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Molecular and Cell Biology > L8 The genetic code > Flashcards

L8 The genetic code Flashcards

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1
Q

What does understanding the genetic code allows us to know?

A
  1. Infer protein sequences from DNA sequence information.
  2. Infer protein structure from its sequence
  3. Infer protein function
  4. Design tools to study protein function.
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2
Q

Was the genetic code determined before or after techniques developed for the isolationd and sequencing of genes?

A

Before

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3
Q

How do tRNA adaptor molecules read mRNA sequences?

A

Through codon and anti codon interactions.

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4
Q

In what direction are codons read?

A

Codons are read in a 5’ to 3’ direction and direct the protein synthesis in an N’ to C’ direction.

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5
Q

How are mRNA codons recognised?

A

They are recognised by base-pairing with anticodon sequences with cognate tRNAs.

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6
Q

What does aminoacylation mean?

A

The process of adding an amino acid to a tRNA molecule.

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7
Q

What is the role of a charged tRNA?

A

A charged tRNA carries an amino acid to the ribosome for protein synthesis.

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8
Q

What are the two groups involved in peptide bond formation?

A

aminoacyl and peptidyl goups.

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9
Q

What are the features of the genetic code?

A
  1. Genetic studies by Crick and Brenner showed that the genetic code was based on triplet codon sequences.
  2. They are nonpunctuated, meaning that all nucleotides have a meaning.
  3. They are degenerate, meaning multiple codons have the same meaning.
  4. Almost all codons have a meaning - Universal.
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10
Q

How was the code figured out?

A

Through in vitro translation and ribosome binding assays

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11
Q

How were cell extracts used to study protein synthesis?

A

Cell extracts were “programmed” to make protein using artificial RNAs synthesized with polynucleotide phosphorylase.

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12
Q

What was the significance of poly(U) RNA?

A

Poly(U) RNA specifically directed the incorporation of phenylalanine into protein.

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13
Q

What codon was deduced to encode phenylalanine?

A

UUU codon

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14
Q

How was the specificity of tRNA binding to ribosomes determined?

A

Binding of charged tRNAs to ribosomes in vitro was dependent upon the cognate trinucleotide codon.

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15
Q

What was the key technique used to decipher the genetic code?

A

The enzymatic synthesis of nearly all 64 trinucleotides.

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16
Q

\What are the start and stop codons?

A

AUG - Methionine is start
UAG,UGA and UAA - Stop codons

17
Q

What does synonymous codons mean?

A

Codons that encode the same amino but tend to differ at the 3rd nucleotide.

18
Q

What is degeneracy in the genetic code?

A

Degeneracy refers to the fact that multiple codons can code for the same amino acid.

19
Q

What are isoacceptor tRNAs?

A

Isoacceptor tRNAs are different tRNA molecules that can recognize different codons for the same amino acid.

20
Q

What is wobble base pairing?

A

Wobble base pairing is a type of non-standard base pairing that occurs between the third position of the codon and the first position of the anticodon. It allows for flexibility in codon-anticodon recognition.

21
Q

What is the role of inosine in tRNA?

A

Inosine can base pair with U, A, and C, which allows for greater flexibility in codon-anticodon recognition.

22
Q

What is the secondary structure of a tRNA molecule?

A
  1. The have a cloverleaf structure.
  2. The 5’ and 3’ ends are drawn together.
  3. The amino acid is attached to the 3’ hydroxyl group of the 3’ terminal A nucleotide.
23
Q

What allows the wobble in tRNA?

A

Modification of the first positions.

24
Q

When are the specific nucleotides within tRNAs modified?

A

They are post-transcriptionally modified

25
Q

How does coaxial stacking contribute to tRNA stability?

A

Coaxial stacking of short helices within tRNA increases its thermodynamic stability.

26
Q

Describe the stacking arrangement of tRNA domains.

A

The acceptor stem is stacked on the TΨC arm. The anticodon is stacked on the D arm.

27
Q

Where does base-pairing occur in tRNA

A

They occur between between the D and TΨC loops.

28
Q

What enzymes are responsible for tRNA charging?

A

Aminoacyl-tRNA synthetases

29
Q

What is the role of aminoacyl-tRNA synthetases?

A

They attach the correct amino acid to its corresponding tRNA molecule.

30
Q

What is the type of bond formed between the amino acid and tRNA?

A

Ester bond.

31
Q

How many different aminoacyl tRNA sythetases are there?

A

There are 20 different ones.

Molecular and Cell Biology (23 decks)

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