1. © 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
How Genes Work
Genes on DNA are used to make RNA
Transcription
RNA is used to make proteins
Translation
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e

2. © 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
Information Flow
Transcription
In the nucleus
Translation
In the cytoplasm
Animation
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e

3. © 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
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. © 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
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

5. © 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
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

6. © 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
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

7. © 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
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

8. © 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
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

9. © 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
The Genetic Code
Possible codons: 4 X 4 X 4 = 64
20 possible amino acids
Most amino acids have more than 1 codon
Degeneracy of the code
Why many mutations are silent (make no protein change)
Three codons code for no amino acid
STOP codons
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e

10. © 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
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

11. © 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
tRNA
Two binding sites:
Amino acid site
Anticodon
Matches the Amino acid with codon
tRNA
mRNA
Serine
Amino Acid
attachment
site
Anticodon
Codon
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e

12. © 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
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

13. © 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
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

14. © 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
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

15. © 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
Process Animation 13.1 The Flow of Genetic Information in a Eukaryotic Cell
Macintosh
Windows
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e

16. © 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
Process Animation 13.3
Translation
Macintosh
Windows
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e