Flashcards
DNA VII - The genetic code and tRNA
Flashcards do conjunto (29)
- 1What is the genetic code? (2)The nucleotide sequence of a gene/mRNA molecule which determines the amino acid sequence of a protein
the genetic code is the dictionary that tells us which codon represents which amino acid. - 2What is a codon? (2)A triplet of amino acids that code for an amino acid.
Only referred to as a codon in the context of amino acids. - 3What what did Nimberg synthesise in 1961?An RNA strand containing only U, incubated in E.coli which created a protein consisting only of Phenylalanine.
- 4Describe the features of the genetic code (3)1. The genetic code is non-overlapping
2. degenerate, as most amino acids are represented by more than one codon
3. almost universal, i.e. same genetic code is used by near all prokaryotes and by genes in the nuclei of near all eukaryotes. - 5Which amino acids are represented by just a single codon? (2)Methionine (AUG)
Tryptophan (UGG) - 6What is essential for translation? (2)The inclusion of stop/start codons in the genetic sequence.
- 7What are the termination codons? (3)UGA UUA UAG
- 8What are the start codons? (2)AUG, Very occasionally GUG
- 9What are some exceptions to the universality of the genetic code? (3)1. Some mycoplasma (primitive bacteria)
2. Some proctists
3. Mitochondria (i.e. UGA represents Trp) - 10How many possible reading frames does the genetic code have?3, depending on where translation starts
- 11What is a reading frame with no termination codon called?An Open Reading Frame (ORF)
- 12Where are ORFs found and not found? What are their functions? (3)Found - genes (introns only)
not found - non-coding strand of DNA
Encode the protein corresponding to the gene - 13What may be featured in a long genetic sequence? (4)A 5' untranslated region before the start codon
A start/stop codon
A 3' untranslated region
A polyadenyl tail - 14What is the function of tRNA?Act as an adaptor molecule that recognises a codon and binds to a specific amino acid.
- 15What is unusual about tRNAs bases? (5)Contains unusual bases for an RNA molecule:
Thymine
Dihydrouracil
Pseudouracil
(all U like ^)
Methylguanine ( - 16How do these abnormal bases arise within the tRNA molecule?Post-transitional modifications
- 17What are the common features of tRNA molecules? (4)Have an anticodon
Have a CCA sequence for amino acid attachment at their 3' end with an exposed 2'/3'-OH group of the adenosine
Have extensive interanal base-pairing - 18What sort of structures do tRNA molecules form?2' structure due to extensive internal base-pairing, with 3 or 4 loops, and 4 double stranded stems.
3' structure resembles an inverted L. - 19How do tRNA molecules recognise codons?They recognise codons via complementary base-pairing of their anticodon loop and a complementary codon of an mRNA strand.
- 20Draw a labelled schematic diagram of the 2' structure of tRNA (7)1. 5' Amino acid arm
2. 3' Amino acid attachment site (CCA-OH)
3. TΨC arm (contains Thymine+Pseudouracil)
4. Variable arm (may be absent)
5. Anticodon arm (anticodon)
6. Codon/mRNA strand
7. D-arm (contains Dihydrouracil) - 21What are aminoacyl-tRNAs?tRNAs attached to their specific amino acids are called aminoacyl-tRNAs or Charged tRNAs.
- 22What happens in terms of bonding energies as an amino acid joins to a tRNA molecule? (3)The amino acid is activated by attachment to a tRNA.
The C-O bond between the adenosine of the 3' end of tRNA and the amino acid is a very high energy mixed anhydride bond
This makes the formation of a peptide bond with adjacent amino acids favourable. - 23State the nomenclature for a bound and unbound tRNa complex (2)tRNA^gly:tRNA for glycine
gly-tRNA^gly:aminoacyl tRNA - 24What is "base wobbling"?tRNAs bend the usual base-pairing rules
some tRNAs can recognise more than one codon
i.e. The ability of some bases at the 5' end of an anticodon to pair with more than one base at the 3' end of a codon - 25Show the bases at the 5' end of the codon which can exhibit base wobbling and their compatible bases at the 3' end of the codon (4)A - U
C - G
G - C,U
U - A,G - 26Give an example of base wobbletRNAgly with the 5' GCC anticodon can recognise the 3' codons GGC and GGU
- 27What is the enzyme that links tRNAs to specific amino acids called?Aminoacetyl-tRNA synthetase
- 28Show the two step reaction catalysed by aminoacetyl-tRNA synthetase (3)Step 1:
AA+ATP -> AA-AMP +PPi
Step 2:
AA-AMP +tRNA -> AA-tRNA + AMP
overall:
AA + ATP + tRNA -> AA-tRNA + AMP +PPi - 29Draw a diagram showing the addition of an amino acid to a tRNA moleculenucleophilic addition of carboxyl oxygen of amino acid to the 1st phosphate group of AN ATP molecule, producing AA-AMP and PPi
Nucleophilic addition of :OH of the tRNA molecule to the carbon of the amino acid, causing the extremely high energy anhydride bond between the amino acid and the AMP molecule to break
tRNA bonded to amino acid, with AMP as a by-product.
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- O usuário eliminou as informações de disciplina FlashCards sobre DNA VII - The genetic code and tRNA, criado por Usuário eliminado em 27-12-2017.
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- Usuário eliminado · dez 2017
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- Criado por J yadonknow · 21 dez 2017
- Copiado por J yadonknow · 27 dez 2017
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