Gene to Protein(KFogler)

8/3/2019 Gene to Protein(KFogler)

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AP Biology 2007-2008

From Geneto Protein

How GenesWork


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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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AP Biology

The Central Dogma

Flow of genetic information in a cell How do we move information from DNA to proteins?

replication

proteinRNADNA trait

DNA getsall the glory,

but proteins doall the work!


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AP Biology

Inheritance of metabolic diseases suggested that genes coded for enzymes

each disease (phenotype) is caused by

non-functional gene product lack of an enzyme

Tay sachs

PKU (phenylketonuria)

albinism

Am I just thesum of my proteins?

Metabolism taught us about genes

A B C D E

disease disease disease disease

enzyme 1 enzyme 2 enzyme 3 enzyme 4

metabolic pathway


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AP Biology

Beadle & Tatum1941 | 1958

George Beadle

Edward Tatum

"for their discovery that genes act byregulating definite chemical events"

one gene : one enzyme hypothesis


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AP Biology

Wild-typeNeurospora

Minimalmedium

Select one ofthe spores

Grow oncomplete medium

Minimalcontrol

Nucleicacid

CholinePyridoxine RiboflavinArginine

Minimal media supplemented only with

ThiamineFolicacid NiacinInositolp-Aminobenzoic acid

Test on minimalmedium to confirmpresence of mutation

Growth oncompletemedium

X rays or ultraviolet light

asexualspores

spores

Beadle & Tatum

create mutations

positive control

negative control

experimentals

amino acidsupplements


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AP Biology

mRNA

From gene to protein

DNAtranscription

nucleus cytoplasm

aa

aa

aa

a

a

aa

aa

a

a

aa

aa

aa

aa

proteintranslation

ribosome

trait


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Transcription

fromDNA nucleic acid language

to

RNA nucleic acid language


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AP Biology

RNA

ribose sugar N-bases

uracil instead of thymine

U : A C : G

single stranded

lots of RNAs mRNA, tRNA, rRNA, siRNA

RNADNA

transcription


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AP Biology

Transcription

Making mRNA transcribed DNA strand = template strand

untranscribed DNA strand = coding strand same sequence as RNA

synthesis of complementary RNA strand transcription bubble

enzyme RNA polymerase

template strand

rewinding

mRNA RNA polymerase

unwinding

coding strand

DNAC C

C

C

C

C

C

C

C CC

G

G GG

G G

G G

G

G

GA

A

AA A

A

A

A

A

A A

A

AT

T T

T

T

T

T

T

T T

T

T

U U

5

353

3

5build RNA 53


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AP Biology

RNA polymerases

3 RNA polymerase enzymes RNA polymerase 1

only transcribes rRNA genes

makes ribosomes RNA polymerase 2

transcribes genes into mRNA

RNA polymerase 3

only transcribes tRNA genes

each has a specific promoter sequenceit recognizes


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AP Biology

Which gene is read?

Promoter region binding site before beginning of gene

TATA box binding site

binding site for RNA polymerase& transcriptionfactors

Enhancer region

binding site farupstream of gene

turns transcription

on HIGH


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AP Biology

Transcription Factors

Initiation complex transcription factors bind to promoter region

suite of proteins which bind to DNA

hormones?

turn on or off transcription

trigger the binding of RNA polymerase to DNA


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AP Biology

Matching bases of DNA & RNA

Match RNA bases to DNAbases on one of the DNAstrands

U

AG 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

G

G

G

A

A

A

A

A

5' 3'


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AP Biology

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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AP Biology

mRNA splicing

eukaryotic DNA



primary mRNAtranscript

mature mRNAtranscript

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 bas

~1,000 bas


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AP Biology

1977 | 1993

RichardRoberts Philip

SharpCSHL

MIT

adenovirus

common cold

Discovery of exons/introns

beta-thalassemia


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AP Biology

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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AP Biology

RNA splicing enzymes

snRNPs

exonexon intron

snRNA

5' 3'

spliceosome

exonexcisedintron

5'

5'

3'

3'

3'

lariat

exonmature mRNA

5'

No,not smurfs!snurps

snRNPs small nuclear RNA

proteins

Spliceosome

several snRNPs

recognize splicesite sequence

cut & paste gene

Whoa! I thinkwe just broke

a biological rule!


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AP Biology

Alternative splicing

Alternative mRNAs produced from same gene when is an intron not an intron

different segments treated as exons

Starting to gethard to

define a gene!


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AP Biology

AmRNA

5'

3'

G PPP

More post-transcriptional processing

Need to protect mRNA on its trip fromnucleus to cytoplasm

enzymes in cytoplasm attack mRNA protect the ends of the molecule

add 5 GTP cap add poly-A tail longer tail, mRNA lasts longer: produces more protein


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AP Biology

mRNA


DNAtranscription

nucleus cytoplasm

aa

aa

aa

a

a

aa

aa

a

a

aa

aa

aa

aa

ribosome

trait

proteintranslation


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Translation

fromnucleic acid language

to

amino acid language


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AP Biology

How does mRNA code for proteins?

TACGCACATTTACGTACGCGGDNA

AUGCGUGUAAAUGCAUGCGCCmRNA

MetArgValAsnAlaCysAlaprotein

?

How can you code for 20 amino acids

with only 4 nucleotide bases (A,U,G,C)?

