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Molecular Biology > Translation in Prokaryotes > Flashcards

Translation in Prokaryotes Flashcards

1
Q

What is the difference between nucleic acids and amino acids?

A

NA- all share similar structure - aromatic rings with some nitrogen NH and OH groups to participate in H bonding.
AA- vary - different properties e.g charge, acidity, hydrophobic/phillic nature.

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2
Q

The genetic code is ______ and links ______ language to ______ language.

A

Nearly universal - nucleic acid language to amino acid language.

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3
Q

How many nucleotides encode for an amino acid?

A

3 - called a codon.

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4
Q

How many amino acids do we use to make our proteins and then, how many possible permutations are there?

A

20 amino acids. We have 4 types of nucleotides and need to use at least 3 so we have (4x4x4) options = 64 possible permutations. This is enough to encode for 20 amino acids

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5
Q

How are codons read?

A

Non-overlapping - 5’ to 3’.

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6
Q

What is meant by the genetic code is degenerate.

A

Can be more than one codon that encodes for a particular amino acid - 64 distinct codons but only 20 amino acids - must be repeated.

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7
Q

How does the degeneracy of the genetic code help in avoiding mutation?

A

Codons can encode for more than one proteins so is mutation changed UUU to UUC it will still encode for the same amino acid.

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8
Q

What is the exception to the rule that there is more than one codon for each amino acid?

A

Tryptophan and Thymine - only one codon.

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9
Q

What can translation error not exceed?

A

1 per 10,000 amino acids.

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10
Q

Transfer RNA binds to _______ and brings _____.

A

A specific codon. An amino acid.

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11
Q

How many tRNAs are attached to each amino acid and where? What else is attached and where?

A

One at the 3’ CCA. An anticodon in a central loop.

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12
Q

What is the role of the anticodon loop?

A

It is different in each tRNA and so binds to different mRNA codons.

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13
Q

What is the amino acid attachment site in tRNA?

A

At the 3’ OH.

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14
Q

How are codons recognised by tRNA?

A

It is not as simple as base pairing to the anticodon as this would suggest each tRNA can only recognise one codon. Not true. E.g XYU and XYC encode for same amino acid - XYA and XYG encode same usually - tRNA molecule usually only care about first two - bind to any as long as it is the same amino acid usually.

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15
Q

What is the steric freedom/wobble effect for the 3rd base pairing between the mRNA codon and the tRNA codon?

A

The third base can be different for one tRNA anticodon as long as it encodes for the same amino acid.

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16
Q

How do the 1st and 2nd bases of the anticodon (tRNA) pair with the codon (mRNA)?

A

In the standard base pair way.

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17
Q

What does the 1st base of the anti-codon determine?

A

If tRNA reads 1, 2 or 3 types of codons. E.g 1st C = G, 1st U = A or G
1st I = U,C or A.

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18
Q

The binding of an amino acid to a particular tRNA establishes a ________.

A

Genetic code

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19
Q

What happens once an amino acid is bound to tRNA?

A

It can find the mRNA that can bind with it.

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20
Q

What does the binding of an amino acid to a tRNA do?

A

Activates the amino acid so that it can bond - forms an amino acid ester.

21
Q

What is the activation of an amino acid done by?

A

Aminoacyl tRNA synthase enzyme using ATP.

22
Q

How is amino acid recognised by aminoacyl-tRNA synthesis?

A

Physical size - card 31.

23
Q

How do amino-acyl tRNA synthases choose the correct tRNA partner?

A

There are multiple nucleotides on the tRNA which are used as recognition sites by amino-acyl tRNA synthases,

24
Q

What are ribosomes composed of?

A

RNA and proteins that coordinate the interplay of mRNA, tRNA and proteins for protein synthesis.

25
Q

In bacteria the _____S ribosome is composed of a large _____S and small _____S subunit.

A

70S, 50S, 30S

26
Q

Ribosomes bind _____ and _____. mRNA is bound within the ______ subunit and tRNA in the ___ and ______ are bound to the _______ via _______>

A

tRNA and mRNA. 30S. A and P sites are bound to the mRNA via anticodon-codon pairing.

