Chapter 21

Chapter 21

DNA and Biotechnology

DNA Is a Double Helix Consisting of Two Strings of

Nucleotides

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

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

DNA Replication

DNA Codes for RNA, Which Codes for a Protein

• Central Dogma

DNA RNA Protein

Central Dogma

Which of the following statements about DNA and RNA is/are incorrect?

A. DNA is double stranded, RNA singleB. DNA contains deoxyribose, RNA riboseC. DNA contains four bases A, T, G, C, RNA

only contain three, A, G, CD. DNA forms a double helix, RNA doesn’t

RNA 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)

RNA Synthesis: Transcription

Transcription of a Gene into mRNA

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

A. A-T-G-C-G-AB. A-U-G-C-G-AC. T-A-C-G-C-T

• 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

Genetic Code

Which amino acids (protein) would the DNA sequence (T-A-C-G-C-T) code for?

A. Val-AlaB. Phenal-IsoleuC. Isoleu-GlyD. Gly-AspE. Met-Arg

• 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

Protein Synthesis: Translation

Three Steps of Translation

• 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

DNA Mutations