1. Molecular Biology of the Gene
Chapter 10
Molecular Biology of the Gene

2.
Video #96 (Genes, DNA, Chrom)

3. Information transfer is from DNA  RNA  protein
Replication
What is it?
Where does it occur?
Copying DNA for division
In the nucleus
REPLICATION

4. Information transfer is from DNA  RNA  protein
Transcription
What is it?
Where does it occur?
Making mRNA from DNA
In the nucleus

5. Information transfer is from DNA  RNA  protein
Translation
What is it?
Where does it occur?
Converting mRNA into a protein
In the cytoplasm, at a ribosome

6. 2. DNA as source of genetic information
a. Hershey-Chase experiment showed DNA rather than protein to be the genetic material passed on from one generation to the next

7. DNA

8. DNA

9. DNA

10. DNA

11. DNA

12. DNA

13. 2. DNA as source of genetic information
b. additional evidence – cell doubles DNA prior to mitosis, and then splits the DNA evenly among daughter cells

14. Watson and Crick

15. 3. Molecular structure of DNA
a. Watson and Crick described the three dimensional structure of DNA one year after Hershey and Chase identified DNA as the genetic material

16. 3. Molecular structure of DNA
b. DNA, along with RNA, are nucleic acids which are composed of nucleotides
c. Nucleotides consist of a sugar (ribose or deoxyribose), a nitrogenous base (A, G, C, T, or U), and a phosphate group

17. 3. Molecular structure of DNA
d. Structure of single DNA strand
1. sugar-phosphate backbone
2. bases covalently attached to sugar and ‘hang off’ the side

18. 3. Molecular structure of DNA
e. double helical structure
1. double stranded
2. arranged in helix

19. 3. Molecular structure of DNA
3. hydrogen bonds between nitrogenous bases hold strands together (remember, hydrogen bonds are weak chemical bonds)

20. 3. Molecular structure of DNA
4. the two strands of DNA run “anti-parallel”; i.e., one strand runs in 5’-3’ direction while the other runs in the 3’-5’ direction The primed numbers refer to the C of the sugar. The bases are attached to the 1’ carbon and the phosphate groups are attached at the 5’ sugars. Nucleotides form covalent bonds between the 3’ carbon of one and the 5’ carbon of the other nucleotide.

21. VIDEO #47 (DNA structure and Replication CC)

22. 4. DNA replication
a. complementary base pairing governs how new DNA molecules are synthesized using existing DNA as templates (fig 10.4)
1. A with T
2. G with C

23. 4. DNA replication
b. DNA synthesis is semiconservative; i.e., the two strands are separated and each strand is used as a separate template.

24. 4. DNA replication
c. DNA synthesis occurs along each of the separated strands thus resulting in two new double-stranded molecules of DNA

25. 4. DNA replication
d. New nucleotides are added to a growing strand of DNA one at a time, and this energy-requiring reaction is catalyzed by an enzyme, DNA polymerase

26. 4. DNA replication
e. The new strands are synthesized 5’-3’ and anti-parallel with the template strands (10.5)

27. 4. DNA replication
f. The two new strands of DNA are synthesized as the leading and lagging strand

28. 4. DNA replication CTATGTCGACATGCAGC CTATGTCGACATGCAGC
GATACAGCTGTACGTCG
CTATGTCGACATGCAGC
CTATGTCGACATGCAGC
GATACAGCTGTACGTCG
g. process of replication
1. the enzyme helicase unwinds the double stranded DNA, while single stranded binding proteins stabilize the templates

29. 4. DNA replication
2. primase adds RNA primers to the exposed templates because DNA polymerase must add new nucleotides to a 3’ end of an existing nucleotide in an already started strand

30. CTATGTCGACATGCAGC GATACAGCTGTACGTCG CTATGTCGACATGCAGC
5’ ’
GATACAGCTGTACGTCG
CTATGTCGACATGCAGC
GATACAGCTGTACGTCG
CTATGTCGACATGCAGC
3’ ’

31. 4. DNA replication
3. DNA polymerase adds one nucleotide at a time in the 5’ – 3’ direction along the leading strand and lagging strand (leading strand is synthesized continuously while the lagging strand is synthesized in Okazaki fragments)

32. 4. DNA replication 4. Another DNA polymerase replaces the RNA primer
5. Ligase seals the Okazaki fragments

33. Video #48 (DNA, Hot Pockets)

34. 1. Overview of protein synthesis
Process = DNA to RNA to protein

35. 1. Overview of protein synthesis
Specific sequences of DNA in genes code for specific sequences of RNA which in turn code for specific sequences of amino acids in proteins

36. 1. Overview of protein synthesis
compartmentalization
transcription in nucleus
translation (protein synthesis) in cytoplasm

37. 2. Genetic Code
mRNA is read 3 nucleotides at a time; i.e., one amino acid coded for by three nucleotides

38. 2. Genetic Code
b. each set of three nucleotides is referred to as a codon
c. use genetic code of RNA codons to predict amino acid sequence in synthesized peptide

39. 2. Genetic Code
c. use genetic code of RNA codons to predict amino acid sequence in synthesized peptide

