1. THE STRUCTURE OF THE GENETIC MATERIAL1

2. DNA is a Double-Stranded Helix
In 1953, James D. Watson and Francis Crick deduced the 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. 2

3. 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 3

4. DNA and RNA are Polymers of Nucleotides
DNA and RNA are nucleic acids composed of long chains of nucleotides
A nucleotide contains a nitrogenous base, five-carbon sugar, and phosphate group
Nucleotides are joined to one another by a sugar-phosphate backbone.
© 2012 Pearson Educaton, Inc. 4

5. Each DNA nucleotide has a different nitrogenous base: Adenine (A), Cytosine (C), Guanine (G) or Thymine (T)
Nitrogenous base (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 5

6. Nitrogenous Bases of DNA
Thymine (T)
Cytosine (C)
Adenine (A)
Guanine (G)
Pyrimidines
Purines
Figure 10.2B The nitrogenous bases of DNA 6

7. Each RNA nucleotide also has a different nitrogenous base: Adenine (A), Cytosine (C), Guanine (G) or Uracil (U)
Nitrogenous base (A, C, G, or U)
Figure 10.2C An RNA nucleotide
Sugar (ribose) 7

8. The DNA Molecule is Antiparallel
The polynucleotide strands of DNA run in opposite directions or, are antiparallel
DNA has 5’ (prime) and 3’ (prime) ends
The sugar on the 3’ end is attached to a hydroxyl group
The sugar on the 5’end is attached to a phosphate group

9. Partial chemical structure
Phosphate
group on
5’ end
Hydrogen bonds
Hydroxyl group on 3’ end
G C
T A
A T
Figure 10.3D_2 Three representations of DNA (part 2)
C G
Partial chemical structure 9

10. DNA Replication Depends on Specific Base Pairing Rules
DNA replication follows a Semiconservative Model
The two DNA strands separate and serve as templates for new DNA
Enzymes read parental strands, linking nucleotides according to base pairing rules; this forms complementary strands
This follows the Semiconservative Model of replication because half of the parental molecule is kept (conserved) in each new DNA helix
DNA replication ensures that all somatic cells in a multicellular organism carry the same genetic information 10

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 producing a replication bubble
Replication proceeds in both directions from the origin
Replication ends when products (new DNA) from the bubbles merge 12

13. Two daughter DNA molecules
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. Daughter Strand Synthesis in DNA Replication
Both daughter strands are synthesized 5’ to 3’; new nucleotides are only added to the 3’ end of a growing strand
The daughter strand that is synthesized toward the replication fork in one continuous piece is the leading strand
The daughter strand synthesized away from the replication fork in (Okazaki) fragments is the lagging strand
Lagging strand synthesis is due to the antiparallel nature of DNA 14

15. Leading Strand Lagging Strand 3 DNA polymerase molecule 5
Parental DNA 5 3
Replication fork
Lagging Strand 3 5 5 3
DNA ligase
Overall direction of replication 15

16. DNA Replication Requires a Host of Enzymes
Important Enzymes are involved in DNA replication
Helicase-breaks H-bonds, unwinding (separating) the DNA double helix
DNA polymerase reads template strand and adds nucleotides to a growing chain, proofreads and corrects improper base pairings
DNA ligase joins Okazaki fragments into a continuous DNA strand
*DNA polymerases and DNA ligase also repair damaged DNA* 16

17. THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN17

18. Connections between genes and proteins:
The DNA Genotype is Expressed as Proteins, Which Provide the Molecular Basis for Phenotypic Traits
Connections between genes and proteins:
In the 1940’s Beadle and Tatum hypothesized that one gene codes for one enzyme by doing studying inherited metabolic diseases
Their hypothesis is still accepted but with important changes:
The hypothesis includes all proteins and that one gene codes for one polypeptide 18

19. The DNA Genotype is Expressed as Proteins, Which Provide the Molecular Basis for Phenotypic Traits
DNA specifies traits by determining the sequence of amino acids in a protein; proteins give us our phenotype so genotype determines phenotype
The molecular chain of command is from DNA to RNA to protein
Transcription is the synthesis of RNA using DNA as a template.
Translation is the synthesis of proteins using RNA as a template. 19

20. DNA Transcription RNA NUCLEUS CYTOPLASM Translation Protein
Figure 10.6A_s3 The flow of genetic information in a eukaryotic cell (step 3)
Protein 20

21. Genetic Information in DNA is written in mRNA as Codons
The genetic instructions for the amino acid sequence of a polypeptide is written in DNA as three base sequences called triplets
During transcription triplets in DNA are copied into complementary three base sequences in mRNA called codons
Each codon determines the amino acid to be added to a growing polypeptide chain
64 codons are possible 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
Translation
amino
acid 1
Polypeptide
amino acid 2
amino acid 3
amino acid 4 21

22. Second base First base Third base
Figure 10.8A Dictionary of the genetic code (RNA codons) 22

23. Transcription RNA polymerase oversees transcription by
RNA polymerase oversees transcription by
Unwinding DNA, reading DNA bases, and joining appropriate RNA nucleotides together
RNA polymerase synthesizes (all) RNA molecules
Transcription occurs in Three Phases:
Initiation - RNA pol. binds the promoter
Elongation - mRNA strand grows longer
Termination –RNA pol. reaches the terminator sequence and detaches from mRNA and the gene 23

