1. Overview: The Flow of Genetic Information
Gene expression, the process by which DNA directs protein synthesis, includes two stages: transcription and translation
© 2011 Pearson Education, Inc. 1

2. Basic Principles of Transcription and Translation
RNA is the bridge between genes and the proteins for which they code
Transcription is the synthesis of RNA under the direction of DNA
Transcription produces messenger RNA (mRNA)
Translation is the synthesis of a polypeptide, using information in the mRNA
Ribosomes are the sites of translation
© 2011 Pearson Education, Inc. 2

3. In prokaryotes, translation of mRNA can begin before transcription has finished
In a eukaryotic cell, the nuclear envelope separates transcription from translation
Eukaryotic RNA transcripts are modified through RNA processing to yield finished mRNA
© 2011 Pearson Education, Inc. 3

4. A primary transcript is the initial RNA transcript from any gene prior to processing
The central dogma is the concept that cells are governed by a cellular chain of command: DNA RNA protein
© 2011 Pearson Education, Inc. 4

5. Figure 17.UN01
DNA
RNA
Protein
Figure 17.UN01 In-text figure, p. 328

6. DNA Pre-mRNA mRNA DNA mRNA Nuclear envelope TRANSCRIPTION
Figure 17.3
Nuclear envelope
DNA
TRANSCRIPTION
Pre-mRNA
RNA PROCESSING
mRNA
DNA
TRANSCRIPTION
mRNA
Figure 17.3 Overview: the roles of transcription and translation in the flow of genetic information.
Ribosome
TRANSLATION
Ribosome
TRANSLATION
Polypeptide
Polypeptide
(a) Bacterial cell
(b) Eukaryotic cell

7. DNA TRANSCRIPTION mRNA (a) Bacterial cell Figure 17.3a-1
Figure 17.3 Overview: the roles of transcription and translation in the flow of genetic information.
(a) Bacterial cell

8. DNA TRANSCRIPTION mRNA Ribosome TRANSLATION Polypeptide
Figure 17.3a-2
DNA
TRANSCRIPTION
mRNA
Ribosome
TRANSLATION
Figure 17.3 Overview: the roles of transcription and translation in the flow of genetic information.
Polypeptide
(a) Bacterial cell

9. Nuclear envelope DNA Pre-mRNA mRNA Ribosome Polypeptide TRANSCRIPTION
Figure 17.3b-3
Nuclear envelope
DNA
TRANSCRIPTION
Pre-mRNA
RNA PROCESSING
mRNA
Figure 17.3 Overview: the roles of transcription and translation in the flow of genetic information.
TRANSLATION
Ribosome
Polypeptide
(b) Eukaryotic cell

10. Codons: Triplets of Nucleotides
The flow of information from gene to protein is based on a triplet code: a series of nonoverlapping, three-nucleotide words
The words of a gene are transcribed into complementary nonoverlaping three-nucleotide words of mRNA
These words are then translated into a chain of amino acids, forming a polypeptide
© 2011 Pearson Education, Inc. 10

11. DNA template strand 5 DNA 3 molecule Gene 1 5 3 TRANSCRIPTION
Figure 17.4
DNA template strand 5
DNA 3 A C C A A A C C G A G T
molecule T G G T T T G G C T C A
Gene 1 5 3
TRANSCRIPTION
Gene 2 U G G U U U G G C U C A
mRNA 5 3
Codon
TRANSLATION
Figure 17.4 The triplet code.
Protein
Trp
Phe
Gly
Ser
Gene 3
Amino acid

12. The template strand is always the same strand for a given gene
During transcription, one of the two DNA strands, called the template strand, provides a template for ordering the sequence of complementary nucleotides in an RNA transcript
The template strand is always the same strand for a given gene
During translation, the mRNA base triplets, called codons, are read in the 5 to 3 direction
© 2011 Pearson Education, Inc. 12

13. Codons along an mRNA molecule are read by translation machinery in the 5 to 3 direction
Each codon specifies the amino acid (one of 20) to be placed at the corresponding position along a polypeptide
© 2011 Pearson Education, Inc. 13

14. Cracking the Code 64 codons Redundant
Codons must be read in the correct reading frame (correct groupings) in order for the specified polypeptide to be produced
© 2011 Pearson Education, Inc. 14

15. First mRNA base (5 end of codon) Third mRNA base (3 end of codon)
Figure 17.5
Second mRNA base U C A G
UUU
UCU
UAU
UGU U
Phe
Tyr
Cys
UUC
UCC
UAC
UGC C U
Ser
UUA
UCA
UAA Stop
UGA Stop A
Leu
UUG
UCG
UAG Stop
UGG
Trp G
CUU
CCU
CAU
CGU U
His
CUC
CCC
CAC
CGC C C
Leu
Pro
Arg
CUA
CCA
CAA
CGA A
Gln
CUG
CCG
CAG
CGG G
First mRNA base (5 end of codon)
Third mRNA base (3 end of codon)
AUU
ACU
AAU
AGU U
Asn
Ser
AUC
Ile
ACC
AAC
AGC C A
Thr
Figure 17.5 The codon table for mRNA.
AUA
ACA
AAA
AGA A
Lys
Arg
AUG
Met or start
ACG
AAG
AGG G
GUU
GCU
GAU
GGU U
Asp
GUC
GCC
GAC
GGC C G
Val
Ala
Gly
Gly
GUA
GCA
GAA
GGA A
Glu
GUG
GCG
GAG
GGG G

