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Genetics- lecture 4, Replication and transcription

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winniesmith1's version from 2017-03-06 20:21

Section 1

Question Answer
What doe complementarity allow(DNA to be copied exactly) hereditary info to be copied digitally; accurately, quickly, and efficiently.
What does semi-conservative replication requirenucleotides (A,C,G,T) and DNA polymerase, helicase, ligase.
Process semi-conservative replicationNucleotides are added only from 5’ to 3’ direction SEMI DISCONTINOUS Okazaki fragments and later joined by DNA ligase.
what is the accuracy of DNA replicationonly 1 error/1 billion nucleotides
What is a gene a specific section of DNA within a chromosome (usually several 10,000's of base pairs long)
what is an exoncoding sequence of DNA
what is an intronnoncoding sequence of DNA
what does splicing doremoves introns
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Section 2

Question Answer
DNA vs RNA: DNAStores RNA-encoding info, and transfers info to daughter cells. Double-stranded. Deoxyribose sugar. Thymine not uracil.
DNA vs RNA: RNACarries protein-encoding info, and helps to make proteins. Generally single-stranded. Ribose as sugar. Contains uracil instead of thymine.
What is the job RNA to carry messages from the DNA (in the nucleus) to the ribosomes (in the cytoplasm).
What does mRNA docarries a message from the DNA to the cytoplasm
What does tRNA do transports amino acids to the mRNA to make a protein
What does rRNA domake up ribosomes, which make protein
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Section 3

Question Answer
What is transcriptionDNA transcribed to mRNA in the nucleus. Nucleotides (ACGU) U replaces T. RNA polymerase. Only one strand copied- sense strand.
What are the complementary strands calledDNA coding strand and DNA template strand.
When DNA is transcribed what does in createpre-mRNA
What happens in transcription after pre-mRNA is formedIntrons are removes by RNA splicing.
How does intron splicing occurIntrons contain sequences that act as clues for their removal. Carried out by assembly of small nuclear ribonucleoprotein particles (snRNPs) – Spliceosomes
How does the same DNA make many proteinsPost-transcriptional modification and Can be spliced differently depending on location (for example in liver mRNA contacts exons 1-5 but in skeletal processing exon 3 is excluded).
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Section 4

Question Answer
What does post-transcriptional modification do used to process primary transcripts to increase the stability of mRNA for its export to the cytoplasm
What are the 2 types of post-transcriptional modificationRNA capping and polyadenylation.
What does RNA capping dohappens at the 5’ end of the RNA, usually adds a methylgaunosine shortly after RNA polymerase makes the 5’ end of the primary transcript
What does polyadenylation domodifies the 3' end of the primary transcript by the addition of a string of A's.
What is the process of 5' capping of transcriptAfter about 30 nt are added, 5’-P is almost immediately modified. A phosphate (terminal) is released by hydrolysis. The diphosphate 5’ end then attacks the α-phosphate of GTP to form a very unusual 5’-5’ triphosphate linkage (condensation). This highly distinctive terminus is called a cap. The N-7 nitrogen of the terminal G is then methylated by S-adenosyl methionine to form cap0.
What are caps important forSubsequent splicing reactions. Contribute to the stability of mRNAs by protecting their 5’ ends from phosphatases and nucleases. They enhance the translation of mRNA by eukaryotic protein-synthesizing systems. tRNA and rRNA molecules do not have caps.
What is 3' polyadenylationMost Eukaryotic mRNAs contain poly A tail. Poly A tail is not encoded by DNA. Some mRNAs contain an internal AAUAAA (AAU = Asn, AAA = Lys). This highly conserved sequence is only a part of the cleavage signal, but its context is also important. The cleavage site is 11 to 30 nt away from the AAUAAA site on the 3’ side. After the cleavage by an endonuclease, 50 to 250 A residues are added by Poly(A)polymerase.
What will mutating the cleavage sequence in parent DNA result inmRNA that is not polyadenylated and not exported to cytoplasm- rapidly degraded.
What else is required for efficient cleavageA 2nd downstream signal that is a G/U rich sequence is required for efficient cleavage and polyadenylation, and is located ca. 50 nucleotides from the site of cleavage. The cleavage and polyadenylation specficity factor (CPSF), a large 4-subunit protein (ca. 360 kDa), forms an unstable complex with the AAUAAA sequence that is subsequently stabilized by the addition of at least 4 separate protein complexes that bind to the CPSF-RNA complex.
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