1. DNA & RNA The Molecular Basis of Inheritance

2. DNA & RNA The Molecular Basis of Inheritance
By the 1940’s, scientists knew that chromosomes carried hereditary material and consisted of DNA and proteins. Most thought proteins were the genetic material because it is a complex macromolecule and little was known about nucleic acids.

3. DNA Griffith and Transformation
In 1928, Frederick Griffith was trying to
determine how bacteria infected people.
He isolated two different strains of pneumonia bacteria
1. smooth strain (S) – polysaccharide coat, on
the bacterial cell prevents attach by the
immune system
2. rough strain (R) – polysaccharide coat is
absent and therefore the immune system
can kill the bacteria

4. DNA Griffith and Transformation
Griffith performed four sets of experiments – Fig. 12-2
Experiment – injected live S strain into the mice;
Results – mice developed pneumonia & died
Conclusion – S strain causes disease
Experiment – injected live R strain into the mice:
Results – mice survived
Conclusion – R strain does not cause disease

5. DNA Griffith and Transformation
Griffith performed four sets of experiments – Fig. 12-2
Experiment – injected heat killed S strain
Results – mice survived
Conclusion – polysaccharide coat does not
cause pneumonia

6. DNA Griffith and Transformation
Griffith performed four sets of experiments – Fig. 12-2
Experiment – Heat killed S strain cells mixed with
the live R strain cells and then injected into mice
Results – mice died from pneumonia & blood
samples from dead mice contained
living S strain cells
Conclusion – R cells had acquired “some
factor” to make polysaccharide coat

7. DNA Griffith and Transformation

8. DNA Griffith and Transformation
Transformation – the assimilation of external genetic material by a cell
The disease causing ability was inherited by the bacterial offspring, therefore information for disease might be located on a gene.

9. Avery & DNA
The above link is an explanation of Griffith’s & Avery’s findings. Great site – please review. Avery discovered that the nucleic acid DNA stores and transmits the genetic information from one generation of an organism to the next.

10. Hershey-Chase Experiment More evidence that DNA is the genetic material
Bacteriophage – a virus that infects a bacterium; made up of DNA or RNA and a protein coat. – Fig. 12-3, 12-4

11. Hershey-Chase Experiment More evidence that DNA is the genetic material
DNA – contains no sulfur but does have phosphorus
Proteins – contain almost no phosphorus but do have sulfur

12. Hershey-Chase Experiment More evidence that DNA is the genetic material
Hershey & Chase performed two sets of experiments
1. T2 with radioactive phosphorus infects
bacterium – 32P shows up in bacterial
DNA
2. T2 with radioactive sulfur infects
bacterium – 35S does not show up in
bacterial DNA
3. Conclusion – genetic material of T2
was DNA not protein

13. Hershey-Chase Experiment More evidence that DNA is the genetic material
(Hershey/Chase experiment animation)

14. Structure of DNA- Fig. 12-5
Nucleotide – functional unit; composed of a phosphate group, sugar (deoxyribose), and a nitrogenous base
T- thymine A – Adenine
G – Guanine C – cytosine
Chargaff’s Rules – Fig. 12-6
[A] = [T] [C] = [G]

15. Structure of DNA- Fig. 12-5
X-ray evidence – x shaped pattern shows DNA strands are twisted and nitrogenous bases are in the center (Rosalind Franklin created this image which was used by Watson & Crick to explain the structure of DNA) She probably would have shared in the Nobel Peace Prize with them for this discovery if she had not died.

16. Structure of DNA- Fig. 12-5

17. Structure of DNA- Fig. 12-5

18. Structure of DNA- Fig. 12-5

19. Chromosomes & DNA Replication
Prokaryotic Cells lack a membrane bound nucleus; only one circular chromosome holds most of the genetic material. Fig. 12-8

20. Chromosomes & DNA Replication
Eukaryotic cells have a membrane bound nucleus; chromosomes are found in pairs and the number is species specific
DNA is a very long molecule and must be a
tightly folded
Chromatin – DNA & histone proteins make
up a unit called a nucleosome Fig

21. DNA Replication – Fig. 12-11 The two DNA strand separate
Each strand is a template for assembling a complementary strand.
Nucleotides line up singly along the template strand in accordance with the base-pairing rules ( A-T and G-C)
DNA polymerase links the nucleotides together at their sugar-phosphate groups.

