1. CHAPTER 10 Molecular Biology of the Gene
Overview:
DNA & RNA Structure
DNA replication
DNA-> RNA-> Protein
Viruses

2. Saboteurs Inside Our Cells
The invasion and damage of cells by the herpesvirus can be compared to the actions of a saboteur intent on taking over a factory
The herpesvirus hijacks the host cell’s molecules and organelles to produce new copies of the virus; the virus remains permanently latent in the body.

3. Experiments showed that DNA is the genetic material
THE STRUCTURE OF THE GENETIC MATERIAL
Experiments showed that DNA is the genetic material
The Hershey-Chase experiment showed that certain viruses reprogram host cells to produce more viruses by injecting their DNA

4. THE STRUCTURE AND REPLICATION OF DNA
Was known as a chemical in cells by the end of the nineteenth century
Has the capacity to store genetic information
Can be copied and passed from generation to generation

5. DNA and RNA: Polymers of Nucleotides
DNA and RNA are nucleic acids
They consist of chemical units called nucleotides
The nucleotides are joined by a sugar-phosphate backbone

6. DNA and RNA are polymers of nucleotides
DNA is a nucleic acid, made of long chains of nucleotides

7. The four nucleotides found in DNA
Differ in their nitrogenous bases
Are thymine (T), cytosine (C), adenine (A), and guanine (G)
RNA has uracil (U) in place of thymine

8. RNA is also a nucleic acid
RNA has a slightly different sugar
RNA has U instead of T

9. DNA is a double-stranded helix
James Watson and Francis Crick worked out the three-dimensional structure of DNA, based on work by Rosalind Franklin

10. The structure of DNA consists of two polynucleotide strands wrapped around each other in a double helix
1 chocolate coat,
Blind (PRA)
The model of DNA is like a rope ladder twisted into a spiral

11. Hydrogen bonds between bases hold the strands together
Each base pairs with a complementary partner
A pairs with T
G pairs with C

12. Detailed representations of DNA
Notice that the bases pair in a complementary fashion

13. DNA replication depends on specific base pairing
In DNA replication, the strands separate
Enzymes use each strand as a template to assemble the new strands

14. Untwisting and replication of DNA

15. DNA can be damaged by ultraviolet light
The enzymes and proteins involved in replication can repair the damage

16. DNA replication Begins at specific sites on a double helix
Proceeds in both directions

17. Each strand of the double helix is oriented in the opposite direction

18. How DNA daughter strands are synthesized3
How DNA daughter strands are synthesized
The daughter strands are identical to the parent molecule

19. THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN
DNA functions as the inherited directions for a cell or organism
How are these directions carried out?

20. How an Organism’s DNA Genotype Produces Its Phenotype
An organism’s genotype, its genetic makeup is the sequence of nucleotide bases in DNA
The phenotype is the organism’s specific traits

21. DNA specifies the synthesis of proteins in two stages
Transcription
Translation

22. From Nucleotide Sequence to Amino Acid Sequence: An Overview
The one gene–one protein hypothesis states that the function of an individual gene is to dictate the production of a specific protein
From Nucleotide Sequence to Amino Acid Sequence: An Overview
The information, or “language,” in DNA is ultimately translated into the language of polypeptides

23. What is the language of nucleic acids?
In DNA, it is the linear sequence of nucleotide bases
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

24. When DNA is transcribed, the result is an RNA molecule
RNA is then translated into a sequence of amino acids in a polypeptide
What is the correspondence between the nucleotides of an RNA molecule and the amino acids of a polypeptide?
Triplets of bases
Specify all the amino acids
Are called codons

25. The Genetic Code
The genetic code is the set of rules relating nucleotide sequence to amino acid sequence

26. Transcription produces genetic messages in the form of RNA

27. Transcription: From DNA to RNA
In transcription
Genetic information is transferred from DNA to RNA
An RNA molecule is transcribed from a DNA template

28. Initiation of Transcription
The “start transcribing” signal is a nucleotide sequence called a promoter
The first phase of transcription is initiation
RNA polymerase attaches to the promoter
RNA synthesis begins
RNA Elongation
The second phase of transcription is elongation
The RNA grows longer

