1. DNA, RNA structure
2. DNA replication
3. Transcription, translation
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• DNA is a nucleic acid, made of long chains of nucleotides
DNA and RNA are polymers of nucleotides
Figure 10.2A
Nucleotide
Phosphate group
Nitrogenous base
Sugar
Polynucleotide Sugar-phosphate backbone
DNA nucleotide
Phosphategroup
Nitrogenous base(A, G, C, or T)
Thymine (T)
Sugar(deoxyribose)
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• DNA has four kinds of bases, A, T, C, and G
Figure 10.2B
Pyrimidines
Thymine (T) Cytosine (C)
Purines
Adenine (A) Guanine (G)
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• RNA is also a nucleic acid– different sugar
– U instead of T
– Single strand, usually
Figure 10.2C, D
Phosphategroup
Nitrogenous base(A, G, C, or U)
Uracil (U)
Sugar(ribose)
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• James Watson and Francis Crick worked out the three-dimensional structure of DNA, based on work by Rosalind Franklin
DNA is a double-stranded helix
Figure 10.3A, B
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• Hydrogen bonds between bases hold the strands together: A and T, C and G
Figure 10.3D
Ribbon model Partial chemical structure Computer model
Hydrogen bond
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Untwisting and replication of DNA
• each strand is a template for a new strand
Figure 10.4B
helicase
DNA polymerase
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• Each strand of the double helix is oriented in the opposite direction
Figure 10.5B
5 end 3 end
3 end 5 end
P
P
P
PP
P
P
P
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• DNA polymerase works in only one direction
5 end
P
P
Parental DNA
Figure 10.5C
DNA polymerasemolecule
53
35
35
Daughter strandsynthesizedcontinuously
Daughter strandsynthesizedin pieces
DNA ligase
Overall direction of replication
53
• Telomere sequences are lost with each replication.
• Cancer, aging
telomeres
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– The DNA is transcribed into RNA, which is translated into the polypeptide
Figure 10.6A
DNA
RNA
Protein
TRANSCRIPTION
TRANSLATION
• The information constituting an organism’s genotype is carried in its sequence of bases
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Transcription produces genetic messages in the form of mRNA
Figure 10.9A
RNApolymerase
RNA nucleotide
Direction oftranscription
Newly made RNA
Templatestrand of DNA
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• In transcription, DNA helix unzips– RNA nucleotides line up along one strand of DNA, following the base-pairing rules
– single-stranded messenger RNA peels away and DNA strands rejoin
RNA polymerase
DNA of gene
PromoterDNA Terminator
DNAInitiation
Elongation
Termination
Area shownin Figure 10.9A
GrowingRNA
RNApolymerase
Completed RNA
Figure 10.9B
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• Noncoding segments, introns, are spliced out
• A cap and a tail are added to the ends
Eukaryotic RNA is processed before leaving the nucleus
Figure 10.10
DNA
RNAtranscriptwith capand tail
mRNA
Exon Intron IntronExon Exon
TranscriptionAddition of cap and tail
Introns removed
Exons spliced together
Coding sequence
NUCLEUS
CYTOPLASM
Tail
Cap
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• The “words” of the DNA “language” are triplets of bases called codons
– The codons in a gene specify the amino acid sequence of a polypeptide
Translation of nucleic acids into amino acids
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 10.7
DNA molecule
Gene 1
Gene 2
Gene 3
DNA strand
TRANSCRIPTION
RNA
Polypeptide
TRANSLATIONCodon
Amino acid
U C A G
U
C
A
G
GACU
GACU
GACU
GACU
UUUUUCUUAUUG
CUUCUCCUACUG
AUUAUCAUAAUG
GUUGUCGUAGUG
phe
leu
leu
ile
met (start)
val
UCUUCCUCAUCG
CCUCCCCCACCG
ACUACCACAACG
GCUGCCGCAGCG
ser
pro
thr
ala
UAUUACUAAUAG
CAUCACCAACAG
AAUAAC
AAGAAA
GAUGACGAAGAG
tyr
stopstop
his
gln
asn
lys
asp
glu
UGUUGCUGAUGG
CGUCGCCGACGG
AGUAGCAGAAGG
GGUGGCGGAGGG
cys
stoptrp
arg
ser
arg
gly
First Base T
hird Base
Second Base
