Term
| Compare DNA & RNA structure. |
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Definition
DNA
- sugar: deoxyribose
- purines: adenine, guanine
- pyrimidines: thymine, cytosine
- strands: double
RNA
- sugar: ribose
- purines: same
- pyrimidines: uracil, cytosine
- strands: single (usually) |
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Term
Outline DNA transcription in terms of formation of complementary RNA strand by RNA polymerase.
A. Initiation: RNA polymerase is an enzyme complex which: |
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Definition
- unwinds and unzips DNA double strand
- attaches to promoter region of gene, which marks the beginning point for transcription |
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Term
Outline DNA transcription in terms of formation of complementary RNA strand by RNA polymerase.
B. Elongation: RNA polymerase: |
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Definition
- uses DNA anti-sense strand as a template
- synthesises a complementary RNA strand using base pairing rules
A=U
T=A
G=C
C=G |
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Term
Outline DNA transcription in terms of formation of complementary RNA strand by RNA polymerase.
C. Termination: RNA polymerase: |
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Definition
- reaches termination region of the gene, which marks the end of the coding sequence
- terminates transcription by releasing both DNA and RNA |
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Term
| Describe the Genetic Code in terms of codons composed of triplets of bases. |
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Definition
- triplet code = 3 nucleotide bases code for one amino acid
- codon = a group of 3 nucleotide bases is called a codon
- there are 64 different codons (4x4x4 = 64) |
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Term
Explain the process of translation, leading to peptide linkage formation.
A. Initiation |
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Definition
- mRNA binds to small subunit of the ribosome
- tRNA anticodon binds to mRNA codon by complementary base pairing
- large ribosomal subunit binds, completing ribosomal structure, and producing two ribosomal bind sites: P site and A site |
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Term
Explain the process of translation, leading to peptide linkage formation.
B. Elongation: |
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Definition
- tRNA with anticodon complementary to second mRNA codon binds to ribosomal A site, with appropriate amino acid attached to tRNA
- enzymes in ribosome catalyze formation of peptide bond between 1st, P site, and 2nd, A site, amino acids
- P site tRNA, now separated from amino acid, exits ribosome
- ribosome moves one codon (3 nucleotides) along the mRNA, thus shifting previous A-site tRNA to P-site, and opening A-site
- tRNA with anticodon complementary to A-site mRNA codon binds to ribosomal A-site, with appropriate amino acid attached to tRNA terminal
- enzymes in ribosomecatalyze formation of peptide bond between 2nd and 3rd amino acids
- P site tRNA, now separated from its amino acid, exits ribosome
- ribosome moves one codon (3 nucleotides) along the mRNA, thus shifting previous A-site tRNA to P-site, and opening A-site
- repetition of process until stop codon is reached |
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Term
Explain the process of translation, leading to peptide linkage formation.
C. Termination |
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Definition
- when ribosomal A-site reaches a stop codon, no tRNA has a complementary anticodon
- release factor protein binds to ribosomal A-site stop codon
- polypeptide and mRNA are released
- large and small ribosomal subunits separate
- polysomes: several to many ribosomes translating the same mRNA into protein; each moving in the 5' to 3' direction
- start codon: the mRNA triplet codon AUG is universally the start codon used to mark the beginning of the coding sequence of a gene; thus, the tRNA withthe anticodon UAC and carrying the amino acid methionine is always the first tRNA to enter the P-site during translation
- stop codon: there are three stop codons in the genetic code; none of these have a corresponding tRNA; instead, when a ribosome encounters a stop codon, a release factor binds to the stop codon, which terminates translation and allows the separation of all of its components |
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