Chapter 10: DNA and RNA

1. Chapter 10: DNA and RNA

2. DNA • Deoxyribonucleic acid • Structure of DNA • Made up of four subunits called nucleotides • Each nucleotide is made up of a sugar, a phosphate and a base

3. Four Bases • Two Purines • Adenine (A) • Guanine (G) • Two pyrimidines • Cytosine (C) • Thymine (T)

4. DNA Double Helix • DNA is made of two nucleotide strands that wrap around each other in the shape of a double helix.

5. DNA Structure • Bonds Hold DNA Together • Nucleotides along each DNA strand are linked by covalent bonds. • Complementary nitrogenous bases are bonded by hydrogen bonds.

6. Chargaff • Amount of adenine equals the amount of thymine and the amount of cytosine equals the amount of guanine • A=T • C=G

7. But what does DNA look like? • Rosalind Franklin • Working in Wilkin’s lab created x-ray pictures of DNA • Wilkins shared this information with another pair of scientists without Franklin’s consent

8. Watson and Crick • Watson and Crick discovered that DNA resembles a twisted ladder shape: double helix

9. DNA Structure • Two side of the ladder are made up of alternating sugar and phosphate molecules • The rungs of the ladder are pairs of bases (A with T, and G with C): Base pair rule • Rungs are anti-parallel (5’->3’ and 3’ ->5’)

10. Making copies: Replication • DNA can “unzip” when it needs to replicate (helicase) • Occurs prior to cell division so each new cell gets the correct information

11. Replication • DNA molecule separates into two strands • Complementary strands form on the template of each of the original sides of the DNA • Each new DNA has one old and one new strand (semiconservative replication)

12. Replication enzymes • Helicase • Unwinds DNA • Primase • Adds an RNA primer on unzipped DNA • DNA polymerase • Add new bases to the 3’ end of previous base • Ligase • Seals fragments after RNA primer removed

13. Steps of DNA Replication • Replication begins with the separation of the DNA strands by helicases. • Then, primase adds an RNA primer where replication will occur • DNA polymerases form new strands by adding complementary nucleotides to each of the original strands. • The new segments of DNA are sealed by ligase

14. http://www.dnareplication.info/images/dnareplication.jpg See it in action: http://www.johnkyrk.com/DNAreplication.html

15. DNA Replication

16. DNA Replication • Each new DNA molecule is made of one strand of nucleotides from the original DNA molecule and one new strand. This is called semi-conservative replication.

17. Replication Forks Increase the Speed of Replication

18. Replication • DNA polymerase can only add to a 3’ end • Leading strand • Runs 5’->3’ • Lagging strand • Runs 3’->5’ SO can’t add directly • Have to replicate in fragments called Okazaki fragments • Ligase bonds the fragments together

19. DNA Replication Overview Origin of replication Lagging strand Leading strand Leading strand Lagging strand Single-strand binding protein Overall directions of replication Helicase Leading strand 5 DNA pol III 3 3 Primer Primase 5 3 Parental DNA Lagging strand DNA polymerase 5 DNA polymerase DNA ligase 4 3 5 3 2 1 3 5

20. Replication animation • http://www.mcb.harvard.edu/Losick/images/TromboneFINALd.swf

21. Central Dogma • Has its exceptions, but gives us a basic idea of how DNA does its job

22. RNA • Single stranded nucleic acid • Made up of nucleotides • Sugar: Ribose • Thymine instead of Uracil • Shorter: length of one gene

23. RNA Structure and Function • Types of RNA • Cells have three major types of RNA: • messenger RNA(mRNA) • ribosomal RNA (rRNA) • transfer RNA (tRNA)

24. Activity • In pairs, create a chart that will fit in your foldable (no more than 1/8th size of construction paper) that compares and contrasts the different forms of RNA • Be sure to include: • Name • Structure • Function • Picture

25. RNA Structure and Function • mRNA carries the genetic “message” from the nucleus to the cytosol. • rRNA is the major component of ribosomes. • tRNA carries specific amino acids, helping to form polypeptides.

26. Making proteins • Cells use a two step process to read each gene and produce the amino acid chain that becomes a protein. • These processes are: • Transcription • Translation http://gslc.genetics.utah.edu/units/basics/transcribe/

27. Fig. 17-4 Gene 2 DNA molecule Gene 1 Gene 3 DNA template strand TRANSCRIPTION mRNA Codon TRANSLATION Protein Amino acid

28. Transcription • The process of building an RNA copy of a DNA sequence • DNA is too big to leave the nucleus • mRNA is a copy of the DNA sequence

29. mRNA • Also known as messenger RNA • Takes the code out into the cell for protein synthesis

30. Steps of Transcription • Initiation • RNA polymerase binds to a promoter (specific nucleotide sequence: TATA box) • Elongation • RNA polymerase adds free RNA nucleotides that are complementary to the DNA strand • Termination • RNA polymerase releases at a termination sequence

31. Steps of Transcription

32. Promoter Transcription unit 5 3 3 5 DNA Start point RNA polymerase Initiation 1 5 3 3 5 Template strand of DNA RNA transcript Unwound DNA Elongation 2 Rewound DNA 5 3 3 5 3 5 RNA transcript Termination 3 5 3 3 5 3 5 Completed RNA transcript

33. Genetic Code • The nearly universal genetic code identifies the specific amino acids coded for by each three-nucleotide mRNA codon.

34. Translation • Steps of Translation • During translation, amino acids are assembled from information encoded in mRNA. • As the mRNA codons move through the ribosome, tRNAs add specific amino acids to the growing polypeptide chain. • The process continues until a stop codon is reached and the newly made protein is released.

35. Ribosome Amino acids Polypeptide tRNA with amino acid attached Ribosome Trp Phe Gly tRNA Anticodon Codons 5 3 mRNA

36. Translation: Assembling Proteins

37. DNA Errors in Replication • Changes in DNA are called mutations. • DNA proofreading and repair prevent many replication errors. • DNA Replication and Cancer • Unrepaired mutations that affect genes that control cell division can cause diseases such as cancer.

38. The Human Genome • The entire gene sequence of the human genome, the complete genetic content, is now known. • To learn where and when human cells use each of the proteins coded for in the approximately 30,000 genes in the human genome will take much more analysis.