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#8 Cytogenetics 1:00-2:00 MW

Falinchao, Joshua Jude P.

BMLS III- E

Messenger RNA (mRNA)

mRNA forms a single, uncoiled chain of nucleotides

mRNA carries genetic information from the DNA in the nucleus to the cytosol

In this sense, they are messengers from the DNA to the rest of the cell

Transfer RNA (tRNA)

tRNA consists of a single chain of about 80 nucleotides folded up into a hairpin shape

tRNA binds to a specific amino acid

Ribosomal RNA (rRNA)

rRNA isthe most abundant form of RNA

rRNA consists of RNA nucleotides in a globular form

rRNA joins with proteins to make ribosomes

Transcription unit- Sequence of nucleotides in DNA that codes for a single RNA molecule, along

with the sequences necessary for its transcription; normally contains a promoter, an RNA-

coding sequence, and a terminator

Primary transcript - the RNA molecule produced bytranscription prior to processing, including splicing.

Proximal- next to or nearest the point of attachment or origin, a central point, or the point of view.

Distal- situated away from the point of attachment or origin or a central point.

Start point- origin of the translation process.

Downstream sequence - Downstream (or 3' to) is in the direction of transcription (or translation).

Upstream sequence - (5' to) is in the direction from which the polymerase (or ribosome) has come.

Consensus sequence- A theoretical representative nucleotide or amino acid sequence in which each

nucleotide or amino acid is the one which occurs most frequently at that site in the different sequences

which occur in nature.

Promoter

a segment of DNA usually occurring upstream from a gene coding region and acting as a controlling element in the expression of that gene.

Antisense strand- DNA normally has two strands, i.e., the sense strand and the antisense strand. In

double-stranded DNA, only one strand codes for the RNA that is translated into protein. This DNA strand

is referred to as the antisense strand.

Sense strand- The strand that does not code for RNA is called the sense strand.
http://medical-dictionary.thefreedictionary.com/transcriptionhttp://medical-dictionary.thefreedictionary.com/transcription


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Enhancers- Enhancer sequences are regulatory DNA sequences that, when bound by specificproteins called transcription factors, enhance the transcription of an associated gene.

Silencers- elements have been identified that decrease transcription of neighboring genes.

Activators- A transcriptional activator is a protein that increasesgene transcription of a gene or set of

genes.

Co-activators- A coactivator is a protein that increasesgene expression by binding to

anactivator (ortranscription factor)which contains aDNA binding domain.

RNA polymerase:

Type Location RNA synthesized Effect of -amanitin

I Nucleolus Pre-rRNA for 18, 5.8 and 28S rRNAs Insensitive

II Nucleoplasm Pre-mRNA, some snRNAs Sensitive to 1 g/ml

III Nucleoplasm Pre-tRNAs, 5S rRNA, some snRNAs Sensitive to 10 g/ml

Subunits - E. coli RNA polymerase is a multi-subunit protein. The five distinct polypeptide subunits of E.

coli RNA polymerase are summarized inTable 26.1.Two copies of the subunit are present, along with

one each of , ', , and , giving an Mr of about 450,000 for the holoenzyme. The subunit may be

involved in regulation, but its precise role is not yet clear. It is not required for the reconstitution of

active enzyme.

Subunit is the target for rifampicin inhibition and also plays a role in transcription initiation. is the

subunit with the catalytic site for chain elongation.

The subunit plays an important role in directing RNA polymerase to bind to template at the proper

site for initiation--the promoter site--and to select the correct strand for transcription. The addition

of to core polymerase reduces the affinity of the enzyme for nonpromoter sites by about 104, thereby

increasing the enzyme's specificity for binding to promoters. In at least some cases, gene expression is

regulated by having core polymerase interact with different forms of , which would in turn direct the

holoenzyme to different promoters.

Prokaryotic/eukaryotic RNA polymerases - RNA polymerases from different prokaryotic sources are

remarkably similar in subunit size and composition. Eukaryotic RNA polymerases have much more

complex and diverse subunit structures.

T7 RNA polymerase - Not all RNA polymerases in prokaryotic systems have multiple subunits. The best-

known exception is RNA polymerase specified by bacteriophage T7. The left-hand 20% of the

chromosome of its linear genome (as usually drawn) is transcribed early in infection by E. coli RNA

polymerase. One of these early gene products is a virus-specified RNA polymerase. This single-subunit

enzyme (Mr = 98,000) responds to different DNA control sequences and is responsible for all T7

transcription late in infection.Recent crystallographic analysis of T7 RNA polymerase shows a DNA-binding domain similar to the

"hand" structure seen in DNA polymerases, with a palm, fingers, and thumb that wrap about the DNA

template
http://en.wikipedia.org/wiki/Transcription_(genetics)http://en.wikipedia.org/wiki/Gene_expressionhttp://en.wikipedia.org/wiki/Activator_(genetics)http://en.wikipedia.org/wiki/Transcription_factorhttp://en.wikipedia.org/wiki/DNA-binding_proteinhttp://www.pearsonhighered.com/mathews/ch26/ta26p1.htmhttp://www.pearsonhighered.com/mathews/ch26/ta26p1.htmhttp://en.wikipedia.org/wiki/DNA-binding_proteinhttp://en.wikipedia.org/wiki/Transcription_factorhttp://en.wikipedia.org/wiki/Activator_(genetics)http://en.wikipedia.org/wiki/Gene_expressionhttp://en.wikipedia.org/wiki/Transcription_(genetics)


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Sources:

http://groups.molbiosci.northwestern.edu/holmgren/Glossary/Definitions/Def-D/downstream.html

http://www.ncbi.nlm.nih.gov/mesh/68016384

http://medical-dictionary.thefreedictionary.com/Promoter+regions+(genetics)

http://www.medterms.com/script/main/art.asp?articlekey=20468

http://www.nature.com/scitable/definition/enhancer-163

http://www.ndsu.edu/pubweb/~mcclean/plsc431/geneexpress/eukaryex4.htm

http://www.pearsonhighered.com/mathews/ch26/c26srp.htm
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