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Chapter 12 and 13
Nucleic Acids, Protein Synthesis
and Mutations
Central Dogma
DNA
RNA
Protein
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Identifying the substance of Genes
• Influential Scientists:
• Griffith - Experimented with mice and bacteria that cause
pneumonia and demonstrated TRANSFORMATION.
- Concluded that some FACTOR (gene) was
responsible for the change.
• Avery - Followed up on Griffith’s experiment; wanted to know
which molecule was important for transformation.
- He then extracted the 4 macromolecules from these heat
killed cells, all of which were considered to be possible
candidates for the carriers of genetic information.
- Treated each mixture with enzymes that destroyed the
macromolecule and transformation still occurred.
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- He concluded that DNA is the source of genetic information.
Figure 12–2 Griffith’s
Experiment
Section 12-1
Heat-killed,
disease-causing
bacteria (smooth
colonies)
Disease-causing
bacteria (smooth
colonies)
Harmless bacteria Heat-killed, disease(rough colonies) causing bacteria
(smooth colonies)
Dies of pneumonia
Lives
Lives
Control
(no growth)
Harmless bacteria
(rough colonies)
Dies of pneumonia
Live, disease-causing
bacteria (smooth colonies)
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DNA
• Influential Scientists continued:
• Hershey and Chase- Studied viruses – non-living particles that can infect living
cells.
- Looked at bacteriophages – a virus that infects bacteria.
- Supported the conclusion that genes were made of DNA.
DNA is the source of genetic information
Bacteriophage with
phosphorus-32 in DNA
Bacteriophage with
sulfur-35 in protein
coat
Phage infects
bacterium
Phage infects
bacterium
Radioactivity inside
bacterium
No radioactivity inside
bacterium
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Where is DNA found?
Inside the nucleus DNA is coiled
into Chromosomes
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Components of DNA
• Nucleotide (monomer)
– Deoxyribose sugar
– Phosphate group
– Nitrogen-containing base
• Adenine (A)
• Guanine (G) Purines
• Cytosine (C)
Pyrimidines
• Thymine (T)
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Components of DNA
• The structure or shape of DNA = Double Helix =
2 strands
– Watson and Crick (1953) – tried to assemble the
structure.
– Rosalind Franklin (1952) – used a technique
known as x-ray diffraction to create a picture.
• The x shape indicated DNA is twisted (helix) around two
strands.
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Components of DNA
• Complementary Base Pairing
– A↔T, G ↔C (Chargaff’s rule)
– Connected by covalent hydrogen bonds
DNA with
Nucleotides
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DNA Replication (duplication)
• Takes place in the nucleus (during the S phase)
• Result: 2 exact copies original DNA
DNA Polymerase
Helicase
Replication fork
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DNA Replication (duplication)
• 1. Helicase unzips the double helix by breaking the hydrogen
bonds forming a replication fork.
• 2. DNA polymerase adds the complimentary base pairs to
each separated strand.
– DNA Polymerase also “proofreads” each new strand.
Helicase
DNA Polymerase
Replication fork
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DNA Replication, Accuracy & Repair
•
•
•
•
•
•
•
Original: A-T-T-C-C-G
Complement: TAAGGC
Original: GCTAAG
• DNA polymerase
Complement:
proofreads &
Original: CTACCA
repairs1error/1Billion
Complement:
Original
– Strand A: GACCTA
– Strand B:
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• Nucleotide
Components
– Ribose Sugar
– Phosphate Group
– Nitrogen Base
• Adenine (A)
• Guanine (G)
• Cytosine (C)
• Uracil (U): not T
• Single Strand
• 3 Types:
– Messenger RNA (mRNA)
– Transfer RNA (tRNA)
– Ribosomal RNA (rRNA)
of RNA
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How to make RNA
Step 1 = Transcription: DNA RNA
Takes place in the nucleus
1. DNA unwinds.
2. RNA Polymerase binds to DNA promoter site (begin
gene)
Gene Begins
RNA Polymerase
3.
Add complementary RNA nucleotides (U↔A)
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Transcription Continued
4. DNA termination sequence signals gene end
RNA Polymerase
5. RNA Polymerase releases DNA & RNA
RNA Strand
DNA Rewinds
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Transcription
DNA makes RNA
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3 Types of RNA
1.
3.
Carries instructions from
DNA to assemble amino
acids into protein.
The site where proteins
get assembled from
mRNA.
2.
Carries the amino acids
to the mRNA at the
ribosome.
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How to make Protein =
Translation
• Involves the decoding of mRNA and assembling a
protein
• Proteins = polymers = macromolecule
– Monomer of protein = amino acid
– Polypeptides = sequence of amino acids
• Genetic code is read 3 letters at a time.
– Codon: every 3 base pairs in mRNA = an amino acid
• START Codon: starts translation- 1 codon only  AUG
• STOP Codon: stops translation- 3 codons  UAA, UAG, UGA
– Universal Codon -Amino Acid Code: p. 367
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mRNA Codon & Codon Chart
• AUG =
– Methionine or
start codon
• AAC = _________
Amino Acids
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How to make Protein =
Translation
• tRNA
– In cytosol
– Binds specific amino acid to
mRNA
– Anticodon:
• complement to mRNA
codons
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Translation: mRNA Protein
1. mRNA leaves nucleus
2. Ribosome attaches to mRNA
start codon
3. mRNA codon pairs with tRNA
anticodon delivering amino acid.
4. Peptide bond forms between
amino acids
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Translation: mRNA Protein
5. mRNA stop codon signals
end of translation. The ribosome
releases the newly formed
polypeptide.
6. mRNA released &
polypeptide complete
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Translation Diagram
Polypeptide Chain
Peptide Bond
Nucleus
Amino Acid
tRNA
Anticodon
mRNA
Codon
Ribosome
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Overview
DNA RNA Protein
Transcription
Translation
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Mutations
• Mutations – are heritable changes in genetic info.
• Occurs in only 2 types of cells
– Sex-cell (germ-cell) mutations: gametes affect
offspring
– Somatic mutations: body cells  affect individual
• 2 categories of mutations
– Gene mutations  produce change in a single gene
– Chromosomal mutations  produce change in a whole
chromosome.
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Gene Mutations
A.K.A. Point Mutations (3 types)
1. Substitution 1 nitrogen base gets substituted by
another nitrogen base; this results in a new codon
– Sickle Cell Anemia: substitute A for T
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Gene Mutations (con’t) Deletion
2.
Nucleotide deletions & insertions
– One base is inserted or removed from
the sequence.
- Causes Frame-shift mutations
– Changes amino acid sequence
Insertion
Deletion
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Chromosomal Mutations (5 types)
• Deletion: lose portion

• Duplication: gain extra portion

• Inversion: segment reverses

• Translocation: transfer segment to non-homologous

• Nondisjunction: gamete gets extra or less
chromosome (Down Syndrome- Trisomy 21)
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Chromosome Mutations Diagrams
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Genetic Traits & Disorders
• Disorders due to nondisjunction
– Nondisjunction: gametes have 1 more or less
chromosome (pairs don’t segregate)
– Monosomy: 45 chromosomes
• Turner’s syndrome: XO
– Trisomy: 47 chromosomes
• Down Syndrome: trisomy-21
• Kleinfelter’s syndrome: XXY
• Patau syndrome: trisomy-13
• Edward’s syndrome: trisomy-18
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