التعبير الجيني: النسخ والترجمة

Gene Expression

• Genetic info from DNA turns into protein building
• This process involves gene to mRNA to protein

Transcription and Translation

• Information from DNA transferred to RNA
• Nucleotide sequence on mRNA translates to amino acid sequence on a protein

Central Dogma

• Genetic information in DNA goes to RNA then protein
• mRNA goes from DNA to ribosome
• tRNA turns mRNA into amino acid sequence
• rRNA works as a catalyst and a structure

RNA Synthesis: Transcription

• RNA is synthesized using a DNA template along with messenger (mRNA), transfer (tRNA), and ribosomal (rRNA)
• There are two differences in chemistry, RNA has ribose instead of deoxyribose and contains uracil instead of thymine
• RNA has a secondary structure which is single stranded except for some viruses

Types of RNA

• mRNA are coding RNA molecules
• tRNA and rRNA are both noncoding RNA molecules
• Small RNAs function in mRNA splicing, rRNA processing, and regulation of gene expression

RNA Stability

• Unfolded messenger RNAs are present in bacteria and archaea but are broken down by enzymes called ribonucleases
• Stable RNAs such as rRNAs and tRNAs are long lived because of their secondary structures

mRNA Turnover

• The rapid turnover of mRNA in bacteria and archaea helps to quickly adapt to changing environmental conditions and halt translation of mRNA that are no longer needed

Stages of RNA Synthesis

• Binding of RNA polymerase to promoter sequences of the DNA template
• Initiation of RNA synthesis
• Elongation of the polynucleotide chain
• Termination of synthesis

RNA Polymerase and Transcription

• RNA polymerase is the enzyme that catalyzes the polymerization of ribonucleoside triphosphates (NTPs)
• Synthesis of the RNA chain occurs in the 5’ to 3’ direction
• The synthesized RNA chain and the template DNA strand run antiparallel to each other
• Prokaryotic organisms only have one RNA polymerase

Bacterial RNA Polymerase Composition

• Prokaryotic RNA is an enzyme complex made up of six polypeptides consisting of 2α, β, β', ω, and σ subunits
• The sigma subunit recognizes special promoter sequences on DNA.
• Newly synthesized RNA reaches a few nucleotides in length and sigma separates from the other subunits

Transcription in Bacteria

• RNA polymerase catalyzes transcription
• Energy drives polymerization and is gained from the hydrolysis of two energy-rich phosphate bonds of incoming ribonucleoside triphosphates
• No priming is needed to begin
• Chain growth occurs in the 5' to 3' direction
• Newly synthesized strand of RNA runs antiparallel to the DNA template strand
• Transcription continues until it runs into specific transcription terminators
• Transcription happens on small units of DNA
• Different genes have different frequencies depending on what the cell requires
• The process is highly regulated

Promoters

• Subunits create an enzyme complex, an RNA polymerase holoenzyme
• RNA polymerase core separates from sigma
• Sigma functions to appropriately recognize locations on DNA
• Beginning transcription needs RNA polymerase to recognize initiation sites on the DNA, which are prompts
• Promoters are recognized by sigma and RNA polymerase binds to them
• Bacteria promoters are marked by sigma

Transcription Termination

• In Bacteria, the termination signal has a GC-rich sequence containing an "inverted repeat"
• During DNA transcription, RNA structures form a "stem-loop," or intrastrand base pairing
• "Stem-loops", followed by a run of adenines in DNA templates yield a run of uridines of mRNA, which are strong transcription terminators
• RNA polymerase stops at the stem loop junction, dissociating DNA and RNA
• Stopping transcription is another mechanism, where the terminator protein is Rho
• Rho binds tightly and is moved further to the RNA polymerase- DNA complex
• Once polymerase has crossed through, the RNA has paused at the "Rho-dependent termination site," the "Rho termination site"
• Termination requires both the RNA and RNA polymerase to be extracted from the DNA

Sigma in E. Coli.

• All promoter sequences are recognized by one sigma factor
• Sigma spots two, highly saved locations for start site
• 10 base pairs stream, region -10, the Pribnow box, and consensus is the TATAAT box
• 35 base pairs also stream start site and the consensus sequence is the TTGACA box
• Such prompts are called strong promoters

Transcription, Polycistronic mRNA

• Gene-formed transcription is contained as RNA from genes
• A majority encode the proteins, RNA (ribosomal, transferred)
• Prokaryotic cell rRNA is 16S, 23S, and 5S are genes to form "single transcriptional unit" and contain "tRNA"

Transcriptional and Polycistronic mRNA functions:

• Gene encoded enzyme and pathway (prokaryotic cell)
• Gene acid, like biosynthesis and amino are cloned along operon
• Assembles genes for pathways and are needed for their processes
• RNA polymerase passes through during trans and transcribes RNA "polycistronic mRNA"

Polycistronic mRNA Info:

• Has multiple open reading frames
• Encodes amino acids
• RNA translated and synthesized
• Polypeptides using ribosome

Eukaryotic Transcription

• Archaeal and eukaryotic RNA polymerases share similarities and more complex than Bacteria
• Archaea has one RNA polymerase and eukaryotes have three
• Archaeal polymerase are similar to eukaryotic RNA polymerase II and has 11–13 subunits

Eukaryotic Prompt Factors

• Significant factors are the "TATA" box (6-8 base-pair) and is located stream for transcription start at 18-27 nucleotides
• The TATA has the binding protein, or TBP, one for many transcription factor to Archaea and eukaryotes
• B identification factor exists for TATA box and is by Archael transcription factor or TFB
• The initiation element is located at launch date

Archaeal and Eukaryotes: RNA Polymer

• TBP has bound TATA and TFB has bound BRE, and archaeal RNA polymerase have bound initiates transcription
• The processes is similar to Eukaryotes

Termination Types

• Archaeal genes are repetitive
• Suspect terminator contains a series of Thymines
• The process is for RNA polymerase (eukaryotes)
• Some processes needs a factor for the protein and transcription

Eukaryotic Processes

• Genes consist of two, coding separation regions
• Exons and Noncoding
• RNA is crucial for forming translation suitable RNAs
• Introns and the m RNA have exons

RNA Processes

• Intervening sequence code
• RNA/ t RNA have introns/transcription in the

RNA Splicing

• Intron and exon removes, joining to process, called splicing
• The splicing is inside nucles
• Includes act macromolecule (RNA/Protein) called spliceosome
• Excision happens, from primary transcript
• Intervening sequence also have rare processes

Two Steps of Processes

• Capping occurs and caps nucleotides at the 5'
• Translation has been removed at mRNA
• Addition comes with poly residues (polyA) is added

Stability in PolyA's

• The mRNA is attacked
• mRNA has to be taken away