1. 1 PROTEIN SYNTHESIS Preview

2. 2 Protein Synthesis  The production (synthesis) of polypeptide chains (proteins)  Two phases: Transcription & Translation  mRNA must be processed before it leaves the nucleus of eukaryotic cells

3. 3 Transcription Translation DNA mRNA Ribosome Protein Prokaryotic Cell DNA  RNA  Protein

4. 4 Nuclear membrane Transcription RNA Processing Translation DNA Pre-mRNA mRNA Ribosome Protein Eukaryotic Cell

5. 5 Pathway to Making a Protein DNAmRNA tRNA (ribosomes) Protein

6. 6 Nucleic Acids

7. 7 DNA or Protein?  1903, Walter Sutton noted the parallelism between chromosome behavior and Mendel's laws, thus identifying genes with chromosomes and marking the beginning of genetics as a science  However, scientists were NOT sure which one (protein or DNA) was the actual genetic material of the cell

8. 8 DNA!  Frederick Griffith in 1928  Frederick Griffith in 1928 discovered what he called a transforming principle, which led to the direct discovery of how DNA works and the beginning of Molecular Genetics. DNA  It wasn't until 1944 that Griffith's "transforming principle" was identified as DNA by Oswald Theodore Avery, along with coworkers Colin MacLeod and Maclyn McCartyColin MacLeod Maclyn McCarty

9. DNA! Rosalind Franklin recorded a x-ray photograph of a DNA molecule that another researcher at King's College, Maurice Wilkins, showed to James Watson and Francis Crick without her knowledge or permission. This image helped Watson and Crick construct a model of DNA, which enabled them to fully understand the molecule's structure.Maurice Wilkins James WatsonFrancis Crick 9

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11. Watson and Crick constructed a model of DNA, which enabled them to fully understand the molecule's structure. Wilkins, Crick and Watson were awarded a Nobel Prize jointly, some years later, after Franklin's death. proposed the double helix or spiral staircase structure of the DNA molecule in 1953double helixDNA1953 11 DNA!

12. 12 Watson Crick

13. 13 Structure of DNA  DNA is made of subunits called nucleotides  DNA nucleotides are composed of a: 1.phosphate, 2.deoxyribose sugar, and 3.nitrogen-containing base  The 4 bases in DNA are: adenine (A), thymine (T), guanine (G), and cytosine (C)

14. 14 DNA Nucleotide

15. 15 Base Pairing Rule Watson and Crick showed that DNA is a double helixWatson and Crick showed that DNA is a double helix A (adenine) pairs with T (thymine)A (adenine) pairs with T (thymine) C (cytosine) pairs with G (guanine)C (cytosine) pairs with G (guanine)

16. 16 Nitrogen Rings Purines have double rings of carbon- nitrogen (G, A)Purines have double rings of carbon- nitrogen (G, A)

17. Nitrogen Rings Pyrimidines have single carbon- nitrogen rings (C, T)Pyrimidines have single carbon- nitrogen rings (C, T) 17

18. Nitrogen Rings This is called complementary base pairing because a purine is always paired with a pyrimidineThis is called complementary base pairing because a purine is always paired with a pyrimidine 18

19. 19. 5’ to 3’ Sugars When the DNA double helix unwinds, it resembles a ladder When the DNA double helix unwinds, it resembles a ladder The sides of the ladder are the sugar-phosphate backbones The sides of the ladder are the sugar-phosphate backbones The rungs of the ladder are the complementary paired bases The rungs of the ladder are the complementary paired bases The two DNA strands are anti-parallel (they run in opposite directions)

20. 20 Anti- Parallel Strands of DNA Template (top part of DNA) always goes from 5’ to 3’

21. 21 DNA Replication

22. 22 Steps in DNA Replication Occurs when chromosomes duplicate (make copies) – Interphase (S-phase) Occurs when chromosomes duplicate (make copies) – Interphase (S-phase) An exact copy of the DNA is produced with the aid of the enzyme DNA polymerase An exact copy of the DNA is produced with the aid of the enzyme DNA polymerase Hydrogen bonds between bases break and enzymes called helicases “unzip” the molecule Hydrogen bonds between bases break and enzymes called helicases “unzip” the molecule Each old strand of nucleotides serves as a template for each new strand Each old strand of nucleotides serves as a template for each new strand New nucleotides move into complementary positions are joined by DNA polymerase New nucleotides move into complementary positions are joined by DNA polymerase

23. 23 Two New, Identical DNA Strands Result from Replication

24. 24 Another View of Replication