Chapter 22 Nucleic Acids and Protein Synthesis

1. Chapter 22 Nucleic Acids and Protein Synthesis 22.10 Genetic Mutations 22.11 Recombinant DNA 22.12 Viruses

2. Mutations A mutation: • Alters the nucleotide sequence in DNA. • Can result from mutagens such as radiation and chemicals. • Can produce one or more incorrect codons in the corresponding mRNA. • Can produce a protein that incorporates one or more incorrect amino acids. • Causes genetic diseases that produce defective proteins and enzymes.

3. Normal DNA Sequence • The normal DNA sequence produces a mRNA that provides instructions for the correct series of amino acids in a protein. Correct order

4. Mutation: Substitution • The substitution of a base in DNA changes a codon in the mRNA. • A different codon leads to the placement of an incorrect amino acid in the polypeptide. Incorrect order Wrong amino acid

5. Frame Shift Mutation • In a frame shift mutation, an extra base adds to or is deleted from the normal DNA sequence. • All the codons in mRNA and amino acids are incorrect from the base change. Incorrect amino acids

6. Genetic Diseases

7. Recombinant DNA • Recombinant DNA combines a DNA fragment from one organism with DNA in another. • Restriction enzymes are used to cleave a gene from a foreign DNA and open DNA plasmids in E. coli. • When the DNA fragments are mixed with the plasmids in E. coli, the ends are joined by ligase. • The new gene in the altered DNA produces protein.

8. Recombinant DNA

9. Products of Recombinant DNA

10. DNA Fingerprinting In DNA fingerprinting (Southern transfer): • Restriction enzymes cut a DNA sample into smaller fragments (RFLPs). • The fragments are sorted by size. • A radioactive isotope that adheres to certain base sequences in the fragments produces a pattern on x-ray film, which is the “fingerprint.” • The “fingerprint” is unique to each individual DNA.

11. Polymerase Chain Reaction A polymerase chain reaction (PCR): • Produces multiple copies of a DNA in a short time. • Separates the sample DNA strands by heating. • Mixes the separated strands with enzymes and nucleotides to form complementary strands. • Is repeated many times to produce a large sample of the DNA.

12. Polymerase Chain Reaction

13. Viruses Viruses: • Are small particles of DNA or RNA that require a host cell to replicate. • Cause a viral infection when the DNA or RNA enters a host cell. • Are synthesized in the host cell from the viral RNA produced by viral DNA.

14. Viruses

15. Reverse Transcription In reverse transcription: • A retrovirus, which contains viral RNA, but no viral DNA, enters a cell. • The viral RNA uses reverse transcriptase to produce a viral DNA strand. • The viral DNA strand forms a complementary DNA strand. • The new DNA uses the nucleotides, and enzymes in the host cell to synthesize new virus particles.

16. Reverse Transcription

17. HIV Virus and AIDS • The HIV-1 virus is a retrovirus that infects T4 lymphocyte cells. • As the T4 level decreases, the immune system fails to destroy harmful organisms. • Pneumonia and skin cancer are associated with AIDS. HIV virus

18. AIDS Treatment • One type of AIDS treatment prevents reverse transcription of the viral DNA. • When altered nucleosides such as AZT and ddI are incorporated into viral DNA, the virus is unable to replicate.

19. AIDS Treatment Azidothymine (AZT) Dideoxyinosine (ddI)

20. AIDS Treatment • Another type of AIDS treatment involves protease inhibitors such as saquinavir, indinavir, and ritonavir. • Protease inhibitors modify the active site of the protease enzyme, which prevents the synthesis of viral proteins. Inhibited by Inhibited by AZT, ddI protease inhibitors reverse transcriptase protease Viral RNA Viral DNA Viral proteins