© 2006 w.w. norton & company, inc. discover biology 3/e1 how genes work genes on dna are used...
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© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
1
How Genes Work
Genes on DNA are used to make RNATranscription
RNA is used to make proteinsTranslation
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
2
Information Flow
Transcription In the nucleus
Translation In the cytoplasm
Animation
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
3
RNA vs. DNA
Both are linear nucleotide polymers
RNA differs from DNA Single stranded Ribose instead of
deoxyribose U base instead of T
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
4
Three Types of RNA
Messenger RNA (mRNA)Encodes proteins
Transfer RNA (tRNA)Aids translation
Ribosomal RNA (rRNA)Used to make ribosomes
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
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Transcription
DNA information is copied into RNA Similar to replication with three differences:
RNA polymerase is used instead of DNA polymerase Only genes are transcribed not the entire genome RNA is made instead of DNA
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
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Transcription
RNA polymerase starts at promoter
Its complex unwinds DNA It copies bases using
complimentary base pairing (U v.s. T)
Moves down one strand Stops at terminator
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
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Introns & Exons
Eukaryotic cells have non-coding regions in genes (introns)
Removed after transcription
Exons are connected to produce the mature mRNA
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
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The Genetic Code
Translation of RNA 3 bases = 1 codon 1 codon = 1 amino
acid
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
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Possible codons: 4 X 4 X 4 = 64 20 possible amino acids Most amino acids have more than 1 codon
Degeneracy of the codeWhy many mutations are silent (make no
protein change) Three codons code for no amino acid
STOP codons
The Genetic Code
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
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Translation
RNA sequence translated into protein sequence
Genetic code used like a dictionary Ribosome
Holds mRNA Links amino acids together
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
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tRNA Two binding sites:
Amino acid siteAnticodon
Matches the Amino acid with codon
tRNA
mRNA
SerineAmino Acid
Amino Acidattachmentsite
Anticodon
Codon
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
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Translation Ribosome holds mRNA tRNA binds to first codon
AUG – start codon = methionine Second tRNA binds to next codon Amino acids are linked Move to next codon Animation
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
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From Gene to Phenotype
Genes are inherited as DNA DNA is transcribed into RNA RNA is translated into protein Proteins give the organism traits
Mutations in DNA produce changes in traits
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
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Sickle Cell Anemia
Gene for hemoglobin One base pair
change Causes one amino
acid change Sickle Cell phenotype
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
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Process Animation 13.1The Flow of Genetic Information in a Eukaryotic Cell
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