DNA DNA Structure Replication Biotech Transcription Translation 100 100 100 100 100 200 200 200 200 200 300 300 300 300 300 400 400 400 400 400 500 500 500 500 500 What are the three components of a nucleotide? Answer •Sugar •Phosphate •Nitrogen base Name the nitrogen bases in DNA Answer •Thymine •Adenine •Guanine •Cytosine Indicate the type and number of bonds that hold the DNA strands together Answer •Hydrogen bonds •2 between adenine and thymine •3 between guanine and cytosine If the percentage composition of adenine in a DNA molecule is 10% then what are the percent compositions of the other 3 bases. Answer •Thymine = 10% •Guanine = 40 % •Cytosine = 40% What specific types of bond attaches the nitrogen base to the sugar? The phosphate to the sugar? Answer Nitrogen base + sugar = glycosyl Phosphate + sugar = phosphodiester Note: Both are covalent bonds! What enzyme unwinds DNA at the fork by breaking hydrogen bonds between nitrogen bases? Answer helicase What enzyme relieves stress further up the fork? Answer DNA gyrase What enzyme binds complimentary bases and what direction does it move? What has to be in place first before this enzyme can bind to the template? Answer DNA polymerase III which moves in a 5′ to 3′ direction. An RNA primer laid down by RNA primase must be in place first. What are the names of the fragments of the sections on the lagging strand and what enzyme joins these sections? Answer Okazaki fragments are joined by DNA ligase. How does the fact that DNA replicates semi-conservatively decrease the possibility of errors made during DNA replication? You must first explain the term semiconservatively. Answer Semi-conservative replication means that each parent strand serves as a template from which a copy can be made. This template serves as the checkpoint when DNA polymerase I and III proofread the newly synthesized strand. What molecular biology technique would be the most appropriate for analyzing the size of DNA fragments? Answer Gel electrophoresis What are three circumstances where one might want to amplify the amount of DNA by PCR? Answer Studying fossil remains DNA found at scene of crime Early diagnosis of disease (HIV) Observe the following DNA fingerprint and determine who should remain a suspect. Answer JOHN What does a restriction endonuclease do? Answer Recognizes and cuts DNA at a specific sequence. How are recombinant bacteria differentiated from the original bacteria? Answer Recombinant bacteria also received a marker gene (eg. Antibiotic resistance) that allows them to be easily distinguished when culturing. Does transcription require a primer? Answer No What must be recognized to initiate transcription? Answer Promoter What enzyme creates the mRNA strand and what direction does it move? Answer RNA polymerase synthesizes mRNA in a 5′ to 3′ direction. What is an intron? An exon? Which is removed by what enzyme? Answer Introns = non-coding regions of mRNA Exons = coding regions of mRNA Spliceosomes remove introns What modifications must be made to the ends of the mRNA transcript before it can leave the nucleus and why must these occur? Answer Cap – methyl guanine Tail – Poly A tail by poly A polymerase To prevent degradation by enzymes in the cytoplasm Where in the cell does translation occur? Answer Cytoplasm at the ribosomes What is necessary to initiate translation? Indicate the specific sequence of this initiator. Answer Start codon (AUG) on mRNA is recognized by the ribosome. Differentiate between a codon and an anticodon. Answer Codon = 3 nucleotide bases on mRNA that code for one amino acid Anticodon = 3 nitrogen bases on tRNA that are complimentary to the codon on mRNA. What are the three types of RNA and what are their functions in translation Answer Messenger RNA – brings copy of gene to be read Ribosomal RNA – reads or translates mRNA copy by exposing 3 bases at a time Transfer RNA – brings in amino acids to form polypeptide Which is more harmful; a substitution or a deletion?