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23 Cards in this Set
- Front
- Back
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What is the wobble hypothesis? |
The third base in codons is variable |
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What are the three loops in tRNA called? |
D loop Anticodon loop T loop |
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Describe the modified guanine found in tRNA |
Two methyl groups added, making it N,N dimethyl-G
(N refers to them being bound to a nitrogen) |
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Describe the two modified uracil bases in tRNA |
Two hydrogens added to U (dihydro U)
Sulphur replaces oxygen in U (4-thiouridine) |
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Describe the modified adenosine base in tRNA |
Deamination of adenine (inosine) |
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How is dihydro U denoted and where is it found? |
Denoted as D and found in the D loop |
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How is inosine denoted and where is it found? |
Denoted as I and often found as the third base of the anticodon |
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What is special about the base pairing of inosine? |
It can form base pairs with C, U and A |
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What causes wobble at the third base? |
Less steric hinderance |
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What is the name of the type of enzyme which adds amino acids onto tRNA molecules? |
Aminoacyl-tRNA synthetase |
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Give the two regions where aminoacyl-tRNA synthetase and tRNA are bound |
Anticodon Acceptor site |
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Give the steps that result in an amino acid being added to a tRNA molecule |
1) Amino acid is activated by adenylation. In the process 1ATP is used and two Pi are released. 2) Activated amino acid is transferred onto tRNA by an activated ester linkage. AMP is released. |
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How is it ensured that the correct amino acid is added to tRNA? |
The enzyme possesses a highly specific editing site which is complementary to the correct amino acid. Any incorrect amino acids are removed. |
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Give two amino acids that, due to having a similar shape, may be incorrectly added to a tRNA |
Threonine and serine |
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What does the 'S' refer to in ribosomes? (70S, 80S etc) |
Svedberg unit - a unit of the amount of sedimentation |
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Give two differences between prokaryotic and eukaryotic ribosomes |
Pro - MW of 2,500,000, Euk - MW of 4,200,000 Pro - 50S and 30S, Euk - 60S and 40S
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Where are ribosomal proteins and rRNA processing proteins formed? |
Cytosol - imported into the nucleolus |
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What do ribosomal proteins and rRNAs form? |
Ribonucleoprotein particles |
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What happens to the ribonucleoprotein particles? |
They dissociate, releasing the small and immature large subunits as well as some of the rRNA processing factors |
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What happens to the immature large subunits? |
Remaining rRNA processing factors are released |
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What happens to the mature large and small ribosomal subunits? |
They leave the nucleolus and nucleus and reform in the cytosol when they bind to mRNA |
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Give the names of the three sites |
E = Exit site P = Peptidyl site A = Aminoacyl site |
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Where on the ribosome is the mRNA associated? |
Small subunit |
