1. THE STRUCTURE OF THE GENETIC MATERIAL
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2. SCIENTIFIC DISCOVERY: DNA is a double-stranded helix
In 1953, James D. Watson and Francis Crick deduced the secondary structure of DNA, using X-ray crystallography data of DNA from the work of Rosalind Franklin and Maurice Wilkins and Chargaff’s observation that in DNA the amount of adenine was equal to the amount of thymine and the amount of guanine was equal to that of cytosine.
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3. SCIENTIFIC DISCOVERY: DNA is a double-stranded helix
Watson and Crick reported that DNA consisted of two polynucleotide strands wrapped into a double helix.
The sugar-phosphate backbone is on the outside.
The nitrogenous bases are perpendicular to the backbone in the interior.
Specific pairs of bases give the helix a uniform shape.
A pairs with T, with two hydrogen bonds
G pairs with C, with three hydrogen bonds
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4. DNA and RNA are polymers of nucleotides
DNA and RNA = nucleic acids composed of long chains of nucleotides
A nucleotide = nitrogenous base, five-carbon sugar, and phosphate group
Nucleotides are joined to one another by a sugar-phosphate backbone.
DNA is antiparallel
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5. Partial chemical structure
Figure 10.3D_2
Hydrogen bond
G C
T A
A T
Figure 10.3D_2 Three representations of DNA (part 2)
C G
Partial chemical structure 5

6. Each DNA nucleotide has a different nitrogen-containing base: adenine (A), cytosine (C), thymine (T), guanine (G).
Nitrogenous base (can be A, G, C, or T)
Thymine (T)
Phosphate group
Figure 10.2A_3 The structure of a DNA polynucleotide (part 3)
Sugar (deoxyribose)
DNA nucleotide 6

7. Thymine (T) Cytosine (C) Adenine (A) Guanine (G) Pyrimidines Purines
Figure 10.2B The nitrogenous bases of DNA 7

8. RNA contains the nitrogenous base uracil (U) instead of thymine
Figure 10.2C An RNA nucleotide
Sugar (ribose) 8

9. DNA REPLICATION
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10. DNA replication depends on specific base pairing
In their description of the structure of DNA, Watson and Crick noted that the structure of DNA suggests a possible copying mechanism.
DNA replication follows a semiconservative model where,
The two DNA strands separate.
Each strand is used as a template to produce a complementary strand, using specific base pairing.
Semiconservative replication means that each new DNA helix has one old strand with one new strand.
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11. Daughter DNA molecules
A T
G C
A T
Parental DNA molecule
A T
T A C G C G T
Daughter strand A
C G
C G
C G
Parental strand T
C G A
Figure 10.4B The untwisting and replication of DNA
C G
A T
T A
A T
C G
G C
A T T
A T A
A T
G C
Daughter DNA molecules 11

12. DNA replication proceeds in two directions at many sites simultaneously
DNA replication begins at the origins of replication where
DNA unwinds at the origin to produce a replication bubble
Replication proceeds in both directions from the origin
Replication ends when products from the bubbles merge with each other
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13. Two daughter DNA molecules
Figure 10.5A
Parental DNA molecule
Origin of replication
Parental strand
Daughter strand
“Bubble”
Figure 10.5A Multiple bubbles in replicating DNA
Two daughter DNA molecules 13

14. DNA replication proceeds in two directions at many sites simultaneously
Both daughter strands are synthesized in the 5’ to 3’ direction = new nucleotides are only added to the 3’ end of the growing strand
One daughter strand is synthesized in one continuous piece, toward replication fork=leading strand
The other daughter strand is synthesized in (Okazaki) fragments =lagging strand
Consequence of the antiparallel nature of DNA
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15. DNA replication proceeds in two directions at many sites simultaneously
Two key proteins are involved in DNA replication.
DNA polymerase adds nucleotides to a growing chain and proofreads and corrects improper base pairings.
DNA ligase joins Okazaki fragments into a continuous chain.
Helicase-is a helix breaker; it unwinds the DNA double helix by breaking the H-bonds.
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16. Leading Strand Lagging Strand 3 DNA polymerase molecule 5
Parental DNA 5 3
Replication fork
Lagging Strand 3 5
Figure 10.5C How daughter DNA strands are synthesized 5 3
DNA ligase
Overall direction of replication 16

