2. Chapter 10 DNA, RNA, and Protein Synthesis

3. Section 10.1 Discovery of DNA

4. 3 experiments lead to the discovery of DNA: – Griffith – Avery – Hershey-Chase

5. Griffith’s Experiment: – Studying a bacterium  S. pneumoniae – Some strains can cause lung disease pneumonia in mammals. – Trying to develop a vaccine against this virulent strain. – Bacteria have a capsule made of polysaccharides that protect it from the body’s defense system.

6. 2 strains of bacteria: – S strain: Smooth-edge colonies Causes pneumonia – R strain: Does not cause pneumonia Lacks capsule Rough colonies 4 experiments:

8. Conclusions: – Heat-killed virulent bacterial cells release a hereditary factor that transfers the disease – causing ability to the live harmless cells. – Transformation

9. Avery’s Experiment: – Testing Griffith’s experiment to see if the transforming agent was RNA or DNA – Used enzymes specific to what they were testing – Conclusions: DNA is responsible for the transformation in bacteria

10. How did Avery’s Experiment differ from Griffith’s Experiment? Griffith found that 1 strain of bacteria could be transformed to another and concluded that a transforming factor was involved. Avery tested to see which molecule changed the R strain into the S strain of bacteria. He found that DNA was the transforming molecule.

11. Hershey-Chase Experiment: – Test whether DNA or protein is the hereditary material viruses transfer when they enter a bacterium. Bacteriophages – used radioactive isotopes to label protein and DNA – 35 S  protein – 32 P  DNA Conclusion: – All of the viral DNA entered the E.coli – Little of the protein entered the E.coli – DNA is the hereditary molecule in viruses.

13. Section 10.2 DNA Structure

14. DNA Double Helix James Watson Francis Crick Found DNA is made of two chains that wrap around each other  double helix – Explained how DNA replicates Received Noble Prize in medicine

15. DNA Nucleotides DNA: – Nucleic acid – 2 long chains (strands) of repeating subunits called nucleotides Consist of 3 parts: – 5-carbon sugar: » deoxyribose – Phosphate group: » P atom bonded to 4 oxygen atoms – Nitrogenous base: » Face toward center of molecule – form H bonds » Bonded in pairs – by 2 /3 H bonds Form the steps of the staircase – H bonds hold 2 chains of helix together

16. Nitrogenous Bases 4 bases: – Thymine  T – Cytosine  C – Adenine  A – Guanine  G Purines: – Double ring of C and N atoms A and G Pyrimidines: – Single ring of C and N atoms C and T

18. Complementary Bases Structure of DNA paired by base-pairing rules – Amount of adenine = thymine – Amount of cytosine = guanine Complementary base pairs: – A – T – C – G – Each pair contains 1 purine and 1 pyrimidine Base sequence: – ATTC – TAAG

19. Complementary base pairing: – Important in structure and function: H bonds between base pairs help hold 2 strands of DNA together Complementary nature of DNA helps explain how DNA replicates before cell division. – 1 strand serves as a template

20. What would be the complementary strand of the follow: – AGTA: TCAT – GACT: CTGA – GGTA: CCAT – CACT: GTGA

21. Section 10.3 DNA Replication

22. Steps of DNA Replication 1.An enzyme - helicase separates the DNA strands. – Forms the replication fork 2.Enzymes – DNA polymerase adds complementary nucleotides to each original strand 3.DNA polymerase finishes to replicate the DNA and it falls off. – Result = 2 separate & identical DNA molecules that are ready to move to a new cell in cell division

23. Each new DNA double helix: – Semi-conservative replication: 1 strand from the original 1 new strand DNA replication occurs in different directions – Forms gaps which are joined together by an enzyme  DNA ligase.

24. Prokaryotic and Eukaryotic Replication Prokaryotic cells: – 1 circular chromosome – 2 replication forks are formed & proceed in opposite directions – Replication continues along each fork until they meet and the entire molecule is copied Eukaryotic cells: – Chromosomes are long, not circular – At the rate that DNA polymerase adds nt(50nt/s) it would take 53 days to replicate the largest human chromosome Instead replication occurs at many origins (points)along DNA 2 replication forks move in opposite directions. Copying organism’s entire DNA

25. DNA Errors in Replication 1 error for every billion paired nucleotides added. DNA polymerase has repair enzymes that “proofread” DNA. When mistakes do occur: – Base sequence of newly formed DNA differs from the base sequence of original  mutation Can have serious effects on the function of an important gene and disrupt an important cell function Some errors escape repair  cancer

26. Section 10.4 Protein Synthesis

27. Flow of genetic information Gene: – Segment of DNA that is located on a chromosome and that codes for a hereditary character. Nucleic acid  ribonucleic acid (RNA) 2 steps in protein synthesis (gene expression): – Transcription: nucleus DNA acts as a template for the synthesis of RNA – Translation: cytoplasm RNA directs the assembly of proteins DNA  RNA  Protein

28. RNA Sugar ribose Uracil instead of thymine – U will pair with A Single stranded Shorter in length than DNA

29. 3 types of RNA: – mRNA: Carries instruction from a gene to make a protein Eukaryotic cells, mRNA carries genetic “ message” from DNA in the nucleus to the ribosomes in the cytosol. – rRNA: Part of the structure of ribosomes Protein synthesis occurs in ribosomes – tRNA: Transfer amino acids to the ribosome to make a protein

30. Transcription Process by which the genetic instruction in a specific gene is transcribed or “rewritten” into a RNA molecule Nucleus – eukaryotic cells Cytoplasm – prokaryotic cells

31. 3 steps: 1.RNA polymerase (enzyme that catalyzes the formation of RNA on a DNA template) binds to a promoter. DNA strands unwind and separate 2.Free RNA nucleotides are added on one of the DNA strands by RNA polymerase  RNA molecule DNA strand  ATCGAC RNA Strand  UAGCUG 3.RNA polymerase reaches a termination signal: End of the gene  stop signal New gene is transcribed – mRNA, rRNA, tRNA

33. Genetic Code Next process of gene expression, amino acids are assembled based on the genetic code. – 3 adjacent nucleotides (“letters”) in mRNA =amino acid “word” – 3 letters = codon – 64 possibilities

34. How many codons code for amino acids? 61 How many codons code for stop? 3 What amino acid is coded by the codon AUG? Methionine What is special about this particular codon (AUG)? Start codon for all mRNAs.

35. Translation All 3 types of RNA are involved Protein structure: – 20 different amino acids – 3-D structure – Shape is important to its function Translation or decoding of the genetic instruction to form a polypeptide involves 5 steps:

36. Steps: 1.Initiation: tRNA and mRNA join together Specific a.a are attached to tRNA Other end of tRNA is anticodon 2.Elongation: Polypeptide chain is put together 3.Elongation continued: Chain continues to grow 4.Termination: Ribosomes reach a stop codon. Polypeptide falls off 5.Disassembly: Components of translation come apart

38. Human Genome Entire gene sequence of the human genome is known. 3.2 billion base pairs in the 23 pairs of human chromosomes Large = 10yrs to read entire sequence Important: – Help diagnose, treat, and prevent genetic disorders, cancers, and infectious diseases in the future.