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DNA or Protein?DNA or Protein? Walter Sutton discovered Walter Sutton discovered
chromosomes chromosomes were made were made of of DNA and ProteinDNA and Protein
However, scientists were However, scientists were NOTNOT sure which one sure which one (protein or DNA) was (protein or DNA) was the the actual genetic material actual genetic material of the cellof the cell
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DNA!DNA! Frederick GriffithFrederick Griffith in in
1928 showed the 1928 showed the DNADNA was the cell’s was the cell’s genetic materialgenetic material
Watson & CrickWatson & Crick in in the 1950’s the 1950’s builtbuilt the the 11stst model of DNA model of DNA
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Structure of DNAStructure of DNA DNA is DNA is made of subunits made of subunits
called called nucleotidesnucleotides DNA nucleotides are DNA nucleotides are
composed of a composed of a phosphatephosphate, , deoxyribosedeoxyribose sugar, sugar, and and a a nitrogen-containing basenitrogen-containing base
The 4 bases in DNA are: The 4 bases in DNA are: adenine (A), adenine (A), thymine (T),thymine (T), guanine (G),guanine (G), and cytosine (C) and cytosine (C)
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Base Pairing RuleBase Pairing Rule• Watson and Crick showed that Watson and Crick showed that DNA DNA
is a is a double helixdouble helix• AA (adenine) pairs (adenine) pairs with with TT (thymine) (thymine)• CC (cytosine) pairs (cytosine) pairs with with GG (guanine) (guanine)
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Nitrogen RingsNitrogen Rings• PurinesPurines have have doubledouble ringsrings of of
carbon-nitrogen (G, A)carbon-nitrogen (G, A)• PyrimidinesPyrimidines have have singlesingle
carbon-nitrogen carbon-nitrogen ringsrings (C, T) (C, T)• This is called This is called
complementary base pairingcomplementary base pairing because a because a purinepurine is always is always paired with a paired with a pyrimidinepyrimidine
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.5’ to 3’ Sugars5’ to 3’ Sugars
When the DNA When the DNA double helixdouble helix unwinds, it unwinds, it resembles a ladderresembles a ladder The The sidessides of the ladder are the of the ladder are the sugar-phosphate backbonessugar-phosphate backbones The The rungsrungs of the ladder are of the ladder are the the complementary paired complementary paired basesbasesThe two DNA strands are The two DNA strands are anti-anti-parallelparallel (they run in opposite (they run in opposite directions)directions)
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Steps in Steps in DNA DNA ReplicationReplication
Occurs when Occurs when chromosomes duplicatechromosomes duplicate (make copies)(make copies) An An exact copyexact copy ofof the the DNADNA is is produced produced with the aid of the enzyme with the aid of the enzyme DNA polymeraseDNA polymerase Hydrogen bondsHydrogen bonds between bases between bases breakbreak and enzymes “unzip” the and enzymes “unzip” the moleculemolecule Each Each old strandold strand of nucleotides of nucleotides servesserves as a as a templatetemplate for each new strand for each new strand New nucleotidesNew nucleotides move into move into complementary positions are joined complementary positions are joined by DNA polymeraseby DNA polymerase
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Two New, Two New, Identical Identical
DNA DNA Strands Strands Result Result from from
ReplicatiReplicati
onon
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RNA Differs from DNARNA Differs from DNA1.1. RNARNA has a sugar has a sugar riboseribose
DNADNA has a sugar has a sugar deoxyribosedeoxyribose
2.2. RNARNA contains the base contains the base uracil uracil (U)(U)
DNADNA has has thymine (T)thymine (T)
3.3. RNARNA molecule is molecule is single-single-strandedstranded
DNADNA is is double-strandeddouble-stranded
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.
