Expression of Genetic Information

8/12/2019 Expression of Genetic Information

1/33

Expression of Genetic Information : FromTranscription to Translation

Prof. DR. dr. Hadyanto Lim, M.Kes, SpFK, FESC, FIBADepartment of Pharmacology and Molecular Biology

Faculty of Medicine, Methodist University of Indonesia - Medan

Molecular Biology Research, Postgraduate School,

University of Sumatra Utara - Medan


2/33

The DNA Double Helix


3/33

The Flow of Information in a Eukaryotic Cell

DNA RNA Protein


4/33

The pathway from DNA to Protein


5/33

How is the relationship

between genes and proteins ?


6/33

A Scottish Physician

1908 Archibald Garrot, reported thesymptoms exhibited by persons with certainrare inherited diseases were caused by the

absence of specific enzyme. The disease wasalcaptonuria, because the urine becomesdark on exposure to air.

Garrod found that persons with alcaptonurialacked an enzyme in their blood.


7/33

Lack of homogentisate oxidase in alcaptonuria


8/33

Inborn error of metabolism by Garrod

Relationship between a genetic defect, a specificenzyme, and a specific metabolism condition.

Hypothesis One gene - one enzyme.

One gene - one polypeptide.

Modification

A single gene often generates a variety of

polypeptide.


9/33

The BeadleTatum Experiment in 1940s


10/33

Conclusion of the BeadleTatum Experiment

The cell have an enzymatic deficiency that prevents them

from synthesizing this essential compound (e.g.

panthothenic acid of coenzyme A).


11/33

Genes can be expressed with different efficiencies


12/33

Complementary base pairs in the DNA

double helix

Uracil form base pairs with adenine


13/33

Differences

between DNA

and RNA

1. The nucleotide in

RNA are

ribonucleotides,

containing sugar ribose

(ribonucleic acid)rather than

deoxyribose

2. Like DNA, RNA

contains the basesadenine (A), guanine

(G), and cytosine (C), it

contains the base uracil

(U) instead of thymine

(T) in DNA.


14/33

DNA always occur in cells as a double-strandedhelix, RNA is single-stranded.

RNA chain can fold up into a particular shape, justas a polypeptide chain folds up to form the final

shape of a protein.

The ability of RNA to fold into complex three-

dimensional shapes allows some RNA molecules to

have precise structural and catalytic functions.

Differences between DNA and RNA


15/33

RNA can fold into specific structure


16/33

From DNA to RNA

The RNA in a cell is made by DNA transcription.

Transcription begins with the opening and

unwinding of a small portion of the DNA doublehelix.

One of the two strands of the DNA double helixthen acts as a template for the synthesis of an RNAmolecule.


17/33

From DNA to RNA


18/33

The nucleotide sequence of the RNA chain is

determined by the complementary base-pairing

between incoming nucleotides and the DNA

template.

The RNA chain producedthe transcriptis

therefore elongated one nucleotide at a time. It hasa nucleotide sequence that is exactly

complementary to the strand used as the template.

From DNA to RNA


19/33

Unlike a newly formed DNA, the RNA strand doesnot remain hydrogen-bonded to the DNA templatestrand. Instead, just behind the region whereribonucleotides are being added.

The RNA chain is displaced and the DNA helixreforms.

Because RNA are copied from only a limited regionof the DNA, RNA molecules are much shorter thanDNA molecule.

Differences in DNA and RNA Replication


20/33

Transcription of two genes as observed under

the electrone microscope


21/33

Question

How DNA molecule is copied

into RNA (transcription) inprocaryote and eucaryote ?


22/33

Transcription Process in Procaryote

Require RNA polymerase holoenzyme

Play a role in transcription process :

- Binding of the polymerase to the DNA

template.

- Initiation of transcription.

- Elongation.

- Termination.


23/33

Steps in transcription cycle of bacterial RNA polymerase

1. The RNA polymerase holoenzyme (polymerase coreenzyme plus factor) assembles and locates a promoter.

2. Promoter unwinds the DNA at the position in whichtranscription is to begin.

3. The initial RNA synthesis (aborted initiation) is relativelyinefficient.

4. Once RNA polymerase has managed to synthesize about10 nucleotides of RNA, it breaks its interaction with thepromoter DNA.


24/33

5. During the elongation mode, transcription is

highly processive, with the polymerase leaving the

DNA template and releasing the newly transcribed

RNA only when it encounters a termination signal.

Step 6 & 7. Termination signal are typically

encoded in DNA. Many function by forming an

RNA structure that destabilizes the polymerases

hold on the RNA.

Steps in transcription cycle of bacterial RNA polymerase

h l f b l l


25/33

The transcription cycle of bacterial RNA polymerase

(Procaryote)


26/33


27/33

The importance of RNA polymerase orientation


28/33

Transcription Process in Eukaryotes

Require for a large variety of accessoryproteins, or transcription factors.

Play a role in transcription process :- Binding of the polymerase to the DNA

template.

- Initiation of transcription.

- Elongation.

- Termination.


29/33

Transcription Initiation in eucaryotic cell requires many proteins


30/33

Initiation of transription of a

eucaryotic gene by RNA

polymerase

The promoter contains a DNAsequence called the TATA box, located

25 nucleotides away from the sites at

which transcription is initiated.

Through its subunit TBP, TFIIDrecognizes and binds the TATA box.

The RNA polymerase itselfassemble at the promoter.

TFII H uses ATP to pry apart theDNA double helix.

The site of phosphorylation is along C terminal polypeptide tail,

called C terminal domain (CTD).


31/33

Summary of the steps leading from gene to protein in

eucaryote and bacteria (procaryote)


32/33


33/33

Next

Control of Gene Expression

Documents

Expression of Genetic Information