17. DNA replication proceeds in two directions at many sites simultaneously
DNA polymerases and DNA ligase also repair DNA damaged by harmful radiation and toxic chemicals.
DNA replication ensures that all somatic cells in a multicellular organism carry the same genetic information.
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18. THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN
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19. The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits
DNA specifies traits by dictating protein synthesis.
The molecular chain of command is from DNA to RNA to protein
Transcription is the synthesis of RNA under the direction of DNA.
Translation is the synthesis of proteins under the direction of RNA.
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20. DNA Transcription RNA NUCLEUS CYTOPLASM Translation Protein
Figure 10.6A_s3
DNA
Transcription
RNA
NUCLEUS
CYTOPLASM
Translation
Figure 10.6A_s3 The flow of genetic information in a eukaryotic cell (step 3)
Protein 20

21. The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits
The connections between genes and proteins
In the 1940’s Beadle and Tatum suggested a one gene–one enzyme hypothesis based on studies of inherited metabolic diseases
Their hypothesis is still accepted but with important changes:
The hypothesis includes all proteins not just enzymes, and that one gene specifies a polypeptide
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22. Genetic information written in codons is translated into amino acid sequences
The genetic code is written in DNA as a series of three base sequences called triplets
During transcription the genetic code in DNA is copied into a complementary three base sequences in RNA called codons
Translation involves switching from the nucleotide “language” to the amino acid “language.”
Each amino acid is specified by a codon.
64 codons are possible.
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23. DNA Transcription RNA Codon Translation Polypeptide Amino acid A A A C
Figure 10.7_1
DNA A A A C C G G C A A A A
Transcription U U U G G C C G U U U U
RNA
Codon
Translation
Figure 10.7_1 Transcription and translation of codons (partial)
Polypeptide
Amino acid 23

24. The genetic code dictates how codons are translated into amino acids
Characteristics of the genetic code
Three nucleotides (a codon) specify one amino acid.
AUG = start codon that codes for methionine; signals the start of translation
3 “stop” codons signal the end of translation.
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25. The genetic code dictates how codons are translated into amino acids
The genetic code is
redundant, more than one codon for the same amino acid
Unambiguous, in that any codon for one amino acid does not code for any other amino acid,
nearly universal, the genetic code is shared by organisms from the simplest bacteria to the most complex plants and animals
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26. Second base First base Third base
Figure 10.8A Dictionary of the genetic code (RNA codons) 26

27. T A C T T C A A A A T C A T G A A G T T T T A G A U G A A G U U U U A
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 T T T A G
Transcription
RNA A U G A A G U U U U A G
Figure 10.8B_s3 Deciphering the genetic information in DNA (step 3)
Start codon
Stop codon
Translation
Polypeptide
Met
Lys
Phe 27

28. Transcription produces genetic messages in the form of RNA
Overview of transcription
RNA polymerase oversees transcription by unwinding DNA, and linking RNA nucleotides together to synthesize an RNA molecule
The promoter is a nucleotide sequence in DNA that signals the start of transcription
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29. Transcription produces genetic messages in the form of RNA
Steps of Transcription
Initiation
RNA polymerase attaches to promoter.
Elongation
RNA grows longer.
As RNA peels away, DNA strands rejoin.
Termination
RNA polymerase reaches a sequence of bases in the DNA template called a terminator, signaling the end of the gene.
RNA pol detaches from RNA and the gene being transcribed
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30. RNA polymerase Terminator DNA DNA of gene Promoter DNA 1 Initiation
Figure 10.9B_1 The transcription of a gene (part 1) 30

31. 2 Elongation Area shown in Figure 10.9A Growing RNA
Figure 10.9B_2 The transcription of a gene (part 2)
Growing RNA 31

32. Growing RNA 3 Termination Completed RNA RNA polymerase
Figure 10.9B_3 The transcription of a gene (part 3)
Completed RNA
RNA polymerase 32

33. Eukaryotic RNA is processed before leaving the nucleus as mRNA
Messenger RNA (mRNA)
The RNA formed from transcription, carrying the genetic code is called mRNA
mRNA carries the message from DNA (nucleus) to ribosomes (cytoplasm)
In prokaryotes transcription and translation occur in the same place
In eukaryotes, mRNA must exit nucleus via nuclear pores to enter cytoplasm.
Eukaryotic mRNA has introns or interrupting sequences that separate exons, the coding regions
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34. Eukaryotic RNA is processed before leaving the nucleus as mRNA
Eukaryotic mRNA undergoes processing before leaving the nucleus.
RNA splicing removes introns and joins exons to produce a continuous coding sequence.
A 5’ cap and a 3’ tail of extra nucleotides are added to the ends of mRNA to
Facilitate export of mRNA from nucleus,
Protect the mRNA from attack by cellular enzymes
To help ribosomes bind to the mRNA.
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35. Transcription Addition of cap and tail Cap
Figure 10.10
Exon
Intron
Exon
Intron
Exon
DNA
Transcription Addition of cap and tail
Cap
RNA transcript with cap and tail
Introns removed
Tail
Exons spliced together
mRNA
Coding sequence
Figure The production of eukaryotic mRNA
NUCLEUS
CYTOPLASM 35

