(02) Gene to Protein

Question 1

central dogma of gene expression

Answer 1

DNA –> RNA –> Protein

Question 2

define genotype

Answer 2

an organism’s genetic makeup - its complete set of genes

Question 3

define phenotype

Answer 3

actual observable physiological traits
determined by genotype + environment

Question 4

what is RNA

Answer 4

riboneucleic acid -
mRNA acts as a messenger to allow info stored in DNA to be used to make proteins

Question 5

what is RNA

Answer 5

riboneucleic acid - acts as a messenger to allow info stored in DNA to be used to make proteins

Question 6

three main steps involved in gene expression

Answer 6

Transcription
(RNA) Processing
Translation

Question 7

describe transcription (general)

Answer 7

copying a gene’s DNA sequence to make a RNA molecule

Question 8

what is the enzyme involved in the transcription step and what does it do?

Answer 8

RNA Polymerase
builds an RNA strand in the 5’ - 3’ direction using the template DNA strand

Question 9

three steps of transcription + describe each

Answer 9

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

Question 10

what is the TATA box and what does it do?

Answer 10

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

Question 11

what has to happen in the initiation stage of transcription before transcription can actually commence?

Answer 11

assembly of multiple proteins

several transcription factors bind to DNA at the TATA box

Question 12

example of transcription factor binding to TATA box

Answer 12

TATA box binding protein (TBP)

Question 13

what is the transcription initiation complex

Answer 13

RNA polymerase + transcription factors (proteins) bound to DNA near TATA box, must form in the initiation stage before transcription can occur

Question 14

how many nucleotides exposed when DNA is unwound in elongation stage

Answer 14

10-20

Question 15

how are RNA nucleotides added to the strand in the elongation process?

Answer 15

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)

Question 16

what is produced by the end of the transcription stage?

Answer 16

a pre-mRNA transcript
(still requires further processing)

Question 17

three processes that occur in RNA processing

Answer 17

capping
tailing
splicing

Question 18

define introns and exons

Answer 18

introns = non-coding regions (INTRuders lol)
exons = coding regions (including UTRs)

Question 19

describe capping and tailing

Answer 19

capping: chemical group (methyl) added at 5’ end
tailing: Poly-A-tail added at 3’ end

Question 20

describe splicing of RNA

Answer 20

introns are identified and removed by a spliceosome (an RNA protein complex), and exons are pasted together

Question 21

describe alternative splicing

Answer 21

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

Question 22

what is a codon

Answer 22

three bases / nucleotides together which translate to 1 amino acid

Question 23

name the three main steps of translation

Answer 23

initiation, elongation, termination
(same as for transcription)

Question 24

describe the structure of a ribosome

Answer 24

hamburger bun - large unit (top) and small subunit (bottom)
three sites: E, P and A (left to right)

Question 25

name the three binding sites in ribosomes

Answer 25

A = aminoacyl-tRNA binding site
P = peptidyl-tRNA site
E = exit site

Question 26

describe the initiation step of translation

Answer 26

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

Question 27

what fuels the assembly of the initiation complex in translation

Answer 27

Energy in the form of GTP (guanosine triphosphate)
GTP –> GDP + P

Question 28

describe the elongation step of translation

Answer 28

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

Question 29

how do empty tRNA get “reloaded”?

Answer 29

reloadewd in the cytoplasm using aminoacyl-tRNA synthetases (type of enzyme)

Question 30

describe translation termination

Answer 30

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

Question 31

why is control of gene expression important?

Answer 31

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

Question 32

where does all translation commence?

Answer 32

on FREE ribosomes floating in the cytosol

Question 33

where do proteins destined for function in the cytosol complete translation?

Answer 33

commences translation of free ribosomes, also completes translation on free ribosomes in the cytosol
(obv they don’t need to go anywhere)

Question 34

where do proteins that go through the endomembrane system (eg used for secretion) complete translation?

Answer 34

at fixed ribosomes on the Rough Endoplasmic Reticulum

Question 35

how do proteins communicate where translation should be completed

Answer 35

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

Question 36

what are post-translational modifications, where do they occur?

Answer 36

occurs in golgi (modifications) and cytosol
eg. phosphorylation!

Question 37

where does transcription and translation occur in the cell?

Answer 37

transcription (and processing!) occurs in the nucleus
translation occurs in the cytosol after the completed mRNA has left though a nuclear pore