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Chapter 10
Molecular Biology of the Gene
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
© 2012 Pearson Education, Inc.
Lecture by Edward J. Zalisko
FROM DNA TO PROTEIN Part 1:
Transcription
© 2012 Pearson Education, Inc.
Genes Determine the Production of RNA and
Proteins
 Gene = a DNA sequence that specifies an RNA or
protein sequence
 Transcription is the synthesis of RNA under the
direction of DNA.
 DNA
mRNA (recipe for protein’s amino acid seq)
 DNA
tRNA
 DNA
rRNA
Used in translation of mRNA
 Translation is the synthesis of proteins under the
direction of RNA.
© 2012 Pearson Education, Inc.
Figure 10.7
DNA
molecule
Gene 1
Gene 2
Gene 3
DNA
A A A C C G G C A A A A
Transcription
RNA
Translation
U U
U G G C
Codon
Polypeptide
Amino
acid
C G U
U
U U
Figure 10.8B_s3
Strand to be transcribed
T A C T
T
C A A A A T
C
DNA
A T G A A G T
Transcription
RNA
T T
T A G
RNA is complementary to ONE DNA strand!
A U G A A G U U U U A G
Translation
Start
codon
Polypeptide
Met
Stop
codon
Lys
Phe
The Genetic Code
 Codon is a 3-nucleotide sequence in mRNA that specifies
an amino acid
 Genetic Code is:

Triplet: 3 nucleotides = 1 amino acid (This allows for 64 possible
codons)

Redundant:
codon.
1 amino acid may be coded for by more than 1
 Ex: 4 codons = proline

Specific: Only 1 amino acid per codon
 Ex: CCU only = proline

Universal: Every organism uses the same genetic code!!!!!
© 2012 Pearson Education, Inc.
Figure 10.8A
Third base
First base
Second base
Transcription: DNA to RNA
 Location = Nucleus in Eukaryotes
 RNA Polymerase links RNA nucleotides together
Animation: Transcription
© 2012 Pearson Education, Inc.
Figure 10.9B_1
RNA polymerase
Terminator
DNA
DNA of gene
Promoter
DNA
Promoter =
DNA sequence
that marks
beginning of
gene
1
Initiation
RNA Polymerase
binds DNA at
promoter and
transcription
begins
Figure 10.9B_2
2
Elongation
RNA Polymerase
synthesizes RNA
using ONE DNA
strand as a
template.
Growing
RNA
Note: RNA
synthesized
using base pair
rules!! (A-U and
G-C)
Free RNA
nucleotides
RNA
polymerase
C C A A
Only ONE strand
of DNA is ‘read’!
A U C C A
T A G G T
Direction of
transcription
Newly made RNA
T
Template
strand of DNA
Transcription
STOPS at
terminator -- RNA
polymerase
detaches from
3
DNA.
Completed
RNA
Growing
RNA
Termination
Terminator =
DNA sequence
that marks end
of gene
RNA
polymerase
Eukaryotic RNA is processed before leaving the
nucleus as mRNA
 Messenger RNA (mRNA)
– encodes amino acid sequences for a protein
 In prokaryotes transcription and translation occur in the
same place
 But in eukaryotes, mRNA must exit the nucleus to enter
the cytoplasm (site of translation).
– Eukaryotic mRNA has
– introns, non-coding, interrupting sequences
– exons, the coding regions.
© 2012 Pearson Education, Inc.
Eukaryotic RNA is processed before leaving the
nucleus as mRNA
 5’ cap
 Modified G nucleotide added to 5’ end
 3’ poly A tail
 Long sequence of A nucleotides added to 3’ end
– facilitate the export of the mRNA from the nucleus,
– protect the mRNA from destruction, and
– help ribosomes bind to the mRNA.
 RNA splicing removes introns and joins exons to
produce a continuous coding sequence.
© 2012 Pearson Education, Inc.
Figure 10.10
Exon Intron
Exon
Intron
Exon
DNA
Cap
RNA
transcript
with cap
and tail
Transcription
Addition of cap and tail
Introns removed
Tail
Exons spliced together
mRNA
Coding sequence
NUCLEUS
CYTOPLASM