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

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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