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1. DNA, RNA structure
2. Transcription, translation
DNA is a double-stranded helix
• James Watson and Francis Crick worked out
the three-dimensional structure of DNA, based
on work by Rosalind Franklin
Figure 10.3A, B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
DNA and RNA are polymers of nucleotides
• DNA is a nucleic acid, made of long chains of
nucleotides
Phosphate
group
Nitrogenous
base
Sugar
Phosphate
group
Nitrogenous base
(A, G, C, or T)
Nucleotide
Thymine (T)
Sugar
(deoxyribose)
DNA nucleotide
Polynucleotide
Sugar-phosphate backbone
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 10.2A
• DNA has four kinds of bases,
– Adenine(A), Thymine (T), Cytosine (C), and
Guanine (G)
Thymine (T)
Cytosine (C)
Adenine (A)
Guanine (G)
Figure 10.2B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Each strand of the
double helix is
oriented in the
opposite direction
5 end
3 end
P
P
P
P
P
– Anit-Parellel: means
parellel but moving
in different
directions
P
P
P
Figure 10.5B
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3 end
5 end
• RNA is also a nucleic acid
– different sugar (ribose)
– Uracil instead of Thymine
– Still has Adenine, Guanine, Cytosine
– Single strand, usually
Nitrogenous base
(A, G, C, or U)
Phosphate
group
Uracil (U)
Sugar
(ribose)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 10.2C, D
Types of RNA
Genetic information copied from DNA is
transferred to 3 types of RNA:
__________ RNA: mRNA
Copy of information in DNA that is brought to the
ribosome and translated into protein by tRNA &
rRNA.
__________ RNA: rRNA
Most of the RNA in cells is associated with structures
known as ribosomes, the protein factories of the
cells.
It is the site of translation where genetic information
brought by mRNA is translated into actual
proteins.
___________ RNA: tRNA
Brings the amino acid to the ribosome that mRNA
coded for.
Copyright
© 2003
Pearson
Education,
Inc. on
publishing
as Benjamin Cummings
From
the Virtual
Cell
Biology
Classroom
ScienceProfOnline.com
Images: Blueprint, clipart; Factory, Andreas Praefcke; Truck, PRA.
• The information constituting an organism’s
genotype is carried in its sequence of bases
– The DNA is transcribed into RNA, which is translated
into a chain of amino acids
– Bases of Central Dogma
DNA
TRANSCRIPTION
RNA
TRANSLATION
Protein
Figure 10.6A
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Transcription produces mRNA
RNA
polymerase
RNA nucleotide
Direction of
transcription
Template
strand of DNA
Figure 10.9A
Newly made RNA
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RNA polymerase
• In transcription,
DNA helix unzips
DNA of gene
Promoter
DNA
– RNA nucleotides line
up along one strand
of DNA, following the
base-pairing rules
– single-stranded
messenger RNA peels
away and DNA
strands rejoin
Initiation
Elongation
Terminator
DNA
Area shown
in Figure 10.9A
Termination
Growing
RNA
Completed RNA
Figure 10.9B
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RNA
polymerase
RNA transcripts of DNA
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Translation of mRNA into amino acids
• The “words” of the DNA “language” are triplets
of bases called codons
– The codons in a gene specify the amino acid
sequence of a protein
– In other words, codons are every 3 bases.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Gene 1
Gene 3
DNA molecule
Gene 2
DNA strand
TRANSCRIPTION
RNA
Codon
TRANSLATION
Protein
Figure 10.7
Amino acid
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• An exercise in translating the genetic code
Transcribed strand
DNA
Transcription
RNA
Start
codon
Polypeptide
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Translation
Stop
codon
Figure 10.8B
Transfer RNA molecules serve as interpreters
during translation
• In the cytoplasm, a
ribosome attaches
to the mRNA and
translates its
message into a
protein
• The process is aided
by transfer RNAs
Amino acid attachment site
Hydrogen bond
RNA polynucleotide chain
Anticodon
Figure 10.11A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Each tRNA molecule has a triplet anti-codon
on one end and an amino acid attachment site
on the other
Amino acid
attachment
site
Anticodon
Figure 10.11B, C
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Ribosomes build chains of amino acids
Next amino acid
to be added to
protein
Growing
protein
tRNA
molecules
P site
A site
Growing
protein
Large
subunit
tRNA
P
A
mRNA
mRNA
binding
site
Codons
mRNA
Small
subunit
Figure 10.12A-C
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An initiation codon marks the start of an
mRNA message
AUG = methionine
Start of genetic message
End
Figure 10.13A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• mRNA, a specific tRNA, and the ribosome
subunits assemble during initiation
Large
ribosomal
subunit
Initiator tRNA
P site
A site
Start
codon
mRNA
Small ribosomal
subunit
1
