AP Biology 2007-2008

From Gene to Protein

How Genes Work

AP Biology

What do genes code for?

proteins cells bodies

How does DNA code for cells & bodies? how are cells and bodies made from the

instructions in DNA

DNA

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The “Central Dogma” Flow of genetic information in a cell

How do we move information from DNA to proteins?

transcriptiontranslation

replication

protein

RNA

DNA

trait

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mRNA

From gene to protein

DNAtranscription

nucleus cytoplasm

aa

aa

aa

aa

aa

aa

aa

aa

aa

aa

aa

ribosome

proteintranslation

trait

AP Biology

Transcriptionfrom

DNA languageto

RNA language

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RNA Review… ribose sugar N-bases

uracil instead of thymine U : A C : G

single stranded Many types of RNA

mRNA, tRNA, rRNA, siRNA…

RNADNAtranscription

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Transcription Making mRNA

transcribed DNA strand = template/coding strand

enzyme RNA polymerase

RNA polymerase is versatile (it slices, it dices!) Unwinds, unzips, adds in complementary RNA bp’s

template strand

rewinding

mRNA RNA polymerase

unwinding

DNAC C C

C

C

C

C

C

C CC

G

G G G

G G

G G

G

G

GAA

AA A

A

A

AA

A A

A

AT

T T

T

T

T

T

T

T T

T

T

U U

5

35

3

3

5build RNA 53

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Initiation: Where to begin? Promoter region

= binding site before beginning of gene “TATA box” binding site indicates location “Upstream” of gene to transcribe/copy

= binding site for RNA polymerase

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Elongation Match RNA bases to DNA

bases on one of the DNA strands

5’ 3’ direction

U

A G GGGGGT T A C A C T T T T TC C C CA A

U

UU

U

U

G

G

A

A

A C CRNA

polymerase

C

C

C

C

C

G

GG

G

A

A

A

AA

5' 3'

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Termination Eventually…

RNA transcript is released RNA polymerase detaches (complete

mechanism still not fully known)

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Eukaryotic genes have junk! Eukaryotic genes are not continuous

exons = the real gene expressed / coding DNA

introns = the junk inbetween sequence

eukaryotic DNA

exon = coding (expressed) sequence

intron = noncoding (inbetween) sequence

intronscome out!

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mRNA splicing

eukaryotic DNA

exon = coding (expressed) sequence

intron = noncoding (inbetween) sequence

primary mRNA

transcriptmature mRNA

transcript

pre-mRNA

spliced mRNA

= “Post-transcriptional processing” eukaryotic mRNA needs work after transcription primary transcript = pre-mRNA mRNA splicing

edit out introns make mature mRNA transcript

~10,000 bases

~1,000 bases

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Splicing must be accurate No room for mistakes!

a single base added or lost throws off the reading frame

AUG|CGG|UCC|GAU|AAG|GGC|CAU

AUGCGGCTATGGGUCCGAUAAGGGCCAUAUGCGGUCCGAUAAGGGCCAU

AUG|CGG|GUC|CGA|UAA|GGG|CCA|U

AUGCGGCTATGGGUCCGAUAAGGGCCAUAUGCGGGUCCGAUAAGGGCCAU

Met|Arg|Ser|Asp|Lys|Gly|His

Met|Arg|Val|Arg|STOP|

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RNA splicing enzymessnRNPs

exonexon intronsnRNA

5' 3'

spliceosome

exonexcisedintron

5'

5'

3'

3'

3'

lariat

exonmature mRNA

5'

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Alternative splicing Alternative mRNAs produced from same gene

when is an intron not an intron… different segments treated as exons

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A A A AA3' poly-A tail

mRNA

5'5' cap

3'

G PPP

50-250 A’s

More post-transcriptional processing Need to protect mRNA on its trip from

nucleus to cytoplasm Enzymes in cytoplasm attack mRNA

protect the ends of the molecule from degrading add 5 GTP cap add poly-A tail

longer tail = mRNA lasts longer: produces more protein

AP Biology

mRNA

From gene to protein

DNAtranscription

nucleus cytoplasm

aa

aa

aa

aa

aa

aa

aa

aa

aa

aa

aa

ribosome

proteintranslation

trait