Transcription - Gene Expression Flashcards
(25 cards)
what is gene expression
the process by which information from a gene is used in the synthesis of a functional gene product
what is a functional gene product
an action molecule that has been produced by DNA information
what is gene
a defined region (sequence) of DNA that produces a type of RNA molecule that has some function
what sequences may a gene contain
- responsible for the regulation of the synthesis of the RNA
- that produce the RNA
- responsible for the further processing of the RNA
what is transcription
DNA dependent RNA synthesis - synthesis of a single strand RNA molecules using a double strand DNA molecule
what is the RNA polymerase
a crucial enzyme that transcribes DNA into RNA, acting as the molecular engine of gene expression by synthesizing RNA from a DNA template
function of the RNA polymerase
- catalyses extension of the 3’ end of an RNA strand by one nucleotide at a time
- forms an RNA molecule by catalysing the information of phosphodiester bonds between ribonucleotides
- selects the correct nucleotides to incorporate into RNA based on the sequence of the DNA which is being transcribed
what is the RNA polymerase II
a crucial enzyme that transcribes DNA into RNA, acting as the molecular engine of gene expression by synthesizing RNA from a DNA template
what is de novo
the creation of a new chain from basic building blocks, rather than pre-existing or modified chains
what is primase
an enzyme that has an active site that can bind 2 ribonucleotide triphosphates (dNTP) and catalyse the formation of a phosphodiester bond to form a dinucleotide which provides a 3’ OH group for further dNTP addition
what is a coding strand
codes all the information (reads from 5’ to 3’)
what is a template strand
where mRNA is transcribed from (reads from 3’-5’ but RNA synthesis occurs from 5’ to 3’)
what are the 3 stages of transcription
- initiation
- elongation
- termination
explain the initiation stage of transcription
- transcription factors bind to the TATA box and other regions of the promoter
- RNA pol II binds forming a transcriptional initiation complex together with the transcription factors
- the DNA strands separate and RNA pol II starts mRNA synthesis
what is a helicase
an enzyme that unzips the DNA by breaking H-bonds between the DNA base components
what is the purpose of helicase in transcription
helicase is recruited by RNA pol II and binds to AT rich region of the promoter to start unzipping
explain the elongation stage of transcription
- RNA pol II uses the template strand as a template
- inserts complementary RNA nucleotides in the 5’-3’ direction
what is a topoisomerase II
an enzyme that releases the tension (supercoil) that builds up ahead of RNA pol II
what is a coding sequence
portion of a gene’s DNA that is translated into a protein
what is a promoter
DNA segment that is rgcognised by RNA polymerase to initiate transcription
what are untranslated regions (UTR’s)
transcribed but usually not translated region that contains regulatory elements (sequence) that has an influence on gene expression at the transcriptional and/or translational level
function of 5’ UTR
facilitates the addition of the 5’ G cap
function of 3’ UTR
facilitates the addition of the poly-A tail
Function of the 5’ G cap
- prevents mRNA degradation
- promote intron excision
- provides a binding site for small ribosomal subunits
