Bio 151 Exam 2: Learning Objectives Questions With Complete Solutions!!!

Explain why misconceptions about the nature of life, such as the theories of spontaneous generation or preformation, slowed our understanding of heredity and genetics. - ANS SPONTANEOUS GENERATION - the idea that new life had to come from old life, so life was spontaneously produced from non-living substances - ex: maggots came from dead meat, flies came from fruit - disproved by Redi when he covered a Petri dish filled with mean with a cloth and he left one exposed to the open air; flies only were in the dish that was uncovered - Pasteur also disproved this with broth and a swan neck flask; when broth was exposed to air, the broth became spoiled, but it stayed fresh if it was not exposed to the air (which caries bacteria) PREFORMATION - the idea that all life had been pre-formed and there was no such thing as inheritance INHERITANCE OF ACQUIRED TRAITS - inheritance occurred but information from nature was passed on (ex: knowledge and traits) Because sexual inheritance is complicated, it was a laborious process to determine how it actually occurred. Since previous inheritance theories were already in place, no one intentionally put effort into solving the question of inheritance (because there wasn't a question, it had already been "solved"). It took time to even realize these theories were incorrect, especially that of spontaneous generation, to even see the need to disprove them. Explain why the behavior of chromosomes during meiosis suggested that chromosomes were the physical location of Mendelian genes. - ANS - Mendelian genes were different traits present in an individual - adults have two versions of these genes - when cell division occurs during meiosis, two chromosomes are present at the beginning but only one is passed on to the sperm or egg cell - this means that one chromosome is kept and one is passed on = inheritance Describe the experiments that indicated that genes are made of DNA instead of proteins. - ANS - it was though that genes were made of proteins bc: * they had many different functions and could perform many different activities, like proteins * DNA had about equal concentrations of 4 different nucleotides Clue 1: Chargaff's Analysis of DNA - different organisms had different ratios of A, T, C, and G - A%=T% and C%=G% Clue 2: Bacteria Growing in Dish Could Be Transformed by DNA (Griffith and Avery) + Griffith - smooth bacteria was deadly, where as rough was not - if rough cells were grown with ground up smooth cells, the rough cells transformed into smooth cells - this occurred bc genetic information was leaked into the surrounding media and was accepted by the rough cells - this is known as transformation, and the smooth cells were stably inherited (meaning the cells won't go back to being rough bacteria) + Avery - used Griffeth's knowledge to continue the experiment - he removed proteins, RNA, lipids, carbs, or DNA - the only time that smooth cells didn't appear upon addition of rough cells was when DNA was removed - this indicated DNA was the cause of the transformation Clue 3: Virus DNA Infects Cells - when viral particles infect cells, the cells produce more viral proteins - known as bacteriophage - Hershey and Chase grew viruses with nutrients that radioactively labels either protein or DNA - virus proteins can be washed off cells - virus DNA can't be washed off and infects cells Describe the structure of a nucleotide (sugar, phosphates, nitrogenous base) and how nucleotides are bound together to make a single DNA strand. - ANS - made up of nitrogenous base, a phosphate group, and a pentose sugar - nucleotides are bonded together at the nitrogenous base with hydrogen bonds Understand how complementary nucleotides on opposite DNA strands match through hydrogen bonding between their nitrogenous bases - ANS - A hydrogen bonds to T through ligation - C hydrogen bonds to G through ligation Use the antiparallel structure of the two DNA strands and the binding between complementary nitrogenous bases to predict the nucleotide sequence of one strand based on the sequence of the other strand. - ANS ANTIPARALLEL - two strands of a double helix run in opposite directions - one strand runs from 5' (phosphate end) to 3' (hydroxyl end) and the other runs from 3' to 5' COMPLEMENTARY NITROGENOUS BASES - A binds to T - C binds to G ex: template strand - ATCTGCATGCTGCA new strand - TAGACGTACGACGT Explain why DNA replication is considered semi-conservative. - ANS - considered semi-conservative because the template strand remains while a new complementary strand is made - conserve one strand of DNA, and use it as template to make new strand - each new DNA double helix consists of one new and one old strand Diagram replicating prokaryotic and eukaryotic chromosomes including the origins of replication, replication bubbles, replication forks, and the location of the template and newly synthesized strands. - ANS PROKARYOTES - have smaller, circular chromosomes with only one orgin of replication - singular replication bubble and replication fork - template DNA is on outside while daughter strand forms on inside, until cell splits and two daughter DNA molecules form - when daughter strand starts laying down, replication fork opens and is split into two daughter cells EUKARYOTES - have multiple orgins of replicaiton, replication bubbles, and replication forks - occurs in linear fashion - forms two newly synthesized double helices, with one new and one old DNA strand in each Diagram how the enzymes helicase, primase, DNA polymerase, and DNA ligase act in a replication fork. - ANS **topoisomerase occurs first HELICASE - unwinds DNA at replication fork PRIMASE - builds short RNA primer from RNA nucleotides DNA POLYMERASE - extends RNA primers and replaces with DNA - this creates Okazaki fragments