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Molecular Biology > Mod 7- From RNA To Protein > Flashcards

Mod 7- From RNA To Protein Flashcards

1
Q

What is the genetic code composed of?

A

20 amino acids but only 4 nucleotides in messenger RNA

So a group of nucleotide is required to code for 20 amino acids

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2
Q

What is a codon?

A

A 3 nucleotide or triplet code used to specify the amino acids

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3
Q

How many possible codons are there?

A

64 possible codons

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4
Q

How many codons specify amino acids?

A

61 codons

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5
Q

How many codons are stop codons?

A

3 codons

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6
Q

What does the term ‘degeneracy’ refer to in the genetic code?

A

Many amino acids have more than one codon

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7
Q

What is an open reading frame?

A

The sequence of codons that runs from a specific start codon to a specific stop codon

There are 3 reading points

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8
Q

What is the start codon for almost every protein chain?

A

AUG (codes for Methionine)

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9
Q

What are the three stop codons?

A

UAA, UGA, UAG

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10
Q

What is the function of tRNA?

A

To link to a specific amino acid and to recognize a codon in mRNA

Ensures amino acid-codon match

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11
Q

What is the role of aminoacyl-tRNA synthetases?

A

Each tRNA is recognized by only one of 20 aminoacyl-tRNA synthetases

aminoacyl-tRNA = tRNA joined to an amino acid

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12
Q

True or False: Each aminoacyl-tRNA synthetase is specific for both an amino acid and a tRNA.

A

True

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13
Q

What is the paradox regarding tRNAs and codons?

A

> 20 tRNAs but < 61 codons

So some tRNAs recognise more than 1 codon

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14
Q

What is ‘wobble’ in the context of tRNA?

A

A mechanism that allows unconventional base pairing between the third base in codon and the first base in anticodon

This allows the tRNA to recognise more than 1 codon

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15
Q

What does the wobble mechanism permit?

A

Degeneracy in the genetic code

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16
Q

Fill in the blank: The genetic code is primarily specified by _______ interactions.

A

amino acid-tRNA

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17
Q

What is the significance of modified nucleotides in tRNA?

A

They are especially present in the anticodon loop

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18
Q

What are the implications of degeneracy in the genetic code?

A

61 codons for 20 amino acids and >1 tRNA species for certain amino acids

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19
Q

What does the term ‘anticodon’ refer to?

A

The part of tRNA that interacts with the codon

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20
Q

What is the amino-acid acceptor arm?

A

The part of tRNA where the amino acid binds

21
Q

What are the three stages of translation?

A

Initiation, Elongation, Termination

22
Q

What is the role of the ribosome in translation?

A

The ribosome facilitates the assembly of amino acids into polypeptide chains.

It is where protein synthesis occurs

23
Q

What are the two subunits of the ribosome?

A

Small subunit and Large subunit

24
Q

What does the term ‘Svedberg’ (S) refer to?

A

A measure of the sedimentation rate of suspended particles centrifuged under standard conditions.

25
Q

What is the significance of the Shine-Dalgarno sequence?

A

It interacts with 16S rRNA of the 30S small subunit to identify the site of initiation of protein synthesis.

26
Q

What is the function of initiation factors in translation?

A

They assist in the assembly of the initiation complex and ensure the accuracy of tRNA binding.

27
Q

Which amino acid is used for initiation in prokaryotes?

A

Formylmethionine (fMet)

28
Q

Fill in the blank: The process of attaching amino acids to tRNA is known as _______.

A

Amino acid activation

29
Q

What are the roles of EF-Tu and EF-G during elongation?

A
  • EF-Tu: mediates aminoacyl-tRNA entry to ribosome
  • EF-G: mediates translocation
30
Q

What happens during the termination stage of translation?

A

Release factors bind to the A site, hydrolyzing the polypeptide chain from tRNA.

31
Q

True or False: GTP is involved in all stages of protein synthesis.

A

True

32
Q

What are the three prokaryotic release factors?

