DNA, RNA and Protein How the Information in DNA Is Used to Build a Protein

DNA, RNA and ProteinDNA, RNA and Protein

How the Information in DNA How the Information in DNA Is Used to Build a ProteinIs Used to Build a Protein

DNADNA

RNARNA

ProteinProtein

Information Flow From DNAInformation Flow From DNA

transcriptiontranscription

translationtranslation

replicationreplication(before cell (before cell duplicates)duplicates)

(ongoing parts of (ongoing parts of cell metabolism)cell metabolism)

Gene: sequence of DNA that codes

for a protein

DNA and RNA StructureDNA and RNA Structure DNADNA RNARNA

Primary Primary StructureStructure

Chain of Chain of nucleotidesnucleotides

Chain of Chain of nucleotidesnucleotides

Secondary Secondary StructureStructure

Double Double helixhelix

Single Single folded chainfolded chain

Nucleotide = Nucleotide = phosphate + sugar + nitrogen-containing basephosphate + sugar + nitrogen-containing base

DNA and RNA StructureDNA and RNA Structure

DNADNA RNARNA

PurinePurine bases bases Adenine (A)Adenine (A)

Guanine (G)Guanine (G)

Adenine (A)Adenine (A)

Guanine (G)Guanine (G)

PyrimidinePyrimidine bases bases Cytosine (C)Cytosine (C)

Thymine (T)Thymine (T)

Cytosine (C)Cytosine (C)

Uracil (U)Uracil (U)

5-carbon sugar5-carbon sugar deoxyribosedeoxyribose riboseribose

PhosphatePhosphate POPO44 POPO44

OHOH OHOHOHOH HH

Nucleotide ChainNucleotide Chain

Nucleotides are joined Nucleotides are joined together by dehydration together by dehydration synthesissynthesis

The phosphate of one The phosphate of one nucleotide is joined to nucleotide is joined to sugar of next sugar of next nucleotide, forming a nucleotide, forming a “sugar-phosphate “sugar-phosphate backbone”backbone”

DNA StructureDNA Structure

•Two nucleotide Two nucleotide chains chains•In opposite In opposite orientations orientations•Held together Held together by hydrogen by hydrogen bonds bonds•Twisted into a Twisted into a helix helix

GG

AA

CC

AA

CC

TT

GG

TT

AA

TT

TT

AA

5’ endhas free phosphate

3’ endhas free sugar

3’ end

5’ endA pairs with T

G pairs with C

Applying Your KnowledgeApplying Your Knowledge

In the DNA double helix, which base In the DNA double helix, which base is paired with adenine? is paired with adenine?

1.1. AdenineAdenine2.2. CytosineCytosine3.3. GuanineGuanine4.4. ThymineThymine5.5. UracilUracil

DNA ReplicationDNA Replication•DNA chains separateDNA chains separate

•Each chain is used Each chain is used as a pattern to as a pattern to produce a new chain produce a new chain

•Each new DNA helix Each new DNA helix contains one “old” contains one “old” and one “new” chain and one “new” chain

DNA ReplicationDNA Replication

DNA replication requires DNA replication requires 1. Enzymes, including DNA polymerase 1. Enzymes, including DNA polymerase that adds nucleotides in a 5’ that adds nucleotides in a 5’3’ direction.3’ direction. 2. nucleotides 2. nucleotides 3. energy3. energy

5’—A G C T — 3’

3’—T C G A — 5’

A — 5’GC

G

3’— T

C T— 3’5’— A

Enzymes InvolvedEnzymes Involved

in DNA Replicationin DNA Replication

EnzymeEnzyme FunctionFunction

HelicaseHelicase Unwinds Double HelixUnwinds Double Helix

PrimasePrimase Produces RNA primer as Produces RNA primer as starter for DNA strandstarter for DNA strand

DNA PolymeraseDNA Polymerase Synthesizes DNA in a Synthesizes DNA in a

5’ 5’ 3’ direction from a primer 3’ direction from a primer

ExonucleaseExonuclease Removes RNA primersRemoves RNA primers

DNA ligaseDNA ligase Seals gaps in sugar-phosphate Seals gaps in sugar-phosphate backbonebackbone

4

Directionality of DNA ReplicationDirectionality of DNA Replication

Continuous Continuous SynthesisSynthesis

On the 3’On the 3’ 5’ template 5’ template

Discontinuous Discontinuous SynthesisSynthesis

On the 5’On the 5’ 3’ template 3’ template

Forms small Okasaki fragments that Forms small Okasaki fragments that are joined by DNA ligaseare joined by DNA ligase


After DNA replication, what is the composition After DNA replication, what is the composition of the new double-helical molecules?of the new double-helical molecules?