29. Termination of Transcription
The third phase of transcription is termination
RNA polymerase reaches a sequence of DNA bases called a terminator

30. In transcription, the DNA helix unzips
RNA nucleotides line up along one strand of the DNA following the base-pairing rules
The single-stranded messenger RNA peels away and the DNA strands rejoin

31. The Processing of Eukaryotic RNA
The eukaryotic cell processes the RNA after transcription

32. RNA processing includes
Adding a cap and tail
Removing introns (Noncoding segments)
Splicing exons together

33. Translation: Translation
Is the conversion from the nucleic acid language to the protein language

34. Transfer RNA molecules serve as interpreters during translation
In the cytoplasm, a ribosome attaches to the mRNA and translates its message into a polypeptide
The process is aided by transfer RNAs

35. Each tRNA molecule has a triplet anticodon on one end and an amino acid attachment site on the other

36. Transfer RNA (tRNA) tRNA Acts as a molecular interpreter
Carries amino acids
Matches amino acids with codons in mRNA using anticodons

37. Ribosomes Ribosomes Are organelles that actually make polypeptides
Are made up of two protein subunits
Contain ribosomal RNA (rRNA)

38. A fully assembled ribosome holds tRNA and mRNA for use in translation

39. Translation: The Process
Translation is divided into three phases
Initiation
Elongation
Termination

40. Initiation The first phase brings together The mRNA
The first amino acid with its attached tRNA
The two subunits of the ribosome

41. An mRNA molecule has a cap and tail that help it bind to the ribosome

42. Elongation Step 1, codon recognition Step 2, peptide bond formation
The anticodon of an incoming tRNA pairs with the mRNA codon
Step 2, peptide bond formation
The ribosome catalyzes bond formation between amino acids
Step 3, translocation
A tRNA leaves the P site of the ribosome
The ribosome moves down the mRNA

43. Review: DNA RNA Protein
Termination
Elongation continues until the ribosome reaches a stop codon
Review: DNA RNA Protein
The flow of genetic information in a cell

44. In eukaryotic cells Transcription occurs in the nucleus
Translation occurs in the cytoplasm

45. Mutations A mutation Is any change in the nucleotide sequence of DNA
These are caused by errors in DNA replication or by mutagens Physical or chemical agents

46. Types of Mutations Mutations within a gene
Can be divided into two general categories
Can result in changes in the amino acids in proteins

47. Insertions and deletions
Can have disastrous effects
Change the reading frame of the genetic message

48. VIRUSES: GENES IN PACKAGES
Viruses sit on the fence between life and nonlife
They exhibit some but not all characteristics of living organisms

49. Bacteriophages Bacteriophages, or phages Attack bacteria Bacterial
cell

50. Connection: Many viruses cause disease in animals
Many viruses have RNA, rather than DNA, as their genetic material
Example: flu viruses

51. Plant Viruses Viruses that infect plants Most plant viruses have RNA
Can stunt growth and diminish plant yields
Can spread throughout the entire plant
Most plant viruses have RNA
Example: tobacco mosaic disease
Genetic engineering methods
Have been used to create virus-resistant plants

52. Connection: Emerging viruses threaten human health
The deadly Ebola virus causes hemorrhagic fever
Each virus is an enveloped thread of protein-coated RNA
Hantavirus is another enveloped RNA virus

53. The AIDS virus makes DNA on an RNA template
HIV is a retrovirus

54. HIV is a retrovirus
A retrovirus is an RNA virus that reproduces by means of a DNA molecule
It copies its RNA to DNA using reverse transcriptase

55. Inside a cell, HIV uses its RNA as a template for making DNA to insert into the host chromosome

56. AIDS is Acquired immune deficiency syndrome
The disease caused by HIV infection
Treated with the drug AZT
Virus studies help establish molecular genetics
Molecular genetics helps us understand viruses
such as HIV, seen here attacking a white blood cell

57. How do new viruses arise?
Mutation of existing viruses
Spread to new host species