Nucleic Acids Nucleic Acids andand

Protein SynthesisProtein Synthesis

Nucleic AcidsNucleic AcidsDNADNA Deoxyribonucleic AcidDeoxyribonucleic Acid

RNARNA Ribonucleic AcidRibonucleic Acid

DNADNADouble stranded helixDouble stranded helixNever leaves the nucleusNever leaves the nucleusWatson, Crick, Wilkins won Watson, Crick, Wilkins won

Nobel Prize in 1962 Nobel Prize in 1962 Franklin died in 1958 never Franklin died in 1958 never

recognizedrecognized

DNADNA

NucleotideNucleotide

Building Blocks of nucleic acids are Building Blocks of nucleic acids are NUCLEOTIDES!NUCLEOTIDES!Phospate groupPhospate groupSugar molecule (deoxyribose)Sugar molecule (deoxyribose)Nitrogenous basesNitrogenous bases

Nitrogenous Bases of DNANitrogenous Bases of DNA

How do the N-Bases pair up?How do the N-Bases pair up?

A-T (2 bonds)A-T (2 bonds)G-C (3 bonds)G-C (3 bonds)

How Does DNA How Does DNA Replicate?Replicate?

1. double helix unwinds1. double helix unwinds 2. Each chain serves as a template for new 2. Each chain serves as a template for new

nucleoide chainnucleoide chain 3. point at which 2 chains separate is called the 3. point at which 2 chains separate is called the

REPLICATION FORK.REPLICATION FORK. 4. HELICASE = the enzyme that separates the 4. HELICASE = the enzyme that separates the

chains (breaks H bonds)chains (breaks H bonds) 5. DNA POLYMERASE moves along the chains and 5. DNA POLYMERASE moves along the chains and

helps assemble new nucleotides forming new chains helps assemble new nucleotides forming new chains (3(3’’ to 5 to 5’’ ONLY) ONLY)

DNA LIGASE – ligates 5DNA LIGASE – ligates 5’’ to 3 to 3’’ (DNA polymerase (DNA polymerase brings the nucleotides)brings the nucleotides)

DNA replication continue…DNA replication continue…

The 3The 3’’ sugar has an –OH GROUP sugar has an –OH GROUPThe 5The 5’’ sugar has a PHOSPHATE GROUP sugar has a PHOSPHATE GROUP

LEADING STRAND – formed from 3LEADING STRAND – formed from 3’’-5-5’’LAGGING STRAND – formed from 5LAGGING STRAND – formed from 5’’- 3- 3’’

with the help of DNA LIGASE!with the help of DNA LIGASE!OKAZAKI FRAGMENTS – fragments that OKAZAKI FRAGMENTS – fragments that

will be ligated togetherwill be ligated together

Can you see how DNA is making Can you see how DNA is making an exact copy of itself!an exact copy of itself!

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This a little more difficultThis a little more difficult

Can you figure out the diagram?Can you figure out the diagram?

Simplest Illustration of DNA Simplest Illustration of DNA replication…replication…

What is a What is a mutationmutation????

A CHANGE in the A CHANGE in the nucleotide sequence at nucleotide sequence at even ONE location!!even ONE location!!

ProtectionProtectionAbout 1 in a billion nucleotides in About 1 in a billion nucleotides in

DNA is INCORRECTLY paired.DNA is INCORRECTLY paired.DNA polymerase proofreads and DNA polymerase proofreads and

removes nucleotides that base pair removes nucleotides that base pair incorrectly.incorrectly.

DNA polymerase & DNA ligase DNA polymerase & DNA ligase also also repair damage caused by ultraviolet repair damage caused by ultraviolet light, xrays, and toxic chemicalslight, xrays, and toxic chemicals

Archibald Garrod Archibald Garrod 1909 English Physician1909 English Physician

Suggested that genes dictate phenotypes Suggested that genes dictate phenotypes through enzymes, the proteins that through enzymes, the proteins that catalyze chemical processes in the cellcatalyze chemical processes in the cell

GENOTYPEGENOTYPE genetic make up genetic make upPHENOTYPE PHENOTYPE physical appearance physical appearanceDNA –(transcription)DNA –(transcription) RNA – RNA –

(translation)(translation) protein synthesis protein synthesisGenotype ------Genotype ------ phenotype phenotype

Garrod 1900Garrod 1900’’ss

Children -> defect in 2 a.a. due to defect in Children -> defect in 2 a.a. due to defect in the enz. That helps make the a.athe enz. That helps make the a.a

Phenylalanine->PKUPhenylalanine->PKUTyrosine ->albinismTyrosine ->albinismGeneGeneenzymeenzymeamino acid (canamino acid (can’’t be t be

made)made)CouldnCouldn’’t prove it due to lack of technologyt prove it due to lack of technology

George Beadle & Edward George Beadle & Edward TatumTatum

19401940’’s American s American GeneticistsGeneticistsONE GENE ONE ENZYMEONE GENE ONE ENZYME (polypeptide) (polypeptide)

HYPOTHESIS: the function of a gene is HYPOTHESIS: the function of a gene is to dictate the production of a specific to dictate the production of a specific enzyme. enzyme.

