biologi molekuler 2. dna dan rna (molekul...

BIOLOGI MOLEKULER4. TRANSKRIPSI dan mRNA Splicing

drh. Fajar Shodiq Permata, M.Biotech

3. REPLIKASI DNA dan OKAZAKI FRAGMENT

SUBPOKOK BAHASAN• PROSES TRANSKRIPSI DNA• mRNA splicing

TUJUAN PEMBELAJARAN1. Mahasiswa mampu memahami proses

transkripsi DNA dan mRNA splicing

REFERENSI

• Alberts, B, et al., 2008, Molecular Biology of The Cell, 5th ed., Garland Science Taylor and Francis Group: UK

• Cooper, G.M., and Hausman, R.E., 2007, The Cell: A Molecular Approach, 4th ed., ASM Press: Washington D.C.

• Alberts, B., et al., 2013, Essential Cell Biology, Garland Science: UK

POSTTEST

• Apa yang dimaksud replikasi DNA

• Apa fungsi Helicase, dan DNA polymerase

• Apa yang dimaksud dengan leading strand

• Apa yang dimaksud dengan lagging strand

• Apa yang dimaksud dengan Okazaki fragment

• Apa fungsi DNA ligase

OVERVIEW REPLIKASI DNA DAN OKAZAKI FRAGMENT

TRANSKRIPSI DNA

• Transcription is the first step of gene expression, in which a particular segment of DNA is copied into RNA (especially mRNA) by the enzyme RNA polymerase.

• Both DNA and RNA are nucleic acids, which use base pairs of nucleotides as a complementarylanguage.

• During transcription, a DNA sequence is read by an RNA polymerase, which produces a complementary, antiparallel RNA strand called a primary transcript.

TAHAPAN TRANSKRIPSI DNA

Initiation

Promoter escape

Elongation

Termination

INITIATION

• Transcription begins with the binding of RNA polymerase, together with one or more general transcription factor, to a specific DNA sequence referred to as a "promoter" to form an RNA polymerase-promoter "closed complex" (called a "closed complex" because the promoter DNA is fully double-stranded).[4]

INITIATION

• RNA polymerase, assisted by one or more general transcription factors, then unwinds approximately 14 base pairs of DNA to form an RNA polymerase-promoter "open complex" (called an "open complex" because the promoter DNA is partly unwound and single-stranded) that contains an unwound, single-stranded DNA region of approximately 14 base pairs referred to as the "transcription bubble."

TRANSCRIPTION FACTOR

• In molecular biology, a transcription factor (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcriptionof genetic information from DNA to messenger RNA, by binding to a specific DNA sequence.

• In turn, this helps to regulate the expression of genes near that sequence. This is essential in embryogenesis.

TRANSCRIPTION FACTOR

• Transcription factors work alone or with other proteins in a complex, by promoting (as an activator), or blocking (as a repressor) the recruitment of RNA polymerase (the enzyme that performs the transcription of genetic information from DNA to RNA) to specific genes.

TRANSCRIPTION FACTOR

SINTESIS TRANSCRIPTION FACTOR

• Transcription factors (like all proteins) are transcribed from a gene on a chromosome into RNA, and then the RNA is translated into protein.

• An implication of this is that transcription factors can regulate themselves.

• For example, in a negative feedback loop, the transcription factor acts as its own repressor: If the transcription factor protein binds the DNA of its own gene, it down-regulates the production of more of itself.

• This is one mechanism to maintain low levels of a transcription factor in a cell.

TERMINOLOGI

• gene expression – the process by which information from a gene is used in the synthesis of a functional gene product such as a protein

• transcription – the process of making RNA from a DNA template by RNA polymerase

• transcription factor – a protein that binds to DNA and regulates gene expression by promoting or suppressing transcription

• transcriptional regulation – controlling the rate of gene transcription for example by helping or hindering RNA polymerase binding to DNA

• upregulation, activation, or promotion – increase the rate of gene transcription

• downregulation, repression, or suppression – decrease the rate of gene transcription

• coactivator – a protein that works with transcription factors to increasethe rate of gene transcription

• corepressor – a protein that works with transcription factors to decreasethe rate of gene transcription

• response element /promoter– a specific sequence of DNA that a transcription factor binds to

ABORTIVE INITIATION

• After the first bond is synthesized, the RNA polymerase must escape the promoter.

