How are splice site junctions recognized during pre-mRNA Splicing?
The splice sites are recognized by the splicing machinery based on sequences within the pre-mRNA. Here, we show that the exon sequences at the splice junctions play a significant, previously unrecognized role in the selection of 3′ splice sites during the second step of splicing.
What is the branch site in splicing?
The branch site is a short motif upstream of the polypyrimidine tract that includes a BP adenosine, in 92% of human BP . During the first step of the splicing reaction the 2’OH of the BP adenosine attacks the first intronic nucleotide (nt) of the upstream 5’ss to form a lariat intermediate .
What components of the introns of nuclear genes that encode proteins in higher eukaryotes are conserved and required for the correct excision of intron sequences from primary transcripts by Spliceosomes?
ANS: The introns of protein-encoding nuclear genes of higher eukaryotes almost invariably begin (5′) with GT and end (3′) with AG. In addition, the 3′subterminal A in the “TACTAAC box” is completely conserved; this A is involved in bond formation during intron excision.
Which of the following are roles of the spliceosome quizlet?
Which of the following are roles of the spliceosome? They are responsible for positioning the mRNA in a way that allows for the transesterification reactions to occur. They are responsible for identifying splice sites on the mRNA. -If tryptophan is absent from the cell, the operon is active.
Which protein level best matches the description blocks on a string?
The primary structure of a protein is the linear sequence of all the linked amino acids while the secondary, tertiary, and quaternary structures of a protein involve some level of three-dimensional protein folding. For this reason, the primary structure of a protein best matches the description “blocks on a string.”
Which kind of gene encodes a protein?
The type of RNA that contains the information for making a protein is called messenger RNA (mRNA) because it carries the information, or message, from the DNA out of the nucleus into the cytoplasm. Translation, the second step in getting from a gene to a protein, takes place in the cytoplasm
What happens to DNA and mRNA Once base pairing has been completed?
As the RNA polymerase continues down the strand of DNA, more nucleotides are added to the mRNA, thereby forming a progressively longer chain of nucleotides (Figure 2). When this base-pairing happens, RNA uses uracil (yellow) instead of thymine to pair with adenine (green) in the DNA template below.
Why is uracil found in RNA and not DNA?
Uracil is energetically less expensive to produce than thymine, which may account for its use in RNA. In DNA, however, uracil is readily produced by chemical degradation of cytosine, so having thymine as the normal base makes detection and repair of such incipient mutations more efficient.