Experimented with Experimented with bread moldbread mold lacked lacked an enzyme in a metabolic pathway that an enzyme in a metabolic pathway that produced some molecules that mold produced some molecules that mold needed to produce an amino acid called needed to produce an amino acid called arginine.arginine.

Tatum & Beadle 1958 Nobel PrizeTatum & Beadle 1958 Nobel Prize

Proved Garrod correctProved Garrod correctBread mold -> can make all of itBread mold -> can make all of it’’s own a.a. s own a.a.

that it needsthat it needsGene -> enzyme -> amino acidGene -> enzyme -> amino acidOne gene = enzymeOne gene = enzymeOne gene = one protein!!One gene = one protein!!

RNARNARIBONUCLEIC ACIDRIBONUCLEIC ACID

SINGLE STRANDEDSINGLE STRANDED

RESPONSIBLE FOR BRINGING RESPONSIBLE FOR BRINGING THE GENETIC INFO. FROM THE THE GENETIC INFO. FROM THE NUCLEUS TO THE CYTOSOL!NUCLEUS TO THE CYTOSOL!

RNA NucleotideRNA Nucleotide

Phosphate groupPhosphate group

Sugar molecule (ribose)Sugar molecule (ribose)

Nitrogenous basesNitrogenous basesAdenine – URACILAdenine – URACILCytosine - guanineCytosine - guanine

3 Kinds of RNA3 Kinds of RNAmRNAmRNA – (messenger) brings info from – (messenger) brings info from

DNA in nucleus to cytosol in eukaryotic DNA in nucleus to cytosol in eukaryotic cells (uncoiled)cells (uncoiled)

tRNAtRNA –(transfer) brings amino acids to –(transfer) brings amino acids to mRNA for translation (hairpin shape)mRNA for translation (hairpin shape)

rRNArRNA –(ribosomal) most abundant, rRNA –(ribosomal) most abundant, rRNA makes up the ribosomes where proteins makes up the ribosomes where proteins are made (globular)are made (globular)

TRANSCRIPTION!!TRANSCRIPTION!!DNA DNA RNA RNA

1.RNA polymerase-initiates transcription by 1.RNA polymerase-initiates transcription by binding to region on DNA called binding to region on DNA called PROMOTER PROMOTER (causes DNA to separate)-(causes DNA to separate)-INITIATION PHASEINITIATION PHASE

2. only ONE of the DNA chains will be used for 2. only ONE of the DNA chains will be used for transcription ittranscription it’’s called the s called the TEMPLATETEMPLATE (promoter (promoter dictates which of the two strands will be used)dictates which of the two strands will be used)

3. 3. RNA POLYMERASERNA POLYMERASE – attached to first DNA – attached to first DNA nucleotide of template chain – then begins nucleotide of template chain – then begins adding complementary RNA nucleotides-adding complementary RNA nucleotides-ELONGATION PHASEELONGATION PHASE

Cont. TranscriptionCont. Transcription

4. transcription continues until RNA 4. transcription continues until RNA polymerase reaches a polymerase reaches a TERMINATION TERMINATION SIGNALSIGNAL on the DNA- on the DNA-TERMINATION TERMINATION PHASEPHASE

5. RNA polymerase releases both the 5. RNA polymerase releases both the DNA mol. And newly formed RNA mol. Are DNA mol. And newly formed RNA mol. Are transcribed in this way (all three!!!)transcribed in this way (all three!!!)

RNARNA

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RNA replicationsRNA replications

PROKARYOTESPROKARYOTES

Transcription and Transcription and translation occur in the translation occur in the SAME place!SAME place!

NO NUCLEUS!NO NUCLEUS!

EukaryotesEukaryotes1. Before RNA leaves the nucleus:1. Before RNA leaves the nucleus: G (guanine) G (guanine) capcap is attached is attached A (adenine)A (adenine) tail tail is attached is attached ““manymany””

2. These protect the RNA from attack by 2. These protect the RNA from attack by cellular enzymes and help ribosomes to cellular enzymes and help ribosomes to recognize the mRNA (cap & tail are NOT recognize the mRNA (cap & tail are NOT translated)translated)

Cont. EukaryotesCont. Eukaryotes3. 3. INTRONSINTRONS (non coding sequence) are (non coding sequence) are

removed removed

4. 4. EXONSEXONS (part of gene that are (part of gene that are expressed) are joined to produce a mRNA expressed) are joined to produce a mRNA molecule with a continuous coding molecule with a continuous coding sequence.sequence.

NOW RNA CAN LEAVE THE NUCLEUS!NOW RNA CAN LEAVE THE NUCLEUS!

