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biomolecular science > transcription, translation and replication > Flashcards

transcription, translation and replication Flashcards

1
Q

what is central dogma

A

the overarching term and theory that describes the process of how we get from DNA to the actual expression and creation of proteins

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2
Q

where does transcription take place

A

nucleus

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3
Q

where does translation take place

A

ribosome

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4
Q

what is transcription in general

A

the synthesis of RNA from a DNA template - the process that converts the genetic information contained within the DNA strands into RNA to provide information for protein synthesis

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5
Q

what are the 4 stages of transcription

A

initiation
unwinding of the DNA
elongation
termination

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6
Q

what is the catalyst involved in transcription and what does it do

A

RNA polymerase - catalyses the initiation and elongation of RNA chains in a 5’ to 3’ direction

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7
Q

what is the promoter region in DNA

A

where RNA polymerase recognises the DNA and initiates transcription

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8
Q

which nucleotide is usually transcribed first

A

purine

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9
Q

explain the initiation stage in transcription

A

RNA polymerase binds to the promoter region and unwinds 17 base pairs of DNA to form a ‘bubble’ for the beginning of transcription

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10
Q

explain the elongation stage of transcription

A

duplex DNA is unwound at the forward end of the RNA polymerase and rewound at the rear end. The RNA/DNA hybrid rotates during elongation. The RNA polymerase moves along the DNA. The length of the RNA-DNA hybrid is determined by enzyme, hybrid is separated and RNA leaves the enzyme

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11
Q

explain the termination stage of transcription

A

this is where a stop signal/codon stops transcription and; the RNA-DNA hybrid dissociates, the melted region of DNA rewinds and RNA polymerase releases the DNA

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12
Q

provide a brief summary of transcription

A

RNA polymerase unwinds the DNA double helix to expose the DNA template strand, elongation then moves along the DNA templates strand due to the formation of phosphodiester bonds, creating a complementary RNA strand

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13
Q

what does the addition of a cap on the front end of an mRNA molecule do

A

protect the mRNA and initiate translation

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14
Q

what does the addition of a poly(A) tail on the rear end of a mRNA molecule do

A

protects mRNA from degradation and helps export the mRNA from the nucleus to the cytoplasm

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15
Q

describe the structure of rRNA

A

it is folded into complex, distinctive 3D shapes with multiple sub-units - small and large - which vary between prokaryotic and eukaryotic cells

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16
Q

what are the subunits of rRNA in prokaryotes

A

small subunit = 30S
large subunit = 50S - made of 2 rRNA subunits

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17
Q

what are the subunits of rRNA in eukaryotes

A

small subunit = 40S
large subunit = 60S - made of 3 rRNA subunits

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18
Q

what do tRNA contain

A

an amino acid attachment site and a template-recognition site called an anti-codon - 3 nucleotides that are complementary to a specific codon on an mRNA strand

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19
Q

what is the structure of a tRNA molecule

A

a clover-leaf structure held together by hydrogen bonds between bases, with the anticodon and amino acid binding site on opposite sides of the clover

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20
Q

simply what is translation

A

the synthesis of proteins

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21
Q

what are the three binding sites on a ribosome during translation

A

P (peptidyl-tRNA)
A (aminoacyl-tRNA)
E (exit)

