ASAM NUKLEAT

24 OKTOBER 2011

QUOTATION

It's not that I'm so smart, it's just that I stay with problems longer.

(Albert Einstein )

Factors Affecting Enzyme Activity

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SEJARAH PENEMUAN ASAM NUKLEAT

Who really discovered DNA?

Fredrick Griffith

•Worked in the 1920’s •Taxonomist – a scientist who classifies

and names organisms – He specialized in pathogens (disease-causing organisms)

•Used mice and bacterium (Streptococcus pneumonia) to see if inherited material is passed though DNA or protein.

Oswald Avery

•Continued Griffith’s work•Identified DNA as the material that passes

on the inherited information.•He used large amounts of bacteria and a

process of heating and mixing the liquids to extract the nitrogen bases away from the protein

•Became world’s first genetic engineer

The “Transforming Factor” 1928

•Frederick Griffith ▫Streptococcus pneumonia

bacteria was working to find cure for

pneumonia▫harmless live bacteria mixed

with heat-killed infectious bacteria causes disease in mice

▫substance passed from dead bacteria to live bacteria = “Transforming Factor”

The “Transforming Factor”

Transformation?something in heat-killed bacteria could still transmit disease-causing properties

live pathogenicstrain of bacteria

live non-pathogenicstrain of bacteria

mice die mice live

heat-killed pathogenic bacteria

mix heat-killed pathogenic & non-pathogenicbacteria

mice live mice die

A. B. C. D.

DNA is the “Transforming Factor”

•Avery, McCarty & MacLeod▫purified both DNA & proteins from

Streptococcus pneumonia bacteria which will transform non-pathogenic

bacteria?▫injected protein into bacteria

no effect▫injected DNA into bacteria

transformed harmless bacteria into virulent bacteria

1944

What’s theconclusion?

Virus Experiments Provides More Evidence

• Despite Avery's findings, many scientists remained skeptical that genes were made of DNA rather than protein.▫ Protein = 20 amino acids▫ DNA = 4 nucleotides

• Which one, DNA or protein, was truly the hereditary material?

• In 1952, biologists Alfred Hershey and Martha Chase provided more evidence to distinguish between these two possibilities. They conducted a series of experiments using viruses.

Hershey and Chase Experiment

                                                                                                                

                                                                                                                                                                              

A bacteriophage at work…

Erwin Chargaff and his rule• In 1950, biochemist Erwin Chargaff

found that the arrangement of nitrogen bases in DNA varied widely,

• The amount of certain bases always occurred in a one-to-one ratio.

• Nitrogen bases always match up like this:

Adenine – Thymine and Cytosine -- Guanine

Rosalind Franklin(1920-1953)•Using X-ray techniques took pictures of

DNA and discovered the double helix shape of DNA.

•Died of cancer due to unknown harmful affects of X-ray

James Watson and Francis Crick• First scientists to create a model of DNA• It is still the model used today• Sides are made of sugar and phosphate

molecules• Rungs of the ladder are made of

nitrogen bases • Made of 5 elements: carbon,

hydrogen, oxygen, nitrogen, and phosphorus

                                

1953Watson and Crick made a model of the DNA – the Double

Helix

Watson & Crick proposed…Watson & Crick proposed…•DNA had specific pairing between the DNA had specific pairing between the

nitrogen bases:nitrogen bases:

ADENINEADENINE – – THYMINETHYMINE

CYTOSINECYTOSINE - - GUANINEGUANINE

•DNA was made of DNA was made of 22 long stands of long stands of nucleotides arranged in a specific way nucleotides arranged in a specific way

called the called the “Complementary Rule”“Complementary Rule”

Watson & Crick relied heavily on evidence reported by other scientists

to construct their model.

X-ray photographs from Rosalind Franklin & Maurice Wilkins

show that DNA is a helix with a sugar-phosphate backbone on the outside

and more than one chain of nucleotides

•In 1962, Watson, Crick and Wilkins received the Nobel Prize in medicine for their work on DNA

•Rosalind Franklin had died in 1958 from cancer (most likely caused by working with X-rays) and was not recognized

PenelitianPenelitianWatson dan CrickWatson dan Crick

Dengan dukungan data difraksi Dengan dukungan data difraksi sinar-X dari Rosalind Franklin sinar-X dari Rosalind Franklin dan Maurice Wilkins dan Maurice Wilkins

Dengan dukungan data analisis Dengan dukungan data analisis kimia basa nitrogen dari Erwin kimia basa nitrogen dari Erwin ChargaffChargaff

Memformulasikan struktur DNAMemformulasikan struktur DNA

Mengelompokkan basa DNA Mengelompokkan basa DNA menjadi purin dan pirimidin menjadi purin dan pirimidin

Memformulasikan model Memformulasikan model replikasi DNAreplikasi DNA

KOMPOSISI BASA PENYUSUN ASAM NUKLEAT

OrganismeOrganisme AA GG CC TT

Escherichia coliEscherichia coli 24,724,7 26,026,0 25,725,7 23,623,6

KhamirKhamir 31,331,3 18,718,7 17,117,1 32,932,9

GandumGandum 27,327,3 22,722,7 22,822,8 27,127,1

SalmonSalmon 29,729,7 20,820,8 20,420,4 29,129,1

AyamAyam 28,828,8 20,520,5 21,521,5 29,329,3

HASIL PENELITIAN CHARGAFF

1. Asam nukleat yang diisolasi dari berbagai jaringan organisme yang sama memiliki komposisi basa yang sama

2. Komposisi basa Asam nukleat beragam pada organisme yang berbeda

3. Komposisi basa Asam nukleat suatu spesies tidak berubah oleh umur, nutrisi, dan lingkungan

4. Jumlah residu adenin selalu setara dengan jumlah residu timin, sedangkan jumlah residu guaninn selalu setara dengan jumlah residu sitosin

KESIMPULAN PENELITIAN CHARGAFF

•Asam nukleat merupakan bahan penentu sifat mahluk hidup

•Asam nukleat diturunkan/ditransfer dari induk ke keturunannya

•Nucleic acids store information in their sequences of chemical units.

