The Central Dogma of Molecular Biology

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The Central Dogma of The Central Dogma of Molecular BiologyMolecular Biology

Mark MayoMark MayoCypress CollegeCypress College

Last update 3/11/14

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The Central Dogma of The Central Dogma of Molecular BiologyMolecular Biology

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Importance of Proteins Importance of Proteins There are three There are three

main kinds:main kinds: structural - make up structural - make up

most body partsmost body parts hormone - chemical hormone - chemical

that controls the that controls the bodybody

enzyme - catalyst - enzyme - catalyst - speeds up chemical speeds up chemical reactionsreactions

Insulin, a protein

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Importance of Proteins Importance of Proteins Without proteins there Without proteins there

would be no lifewould be no life All cells make proteinsAll cells make proteins Proteins in your body Proteins in your body

make up your:make up your: HairHair NailsNails MusclesMuscles SkinSkin CartilageCartilage

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Discovery of DNA Discovery of DNA (deoxyribonucleic acid) (deoxyribonucleic acid)

1953 Watson, 1953 Watson, Crick and Crick and Wilkins Wilkins determined the determined the structure of DNA structure of DNA to be a to be a double double helixhelix

They won a They won a Nobel Prize for Nobel Prize for their work their work

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Structure of the DNA Structure of the DNA molecule molecule

DNA is DNA is shaped like shaped like a a double double helixhelix

It is like a It is like a spiral spiral staircasestaircase

Another Another way to way to think of it think of it is a twisted is a twisted ladderladder

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Connecting the DNA moleculeConnecting the DNA molecule

RailsRails** of the DNA of the DNA ladder are alternating ladder are alternating sugar & phosphatessugar & phosphates

RungsRungs** are composed are composed of pairs of basesof pairs of bases A bonds with TA bonds with T** G bonds with CG bonds with C**

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Connecting the DNA Connecting the DNA MoleculeMolecule

The DNA The DNA LadderLadder**

PS – APS – TPS – GPS - C

PT - S PA - S PC - S PG - S

PS – APS – TP? – GPS - C

PT - ? P? - S PC - S PG - S

* * ** * *

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Connecting the DNA Connecting the DNA moleculemolecule

The two strands of DNA are The two strands of DNA are differentdifferent

One is called the One is called the sense strandsense strand and it is the plan to make a and it is the plan to make a proteinprotein

The other strand is the The other strand is the antisense antisense strandstrand and it is only used for and it is only used for protection of the sense strandprotection of the sense strand

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The two strands of DNA The two strands of DNA are said to be are said to be antiparallelantiparallel**

One strand is oriented in a One strand is oriented in a 5’ to 3’ direction5’ to 3’ direction**

The other strand is The other strand is oriented in the opposite 3’ oriented in the opposite 3’ to 5’ directionto 5’ direction**

5’ 3’

3’ 5’

sense

antisense

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NucleotideNucleotides are units s are units composed composed of aof abase, base, phosphate phosphate and a and a sugar sugar

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The two strands of DNA bases are connected The two strands of DNA bases are connected by weak forces called hydrogen bondsby weak forces called hydrogen bonds**

2 hydrogen 2 hydrogen bondsbonds

3 hydrogen 3 hydrogen bondsbonds

**

**

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Components of DNA Components of DNA Phosphate Phosphate

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Components of DNAComponents of DNA Deoxyribose Deoxyribose

(sugar) (sugar)

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Components of DNAComponents of DNA DNA bases DNA bases

(4 different types)(4 different types) AdenineAdenine ThymineThymine** GuanineGuanine Cytosine Cytosine

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Components of DNAComponents of DNA Proteins Proteins

are are attached attached to the DNA to the DNA helix in helix in cellscells

These These proteins proteins are known are known as as histoneshistones

They assist They assist in DNA in DNA storagestorage

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DNA and RNA Compared DNA and RNA Compared DNADNA

Found only in Found only in nucleusnucleus**

Double stranded Double stranded helixhelix

Bases = ATGCBases = ATGC** Sugar = Sugar =

DeoxyriboseDeoxyribose

RNARNA Found in Found in

ribosomes, ribosomes, nucleolusnucleolus**

Single stranded Single stranded helix helix **

Bases = AUGC Bases = AUGC (URACIL) (URACIL) **

Sugar = RiboseSugar = Ribose* DNA is also found in a select number of other organelles

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Replication of DNA Replication of DNA ReplicationReplication - the making of an exact copy - the making of an exact copy

of the DNA moleculeof the DNA molecule Replication occurs whenever a cell dividesReplication occurs whenever a cell divides The copy must be 100% accurate The copy must be 100% accurate

(errors = death possibly)(errors = death possibly) Replication practice (find the complimentary Replication practice (find the complimentary

bases or base sequence)bases or base sequence)** A – pairs with ?A – pairs with ? T – pairs with ?T – pairs with ? G – pairs with ?G – pairs with ? C – pairs with ?C – pairs with ?

