Chapter 4 Sec 1 – What does DNA Look Like?

1. Chapter 4Sec 1 – What does DNA Look Like?

2. DNA stands for… Deoxyribonucleic acid

4. What does DNA do? • DNA stores and passes on genetic information from one generation to the next

5. 1950’s • Rosalind Franklinand Maurice Wilkinstook x-ray photographs of DNA

6. 1953 James Watsonand Francis Crickused these pictures to determine that the shape of DNA is a double helix.

7. What is a DOUBLE HELIX? A staircase in the shape of a double helix, in the Vatican Museum

8. Calling DNA a double helix is the same as saying it’s like a twisted ladder.

10. The Sides of the Ladder are made up of millions of alternating sugarsand phosphates. • The sugar is named deoxyribose. • The two sides of the ladder are held together by rungs (steps) attached to the sugars.

11. Rungs of ladder:Rungs of the ladder are made up of two bases Bases contain nitrogen so we call them nitrogenous bases The 2 bases of each rung are held together by a hydrogen bond There are 4 bases to choose from:AdenineThymine GuanineCytosine

12. Erwin Chargraffdiscovered that the amount of adenine (A) is always equal the amount of thymine (T), AND the amount of cytosine (C) is always equal the amount of guanine (G). • He concluded that a rung can either have Aand T OR it can have Cand G but no other combinations are possible.

13. This is calledComplementaryBase Pairing Adenine always pairs with Thymine. Guanine always pairs with Cytosine. Thymine always pairs with Adenine. Cytosine always pairs with Guanine. So, if you know ONE side of the DNA, you should be able to figure out the other!

14. 1 Try it: Name the nitrogenous base that’s missing from each spot. 2 3 4 5 6 7 8

15. The species with the largest genome is the South American marbled lungfish with a total length of 133 billion base pairs. How long is a DNA molecule? The smallest genome discovered to date is from a symbiotic insect bacteria, Carsonella ruddii, clocking in at a mere 159,662 base pairs. The human genome contains 3 billion (3,000,000,000) base pairs

17. What is a nucleotide? A nucleotide is a small piece of DNA which contains: 1 base 1 sugar 1 phosphate Lots of nucleotides connect to form a large DNAmolecule.

18. DNA Replication • DNA Replication - Process in which DNA makes an exact copy of itself • When does DNA replication take place? • During Interphase before Mitosis

19. DNA Replication

20. half saved DNA Replication is semi-conservative. It means that one half is the original (saved) strand and the other half is the new strand.

21. What does it mean to say that DNA Replication is semi-conservative? • Each new DNA has ½ new and ½ old nucleotides

22. Steps of DNA Replication • When it is time to replicate, the DNA unzips (at the hydrogen bonds). • New complementary nucleotides move in to match BOTH halves of the DNA and form hydrogen bonds with the old nucleotides. • The finished product is: 2 identical DNA molecules!

23. Identical base sequences Important: Why is it important that the 2 new DNAs be identical to each other and to the original DNA? • So that when they go into different cells, each cell has the same DNA. How is it possible that the new DNAs and the original DNA are identical? • Because the bases are complementary.

24. DNA replication animation

25. Chapter 4Sec 2 - How DNA Works

26. Protein Synthesis DNA carries a code for making proetins.

27. DNA is like the blueprints for a house.

28. No, not those jeans! DNA is made up of smaller segments called genes. No, not these jeans…. No, not that GENE.

29. genes genes

30. How genes work Genes carry the code for making specific proteins(they do not do the work themselves). When a particular protein is needed, that part of the DNA (the gene) is copied. The copy of the gene is called mRNA or messenger ribonucleic acid.

31. How to Make a Protein? Transcription– the gene for the protein that it wants is copied (called mRNA) in the nucleus so that the original DNA never has to leave the nucleus. The copy then goes to the ribosome.

32. Transcription is like taking the blueprints and copying a single section about one specific part of the house. Ex. Copying the blueprint to the kitchen

33. Differences between mRNA & DNA

34. mRNA strands are broken down into smaller sections of 3 bases calledcodons. Codons = 3 letters on mRNA • The combination of the 3 letters on a codon calls for a specific amino acid.

35. mRNA

36. After the mRNA is made, it goes to the ribosome where proteins are made by connecting amino acids. Something to think about….. If the mRNA is made in the nucleus, how does it get out of the nucleus to get to the ribosome? How does it get through the nuclear membrane??

37. The codons on mRNA tell the ribosome which amino acid to assemble together. Many amino acids connected together makes a protein.

38. Peptide Bond = bond that connects 2 amino acids

39. When DNA replication or transcription, makes a mistake, a mutationoccurs. • There are 3 types of mutation: • Deletion - one pair of bases is removed. • Insertion-one pair of bases is added. • Substitution - one pair of bases is replaced with another pair

40. Deletion • When one pair of bases is removed.

41. Insertion • When one pair of bases is added.

42. Substitution • When one pair of bases is replaced with another pair of bases.