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40 Cards in this Set
- Front
- Back
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Transcription First stage of gene expression |
synthesis of RNA using information in the DNA |
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mRNA Messenger RNA |
carrier of information from DNA to the cell's protein - synthesizing machinery is transcribed from a template strand of gene |
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transcription unit |
the stretch of DNA downstream from the promoter that is transcribed into an RNA molecule *portion of gene copied to RNA |
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RNA polymerase - able to start a chain from scratch *transcribes RNA from a DNA template strand |
enzyme that pries the two strands of DNA apart and joins together RNA nucleotides complementary to the DNA template strand, elongating the RNA polynucleotide * upstream 5' of the transcription site |
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promoter |
DNA sequences before the transcription unit allow - where the RNA polymerase attaches and initiates transcription *starting point* |
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start point |
the nucleotide where RNA synthesis actually begins - typically extends several dozen or more nucleotide pairs upstream from the start point |
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initiation - RNA polymerase opens DNA begins transcription |
after RNA polymerase binds to the promoter, the DNA strands unwind, and the polymerase initiates RNA synthesis at the start point in the template strand |
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elongation |
the polymerase moves downstream, unwinding the DNA and elongating the RNA transcript 5' to 3'. In the wake of transcription, the DNA strands re-form a double helix, *a growing strand of RNA trails off from each polymerase w/each length of each new strand reflecting how far along the template the enzyme has traveled from the start point |
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terminator |
in bacteria, the sequence that signals the end of transcription |
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termination |
eventually the RNA transcript is released, and the polymerase detaches from the DNA *mRNA is destined to be translated *many RNA's are not translated (tRNA's and others) |
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stages of transcription |
initiation, elongation, termination |
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transfer RNA (tRNA) |
*single strand (RNA) can fold back on itself and form a molecule with a 3D structure *transcribed from DNA templates, made in nucleus to the cytoplasm *function is to transfer amino acids from the cytoplasmic pool of amino acids to a growing polypeptide in a ribosome *reads the mRNA codon and interpret it as a protein word |
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ribosome |
a structure made of proteins and RNA's, adds each amino acid brought to it by tRNA to the growing end of a polypeptide chain *consists of a large subunit and a small subunit, each made up of proteins and one or more ribosomal RNA's |
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anticodon |
the loop extending from one end of the L includes the anticodon, the particular nucleotide triplet that base pairs to a specific mRNA codon *the opposite side of the anticodon is the 3' end which is the site for the amino acid |
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ribosomal RNA (rRNA) |
*RNA molecules that together with proteins make up ribosomes the most abundant type of RNA rRNA genes are transcribed and the RNA is processed and assembled with proteins imported from the cytoplasm *most abundant type of cellular RNA |
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E site (exit site) |
discharged tRNA's leave the ribosome from the Esite |
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Inititiaion |
brings together mRNA, a tRNA bearing the first amino acid of the polypeptide and 2 subunites of a ribosome, 1 small ribosomal subunit binds with a mRNA and a specific initiater tRNA which carries the amino acid Met *the start codon signals the start of translation-this establishes the codon reading frame for the mRNA *small subunit bind mRNA near the first AUG *large ribosomal subunit attaches |
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translation initiation complex |
the arrival of a large ribosomal subunit completes the initiation complex *proteins called initiation factors bring all components together GTP hydrolysis forms the initiation complex *at completion of initiation process, the initiator tRNA sits in the P site of the ribosome and the vacant A site is ready for the next tRNA |
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Elongation of the polypeptide chain |
*amino acids are added one by one to the previous amino acid at the C-terminus of the growing chain 1. codon recognition - the incoming tRNA base pairs with the complementary mRNA codon in the A site hydrolysis of GTP increases the accuracy 2. peptide bond formation - peptide bond joins polypeptide (P site) to the new amino acid (A site) 3. translocation - ribosome slides down the RNA uncharged tRNA exits the ribosome released thru the E site to return to the cytoplasm where they will be reloaded with the appropriate amino acid *elongation continues until a stop codon in the mRNA reaches the A site of the ribosome |
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termination of translation (final stage of translation) |
UAG, UAA, UGA do not code for amino acids, they act as signals to stop translation *release factor, a protein shaped like an aminoacyl tRNA, binds directly to the stop codon in the A site; the release factor causes the addition of a water molecule instead of an amino acid to the polypeptide chain - this reaction breaks the bond in the completed polypeptide and the tRNA in the P site releasing the polypeptide thru the E tunnel of the large subunit breakdown of the translation assembly requires the hydrolysis of 2 more GTP molecules |
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the process of translation (synthesis of a polypeptide chain) 3 stages - initiation, elongation, termination |
genetic information flows from mRNA to protein *a cell "reads" a genetic message and builds a polypeptide *translation requires mRNA, ribosomes (tRNA and proteins) and tRNA *mRNA sequence specifies amino acid sequence |
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P site (peptidyl-tRNA binding site) |
holds the tRNA carrying the growing polypeptide chain |
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A-site (aminoacyl-tRNA binding site) |
holds the tRNA carrying the next amino acid to be added to the chain |
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translation - basic concept |
as a molecule of mRNA is moved through a ribosome, codons are translated into amino acids, one by one. the interpreters are tRNA molecules, each type with a specific nucleotide triplet called an anticodon at one end and a corresponding amino acid at the other end. A tRNA adds its amino acid cargo to a growing polypeptide chain when the anticodon hydrogen bonds to the complementary codon in the mRNA |
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codons |
mRNA nucleotide triplets *customarily written in the 5' to 3' direction 64 codons (triplets) 20 amino acids |
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stop codons |
end of translation UAA - UGA - UAG do not encode amino acids |
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start codon |
dual function codes for the amino acid Met and also functions as a start signal or initiation codon *signals the protein-synthesizing machinery to begin translation the mRNA at that location |
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reading frame |
phase of codons - established by start codon |
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triplets |
smallest units of uniform length that can code for all the amino acids *the genetic instructions for a polypeptide chain are written in the DNA as a series of nonoverlapping 3 nucleotide words the series of words in a gene is transcribed into a complementary series of nonoverlapping 3 nucleotide words in mRNA which is translated into a chain of amino acids |
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E-coli chromosome |
5 million base pairs |
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origin of replication |
DNA begins to replicate at a specific place on the chromosome |
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semiconservative model |
2 strands of the parental molecule separate, and each functions as a template for synthesis of a new, complementary strand |
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replication fork *site of DNA polymerazation |
end of the replication bubble - a Y shaped region where the parental strands of DNA are being unwound |
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helicases |
enzymes that untwist the double helix at the replication forks, separating the 2 parental strands & making them available as template strands |
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DNA polymerase |
can only move 5' to 3' *only adds to an existing strand |
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lagging strand |
*okazaki fragments elongate away from fork |
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leading strand |
Elongates as the replication fork expands |
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okazaki fragments |
*short DNA segments added 5' to 3' *added to the newly exposed template DNA at the replication fork |
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primase |
adds RNA primer |
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primer |
RNA chain - |
