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Chapter 10
Molecular Biology of the Gene
PowerPoint Lectures
Campbell Biology: Concepts & Connections, Eighth Edition
REECE • TAYLOR • SIMON • DICKEY • HOGAN
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Lecture by Edward J. Zalisko
• DNA
• DNA Replication
• DNA Transcription and Translation
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THE FLOW OF GENETIC INFORMATION
FROM DNA TO RNA TO PROTEIN
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• Intro to Transcription and Translation
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10.6 Genes control phenotypic traits through
the expression of proteins
• DNA specifies traits by dictating
synthesis.
• Proteins are the links between genotype and
phenotype.
• The molecular chain of command is from DNA in
the nucleus to RNA and RNA in the cytoplasm to
protein.
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10.6 Genes control phenotypic traits through
the expression of proteins
•
is the synthesis of RNA
under the direction of DNA.
•
is the synthesis of
proteins under the direction of RNA.
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Figure 10.6a-3
DNA
Transcription
RNA
NUCLEUS
Translation
Protein
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CYTOPLASM
10.6 Genes control phenotypic traits through
the expression of proteins
• Genes provide the instructions for making specific
proteins.
• The sequence of nucleotides in DNA provides a
code for constructing a protein.
• Protein construction requires a conversion of a
nucleotide sequence to an amino acid sequence.
• Transcription rewrites the DNA code into RNA
using the same nucleotide “language.”
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Answer in Notebooks
#6. Describe the significance of Transcription and
Translation.
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10.9 VISUALIZING THE CONCEPT:
Transcription produces genetic messages in
the form of RNA
• Transcription of a gene occurs in three main steps:
1.
, involving the attachment of RNA
polymerase to the promoter and the start of RNA
synthesis
2.
, as the newly formed RNA strand
grows
3.
, when RNA polymerase reaches
the terminator DNA and the polymerase molecule
detaches from the newly made RNA strand and
the gene.
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Animation: Transcription
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Figure 10.9-3
Direction of transcription
Initiation
RNA synthesis begins after RNA
polymerase attaches to the promoter.
Unused
strand
of DNA
RNA polymerase
Terminator
DNA
DNA
of gene
Newly formed
RNA
Promoter
Elongation
Template strand
of DNA
Direction of transcription
Using the DNA as a template, RNA
polymerase adds free RNA nucleotides
one at a time.
Free RNA
nucleotide
DNA strands
reunite
T C C A A
U C C A
A GG T T
DNA strands
separate
Newly made RNA
Termination
RNA synthesis ends when RNA
polymerase reaches the
terminator DNA sequence.
Terminator
DNA
Completed RNA
RNA polymerase
detaches
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10.10 Eukaryotic RNA is processed before
leaving the nucleus as mRNA
•
• encodes amino acid sequences
• conveys genetic messages from DNA to the translation
machinery of the cell.
• Eukaryotic mRNA has
sequences that separate
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, interrupting
, the coding regions.
10.10 Eukaryotic RNA is processed before
leaving the nucleus as mRNA
• Eukaryotic mRNA undergoes processing before
leaving the nucleus.
•
removes introns
(intervening sequences) and joins exons
(expressed sequences) to produce a continuous
coding sequence.
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10.10 Eukaryotic RNA is processed before
leaving the nucleus as mRNA
•A
of extra nucleotides are
added to the ends of the mRNA
• facilitate the export of the mRNA from the nucleus
• protect the mRNA from degradation by cellular enzymes
• help ribosomes bind to the mRNA
• The cap and tail themselves are not translated into protein.
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Figure 10.10
Exon
DNA
Exon
Intron
Cap
RNA
transcript
with cap
and tail
Exon
Intron
Transcription
Addition of cap and tail
Introns removed
Tail
Exons spliced together
mRNA
Coding sequence
NUCLEUS
CYTOPLASM
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10.7 Genetic information written in codons is
translated into amino acid sequences
• The flow of information from gene to protein is based on a
triplet code.
