Molecular Biology Molecular Biology of the Geneof the Gene

PART 2PART 2Debbi Ann MorrissetteDebbi Ann Morrissette

Graduate Student ResearcherGraduate Student ResearcherLaboratory of Molecular Laboratory of Molecular

NeuropathogenesisNeuropathogenesisUniversity of California, IrvineUniversity of California, Irvine

PART 1PART 1

Structure of DNAStructure of DNA DNA ReplicationDNA Replication DNA vs. RNADNA vs. RNA

PART 2PART 2 Flow of Genetic InfoFlow of Genetic Info MutationsMutations CloningCloning DifferentiationDifferentiation X Chromosome InactivationX Chromosome Inactivation

The 2 Main Functions of The 2 Main Functions of DNADNA

Passing genetic information to Passing genetic information to daughter cellsdaughter cells Through DNA replicationThrough DNA replication

Directing the synthesis of proteinsDirecting the synthesis of proteins Through Through transcriptiontranscription of the DNA code of the DNA code

and and translationtranslation of the nucleotide code of the nucleotide code into an amino acid sequenceinto an amino acid sequence

Basic Nucleotide Basic Nucleotide StuctureStucture

Sugar

Phosphate

Nitrogenous Base

HDeoxyribose

Sugar

Phosphate

Nitrogenous Base

Sugar

Phosphate

Nitrogenous Base

DNA vs. RNADNA vs. RNA

Deoxyribonucleic Acid Ribonucleic Acid

Nitrogenous Bases

T C A GNitrogenous Bases

U C A G

OH

Uracil

Thymine HCH3

Ribose

Base Pairing Base Pairing

DNA:DNA (replication)DNA:DNA (replication) A:TA:T C:GC:G

T

C G

A

G C

A

A

T

T

DNA:RNA (transcription)DNA:RNA (transcription) A:UA:U C:GC:G T:AT:A

T A AC CA

C

T

C C AA

U

TT

GG

G T T A ACUAC

GG

T A

From DNA to ProteinsFrom DNA to Proteins

DNA

RNA

Protein

Translation

Transcription

Genotype

Phenotype

DNA molecule

Gene 1

Gene 2

Gene 3

AAAAA C C GG C

CCGG G U U U UUUU

AADNA strand

Transcription

RNA

Translation

Polypeptide

Amino acid

Codon

OvervieOvervieww

Genotype

Phenotype

Note:

U pairs with A

A still pairs with T

The RNA “Players”The RNA “Players” mRNA = messenger mRNA = messenger

RNA RNA ““The Mailman”The Mailman”

rRNA = ribosomal rRNA = ribosomal RNARNA ““The Recruiter”The Recruiter”

tRNA = transfer RNA tRNA = transfer RNA ““The Translator”The Translator”

G A A U UG U U A G

TranscriptioTranscriptionn

TerminationTermination RNA reaches the RNA reaches the terminatorterminator sequence sequence on the DNA strand on the DNA strand and releases from and releases from the DNAthe DNA

ElongationElongation RNA polymerase moves RNA polymerase moves

along the DNA strand along the DNA strand adding complementary adding complementary RNA nucleotides to make RNA nucleotides to make the mRNA strandthe mRNA strand

InitiationInitiation RNA polymerase attaches RNA polymerase attaches

to the to the promoterpromoter sequence sequence on DNA strand on DNA strand

RNA polymerase

Initiation

PromoterDNA

TerminatorDNA

Initiation

Elongation

TerminationGrowingRNA

Completed RNA RNApolymerase

DNA of gene

Elongation –A Closer Elongation –A Closer LookLook

RNApolymerase

RNA nucleotides

Templatestrand of DNA

Direction oftranscription

Newly made RNA

T A AC CA

CT

C C AA

U

TT

GG

U

G T T AA

CCUAC

GG

T A

mRNAmRNA

Following Following transcription, the transcription, the “message” is “message” is brought from the brought from the nucleus to the nucleus to the cytoplasm.cytoplasm.

