Chapter 13 The Genetic Code and Transcriptioncontents.kocw.net/KOCW/document/2013/gacheon/... ·...

Copyright © 2009 Pearson Education, Inc.

Chapter 13 The Genetic Code and Transcription


13.1 The Genetic Code Uses Ribonucleotide Bases as “Letters”

triplet unambiguous degenerate start and stop signals commaless nonoverlapping almost universal


13.2 Early Studies Established the Basic Operational Patterns of the Code


The Triplet Nature of the Code

The code is non-overlapping

GTACA

If overlapping: “GTA, TAC, ACA”

Protein sequence is limited Not actually limited

Also, one basepair change results in only one amino acid change

The code is degenerate

20 amino acids and 64 possible codons 44 extra codons

More than one codon causes insertions of the same amino acid

The code is unambiguous

Each codon only codes for one amino acid (invariant)

How were codons matched with their amino acids?

Cell free synthesis with polynucleotide phosphorylase

Initiation & Stop codons

Start: AUG – Methionine

Stop: UAG, UAA or UGA No tRNA binds


13.3 Studies by Nirenberg, Matthaei, and Others Led to Deciphering of the Code

Synthesizing Polypeptides in a Cell-Free System


Homopolymer Codes


A mixed copolymer experiment in which a ratio of 1A:5C is used


The Triplet Binding Assay

Copyright © 2009 Pearson Education, Inc. Figure 13.6

Repeating Copolymers


13.4 The Coding Dictionary Reveals Several Interesting Patterns among the 64 Codons

The wobble hypothesis Base-pairing is less constrained for the third letter of

each codon


13.6 The Genetic Code Is Nearly Universal


13.8 Transcription Synthesizes RNA on a DNA Template


13.9 Studies with Bacteria and Phages Provided Evidence for the Existence of mRNA


Evidence for RNA as the intermediate Phage infection of bacteria


13.10 RNA Polymerase Directs RNA Synthesis


13.11 Transcription in Eukaryotes Differs from Prokaryotic Transcription in Several Ways


Heterogeneous Nuclear RNA and Its Processing: Caps and Tails


13.12 The Coding Regions of Eukaryotic Genes Are Interrupted by Intervening Sequences


RNA Editing May Modify the Final Transcript


13.13 Transcription Has Been Visualized by Electron Microscopy

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