22
Q

what is a codon

A

a group of 3 bases

23
Q

why can the genetic code be described as degenerate

A

one amino acid can be coded for by several different codons

24
Q

why can the genetic code be described as unambiguous

A

a codon only codes for one amino acid

25
why can the genetic code be described as universal
as the same codons and amino acids are used by different species
26
what does a tRNA molecule do
it delivers one amino acid, that is specific to a codon of mRNA, to a ribosome
27
what is wobble pairing between tRNA and mRNA during translation
a protective feature that allows for some flexibility in the pairing between the third nucleotide in the codon and the corresponding nucleotide in the tRNA - some tRNA molecules can recognise the same amino acid
28
what is the codon for initiation in eukaryotes and where can it be found
AUG - found nearly always 25 nucleotides away from the 5' end of an mRNA strand
29
in addition to the start codon what else helps align the mRNA with the correct binding sites in order to initiate translation (different for prokaryotes and eukaryotes)
prokaryotes = a purine-rich sequence on the 5' side of the initiator sequence eukaryotes = Kozak sequence followed by AUG
30
what happens during the elongations stage of translation
- the tRNA binds to the AUG codon in the P site of the ribosome - the next tRNA binds to the exposed codon in the A site of the ribosome - a peptide bond forms between the two adjacent amino acids that each tRNA molecule holds - translocation occurs - this is where the ribosome moves one codon to the right shifting the tRNA molecules into different sites - this releases the first tRNA molecule and allows another one to join the A site
31
what are the 4 models suggested for DNA replication and which is accepted today
1. the duplication of the entire DNA molecule 2. the semi-conservative model (accepted model) 3. conservative model 4. dispersive model
32
what does the semiconservative model suggests occurs during DNA replication
one original parental strand will produce a first generation of 2 DNA strands, each containing one strand of parental DNA and one strand made up of DNA nucleotides
33
who proposed the semiconservative model and who confirmed it (and with what)
James Watson and Francis Crick suggested it, Meselson and Stahl confirmed it using isotopic labelling of nitrogen
34
describe the experiment conducted to confirm the semiconservative model of DNA replication
- E Coli bacteria was grown in a medium containing a heavy isotope of nitrogen, resulting in the heavy nitrogen being incorporated into the DNA molecules, making them denser - the bacterial culture was then moved to a light isotope of nitrogen medium - DNA samples were collected at different time points after the shift to the lighter nitrogen, and these samples were subjected to density gradient centrifugation -the first generation exhibited an intermediate density with the presence of one heavy and one light strand and the next generation exhibited two distinctive bands - one at the intermediate density and one at the lighter density
35
describe the conservative model for DNA replication
the entire DNA double stranded molecule acts as a template for the synthesis of an entirely new double stranded molecule
36
describe the dispersive model theory for DNA replication
the newly synthesised DNA strands consisted of alternating fragments of old and new DNA - ending with a mixture of DNA instead of duplication
37
what is the main enzyme involved in DNA replication
DNA polymerase (1)
38
what does DNA polymerase primarily do
promote the formation of phosphodiester bonds joining units of DNA backbone
39
what are the 4 things DNA synthesis requires
1. The four deoxynucleotide 5' triphosphates (dATP/GTP/CTP/TTP) 2. Mg2+ 3. A DNA template 4. A primer strand with a free 3'-OH
40
what other two functions can DNA polymerase do during DNA replication
1. Proofread the new strand of DNA and go backwards when a mistake is made in the base pairing 2. Primer removal during DNA repair
41
name 4 other enzymes used in DNA replication
1. DNA polymerase 3 2. DNA ligase 3. DNA primase 4. Helicase and gyrase
42
what are the two strands called in DNA replication
leading and lagging strands
43
what is the leading strand in DNA replication
where helicase is unwinding the strand and DNA polymerase makes new DNA in a 5' to 3' direction
44
what is the lagging strand in DNA replication
where DNA polymerase cannot synthesise because it would have to go in a 3' to 5' direction (which it can't), so synthesis is in short segments called Okazaki fragments
45
what are DNA topoisomerases and what do they do during DNA replication
they are enzymes that prevent the build up of twisting that would naturally form during DNA unwinding, that would cause a resistance to the progress of replication
46
what is the difference between topoisomerase 1 and 2
topoisomerase 1 cuts a single backbone on the DNA, enabling the strands to swivel around each other, whereas topoisomerase 2 cuts both backbones, enabling one double-stranded DNA to pass through another
47
what is the action of NA primase during DNA replication
it synthesises RNA primer on both the leading and lagging strands
48
what is the action of DNA polymerase 3 in DNA replication
it catalyses the synthesis of new DNA in 5' to 3' direction using free 3'-OH groups on RNA primers
49
what enzymes doe the joining of Okazaki fragments on the lagging strand of DNA replication require and why
DNA polymerase 1 - removes RNA primers and allows 5' to 3' polymerase activity to fill the gaps DNA ligase - joins the fragments
50
what are the function and composition of telomeres
function: replication of linear chromosome ends composition: RNA and proteins (reverse transcriptase)

biomolecular science (14 decks)

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