Due 15 Thursday 2012 end of class Modern Biology HW 3 37 pts Name Rajiv Ravishankar Group 9 Ch 14 DNA Synthesis 1 The structure of DNA introduced by Watson and Crick s model gave a hint to the mechanism of how DNA might be replicated What did the structure suggest Explain how the parent strand of DNA is copied to each daughter molecule 2 pts Watson and Crick realized that the A T and G C pairing rule suggested a way for DNA to replicate They suggested that the existing strands of DNA served as a template for the production of new strands with bases being added to the new strands according to their complementary base pair If the parent strand contains a T then an A would be added to the new strand similarly T A G C and C G 2 a When DNA is actively being synthesize why does it appear as if a bubble in the DNA forms at the origin of replication 1 pts Bubbles are formed during replication because DNA replication is a bidirectional process b Describe the difference in origin of replications for bacterial chromosomes and eukaryotic chromosomes 1 pts Bacterial chromosomes have a single location where the replication begins Eukaryotes have multiple sites along each chromosome where DNA synthesis begins 3 a What is different about leading strand DNA synthesis and lagging strand synthesis by DNA polymerase 2 pts The lagging strand is synthesized in the opposite direction of the replication fork b What are the newly synthesized fragments from the lagging strand called What enzyme connects them to a continuous piece 2 pts Okazaki fragments DNA Ligase 4 Place the letter of the correct function next to the name of the molecule involved in DNA synthesis 9 pts Molecule DNA Polymerase III Match the function with the molecule Place letter of function in this column F DNA ligase H Sliding Clamp Helicase G E Topoisomerase I Primase A DNA Polymerase I B Single stranded DNAbinding proteins Telomerase C D Functions A Catalyzes the synthesis of the RNA primer B Removes the RNA primer and replaces it with DNA C Stabilizes single stranded DNA D Synthesizes DNA at the end of linear chromosomes E Breaks hydrogen bonds between base pairs F Adds bases to the growing DNA strand G Holds DNA polymerase in place during strand elongation H Joins Okazaki fragments into a continuous strand I Breaks and rejoins DNA strand to untwist the double helix Ch 15 How Genes Work 1 The genetic make up of an organism is called its Genotype which when expressed gives rise to the observable traits or characteristics of an organism called its Phenotype 1 pts 2 Describe the meaning of the 4 characteristics of the genetic code 4 pts It is redundant All but methionine and tryptophan are coded by one codon It is conservative When several codons specify the same amino acid the first two bases in those codons are almost always identical It is unambiguous A single codon never codes for more than one amino acid It is nearly universal With a few minor exceptions all codons specify the same amino acids in all organisms 3 Label the following events of transcription in chronological order 1 5 5 pts 2 3 1 4 5 Sigma binds to the promoter region The double helix of DNA is unwound breaking hydrogen bonds between complementary strands Sigma binds to RNA polymerase Sigma is released Transcription begins 4 In bacteria the information in DNA is converted directly to mRNA and immediately ready for translation Why must pre RNA be processed before translation in eukaryotes Describe in detail the splicing mechanism in eukaryotes naming all key components and the type of bond that completes the splice 4 pts The machinery required for transcription in eukaryotes is more complex as compared to prokaryotes Unlike bacterial genes eukaryotic genes do not consist of one continuous DNA sequence that codes for a product Instead the regions in a eukaryotic gene that code for proteins are interrupted by many intervening bases These bases do not code for a product Therefore to make a functional mRNA the eukaryotic cell must then dispose of certain sequences inside the primary transcript and then combine the separated coding sections as a whole 1 2 3 4 snRNPs bind to 5 exon intron boundary Other snRNPs arrive to form spliceosome The intron forms a loop with the key adenine at its connecting point The loop is cut and a phosphodiester bond links the exons on the other side which produces a contiguous coding sequence 5 a What is charging a tRNA Which enzyme is involved in this activity 2 pts Enzymes called aminoacyl tRNA synthetases catalyze the addition of amino acids to tRNA is called charging Aminoacyl tRNA synthetases b There are 20 major amino acids how many different types of the above mentioned enzyme would you expect to exist 1 pts 20 6 Fill in the blanks about how the ribosome synthesizes proteins 3 pts 1 An amino acyl tRNA diffuses into the A site E P or A its anticodon binds to a codon in the mRNA 2 A peptide bond forms between the amino acid held by the aminoactyl tRNA in the A E P or A site and the growing polypeptide which is held by a tRNA in the P site E P or A 3 The ribosome moves ahead and all three tRNAs move one position down the line The tRNA in the E E P or A site exits the tRNA in the A site moves to the E site and the tRNA in the A site switches to the P site
View Full Document
Unlocking...