ASCP Molecular Biology Certification Exam Question With Complete solutions

ASCP Molecular Biology Certification Exam Question With Complete solutions Pyrimidine - ANSWER One carbon ring Cytosine, Thymine, Uracil Purine - ANSWER Two carbon rings Adenine, Guanine How are nucleotides joined together? - ANSWER Condensation to form phosphodiester bond What is the function of mRNA? - ANSWER Carries genetic info out of nucleus Transcript translated to protein What is the function of tRNA? - ANSWER Carries aa to ribosome Anticodon pairs with codon on mRNA strand What is the function of rRNA? - ANSWER part of ribosome structure most abundant RNA coordinated coupling of tRNA to mRNA codons Feedback inhibition - ANSWER Product of pathway is noncompetitive inhibitor Binds to allosteric site to slow down rxn b/c too much product Exonucleases - ANSWER Degrades nucleic acids by removing one terminal nt at a time Cleaves phosphodiester bond at end of chain 5' --> 3' and 3' --> 5' Endonucleases (Prok) - ANSWER Restriction enzymes Cleaves phoshpodiester bonds w/i poly-nt chain Recognition site is palindromic sequence Types I-V ORI sites - ANSWER nt sequence where replication is initiated Topoisomerase I - ANSWER Induces ss breaks Remove DNA supercoils during TXN and DNA replication; for strand breakage during recombination; for chr condensation; and to disentangle intertwined DNA during mitosis topoisomerase II - ANSWER cuts both strands of one DNA double helix, passes another unbroken DNA helix through it, and then reanneals the cut strands Gyrase (topoisomerase II) - ANSWER Unwinds supercoiling caused by unwinding at the rep fork by introducing DSBs Helicase - ANSWER Breaks H-bonds of double helix at the replication fork Primase - ANSWER DNApol α (DNA dep RNA pol) adds short segments of complementary RNA to ssDNA template (primers), serves as starting points for replication single-strand DNA binding proteins (SSBPs) - ANSWER Binds ssDNA and prevents it from re-annealing during TXN, replication, repair, and recombination Okazaki fragments - ANSWER Short fragments of DNA synthesized by DNApol δ using the lagging strand (3'->5') as a template Ligase - ANSWER Closes gaps in DNA Catalyzes phosphodiester bond between 3'OH and 5'P What are the steps in DNA replication? - ANSWER 1. Initiate 2. Elongate 3. Terminate Telomeres - ANSWER Repeat sequence (TTAGGG) at the ends of chr, protect chr from degradation RNA polymerase - ANSWER DNA dependent RNApol Transcribes DNA template to RNA (3'-->5'; anti-parallel) Splicesomes - ANSWER Complex of snRNPs Removes introns from pre-mRNA and splices exons together Enhancers - ANSWER Short regions of DNA that bind proteins (TXN factors) that enhance TXN of a gene Poly-A tail - ANSWER Prevents mRNA from being degraded in cytoplasm 100-250 A's at 3' end 5' cap - ANSWER 5'-5' pyrophosphate bridge to a methylated G added to 5' end of a mRNA Protects against degradation and as a recognition signal for TLN apparatus aminoacyl tRNA - ANSWER tRNAs that carry amino acids Ribosomes - ANSWER Where TLN occurs Prok: 30s and 50s Euk: 40s and 60s Catalyzes peptide bond between a.a.'s What is the path of a tRNA in a ribosome? - ANSWER Acceptor > Peptidyl > Exit How is translation initiated? - ANSWER small rRNA (40S) subunit binds mRNA and scans for start codon (AUG) Met-tRNA is brought to the P site Large rRNA (60S) subunit binds How is translation terminated? - ANSWER Occurs when stop codon enters A site Release factor recognizes stop codon, hydrolyzes ester bond with P site, releasing aa chain Reverse transcriptase - ANSWER enzyme that transcribes RNA to cDNA (lacks introns) RNA --> RNA:DNA --> cDNA (dsDNA) Pleiotrophy - ANSWER a single gene controls the expression of many phenotypic traits ie Sickle Cell Anemia