Figure 10.13B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
2
How does translation happen?
• The mRNA moves one codon at a time relative
to the ribosome
– A tRNA pairs with each codon, adding an amino
acid to the growing protein
– A STOP codon causes the mRNA-ribosome
complex to fall apart
– This results in a chain of amino acids
• Amino Acid (AA) + AA + AA + AA…etc = Protein
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Transcription
RNA
RNA polymerase
DNA
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Translation
Lysin
e
mRN
A
tRNA
Translation direction
Ribosome
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Pause for Worksheet
COMPLETE
-PROTEIN SYNTHESIS
WORKSHEET
-BOOK WORKSHEET
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
b
a
Red object = ?
What molecules are present
in this photo?
Table 14.2
Types of RNA
Type of RNA
Functions in
Messenger RNA
(mRNA)
Nucleus,
migrates
to ribosomes
in cytoplasm
Transfer RNA
(tRNA)
Cytoplasm
Provides linkage
between mRNA
and amino acids;
transfers amino
acids to ribosomes
Ribosomal RNA
(rRNA)
Cytoplasm
Structural
component
of ribosomes
Function
Carries DNA
sequence
information to
ribosomes
Review: The flow of genetic information in the cell
is DNARNAprotein
• The sequence of codons in DNA spells out the
primary structure of a protein
– A chain of amino acids form proteins that cells
and organisms use
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Overview
Eukaryotic Cell
______________
Synthesis of RNA under
the direction of DNA
(mRNA).
______________
Actual synthesis of a
polypeptide (protein)
under the direction of
mRNA.
Copyright
© 2003
Pearson
Education,
Inc. on
publishing
as Benjamin Cummings
From
the Virtual
Cell
Biology
Classroom
ScienceProfOnline.com
Diagram: Transcription & Translation, NIH
Pause for Worksheet
COMPLETE
-DNA MOLECULE &
REPLICATION
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
So how is DNA read to make Amino acids
• We use the Genetic
Coding Chart
• Virtually all
organisms share the
same genetic codethe sequence is
what is important
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
This is another one
Second Base
C
U
UUU
UUC
UUA
UUG
C
CUU
CUC
CUA
CUG
A
AUU
AUC
ile
AUA
AUG met (start)
ACU
ACC
ACA
ACG
G
GUU
GUC
GUA
GUG
GCU
GCC
GCA
GCG
phe
leu
leu
val
UCU
UCC
UCA
UCG
CCU
CCC
CCA
CCG
A
ser
UAU
UAC
UAA
UAG
pro
CAU
CAC
CAA
CAG
thr
AAU
AAC
AAA
AAG
ala
GAU
GAC
GAA
GAG
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
G
tyr
stop
stop
his
gln
asn
lys
asp
glu
UGU
UGC
UGA
UGG
CGU
CGC
CGA
CGG
AGU
AGC
AGA
AGG
GGU
GGC
GGA
GGG
cys
stop
trp
arg
ser
arg
gly
U
C
A
G
U
C
A
G
U
C
A
G
U
C
A
G
Third Base
First Base
U
Before we begin
• In DNA
– A binds with T (like AT&T)
– C binds with G (like Cover Girl)
– RNA is the same BUT there is no T
• It is a U so A and U bind together
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Step 1:
• Create a DNA sequence with 30 bases
– Must start with TAC
– Must end with ATT
– After that you are good to go with any bases
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Step 2:
• Using your DNA, make a complimentary
mRNA strand
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Step 3:
• Using your mRNA strand
– Start at the beginning and circle every 3 codons
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Step 4:
• Look at your first
codon
– Match the first letter,
second letter and third
letter to the Genetic
Coding Chart.
– Write the Amino Acid
under the circled
codon
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Step 5:
• Continue until all codons are labeled with an
amino acid
• Now you have a chain of Amino Acids
– Also called a PROTEIN
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Example

DNA strand
A–T–G–C–C–T–T–T–G
T–A–C–G–G–A–A–A–C
–

mRNA strand A – U – G – C – C – U – U – U – G

1st codon A-U-G
amino acid = methionine

2nd codon
C-C-U
amino acid = proline

3rd codon
U-U-G
amino acid = leucine
methionine
proline
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leucine
Pause for Worksheet
COMPLETE THE 3 GENETIC
CODING WORKSHEETS
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Confused?
Here are links to fun resources that further
explain genetic transcription & translation:
•
Molecular Genetics: Transcription &
Translation Main Page on the Virtual Cell Biology
Classroom of Science Prof Online.
•
“That Spells DNA” song by Jonathan Coulton.
•
DNA Transcription
•
Transcribe & Translate a Gene, from
•
DNA Transcription and Protein Assembly
•
Genetic by Sonic Youth.
•
Transcription and Translation animated movie
•
“The Protein Synthesis Song” by
Kyrk.
step-through animation by John
University of Utah.
animated movie by RedAndBrownPaperBag.
from PBS production “DNA: The Secret of Life.
MrsPurpleMonster18.
(You must be in PPT slideshow view to click on links.)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
From the Virtual Cell Biology Classroom on ScienceProfOnline.com