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Chapter 11
DNA and Protein Synthesis
Mrs. Svencer
11.1 Genes are made of DNA
Frederick and Griffith
Transformation –bacteria with mice
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Strain A – pneumonia, fatal
Strain B – harmless
Heated strain A – harmless
Mix heated strain A and strain B - death
Harmless bacteria - “transformed”
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Descendents were too - trait was passed on
Heritable change
Figure 11-1
Griffith showed that although a deadly strain
of bacteria could be made harmless by
heating it, some factor in that strain is still
able to change other harmless bacteria into
deadly ones. He called this the "transforming
factor."
Oswald Avery – focused on protein and
DNA
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Heat strain A + strain B + proteindestroying enzymes
 Offspring still transformed
 Protein not accountable for transformation
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Heat strain A + strain B + DNA-destroying
enzymes
 Colonies did not transform
 Therefore, DNA = genetic material
Hershey and Chase – used viruses
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Virus = nucleic acid in a protein coat
Bacteriophage = virus that infects bacteria
Batch 1
 Labeled protein coats with radioactive sulfur
 Radioactivity detected outside of the cells
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Batch 2
 Labeled DNA with radioactive phosphorus
 Radioactivity inside cells
 Therefore, phage’s DNA entered bacteria
 Therefore, DNA is the hereditary material
Figure 11-4
Hershey and Chase offered further evidence
that DNA, not proteins, is the genetic material.
Only the DNA of the old generation of viruses
is incorporated into the new generation.
11.2 Nucleic Acids store
information
DNA (deoxyribonucleic acid)
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Stores genetic information
Built from nucleotides – 3 parts
 1. Sugar – ring shape, “deoxyribose”
 2. Phosphate group
 3. Nitrogenous base – single or double ring of C
and N atoms
Figure 11-5
A nucleotide
has three
components:
a sugar, a
phosphate
group, and a
nitrogenous
base.
4 bases in DNA
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Pyrimidines: single rings
 Thymine (T)
 Cytosine (C)
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Purines: double rings
 Adenine (A)
 Guanine (G)
Figure 11-6
DNA contains four different
nitrogenous bases. Thymine and
cytosine have single-ring
structures. Adenine and guanine
have double-ring
DNA Strands
Covalent bonds connect sugar to
phosphate between nucleotides
Sugar-phosphate “backbone”
Nucleotides arrange in different
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1. Numbers
2. Sequences
(combinations are unlimited)
Rosalind Franklin and Maurice Wilkins
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X-ray crystallography
DNA = helix shape
Watson and Crick
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Made model of double helix using Franklin’s
pictures
Twisted ladder
Complementary Base Pairs
 Purine + Pyrimidine
A-T (2 hydrogen bonds)
G-C (3 hydrogen bonds)
11.3 DNA Replication –
mechanism of inheritance (DNA – copying)
Template Mechanism
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2 strands of double helix separate at
origins of replication
 Copying goes outward from origin in both
directions, making a “bubble”
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Each strand is a “template” for a new,
complementary strand
 Bases line up according to base-pairing rules
Figure 11-9
During DNA replication,
the two strands of the
original parent DNA
molecule, shown in blue,
each serve as a template
for making a new strand,
shown in yellow.
Replication results in two
daughter DNA molecules,
each consisting of one
original strand and one
new strand.
Figure 11-10
DNA replication begins at
origins of replication and
proceeds in both
directions, producing
"bubbles." Eventually, all
the bubbles merge,
resulting in two separate
daughter DNA molecules.
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DNA polymerase (enzyme) links
nucleotides together using covalent bonds
 DNA opens further as nucleotides added
 Eukaryotic DNA – many origins - speedy
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New strands = daughter strands
Fast and accurate
 1 error / billion nucleotides
Review: DNA Replication
occurs before a cell divides
during the S phase of
interphase of the cell cycle
11.4 Genes Provide Information
for Making Proteins
Beadle and Tatum – orange bread mold
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Mutant strains unable to grow on nutrient
medium
Lacked single enzyme needed to produce a
needed molecule
Each mutant defective in a single gene
“one gene-one enzyme” hypothesis – one
gene produces one specific enzyme
NOW, “one gene – one polypeptide”
RNA is needed to make a protein
Nucleic Acid RNA –
ribonucleic acid
Sugar
Ribose
DNA –
deoxyribonucleic
acid
Deoxyribose
Nitrogenous AUCG
bases
ATCG
Shape
Double helix
Single helix
Gene to Protein
1. Transcription - DNA to RNA
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Transcribed message (RNA) leaves nucleus
to cytoplasm
2. Translation – RNA to amino acid
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Codon = on RNA - 3 bases that code for
amino acid
Table of Codons
RNA
Figure 11-13
61/64 code for amino acids – some
amino acids coded for by more than 1
codon
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Ex: UUU UUC – both code for
phenylalanine
3/64 – stop codons – end of each gene
sequence
Figure 11-13
Each codon stands for a
particular amino acid. (The
table uses abbreviations for
the amino acids, such as
Ser for serine.) The codon
AUG not only stands for
methionine (Met), but also
functions as a signal to
"start" translating an RNA
transcript. There are also
three "stop" codons that do
not code for amino acids,
but signal the end of each
genetic message.
