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Description
Flashcards by J yadonknow, updated more than 1 year ago
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Created by J yadonknow
almost 7 years ago
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| Question | Answer |
| What 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. |
| What 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. |
| What what did Nimberg synthesise in 1961? | An RNA strand containing only U, incubated in E.coli which created a protein consisting only of Phenylalanine. |
| Describe 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. |
| Which amino acids are represented by just a single codon? (2) | Methionine (AUG) Tryptophan (UGG) |
| What is essential for translation? (2) | The inclusion of stop/start codons in the genetic sequence. |
| What are the termination codons? (3) | UGA UUA UAG |
| What are the start codons? (2) | AUG, Very occasionally GUG |
| What 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) |
| How many possible reading frames does the genetic code have? | 3, depending on where translation starts |
| What is a reading frame with no termination codon called? | An Open Reading Frame (ORF) |
| Where 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 |
| What 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 |
| What is the function of tRNA? | Act as an adaptor molecule that recognises a codon and binds to a specific amino acid. |
| What is unusual about tRNAs bases? (5) | Contains unusual bases for an RNA molecule: Thymine Dihydrouracil Pseudouracil (all U like ^) Methylguanine (<G like) |
| How do these abnormal bases arise within the tRNA molecule? | Post-transitional modifications |
| What 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 |
| What 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. |
| How do tRNA molecules recognise codons? | They recognise codons via complementary base-pairing of their anticodon loop and a complementary codon of an mRNA strand. |
| Draw 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) |
| What are aminoacyl-tRNAs? | tRNAs attached to their specific amino acids are called aminoacyl-tRNAs or Charged tRNAs. |
| What 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. |
| State the nomenclature for a bound and unbound tRNa complex (2) | tRNA^gly:tRNA for glycine gly-tRNA^gly:aminoacyl tRNA |
| What 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 |
| Show 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 |
| Give an example of base wobble | tRNAgly with the 5' GCC anticodon can recognise the 3' codons GGC and GGU |
| What is the enzyme that links tRNAs to specific amino acids called? | Aminoacetyl-tRNA synthetase |
| Show 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 |
| Draw a diagram showing the addition of an amino acid to a tRNA molecule | nucleophilic 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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