DNA and RNA Chapter 12

1. DNA and RNAChapter 12 Wakefield

2. 12.1 DNA • How do genes work? • Must uncover chemical nature of the gene • 1928 FREDERICK GRIFFITH • Studying bacteria • 2 strains – one caused pneumonia, other was harmless

3. Griffith’s Experiments - 1928

4. Avery and DNA - 1944 • Destroyed bacterial cells to see if that made a difference • Transformation still occurred • Sooooo, what was responsible for the transformation? • Repeated using enzyme to specifically destroy DNA, and what happened? • No transformation • Determined that DNA stores and transmits genetic information

5. Hershey-Chase Experiment - 1952 • Studied viruses • Bacteriophages • Viruses that infect bacterial cells • Inject DNA • Direct bacterial cell to make more viruses • Destroy bacterial cell

6. BACTERIOPHAGE

8. Structure of DNA • DNA – deoxyribonucleic acid • Made up to “nucleotides” • 3 Components of nucleotides • 5-carbon sugar-deoxyribose • Phosphate group • Nitrogenous base (contains nitrogen)

9. Nitrogenous Bases • 4 kinds • 2 are PURINES • Adenine • Guanine • 2 are PYRIMIDINES • Thymine • Cytosine • Backbone • Sugar and phosphate

10. Chargaff’s Rules • A = T • C = G • From humans to bacteria • No idea why

11. X-ray Evidence – 1950’s • Rosalind Franklin used x-ray diffraction • Aim x-ray at DNA and recorded the scattering pattern on film • Showed twisted pattern

12. Watson and Crick- 1953

13. The Double Helix • Watson and Crick built 3-dimensional models • Used Franklins pictures as clues • Double helix • Two strands wound around each other • Twisted ladder

14. Double Helix Hydrogen bonds hold bases together “Base Pairing”

15. 12.2 Chromosomes & DNA Replication • Found in – • Prokaryotic cells – in the cytoplasm • Short in length and complexity • Eukaryotic cells – in the nucleus • 1000 times longer and more complex • Each species has a specific # of chromosomes • The human colon has 4,639,221 base pairs and is about 1.6 mm long • Human cells contain about 1000 times as many base pairs as do bacteria • Packaged as DNA & protein in the form of chromatin – the proteins are called histones

16. 12.2 Chromosomes & DNA Replication • histones

17. 12.2 Chromosomes & DNA Replication • DNA Replication – • Each strand of DNA has the info needed to reconstruct its complimentary half of its double helix • Replication begins @ a single point and moves in both directions from there – often @ hundreds of places @ a time – until all of every chromosome is copied

18. 12.2 Chromosomes & DNA Replication • DNA Replication – the DNA molecule separates into 2 strands • Then produces 2 new complimentary strands • Follows the rules of base pairings • Each strand of the double helix serves as a template, or model, for the new strand • Results in 2 DNA molecules identical to each other and to the original molecule

19. 12.2 Chromosomes & DNA Replication • DNA Replication – • Is carried out by a series of enzymes which “unzips” a molecule of DNA • The molecule “unzips” @ the hydrogen bonds between the base pairs • The principal enzyme is DNA polymerase • Joins to a molecule of DNA • Also “proofreads” each new DNA strand, helping to maximize the odds that each molecule is perfect

20. 12.3 RNA & Protein Synthesis • Structure of RNA / DNA • 5 carbon sugar called ribose sugar • PO4 • Bases • Purines – Adenine & Guanine • Pyramidines – Uracil & Cytosine • Types of RNA • Messenger RNA • Carries copies of the DNA instructions • Found in the nucleus • Ribosomal RNA • Transfer RNA

21. 12.3 RNA & Protein Synthesis • Types of RNA • Messenger RNA • Carries copies of the DNA instructions • Found in the nucleus • Ribosomal RNA • Receives the DNA instructions from MRNA • Combines with proteins • Found on the endoplasmic reticulum • Transfer RNA • Translates the message and transfers each amino acid to the ribosome as it is specified by the coded message from MRNA

22. Figure 12–14 Transcription Adenine (DNA and RNA) Cystosine (DNA and RNA) Guanine(DNA and RNA) Thymine (DNA only) Uracil (RNA only) RNApolymerase DNA RNA

23. Transcription – • RNA binds to DNA and separates the DNA strands • RNA polymerase then uses one strand of DNA as a template from which nucleotides as assembled into a strand of RNA • RNA polymerase only binds to certain areas called promoters • Promoters are signals which tell the enzyme where to bind to make RNA

24. Section 12-2 Original strand DNA polymerase New strand Growth DNA polymerase Growth Replication fork Replication fork Nitrogenous bases New strand Original strand

25. RNA Editing • Some RNA molecules require editing before they go into action • DNA contains both introns & exons • Both are copies during replication • Introns are however cut out when RNA molecules are formed in the nucleus • The remaining exons are then spliced back together • Biologists don’t know why this happens • Cell Specialization? • Evolution? • Allowing many proteins to be made from just one template?

