D.N.AObjective: SWBAT describe the process of transcription and translation IOT understand how proteins are created

1. The information carried by a DNA molecule is in

A. Its amino acid sequence

B. The sugars and phosphates forming its backbone

C. The order of the bases in the molecule

D. The total number of nucleotides it contains

E. The RNA units that make up a molecule

2. DNA replication occursA. Whenever a cell makes protein

B. To repair gene damage caused by mutation

C. Before a cell divides

D. Whenever a cell needs RNA

E. In the cytoplasm of a eukaryotic cell

3. The complementary strand of DNA to the DNA fragment 5’- GGC ATA CAT – 3” is

A . 3’ – CCG UAU GUA – 5’

B. 3’ – GTA TAT CCG -5’

C. 3’ – ATG TAT GCC – 5’

D. 3’ – CCG TAT GTA – 5’

E. 3’ – CCG AUA GUA – 5’

2007-2008

From Gene to Protein

How Genes Work

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

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

How do we move information from DNA to proteins?

transcriptiontranslation

replication

proteinRNADNA trait

DNA gets all the glory, but proteins do all the work!

Inheritance of metabolic diseasessuggested that genes coded for enzymeseach disease (phenotype) is caused by non-

functional gene product • lack of an enzyme• Tay sachs• PKU (phenylketonuria)• albinism

Am I just the sum 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

2007-2008

Transcription

fromDNA nucleic acid language

toRNA nucleic acid language

Transcription

Transcription is the synthesis of messenger RNA (mRNA) from DNA

Occurs in the nucleus DNA does not leave the nucleus

Analogy: blueprints do not get used at the job site when constructing a house

DNA vs. RNA

DNA RNA

Contains:

Adenine, guanine, cytosine, thymine

Contains:

Adenine, guanine, cytosine, uracil

5-carbon sugar is deoxyribose

5-carbon sugar is ribose

Double-stranded Single-stranded

Transcription Making mRNA

transcribed DNA strand = template strand enzyme

• RNA polymerase

template strand

rewinding

mRNA RNA polymerase

unwinding

coding strand

DNAC C

C

C

C

C

C

C

C CC

G

GG

G

G G

G G

G

G

GAA

AA A

A

A

A

A

A A

A

AT

T T

T

T

T

T

T

T T

T

T

U U

5

35

3

3

5build RNA 53

Transcription: Initiation Promoter = a specific

sequence of DNA (starting point)

RNA polymerase binds to the promoter on the DNA molecule

Transcription factors (proteins) bind to promoter region to help RNA polymerase find the starting point.

RNA polymerase then separates the 2 DNA strands

Transcription: Elongation As RNA polymerase

moves along the DNA, it untwists the double helix and separates the strands

RNA polymerase adds nucleotides to the 3’ end of the mRNA molecule Follows the base-pairing

rules

G = C

A = U

Matching bases of DNA & RNA

Match RNA bases to DNA bases on one of the DNA strands

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

G

G

G

A

A

A

AA

5' 3'

Transcription: Termination

Termination signal = sequence of bases in DNA molecule that tell RNA polymerase to stop transcription“finish line” in a race

mRNA is released from the DNA

RNA Modifications

In eukaryotes, mRNA is edited before it’s sent out of the nucleus

2 major types of modifications:Alteration of mRNA endsRNA splicing

RNA Splicing Genes have stretches of nucleotides that don’t code for anything

“junk DNA” Noncoding sequence = introns

“intervening sequences” Coding regions = exons During RNA splicing, the introns are removed by enzymes and the

exons are joined together

A A AA

A3' poly-A tail

mRNA

5'5' cap

3'

G PPP

50-250 A’s

Need to protect mRNA on its trip from nucleus to cytoplasmenzymes in cytoplasm attack mRNA

• protect the ends of the molecule• add 5 cap• add poly-A tail

• longer tail, mRNA lasts longer: produces more protein

Alteration of mRNA Ends

Translation

fromnucleic acid language

toamino acid language

How does mRNA code for proteins?

TACGCACATTTACGTACGCGGDNA

AUGCGUGUAAAUGCAUGCGCCmRNA

Met Arg Val Asn Ala Cys Alaprotein

?

