Transcript The Initiation of Translation

Benjamin A. Pierce
•GENETICS ESSENTIALS
•Concepts and Connections
• SECOND EDITION
CHAPTER 11
From DNA to Proteins: Translation
© 2013 W. H. Freeman and Company
CHAPTER 11 OUTLINE
•
11.1 The Genetic Code Determines How
the Nucleotide Sequence Specifies the
Amino Acid Sequence of a Protein, 288
•
11.2 Amino Acids Are Assembled into a
Protein Through the Mechanism of
Translation, 293
• 11.3 Additional Properties of Translation and
Proteins, 299
11.1 THE GENETIC CODE DETERMINES HOW
THE NUCLEOTIDE SEQUENCE SPECIFIES
THE AMINO ACID SEQUENCE OF A PROTEIN
• The One Gene, One Enzyme Hypothesis
• Genes function by encoding enzymes, and each gene encodes a
separate enzyme.
• More specific: one gene, one polypeptide hypothesis
11.1 THE GENETIC CODE DETERMINES HOW
THE NUCLEOTIDE SEQUENCE SPECIFIES
THE AMINO ACID SEQUENCE OF A PROTEIN
• The Structure and Function of Proteins
• Proteins are polymers consisting of amino acids linked
by peptide bonds.
• Amino acid sequence is its primary structure.
• This structure folds to create secondary and tertiary
structures.
• Two or more polypeptide chains associate to form
quaternary structure.
11.2 The Genetic Code Determines How the Nucleotide
Sequence Specifies the Amino Acid Sequence of a
Protein
Characteristics of the Genetic Code
• The degeneracy of the code
• The reading frame and initiation codons
• Termination codons
• The universality of the code
Breaking the Genetic Code
• Homopolymers
• Random copolymers
• Ribosome-bound tRNAs
• Codon: a triplet RNA code
The Degeneracy of the Code
• Degenerate code: Amino acid may be specified
by more than one codon.
• Synonymous codons: codons that specify the
same amino acid.
• Isoaccepting tRNAs: different tRNAs that accept
the same amino acid but have different
anticodons.
The Degeneracy of the Code
• Codons
• Sense codons:
encoding amino acid
• Initiation codon: AUG
• Termination codon:
UAA, UAG, UGA
• Wobble hypothesis
The Degeneracy of the Code
• Wobble hypothesis
The Reading Frame and Initiation Codons
• Reading frame: three ways
in which the sequence can
be read in groups of three.
Each different way of reading
encodes a different amino
acid sequence.
• Non-overlapping: A single
nucleotide may not be
included in more than one
codon.
• The universality of the
code: near universal, with
some exceptions.
11.2 Amino Acid Are Assembled into a Protein Through
the Mechanism of Translation
• The Binding of Amino Acids to Transfer RNAs
• The Initiation of Translation
• Elongation
• Termination
The Binding of Amino Acids to Transfer
RNAs
• Aminoacyl-tRNA syntheses and tRNA
charging
• The specificity between an amino acid and its tRNA is determined
by each individual aminoacyl-tRNA synthesis. There are exactly
20 different aminoacyl-tRNA syntheses in a cell.
The Initiation of Translation
• Initiation factors IF-3, initiator tRNA with Nformylmethionine attached to form fmet-tRNA
• Energy molecule: GTP
The Initiation of Translation
• The Shine-Dalgarno consensus sequence in
bacterial cells is recognized by the small unit of
ribosome.
• The Kozak sequence in eukaryotic cells
facilitates the identification of the start codon.
The Initiation of Translation
• The Kozak sequence in eukaryotic cells
facilitates the identification of the start codon.
Elongation
• Aminoacyl site A
• Peptidyl site P
• Exit site E
• Elongation factors: Tu, Ts, and G
Termination
• Termination codons:
UAA, UAG, and UGA
• Release factors
11.3 Additional Properties of Translation
and Proteins
• The three-dimensional structure of the ribosome
• Polyribosomes:
• An mRNA with several ribosomes attached
11.3 Additional Properties of Translation
and Proteins
• Post-translational Modifications of Proteins
• Chaperons
• Translation and Antibiotics