40. Using the Chart
CAU
The codon CAU codes for His

41. 3. Transcription
Initiation- RNA polymerase binds to promoter sequence of DNA, unwinds DNA and starts transcription at start site

42. 3. Transcription
ATG CAT GTC GAT CAC TAA AGT TTA
ATG CAT GTC GAT CAC TAA AGT TTA
AUG CAU GUC GAU CAC UAA AGU UUA
TAC GTA CAG CTA GTG ATT TCA AAT
b. Elongation – RNA polymerase makes new strand of RNA in 5’ to 3’ direction; i.e., it adds new nucleotides to the 3’ end of the growing RNA strand, DNA reforms double strand behind polymerase

43. 3. Transcription
c. Termination – RNA polymerase reaches a terminator sequence of DNA and polymerase along with the newly synthesized mRNA are released

44. 3. Transcription
d. Eukaryotic RNA is processed in the nucleus before final mRNA is sent to cytoplasm

45. 3. Transcription
e. One gene (DNA) is read at a time by RNA polymerase in eukaryotes (monocystronic)

46. 3. Transcription
f. Multiple genes can be read at a time by RNA polymerase in prokaryotes (polycystronic)

47. 4. Translation synthesis of proteins using RNA as a template
catalyzed by ribosomes in the cytoplasm

48. What Translation Looks Like

49. 4. Translation c. involves a variety of other players
1. t RNA transfer
2. m RNA messenger
3. r RNA ribosomal

50. 5. tRNA
interpreters between nucleic acid language and protein language; i.e., translation
single stranded nucleic acid made via transcription just like mRNA

51. 5. tRNA c. 3’ end of tRNA binds amino acid
d. anticodon sequence of tRNA base pairs with corresponding codon on mRNA; therefore, anitcodon – codon binding determines which amino acid is added to the growing peptide

52. 6. Ribosome (fig 10.12) Catalyze protein synthesis
two ribosomal subunits; large and small

53. 6. Ribosome c. mRNA binding site on small ribosomal subunit
d. two tRNA binding sites known as P and A on large ribosomal subunit

54. 6. Ribosome (fig 10.12)
e. an anticodon of a tRNA binds to the ribosome when its anticodon base pairs with a mRNA codon present in that same binding site

55. 6. Ribosome (fig 10.12)
f. P site holds the tRNA attached to growing peptide
g. A sites holds the tRNA attached to the new (incoming) amino acid

56. What Translation Looks Like

57. 7. Initiation of translation
small ribosomal subunit binds mRNA
a special initiator tRNA with anticodon UAC binds to start codon AUG (this tRNA carries amino acid methionine)

58. 7. Initiation of translation
c. large ribosomal subunit binds with small ribosomal subunit placing initiator tRNA in P site and leaving A site empty for the next tRNA to bind

59. 8. Elongation of translation (fig 10.14)
an incoming tRNA/amino acid binds to unoccupied A site
ribosome catalyzes formation of peptide bond between new amino acid and growing peptide, and the growing peptide is released from the tRNA in the P site
tRNA in A site is translocated to P site, moving the mRNA along with it a distance of 3 nucleotides; i.e., one codon
the mRNA moves along the ribosome one codon at a time

60. 9. Termination of translation
The A site of the ribosome reaches a stop codon (UAA, UAG, or UGA) in the mRNA molecule
a releasing factor binds to the stop codon instead of another tRNA molecule
Releasing factor catalyzes release of peptide from ribosome
Translation assembly falls apart and can be used again

61. 10. Overview of translation (fir 10.15)
amino acids  polypeptide (protein)
mRNA carries the “message” of the genetic code from the nucleus to the cytoplasm
tRNA/amino acid complex in cytoplasm
ribosome brings tRNA/amino acid to mRNA in a particular order as dictated by mRNA nucleotide sequence
ribosomes catalyze binding of amino acids into polypeptide; i.e., formation of peptide bonds

62. Mutations Mutations are random changes in the DNA sequence.
Gene mutations are relatively small affecting only one or two genes.
Point mutations are caused by substitutions and usually result in the change of one amino acid, and causing no change about 30% of the time.
Frameshift mutations are usually caused by a deletion. The affect all of the codons that follow the deletion. This will change many of the amino acids in the protein molecule.

63. Substitution / Point Mutation
AUG CAU GUC GAU CAC UAA AGU UUA
AUG CAU GUC GGU CAC UAA AGU UUA
AUG CAU GUC GAU CAU UAA AGU UUA
AUG CAU GUC GAU CAC GAA AGU UUA

64. Deletion / Frameshift AUG CAU GUC GAU CAC UAA AGU UUA
AUG CAU GUC GUC ACU AAA GUU UAG

65. Protein Synthesis (Copy)
1st Step
2nd step
Name of process
Transcription
Translation
Location
Nucleus
Cytoplasm
Enzymes or other substances required
DNA, Helicase,
RNA Polymerase
tRNA, amino acids,
Ribosome
What is read (goes in)
DNA
mRNA
Is Produced
mRNA,
Replicated DNA
Protein,
(polypeptides)