1 DNA, RNA, and PROTEIN SYNTHESIS. 2 Transcription Translation DNA mRNA Ribosome Protein Prokaryotic Cell DNA RNA Protein

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DNA, RNA, DNA, RNA, and PROTEIN and PROTEIN SYNTHESISSYNTHESIS

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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


RNA ProcessingRNA Processing


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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Nucleic Nucleic AcidsAcids

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DNA or Protein?DNA or Protein? 1903, Walter Sutton noted the parallelism

between chromosome behavior and Mendel's laws, thus identifying genes with chromosomes and marking the beginning of genetics as a science

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 of actual genetic material of the cellthe cell

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DNA!DNA! Frederick GriffithFrederick Griffith in 1928 in 1928

discovered what he called a transforming principle, which led to the direct discovery of how DNA works and the beginning of Molecular

Genetics.

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DNA!DNA! It wasn't until 1944 that

Griffith's "transforming principle" was identified as DNA by Oswald Theodore Avery, along with coworkers Colin MacLeod and Maclyn McCarty

• Protein was finally excluded as the hereditary material following a series of experiments published by Alfred Hershey and Martha Chase in 1952. These experiments involved the T2 bacteriophage, a virus that infects the E. coli bacterium.

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DNA!DNA!

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DNA!DNA!• Rosalind Franklin recorded a x-ray

photograph of a DNA molecule that another researcher at King's College, Maurice Wilkins, showed to James Watson and Francis Crick without her knowledge or permission. This image helped Watson and Crick construct a model of DNA, which enabled them to fully understand the molecule's structure.

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• Watson and Crick constructed a model of DNA, which enabled them to fully understand the molecule's structure. Wilkins, Crick and Watson were awarded a Nobel Prize jointly, some years later, after Franklin's death.

• proposed the double helix or spiral staircase structure of the DNA molecule in 1953

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DNA!DNA!

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Watson

Crick

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Structure of DNAStructure of DNA DNA is made of subunits called DNA is made of subunits called

nucleotidesnucleotides DNA nucleotides are composed DNA nucleotides are composed

of a:of a:1.1. phosphatephosphate, ,

2.2. deoxyribose deoxyribose sugar, and sugar, and

3.3. nitrogen-containing basenitrogen-containing base The 4 bases in DNA are: The 4 bases in DNA are: adenine adenine

(A), (A), thymine (T),thymine (T), guanine (G),guanine (G), and cytosine (C)and cytosine (C)

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DNA NucleotideDNA Nucleotide

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Base Pairing RuleBase Pairing Rule• Watson and Crick showed that DNA Watson and Crick showed that DNA

is a is a double helixdouble helix• AA (adenine) pairs with (adenine) pairs with TT (thymine) (thymine)• CC (cytosine) pairs with (cytosine) pairs with GG (guanine) (guanine)

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Nitrogen RingsNitrogen Rings• PurinesPurines have have double double rings of rings of

carbon-nitrogen (G, A)carbon-nitrogen (G, A)

Nitrogen RingsNitrogen Rings

• PyrimidinesPyrimidines have have single single carbon-nitrogen rings (C, T)carbon-nitrogen rings (C, T)

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Nitrogen RingsNitrogen Rings

• This is called This is called complementarcomplementary base pairingy base pairing because a because a purinepurine is is always paired always paired with a 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-parallel parallel (they run in opposite (they run in opposite directions)directions)

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Anti-Parallel Strands of DNA

Template (top part of DNA)

always goes

from 5’ to 3’

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DNA DNA ReplicatiReplicati

onon

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Steps in DNA Steps in DNA ReplicationReplication

Occurs when Occurs when chromosomes duplicatechromosomes duplicate (make copies) – Interphase (S-phase)(make copies) – Interphase (S-phase) An An exact copyexact copy of the DNA is produced of the DNA is produced with the aid of the enzyme with the aid of the enzyme DNA DNA polymerasepolymerase Hydrogen bondsHydrogen bonds between bases between bases breakbreak and enzymes called and enzymes called helicaseshelicases “unzip” “unzip” the moleculethe molecule Each Each old strandold strand of nucleotides serves of nucleotides serves as a as a templatetemplate for each new strand for each new strand New nucleotidesNew nucleotides move into move into complementary positions are joined by complementary positions are joined by DNA polymeraseDNA 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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Another View of Another View of ReplicationReplication

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RNARNA

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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 (U)uracil (U)

DNADNA has has thymine (T)thymine (T)

3.3. RNARNA molecule is molecule is single-strandedsingle-stranded

DNADNA is is double-strandeddouble-stranded

4.4. RNARNA molecule molecule can leave the nucleuscan leave the nucleus

DNADNA is is cannot leave the nucleuscannot leave the nucleus

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Structure of RNAStructure of RNA

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. Three Types of RNAThree Types of RNA

• Messenger RNA (mRNA)Messenger RNA (mRNA) carries carries genetic information to the genetic information to the ribosomesribosomes