4

4

20

ATCG

AUCG


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AP Biology


mRNA codes for proteins in triplets



MetArgValAsnAlaCysAlaprotein

?

codon


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AP Biology

Cracking the code1960 | 1968

Crick determined 3-letter (triplet) codon system

Nirenberg & Khorana

WHYDIDTHEREDBATEATTHEFATRAWHYDIDTHEREDBATEATTHEFATRA

Nirenberg (47) & Khorana (17)

determined mRNAamino acid match

added fabricated mRNA to test tube ofribosomes, tRNA & amino acids

created artificial UUUUU mRNA

found that UUU coded for phenylalanine


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AP Biology

1960 | 1968Marshall Nirenberg

Har Khorana


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AP Biology

The code

Code for ALL life! strongest support for

a common origin forall life

Code is redundant

several codons foreach amino acid

3rd base wobble

Start codon

AUG

methionine

Stop codons

UGA, UAA, UAG

Why is the

wobble good?


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AP Biology

How are the codons matched to

amino acids?



aminoacid

tRNA anti-codon

codon

5 3

3 5

3 5UAC

Met GCAArg

CAU

Val


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AP Biology

mRNA


DNA transcription

nucleus cytoplasm

aa

aa

aa

a

a

aa

aa

aa

aa

a

a

aa

aa

ribosome

traitaa

proteintranslation


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AP Biology

Transfer RNA structure

Clover leaf structure anticodonon clover leaf end

amino acid attached on 3 end


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AP Biology

Loading tRNA

Aminoacyl tRNA synthetase enzyme which bonds amino acid to tRNA

bond requires energy

ATP AMP bond is unstable so it can release amino acid at ribosome easily

activatingenzyme

anticodon

tRNATrp binds to UGGcondon of mRNA

Trp Trp Trp

mRNAACCUGG

C=O

OHOH

H2

OO

tRNATrp

tryptophan attached

to tRNATrp

C=O

O


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AP Biology

Ribosomes

Facilitate coupling oftRNA anticodon tomRNA codon

organelle or enzyme? Structure

ribosomal RNA (rRNA) & proteins

2 subunits

large

smallE P A


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AP Biology

Ribosomes

Met

5'

3'

UUA C

A G

APE

A site (aminoacyl-tRNA site) holds tRNA carrying next amino acid to

be added to chain

P site (peptidyl-tRNA site) holds tRNA carrying growing

polypeptide chain

E site (exit site)

empty tRNAleaves ribosomefrom exit site


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AP Biology

Building a polypeptide

Initiation brings together mRNA, ribosome

subunits, initiator tRNA

Elongation

adding amino acids based oncodon sequence

Termination end codon 123

Leu

Leu Leu Leu

tRNA

Met MetMet Met

PE A

mRNA5' 5' 5' 5'

3' 3' 3'3'

U UA AAAC

CC

AU UG GGU

UA

AAAC

CC

AU UG GGU

UA

AAAC

CC

AU UG GGU U

AAA

CCAU UG G

Val Ser

AlaTrp

releasefactor

AAA

CCU UGG 3'


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AP Biology

Protein targeting

Signal peptide address label

Destinations: secretion nucleus

mitochondria chloroplasts cell membrane cytoplasm etcstart of a secretory pathway

RNA l


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AP Biology

Can you tellthe story?

DNA

pre-mRNA

ribosome

tRNA

aminoacids

polypeptide

mature mRNA

5' GTP cap

poly-A tail

large ribosomal subunit

small ribosomal subunit

aminoacyl tRNAsynthetase

E P A

5'

3'

RNA polymerase

exon intron

tRNA


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AP Biology AAAAAAAAGTP

20-30b

3'

promoter transcriptionstop

transcriptionstart

introns

The Transcriptional unit (gene?)

transcriptional unit (gene)TAC ACT

DNA

DNATATA5'RNA

polymerase

pre-mRNA

5' 3'

translationstart

translationstop

mature mRNA

5' 3'

UTR UTR

exonsenhancer1000+b


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ProteinSynthesis in

Prokaryotes

Bacterial chromosome

mRNA

Cell wall

Cellmembrane

Transcription

Psssstno nucleus!


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AP Biology

Prokaryote vs. Eukaryote genes

Prokaryotes DNA in cytoplasm

circularchromosome

naked DNA

no introns

Eukaryotes DNA in nucleus

linearchromosomes

DNA wound onhistone proteins

introns vs. exons

eukaryoticDNA



introns

come out!


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AP Biology

Transcription & translation are simultaneousin bacteria

DNA is incytoplasm

no mRNAediting

ribosomes

read mRNAas it is beingtranscribed

Translation in Prokaryotes


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AP Biology

Translation: prokaryotes vs. eukaryotes

Differences between prokaryotes &eukaryotes

time & physical separation betweenprocesses takes eukaryote ~1 hour

from DNA to protein

no RNA processing


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Any Questions??What color would a smurf turn

if he held his breath?


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Substitute Slidesfor Student Print version


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AP Biology

Can you tellthe story?


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20-30b

3'

introns

The Transcriptional unit

transcriptional unitTAC ACT

DNATATA5'RNA

polymerase

5' 3'

5' 3'

exonsenhancer

1000+b

Gene to Protein(KFogler)

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