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Genes and How They WorkChapter 15
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The Nature of Genes
information flows in one direction:
DNA (gene) RNA proteinTranscription Translation
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U
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GENE
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The Genetic Code
codon: set of 3 nucleotides(mRNA) that specifies a particular amino acid (64 possible codons)
stop codons: (UUA, UGA, UAG) used to terminate translation
start codon: (AUG) used to start translation
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Gene Expression Overview
template strand: used to make RNA
coding strand: complementary to the template strand
RNA polymerase: puts nucleotides together to make RNA strand
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Gene Expression Overview
types of RNA:messenger RNA (mRNA) carries the info
from DNA that encodes proteins
ribosomal RNA (rRNA) part of ribosome
transfer RNA (tRNA) carries amino acids to the ribosome
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Transcription
Transcription proceeds through:
1. initiation
2. elongation – RNA nucleotides are added to the 3’ end of the new RNA
3. termination
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Eukaryotic pre-mRNA Splicing
• introns – non-coding sequences
• exons – sequences that will be translated
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tRNA and Ribosomes
The ribosome has two primary functions:
– decode the mRNA
– form peptide bonds
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Translation
1. initiation
2. elongation – tRNAs bring amino acids to the ribosome
3. Termination – stop codon
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tRNA and Ribosomes
tRNA
– amino acids carried by the acceptor arm
– the anticodon loop 3 nucleotides complementary to mRNA codons
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Mutation: Altered Genes
Too much genetic change (mutation) can be harmful to the individual.
However, genetic variation (caused by mutation) is necessary for evolutionary change of the species.
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Mutation: Altered Genes
Point mutations alter a single base.
Chromosomal mutations change part of a chromosome (deleted/repeated/moved)
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