(02) Gene to Protein Flashcards
central dogma of gene expression
DNA –> RNA –> Protein
define genotype
an organism’s genetic makeup - its complete set of genes
define phenotype
actual observable physiological traits
determined by genotype + environment
what is RNA
riboneucleic acid -
mRNA acts as a messenger to allow info stored in DNA to be used to make proteins
what is RNA
riboneucleic acid - acts as a messenger to allow info stored in DNA to be used to make proteins
three main steps involved in gene expression
Transcription
(RNA) Processing
Translation
describe transcription (general)
copying a gene’s DNA sequence to make a RNA molecule
what is the enzyme involved in the transcription step and what does it do?
RNA Polymerase
builds an RNA strand in the 5’ - 3’ direction using the template DNA strand
three steps of transcription + describe each
Initiation - Polymerase binds to promotor (upstream), splits DNA strands
Elongation - builds RNA out of complimentary nucleotides using template DNA strand, carries same info as Coding DNA strand but with Uracil instead of Thymine
Termination - detaches after terminator is reached
what is the TATA box and what does it do?
a small chunk of the DNA made up of T’s and A’s = eukaryotic PROMOTOR (so before initiation)
lies upstream of the Gene section
what has to happen in the initiation stage of transcription before transcription can actually commence?
assembly of multiple proteins
several transcription factors bind to DNA at the TATA box
example of transcription factor binding to TATA box
TATA box binding protein (TBP)
what is the transcription initiation complex
RNA polymerase + transcription factors (proteins) bound to DNA near TATA box, must form in the initiation stage before transcription can occur
how many nucleotides exposed when DNA is unwound in elongation stage
10-20
how are RNA nucleotides added to the strand in the elongation process?
goes 5’ - 3’
so the nucleotides are added to the 3’ end
3’OH of transcript binds with 5’ phosphate of incoming nucleotide
forming a phosphodiester bond
(this is just bonds between bases basically)
what is produced by the end of the transcription stage?
a pre-mRNA transcript
(still requires further processing)
three processes that occur in RNA processing
capping
tailing
splicing
define introns and exons
introns = non-coding regions (INTRuders lol)
exons = coding regions (including UTRs)
describe capping and tailing
capping: chemical group (methyl) added at 5’ end
tailing: Poly-A-tail added at 3’ end
describe splicing of RNA
introns are identified and removed by a spliceosome (an RNA protein complex), and exons are pasted together
describe alternative splicing
the process by which different combinations of exons are joined together, so multiple forms of mRNA / gene products can be produced from the same strand of pre-mRNA / gene
what is a codon
three bases / nucleotides together which translate to 1 amino acid
name the three main steps of translation
initiation, elongation, termination
(same as for transcription)
describe the structure of a ribosome
hamburger bun - large unit (top) and small subunit (bottom)
three sites: E, P and A (left to right)
name the three binding sites in ribosomes
A = aminoacyl-tRNA binding site
P = peptidyl-tRNA site
E = exit site
describe the initiation step of translation
small ribosomal subunit with initiator tRNA (carrying methionine, MET) binds 5’ cap of mRNA
small subunit scans downstream to find the translation start site (AUG)
H bonds form between initiator anticodon and mRNA
large ribosome subunit binds, completing INITIATION COMPLEX
what fuels the assembly of the initiation complex in translation
Energy in the form of GTP (guanosine triphosphate)
GTP –> GDP + P
describe the elongation step of translation
codon recognition - occurs at the A-site
Peptide bond formation - between two amino acids
Translocation - tRNA moves one place along, one leaving through E site, exposing A site
how do empty tRNA get “reloaded”?
reloadewd in the cytoplasm using aminoacyl-tRNA synthetases (type of enzyme)
describe translation termination
stop codon (UAG, UAA, UGA) enters A site
recognised by RELEASE FACTORS
promotes hydrolysis: causes water molecule to be added to the last amino acid so it is hydrolysed, releasing polypeptide
ribosomal subunits + components dissociate
why is control of gene expression important?
temporal and spatial control - to achieve the right thing at the right time in the right place
housekeeping - constant production of proteins
other proteins are produced in response to stimuli
where does all translation commence?
on FREE ribosomes floating in the cytosol
where do proteins destined for function in the cytosol complete translation?
commences translation of free ribosomes, also completes translation on free ribosomes in the cytosol
(obv they don’t need to go anywhere)
where do proteins that go through the endomembrane system (eg used for secretion) complete translation?
at fixed ribosomes on the Rough Endoplasmic Reticulum
how do proteins communicate where translation should be completed
signal peptide at N-terminus of protein binds to signal recognition peptide (SRP) (tells ribosome to pause translation and move to RER) which binds to SRP Receptor protein on lumen of ER
Translation restarts after the loss of the SRP, protein folds and creates final product in lumen of ER
what are post-translational modifications, where do they occur?
occurs in golgi (modifications) and cytosol
eg. phosphorylation!
where does transcription and translation occur in the cell?
transcription (and processing!) occurs in the nucleus
translation occurs in the cytosol after the completed mRNA has left though a nuclear pore
