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Nucleic acidsNucleic acids

Nucleic acidsNucleic acids: – Maintain genetic informationMaintain genetic information– Determine Protein SynthesisDetermine Protein Synthesis

DNADNA = deoxydeoxyribonucleic acid– “Master Copy” for most cell information.– Template for RNA

RNA =RNA = ribonucleic acid– Transfers information from DNA– Template for Proteins

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Nucleic AcidsNucleic AcidsChromosomes

(in nucleus)

Have genesgenes

1 gene

1 enzyme or protein

EnzymesEnzymes determine determine

external & internal characteristicsexternal & internal characteristics

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NUCLEIC ACIDSNUCLEIC ACIDS

Long chains (polymers) of repeating nucleotides.nucleotides.– Each nucleotide has 3 parts:3 parts:

A A phosphate unitphosphate unit H H

OO

H

H

OH

H

H

HO

A sugarsugar

A heterocyclic heterocyclic Amine BaseAmine BaseN

H

P OH

O

OH

HO

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NucleoNucleottide ide = phosphate + sugar + base= phosphate + sugar + baseNucleoNucleottide ide = phosphate + sugar + base= phosphate + sugar + base

P

O

O

ON

H H

OH

OH

H

H

O

-N-glycosidiclinkage

-N-glycosidiclinkage

BaseBase

SugarSugar

PhosphatePhosphate

Nucleoside = Nucleoside = sugar + basesugar + baseNucleoside = Nucleoside = sugar + basesugar + base

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Nucleic AcidsNucleic Acids

Nucleic AcidsNucleic Acids = polymerspolymers of Nucleotides.Nucleotides.

phosphate sugar

base

SS SS SSSSSSSS

BB BB BBBBBBBB

PPPP PP PPPPPP

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THE SUGAR PARTTHE SUGAR PART• The major difference between RNA and DNA is

the different form of sugar used.

OHOCH2

H HHH

OH OHOH

OHOHOCH2

H HHH

OH HH

OH

Ribose C5H10O5

in RNADeoxyDeoxyRibose C5H10O4

in DNA

The difference is at carbon #2carbon #2.

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The Nitrogenous BasesThe Nitrogenous Bases

5 bases5 bases used fall in two classestwo classes

Purines Purines & & PyrimidinesPyrimidines

N

N

N

NH

A double ringdouble ring (6 & 5 members)

A single ringsingle ring(6 membered)

N

N

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Pyrimidines:Pyrimidines:

The Nitrogenous BasesThe Nitrogenous Bases

Purines:Purines:N

N

N

N

NH2

H

N

N

N

NH

H2N

O

H

N

N

O

O

CH3

H

HN

N

O

O

H

H N

NO

H

H

NH2

Adenine (A)Adenine (A)Adenine (A)Adenine (A) Guanine (G)Guanine (G)Guanine (G)Guanine (G)

Thiamine (T)Thiamine (T)In In DNADNA only onlyThiamine (T)Thiamine (T)In In DNADNA only only

Uracil (U)Uracil (U)In In RNARNA only only

Uracil (U)Uracil (U)In In RNARNA only only

Cytosine (C)Cytosine (C)Cytosine (C)Cytosine (C)

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H

N

N

N

N

NH2

P

O

O

H H

OH

OH

H

O

OH

1'

2'3'

4'

5'

H

HN

N

N

NP

O

O

H H

OH

OH

H

O

OH

O

H2N

1'

2'3'

4'

5'

1'

2'3'

4'

5'

H

N

P

O

O

H H

OH

OH

H

O

OH

N

O

O

CH3

Primary structurePrimary structure

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H

N

N

N

N

NH2

P

O

O

H H

OH H

O

OH

H

HN

N

N

NP

O

O

H H

OH H

O

O

O

H2N

H

N

P

O

O

H H

OH

OH

H

O

N

O

O

CH3

O

1'

2'3'

4'

5'

1'

2'3'

4'

5'

1'

2'3'

4'

5'

Primary structurePrimary structure

Phosphate bondsPhosphate bondslink DNA or RNAlink DNA or RNAnucleotides togethernucleotides togetherin a linear sequence.

Similar to proteinswith their peptide

bonds and sidegroups.

5’

3’

Adenine (A)

Guanine (G)

Thymine (T)

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Structure of DNAStructure of DNA

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In 1938 William Thomas Astbury took the first fiber diffraction pictures of DNA, correctly predicting, in an article in the journal Nature, the overall dimensions of the molecule and that the nucleotide bases were stacked at intervals of 3.3Å perpendicular to its long axis. It was left, however, to Watson and Crick after the Second World War to elucidate the detailed double helical structure of DNA.

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Maurice Wilkins with one of the cameras he developed specially for X-ray diffraction studies

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Work on x-ray diffraction patterns by Maurice Wilkins and Rosalind Franklin in 1953, revealed that the molecule had a "helical shape“.

