Transcription and mRNA Processing

Vocabulary flashcards related to transcription and mRNA processing.

Primary Transcript

The first version of mRNA made from DNA during transcription; also known as pre-mRNA.

Messenger RNA (mRNA)

Carries information needed to make a protein.

Post-transcriptional processing

Occurs in the nucleus of eukaryotes to convert pre-mRNA into mature mRNA.

Prokaryotic mRNA Processing

In prokaryotes, translation often starts during transcription due to limited time for extensive post-transcriptional processing.

Modifications to Pre-mRNA

1. Addition of a 5' cap

2. Addition of a poly(A) tail

3. Splicing

Addition of 5' cap

Involves adding an altered guanine nucleotide to the 5' end of the pre-mRNA.

Primary Function of 5' Cap

Required for translation in eukaryotes; the ribosome initially binds here and scans downstream along the mRNA to find the start codon.

what is the poly (A) tail

binds to poly (A) binding protiens.

its made of 50-250 A added at the 3’ end (polyadenylation)

the Poly (A) tail was not coded by DNA its added by a enzyme called poly (A) polymerase so it the tail has no template

poly (A) tails primary function

protects mRNA from degradation and it helps mRNA stablity and it helps export the mRNA from the nucleus to the cytoplasm.

what is the poly(A) binding protiens

Proteins that bind the poly (A) tail of mRNA, involved in mRNA stability, nuclear export, and initiation of translation. and protenction of being eaten up by exoribonucleases

exoribonucleases

enzymes that degrade RNA molecules in cytoplasm from the outside (chews up RNA from ends), important in the regulation of mRNA stability and turnover.

what happens when the poly(A) tail shortens over time

when tail shortens over time and it gets to short the mRNA gets to unstable and is quickly degraded

what is splicing

removes interior portion of RNA. this happens in the nucleus during RNA processing

what are the interior portions of RNA

non-coding section of the RNA called introns and splicing joins exons which are coding regions together

spliciesomes

ribonucleoprotien enzymes-cut RNA and splice- “tape” it together again to create the final mRNA molecule for translation.

exons

are expressed and are kept in the final mRNA and are used to build the final protien

introns

are intervening and are eliminated/cut during splicig it is cut out in post transcriptioned processing mRNA

what type of organisms are exons and introns common in

eukaryotes

results of exons and introns

DNA sequence may not correspond with final protien becuase of introns, the DNA sequence does not directley match the protien that is eventually made. thats why RNA processing (especially splicing) is crucial for eukaryotic gene expression

what is Alternative processing pathway

when parts of the same pre-mRNA are spliced diffrently,it can result in diffrent mRNA and diffrent protiens. it happens in 90% of human genes

what does alternative processing pathway allow for

may allow specialization to various tissues

and this allows one gene to code for many protiens

What types of RNAs are modified before becoming functional

tRNAs adn rRNAs

RNAi

control gene expression or protect against viruses by silencing viral genes (RNA interfrence)

CRISPR RNAs (crRNAs) stands for

clustered regularly interspaced short palindromic (sequence read the same in both directions) repeats (need some in both directions).

Where is CRISPR found

found in naturally in bacteria and archea it acts as part of their immune system against viruses

process of acquision

first stage of CRISPR-Cas immunity where bacteria acquire segments of viral DNA

phage DNA

viral DNA from bacteriophage repersents the foreign genetic material from a virus that has infected the bacterium

spacers (viral)

pieces of phage DNA is inserted into CRISPR array (which is located in bacterial c’some)

the spagers aer small segments of the phage DNA and this is where the viral DNA is “remembered”

CRISPR array and spacers

aer part of the bacterial genome and consists of alternating spacers (viral DNA segments) and palindormic repeats

palindormes

flank of the newely inserted viral spacers,forming a record of past infections

once the the trancription of the CRISPR array happens then what happens

expressoin the goal of expression was to process the stored viral DNA (spacers) into functional guide molecules (crRNAs) for futrure viral attacks

pre-crRNA

transcription of the CRISPR array results in a long RNA molecule called pre crRNA

what does the CAS protiens do

they are protiens that cut the long pre-crRNA into shorter crRNA (guides for cuts)

CRISPR-associated with

CAS protiens, and leads to effector complex

what is the goal of the effector complex

Assemble the “guided missle” to target and destroy viral DNA

“guided missle”

The crRNA guides the cas protien to the matching viral DNA for specific targeting and cleavage.

what is the effector complex

crRNA binds to the cas protein froming a “guided missle” complex

goals and results of interfernce stage of CRISPR

goal-to destroy the viral DNA tha has entered the bacteral cell

results: virus is neutralized and prevented from replicating and the bacterial cell is protected from infection

DNA repair mechanims of jamming together ends

After CAS9 protien cuts DNA the cell uses its natural DNA as a repair mechanism to fix the break through pathways like non-homologous end joining often resulting in gene (becoming a nonfuctional allele) knokouts

nonhomologus end joining

the cells “jam together” the broken ends of DNA,essentially stitcing them back together resulting some times in erro during repair,like changes to the DNA sequence.

DNA repair mechanism that fixes with matching squences

if template DNA is provided (usually with the desired seq.) the cell uses it to repair the break in a more accurate manner, a process known as homologus recombonation

homologus recombonation

Added DNA sequence on ends homologus to seuqence on each side of the cut internal sequence can be whatever DNA you want to add

Uses of CRISPR include

Gene therapy

replacing harmful alleles in the body

only works when fixing SOME cells is enough