• Ribosomal RNA (rRNA)Ribosomal RNA (rRNA),, along along with protein, makes up the with protein, makes up the ribosomesribosomes

• Transfer RNA (tRNA)Transfer RNA (tRNA) transfers transfers amino acids to the ribosomes amino acids to the ribosomes where proteins are where proteins are synthesizedsynthesized

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Making a Making a ProteinProtein

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Genes & ProteinsGenes & Proteins A gene A gene is a specific location on a is a specific location on a

chromosome, consisting of a segment of chromosome, consisting of a segment of DNA, that codes for a particular protein.DNA, that codes for a particular protein. Genes code for particular proteins Genes code for particular proteins

that determine specific characteristicsthat determine specific characteristics Each chromosome has thousands of Each chromosome has thousands of

genesgenes Organizms that are similar share Organizms that are similar share

many of the same genesmany of the same genes

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Genes & ProteinsGenes & Proteins When a particular protein is needed When a particular protein is needed

the cell must make that protein and the cell must make that protein and DNA is the molecule with the DNA is the molecule with the instructions on how to make itinstructions on how to make it

The The type of protein type of protein produced is produced is determined by the order of basesdetermined by the order of bases

ProteinsProteins are made of are made of amino acidsamino acids 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

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Two Parts of Protein Two Parts of Protein SynthesisSynthesis

1.1. TranscriptionTranscription makes an RNA makes an RNA molecule complementary to molecule complementary to a portion of DNAa portion of DNA

2.2. TranslationTranslation occurs when the occurs when the sequence of bases of mRNA sequence of bases of mRNA 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 DNA Every three bases on DNA

stands for stands for ONE amino acidONE amino acid But DNA is But DNA is

located in the located in the nucleus and nucleus and cannot leave cannot leave however proteins however proteins are made at the are made at the ribosomes in the ribosomes in the cytoplasmcytoplasm

So how does the So how does the information DNA information DNA has get to the has get to the ribosomesribosomes

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Genetic CodeGenetic Code DNA contains a DNA contains a triplet codetriplet code Every three bases on DNA Every three bases on DNA

stands for stands for ONE amino acidONE amino acid Each three-letter unit on Each three-letter unit on mRNAmRNA

is called a is 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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TranscriptioTranscriptionn

TranslatiTranslationon

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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 promoter Starts at promoter DNADNA (TATA box) (TATA box) Ends at terminator Ends 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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DNADNA

pre-mRNApre-mRNA

RNA PolymeraseRNA Polymerase

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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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Answer:Answer:

•DNA 5’-GCGTATG-3’DNA 5’-GCGTATG-3’•RNA 3’-CGCAUAC-5RNA 3’-CGCAUAC-5’’

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Processing Pre-mRNAProcessing Pre-mRNA

• Also occurs in the Also occurs in the nucleusnucleus• Pre-mRNA Pre-mRNA made up of segments made up of segments

called called introns & exonsintrons & exons• Exons code for proteins, while Exons code for proteins, while

introns do NOT!introns do NOT!• Introns spliced out by Introns spliced out by splicesome-splicesome-

enzymeenzyme and exons re-join and exons re-join

• End product is a End product is a mature RNAmature RNA molecule that leaves the nucleus molecule that leaves the nucleus to the cytoplasmto the cytoplasm

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RNA ProcessingRNA Processing

pre-RNA molecule

intron

intronexon exon exon

exon exon exon

Mature RNA moleculeMature RNA molecule

exon exon exon

intron intron

splicesome splicesome

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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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Transfer RNA (tRNA)Transfer RNA (tRNA)• Made up of Made up of 75 to 80 nucleotides75 to 80 nucleotides

longlong• Picks up the appropriate Picks up the appropriate amino amino

acidacid floating in the cytoplasm floating in the cytoplasm • Transports Transports amino acidsamino acids to the to the

mRNAmRNA• Have Have anticodonsanticodons that are that are

complementary to complementary to mRNA codonsmRNA codons• Recognizes the appropriate Recognizes the appropriate codonscodons

on the on the mRNAmRNA and bonds to them and bonds to them with H-bondswith H-bonds

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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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Ribosomal RNA (rRNA)Ribosomal RNA (rRNA)• Made up of Made up of

rRNA is rRNA is 100 to 100 to 3000 3000 nucleotidesnucleotides long long

• Made inside the Made inside the nucleusnucleus of a cell of a cell

• Associates with Associates with proteins to form proteins to form ribosomesribosomes

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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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RibosomesRibosomes

PSite

ASite

Largesubunit

Small subunit

mRNAmRNA

A U G C U A C U U C G

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• 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


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InitiationInitiation

mRNAmRNA


2-tRNA

G

aa2

A U

A

1-tRNA

U A C

aa1

anticodon

hydrogenbonds codon

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mRNAmRNA


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


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


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


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)


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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


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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

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Documents

1 DNA, RNA, and PROTEIN SYNTHESIS. 2 Transcription Translation DNA mRNA Ribosome Protein Prokaryotic Cell DNA RNA Protein