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12 Cards in this Set
- Front
- Back
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The sequence of events for transcription. (6)
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1) RNA polymerase binds to promoter region of DNA
2) DNA double helix unwinds; one strand used as template for mRNA synthesis (Sense Strand) 3) RNA poly. moves from 3' -> 5' of DNA chain; free ribonucleotides taken up and matched to template by complementary base-paring; mRNA strand grows 5' -> 3' 4) A with U, T with A, G with C, C with G; adjacent ribonucleotides joined by phosphodiester bonds 5) RNA poly. reaches end of gene; mRNA released; DNA rewinds. 6) mRNA leaves through nuclear pores |
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What is required for transcription?
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1) RNA polymerase
2) Free ribonucleotides: uracil, adenine, guanine, cytosine |
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Where does transcription occur?
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In the nucleus
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What's required for translation?
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1) mRNA
2) rRNA 3) tRNA (anticodon made up of a specific triplet base sequence) 4) Free amino acids 5) Ribosomes |
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Where does translation occur?
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In cytoplasm
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Describe the sequence of events for amino acid activation.
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1) Enzymes involved are aminoacyl-tRNA synthetase
2) Amino acid reacts with ATP to form a.a-AMP 3) a.a.-AMP is then attached to specific tRNA molecule, to form amino acid-tRNA complex 4) Amino acid attached to the hydroxyl group of C3 of ribose of last nucleotide (A) of tRNA. 5) Aminoacyl-tRNA synthetase is specific to each of 20 amino acids |
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Describe the main stages of translation.
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1) Binding of mRNA to ribosome
2) Initiation of polypeptide chain 3) Chain elongation 4) Chain termination |
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Describe the sequence of events of translation.
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1) Binding of mRNA to ribosome
-Information processing region of 40S subunit binds to mRNA at 5' -Ribosome covers 2 codons at a time 2) Polypeptide chain initiation -Amino acid-tRNA complex with anticodon UAC binds to start codon AUG on mRNA -a.a-tRNA complex held in 'P' site of 60S subunit -tRNA with UAC always carries methionine; it is always the first amino acid 3) Chain elongation -2nd a.a-tRNA complex with anticodon complementary to the second codon of mRNA binds to the latter; complex held at 'A' site of 60S -peptide bond between first and second a.a. is formed; energy from ATP hydrolysis; catalysed by catalytic region in 60S -Ribosome moves along mRNA to next codon -First tRNA is released and recycled -Second a.a-tRNA complex moves from 'A' to 'P', leaving 'A' empty for next a.a-tRNA complex with anticodon complementary to 3rd mRNA codon -Process continues until stop codon is reached 4) Chain termination -Polypeptide is released from the ribosome; secondary and tertiary structures assumed -may undergo modification at Golgi -Ribosome disassembles to subunits -tRNA re-attached to respective a.a. |
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What is the role of mRNA in protein synthesis?
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mRNA:
-Genetic message for synthesis of polypeptide found on DNA -mRNA is formed from transcription of gene coding for polypeptide -mRNA conveys genetic message from nucleus to the ribosomes -Each mRNA has a sequence of nucleotides complementary to that of gene -Each triplet codes for one amino acid -mRNA codons specify the order in which amino acids are sequenced to form a polypeptide |
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What is the role of tRNA in protein synthesis?
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tRNA:
-The CCA site at 3' end allows for attachment of an amino acid -tRNA carries amino acid to ribosome -Each tRNA molecule is specific—has specific anticodon, and carries corresponding amino acid -Every codon on mRNA has a corresponding anticodon on tRNA, allows for correct sequencing of amino acids in polypeptide |
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What is the role of rRNA in protein synthesis?
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rRNA:
-surrounds part of mRNA during protein synthesis -holds mRNA, amino acid-tRNA complex & enzymes in precise orientation |
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What is the role of ribosomes in protein synthesis?
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Ribosomes
-Important in translation -Small subunit binds to mRNA -Large subunit has 2 sites: *'P' site for recognition of start codon, initiation of chain formation, and for formation of peptide bonds *'A' site for holding amino acid-tRNA complex next in sequence -Catalytic site on 60S catalyses formation of peptide bond b/w amino acids -Many ribosomes may move along Ribosomes -Important in translation -Small subunit binds to mRNA -Large subunit has 2 sites: *'P' site for recognition of start codon, initiation of chain formation, and for formation of peptide bonds *'A' site for holding amino acid-tRNA complex next in sequence -Catalytic site on 60S catalyses formation of peptide bond b/w amino acids -Many ribosomes may move along mRNA at same time to increase rate of translation |
