© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e1 How Genes Work Genes on DNA are used to make RNA Transcription RNA is used to make proteins

© 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


2

Information Flow

Transcription In the nucleus

Translation In the cytoplasm

Animation


3

RNA vs. DNA

Both are linear nucleotide polymers

RNA differs from DNA Single stranded Ribose instead of

deoxyribose U base instead of T


4

Three Types of RNA

Messenger RNA (mRNA)Encodes proteins

Transfer RNA (tRNA)Aids translation

Ribosomal RNA (rRNA)Used to make ribosomes


5

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


6

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


7

Introns & Exons

Eukaryotic cells have non-coding regions in genes (introns)

Removed after transcription

Exons are connected to produce the mature mRNA


8

The Genetic Code

Translation of RNA 3 bases = 1 codon 1 codon = 1 amino

acid


9

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


10

Translation

RNA sequence translated into protein sequence

Genetic code used like a dictionary Ribosome

Holds mRNA Links amino acids together


11

tRNA Two binding sites:

Amino acid siteAnticodon

Matches the Amino acid with codon

tRNA

mRNA

SerineAmino Acid

Amino Acidattachmentsite

Anticodon

Codon


12

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


13

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


14

Sickle Cell Anemia

Gene for hemoglobin One base pair

change Causes one amino

acid change Sickle Cell phenotype


15

Process Animation 13.1The Flow of Genetic Information in a Eukaryotic Cell

MacintoshWindows


16

Process Animation 13.3Translation

MacintoshWindows

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© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e1 How Genes Work Genes on DNA are used to make RNA Transcription RNA is used to make proteins