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NUT1004 > RNA > Flashcards

RNA Flashcards

1
Q

What is RNA a polymer of

A

Ribonucleotides

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2
Q

What is the structure of RNA

A

single stranded structure of ribonucleotides linked by 5’ to 3’ phosphodiester bonds
Each ribonucleotide has a ribose sugar, phosphate group and nitrogenous bases (A, C, G, U)

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3
Q

Does RNA follow chargaff’s rule

A

No as single stranded

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4
Q

Is DNA or RNA more prone to degradation

A

RNA as DNA is more stable

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5
Q

What size is RNA

A

Variable but usually between 100-5000nt

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6
Q

What is the difference between a ribose and deoxyribose sugar

A

Ribose contains oxygen (OH instead of H)

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7
Q

When is RNA double stranded

A

When self anneals to form hairpin loop structure

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8
Q

What are the 3 main types of RNA in cells

A

mRNA, tRNA and rRNA

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9
Q

What are the characteristics of mRNA

A
  • complementary to DNA code
  • 5% of total cell RNA
  • most heterogeneous in size and base sequence
  • Largest RNA molecule
  • codon
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10
Q

What are the functions of mRNA

A
  • carries one gene at a time from DNA to protein synthesis machinery in the cytoplasm
  • easily degraded and only exists when needed to manufacture a protein
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11
Q

What is DNA strand is RNA identical to

A

Coding strand/ non-template

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12
Q

What is DNA strand is RNA complementary to

A

Template/ non-coding strand

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13
Q

What is a codon

A

Component of mRNA sequence where the sequence is organised into sets of three nucleotides that code for one amino acid

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14
Q

What is the start codon of mRNA

A

First codon of an mRNA transcript to be translated (AUG which codes the the AA methionine)

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15
Q

What are the stop codons of mRNA

A

Codons that signal the end of translation

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16
Q

What are the 3 stop codons in mRNA

A

UAA, UAG, UGA

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17
Q

What is meant by the degeneracy of the genetic code

A

The GC is degenerate as there are many codons which code for the same amino acid

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18
Q

What is pre-mRNA

A

What mRNA is originally synthesised as before processing and translation, containing both introns and exons

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19
Q

What regions of the mRNA molecule are not translated

A

The 5’ cal and poly(A) tail in 3’ (mRNA extremities) and any regions 5’UTR (upstream start codon) and 3’UTR (following stop codon)

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20
Q

What are UTRS and what are their roles

A

Untranslated regulatory regions
5’UTR is involved in translation regulation and 3’UTR is involved in translation efficiency and mRNA localisation and stability

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21
Q

What is the role of the 5’ cap and poly(A) tail in 3’

A

Protect mRNA extremities from digestion by enzymes

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22
Q

What are the characteristics of tRNA

A
  • small single stranded molecule
  • some base pairing to fold into 3D clover leaf shape
  • Anticodon
  • 15% of total cell RNA
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23
Q

Which end of tRNA is slightly longer and why

A

3’ end as attached to specific amino acid

24
Q

What is the function of tRNA

A

Carry amino acids and have different anticodons to transfer the AA from the cytoplasm to the protein synthesis machinery

25
Q

What is the primary structure of tRNA

A

Extensive internal base complementarity in the ribonucleotide sequence of the tRNA strand results in extensive base pairing and the formation of the secondary structure

26
Q

What is the secondary structure of tRNA

A

clover leaf structure stabilised by hydrogen bonding with 5 main arms/ loops

27
Q

What is the tertiary structure of tRNA

A

L shaped structure formed by further folding of the clover leaf and hydrogen bonding between T and D arms

28
Q

What are the 5 arms of tRNA

A

Acceptor arm, T arm, extra arm, anticodon arm and D arm

29
Q

What is the acceptor arm

A

Arm containing amino acid

30
Q

Where are the D and T arms located

A

T- 3’ side
D- 5’ side

31
Q

What are ribosomes

A

Small organelles found in the cytoplasm or attached to the endoplasmic reticulum that consist of two subunits

