand. This is called semi-conservative
  replication.

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Replication Forks Increase the Speed of
Replication
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Replication

• DNA polymerase can only add to a 3 end
• Leading strand
• Runs 5-gt3
• Lagging strand
• Runs 3-gt5 SO cant add directly
• Have to replicate in fragments called Okazaki
  fragments
• Ligase bonds the fragments together

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DNA Replication
Overview
Origin of replication
Lagging strand
Leading strand
Leading strand
Lagging strand
Single-strand binding protein
Overall directions of replication
Helicase
Leading strand
DNA pol III
5?
3?
3?
Primer
Primase
5?
Parental DNA
3?
Lagging strand
DNA polymerase
5?
DNA polymerase
DNA ligase
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3?
5?
3
1
2
3?
5?
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Replication animation

• http//www.mcb.harvard.edu/Losick/images/TromboneF
  INALd.swf

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Central Dogma

• Has its exceptions, but gives us a basic idea of
  how DNA does its job

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RNA

• Single stranded nucleic acid
• Made up of nucleotides
• Sugar Ribose
• Thymine instead of Uracil
• Shorter length of one gene

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RNA Structure and Function

• Types of RNA
• Cells have three major types of RNA
• messenger RNA (mRNA)
• ribosomal RNA (rRNA)
• transfer RNA (tRNA)

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Activity

• In pairs, create a chart that will fit in your
  foldable (no more than 1/8th size of construction
  paper) that compares and contrasts the different
  forms of RNA
• Be sure to include
• Name
• Structure
• Function
• Picture

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RNA Structure and Function

• mRNA carries the genetic message from the
  nucleus to the cytosol.
• rRNA is the major component of ribosomes.
• tRNA carries specific amino acids, helping to
  form polypeptides.

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Making proteins

• Cells use a two step process to read each gene
  and produce the amino acid chain that becomes a
  protein.
• These processes are
• Transcription
• Translation

http//gslc.genetics.utah.edu/units/basics/transcr
ibe/
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Fig. 17-4
Gene 2
DNA molecule
Gene 1
Gene 3
DNA template strand
TRANSCRIPTION
mRNA
Codon
TRANSLATION
Protein
Amino acid
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Transcription

• The process of building an RNA copy of a DNA
  sequence
• DNA is too big to leave the nucleus
• mRNA is a copy of the DNA sequence

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mRNA

• Also known as messenger RNA
• Takes the code out into the cell for protein
  synthesis

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Steps of Transcription

• Initiation
• RNA polymerase binds to a promoter (specific
  nucleotide sequence TATA box)
• Elongation
• RNA polymerase adds free RNA nucleotides that are
  complementary to the DNA strand
• Termination
• RNA polymerase releases at a termination sequence

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Steps of Transcription
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Promoter
Transcription unit
5?
3?
5?
3?
DNA
Start point
RNA polymerase
Initiation
1
3?
5?
3?
5?
Template strand of DNA
RNA transcript
Unwound DNA
Elongation
2
Rewound DNA
5?
3?
3?
5?
3?
5?
RNA transcript
Termination
3
5?
3?
5?
3?
5?
3?
Completed RNA transcript
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Genetic Code

• The nearly universal genetic code identifies the
  specific amino acids coded for by each
  three-nucleotide mRNA codon.

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Translation

• Steps of Translation
• During translation, amino acids are assembled
  from information encoded in mRNA.
• As the mRNA codons move through the ribosome,
  tRNAs add specific amino acids to the growing
  polypeptide chain.
• The process continues until a stop codon is
  reached and the newly made protein is released.

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Ribosome
Amino acids
Polypeptide
tRNA with amino acid attached
Ribosome
Trp
Phe
Gly
tRNA
Anticodon
Codons
5?
3?
mRNA
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Translation Assembling Proteins
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DNA Errors in Replication

• Changes in DNA are called mutations.
• DNA proofreading and repair prevent many
  replication errors.
• DNA Replication and Cancer
• Unrepaired mutations that affect genes that
  control cell division can cause diseases such as
  cancer.

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The Human Genome

• The entire gene sequence of the human genome, the
  complete genetic content, is now known.
• To learn where and when human cells use each of
  the proteins coded for in the approximately
  30,000 genes in the human genome will take much
  more analysis.