_______________

_______________

_______________

The RNA “Players”The RNA “Players” mRNA = messenger mRNA = messenger

RNA RNA ““The Mailman”The Mailman”

rRNA = ribosomal rRNA = ribosomal RNARNA ““The Recruiter”The Recruiter”

tRNA = transfer RNA tRNA = transfer RNA ““The Translator”The Translator”

G A A U UG U U A G

TranslationTranslation

rRNA recruits both mRNA and tRNArRNA recruits both mRNA and tRNA

rRNA

G A A U UG U U A G

mRNA

tRNA

Met

Small ribosomalsubunit

CAUA GU

Large ribosomalsubunit

tRNAtRNA tRNA must tRNA must

translate the RNA translate the RNA message carried message carried by mRNAby mRNA

Translation of RNA Translation of RNA nucleotides to nucleotides to amino acidsamino acids

tRNA has to be tRNA has to be “bilingual”“bilingual”

Anticodon

Amino acidattachment site

Translation of the Translation of the Genetic CodeGenetic Code

3 nucleotide bases = 1 amino acid3 nucleotide bases = 1 amino acid Every group of 3 mRNA nucleotides = Every group of 3 mRNA nucleotides =

CodonCodon Corresponding triplet of bases on the Corresponding triplet of bases on the

tRNA = AnticodontRNA = AnticodonCCGG G U U U UUUU

Amino acid

Codon

Anticodon

Amino acidattachment site

The mRNA to Amino Acid The mRNA to Amino Acid DictionaryDictionary

AUG =StartAUG =Start UAA and UAG = StopUAA and UAG = Stop The code is The code is

redundant:redundant: Just as “drink” and Just as “drink” and

“beverage” both “beverage” both representrepresent

GCU and GCG both GCU and GCG both code for alaninecode for alanine

Second base

Fir

st

bas

e

Th

ird

bas

e

UUU

U C A G

G

AA

C

U

U

U

C

A

C

A

G

G

U

C

A

G

U

C

A

G

UUC

UUA

UUG

CUU

CUC

CUA

CUG

AUU

AUC

AUA

Leu

lle

AUG Met orstart

GUU

GUC

GUA

GUG

Val Ala

Thr

GCG

GCA

GCC

GCU

ACG

ACA

ACC

ACU

Pro

CCG

CCA

CCC

CCU

UCG

UCA

UCC

UCU

Ser

Tyr CysUAU

UAC

UAA

UAG

CAU

CAC

CAA

CAG

His

Gln

Stop

Stop

UGU

UGC

UGA

UGG Trp

Stop

Arg

CGU

CGU

CGA

CGG

Asn

Lys

Asp

Glu

Gly

Arg

SerAAU AGU

AAC

AAA

AAG

GAU

GAG

AGC

AGA

AGG

GGU

GGC

GGG

Phe

Leu

GAC

GAA

GAG

GGA

Translation OverviewTranslation Overview

IntitiationIntitiation

ElongationElongation

TerminationTermination

TranslationTranslation

IntitiationIntitiation

Initiator tRNA binds to START codonInitiator tRNA binds to START codon

Met

CAU

A GU

Amino acid

tRNA rRNA

mRNAAnticodon

Codon

TranslationTranslationPolypeptide

mRNA Codons

Anticodon

Aminoacid

Condon recognition

Peptide bondformation

Newpeptidebond

Translocation

Stop codon

mRNAmovement

ElongationElongation Codon recognitionCodon recognition

TranslocationTranslocation

Peptide bond formationPeptide bond formation rRNA also functions as an enzymerRNA also functions as an enzyme

TranslationTranslation

Stop codon

Growingpolypeptide

New peptidebond forming

mRNA

Polypeptide

Codons

Elongation

Termination

The ribosome recognizesa stop codon. The poly-peptide is terminatedand released.

TerminationTermination

STOP codon on mRNASTOP codon on mRNA Polypeptide (protein) is Polypeptide (protein) is

releasedreleased

SummarySummary The DNA code that The DNA code that

makes up a gene makes up a gene is is transcribedtranscribed into into mRNAmRNA

rRNA brings rRNA brings mRNA and tRNA mRNA and tRNA togethertogether

tRNA tRNA translatestranslates the code from the code from nucleotides to nucleotides to amino acidsamino acids

Newly made Newly made protein is releasedprotein is released

Genotype

Phenotype