DNA, RNA, & Protein Synthesis

1. DNA, RNA, & Protein Synthesis The foundation of the study of Genetics

2. Discovery of DNA & its structure • DNA structure was not discovered until the 1950’s • After looking at an X-ray diffraction photo stolen from Rosalind Franklin by her co-worker (Wilkins), James Watson and Francis Crick were able to create a model of DNA • The model depicted a double helix of even width • In 1953, James Watson, Francis Crick, and Maurice Wilkins received the Nobel Prize (no mention of Rosalind Franklin)

3. Rosalind Franklin • Franklin’s x-ray images suggested that DNA was a double helix of even width.

4. James Watson & Francis Crick

5. Other Evidence • Erwin Chargaff, in his biochemical studies, discovered: • The amount of Adenine in a DNA sample always equaled the amount of Thymine • The amount of Cytosine, likewise, was equal to the amount of Guanine • This became known as Chargaff’s rule • This information further served to confirm the model created by James Watson and Francis Crick • Adenine pairs with Thymine • Cytosine pairs with Guanine

6. Structure of DNA • DNA (deoxyribonucleic acid) is made up of long chains of nucleotides • Nucleotide structure • Phosphate Group • 5 carbon sugar (deoxyribose) • Nitrogen Base (4 different bases) • Adenine • Thymine • Guanine • Cytosine

7. phosphate group nitrogen-containing base deoxyribose (sugar) Nucleotide

8. DNA structure Continued • DNA is double stranded • The two strands are equally spaced & twist • This is why the structure of DNA is referred to as a double helix

9. Bonding in DNA • The backbone of each side of DNA is held together by covalent bonds and is made up of the phosphate groups and deoxyribose sugars

10. Bonding in DNA • The two complementary strands (the rungs of the DNA ladder) of DNA are held together by weak hydrogen bonds between the complementary nitrogen base pairs • These attractions are easily broken and reformed • Important for DNA replication and transcription

11. covalent bond hydrogen bond Bonding in DNA

12. DNA Replication Making copies of DNA

13. DNA Replication • Occurs during Interphase (S phase) of the cell cycle • DNA replication is required such that the two new daughter cells created will have a complete set of DNA • Enzymes break the hydrogen bonds, separating the two strands • Other enzymes bring free nucleotides in the nucleus to build the new strands of DNA

14. Semiconservative • DNA replication is called a semiconservative process as the two double helices created consists of: • One old strand of DNA • One new strand of DNA • The “old” sides of the DNA strands are used as the template (building instructions) for building the “new” strands of DNA • Two double helices are created in the end

15. nucleotide The DNA molecule unzips in both directions. DNA Replication

16. new strand original strand Two molecules of DNA End Result DNA Replication

17. Protein Synthesis The basis of gene expression

18. Central Dogma • States that information stored in DNA flows in one direction from DNA, to RNA, to proteins

19. Protein Synthesis Phases • Transcription • The 1st phase of protein synthesis • DNA can’t leave the nucleus, so a smaller molecule that can leave has to be made • Occurs in the nucleus • Translation • The 2nd and final phase of protein synthesis • The molecule made in transcription is used to build a protein • Occurs at the site of a ribosome

20. Organelles Review • Nucleus- where DNA is located; where transcription occurs • Ribosome- where proteins are built (site of protein synthesis); where translation occurs • Rough ER- Newly made proteins enter this transport organelle • Golgi Apparatus/Body-The protein is checked, modified, and re-packaged for transport to its final destination • Vesicles-Transport vehicles for the protein around the cell

21. Transcription • A segment of DNA called a gene with the information for building a protein is used as a template (building instructions) to build a messenger RNA (mRNA) molecule • Enzymes open the double helix • Other enzymes build the mRNA molecule from the gene of DNA • Messenger RNA is a copy of the DNA instructions • Like a secretary or a transcriptionist that records information

22. DNA Transcription

23. DNA vs RNA • Double helix • Nucleotide sugar: deoxyribose • Nitrogen bases • Adenine • Thymine • Cytosine • Guanine • Base Pair Rule • A-T • C-G • Single stranded • Nucleotide sugar: ribose • Nitrogen bases • Adenine • Uracil • Cytosine • Guanine • Base Pair Rule • A-U • C-G DNA RNA

25. Translation

26. RNA molecules involved in Transcription & Translation • DNA • Messenger RNA (mRNA) • Messenger RNA (mRNA) • Ribosomal RNA (rRNA) • Transfer RNA (tRNA) Transcription Translation

27. Ribosome Structure

28. Translation • The mRNA molecule leaves the nucleus and moves to a ribosome • The mRNA “sticks” to the small subunit of the ribosome, which is made up of a ribosomal RNA (rRNA) molecule • The mRNA is fed between the small subunit of the ribosome and the large subunit • The mRNA message is “read” by the ribosome 3 nucleotides at a time • Each set of 3 nucleotides on mRNA is called a codon

29. codon for methionine (Met) codon for leucine (Leu) Messenger RNA & codons

30. Translation Continued • For each codon of mRNA, there is a transfer RNA (tRNA) molecule that has the anticodon • An anticodon is a set of three nucleotides that is complementary to the mRNA codon • Needed for bonding to the mRNA to make a “drop off” • The transfer RNA also carries ONE amino acid • The transfer RNA bonds temporarily to its mRNA complement codon • A chemical reaction occurs that causes the tRNA to let go of its amino acid

31. Transfer RNA

32. Translation Continued • The amino acids that are dropped off by the tRNA are linked together by a peptide bond • This continues until a polypeptide chain or a protein is made based on the instructions originally provided by the DNA.

33. Transfer RNA at Work

34. A closer Look at Translation

35. DNA Mutations How protein synthesis is altered when there is a change in the DNA

36. Mutations • Any change in the DNA nucleotide sequence • The DNA is checked twice for this during Interphase of the cell cycle • After G1: The existing DNA is checked • After G2: The replicated DNA is checked to make sure no mutations occurred in the replication of DNA • Causes of mutations • DNA Replication errors • Caused by mutagens: UV light, chemicals, pollutants, changes in the environment etc.

37. Protein Synthesis & Mutations • How mutations can effect protein synthesis • No effect: The same amino acid sequence is created regardless • Good result: A new adaptive trait comes about as a result (evolution) • Bad result: Controls over the cell cycle are lost and rapid cell division (cancer) results.

38. Two Types of Mutations • The overall length of the DNA does NOT change • Substitution: Another nucleotide replaces an existing one • Inversion: Two, or more, nucleotides switch locations • The overall length of the DNA is changed • Deletion: One or more nucleotides are removed • Insertion: One or more extra nucleotides are added • Translocation: A part of one DNA moves to another strand of DNA Point Mutations Frameshift Mutations

39. mutated base Point Mutations

40. Frameshift Mutations

41. Translocation

42. Can mutations be passed on? • Yes • If the mutation occurs in the germ cells that divide through meiosis to create a sperm or an egg • These remain “hidden” until an offspring is created using either the sperm or the egg with the mutation • No • If the mutation occurs in the somatic cells that divide through mitosis • These will only affect the individual, not their offspring