Three Types of RNAThree Types of RNA• Messenger RNAMessenger RNA (mRNA)(mRNA)
carriescarries genetic genetic infoinformation rmation toto the the ribosomesribosomes
• Ribosomal RNARibosomal RNA (rRNA)(rRNA),, along with protein, along with protein, makes makes upup the the ribosomesribosomes
• Transfer RNA (tRNA)Transfer RNA (tRNA) transferstransfers amino acids to the amino acids to the ribosomesribosomes where proteins where proteins are synthesizedare synthesized
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Protein SynthesisProtein Synthesis The production (synthesis) of The production (synthesis) of
polypeptide chains polypeptide chains (proteins)(proteins) Two phases:Two phases:
Transcription Transcription & & TranslationTranslation mRNA must be mRNA must be processed before processed before
it leaves the nucleusit leaves the nucleus of of eukaryotic cellseukaryotic cells
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TranscriptionTranscription
TranslationTranslation
DNA
mRNA
Ribosome
Protein
Prokaryotic CellProkaryotic Cell
DNA DNA RNA RNA ProteinProtein
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DNA DNA RNA RNA ProteinProtein
Nuclearmembrane
TranscriptionTranscription
RNA ProcessingRNA Processing
TranslationTranslation
DNA
Pre-mRNA
mRNA
Ribosome
Protein
EukaryotEukaryotic Cellic Cell
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Pathway to Making a Pathway to Making a ProteinProtein
DNADNA
mRNAmRNA
tRNA (ribosomes)tRNA (ribosomes)
ProteinProtein
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Genes & ProteinsGenes & Proteins ProteinsProteins are made of are made of amino amino
acidsacids linked together by linked together by peptide bondspeptide bonds
2020 different amino acids different amino acids existexist Amino acids chains are called Amino acids chains are called
polypeptidespolypeptides Segment of DNA that codes Segment of DNA that codes
for the amino acid sequence for the amino acid sequence in a protein are called in a protein are called genesgenes
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Two Parts of Protein Two Parts of Protein SynthesisSynthesis
TranscriptionTranscription makes an RNAmakes an RNA molecule molecule complementary tocomplementary to a portion of a portion of DNADNA
TranslationTranslation occursoccurs whenwhen the the sequence of bases of sequence of bases of mRNAmRNA DIRECTSDIRECTS the the sequence of sequence of amino acidsamino acids in a polypeptide in a polypeptide
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Genetic CodeGenetic Code DNA contains a DNA contains a triplet codetriplet code Every three bases on DNAEvery three bases on DNA
standsstands for for ONE amino acidONE amino acid Each three-letter unitEach three-letter unit on on mRNAmRNA
is is called a called a codoncodon Most amino acids have more Most amino acids have more
than one codon!than one codon! There are There are 20 amino acids20 amino acids with with
a possible 64 different tripletsa possible 64 different triplets The code is nearly The code is nearly universal universal
among living organismsamong living organisms
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Overview of Overview of TranscriptionTranscription
During During transcriptiontranscription in the in the nucleus, a segment of DNA nucleus, a segment of DNA unwinds and unzips, and the unwinds and unzips, and the DNA DNA serves as aserves as a template for template for mRNA formationmRNA formation
RNA polymeraseRNA polymerase joins the RNA joins the RNA nucleotides so that the nucleotides so that the codons codons in mRNA are complementaryin mRNA are complementary to to the triplet code in DNAthe triplet code in DNA
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Steps in Steps in TranscriptionTranscription
The transfer of information in the The transfer of information in the nucleusnucleus from a from a DNADNA molecule to an molecule to an RNARNA molecule molecule
Only 1 Only 1 DNADNA strand serves as the strand serves as the templatetemplate
Starts at promoterStarts at promoter DNADNA (TATA box) (TATA box) Ends at terminatorEnds at terminator DNADNA (stop) (stop) When complete, When complete, pre-RNApre-RNA molecule is molecule is
releasedreleased
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What is the What is the enzymeenzyme
responsible for responsible for the production of the production of
the mRNA the mRNA molecule?molecule?
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RNA PolymeraseRNA Polymerase
EnzymeEnzyme found in the found in the nucleusnucleus
Separates Separates the two DNA the two DNA strands by strands by breaking the breaking the hydrogen bondshydrogen bonds between between the basesthe bases
Then moves along one of Then moves along one of the DNA strands and the DNA strands and links links RNA nucleotidesRNA nucleotides together together
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Question:Question:
What would be the What would be the complementary RNA complementary RNA strand for the following strand for the following DNA sequence?DNA sequence?