16. Concept 17.2: Transcription is the DNA-directed synthesis of RNA: a closer look
Transcription is the first stage of gene expression
© 2011 Pearson Education, Inc. 16

17. Molecular Components of Transcription
RNA synthesis is catalyzed by RNA polymerase, which pries the DNA strands apart and hooks together the RNA nucleotides
© 2011 Pearson Education, Inc. 17

18. The stretch of DNA that is transcribed is called a transcription unit
The DNA sequence where RNA polymerase attaches is called the promoter; in bacteria, the sequence signaling the end of transcription is called the terminator
The stretch of DNA that is transcribed is called a transcription unit
Animation: Transcription
© 2011 Pearson Education, Inc. 18

19. Promoter Transcription unit 5 3 3 5 DNA Start point RNA polymerase
Figure
Promoter
Transcription unit 5 3 3 5
DNA
Start point
RNA polymerase
Figure 17.7 The stages of transcription: initiation, elongation, and termination.

20. Nontemplate strand of DNA 5 3 3 5 Template strand of DNA
Figure
Promoter
Transcription unit 5 3 3 5
DNA
Start point
RNA polymerase 1
Initiation
Nontemplate strand of DNA 5 3 3 5
Template strand of DNA
RNA transcript
Unwound DNA
Figure 17.7 The stages of transcription: initiation, elongation, and termination.

21. Nontemplate strand of DNA 5 3 3 5 Template strand of DNA
Figure
Promoter
Transcription unit 5 3 3 5
DNA
Start point
RNA polymerase 1
Initiation
Nontemplate strand of DNA 5 3 3 5
Template strand of DNA
RNA transcript
Unwound DNA 2
Elongation
Rewound DNA 5 3 3 3 5 5
Figure 17.7 The stages of transcription: initiation, elongation, and termination.
RNA transcript

22. Nontemplate strand of DNA 5 3 3 5 Template strand of DNA
Figure
Promoter
Transcription unit 5 3 3 5
DNA
Start point
RNA polymerase 1
Initiation
Nontemplate strand of DNA 5 3 3 5
Template strand of DNA
RNA transcript
Unwound DNA 2
Elongation
Rewound DNA 5 3 3 3 5 5
Figure 17.7 The stages of transcription: initiation, elongation, and termination.
RNA transcript 3
Termination 5 3 3 5 5 3
Completed RNA transcript
Direction of transcription (“downstream”)

23. Synthesis of an RNA Transcript
The three stages of transcription
Initiation
Elongation
Termination
© 2011 Pearson Education, Inc. 23

24. RNA Polymerase Binding and Initiation of Transcription
Promoters signal the transcriptional start point and usually extend several dozen nucleotide pairs upstream of the start point
Transcription factors mediate the binding of RNA polymerase and the initiation of transcription
The completed assembly of transcription factors and RNA polymerase II bound to a promoter is called a transcription initiation complex
A promoter called a TATA box is crucial in forming the initiation complex in eukaryotes
© 2011 Pearson Education, Inc. 24

25. Several transcription factors bind to DNA Transcription factors
Figure 17.8 1
A eukaryotic promoter
Promoter
Nontemplate strand
DNA 5 T A T A A A A 3 3 A T A T T T T 5
TATA box
Start point
Template strand 2
Several transcription factors bind to DNA
Transcription factors 5 3 3 5 3
Transcription initiation complex forms
RNA polymerase II
Figure 17.8 The initiation of transcription at a eukaryotic promoter.
Transcription factors 5 3 3 3 5 5
RNA transcript
Transcription initiation complex

26. Nontemplate strand of DNA
Figure 17.9
Nontemplate strand of DNA
RNA nucleotides
RNA polymerase T C C A A A 3 T 5 U C T 3
end T G U A G A C A U C C A C C A 5 A 3 T
Figure 17.9 Transcription elongation. A G G T T 5
Direction of transcription
Template strand of DNA
Newly made RNA

27. Alteration of mRNA Ends
Each end of a pre-mRNA molecule is modified in a particular way
The 5 end receives a modified nucleotide 5 cap
The 3 end gets a poly-A tail
These modifications share several functions
They seem to facilitate the export of mRNA
They protect mRNA from hydrolytic enzymes
They help ribosomes attach to the 5 end
© 2011 Pearson Education, Inc. 27

28. Protein-coding segment Polyadenylation signal
Figure 17.10
Protein-coding segment
Polyadenylation signal 5 3 G P P P
AAUAAA
AAA …
AAA
Start codon
Stop codon 5
Cap 5
UTR 3
UTR
Poly-A tail
Figure RNA processing: Addition of the 5 cap and poly-A tail.