DNA transcription - L4

Differnet types of RNA

• Ribosomal RNA

• tRNA

• mRNA

all made using different RNA polymerases

Differnet types of RNA polymerase

1—> Pre ribosomal RNA —> used to make ribosme components which ae used in portein sytheiss

2—> siRNA, miRNA —> regulatory RNA e.g. in splicing

3—> tRNA —> protein synthesis

what is mRNA made form

• Formed form replication bubble of DNA separating out DNA into single stands

• It exposes template stand - which mRNA is generated form (primary RNA trascript)

• mRNA will be the same as coding strand - except have U instead of T

How RNA polymerase binds to mrna in prok

• site of where tarscription starts is known as +1

• coding region is downstream/ comes after +1

• there is also a promotor region upstream of +1 site this is where RNA polymerase binds as recognises sequnce to then start trascription - so tarscription starts form +1 and to the right until reaches stop codon

• mRNA has sequence to show the start of translation AUG

what are at the begining and end of teh mRNA

• beginning have leader - 5’ UTR

• at the end have trailer region - 3’ UTR

• they are regulatory for ribosome, act as signal for ribosomes to translate sequence int o proteins

what is added ONLY to Euk mRNA

• have 5’ Cap and at 3’ position get Polyateal

• 5’ cap helps against degradation and used as signals for when ribsome comes along

Gene promoter region in Prok:

• in promoter region have specific sequences that are recognized by RNA polymerase

• these are -35 sewynec and -10 sequence

• RNA polymerase recognized these and binds knowing there is a gene to transcribe

• these sequences are consensus sequences (just means most commonly occurring sequence in all examples that have been studied)

Gene promotor in Euk:

• in promotor region have a TATA box and further upstream have CAAT box and GC box

• proetin that bids to these boxes are TF (DNA bidning proetins)

• these boxes are recognised by RNA polymerase that its the start fo a gene

• different gene have different boxes its a way to help regulate gene activity

• The immature mRNA produces contains; 5’ cap, leader region, trailer region, Poly(A), exons and introns

• later modified to then get mature mRNA

In eukaryotes genome gene structure

• each gene has its own promoter region

• this is called monocistronic gene organisation

• so each gene has its own mRNA sequence and its start site for translation

• at the end makes proteins

Prok genome gene structure

• have Polycistronic gene organisation

• gene that are related in function group together ad so share a promotor region

• will make a single strand of mRNA but each gene will still have its own promotor

• at end of translation will still produce separate proteins even though had a single stand of mRNA

Lac operon in E.coli

• in operon have LacZ, lacY and LacA

• LacZ —> encodes enzyme beta galactoside which breaks down glucose into lactose and glactose

  when not enough glucose breaks down lactose to glucose and galactose to gen gucose for energy

• LacY —> encodes lactose eprmase which is imbedded in cel emembrane to allow lactose to move into cell

• LacA —> encodes enzyme thioglactoside transacetylase which breask down toxic thiglucatoside that moves into cell with lactose

what is at the opertor region

• have LacI in opertor region locate din promotor region

• not included in operon

• it encodes repressor molecule which regulate transcription of operon

what happens in this situation?

• preferred substrate of glucose is present so do not need lactose

• Repressor molecule which is made by LacI (not part of operon) is bound to opperator region

• stops RNA polymerise form binding so get no transcription as do not need it

what happens here ?

• operator region not boudn to by repressor

• so RNA polymerase can bind and transcribe

• get low level transcription/basal level as have both glucose and lactose

what happens in this situation?

• we have no glucose

• have CAP binding to cap site which secures RNA polymerase to have elevated level of tarnscription

what happens on a molecular level

• when lactose is present have some lactose that change structure to form isomer called allolactose

• allolactose binds to repressor changing its shape so no longer able to bind to operator region allowing RNA polymerase to bind and transcribe genes

• when have no glucose have high levels of cAMP, cAMP binds to CAP which causes taht to bind to CAP site and so have higher levels of tarsncription as secures RNA polymerase

regulation of transcription in Euk

• each gene has its own promotor region

• need a set of TF to start

• A,B,D,E,F,H are the TF used

• D recognises TATA box and bi=rings A + B

• the brings RNA polymerase 2 with 2F

• THIS THEN BRING E AND H (H is a helicase)

• RNA polymerase is then polymerised and actiavted so breaks away from all these TF and transcribes genes

how is transcription upregulated in Euk

• area called enhancer region where other DNA binding proteins can bend

• when these bind are called enhansersomes which cause DNA to bend backwards on itself for the enhansersomes to interact with RNA polymerase machinary

• also have co-activators which also up regulate

what is removed ot make mature mRNA

• 5’ Cap

• Poly(A)

• Introns

removing different introns….

• results in different proteins being produced

• e.g. Calcitonin produced form exons 1,2,3,4 controls Ca levels

• but calcitonin gene-related peptide produced form exons 1,2,3,5,6 is an important molecules that causes migraines