36. Start of genetic message
Figure 10.13A
Start of genetic message
Cap
Figure 10.13A A molecule of eukaryotic mRNA
End
Tail 36

37. Transfer RNA molecules serve as interpreters during translation
Transfer RNA (tRNA) molecules convert the codons of mRNA into the amino acid sequence of proteins.
tRNA’s recognize the codons in mRNA with a three base sequence alled an anticodon
Amino acid attachment site
Anticodon
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38. Ribosomes build polypeptides
Translation occurs on the surface of the ribosome.
Ribosomes coordinate the functioning of mRNA , tRNA & therefore 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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39. tRNA binding sites Large subunit Small subunit mRNA binding site
P site
A site
Small subunit
Figure 10.12B A ribosome with empty binding sites
mRNA binding site 39

40. The next amino acid to be added to the polypeptide Growing polypeptide
Figure 10.12C
The next amino acid to be added to the polypeptide
Growing polypeptide
mRNA
tRNA
Codons
Figure 10.12C A ribosome with occupied binding sites 40

41. An initiation codon marks the start of an mRNA message
Initiation occurs in two steps.
An mRNA molecule binds to a small ribosomal subunit and the first tRNA binds to mRNA at the start codon.
Start codon = AUG and codes for methionine.
The first tRNA has the anticodon UAC.
A large ribosomal subunit joins the small subunit, allowing the ribosome to function.
The first tRNA occupies the P site, which will hold the growing peptide chain.
The A site is available to receive the next tRNA.
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42. Large ribosomal subunit
Figure 10.13B
Met
Met
Initiator tRNA
Large ribosomal subunit
P site
A site
mRNA U A C U A C A U G A U G
Start codon
Figure 10.13B The initiation of translation
Small ribosomal subunit 1 2 42

43. Elongation adds amino acids to the polypeptide chain until a stop codon terminates translation
Elongation is the addition of amino acids to the polypeptide chain and each cycle of elongation has three steps.
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44. Elongation adds amino acids to the polypeptide chain until a stop codon terminates translation
Codon recognition: The anticodon of an incoming tRNA molecule, carrying its amino acid, pairs with the mRNA codon in the A site of the ribosome.
Peptide bond formation: The new amino acid is joined to the chain.
Translocation: tRNA is released from the P site and the ribosome moves tRNA from the A site into the P site.
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45. Elongation adds amino acids to the polypeptide chain until a stop codon terminates translation
Termination
1. Ribosome reaches a stop codon
2. Completed polypeptide is freed from the last tRNA,
3. The ribosome splits into separate subunits.
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46. Polypeptide Amino acid Anticodon mRNA Codons Codon recognition
Figure 10.14_s4
Polypeptide
Amino acid
P site
A site
Anticodon
mRNA
Codons 1
Codon recognition
mRNA movement
Stop codon 2
Peptide bond
formation
New peptide bond 3
Translocation 46

47. Mutations can change the meaning of genes
A mutation is any change in the nucleotide sequence of DNA.
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48. Mutations can change the meaning of genes
Mutations within a gene can be divided into two general categories.
Base substitutions involve the replacement of one nucleotide with another. Base substitutions may
Have no effect at all, producing a silent mutation,
A missense mutation still produces an amino acid, just not the correct amino acid
A nonsense mutation changes an amino acid codon into a stop codon, usually producing a nonfunctional protein
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49. Missense Mutation

50. Nonsense Mutation

51. Mutations can change the meaning of genes
Mutations can result in deletions or insertions that may
alter the reading frame (triplet grouping) of the mRNA, so that nucleotides are grouped into different codons
This leads to significant changes in amino acid sequence downstream of the mutation, and produce a nonfunctional polypeptide.
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53. Mutations can change the meaning of genes
Mutations can be caused by
spontaneous errors that occur during DNA replication or recombination
mutagens, which include high-energy radiation (X-rays) and UV light and chemicals
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