RNA polymerase creates a short DNA RNA hybrid at its center that matches the

Rna polymerase creates a short dna rna hybrid at its

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RNA polymerase creates a short DNA-RNA hybrid at its center that matches the correct RNA nucleotides to the DNA sequence it is transcribing.
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Once RNA is finished being made, the newly synthesized RNA is released as a single-stranded molecule. Both during and after transcription, RNA is is processed to generate a mature, functional form of RNA. This includes putting a “cap” on the 5’ end and a polyadenylated (poly-A) “tail” at the 3’ end. The 5’ cap is added to the 5’ end of the nascent RNA during transcription, but the poly-A tail is added to the 3’ end of the RNA only after transcription termination. Splicing: Allows cells to increase variation in gene expression through alternative splicing. Alternative splicing: skipping particular exons or retaining an intron, causing certain exons present in the gene may or may not be included in the mature RNA transcript. Causes: A given gene to generate more than one protein product. Gene expression can be finely tailored to suit the needs of different types of cells. DNA DAMAGE AND REPAIR Key Concepts: F DNA damage: Can block essential processes including DNA replication and transcription and can lead to mutations. Types of Mutations: Mutations are heritable changes in the DNA sequence. They can result from replication errors , from damage to the DNA , or from errors introduced during repair of damage. Point Mutations: Missense mutation (A to C): Nonsense mutation (U to A): Insertions and Deletions: Insertion (of A): Deletion (of first C): Point mutations. (a) A missense mutation changes a single amino acid in the encoded polypeptide. (b) A nonsense mutation changes a codon for an amino acid into a stop codon, terminating synthesis of the encoded polypeptide. Insertion/deletion mutations. (c) Insertion of a single nucleotide changes the reading frame of all codons beyond the point of insertion; this usually leads to formation of a new stop codon that terminates synthesis. (d) Deletion of a single nucleotide changes the reading frame of all codons beyond the point of insertion; this usually leads to formation of a new stop codon that terminates synthesis. Frameshift mutation: Once the initiation codon is determined, successive triplets are read as codons. Therefore, whereas addition (or deletion) of a multiple of three base pairs in a coding region would add (or subtract) amino acids to (or from) a protein, the addition of other numbers of base pairs shifts the reading frame from that point onward. Some chemicals can insert themselves between adjacent base pairs (known as intercalating ) with the DNA, which can lead to insertions or deletions of a single base pair, and thus a frameshift.
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DNA Repair: Base Excision Repair: A. The damaged site (blue dot) is recognized by the repair enzymes. B. and C. Repair enzymes remove the altered/damaged nucleotide in a stepwise fashion. D. The single nucleotide gap is filled by a DNA polymerase. E. The remaining nick is sealed by a DNA ligase (ligase = to tie or join).
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  • Winter '19
  • DNA, DNA Damage

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