• During this time there is a tendency to release the RNA transcript and produce truncated transcripts.

• This is called abortive initiation, and is common for both eukaryotes and prokaryotes.[5]

• Abortive initiation continues to occur until an RNA product of a threshold length of approximately 10 nucleotides is synthesized, at which point promoter escape occurs and a transcription elongation complex is formed

ELONGATION

• One strand of the DNA, the template strand (or noncoding strand), is used as a template for RNA synthesis.

• As transcription proceeds, RNA polymerase traverses the template strand and uses base pairing complementarity with the DNA template to create an RNA copy.

• This produces an RNA molecule from 5' → 3', an exact copy of the coding strand (except that thymines are replaced with uracils, and the nucleotides are composed of a ribose (5-carbon) sugar where DNA has deoxyribose (one fewer oxygen atom) in its sugar-phosphate backbone)

ELONGATION

• mRNA transcription can involve multiple RNA polymerases on a single DNA template and multiple rounds of transcription (amplification of particular mRNA), so many mRNA molecules can be rapidly produced from a single copy of a gene.

• The characteristic elongation rates in prokaryotes and eukaryotes are about 10-100nts/sec.

ELONGATION

• Elongation also involves a proofreading mechanism that can replace incorrectly incorporated bases. In eukaryotes, this may correspond with short pauses during transcription that allow appropriate RNA editing factors to bind. These pauses may be intrinsic to the RNA polymerase or due to chromatin structure.

ELONGATION

TERMINATION

• RNA transcription stops when the newly synthesized RNA molecule forms a G-C-rich.

• The poly-U transcript out of the active site of the RNA polymerase, terminating transcription.

• In the "Rho-dependent" type of termination, a protein factor called "Rho" destabilizes the interaction between the template and the mRNA, thus releasing the newly synthesized mRNA from the elongation complex.

• Transcription termination in eukaryotes is less well understood than in bacteria, but involves cleavage of the new transcript followed by template-independent addition of adenines at its new 3' end, in a process called polyadenylation

TERMINATION

EXON-INTRON in mRNA

• An intron is any nucleotide sequence within a gene that is removed by RNA splicing during maturation of the final RNA product.

• The term intron refers to both the DNA sequence within a gene and the corresponding sequence in RNA transcripts.[3]

• Sequences that are joined together in the final mature RNA after RNA splicing are exons. .

EXON-INTRON in mRNA

• Introns are found in the genes of most organisms and many viruses, and can be located in a wide range of genes, including those that generate proteins, ribosomal RNA(rRNA), and transfer RNA (tRNA).

• When proteins are generated from intron-containing genes, RNA splicing takes place as part of the RNA processing pathway that follows transcription and precedes translation.

EXON-INTRON in mRNA

• An exon is any part of a gene that will encode a part of the final mature RNA produced by that gene after introns have been removed by RNA splicing.

• The term exon refers to both the DNA sequence within a gene and to the corresponding sequence in RNA transcripts.

• In RNA splicing, introns are removed and exonsare covalently joined to one another as part of generating the mature messenger RNA.

EXON-INTRON in mRNA

mRNA splicing

• mRNA splicing is conducted by Spliceosomeand aided by snRNP (small nuclear Ribonucleo Protein)

• Removed Intron will be lariat shape

• Exons will combined each other to be mature RNA

mRNA Splicing

TERIMA KASIH

SOURCE : https://en.wikipedia.org/wiki/DNA_replicationhttps://en.wikipedia.org/wiki/Okazaki_fragments