24. RNA polymerase Terminator DNA DNA of gene Promoter DNA 1 Initiation
Figure 10.9B_1 The transcription of a gene (part 1) 24

25. 2 Elongation Area shown in Figure 10.9A Growing RNA
Figure 10.9B_2 The transcription of a gene (part 2)
Growing RNA 25

26. Growing RNA 3 Termination Completed RNA RNA polymerase
Figure 10.9B_3 The transcription of a gene (part 3)
Completed RNA
RNA polymerase 26

27. Eukaryotic mRNA Messenger RNA (mRNA)
Messenger RNA (mRNA)
The RNA formed from transcription, carrying information to build a protein is called mRNA
mRNA carries the message from DNA (nucleus) to ribosomes (cytoplasm)
In prokaryotes transcription and translation occur at the same place and time
In eukaryotes, mRNA exits nucleus via nuclear pores
Eukaryotic mRNA has introns or interrupting sequences that separate exons or coding regions 27

28. Eukaryotic RNA is Processed Before Leaving the Nucleus
mRNA processing :
Occurs in nucleus of eukaryotic cells
Involves the addition of extra nucleotides to the ends of mRNA. A 5’ guanine cap and 3’ poly A tail helps to:
facilitate export of mRNA from nucleus
protect mRNA from attack by cellular enzymes
help ribosomes bind mRNA
RNA splicing removes introns and joins exons to produce a continuous coding sequence. 28

29. Transcription Addition of cap and tail Cap
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 29

30. The Genetic Code Dictates How Codons are Translated into Amino Acids
Translation involves switching from nucleotide “language” to amino acid “language”
tRNA’s act as interpreters
Transfer RNA (tRNA) molecules read codons in mRNA to help synthesize a polypeptide chain
Each tRNA has a three base sequence or anticodon it uses to read an mRNA codon
Amino acid attachment site
Anticodon 30

31. 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
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 31

32. The Genetic Code Dictates How Codons are Translated into Amino Acids
Characteristics of the Genetic Code
Three RNA nucleotides (one codon) specify one amino acid
AUG = the start codon signals the ribosome to start translating; AUG also codes for methionine
There are 3 “stop” codons that signal the ribosome to stop translating
The Genetic Code is:
Redundant, there is more than one codon for the same amino acid
Unambiguous, any codon for an 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 32

33. Ribosomes Build Polypeptides With the Help of tRNA’s
Translation occurs on the surface of a Ribosome.
Ribosomes have binding sites for mRNA and tRNA to coordinate protein synthesis
Ribosomes have small and large subunits composed of ribosomal RNA (rRNA) and proteins
The next amino acid to be added to the polypeptide
Growing polypeptide
tRNA
Codons
mRNA 33

34. Translation Translation occurs in Three Phases Initiation
Translation
Translation occurs in Three Phases
Initiation
An mRNA molecule binds to a small ribosomal subunit and the first tRNA binds to mRNA at the start codon
The first tRNA has the anticodon UAC
The large ribosomal subunit joins the small subunit, forming a functional ribosome
The first tRNA occupies the P site, which will hold the growing polypeptide chain
The A site is available to receive the next tRNA 34

35. Large ribosomal subunit
Met
Met
Initiator tRNA
Large ribosomal subunit
mRNA
P site
A site 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 35

36. Translation
Elongation involves the addition of amino acids to the polypeptide chain. Each cycle of elongation has three steps.
Codon recognition: The anticodon of an incoming tRNA molecule, (w/ 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 held by tRNA in A site.
Translocation: the P site tRNA now lacking an amino acid leaves ribosome; the ribosome moves tRNA (holding the polypeptide) from the A site to the P site. 36

37. Polypeptide Amino acid Anticodon mRNA Codons Codon recognition
P site
A site
Anticodon
mRNA
Codons 1
Codon recognition
mRNA movement
Stop codon
Figure 10.14_s4 Polypeptide elongation (step 4) 2
Peptide bond
formation
New peptide bond 3
Translocation 37

38. Translation Termination The Ribosome reaches a stop codon
Translation
Termination
The Ribosome reaches a stop codon
The completed polypeptide is freed from the last tRNA
The ribosome splits into separate subunits 38

39. Mutations Can Change the Meaning of Genes
A mutation is any change in the nucleotide sequence of DNA.
Mutations can be caused by
spontaneous errors that occur during DNA replication or crossing over
mutagens, like high-energy radiation (X-rays), UV light and chemicals, viruses 39

40. 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 and its base pairing partner. Base substitutions may
Produce a silent mutation there is no effect on the polypeptide because the right amino acid is still added
Produce a missense mutation where the mutation causes the wrong amino acid to be added to the polypeptide
Produce a nonsense mutation where the mutation produces a stop codon in the mRNA instead of an amino acid. 40

43. Mutations Can Change the Meaning of Genes
Mutations can result in deletions or insertions that may
Cause frame shift mutations that alter the reading frame (triplet grouping) of the mRNA; all nucleotides after the insertion or deletion will be regrouped into different codons
This leads to significant changes in amino acid sequence downstream of the mutation, and produces a nonfunctional polypeptide 43