A
  • RF1: UAA/UAG
  • RF2: UAA/UGA
  • RF3: assists RF1 or 2 binding to ribosome
33
Q

What energy sources are required for protein synthesis?

A
  • ATP
  • GTP
34
Q

What does the P site of the ribosome do?

A

It is the peptidyl-tRNA site where peptide bonds form.

35
Q

What does the A site of the ribosome do?

A

It is the aminoacyl-tRNA site where incoming aminoacyl-tRNA binds.

36
Q

What is the role of GTP in translation?

A

GTP = Guanosine triphosphate

Provides energy through hydrolysis during:
initiation- addition of large subunit

elongation- addition of aminoacyl-tRNA by EF-Tu and EF-G, peptide synthesis and translocation

termination- release of peptide chain and dissociation of ribosome

GTP —> GDP + Pi

37
Q

What is the role of tRNA in translation?

A

tRNA transports amino acids to the ribosome for incorporation into polypeptides.

38
Q

What does the term ‘ternary complex’ refer to in translation?

A

The association of aminoacyl-tRNA, EF-Tu, and GTP.

39
Q

Fill in the blank: The mRNA is read in the _______ direction during translation.

A

5’ to 3’

40
Q

What is the function of the large subunit of the ribosome?

A

It catalyzes peptide bond formation between amino acids.

41
Q

What are the key components required for protein synthesis?

A
  • Ribosomes
  • tRNA
  • mRNA
  • Accessory factors
  • Energy (ATP and GTP)
42
Q

What is the primary role of ribosomal RNA (rRNA) in the ribosome?

A

It forms the structural and functional core of the ribosome.

43
Q

What is a key feature of the secondary structure of rRNA?

A

It is made up of 40 or more stem loops.

44
Q

Describe amino acid activation

A
  • attachment of amino acids to tRNA 3’ acceptor arm
  • amino acid + ATP —> amino acid-AMP (AA-AMP) + PP (phosphate)
  • AA-AMP + tRNA —> AA-tRNA + AMP
45
Q

Name the initiation factors in translation

A
  • IF1 = Blocks A (acceptor) site to tRNAi -met, inhibits premature 30S-50S interaction
  • IF2 = tags tRNAi and regulates entry of tRNA into ribosome
  • IF3 = inhibits premature 30S-50S interaction, stabilises free 30S, accuracy check for tRNAi-met binding
46
Q

Describe the initiation of translation

A
  • Initiation factors (active IF2)/ GTP interacts (binds to) with 30S ribosomal subunit
  • Initiator tRNA (tRNAi) and mRNA join complex
  • Start codon aligns with P-site where tRNAi-met binds to complete initiation complex
  • IF2 becomes inactive and dissociates as well as IF3
  • byproducts = ATP —>ADP and GTP —>GDP
47
Q

Describe elongation in translation

A
  • Starts at P site (peptide-tRNA site) where peptide bonds form
  • tRNA-Meti is the only tRNA which can bind to the P site
  • Elongation factors are necessary
  • These bind to the ribosome A site
  • A site (aminoacyl-tRNA site) = where incoming aminoacyl-tRNA binds
  • Ternary complex formed = aminoacyl-tRNA-EFTu-GTP
  • Causes peptide bonds formation
  • Tu-GDP is ejected and recycled
  • Association of EF-G-GTP and ejection of empty tRNA from the P site
  • Ribosome translocates so peptidyl tRNA is now in P site, A site is free
48
Q

What are the 3 prokaryotic release factors in translational termination?

A

RF1 = UAA/UAG

RF2 = UAA/UGA

RF3 = helps RF1 or 2 to bind to ribosome-GTPase

49
Q

Describe termination in translation

A
  • RF-GTP binds to A site when termination codon appears
  • Release factor is recruited (a G-protein)
  • Hydrolysis of polypeptide chain from tRNA
  • This is released to be processed
  • Dissociation of tRNA and RF

Molecular Biology (10 decks)

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