1. Essentials of Biology Sylvia S. Mader
Chapter 11
Lecture Outline
Prepared by: Dr. Stephen Ebbs Southern Illinois University Carbondale
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. 11.1 DNA and RNA Structure and Function
The work of Mendel and others provided information about the nature of deoxyribonucleic acid (DNA).
Genes occur on chromosomes.
Mutations in genes caused metabolic errors.
DNA is composed of nucleotides

3. 11.1 DNA and RNA Structure and Function (cont.)
Without an understanding of DNA structure, it was unclear to scientists how DNA achieved certain functions.
How can DNA structure account for the differences between species?
How is DNA replicated during cell division?
How does DNA store and disseminate the information needed to control metabolism?

4. Structure of DNA
The research of several scientists helped determine the structure of DNA.
Erwin Chargaff
Rosalind Franklin
James Watson and Frances Crick.

5. Chargaff’s Rules
DNA contains four types of nucleotides, differing in the nitrogen-containing base each contains.
The purine base adenine (A)
The pyrimidine base cytosine (C)
The purine base guanine (G)
The pyrimidine base thymine (T)
A nucleotide from DNA contains one base, one phosphate group, and the sugar deoxyribose.

6. Chargaff’s Rules (cont.)

7. Chargaff’s Rules (cont.)

8. Chargaff’s Rules (cont.)
In all organisms, the nucleotide bases are found in specific proportions.
• Chargaff’s rules are based on two observations.
The amount of A, C, G, and T varies from species to species.
In each species, the amount of A is equal to T and the amount of G is equal to C.

9. Chargaff’s Rules (cont.)
Equal proportions between two bases indicated that the bases were paired in the structure of DNA.
The order in which these nucleotides occur differs, producing great variability in the DNA.
With four nucleotides, there are 4140, possible nucleotide sequences.

10. Franklin’s X-Ray Diffraction Studies
Rosalind Franklin used X-ray crystallography to study the structure of DNA.
Franklin took an X-ray of fibers present in a concentrated solution of DNA.
The X-ray diffraction pattern suggested that DNA had a helical shape.

11. Franklin’s X-Ray Diffraction Studies (cont.)

12. The Watson and Crick Model
Watson and Crick developed the definitive model of DNA structure.
The sugar and phosphate groups are bonded in alternating sequences to form the sides of a twisted ladder.
Bases are joined by hydrogen bonds to form the rungs of the ladder.
– Complementary base pairing occurs, meaning A only bonds with T and G with C.

13. The Watson and Crick Model (cont.)

14. The Replication of DNA
• DNA replication is the process of copying a DNA molecule.
During replication, the original strands serve as templates for the new DNA.
DNA replication is considered semiconservative because one of the original strands is present in each new DNA helix.

15. The Replication of DNA (cont.)
DNA replication requires several steps.
The enzyme helicase unwinds the old strands of the DNA helix.
New nucleotides are positioned by complementary base pairing and the enzyme DNA polymerase.
– DNA ligase repairs breaks in the backbone.

16. The Replication of DNA (cont.)

17. The Replication of DNA (cont.)
In eukaryotic cells, DNA replication is initiated at multiple points along the DNA strand, or origins of replication.
The replication bubbles spread bidirectionally until they meet.

18. The Replication of DNA (cont.)

19. RNA Structure and Function
• Ribonucleic acid (RNA) also consists of nucleotides, but these nucleotides contain the sugar ribose.
RNA has adenine, cytosine, guanine, and a fourth base called uracil.

20. RNA Structure and Function (cont.)

21. RNA Structure and Function (cont.)
Although both RNA and DNA are nucleic acids, there are key differences in the structure and function of RNA and DNA.

22. Messenger RNA
There are three types of RNA and each is involved in protein synthesis.
• Messenger RNA (mRNA) is produced in the nucleus by a process called transcription.
Messenger RNA carries genetic information from DNA to the cytosol.

23. Transfer RNA
• Transfer RNA (tRNA) is a carrier molecule for amino acids, delivering them to the site of protein synthesis.
As there are 20 different amino acids, there are also 20 different types of tRNA.

24. Ribosomal RNA
The two ribosomal RNA (rRNA) subunits join with proteins in the cytosol to form the subunits of ribosomes.
The free ribosomes, polyribosomes, and ribosomes attached to the ER all synthesize proteins.

25. 11.2 Gene Expression
DNA and RNA are involved in the synthesis of proteins.
The genes in DNA contain the instructions for the amino acid sequence of a protein.

26. 11.2 Gene Expression (cont.)
Since enzymes are proteins, an error in the gene for that enzyme could render the enzyme non-functional.
If an enzyme is defective, then the biochemical pathway in which the enzyme participates may also be affected.
This can create inborn errors in metabolism that lead to metabolic diseases.

27. Structure and Function of Proteins
Proteins differ in the number and sequence of amino acids.
This sequence of amino acids gives each protein a unique shape and function.
The shape of a protein has different levels of organization.
– Primary structure
– Secondary structure
– Tertiary structure

28. Structure and Function of Proteins (cont.)

29. From DNA to RNA to Protein
In order to synthesize a protein, the genetic information in the DNA must be converted to an amino acid sequence.
• Transcription involves the synthesis of mRNA from template DNA.
During translation, the mRNA directs the sequence of amino acids in the protein.

