1. Chapter 21
DNA and Biotechnology

2. DNA Is a Double Helix Consisting of Two Strings of Nucleotides

3. FIGURE 21.1
DNA is a double-stranded molecule that twists to form a spiral structure called a double helix.

4. During Replication of DNA Each Original Strand Serves As a Template for a New Strand

5. DNA Replication FIGURE 21.2
DNA replication is called semiconservative because each daughter molecule consists of one "old" strand and one "new" strand.

6. DNA Replication Process: DNA strands uncoil and “unzip”
DNA nucleotides are positioned and linked by DNA polymerase
Nucleotide subunits: A = adenine, G = guanine, T = thymine, C = cytosine
A only binds to T; and G only binds to C

7. DNA Codes for RNA, Which Codes for a Protein
Central Dogma
DNA  RNA  Protein

8. Central Dogma

9. TABLE 21.1
COMPARISON OF DNA AND RNA

10. Which of the following statements about DNA and RNA is/are incorrect?
DNA is double stranded, RNA single
DNA contains deoxyribose, RNA ribose
DNA contains four bases A, T, G, C, RNA only contain three, A, G, C
DNA forms a double helix, RNA doesn’t

11. TABLE 21.2
REVIEW OF THE FUNCTIONS OF RNA

12. RNA Transcription FIGURE 21.3
Transcription is the process of producing RNA from a DNA template.

13. RNA Synthesis: Transcription
Process:
DNA for a gene unwinds
RNA polymerase copies base sequence in RNA nucleotides
Ex.: G-C-T-A  C-G-A-U (note U instead of T)

14. Transcription of a Gene into mRNA

15. A-T-G-C-G-A A-U-G-C-G-A T-A-C-G-C-T
Which RNA nucleotide sequence (mRNA) would the DNA sequence (T-A-C-G-C-T) specify?
A-T-G-C-G-A
A-U-G-C-G-A
T-A-C-G-C-T

16. Genetic Code
Codon: sequence of three mRNA bases that codes for an amino acid
Duplicate codons: almost all amino acids have more than one codon (degenerate code)
Genetic Code Grammar
Start: AUG (methionine), begin all genes
Stop: UAA, UAG, UGA, one ends each gene

17. TABLE 21.3
THE GENETIC CODE

18. Val-Ala Phenal-Isoleu Isoleu-Gly Gly-Asp Met-Arg
Which amino acids (protein) would the DNA sequence (T-A-C-G-C-T) code for?
Val-Ala
Phenal-Isoleu
Isoleu-Gly
Gly-Asp
Met-Arg

19. Protein Synthesis: Translation
Components: messenger RNA, transfer RNA, ribosomes of ribosomal RNA and proteins
Process:
Initiation: tRNA finds start (AUG) codon, binds ribosome and mRNA
Elongation: tRNA brings specific amino acids to developing protein chain
Termination: stop codon terminates developing chain, protein is released from ribosome

20. FIGURE 21.7 part 1
Translation occurs in three steps: initiation, elongation, and termination.

21. FIGURE 21.7 part 2
Translation occurs in three steps: initiation, elongation, and termination.

22. FIGURE 21.7 part 3
Translation occurs in three steps: initiation, elongation, and termination.

23. Three Steps of Translation

24. DNA Mutations Point mutations
Result from nucleotide insertion, substitution, or deletion
Replacement of nucleotide in DNA may (or may not) lead to a change of amino acid in protein

25. FIGURE 21.9
A base-pair substitution is a point mutation resulting when a base is paired incorrectly. This may change the amino acid specified by the mRNA and alter the structure of the protein.