•Key Terms▫Deoxyribonucleic

acid (DNA)▫Nucleotide▫Nitrogenous base▫Pyrimidine▫Purine▫Double helix

•DNA stores the information that tells cells which proteins to make and when to use them

•DNA is made up of two chains of nucleotides

•Double Helix

•A DNA nucleotide is composed of a deoxyribose sugar molecule, a phosphate group, and a nitrogen-containing base

•The four nitrogen-containing bases found in DNA molecules are▫adenine (A) ▫guanine (G) ▫cytosine (C) ▫thymine (T)

Adenine and guanine are called purines

Cytosine and thymine are called pyrimidines

The Sugars

•Cytosine pairs with guanine

•Adenine pairs with thymine

•Complementary base pairs are connected to each other by hydrogen bonds

5’ vs. 3’

•5’ end▫Phosphate

•3’ end▫OH-

•Read from 3’ to 5’

•Synthesized from 5’ to 3’

35

Learning Check NA1

Write the complementary base sequence for the matching strand in the following DNA section:

-A-G-T-C-C-A-A-T-G-C- • • • • • • • • • • • • • • • • • • • •

36

Solution NA1

Write the complementary base sequence for the matching strand in the following DNA section:

-A-G-T-C-C-A-A-T-G-C- • • • • • • • • • • • • • • • • • • • •-T-C-A-G-G-T-T-A-C-G-

37

Nucleosides in DNA

Base Sugar NucleosideAdenine (A) Deoxyribose

AdenosineGuanine (G) Deoxyribose

GuanosineCytosine (C) Deoxyribose CytidineThymine (T) Deoxyribose

Thymidine

38

Nucleotides in DNA

dAMP Deoxyadenosine monophosphatedGMP Deoxyguanosine monophosphatedCMP Deoxycytidine monophosphatedTMP Deoxythymidine monophosphate

Nucleotides and Nucleosides

DNA Stabilization--H-bonding between DNA base pair stacks

Advantages to Double Helix

•Stability---protects bases from attack by H2O soluble compounds and H2O itself.

•Provides easy mechanism for replication

RNA

Ribonucleic Acid

•Like DNA, RNA is a nucleic acid made up of repeating nucleotides

•RNA’s structure is different from DNA because it is a single-strand of nucleotides and the sugar backbone is made up of ribose

•Uracil replaces thymine in RNA and pairs with adenine

Forms of RNA•Three forms of RNA are involved in

protein synthesis▫mRNA▫tRNA ▫rRNA

mRNA

•mRNA carries genetic information from the DNA in the nucleus to the cytosol of a eukaryotic cell

•The process of copying genetic information from DNA to mRNA is called transcription

tRNA

•tRNA binds to specific amino acids, helping to form polypeptide chains

rRNA•rRNA makes up the ribosomes where

proteins are made

QUOTATION

The scientist is not a person who gives the right answers, he's one who asks the right questions.  ~Claude Lévi-

Strauss, Le Cru et le cuit, 1964

TAUTOMERISASI DNA

Nucleobases are ambidentate ligands, which offer several different coordination sites for metal ion.

An important aspect is the ability of nucleobases to exist in different tautomeric forms.

Tautomerisasi dari uracil

Keto-enol

The normal bases of DNA/RNA are usually present in the keto form.

The formation of false tautomer may lead to mispairing of nucleobases, and can alter genetic information transfer (mutagenic or carcinogenic)

•DNA replication is the molecular mechanism for inheritance.

•Key Terms▫DNA replication▫DNA polymerase

Copying DNA

•Replication of DNA▫base pairing allows

each strand to serve as a template for a new strand

Models of DNA Replication

• Alternative models▫so how is DNA copied?

conservative semiconservative dispersive

Semi-conservative replication• Meselson & Stahl

▫ label “parent” nucleotides in DNA strands with heavy nitrogen = 15N

▫ label new nucleotides with lighter isotope = 14N

“The Most Beautiful Experiment in Biology”

1958

parent replication

Make predictions…

Semi-conservative replication•Make predictions…

▫ 15N strands replicated in 14N medium ▫1st round of replication?▫2nd round?

1958

where should the bands be?

•Before a cell divides, it copies its DNA by a process called replication

•Replication results in two exact copies of the cell’s DNA

Template Mechanism

•Replication begins with the separation of the DNA chains by helicase enzymes

•Then as DNA polymerases move along the separated chain, new chains of DNA are assembled using nucleotides in the surrounding medium

• Nucleotides in DNA are grouped into genes, which contain the information required for the production of specific proteins

One gene, one polypeptide

• George Beadle & Edward Tatum▫ Orange bread mold

(Neurospora crassa)▫ “One gene-one enzyme”

hypothesis

• Genes actually dictate the production of a single polypeptide (part that makes up a protein/enzyme).▫ One gene-one polypeptide

Information Flow: DNA to RNA to Protein

Triplet Code

Each codon stands for a particular amino acid.

The codon AUG not only stands for methionine (Met), but also functions as a signal to "start" translating an RNA transcript.

There are also three "stop" codons that do not code for amino acids, but signal the end of each genetic message.

1.JELASKAN BEBERAPA FUNGSI ENZIM2.JELASKAN BEBERAPA FUNGSI ASAM

NUKLEAT3.JELASKAN PERBEDAAN DNA DAN RNA4. JELASKAN 3 STRUKTUR DNA