• The genetic instructions for the amino acid sequence of a
polypeptide chain are written in DNA and RNA as a series of
nonoverlapping three-base “words” called
.
• Transcribe the following DNA codons into mRNA codons.
TAC
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CGA
ACA
ATC
Answer in Notebooks:
#7. Find the DNA codons for the mRNA codons
below:
AUG
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CUC
UUA
CGC
10.11 Transfer RNA molecules serve as
interpreters during translation
•
molecules function as
an interpreter, converting the genetic message of
mRNA into the language of proteins.
• Transfer RNA molecules perform this interpreter
task by
• picking up the appropriate amino acid
• using a special triplet of bases, called an
, to recognize the appropriate codons
in the mRNA.
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Figure 10.11a
Amino acid
attachment site
Hydrogen bond
RNA polynucleotide
chain
Anticodon
A tRNA molecule, showing
its polynucleotide strand
and hydrogen bonding
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A simplified
representation of a tRNA
Find the tRNA anticodons for the mRNA codons
below:
AUG
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CUC
UUA
CGC
Answer in Notebooks:
#8. Given the tRNA anticodons write the
corresponding mRNA codons.
UAC
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AUU
GCA
UCG
Answer in Notebooks:
#9. Translate and transcribe the following DNA into
mRNA and tRNA.
TAC
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ATT
GCA
ACT
Answer in Notebooks:
#10. Translate and transcribe the following mRNA
into DNA and tRNA.
AUG
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GCA
GCG
GUA
10.12 Ribosomes build polypeptides
• Translation occurs on the surface of the ribosome.
• Ribosomes coordinate the functioning of mRNA and
tRNA and, ultimately, the synthesis of polypeptides.
• Ribosomes have two subunits: small and large.
• Each subunit is composed of ribosomal RNAs and
proteins.
• Ribosomal subunits come together during translation.
• Ribosomes have binding sites for mRNA and tRNAs.
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Figure 10.12-0
tRNA
molecules
tRNA binding sites
Growing
polypeptide
Ribosome
Large
subunit
P A
site site
Small
subunit
mRNA binding site
The next amino
acid to be added
to the polypeptide
Growing
polypeptide
mRNA
tRNA
Codons
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10.13 An initiation codon marks the start of
an mRNA message
• Translation can be divided into the same three
phases as transcription:
1. initiation
2. elongation
3. Termination
• Initiation brings together
• mRNA,
• a tRNA bearing the first amino acid
• the two subunits of a ribosome
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10.13 An initiation codon marks the start of
an mRNA message
• Initiation establishes where translation will begin.
• Initiation occurs in two steps.
1. An mRNA molecule binds to a small ribosomal
subunit, and a special initiator tRNA binds to
mRNA at the
codon.
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10.13 An initiation codon marks the start of
an mRNA message
2. A large ribosomal subunit joins the small subunit,
allowing the ribosome to function.
• The first tRNA occupies the
hold the growing polypeptide.
, which will
• The
is available to receive the next
amino-acid-bearing tRNA.
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Figure 10.13a
Start of genetic message
Cap
End
Tail
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Figure 10.13b-2
Large
ribosomal
subunit
Initiator
tRNA
mRNA
P
site
A
site
U A C
U A C
A U G
A U G
Start codon
1
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Small ribosomal
subunit
2
10.14 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.
• Each addition occurs in a three-step elongation
process.
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Figure 10.14-4
Amino
acid
Anticodon
A site
Polypeptide
P
site
mRNA
Codons
1 Codon
recognition
mRNA
movement
Stop
codon
New
peptide
bond
3
Translocation
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2 Peptide bond
formation
10.14 Elongation adds amino acids to the
polypeptide chain until a stop codon
terminates translation
• Elongation continues until the termination stage of
translation, when
• the ribosome reaches a
codon
• the completed polypeptide is freed from the last
tRNA
• the ribosome splits back into its separate subunits.