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Rosalind Franklin is most associated with the discovery of the structure of DNA. At 26, after she had her PhD, Franklin began working in x-ray diffraction - using x-rays to create images of crystallized solids. She pioneered the use of this method in analyzing complex, unorganized matter such as large biological molecules, and not just single crystals.Franklin made marked advances in x-ray diffraction techniques with DNA. She adjusted her equipment to produce an extremely fine beam of x-rays. She extracted finer DNA fibers than ever before and arranged them in parallel bundles. And she studied the fibers' reactions to humid conditions. All of these allowed her to discover crucial keys to DNA's structure. Maurice Wilkins, her laboratory's second-in-command, shared her data, without her knowledge, with James Watson and Francis Crick, at Cambridge University, and they pulled ahead in the race, ultimately publishing the proposed structure of DNA in March, 1953.It is clear that without an unauthorized peek at Franklin's unpublished data, Watson and Crick probably would neither have published their famous paper on the structure of DNA in 1953, nor won their Nobel Prizes in 1962. Franklin did not share the Nobel Prize; she died in 1958 at the age of 37.

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1953, James Watson & Francis Crick and their scale model for DNA

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DNA secondary and tertiary structureDNA secondary and tertiary structure

Sugar-phosphate backboneSugar-phosphate backboneCauses each DNA chain to coilcoil around the outsideoutside of the attached basesof the attached bases like a spiral stair case.

Base PairingBase PairingHydrogen bonding occurs between purines and purines and pyrimidinespyrimidines. This causes two DNA strands to bond together.

adenine - thymineadenine - thymine guanine - cytosineguanine - cytosineAlways pair together!Always pair together!

Results in a double helix structure.

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Base pairing and hydrogen bondingBase pairing and hydrogen bonding

N

N

O| |

- H

N - H

N

NN

N

O| |

H - N

N

N O| |

O| |

H3C

- H

guanine cytosine

thymine adenineN

N N

N|

HH

N

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Hydrogen bondingHydrogen bonding

Each base wants toform either two or three hydrogen bonds.

That’s why only certain bases will form pairs.

G

T

C

A

C G

A

C

T

G

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Sugar-Sugar-phosphate phosphate backbonebackboneDNA coilscoils around outsideoutside of of attached attached basesbases like a spiral stair case.

Results in a double helix structure.

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• Crick and Watson (1962 Nobel Prize)

– Proposed the basic structure of DNA

– 2 strands wrap around each other

– Strands are connected by H-bonds between the amines.

• Like steps of a spiral staircase

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ChromosomesChromosomes

The normal number of chromosome pairs varies among the species.

AnimalAnimal Pairs Pairs PlantPlant PairsPairsMan 23 Onion 8Cat 30 Rice 14Mouse 20 Rye 7Rabbit 22 Tomato 12Honeybee, White pine 12

male 8 Adder’s 1262female 16 tongue fern

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Role of RNA and DNA in Heredity

RNA and DNA are involved in three major processes in a cell related to heredity as shown below:

1. Replication (DNA copies itself)

2. Transcription (The genetic code in DNA is rewritten into RNA and carried to the ribosomes by mRNA

3. Translation (tRNA carries amino acids to the ribosomes as part of protein synthesis

Replication is an important process during mitosis

Transcription and translation are two steps in the biosynthesis of a protein

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TTCC

AA

SS SSSS SSSSSS

GG TT CCAA

PPPP PP PPPPPP

CC GG

GG

DNA: Self - ReplicationDNA: Self - Replication

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GGGGAA

SS SSSS SSSSSS

GG TT CCAA

PPPP PP PPPPPP

CC GG

DNA: Self - ReplicationDNA: Self - Replication

TT CCCC

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Replication of DNAReplication of DNA

ReplicationReplication occurs on both halvesboth halvesin opposite directions.opposite directions.

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DNA DNA ReplicationReplication

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RNA synthesisRNA synthesis

In the first step, RNA polymeraseRNA polymerase bindsto a promotorpromotor sequenceon the DNA chain.

This insuresinsures that transcription occurs in the correct directioncorrect direction.

The initial reaction is toseparate the twoseparate the twoDNA strandsDNA strands.

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RNA synthesisRNA synthesis

initiationsequence

terminationsequence

‘Special’ baseSpecial’ basesequencessequences in theDNA indicatewhere RNARNAsynthesis startssynthesis startsand stops.and stops.

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RNA synthesisRNA synthesis

Once the terminationsequence isreached, thenew RNA moleculenew RNA moleculeand the RNA synthaseare released.released.

The DNA recoils.The DNA recoils.

