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Molecular Genetics > Module 2-3 > Flashcards

Module 2-3 Flashcards

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Biology 101 flashcards
1
Q

What are characteristics of the Genetic Code?

A
  1. Unambiguous = each triplet specifies a single amino acid
  2. Degenerate = more than one triplet can code for the same amino acid
  3. The code contains “start” and “stop” signals
  4. Translocation of RNA is continuous
  5. The code is nonoverlapping
  6. The code is “nearly” universal
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2
Q

Who postulated the mRNA?

A

Jacob and Monod in 1961

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3
Q

What code is translated into the amino acid?

A

mRNA

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4
Q

What was the first evidence of triplet nature of the code?

A

Francis crick was involved

  • insertion and deletion mutations in T4 bacteriophage
  • used intercalating agents to cause insertions or deletions upon replication
  • frameshift mutations- cause reading frame to shift
  • one + and one - = normal phenotype
  • +++ and — = normal phenotype
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5
Q

Who developed the first specific coding sequences?

A

Nirenberg and Matthaei in 1961

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6
Q

What method did Nirenberg and Matthaei use?

A
  • an in vitro system that could synthesize protein
  • Polynucleotide phosphorylase (enzyme) that produced synthetic mRNAs, which serve as template for polypeptide synthesis in cell free system
  • -synthesize RNA in vitro
  • the formation of RNA is random, based on the concentration of the four ribonucleoside diphosphates added to the in vitro system
  • THE PROBABILITY OF THE INSERTION OF A PARTICULAR RIBONUCLEOTIDE IS PROPORTIONAL TO ITS AVAILABILITY IN THE SYSTEM
  • gives a means to decipher the code
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7
Q

What are the simple experiments to determine code?

A

Homopolymers which consist of only one ribonucleotide
EX: UUUUUUUUU or AAAAAAAAAA or CCCCCCCCCC or GGGGGGGGGG and radioactively label each of the 20 amino acids and determine what amino acids these homopolymers specify

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8
Q

What were the homopolymer results?

A

UUU: Phenylalanine
AAA: Lysine
CCC: Proline
GGG: no result in the early experiments

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9
Q

How were the heteropolymer amino acids deciphered?

A
  • known concentrations of each nucleotide were used
  • using these, they could predict the frequency of triplets
  • they could match the proportion of amino acids incorporated with the proportion of potential triplets
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10
Q

Who performed the triplet binding assays?

A

Nirenberg and Leder in 1964

  • led to specific assignments of triplets
  • single triplets could be bound by ribosomes which leads to binding of anticodon
  • established degeneracy of the code: >1 codon for 18 of 20 amino acids
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11
Q

How were the triplet binding assays performed?

A

radioactively labeled amino acids linked to RNA were used and if the codon specified a particular anticodon it would be bound up in the ribosome and this large complex would be bound to filter, smaller components would not be bound and would be washed away, and it tells you specific codon assignment

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12
Q

What are repeating copolymers?

A
  • Di, tri, and tetra repeats
  • Confirmed codons already established and filled in remaining gaps
  • established termination signals
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13
Q

How many triplet codons that specify amino acids were on the final codon table?

A

61 and 3 termination codons

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14
Q

What is the degeneracy of the code?

A

almost all amino acids are encoded by 2, 3, 4 codons

  • Serine, arginine, and leucine are encoded by 6
  • Only tryptophan and methionine are encoded by one
  • 3 termination codons
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15
Q

What is the wobble hypothesis?

A
  • A pattern of degeneracy
  • Third letter of the code is usually the one that is different: free to “wobble”
  • First 2 positions are the most critical
  • Allows 1 anticodon of tRNA to pair with >1 codon in mRNA
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16
Q

How can genes overlap?

A

Initiation of transcription is started at different locations producing different reading frames and more than one polypeptide
ex: AUGGGUACCCAUGCUUUUGCCA
^first start ^2nd start
*Usually seen in viruses

17
Q

What is Transcription?

A
  • The synthesization of RNA from a DNA template
  • The first step in the transfer of info from DNA to protein
  • Results in mRNA molecule complementary to the gene sequence from one of the 2 DNA strands
18
Q

What is the evidence that points to RNA as the intermediate?

A
  1. DNA is in the nucleus but protein synthesis occurs outside the nucleus
  2. RNA is made in the nucleus, where DNA is located
  3. Most RNA moves to cytoplasm following synthesis
  4. Amount of RNA is proportional to protein in cells
19
Q

What is the Experimental evidence that mRNA is the intermediate?

A
  • 1956-1958 used bacteriophage
  • use 32P to label new RNA following bacteriophage infection of E. coli
  • base composition of new RNA resembled phage, not bacteria
  • this production preceded protein production
20
Q

Who discovered the enzyme that could synthesize RNA from a DNA template and what was the enzyme called?

A

Weiss et al.

-RNA polymerase holoenzyme

21
Q

What is RNA polymerase holoenzyme made up of?

A

5 subunits, 2 of which catalyze transcription and another, the sigma site is involved in initiation of transcription

22
Q

How does transcription initiation begin?

A

RNA polymerase recognizes specific sequences in the DNA molecule (promoters)

  • Promoters can be either strong or weak
  • TATAAT box (Prinbrow box) is 10 bases upstream of initial transcription location
  • another promoter is farther upstream (-35 region)
  • Promoters are conserved
23
Q

How does Eukaryotic transcription proceed?

A
  • It occurs in the nucleus
  • 3 major forms of RNA polymerases are used
  • It has a more complicated upstream regulation of transcription
  • promoter enhancers are involved
  • mRNAs of eukaryotes are further processed
24
Q

What are eukaryotic promoters?

A
  • cis and trans acting elements
  • TATA box (cis)
  • CAAT box (cis)
  • Enhancers (cis)
  • Trans Factors (facilitate binding), eg: TFIID, TFIIA, TFIIB
25
Q

What are the three major classes of RNA?

A 
Ribosomal RNA (rRNA)
Transfer RNA (tRNA)
Messenger RNA (mRNA)
26
Q

What are other RNA classes?

A

Small nuclear RNAs, small nucleolar RNAs

Small interfering RNAs (siRNAs), micro RNAs (miRNAs), and others that are being discovered

27
Q

What is special about Ribosomal RNA (rRNA)?

A

it has regions of high conservation and high variability

-very useful for phylogenic and evolutionary studies

Molecular Genetics (5 decks)

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