Virtually all organisms share the same genetic code “unity of life”
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• An exercise in translating the genetic code
Figure 10.8B
Startcodon
RNA
Transcribed strand
StopcodonTranslation
Transcription
DNA
Polypeptide
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• In the cytoplasm, a ribosome attaches to the mRNA and translates its message into a polypeptide
• The process is aided by transfer RNAs
Transfer RNA molecules serve as interpreters during translation
Figure 10.11A
Hydrogen bond
Amino acid attachment site
RNA polynucleotide chain
Anticodon
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• Each tRNA molecule has a triplet anticodon on one end and an amino acid attachment site on the other
Figure 10.11B, C
Anticodon
Amino acidattachment site
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An initiation codon marks the start of an mRNA message
Figure 10.13A
End
Start of genetic message
AUG = methionine
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• mRNA, a specific tRNA, and the ribosome subunits assemble during initiation
Figure 10.13B
1
Initiator tRNA
mRNA
Startcodon Small ribosomal
subunit
2
P site
Largeribosomalsubunit
A site
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• The mRNA moves a codon at a time relative to the ribosome
– A tRNA pairs with each codon, adding an amino acid to the growing polypeptide
– A STOP codon causes the mRNA-ribosome complex to fall apart
Elongation
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Figure 10.14
1 Codon recognition
Amino acid
Anticodon
AsiteP site
Polypeptide
2 Peptide bond formation
3 Translocation
Newpeptidebond
mRNAmovement
mRNA
Stopcodon
Table 14.2Types of RNA
Type of RNA Functions in Function
Messenger RNA(mRNA)
Nucleus, migratesto ribosomesin cytoplasm
Carries DNA sequenceinformation to ribosomes
Transfer RNA(tRNA)
Cytoplasm Provides linkage between mRNAand amino acids;transfers aminoacids to ribosomes
Ribosomal RNA(rRNA)
Cytoplasm Structural component of ribosomes
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• The sequence of codons in DNA spells out the primary structure of a polypeptide
– Polypeptides form proteins that cells and organisms use
Review: The flow of genetic information in the cell is DNARNAprotein
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• Mutations are changes in the DNA base sequence
– caused by errors in DNA replication or by mutagens
– change of a single DNA nucleotide causes sickle-cell disease
Mutations can change the meaning of genes
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Figure 10.16A
Normal hemoglobin DNA
mRNA
Normal hemoglobin
Glu
Mutant hemoglobin DNA
mRNA
Sickle-cell hemoglobin
Val
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• Types of mutations
Figure 10.16B
mRNA
NORMAL GENE
BASE SUBSTITUTION
BASE DELETION
Protein Met Lys Phe Gly Ala
Met Lys Phe Ser Ala
Met Lys Leu Ala His
Missing
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Figure 8.23A, B
Deletion
Duplication
Inversion
Homologouschromosomes
Reciprocaltranslocatio
n
Nonhomologouschromosomes
•Chromosomal changes can be large or small
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• Summary of transcription and translation
Figure 10.15
1Stage mRNA istranscribed from aDNA template.
Anticodon
DNA
mRNARNApolymerase
TRANSLATION
Enzyme
Amino acid
tRNA
InitiatortRNA
Largeribosomalsubunit
Smallribosomalsubunit
mRNA
Start Codon
2Stage Each amino acid attaches to its proper tRNA with the help of a specific enzyme and ATP.
3Stage Initiation of polypeptide synthesis
The mRNA, the first tRNA, and the ribosomal subunits come together.
TRANSCRIPTION
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Figure 10.15 (continued)
4Stage ElongationGrowingpolypeptide
Codons
5Stage Termination
mRNA
Newpeptidebondforming
Stop Codon
The ribosome recognizes a stop codon. The poly-peptide is terminated and released.
A succession of tRNAs add their amino acids to the polypeptide chain as the mRNA is moved through the ribosome, one codon at a time.
Polypeptide