1.1. Two new chainsTwo new chains

2.2. Two old chainsTwo old chains

3.3. One old and one new chainOne old and one new chain

4.4. One helix has two new chains One helix has two new chains and one has two old chainsand one has two old chains

5.5. None of these is correct.None of these is correct.

5’

3’

5’

3’Your completed model will have two DNA chains, each with 9 nucleotides.

Building Your DNA Model

Join the phosphate of

one nucleotide to the sugar of the next one

One chain can have bases in any order, the

other chain must be

complementary

Transcription = Production of RNA UsingTranscription = Production of RNA Using DNA as a Template DNA as a Template

•DNA chains separateDNA chains separate

•ONE DNA chain is used ONE DNA chain is used as a pattern to produce as a pattern to produce an RNA chain an RNA chain

•RNA chain is releasedRNA chain is released and the DNA chains and the DNA chains reform the double-helix reform the double-helix

In DNA In RNA A U T A G C C G

Transcription Transcription

Transcription requires Transcription requires 1. Enzymes, including RNA polymerase 1. Enzymes, including RNA polymerase that adds nucleotides in a 5’ that adds nucleotides in a 5’3’ direction. 3’ direction. 2. nucleotides2. nucleotides 3. energy3. energy

3’---TACAAAGAGACT---5’ 5’---ATG TTTCTC TGA---3’

3’---TACAAA GAGACT---5’ DNA template

5’---ATG TTTCTC TGA---3’

5’---AUGUUUCUCUGA---3’ mRNA

5


What is the sequence of an RNA molecule What is the sequence of an RNA molecule transcribed from a DNA template strand transcribed from a DNA template strand that reads 3’-ATG-5’?that reads 3’-ATG-5’?

1.1. 5’-TAC-3’5’-TAC-3’2.2. 5’-CAU-3’5’-CAU-3’3.3. 5’-AUG-3’5’-AUG-3’4.4. 5’-UAC-3’5’-UAC-3’5.5. 3’-TAC-5’3’-TAC-5’

Products of TranscriptionProducts of Transcription

• Messenger RNAMessenger RNA

Contains the code words for Contains the code words for the sequence of amino the sequence of amino acids in a specific proteinacids in a specific protein

CODON = group of three CODON = group of three nucleotides acting as a nucleotides acting as a code word for an amino acidcode word for an amino acid

Interrupted Genes Interrupted Genes

Eukaryotic Genes have interruptions Eukaryotic Genes have interruptions within regions coding for protein within regions coding for protein

intron = interrupting sequenceintron = interrupting sequence

exon = portion of coding regionexon = portion of coding region

intron 1intron 1 intron 2intron 2Exon 1Exon 1 Exon 2Exon 2 Exon 3Exon 3

mRNA ProcessingmRNA ProcessingDNADNA

Add 5’ capAdd 5’ cap

intron 1intron 1 intron 2intron 2Exon 1Exon 1 Exon 2Exon 2 Exon 3Exon 3GG

intron 1intron 1 intron 2intron 2Exon 1Exon 1 Exon 2Exon 2 Exon 3Exon 3GG AAAAAAAA……AAAAAAAA……

Remove IntronsRemove IntronsSplice Exons Splice Exons together together

Add 3’ poly-A tailAdd 3’ poly-A tail

Transcription Transcription

Exon 1Exon 1 Exon 2Exon 2 Exon 3Exon 3GG AAAAAAAA……AAAAAAAA……

Primary transcript RNAPrimary transcript RNAintron 1intron 1 intron 2intron 2Exon 1Exon 1 Exon 2Exon 2 Exon 3Exon 3

5’5’ 3’3’

Mature mRNAMature mRNA leaves for cytoplasm leaves for cytoplasm

In nucleusIn nucleusintron 1intron 1 intron 2intron 2Exon 1Exon 1 Exon 2Exon 2 Exon 3Exon 3

X X X X

Products of TranscriptionProducts of Transcription • Transfer RNATransfer RNA

““Translates” the message by Translates” the message by bringing a specific amino acid into bringing a specific amino acid into the correct position on the growing the correct position on the growing protein chainprotein chain

Has ANTICODON = a group of Has ANTICODON = a group of three nucleotides on a tRNA that three nucleotides on a tRNA that recognizes a mRNA codonrecognizes a mRNA codon

Has amino acid attachment siteHas amino acid attachment site

mRNA

In mRNA In tRNAIn mRNA In tRNA A UA U

U AU A

G CG C

C GC G

GeneticGenetic Code Code

Chart is written as a CODON dictionary, reading 5’Chart is written as a CODON dictionary, reading 5’3’3’