ATCG

AUCG

AUGCGUGUAAAUGCAUGCGCCmRNA

mRNA codes for proteins in triplets

TACGCACATTTACGTACGCGGDNA

AUGCGUGUAAAUGCAUGCGCCmRNA

Met Arg Val Asn Ala Cys Alaprotein

?

codon

Cracking the code1960 | 1968

Crickdetermined 3-letter (triplet) codon system

Nirenberg & Khorana

WHYDIDTHEREDBATEATTHEFATRATWHYDIDTHEREDBATEATTHEFATRAT

Nirenberg (47) & Khorana (17) determined mRNA–amino acid match added fabricated mRNA to test tube of

ribosomes, tRNA & amino acids created artificial UUUUU… mRNA found that UUU coded for phenylalanine

The code Code for ALL life!

strongest support for a common origin for all life

Code is redundant several codons for

each amino acid 3rd base wobble

Start codon AUG methionine

Stop codons UGA, UAA, UAG

How are the codons matched to amino acids?

TACGCACATTTACGTACGCGGDNA

AUGCGUGUAAAUGCAUGCGCCmRNA

aminoacid

tRNA anti-codon

codon

5 3

3 5

3 5

UAC

MetGCA

ArgCAU

Val

mRNA

From gene to protein

DNAtranscription

nucleus cytoplasm

aa

aa

aa

aa

aa

aa

aa

aa

aa

aa

aa

ribosome

traitaa

proteintranslation

DNA strand mRNA strand – codon Amino acid

CGC

AGT

GAC

GCG

UCA

CUG

Serine

Alanine

Leucine

mRNA

From gene to protein

DNAtranscription

nucleus cytoplasm

aa

aa

aa

aa

aa

aa

aa

aa

aa

aa

aa

ribosome

traitaa

proteintranslation

How are the codons matched to amino acids?

TACGCACATTTACGTACGCGGDNA

AUGCGUGUAAAUGCAUGCGCCmRNA

aminoacid

tRNA anti-codon

codon

5 3

3 5

3 5

UAC

MetGCA

ArgCAU

Val

Transfer RNA structure “Clover leaf” structure

anticodon on “clover leaf” endamino acid attached on 3 end

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

anticodontRNATrp binds to UGG condon of mRNA

Trp Trp Trp

mRNAA C CU GG

C=O

OHOH

H2OO

tRNATrp

tryptophan attached to tRNATrp

C=O

O

C=O

Ribosomes Facilitate coupling of

tRNA anticodon to mRNA codonorganelle or enzyme?

Structureribosomal RNA (rRNA) & proteins2 subunits

• large• small E P A

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 tRNA

leaves ribosome from exit site

Building a polypeptide Initiation

brings together mRNA, ribosome subunits, initiator tRNA

Elongation adding amino acids based on

codon sequence

Termination end codon 123

Leu

Leu Leu Leu

tRNA

Met MetMet Met

PE AmRNA5' 5' 5' 5'

3' 3' 3'3'

U UA AAACC

CAU UG G

GUU

A AAAC

CC

AU UG GGU

UA

AAAC

CC

AU UG GGU U

A AACCA U UG G

G AC

ValSer

AlaTrp

releasefactor

AA A

CCU UGG 3'

Protein targeting Signal peptide

address label

Destinations: secretion nucleus mitochondria chloroplasts cell membrane cytoplasm etc…start of a secretory pathway

Can you tell the 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 introntRNA

Prokaryote vs. Eukaryote genes

Prokaryotes DNA in cytoplasm circular chromosome naked DNA

no introns

Eukaryotes DNA in nucleus linear chromosomes DNA wound on

histone proteins introns vs. exons

eukaryoticDNA

exon = coding (expressed) sequence

intron = noncoding (inbetween) sequence

intronscome out!

Transcription & translation are simultaneous in bacteria DNA is in

cytoplasmno mRNA

editing ribosomes

read mRNA as it is being transcribed

Translation in Prokaryotes

Translation: prokaryotes vs. eukaryotes Differences between prokaryotes &

eukaryotestime & physical separation between

processes• takes eukaryote ~1 hour

from DNA to proteinno RNA processing