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MCB 2 > II. Post-transcription | 23. The genetic code; structure and function of tRNAs; aminoacyl-tRNA synthetases; codon- anticodon connections > Flashcards

II. Post-transcription | 23. The genetic code; structure and function of tRNAs; aminoacyl-tRNA synthetases; codon- anticodon connections Flashcards

1
Q
  1. Genetic code
    a/ What is a genetic code?
A

a triplet code (3-nucleotide sequence = codon) which is read from specific starting point on the mRNA.

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2
Q
  1. Genetic code
    b/ How many possible codons can you find?
A

There are 64 possible codons in the genetic code where 61 of them specify individual amino acids.

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3
Q
  1. Genetic code
    c/ What does the codon table describe?
A

The codon table describes 20 amino acids
- 1 codon = 3 nucleotides = 1 amino acid

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4
Q
  1. Genetic code
    d/ List the “stop” codon(s)
A

The three codons: ‘’UAA, UGA, UAG’’ do not specify amino acids, but are referred to as ‘’stop codons’’.

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5
Q
  1. Genetic code
    e/ The role of “stop” codon(s)
A

They mark the carboxyl (-COOH) terminus of polypeptide chains.

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6
Q
  1. Genetic code
    f/ List the “start” codon(s)
A

methionine (AUG) is the ‘’start codon’’

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7
Q
  1. Genetic code
    g/ Which amino acid(s) only have 1 codon code for them?
A

AUG = methionine
UGG = Tryptophan

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8
Q
  1. Genetic code
    h/ What are the 5 characteristics of the genetic code?
A

1/ Degenerated
2/ Non-ambiguous
3/ Non-overlapping
4/ Non-punctuated
5/ Universal

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9
Q
  1. Genetic code
    h5/ Why is genetic code “universal”?
A

Each codon is the same in most known organism
(eg.: same in eukaryotes and prokaryotes)

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10
Q
  1. Genetic code
    h1/ Why is genetic code “degenerated”?
A

Because a single amino acid maybe coded by more than 1 codon (methionine = 1 codon, serine = 6 codons)

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11
Q
  1. Genetic code
    h2/ Why is genetic code “non-ambiguous”?
A

1 amino acid can be coded by several different codons, BUT each codon ONLY codes for one amino acid, not more

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12
Q
  1. Genetic code
    h3/ Why is genetic code “non-overlapping”?
A

reading of the codon sequence does not involve overlapping of codons – the genetic code is read sequentially -> one codon at a time

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13
Q
  1. Genetic code
    h4/ Why is the genetic code non-punctuated?
A

the message is read in a continuous sequence of nucleotides triplets until a stop codon is reached

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14
Q
  1. Genetic code
    I/ What is the rule of genome reading?
A
  • Some genes are encoded by one of the strands, while others are by the other strand
  • But there are no overlapping genes on the two strands
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15
Q
  1. Toolbox of protein synthesis
A
  1. RNA
    - Messenger
    - Transfer
    - Ribosomal
  2. Proteins
    - Ribosomal
    - Aminoacy-tRNA synthetase
    - Translation factors
  3. Ribosome
    - Prokaryotic 70S
    - Eukaryotic 80S
  4. Amino acids
  5. Energy: ATP, GTP
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16
Q
  1. tRNA
    a/ What is the structure of tRNA?
A
  • Terminal 5’-end: is phosphorylated (PO4-2 group)
  • Acceptor stem: 5’-end base-pairs with 3’-end (has a specific amino acid attached to it – CCA)
  • D-loop: contains dihydrouridine
  • Anticodon loop: contains anticodon (sequence of 3
    nucleotides that are complementary to codons in the mRNA).
17
Q
  1. tRNA
    b/ How are amino acids linked to tRNA?
A

Amino acids are linked to the 3’ A via an ester bond

18
Q
  1. tRNA
    c/ Function of tRNA?
A
  • Carries amino acid to the ribosome during translation.
  • As each triplet code is read on the mRNA, the tRNA will deliver its amino acid to a growing polypeptide chain (mRNA -> tRNA anticodon -> protein).
  • It serves as a physical link between the mRNA and the amino acid sequence
19
Q
  1. Wobble
    a/ What is wobble?
A

Wobble is a phenomena that occurs when a base pairing is atypical, meaning base pairing between nucleotides other than A-U and G-C
- Occurs at 3rd position of the codon (mRNA) and 1st position of anticodon (tRNA)
- Wobble pairing follows its own rules – a G in the anticodon can pair with only C/U in the 3rd position of the codon

20
Q
  1. Wobble
    b/ What is function of wobble?
A

allows fewer tRNAs to cover all the codons of the genetic codes while still ensuring that the coding is accurate = allows faster dissociation of tRNA from mRNA

21
Q
  1. What is Codon-anticodon hybridization?
A

the complementary binding between codon- anticodon, since anticodon present a reverse + complementary nucleotide trio for the codon on the mRNA

22
Q
  1. Aminoacyl-tRNA synthetases
    a/ What are Aminoacyl-tRNA synthetases?
A

The genetic code translating enzymes

23
Q
  1. Aminoacyl-tRNA synthetases
    b/ What are the functions of Aminoacyl-tRNA synthetases?
A

They possess a double function
1. Activation of amino acids
2. Translation of genetic code

24
Q
  1. Aminoacyl-tRNA synthetases
    c/ How do Aminoacyl-tRNA synthetases participate in activation of amino acid?
A

The formed ester linkage provides the energy for peptide bond formation
Hydrolysis of pyrophosphate makes the reaction irreversible

25
Q
  1. Aminoacyl-tRNA synthetases
    c/ How do Aminoacyl-tRNA synthetases participate in Translation of genetic code?
A
  • According to the 20 amino acids most organism hold 20 aminoacyl-tRNA synthetases
    => They bring together the appropriate tRNAs and amino acids
26
Q
  1. Aminoacyl-tRNA synthetases
    d/ How is formation of aminoacyl occur?
A

1) Amino acid is first activated by linking its carboxyl group
(-COOH) to AMP, forming adenylated amino acid. This
linkage is driven by the hydrolysis of ATP (ATP  AMP)
2) The adenylated amino acid is transferred to a hydroxyl
group (-OH) at the 3’-end of the tRNA molecule
3) Here, AMP will be released and COOH-group of amino acid with link OH-group of tRNA to give an ester bond

27
Q
  1. Aminoacyl-tRNA synthetases
    e/ What is function of Function of anticodon loop?
A

the triplet at the tip of the anticodon loop base-pairs with the correspond codon in mRNA

28
Q
  1. Aminoacyl-tRNA synthetases
    f/ What is the Function of acceptor stem?
A

located in the 3’- end of tRNA. Has the sequence CCA.
=> This is the site where the specific amino acid becomes attached and where tRNA becomes activated aminoacyl-tRNA

MCB 2 (59 decks)

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