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Animation: Translation
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10.8 The genetic code dictates how codons
are translated into amino acids
• The
is the amino acid
translations of each of the nucleotide triplets.
• Three nucleotides specify one amino acid.
• Sixty-one codons correspond to amino acids.
• AUG codes for methionine and signals the start of
transcription.
• Three “stop” codons signal the end of translation.
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10.8 The genetic code dictates how codons
are translated into amino acids
• The genetic code is
•
, with more than one
codon for some amino acids
•
, in that any codon for
one amino acid does not code for any other amino
acid
•
, in that the genetic code
is shared by organisms from the simplest bacteria
to the most complex plants and animals.
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Figure 10.8a
Second base of RNA codon
C
A
UUU
U
UUC
First base of RNA codon
UUA
C
A
Leu
UCU
UAU
UCC
UAC
UCA
Ser
Tyr
UGU
UGC
Cys
U
C
UAA Stop UGA Stop A
UUG
UCG
UAG Stop UGG Trp
G
CUU
CCU
CAU
U
CUC
CCC
CAC
Leu
Pro
CAA
His
CGU
CGC
CGA
CUA
CCA
CUG
CCG
CAG
CGG
AUU
ACU
AAU
AGU
ACC
AAC
AUC lle
AUA
G
ACA
Thr
Asn
AAA
AGA
GUU
GAU
GUC
GUG
GCC
Val
GCA
GCG
GAC
Ala
GAA
GAG
Ser
Glu
GGC
GGA
GGG
A
U
C
Arg
A
G
GGU
Asp
C
G
AGC
AAG Lys AGG
GCU
Arg
Gln
or
AUG Met
ACG
start
GUA
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Phe
G
U
Gly
C
A
G
Third base of RNA codon
U
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Figure 10.8b-3
Strand to be transcribed
T
A C T
T
C A
A
A A
T
C
G A
A
G T
T
T T
A
G
A U G A
A
G U
U
U U
A
G
DNA
A T
Transcription
RNA
Translation
Start
codon
Polypeptide
Met
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Stop
codon
Lys
Phe
Answer in Notebooks:
#11. Transcribe the following mRNA to proteins.
UAC
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AUU
GCA
UCG
Answer in Notebooks:
#12. Translate and Transcribe the following DNA to
mRNA to proteins – include tRNA anticodons.
DNA:
mRNA:
tRNA:
Proteins:
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TAC
GGA
TCT
ATC
Answer in Notebooks: Translate and Transcribe
#13
the Following: (DNA – mRNA – Anticodon (tRNA) – Amino Acid)
T A C
AUG
UAC
Met
ATG
UAC
AUG
Tyr
CGC
GCG
CGC
ala
TCC
AGG
UCC
arg
GCC
CGG
GCC
arg
GTC
CAG
GUC
Glu
ATG
UAC
AUG
tyr
AAT
UUA
AAU
leu
ACC
UGG
ACC
try
ACT
UGA
ACU
stop
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10.15 Review: The flow of genetic information
in the cell is DNA  RNA  protein
• The flow of genetic information is from DNA to
RNA to protein.
• In transcription (DNA → RNA), the mRNA is
synthesized on a DNA template.
• In eukaryotic cells, transcription occurs in the
nucleus, and the messenger RNA is processed
before it travels to the cytoplasm.
• In prokaryotes, transcription occurs in the
cytoplasm.
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Figure 10.15-5
DNA
Transcription
mRNA
NUCLEUS
Transcription
1
RNA
polymerase
CYTOPLASM
Translation
Amino acid
Amino acid
attachment
Enzyme
2
tRNA
Initiator
tRNA
UA C
AU G
mRNA
Start
codon
ATP
Large
ribosomal
subunit
Anticodon
3 Initiation of
polypeptide
synthesis
Small
ribosomal
subunit
New peptide
bond forming
Growing
polypeptide
4
Elongation
Codons
mRNA
Polypeptide
5
Stop codon
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Termination