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Replication of DNAReplication of DNA

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Stages in replication Stages in replication (basic)(basic)

DNA molecule is split in two at the end by the DNA molecule is split in two at the end by the work of enzymes work of enzymes **

DNA unzips slightly and the two strands unwind DNA unzips slightly and the two strands unwind ** new nucleotides attach to the free ends new nucleotides attach to the free ends **

( A-T, G-C)( A-T, G-C) more DNA unzipsmore DNA unzips more nucleotides attach more nucleotides attach ** process continues until completedprocess continues until completed result is two (2) double strands of DNAresult is two (2) double strands of DNA each strand is 50% new and 50% old DNAeach strand is 50% new and 50% old DNA

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Stages in replicationStages in replication DNA DNA

replication is replication is different on different on the leading the leading and lagging and lagging strands strands **

Lagging Lagging strand has strand has Okazaki Okazaki fragmentsfragments** **

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Stages in replicationStages in replication

DNA DNA replicatioreplication is n is different different on the on the leading leading and and lagging lagging strands strands **

**

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Enzymes Enzymes ** Involved in DNA Involved in DNA ReplicationReplication

DNA polymerase – adds nucleotides in a DNA polymerase – adds nucleotides in a

5’ to 3’ direction5’ to 3’ direction TopoisomeraseTopoisomerase GyraseGyrase RNA primaseRNA primase DNA ligase – connects the gaps in the DNA ligase – connects the gaps in the

lagging strandlagging strand

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DNA DNA ReplicationReplicationin Motionin Motion

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Introns and ExonsIntrons and Exons IntronsIntrons – sequences in the DNA that – sequences in the DNA that

are NOT used to make mRNA or to are NOT used to make mRNA or to make a protein. They are NOT make a protein. They are NOT transcribed transcribed **

ExonsExons – sequences in the DNA that – sequences in the DNA that are expressed or used to make are expressed or used to make mRNA and ultimately are used to mRNA and ultimately are used to make a proteinmake a protein

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Introns and ExonsIntrons and Exons

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Restriction EnzymesRestriction Enzymes Restriction enzymesRestriction enzymes (also known as (also known as restriction restriction

endonucleasesendonucleases) recognize specific DNA sequences and ) recognize specific DNA sequences and CLEAVECLEAVE or cut the DNA into pieces or cut the DNA into pieces **

Generally these cuts occur in a manner which leaves a sticky Generally these cuts occur in a manner which leaves a sticky end of single strand DNAend of single strand DNA

These pieces can be separated by using gel electrophoresis These pieces can be separated by using gel electrophoresis (this is like electronic chromatography)(this is like electronic chromatography)

We use restriction enzymes for cutting bacterial, viral or We use restriction enzymes for cutting bacterial, viral or even human DNA and later insertion of the desired DNA even human DNA and later insertion of the desired DNA fragments – called gene splicing fragments – called gene splicing **

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Restriction EnzymesRestriction Enzymes

sticky ends

sticky ends

blunt ends

blunt ends

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Restriction EnzymesRestriction Enzymes

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Ribonucleic Acid (RNA)Ribonucleic Acid (RNA) Three types of RNA:Three types of RNA:

rRNArRNA = = ribosomal RNAribosomal RNA - makes up the - makes up the ribosomeribosome

mRNAmRNA = = messenger RNAmessenger RNA - is the - is the message from DNA for the construction message from DNA for the construction of the new protein molecule of the new protein molecule **

tRNAtRNA = = transfer RNAtransfer RNA - carries amino - carries amino acids to ribosomes acids to ribosomes

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Ribonucleic Acid (RNA)Ribonucleic Acid (RNA) Ribosomal RNA is used to make a ribosomeRibosomal RNA is used to make a ribosome The ribosome “The ribosome “readsreads” the mRNA plan for the new protein” the mRNA plan for the new protein mRNA is the set of directions for a new proteinmRNA is the set of directions for a new protein**

RibosomeRibosome

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Ribonucleic Acid (RNA)Ribonucleic Acid (RNA) Messenger RNAMessenger RNA

Sense

Antisense

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Ribonucleic Acid (RNA)Ribonucleic Acid (RNA) Transfer RNATransfer RNA

Each tRNA holds one amino acidEach tRNA holds one amino acid Every tRNA has a special region called the Every tRNA has a special region called the

anti-codon (3 bases) anti-codon (3 bases) An tRNA anti-codon "mates" with codon on An tRNA anti-codon "mates" with codon on

the mRNA moleculethe mRNA molecule There are 61 different tRNA molecules, yet There are 61 different tRNA molecules, yet

only about 20 amino acids only about 20 amino acids (hint: 3 stop (hint: 3 stop codons)codons)

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Ribonucleic Acid (RNA)Ribonucleic Acid (RNA) Transfer RNATransfer RNA