27
Q

Prokaryotic transcription and translation take place in very different time and space?

A

No, coupled very closely.

28
Q

The 5’ end of mRNA interacts with ribosomes way before transcription of the 3’ end is finished. What does this imply? How can this occur?

A

Implies that the translation in prokaryotes (when ribosome associates with 5’ end of mRNA) begins before transcription is finished. Occurs because transcription and translation proceed in 5’ to 3’ direction and the template for translation is already transcribed at the 5’ end.

29
Q

What are the stages of translation?

A

Initiation
Elongation
Termination

30
Q

Draw a diagram of the basic process of translation in prokaryotes.

A

Physical card 32.

31
Q

Where does translation start/where is the first translated codon in mRNA?

A

Not at start, almost always >25nt away from the 5’ end.

32
Q

What does polycistronic mRNA refer to?

A

Each gene has its own transcriptional start and stop signals on mRNA. This is in bacteria.

33
Q

What are the translational start signals on prokaryotic mRNA? What do they do?

A
  1. Initiator codon (AUG - methionine) binds to anticodon of first tRNA.
  2. Shine-Dalgarno sequence (purine rich sequence at 10nt upstream from the initiator sequence) This binds to the ribosome.
34
Q

Bacterial translation starts with _______.

A

N-formylmethionine (fMet). A modified methionine.

35
Q

Initiatory tRNA recognizes _____ and brings ______.

A

AUG start codon and brings fMet.

36
Q

The initiator tRNA is positioned at the ______ in the ribosome. fMet is attached to the initiator tRNA by a ____.

A

P site. Amino-acyl tRNA synthase.

37
Q

Why cant methionine attached to tRNA be fomylated?

A

Only the methionine attached to the initiator tRNA can be formylated as the enzyme which does this is highly specific.

38
Q

Provide the steps and an image of translation initiation in prokaryotes.

A

Physical card 33

39
Q

How does elongation begin in translation in prokaryotes.

A

Start with ribosome P site with initiator tRNA. A and E sites empty.

40
Q

What establishes the reading frame for elongation?

A

Binding of the initiator tRNA to the AUG start codon. Will read the three base pairs after that.

41
Q

How is the second (or next) tRNA added into the large ribosomal complex?

A

Delivered by a protein elongation factor EF-Tu to the A site. Will not bring initiator tRNA as it can’t bind to it.

42
Q

What is the role of EF-Tu other than delivering the next tRNA?

A

Protects ester bond in activated amino acid - protects delicate amino acid ester link between amino acid and tRNA. Also check accuracy of anticodon/codon binding.

43
Q

What happens after both the P and A site in the large ribosomal complex become occupied in the elongation phase?

A

Want to form a peptide bond between the two amino acids.

44
Q

How is the peptide bonding of the two amino acids (fMet in P site and amino acid chaperones in A site) catalyzed?

A

This is catalyzed by rRNA in the large subunit - catalysis by proximity and orientation. Uses inherent reactivity of amine group on amino acid A site and ester on the initiator tRNA in the P site.

45
Q

How is the peptide bond chemically formed between the amino acids in the A and P site?

A

Amino group on A site performs nucleophilic attack on ester in P site on other tRNA. Amino acid is transferred from tRNA in P site to the amino acid on the A site. The N terminus of incoming amino acid added to C terminus of growing polypeptide chain - grows from the A site.

46
Q

How does translocation aid in the translation process?

A

During elongation. Physical card 34.

47
Q

Proteins are made ____ to _____ terminus

A

N to C.

48
Q

How do the stop codons work to terminate translation?

A

There is no tRNA than can move into the A site that will be complementary to the codon in the template mRNA. Stop codons are recognized by release factors which bind to the stop codon to bridge the stop codon and the P site. Facilitates cleavage of the polypeptide chain from the tRNA it is bound to.

49
Q

What happens to the ribosomal complex once translation is terminated?

A

It is dissociated by other enzymes and is free to participate in initiation for another mRNA translation.

Molecular Biology (14 decks)

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