30. The Genetic Code
Within a gene, information for the amino acid sequence of a protein is encoded in a triplet code.
This triplet code is transcribed into the codons in mRNA.
These codons provide redundant sequences for the placement of amino acids in a protein.

31. The Genetic Code (cont.)

32. Transcription
During transcription, a strand of mRNA is formed that is complementary to the sequence within the DNA.
Transcription begins when RNA polymerase binds to the DNA promoter for a gene.
The DNA helix is unwound and the primary mRNA strand is formed.

33. Transcription (cont.)

34. Transcription (cont.)
The primary mRNA strand is then processed to remove introns.
The remaining sequence of genetic information, the exons, are retained in the mature mRNA for protein synthesis.

35. Transcription (cont.)

36. Translation: An Overview
The translation of a mature mRNA into proteins requires several enzymes, tRNA, and rRNA.
The tRNA is a single-stranded RNA molecule with an amino acid bound to one end and an anticodon on the other end.

37. Translation: An Overview (cont.)

38. Translation: An Overview (cont.)
The anticodon is complementary to the corresponding mRNA codon.
As a mature mRNA moves to a ribosome, the sequence of codons in the mRNA dictates the sequence of anticodons.
The order of the tRNA molecules determines the order of the amino acids.

39. Translation: An Overview (cont.)

40. Translation: An Overview (cont.)

41. Translation Has Three Phases
In initiation, the small ribosomal subunit, large ribosomal subunit, the mRNA, and a tRNA carrying a methionine bond to the mRNA to start transcription.
The amino acid sequence of the protein is extended during the elongation phase.
• Termination occurs when protein synthesis is completed.

42. Translation Has Three Phases (cont.)

43. Translation Has Three Phases (cont.)

44. Genes and Gene Mutations
A gene mutation changes the sequence of bases in the DNA.
Mutations in DNA are rare (one in 100 million cell divisions).
Mutations can be caused by mutagens.
Radiation (radioactivity, X-rays, UV light)
Chemicals (pesticides, cigarette chemicals)

45. Effects of Mutations
Mutations that are inherited are called germ-line mutations.
• Somatic mutations occur in an organism after birth and can lead to cancer.
• Point mutations involve the mutation (change) of a single DNA nucleotide.

46. Effects of Mutations (cont.)
In a frame shift mutation, the triplet sequence of the DNA is altered, throwing the mRNA codons out of phase.
Although not a mutation, transposons are genes that jump to a different position within the DNA.

47. Effects of Mutations (cont.)

48. 11.3 DNA Technology
Our understanding of genes and the base sequences of DNA has facilitated the development of genetic engineering.
Genetic engineering can be used to clone (copy) genes from an organism and use that gene to alter the genome of another organism.

49. Recombinant DNA Technology
Genetic engineering forms recombinant DNA (rDNA), which contains DNA from two or more different sources.
A vector, such as a bacterial plasmid, serves as a carrier for the foreign gene.
– Restriction enzymes are used to cut the plasmid and splice in the foreign gene.
DNA ligase seals the gene into the plasmid.

50. Recombinant DNA Technology (cont.)

51. Polymerase Chain Reaction
• Polymerase chain reaction (PCR) is a technique that amplifies (quickly makes multiple copies of) a DNA sequence.
PCR requires primers that start the process of DNA replication on the DNA strand.
PCR also requires DNA polymerase to synthesize the new DNA strand.

52. Polymerase Chain Reaction (cont.)

53. Polymerase Chain Reaction (cont.)
PCR has been used to determine the evolutionary history of humans.
PCR can also be used to conduct DNA fingerprinting.
Fingerprinting can be used to identify viral infections or susceptibility to certain cancers.
Fingerprinting can provide forensic data.

54. Polymerase Chain Reaction (cont.)

55. Transgenic Organisms
Biotechnology refers to the use of natural biological systems to achieve a desired use by humans.
Biotechnology can also include the use of recombinant DNA technology to create transgenic organisms.
Transgenic organisms have a foreign gene inserted into them.

56. Transgenic Organisms (cont.)
Transgenic bacteria are grown in bioreactors to produce a variety of products.
Insulin
Human growth hormone
Vaccines
Industrial chemicals
Transgenic bacteria can also be used to degrade pollutants, such as crude oil.

57. Transgenic Organisms (cont.)
Transgenic plants have been engineered.
Insect-resistant plants
Herbicide-resistant plants
Plants with increased yield
Plants that produce human hormones and antibodies

58. Transgenic Organisms (cont.)
Recombinant DNA technology has also been used to create transgenic animals.
Animals expressing bovine growth hormone
Animals that produce pharmaceuticals (gene pharming).
Animals that produce milk containing therapeutic or diagnostic proteins.

59. Transgenic Organisms (cont.)

60. Transgenic Organisms (cont.)
Biotechnology can also be used to clone animals.
The DNA of a donor egg is replaced with the DNA of an animal to be cloned.
The development of the egg is stimulated in vitro.
The developing egg is implanted in the uterus of a surrogate mother.
The cloned animal is born naturally.