DNA 5’-DNA 5’-GCGTATGGCGTATG-3’-3’
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Messenger RNA Messenger RNA (mRNA)(mRNA)
• Carries the information for a Carries the information for a specific proteinspecific protein
• Made up of Made up of 500 to 1000500 to 1000 nucleotides longnucleotides long
• Sequence of 3 bases called Sequence of 3 bases called codoncodon• AUGAUG – methionine or – methionine or start start codoncodon• UAA, UAG, or UGAUAA, UAG, or UGA – – stopstop codons codons
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Messenger RNA Messenger RNA (mRNA)(mRNA)
methionine glycine serine isoleucine glycine alanine stopcodon
proteinprotein
A U G G G C U C C A U C G G C G C A U A AmRNAmRNA
startcodon
Primary structure of a proteinPrimary structure of a protein
aa1 aa2 aa3 aa4 aa5 aa6
peptide bonds
codon 2 codon 3 codon 4 codon 5 codon 6 codon 7codon 1
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RibosomesRibosomes
•Made of a large and small subunit
•Composed of rRNA (40%) and proteins (60%)
•Have two sites for tRNA attachment --- P and A
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Transfer RNA (tRNA)Transfer RNA (tRNA)
amino acidamino acidattachment siteattachment site
U A C
anticodonanticodon
methionine amino acidamino acid
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TranslationTranslation
• Synthesis of proteinsSynthesis of proteins in the in the cytoplasmcytoplasm
• Involves the following:Involves the following:
1.1. mRNA (codons)mRNA (codons)
2.2. tRNA (anticodons)tRNA (anticodons)
3.3. ribosomesribosomes
4.4. amino acidsamino acids
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TranslationTranslation• Three steps:Three steps:
1.1. initiationinitiation: start codon (AUG): start codon (AUG)
2.2. elongationelongation: amino acids : amino acids linkedlinked
3.3. terminationtermination: stop codon : stop codon (UAG, UAA, or UGA).(UAG, UAA, or UGA).
Let’s Make a Protein !Let’s Make a Protein !
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mRNA Codons Join the mRNA Codons Join the RibosomeRibosome
PSite
ASite
Largesubunit
Small subunit
mRNAmRNA
A U G C U A C U U C G
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InitiationInitiation
mRNAmRNA
A U G C U A C U U C G
2-tRNA
G
aa2
A U
A
1-tRNA
U A C
aa1
anticodon
hydrogenbonds codon
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mRNAmRNA
A U G C U A C U U C G
1-tRNA 2-tRNA
U A C G
aa1 aa2
A UA
anticodon
hydrogenbonds codon
peptide bond
3-tRNA
G A A
aa3
ElongationElongation
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mRNAmRNA
A U G C U A C U U C G
1-tRNA
2-tRNA
U A C
G
aa1
aa2
A UA
peptide bond
3-tRNA
G A A
aa3
Ribosomes move over one codon
(leaves)
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mRNAmRNA
A U G C U A C U U C G
2-tRNA
G
aa1
aa2
A UA
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
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mRNAmRNA
A U G C U A C U U C G
2-tRNA
G
aa1aa2
A U
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
(leaves)
Ribosomes move over one codon
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mRNAmRNA
G C U A C U U C G
aa1aa2
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
U G A
5-tRNA
aa5
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mRNAmRNA
G C U A C U U C G
aa1aa2
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
U G A
5-tRNA
aa5
Ribosomes move over one codon
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mRNAmRNA
A C A U G U
aa1
aa2
U
primaryprimarystructurestructureof a proteinof a protein
aa3
200-tRNA
aa4
U A G
aa5
C U
aa200
aa199
terminatorterminator or stopor stop codoncodon
TerminationTermination
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End Product –The End Product –The Protein!Protein!
• The end products of protein The end products of protein synthesis is a synthesis is a primary structureprimary structure of a proteinof a protein
• A A sequence of amino acidsequence of amino acid bonded together by peptide bonded together by peptide bondsbonds
aa1
aa2 aa3 aa4aa5
aa200
aa199