32
Q

What is the role of ribosomes

A

Site of protein synthesis

33
Q

What is the difference between eukaryotic and prokaryotic ribosomes

A

Larger in eukaryotic 80S vs 70s

34
Q

How many strands of rRNA and protein molecules does the large subunit of the ribosome consist of

A

3 strands and 49 molecules

35
Q

How many strands of rRNA and protein molecules does the small subunit of the ribosome consist of

A

1 strand and 33 molecules

36
Q

What size are the large and small ribosome subunits

A

Large is 60S and 40S for small

37
Q

What is the rRNA to protein ratio and what does this mean

A

Close to 1, therefore ribosome is roughly equal parts protein and RNA in terms of mass

38
Q

What sizes are the three strands of rRNA in large subunit

A

28S, 5.8S and 5S

39
Q

What size is the strand of rRNA in small subunit

A

18S

40
Q

What are the characteristics of rRNA

A
  • 80% of total cell RNA
  • part of ribosome in both subunits (3 strands in large 1 in small)
  • formed from a single 45S precursor RNA molecule ( apart from 5S rRNA which is transcribed independently)
41
Q

What is the function of rRNA

A
  • ribosomal assembly
  • maintains the form of ribosome
  • catalyse peptide bond formation in protein translation
42
Q

What 3 ways can eukaryotic mRNA be processed

A

1) addition of m7G cap and Poly A tail
2) exon splicing
3) alternative splicing

43
Q

What is the role of rRNA in translation

A

The AUG start codon on mRNA is recognised by the ribosomes (made of rRNA and proteins) and the 2 subunits of the ribosomes associate and start decoding each codon until the ribosome reaches a stop codon and the ribosomal subunits disassociate

44
Q

Describe the addition of the m7G cap to mRNA

A

7-methyl guanosine triphosphate cap added to 5’ immediately after initiation of transcription

45
Q

What if the function of the m7G cap

A

Increases RNA stability by protecting it form RNases, enables splicing of exons and allows recognition by ribosomes

46
Q

Where is the poly-A tail added on mRNA

A

3’ end

47
Q

What is the function of the poly-A tail on mRNA

A

Allows RNA export by transporter molecules, enables RNA translation, protects RNA from degradation outside the nucleus by RNases, signals end of transcription

48
Q

Describe polyadenylation (addition of polyA tail)

A

After transcription the pre mRNA is cleaved after the AAUAAA consensus sequence in the 3’ region, from here 50-250 adenine nucleotides are added to the cleavage site to form the tail (not coded in DNA sequence)

49
Q

What are introns

A

Long intervening sequences that are removed by cleavage at splice sites (conserved sequences) and are therefore not translated into polypeptide

50
Q

What are exons

A

Short sequences that are translated into amino acids and connected to each other during the splicing process

51
Q

What is splicing

A

The processing of pre mRNA to remove or splice out introns and connect remaining exons

52
Q

What is alternative splicing

A

A regulatory mechanism by which variations in the incorporation of exons in mature mRNA leads to the production of more than one protein

53
Q

What is the function of alternative splicing

A

Generates diversity and complexity in cells

54
Q

How is alternative splicing tissue specific

A

Patterns of alternative splicing mean that certain protein variants are produced in specific tissues

55
Q

What is the RNA world hypothesis

A

In early life self replicating RNA molecules were used as genetic material and a biological catalyst before the appearance of DNA and proteins

56
Q

Why is RNA not used primarily as biological catalyst and genetic material today

A

1) During evolution protein based enzymes created by catalytic RNAs would take over the catalytic function as greater diversity with proteins (20AA) than RNA bases (4) so more diverse enzymatic activity
2) DNA is more stable for the storage of genetic material

NUT1004 (14 decks)

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