Genetic organization of Eukaryotic cells (transcription and translation)

Transcription

the process by which the information in DNA is copied into messenger RNA (mRNA) for protein production.

monocistronic mRNA

each eukaryotic mRNA contains information coding for only one protein, hence monocistronic, whereas prokaryotic mRNAs may encode more than one protein and are said to be polycistronic.

transcription of RNA requires the use of...

3 polymerase enzymes: RNA polymerase 1, RNA polymerase 2, and RNA polymerase 3

RNA polymerase 1

is responsible for the transcription of ribosomal RNA

rRNA

the RNA component of the ribosome and is essential for protein synthesis in all living organisms

RNA polymerase 2

is responsible for the transcription of mRNA (biggest focus)

RNA polymerase 3

is responsible for the transcription of both ribosomal RNA and transfer RNA

tRNA

transfer RNA sometimes archaically referred to as sRNA (soluble RNA) are a necessary component of protein translation (biological synthesis of new proteins according to the genetic code).
tRNA serves as the physical link between the nucleotide sequence of

transcription initiation requires the association of RNA polymerase 2 with..

7 general transcription factors (TFIIA, TFIIB, TFIID, TFIIE, TFIIF, TFIIH, TFIIJ).
However, only TFIID is the only transcription factor to have specific promoter binding ability and in higher eukaryotes it has the proper polypeptide to bind to the TATA bi

TFIID

transcription factor 2 D complex is composed of TBP and more than 8 TAFs

promoter

a region of DNA that initiates transcription of a particular gene and are located near the transcription start sites of genes on the same strand and are upstream (towards the 5' region of the sense strand).
in eukaryotes at least 7 different transcription

TBP

TATA-binding protein is a general transcription factor that binds specifically to a DNA sequence called the TATA box. (only used if a there is a TATA box sequence for TBP to bind to...otherwise TAFs used)

TAFs or TBP-Associated Factors

TATA-binding protein Associated Factors (and TBP) make up TFIID and are important because they add promoter selectivity, especially if there is no TATA box sequence for TBP to bind to,

TATA

a DNA sequence that indicates where a genetic sequences can be read and decoded. It is a type of promoter sequence, which specifics to other molecules where transcription begins. (24%of human genes contain a TATA box within the core promoter)

Initiation Step 1

TFIID recognizes the TATA element (or other promoter if there is no TATA box) on the DNA strand

Initiation Step 2

Assembly of the PIC (pre initiation complex).
TDFII binds to the TATA sequence (or other promoter), followed by the assembly if the other transcription factors and RNA polymerase 2.
however, interactions btw the PIC and DNA make it difficult for polymeras

Initiation Step 3

dismantling of the PIC. this requires hydrolysis of ATP by DNA helicase at subunit TFIIH which changes the conformation of the PIC thus enabling the RNA polymerase 2 to open base pairs around the transcription start site on the DNA strand (aka promoter).

Initiation Step 4

The new hydrolyzed open complex then enters the active site of RNA polymerase 2, which is where the base pairs are complimented to the template DNA strand during elongation.