Lecture 14 - The genetic code Flashcards

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1
Q

How many different combinations of codons are there in nucleotides?

A

64

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2
Q

How many different amino acids are there in nucleotides?

A

20

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3
Q

What is the Nirenberg-Matthaei experiment?

A
  • Bacteria was blended, this created all the means to make a protein apart from a nucleotide sequence
  • Added nucleotide sequence of UUUUUUUU
  • Set up 20 tubes each with a different amino acid
  • Only labelled phenylalanine gave a labelled polypeptide that let the sequences be decoded
  • Found out 3 UUUs was enough to code for an amino acid, and it codes for phenylalanine
  • 61 of 61 codons coded for amino acids
    3 didn’t and were stop codons
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4
Q

What is the meaning of a degenerate code?

A

It means more than one codon will code for the same amino acid

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5
Q

What is a reading frame?

A

The sequence of codons between a specific start codon to a specific stop codon

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6
Q

What is the function of tRNA?

A

To link a specific amino acid and recognise a codon in mRNA
This ensures a match between the amino acid and the codon

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7
Q

What is the structure of tRNA?

A

Made up of
An anticodon that interacts with a codon
An amino acid acceptor arm where the amino acid binds
Modified nucleotides, especially in the anticodon loop

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8
Q

What are aminoacyl-tRNA synthases?

A

Each tRNA is recognised by one of the 20 amino-acyl-tRNA synthases
Each one is specific for amino acid and tRNA
This means some tRNAs recognise more than one codon

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9
Q

How does one tRNA recognise more than one codon?

A

G-U base pairing
Inosine base pairs with A C and U

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