Protein SynthesisProtein Synthesis

PROTEINS CARRY OUT PROTEINS CARRY OUT THE GENETIC THE GENETIC INSTRUCTIONS INSTRUCTIONS ENCODED IN AN ENCODED IN AN ORGANISMORGANISM’’S DNA!!!!S DNA!!!!

TRANSLATIONTRANSLATIONThe process of assembling from The process of assembling from

info. Encoded in a mRNA!info. Encoded in a mRNA!1. mRNA leaves nucleus1. mRNA leaves nucleus2. mRNA migrates to ribosome in cytosol 2. mRNA migrates to ribosome in cytosol

for protein synthesisfor protein synthesis3.amino acids floating in cytosol are 3.amino acids floating in cytosol are

transported to ribosomes by tRNA transported to ribosomes by tRNA moleculemolecule

4. peptide bonds join the amino acids to 4. peptide bonds join the amino acids to make polypeptide chainmake polypeptide chain

Vocabulary!Vocabulary!

1. GENETIC CODE: correlation between a 1. GENETIC CODE: correlation between a nucleotide sequence and an amino acid nucleotide sequence and an amino acid sequencesequence

2. CODON2. CODON 3 mRNA nucleotides, codes for a 3 mRNA nucleotides, codes for a specific amino acid (64)specific amino acid (64)

3. START CODON (AUG) & a.a. methionine3. START CODON (AUG) & a.a. methionine 4. STOP CODON (UAA, UAG, UGA)4. STOP CODON (UAA, UAG, UGA) 5. ANTICODON – 3 tRNA nucleotides carrying 5. ANTICODON – 3 tRNA nucleotides carrying

a specific amino acid!a specific amino acid!

Protein SynthesisProtein Synthesis

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Protein SynthesisProtein Synthesis

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Protein SynthesisProtein Synthesis

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THE SUMMARY!THE SUMMARY!

RibosomeRibosomefactory for polypeptidesfactory for polypeptides

Two subunits:Two subunits:Large subunit (top)Large subunit (top)Small subunit (bottom)Small subunit (bottom)

P site – holds tRNA carrying growing polypeptideP site – holds tRNA carrying growing polypeptideA Site – holds tRNA carrying the next amino acid A Site – holds tRNA carrying the next amino acid

to be addedto be added

Initiation Codon Marks the Start of Initiation Codon Marks the Start of an mRNA messagean mRNA message

3 PHASES:3 PHASES:

1. INITIATION1. INITIATION2. ELONGATION2. ELONGATION3. TERMINATION3. TERMINATION

INITIATION ( 2 steps)INITIATION ( 2 steps)

A) An mRNA mol. Binds to a A) An mRNA mol. Binds to a small small ribosomal subunitribosomal subunit. A special . A special initiator initiator tRNA binds to the specific codon called tRNA binds to the specific codon called the START CODON (UAC binds to start the START CODON (UAC binds to start codon AUG codon AUG methionine) methionine)

B) A B) A large ribosomal subunitlarge ribosomal subunit binds to binds to the small one creating a functional the small one creating a functional ribosome. The initiator tRNA fits into the ribosome. The initiator tRNA fits into the P P sitesite of the ribosome. of the ribosome.

Elongation and TerminationElongation and Termination

Elongation adds amino acids Elongation adds amino acids to the polypeptide chain until a to the polypeptide chain until a stop codon terminates stop codon terminates translation.translation.

3 Steps of Elongation3 Steps of Elongation

1. 1. Codon recognitionCodon recognition anticodon of anticodon of incoming tRNA carrying amino acid pairs incoming tRNA carrying amino acid pairs with mRNA codon in A site.with mRNA codon in A site.

2. 2. Peptide bond formationPeptide bond formation polypeptide separates from tRNA (fr. P polypeptide separates from tRNA (fr. P site). Peptide bond forms between amino site). Peptide bond forms between amino acid in P & A site acid in P & A site ribosome catalyzes ribosome catalyzes formation of bond.formation of bond.CONTINUE…..CONTINUE…..

CONTINUE…CONTINUE…

3. 3. TranslationTranslation P site tRNA now leaves P site tRNA now leaves ribosome, the ribosome translocates (moves) ribosome, the ribosome translocates (moves) the tRNA in the A site, with its attached the tRNA in the A site, with its attached polypeptide to the P site. The codon and polypeptide to the P site. The codon and anticodon remain bonded and the mRNA and anticodon remain bonded and the mRNA and tRNA move as a unit . This movement brings tRNA move as a unit . This movement brings into the A site the next mRNA codon to be into the A site the next mRNA codon to be translated and process can start again! translated and process can start again! ELONGATION CONTINUES UNTIL A STOP ELONGATION CONTINUES UNTIL A STOP CODON REACHES A SITE.CODON REACHES A SITE.