Nucleic Acid Structure and Function

Nucleic Acid Structure Nucleic Acid Structure and Functionand Function

Structures of DNA and RNAStructures of DNA and RNA Duplication of DNA Duplication of DNA

Production of RNA and ProteinProduction of RNA and Protein

DNADNA

RNARNA

ProteinProtein

Information Flow From DNAInformation Flow From DNA

transcriptiontranscription

translationtranslation

replicationreplication(S phase)(S phase)

(G1 and G2(G1 and G2 phases)phases)

Gene: sequence of DNA that codes

for a protein

Macromolecules: Polymers Macromolecules: Polymers Made of Repeating MonomersMade of Repeating Monomers

MacromoleculeMacromolecule Monomer UnitMonomer UnitCarbohydratesCarbohydrates SugarsSugars

LipidsLipids Fatty acidsFatty acids

ProteinsProteins Amino acidsAmino acids

Nucleic AcidsNucleic Acids NucleotidesNucleotides

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 helixDouble helix Single Single folded chainfolded chain

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

phos

phat

ebase

Three Parts of Nucleotide StructureThree Parts of Nucleotide Structure

NitrogenousNitrogenousBase (1 of 5)Base (1 of 5)

OH

HO P O

O

5-Carbon Sugar5-Carbon Sugar

Phosphate GroupPhosphate Group

NNHCHC

NN CCCC

CC

CHCHNN

NN

NHNH22

CHCH22

HH

DeoxyriboseDeoxyriboseoror

RiboseRibose

OO

HH

OHOH HH

HHHH

DNA and RNA StructureDNA and RNA StructureDNADNA 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

Clarification PauseClarification Pause

Turn to a partner and identify the Turn to a partner and identify the differences between DNA and differences between DNA and RNA structureRNA structure

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 polynucleotide Two polynucleotide

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

Chemical BondingChemical Bonding

Covalent Covalent BondBond

StrongStrong Atoms Atoms Share Share ElectronsElectrons

Formation of Formation of NucleotidesNucleotidesand Chainsand Chains

HydrogenHydrogenBondBond

WeakWeak Atoms Atoms “Share” a “Share” a HydrogenHydrogen

Pairing of Pairing of Nucleotide Nucleotide Bases in Bases in Opposite Opposite ChainsChains

T AC G

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 replication is semiconservative.DNA replication is semiconservative.Each strand is used as a template to Each strand is used as a template to produce a new strand.produce a new strand.

AGCTAGCTAGCT TCGATCGATCGA

TCGATCGATCGA new

AGCTAGCTAGCT new

AGCTAGCTAGCT AGCTAGCTAGCT old

TCGATCGATCGA TCGATCGATCGA old


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

Outcome of DNA ReplicationOutcome of DNA Replication


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 chains2.2. Two old chainsTwo old chains3.3. One old and one new chainOne old and one new chain4.4. One helix has two new chains One helix has two new chains

and one has two old chainsand one has two old chains5.5. None of these is correct.None of these is correct.

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


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 RNAContains 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

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

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


InitiationInitiation mRNA binds to ribosomemRNA binds to ribosome First tRNA binds to mRNAFirst tRNA binds to mRNA

5’---AUGUUUCUCUGA---3’ 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-lys2.2. Arg-leu-gluArg-leu-glu3.3. Glu-leu-argGlu-leu-arg4.4. Asn-met-glyAsn-met-gly5.5. Lys-ile-glyLys-ile-gly

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Nucleic Acid Structure and Function