The “Central Dogma” - PowerPoint Presentation

Slide1

The “Central Dogma”

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

transcription

translation

replication

protein

RNA

DNA

trait

DNA gets

all the glory,

but proteins do

all the work

!Slide2

Transcription

Making mRNAtranscribed DNA strand = template strand

untranscribed DNA strand = coding strandsame sequence as RNAsynthesis of complementary RNA strand

enzymeRNA polymerase

template strand

rewinding

mRNA

RNA polymeraseunwindingcoding strand

DNA

C

C

C

C

C

C

C

C

C

C

C

G

G

G

G

G

G

G

G

G

G

G

A

A

A

A

A

A

A

A

A

A

A

A

A

T

T

T

T

T

T

T

T

T

T

T

T

U

U

5



3



5



3



3



5



build RNA 5





3

Slide3

RNA polymerases

3 RNA polymerase enzymes

RNA polymerase 1only transcribes rRNA genesmakes

ribosomes RNA polymerase 2transcribes genes into mRNARNA polymerase 3

only transcribes tRNA geneseach has a specific promoter sequence it recognizesSlide4

Which gene is read?

Promoter regionbinding site before beginning of gene

TATA box binding sitebinding site for RNA polymerase & transcription factorsEnhancer regionbinding site far

upstream of geneturns transcription on HIGHSlide5

Transcription Factors

Initiation complextranscription factors bind to

promoter regionsuite of proteins which bind to DNAhormones?turn on or off transcriptiontrigger the binding of RNA polymerase to DNASlide6

Eukaryotic genes have junk!

Eukaryotic genes are not continuous

exons = the real geneex

pressed / coding DNA“exit” the nucleusintrons = the junkinbetween

sequencestay “in” the nucleus

eukaryotic DNA

exon = coding (expressed) sequence

intron = noncoding (inbetween) sequence

introns

come out

!

Slide7

mRNA splicing

Post-transcriptional processing

eukaryotic mRNA needs work after transcription

primary transcript = pre-mRNAmRNA splicingedit out

introns make mature mRNA transcript

eukaryotic DNA

exon = coding (expressed) sequence

intron = noncoding (inbetween) sequence

primary mRNA

transcript

mature mRNA

transcript

pre-mRNA

spliced mRNA

~10,000 bases

~1,000 basesSlide8

RNA splicing enzymes

snRNPs

small nuclear RNAproteins

Spliceosomeseveral snRNPsrecognize splice site sequencecut & paste gene

snRNPs

exon

exon

intronsnRNA

5'

3'

spliceosome

exon

excised

intron

5'

5'

3'

3'

3'

lariat

exon

mature mRNA

5'

No,

not smurfs

!

“snurps”

Slide9

Alternative splicing

Alternative mRNAs produced from same genewhen is an intron

not an intron…different segments treated as exons

Starting to get

hard to

define a gene

!

Slide10

A

A

A

A

A

3' poly-A tail

mRNA

5'5' cap

3'

G

P

P

P

50-250 A’sMore post-transcriptional processing

Need to protect mRNA on its trip from nucleus to cytoplasmenzymes in cytoplasm attack mRNAprotect the ends of the moleculeadd

5



GTP cap

add

poly-A tail

longer tail, mRNA lasts longer: produces more proteinSlide11

The code

Code for

ALL life!

strongest support for a common origin for all lifeCode is redundantseveral codons for each amino acid3rd base “wobble”

Start

codon

AUG

methionineStop codonsUGA, UAA, UAGWhy is the

wobble good? Slide12

How are the codons matched to amino acids?

TACGCACATTTACGTACGCGG

DNA

AUG

CGUGUAAAUGCA

UGCGCC

mRNA

aminoacidtRNAanti-codoncodon

5

3

3

5



3

5

UAC

Met

GCA

Arg

CAU

ValSlide13

Transfer RNA structure

“Clover leaf” structure

anticodon

on “clover leaf” end

amino acid attached on 3 endSlide14

Loading

tRNA Aminoacyl

tRNA synthetase enzyme which bonds amino acid to

tRNAbond requires energyATP  AMPbond is unstable

so it can release amino acid at ribosome easily

activatingenzyme

anticodon

tRNATrp binds to UGG condon of mRNA TrpTrpTrp

mRNA

A

C

C

UG

G

C=O

OH

OH

H

2

O

O

tRNA

Trp

tryptophan attached to

tRNA

Trp

C=O

O

C=OSlide15

Ribosomes

Facilitate coupling of tRNA anticodon to mRNA codon

Structureribosomal RNA (rRNA) & proteins2 subunitslargesmall

E

P

ASlide16

Ribosomes

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 chainE site (exit site)empty

tRNA leaves ribosome from exit site

Met

5'

3'UUAC

A

G

A

P

ESlide17

Building a polypeptide

InitiationmRNA, ribosome subunits, initiator

tRNA come togetherElongationadding amino acids based on codonsTerminationSTOP

codon = Release factor

1

2

3

LeuLeuLeuLeu

tRNA

Met

Met

Met

MetP

E

A

mRNA

5'

5'

5'

5'

3'

3'

3'

3'

U

U

A

A

A

A

C

C

C

A

U

U

G

G

G

U

U

A

A

A

A

C

C

C

A

U

U

G

G

G

U

U

A

A

A

A

C

C

C

A

U

U

G

G

G

U

U

A

A

A

C

C

A

U

U

G

G

G

A

C

Val

Ser

Ala

Trp

release

factor

A

A

A

C

C

U

U

G

G

3'Slide18

Can you tell the story?

DNA

pre-mRNA

ribosome

tRNA

amino

acids

polypeptidemature mRNA5' GTP cappoly-A taillarge ribosomal subunit

small ribosomal subunit

aminoacyl tRNAsynthetase

E

P

A

5'

3'

RNA polymerase

exon

intron

tRNA