26. The Genetic Code • Proteins are made from joining amino acids together into long chains called polypeptides • The properties of proteins are determined by which amino acids are used to make the protein • Amino Acids are made from a series of 3 DNA bases called codons • Codons consist of 3 consecutive nucleotides that specify a single amino acid

27. The Genetic Code • There are 4 different bases • Adenine • Cytocine • Guanine • Thyamine • Therefore, there are 64 possible 3-base codons (4X4X4)=64 • Most specify an amino acid but some specify “start” or “stop” in the production of a protein chain (polypeptide) • One codon codes for either “methionine” or “start”

28. How do these proteins control my traits? • Proteins are enzymes • Involved in chemical reactions • A gene that codes for a pigment can control the color of a flower • A gene that codes for a antigen on a red blood cell determines your blood type

29. 12.4 Mutations • Now and then a cells make a mistake copying their DNA • “Mutations” • 2 kinds of Mutations • Gene Mutation • In a single gene

30. 12.4 Mutations • Chromosomal mutation • Changes in whole chromosome

31. Examples of Mutations

32. Gene Mutations Deletion

33. Gene Mutations • Point Mutation • Affect one or a few nucleotides • Occur at a single point • Substitutions • Frameshift Mutation • Insertion or deletion of a nucleotide • More dramatic affect than point mutation • Every amino acid that follows is changed

34. Chromosomal Mutations • Changes in GENE not just nucleotide • Involves whole chromosome • Deletions • Duplications • Inversions • Translocations

35. Types of Mutations

36. Sickle Cell Anemia Sickle Cell is caused by a point mutation.

37. Significance of Mutations • Many are neutral • Can be harmful, disrupting normal activities • Source of genetic variability • Polypoidy • Extra set of chromosomes • Chromosomes fail to separate • Produce breeders use to their advantage to make stronger and larger plants

38. Trisomy 21

39. Genetic Diseases

40. Color Blindness • the inability or decreased ability to see color, or perceive color differences, under normal lighting conditions

41. Cystic Fibrosisi • an autosomal recessive genetic disorder that affects most critically the lungs, and also the pancreas, liver, and intestine. It is characterized by abnormal transport of chloride and sodium across an epithelium, leading to thick, viscous secretions.

42. Down’s Syndrome • One in every 691 babies in the United States is born with Down syndrome, making Down syndrome the most common chromosomal condition. • Down syndrome occurs when an individual has a full or partial extra copy of chromosome 21

43. Duchenne Muscular Dystrophy • an inherited disorder that involves muscle weakness, which quickly gets worse

44. Coeliac Disease • a digestive condition triggered by consumption of the protein gluten, which is primarily found in bread, pasta, cookies, pizza crust and many other foods containing wheat, barley or rye • experience an immune reaction in their small intestines, causing damage to the inner surface of the small intestine and an inability to absorb certain nutrients • cause abdominal pain and diarrhea • manage celiac disease by changing your diet.

45. Hemophilia • Causes by a lack of the blood clotting factor • Uncontrollable bleeding • X – linked

46. Klinefelter Syndrome • results in males who have at least one extra X chromosome. • Usually, this occurs due to one extra X. This would be written as XXY • Abnormal body proportions (long legs, short trunk, shoulder equal to hip size) • Abnormally large breasts • Sexual problems • Infertility • Less than normal amount of pubic, armpit, and facial hair • Small, firm testicles • Tall height

47. Phenylketonuria • rare condition in which a baby is born without the ability to properly break down an amino acid called phenylalanine. • autosomal recessive trait – can occur in males or females • harmful to the central nervous system and cause brain damage • Treatment involves a diet that is extremely low in phenylalanine • Milk, Eggs, NutraSweet

48. Sickle-Cell Disease • Autosomal recessive pattern • Affects the red blood cells • Lacks a hemoglobin protein • Causing red blood cells to be rigid and have a concave shape • causing red blood cells to be rigid and have a concave shape • These irregularly shaped cells get stuck in the blood vessels and are unable to transport oxygen effectively, causing pain and damage to the organs

49. Tay-Sachs Disease • Deadly disease of the nervous system passed down through families • Child usually dies by age 4-5 • Caused by a defective gene on chromosome 15 • Autosomal recessive • Deafness • Decreased eye contact, blindness • Decreased muscle tone (loss of muscle strength) • Delayed mental and social skills • Dementia • Increased startle reaction • Irritability • Listlessness • Loss of motor skills • Paralysis or loss of muscle function • Seizures • Slow growth

50. Turner Syndromeaka Monosomy X • female does not have the usual pair of two X chromosomes • Possible symptoms in young infants include: • Swollen hands and feet • Wide and webbed neck • A combination of the following symptoms may be seen in older females: • Absent or incomplete development at puberty, including sparse pubic hair and small breasts • Broad, flat chest shaped like a shield • Drooping eyelids • Dry eyes • Infertility • No periods (absent menstruation) • Short height • Vaginal dryness Estrogen replacement therapy is often started when the girl is 12 or 13 years old as treatment