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• The messenger RNAmessenger RNA (mRNA) move outside the nucleus to the cytoplasmto the cytoplasm where RibosomesRibosomes are anxiously awaiting their arrival.

rRNA

rRNA

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• The messenger RNAmessenger RNA (mRNA) move outside the nucleus to the cytoplasmto the cytoplasm where RibosomesRibosomes are anxiously awaiting their arrival.

rRNA

rRNA

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• The messenger RNAmessenger RNA (mRNA) move outside the nucleus to the cytoplasmto the cytoplasm where RibosomesRibosomes are anxiously awaiting their arrival.

rRNA

rRNA

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• The messenger RNAmessenger RNA (mRNA) move outside the nucleus to the cytoplasmto the cytoplasm where RibosomesRibosomes are anxiously awaiting their arrival.

rRNA

rRNA

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rRNA

rRNA

Ribosomal RNA – rRNARibosomal RNA – rRNA: Platform for protein synthesis. Holds mRNA in place and helps assemble proteins.

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AUG GCU AUG UUG

5’

3’

rRNArRNA

•The RibosomesRibosomes are like train stationslike train stations

–The mRNA is the trainmRNA is the train slowly moving through the station.

rRNArRNA

Codons

mRNAmRNA

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Transfer RNA Transfer RNA - tRNA- tRNA =• relatively small small compared to other RNA’s

(70-90 bases.)70-90 bases.)• transports amino acidstransports amino acids to site of protein synthesis.

A

C

C

A

C

C

U

C

G

U

CU

U

C

G

G

G

G

G

CC GGG

CC GG

A CGG

CC GGU

C

C

C

C

U

C

A

U

G

G

A

G

G

G

G

GU

U

CC G

U

C GC

AU

G

G

C

U

AG U

A GU

G

GC

HO-A

C

C

A

C

C

U

C

G

U

CU

U

C

G

G

G

G

G

CC GGG

CC GG

A CGG

CC GGU

C

C

C

C

U

C

A

U

G

G

A

G

G

G

G

GU

U

CC G

U

C GC

AU

G

G

C

U

AG U

A GU

G

GC

HO-

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Anticodons on t-RNAAnticodons on t-RNA

A

C

C

A

C

C

U

C

G

U

CU

U

C

G

G

G

G

G

CC GGG

CC GG

A CGG

CC GGU

C

C

C

C

U

C

A

U

G

G

A

G

G

G

G

GU

U

CC G

U

C GC

AU

G

G

C

U

AG U

A GU

G

GC

HO-

Site of aminoacid attachment

Site of aminoacid attachment

Three base anticodon site

Three base anticodon site

Point ofattachmentto mRNA

Point ofattachmentto mRNA

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UUU or UUC is the codon for Phe. UUG is the codon for Leu. AUG is the codon for Met.

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CodonsCodons

There are two additional types of codons:

Initiation Initiation AUGAUG(same as methionine)

TerminationTermination UAG, UAA, UGAUAG, UAA, UGA

A total of 64 condons are used for all aminoacids and for starting and stopping. All proteinsynthesis starts with methionine. After the poly-peptide has been made, an enzyme removes thisamino acid.

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Protein SynthesisProtein Synthesis1: Activation1: Activation

Each AA is activated by reacting with an ATP

The activated AA is then attached to particular tRNAtRNA... (with the correct anticodon)

C G A

MET

anticodon

activated AA

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TranslationTranslation

AUG GCU AUG UUG mRNA

5’

3’

Initiationfactors

ribosome unit

U A C

MET

PPsitesite AA site site

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U A C

MET

TranslationTranslation

ribosome unit

AUG GCU AUG UUG mRNA

5’

3’

PPsitesite AA site site

C G A

Ala

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ribosome unit

AUG GCU AUG UUG mRNA

5’

3’

TranslationTranslation

U A C

MET

C G A

Ala

peptide bondforms

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ribosome unit

GCU UUC UUGmRNA

5’

3’

TranslationTranslation

C G A

Ala

peptide bond

Met

A A G

Phe

AU G

U A C

U A C

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ribosome unit

GCU UUC UUGmRNA

5’

3’

TranslationTranslation

C G A

Ala

peptide bondforms

Met

A A G

Phe

AU G

U A C

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TerminationTermination

After the last translocation (the last codon is a STOP), no more AA are added.

“Releasing factors” cleave the last AA from the tRNA

The polypeptide is complete

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Recombinant DNARecombinant DNA

Circular DNA found in bacteriaE.Coli plasmid bodiesRestriction endonucleases cleave DNA at

specific genesResult is a “sticky end”Addition of a gene from a second

organismSpliced DNA is replaced and organism

synthesizes the new protein

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Recombinant DNARecombinant DNA

Bacterium

Remove gene segment

DNAPlasmid sticky ends

Cut genefor insulin

Replace inbacterium