11.5 Two steps from Gene to Protein
Transcription: DNA to RNA
Messenger RNA (mRNA) transcribed from
DNA template – only 1 strand of DNA
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RNA nucleotides pair to complementary bases –
AUCG
RNA polymerase - RNA nucleotides together
RNA splicing – introns are removed and exons are
joined together
Therefore, mRNA has a continuous coding
sequence
mRNA leaves nucleus
Figure 11-12
Information flows from gene to
polypeptide. First, a sequence of
nucleotides in DNA (a gene) is
transcribed into RNA in the cell's
nucleus. Then the RNA travels to
the cytoplasm where it is translated
into the specific amino acid
sequence of a polypeptide.
Figure 11-15
In eukaryotes, the RNA
transcript is edited
before it leaves the
nucleus. Introns are
removed and the exons
are spliced together
before the "final draft"
transcript moves into the
cytoplasm where it gets
translated.
Intron = noncoding region of
mRNA
Exon = coding region of mRNA
that is “expressed” or translated
Translation: RNA to protein
1. Start codon: AUG –translation begins
2. Amino acids added one-by-one to a
chain of amino acids
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A. tRNA (transfer RNA) translates codons
of mRNA to amino acids
 1. tRNA molecule binds to appropriate amino
acid
 2. tRNA recognizes, using base-pairing
rules, codons in mRNA by its own
complementary anticodon
 Anticodon = 3 bases at one end of
tRNA
 3. Other end of tRNA = where amino
acid attaches
 4. An enzyme links tRNA to its amino
acid, using ATP
Figure 11-16
During translation,
tRNAs transport and
match amino acids to
their appropriate
codons on the mRNA
transcript. One end of
the tRNA attaches to
an amino acid. At the
other end, a triplet of
bases called the
anticodon matches to
the complementary
mRNA codon.
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B. occurs at ribosome
 2 subunits – made of protein and rRNA
(ribosomal RNA)
 Small subunit – binding site for mRNA
 Large subunit – 2 binding sites for tRNA
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1. “P” site (polypeptide) – holds tRNA carrying the
growing polypeptide chain
2. “A” site (amino acid) – holds tRNA carrying next
amino acid to be added to the chain
 2 subunits hold mRNA and tRNA close together
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C. ribosome connects new amino acid to
the growing polypeptide chain
Figure 11-17
Ribosomes bring
mRNA and tRNAs
together during
translation. Each
ribosome has an
attachment site for
an mRNA
transcript, and two
sites for tRNAs.
3. Reaches stop codon
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UAA, UAG, UGA
No amino acid at “A” site
Translation stops
4. Completed polypeptide set free from
tRNA by hydrolysis
11.6 Mutations
Mutation – any change in the nucleotide
sequence of DNA
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Can be
 Large regions of chromosomes
 Single nucleotide pairs
Base substitutions
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Replacement of 1 base or nucleotide with
another
Sometimes no effect – “silent mutation”
Sometimes large effect
Why?
 Several amino acids have more than 1 codon
More disastrous mutations
Insertion
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Putting in an additional nucleotide
Deletion
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Taking away 1 nucleotide
 Both insertion and deletion alter the triplet
groupings
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Now they code for new amino acids
Cause of mutations
Error during DNA replication
Error during crossing over in meiosis
Mutagens – physical / chemical agents
that cause mutations
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Ex: high-energy radiation, x-rays, UV light
Usually harmful, sometimes helpful
 Ex: dark color in female tiger swallowtails
Mutations may be passed to offspring, if
they occur in gametes
Ultimate source of genetic diversity