Information

• Today– Chapter 14 and 16 highlights

• Wed., 30 November– Final exam review – BRING YOUR QUESTIONS!– Instructor evaluations

• Mon., 12 December, 2:15-4:15pm in C317– Final Exam

• kpeterson@oeb.harvard.edu• Office: B-203 (by appointment)

Chapter 14

READ: – Key Concepts– 14.1– 14.2

1) DNA is transcribed to form RNA

2) RNA is translated to form polypeptide chains, which fold to form proteins

DNA to Proteins

3 Classes of RNAs

• Messenger RNA (mRNA)

– Protein-building instruction

• Ribosomal RNA (rRNA)

– Major component of ribosomes

• Transfer RNA (tRNA)

– Delivers amino acids to ribosomes

Base Pairing during Transcription

DNA

DNA DNA

RNAG C A T

C G T A

G C A U

C G T A

base pairing in DNA replication base pairing in transcription

Transcription• Small DNA stretch = template

• RNA polymerase = enzyme

• Product = 1 RNA strand

transcribed DNA winds up again

DNA to be transcribed unwinds

mRNAtranscript RNA

polymerasePROTEIN INSTRUCTIONS

Genetic Code

• 64 base triplets

• Triplets = codons– 61 = amino acids

– 3 = stop

Figure 14.7Page 230

tRNA Structure

codon in mRNA

anticodon

amino acid OH

amino-acidattachment site

Figure 14.8Page 231

BRINGS AMINO ACIDS TO RIBOSOMES

Overview

Transcription

Translation

mRNA rRNA tRNA

Mature mRNA transcripts

ribosomal subunits

mature tRNA

Chapter 16

READ 16.2, 16.4

Polymerase Chain Reaction(PCR)

Double-stranded DNA to copy

DNA heated to 90°– 94°C

Primers added to base-pair with ends

Mixture cooled; base-pairing of primers and ends of DNA strands

DNA polymerasesassemble new DNA strands

Figure 16.6Page 256

Stepped Art

Polymerase Chain Reaction

Figure 16.6Page 256

Stepped Art

Mixture heated again; makes all DNA fragments unwind

Mixture cooled; base-pairing between primers and ends of single DNA strands

DNA polymerase action again doubles number of identical DNA fragments

Gel Electrophoresis

• DNA placed at one end of a gel

• A current is applied

• DNA molecules (-) move to + end

• Small molecules faster than large

Nucleotides for Sequencing

• Standard nucleotides (A, T, C, G)

• Modified versions– Fluoresce

– Stop DNA synthesis

Reactions Proceed

• PCR

• Stops with modified nucleotide

• Millions of copies of varying length

Recording the Sequence

T C C A T G G A C CT C C A T G G A C

T C C A T G G A

T C C A T G G

T C C A T G

T C C A T

T C C A

T C C

T C

T

electrophoresisgel

one of the many fragments of DNA migratingthrough the gel

one of the DNA fragmentspassing through a laser beam after moving through the gel

T C C A T G G A C C A

•DNA placed on gel

•Fragments move by

size

•Pass through laser

beam

•Color of each fragment

is recorded on printout

Figure 16.8Page 258

Information

• Today– Chapter 14 and 16 highlights

• Wed., 30 November– Final exam review – BRING YOUR QUESTIONS!– Instructor evaluations

• Mon., 12 December, 2:15-4:15pm in C317– Final Exam

• kpeterson@oeb.harvard.edu• Office: B-203 (by appointment)