Question

Complete the following questions. Illustrates the process of DNA transcription, translation, and protein synthesis.

1.    The stages of transcription are initiation, elongation, and termination. Draw a representation of each of these stages . Be sure to include the names of important enzymes and locations.

2.    Once mRNA is created through transcription, it is often processed. Explain how mRNA can be processed. Include the names of important enzymes or structures.

3.    Translation is how mRNA gets used to create the peptide sequence. Draw what is going on inside a ribosome. Be sure to include the locations of mRNA, tRNA, each subunit of the ribosome, and where the amino acid sequence forms.     

Answer 1

1.Transcription is the process in which the gene's DNA sequence is copied or transcribed to make an RNA molecule.RNA polymerase is the main transcription enzyme.Transcription begins whwn RNA polymerase binds to a promoter sequence near the beginning of a gene(directly or through helper proteins).RNA polymerase uses one of the DNA strands(the template strand) as a template to make a new complementary RNA molecule.Transcription ends in a process called termination.Termination depends on sequences in the RNA,which signal that the transcript is finished.

Transcription is an essential step in using the information from genes in our DNA to make proteins.Proteins are key molecules that gives cell structure and keep them running.

Transcription is the first step of gene expression.Before transcription can takes place,the double helix must unwind near the gene that is getting transcribed.the region of opened up DNA is called transcription bubble.

Transcription uses one of the two exposed DNA strands as a template,this starnd is called template strand.The RNA product is complementary to the template strand and is almost identical to the other DNA strand,called the non template strand.However,there one important difference,in the newly made RNA,all of the T nucleotides are replaced with U nucleotides.

The site on the DNA from which the first RNA molecule is transcribed is called the +1 site or the initiation site.Nucleotides that come before the initiation are given negative numbers and said to be upstream.Nucleotides that come after the initiation are marked with positive numbers and called downstream.

If the gene that is transcribed encodes protein the mRNA molecule will be read to make a protein in a process called translation.

RNA polymerase are enzymes that transcribe DNA into RNA.Using a DNA template,RNA polymerase builds a new RNA molecule through base pairing.RNA polymerase always builds a new RNA strand in the 5' to 3' direction.That is,it can only add RNA nucleotdes to the 3' end of the strand.

Transcription iitiation:

To begin transcribing a gene,RNA poymerases binds to the DNA of the gene at a region called the promotor.Basically,the promotor tells the polymerase where to begin with transcribing DNA.

Each gene,has its own promotor.A promotor contains DNA sequences that let RNA polymerase or its helper proteins attach to the DNA.Once the transcription bubble has formed,the polymerase can start transcribing.

Elongation:Once the RNA polymerase is in position at the promotor,the eongation begins.Elongation is the stage when the RNA strand gets longer.

During elongation,RNA polymerase walks along one strand of DNA,known as template strand,in the 3' to 5'direction.For each nucleotide in the template,RNA polymerase adds a matching RNA nucleotid to the 3' end of the RNA strand.

The RNA transcript is nearly identical to the non template or coding,strand of DNA.

Termination:RNA polymerase will keep transcribing untill it gets signals to stop.The process of ending transcription is called termination and it happens once the polymerase transcribes a sequence of DNA known as terminator.

After termination,transcription is finished.An RNA transcription that is ready to be used in translation is called messanger RNA or mRNA.

2.Messanger RNA is a large family of RNA molecules that convey genetic information from DNA to ribosome,where they specify the amino acid sequence of the protein products of gene expression.RNA polymerase transcribes primary transcript mRNA into processed,mature mRNA.This mature mRNA is then translated into polymer of amino acids, a protein.

The brief existance of mRNA molecule begins with transcription and ultimately ends in degradation.During its life,an mRNA may also be processed,edited and transported prior to translation.

Processing of mRNA differs greatly among eukaryotes,bacteria and archea.Non eukaryotic mRNA is become mature upon transcription and requires no processing,except in rare cases.Eukaryotic pre mRNA requires extensive processing.

5' cap addition

A 5' cap is modified guanine nucleotide that has been added to the front or 5' end of eukaryotic messanger RNA shortly after the start of transcription.The 5' cap consists of terminal 7-methylguanosine residue that is linked through a 5'-5' triphosphate bond to the first transcribed nucleotide.Its presence is critical for recognition by the ribosome and protection from RNases.

Cap addition is coupled to transcription and occurs co-transcriptioally,such that each influence to other.Shortly after the start of transcription,the 5'end of mRNA is bound by a cap synthesizing complex assiciated with RNA polymerase.This enzymatic complex catalyzes the chemical reactions that are required for mRNA capping.

Editing

In some cases, an mRNA is edited changing the nucleotide composition of that mRNA.The editing creates an early stop codon,which,upon translation produces shorter protein.

Polyadenylation

Polyadenylation is the covalent linkage of a polyadenylyl moiety to mRNA molecule.The PolyA tail and the protein bound to it aid in protection the mRNA from degradation by exonucleases.Polyadenylation is also important fpr transcription termination,export of the mRNA from the nucleus and translation.

Polyadenylation occurs during or immediately after transcription of DNA into RNA.After transcription has been terminated,the mRNA chain is cleaved through the action of an endonuclease complex associted with RNA polymerase.After the mRNA has been cleaved,around 250 adenosine residues are added to the free 3' end at the cleavage site.This reaction is catalyzed by polyadenylate polymerase.Just as an alternative splicing,there can be more than one polyadenylation varient of an mRNA.

Transport

Because eukaryotic transcription and translation are compartmentally separated,eukaryotic mRNA must be exported from the nucleus to the cytoplasm a process that may be regulated by different signnalling pathways.Multiple mRNA export pathways have been identified in eukaryotes.

Translation

As prokaryotic mRNA does not need to be processed or transported,translation by ribosome can begin immediately after the end of transcription.

Eukaryotic mRNA that has been processed and transported to the cytoplasm can then be translated by the ribosome.Translation may occur at ribosomes free floating in the cytoplasm,or directed to the endoplasmic reticulum by the signl recognition particle.

3.Once the mRNA has been produced,by transcription and processing the information present in the nucleotide sequence is used to synthesize the protein.

Translation involves decoding a messanger RNA and using its information to build a polypeptide or chain of amino acids.

In an mRNA the instructions for building a polypeptide come in groups of three nucleotides called codons.

There are 61 codons for amino acids.Three stop codons mark the polypeptide as finished.

One codon,AUG is a start signal to kick off translation.

These relationships between mRNA codons and amino acids are known as genetic code.

in translation,the codons of mRNA are read in order by molecules called transfer RNA or tRNA.

Each tRNA has an anticodon,a set of three nucleotides that binds to a matching mRNA codon through base pairing.The other end of tRNA carries the amino acid that is specified by the codon.

tRNA bind to mRNAs inside of a protein and RNA structure called ribosome.As tRNA enter slots in the ribosome and binds to codons,their amino acids are liked to the growing polypeptide chain in a cheical reaction.The end result is the polypeptide whose amino acid sequence mirrors the sequence of codons in the mRNA.