Products of TranscriptionProducts of Transcription • Ribosomal RNARibosomal RNA One of the structural One of the structural

components of the components of the ribosomeribosome

Ribosome = organelle Ribosome = organelle where protein where protein synthesis occurssynthesis occurs

Has sites to bind both Has sites to bind both mRNA and tRNAmRNA and tRNA

small ribosomal subunit

for tRNA

for tRNA

mRNA binding site


Which molecule contains the information Which molecule contains the information for assembling the amino acids in the for assembling the amino acids in the correct order in the protein? correct order in the protein?

1.1. rRNArRNA2.2. tRNAtRNA3.3. mRNAmRNA4.4. All of theseAll of these5.5. None of theseNone of these

5’

3’

5’

3’Your completed messenger RNA will have 9 nucleotides.


Choose one DNA chain as the template

for RNA

Read the template from

3’5’ to produce the mRNA from

5’3’

Translation Translation

At the ribosome, codons in mRNA are At the ribosome, codons in mRNA are recognized by tRNA anticodons to place recognized by tRNA anticodons to place amino acids in the specific sequence specified amino acids in the specific sequence specified by the DNA. by the DNA.

Three Stages of Translation:Three Stages of Translation: Initiation- assemble components to start processInitiation- assemble components to start process Elongation- add amino acids in repeated cyclesElongation- add amino acids in repeated cycles Termination- release protein productTermination- release protein product

6


InitiationInitiation

mRNA binds to ribosomemRNA binds to ribosome

First tRNA binds to mRNAFirst tRNA binds to mRNA


UAC

met


ElongationElongation

Next tRNA binds to mRNA Next tRNA binds to mRNA

5’---AUGUUUCUCUGA---3’ mRNA UAC

met phe

AAA


ElongationElongation Amino acids are joined Amino acids are joined First tRNA is releasedFirst tRNA is released


UAC met phe

AAA


ElongationElongation Ribosome moves by one codonRibosome moves by one codon


UAC met phe

AAA


Elongation (second cycle)Elongation (second cycle) Next tRNA binds to mRNA Next tRNA binds to mRNA


UAC met phe

AAA GAG

leu


Elongation (second cycle)Elongation (second cycle) Amino acids are joinedAmino acids are joined Second tRNA is releasedSecond tRNA is released


UAC met phe

AAA

GAG

leu


Elongation (second cycle)Elongation (second cycle) Ribosome moves by one codonRibosome moves by one codon


UAC met phe

AAA

GAG

leu


TerminationTermination Termination factor binds to stop codonTermination factor binds to stop codon


UAC met phe

AAA

GAG

leu

T


TerminationTermination Protein chain is releasedProtein chain is released Other components separateOther components separate


UAC met phe

AAA

GAG

leu

T


If the mRNA sequence for codons 5, 6, and 7 of If the mRNA sequence for codons 5, 6, and 7 of a protein is 5’-AAG-AUU-GGA-3’, what is a protein is 5’-AAG-AUU-GGA-3’, what is the amino acid sequence in the protein? the amino acid sequence in the protein?

1.1. Gly-ile-lysGly-ile-lys

2.2. Arg-leu-gluArg-leu-glu

3.3. Glu-leu-argGlu-leu-arg

4.4. Asn-met-glyAsn-met-gly

5.5. Lys-ile-glyLys-ile-gly

Your completed model will have 3 tRNAs, one for each codon in mRNA. Show the name of the amino acid carried by each tRNA.

Serin

e


Attach 3 bases to the tRNA to

form the anticodon

Read the CODON from 5’3’ to

find the name of the amino acid

CO

DO

N

Summary of Completed DNA ModelSummary of Completed DNA Model • One DNA double helix, two chains of 9 One DNA double helix, two chains of 9

nucleotides eachnucleotides each– one chain can have any sequenceone chain can have any sequence– second chain must be complementarysecond chain must be complementary

• One chain of mRNA, 9 nucleotides longOne chain of mRNA, 9 nucleotides long– must be complementary to one of the two must be complementary to one of the two

DNA chains (DNA template is 3’DNA chains (DNA template is 3’5’, 5’, mRNA is 5’mRNA is 5’3’)3’)

• Three tRNAs with appropriate amino Three tRNAs with appropriate amino acids attachedacids attached– tRNA anticodons must match mRNA codonstRNA anticodons must match mRNA codons

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DNA, RNA and Protein How the Information in DNA Is Used to Build a Protein