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TranscTranscrription iption TranscriptionTranscription is the special copying of is the special copying of

one side of the DNA molecule (the one side of the DNA molecule (the sense strand) that results in the sense strand) that results in the production of a single strand of RNA production of a single strand of RNA **

The original DNA is not changedThe original DNA is not changed This process can be repeatedThis process can be repeated The amount of DNA that is transcribed The amount of DNA that is transcribed

is usually one geneis usually one geneThe r in the title is red to remind you that transcription makes RNA

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TranscriptionTranscription Process of TranscriptionProcess of Transcription

DNA is unzipped by an enzymeDNA is unzipped by an enzyme Only one side fills with RNA nucleotides by Only one side fills with RNA nucleotides by

the action of another enzyme the action of another enzyme RNA RNA polymerasepolymerase A-U, G-C (A-U, G-C (NO THYMINE = TNO THYMINE = T) )

As the RNA strand separates the DNA strands As the RNA strand separates the DNA strands reattach as before the process startedreattach as before the process started

4. The result is the original DNA 4. The result is the original DNA plus a new plus a new RNA strandRNA strand

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TranscriptionTranscription

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TranscriptionTranscription Uracil – a base only found in RNAUracil – a base only found in RNA

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TranscriptionTranscription Transcription Practice Transcription Practice **

A (in DNA) pairs with ___ in RNA A (in DNA) pairs with ___ in RNA T (in DNA) pairs with ___ in RNA T (in DNA) pairs with ___ in RNA G (in DNA) pairs with ___ in RNAG (in DNA) pairs with ___ in RNA C (in DNA) pairs with ___ in RNAC (in DNA) pairs with ___ in RNA

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Sometimes two or more ribosomes attach to the mRNA transcript at the same time and this is called a polysome **

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TranslationTranslation Translation Translation ** is is

the reading of the reading of the RNA code, the RNA code, by ribosomes, by ribosomes, to make to make proteins proteins ** or or polypeptides polypeptides

Translation is Translation is often called often called protein protein synthesissynthesis

**

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TranslationTranslation mRNA is the message (the plan for the mRNA is the message (the plan for the

protein)protein) rRNA "reads" the mRNA (the ribosome) rRNA "reads" the mRNA (the ribosome) ** tRNA molecules carry amino acids to the tRNA molecules carry amino acids to the

ribosome for assembly into proteinsribosome for assembly into proteins The ribosome allows only the correct tRNA The ribosome allows only the correct tRNA

to add its amino acid – others are rejectedto add its amino acid – others are rejected

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Translation Translation **

**

**

Anticodons **

Codons **

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TranslationTranslation

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TranslationTranslation Triplet Triplet

codonscodons - -groups of groups of three three bases on bases on mRNA mRNA that code that code for for specific specific amino amino acids acids **

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TranslationTranslation The function of special stop codons is to The function of special stop codons is to

terminateterminate** or end the translation process or end the translation process** The stop codons are: UAA, UAG and UGAThe stop codons are: UAA, UAG and UGA

The function of the start codon is to serve The function of the start codon is to serve as a place for the ribosome to begin as a place for the ribosome to begin translationtranslation The only start codon is AUGThe only start codon is AUG

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TranslationTranslation 9 bases would give __?__ amino acids 9 bases would give __?__ amino acids

** 27 bases would give __?__ amino 27 bases would give __?__ amino

acids acids **

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TranslationTranslation Anticodon practice Anticodon practice **

codoncodon anticodonanticodonAAAAAA UUUUUUCCCCCC ? ?UUUUUU ? ?UCGUCG ? ?

NEVER look up the anticodon in the chart or table!NEVER look up the anticodon in the chart or table!

Look the CODON in the table or chartLook the CODON in the table or chart

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TranslationTranslation

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Central Dogma PracticeCentral Dogma PracticeAntisense DNA

Sense DNA

mRNA

Protein

A T G G G G C C C T T T A A A G G C T A A

First you R E P L I C A T E the top line of DNA

using the DNA bases A T G C

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Sense DNA

mRNA

Protein


T A C C C C G G G A A A T T T C C G A T T

Second you T R A N S C R I B E the second line of DNA (sense DNA) using the RNA bases A

U G C

NO T’s

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Sense DNA

mRNA

Protein


T A C C C C G G G A A A T T T C C G A T T

A U G G G G C C C U U U A A A G G C U A A

Lastly, you T R A N S L A T E the mRNA line

using the chart and find out the amino acids,Start and Stop

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Central Dogma PracticeCentral Dogma Practice

Antisense DNA

Sense DNA

mRNA

Protein


T A C C C C G G G A A A U U U C C G A T T

A U G G G G C C C U U U A A A G G C U A A Start Glycine Proline Phenylal. Lysine Glycine Stop

Proteins are made up of a string or amino acids

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The Central Dogma of Molecular Biology