22. DNA Replication – Fig

23. RNA and Protein Synthesis
DNA  RNA  Protein  Trait
Stucture of RNA
Single stranded
Sugar is ribose instead of
deoxyribose
Uracil (U) replaces Thymine (T)

24. RNA vs DNA

25. Types of RNA – Fig
Messenger RNA – mRNA, contains “code” or instructions for making a particular protein
Ribosomal RNA – rRNA (part of the ribosome), facilitates the orderly linking of amino acids into polypeptide chains
Transfer RNA – tRNA, brings amino acids from the cytoplasm to the ribosome

26. mRNA

27. tRNA

28. rRNA

29. Transcription
Transcription is the synthesis of RNA using DNA as a template: Fig
RNA polymerase binds to DNA strand and separates it
RNA polymerase will bind to a promoter, a specific “start’ region of the DNA molecule
Nucleotides are assembled into a strand of RNA
Transcription stops when RNA polymerase reaches a specific “stop” region of the DNA molecule

30. Transcription

31. Transcription https://www.youtube.com/watch?v=rKxZrChP0P4
This video also shows translation

32. RNA Editing
Only a small portion of the original RNA sequence leaves the nucleus as mRNA because portions are edited out. Fig
Introns are the noncoding sequences in the DNA that are edited out of the pre mRNA molecule
Exons are the coding sequences of a gene that are transcribed and expressed (translated into a protein)

33. RNA Editing

34. Transcription

35. The Genetic Code
Fig , 12-17
A codon is a three-nucleotide sequence in mRNA that:
signals the starting place for translation
specifies which amino acid will be added to a growing polypeptide chain
signals termination of translation
Some amino acids are coded for by more than one codon

36. The Genetic Code

37. Translation Fig. 12-18 Translation is the synthesis of a
polypeptide chain, which occurs under the idrection of mRNA
Three major steps of translation include: Initiation, Elongation, and Termination
Initiation - must bring together the mRNA, two ribosomal subunits, and a tRNA

38. Translation (cont.) Fig. 12-18 Elongation – polypeptide assembly line
1) Codon on mRNA bonds with anticodon site on tRNA
The amino acid that is brought in by tRNA is added to the growing polypeptide chain
3) tRNA leaves ribosome
Termination – stop codon is reached and the entire complex separates

39. Translation

40. Translation (cont.) http://www.youtube.com/watch?v=5bLEDd-PSTQ
You can also go back to transcription slide to see
another video on translation

41. Translation (cont.)
From Polypeptide to Functional Protein – depends upon a precise folding of the amino acid chain into a three-dimentional conformation

42. Mutations Any change in the genetic material is a mutation.
Gene mutations – changes in a single gene – Fig
1. point mutations – changes involving only one or a few nucleotides (substitution, insertion, deletion) that affects only one amino acid

43. Mutations (cont.)
2. frameshift mutation (a type of point mutation) – “reading frame” of the genetic message is changed because of insertion or deletion of a nucleotide, therefore the entire sequence of amino acids can change

44. Mutations (cont.)
Substitution

45. Mutations (cont.)
Insertion and Deletion

46. Mutations (cont.)
Chromosomal mutations – changes in the number of structure of chromosomes; includes – deletion, duplication, inversion, and translocation – Fig

47. Gene Regulation
Genes can be switched “on” or “off” depending on the cell’s metabolic needs, (i.e. muscle cell vs. neuron, embryonic cell vs. adult cell) Fig

48. Gene Regulation in Prokaryotes – Fig. 12-23
Structural gene – gene that codes for a protein
Operon – a group of genes that operate together
Operator – a DNA segment between an operon’s promoter and structural genes, which controls access of RNA polymerase to structural genes

49. Gene Regulation in Prokaryotes – (cont.)
Repressor – a specific protein that binds to an operator and blocks transcription of the operon
The lac operon is turned off by repressors and turned on by the presence of lactose.

50. Gene Regulation
(lac operon animation)

51. Gene Expression in Eukaryotes
Eukaryotic genes coding for enzymes of ametabolic pathway are often scatttered over different chromosomes and havew their own promoters. Fig
TATA box – a repeating sequence of nucleotides that helps position RNA polymerase to the promoter site
TATA box animation

52. Gene Expression in Eukaryotes

53. Gene Expression in Eukaryotes
2. Enhancer – noncoding DNA control sequence that enhances a gene’s transcription and that is located thousands of bases away from the gene’s promoter

54. Development and Differentiation
Differentiation – to become more specialized
Hox – genes – a series of genes that control the differentiation of cells and tissues in the embryo – Fig