Review for Chapter 5 Lecture 3 I already answered most questions during lecture Please do not memorize the answers You must understand the concepts Please do not share upload all and any lecture contents with other students who are not taking this course and at websites like Chegg and CourseHero as these sites will be monitored That is against copyright law of UNT and the book publisher so you WILL be reported and face consequences according to UNT s policies 1 Use the terms listed to fill in the blanks in Figure there is a slide you can use A B C D E F A T base pair G C base pair deoxyribose phosphodiester bonds purine base pyrimidine base 2 A DNA strand has a polarity because its two ends contain different bases True or False 3 G C base pairs are more stable than A T base pairs True or False 4 The two polynucleotide chains in the DNA double helix are held together by between the bases on the different strands All the bases are therefore on the outside inside of the double helix with the sugar phosphate backbones on the outside inside 5 A is often defined as a segment of DNA that contains the instructions for making a particular protein or RNA molecule is the total amount of genetic information carried in the complete set of chromosomes in an organism 6 Each DNA molecule is packaged in a separate chromosome and the total genetic information stored in the chromosomes of an organism is said to constitute its genome 7 Each chromosome contains a single long DNA molecule True or False 8 Each human cell contains about of DNA yet the cell nucleus is only in diameter Tucking all this material into such a small space is the equivalent of trying to fold 40km 24miles of extremely fine thread into a tennis ball 9 10 Two copies of each of H2A H2B H3 and H4 form a nucleosome core particle around which the double stranded DNA helix is twice 11 Histones are relatively small proteins with a very high proportion of positively charged amino acids positive charge helps the histones bind tightly to DNA True or False 12 In living cells nucleosomes are packed upon one another to generate regular arrays in which the DNA is more highly condensed usually in the form of a 30nm fiber True or False 13 By light microscopy there are two types of chromatin in interphase nuclei of higher eukaryotic cells a highly condensed form called and all the rest which is less condensed called 14 During interphase the chromosomes are extended as long thin tangled threads of DNA in the nucleus and cannot be easily distinguished in the light microscope We refer to chromosomes in this extended state as 15 Chromosomes from nearly all cells are visible during mitosis where they coil up to form much more condensed structures called 16 In eukaryotic chromosomes DNA is complexed with proteins to form chromatin The paternal and maternal copies of human Chromosome 1 are homologous whereas the paternal copy of Chromosome 1 and the maternal copy of Chromosome 3 are nonhomologous chromosomes Cytogeneticists can determine large scale chromosomal abnormalities by looking at a patient s karyotype 17 The display of the 46 human chromosomes at mitosis is called the human karyotype 18 Given the sequence of one strand of a DNA helix below provide the sequence of the complementary strand and label the 5 and 3 ends 5 GCATTCGTGGGTAG 3 5 CTACCCACGAATGC 3 Be careful with the polarity 19 The human genome comprises 23 pairs of chromosomes found in nearly every cell in the body Answer the quantitative questions below by choosing one of the numbers in the following list 23 200 69 46 A B C How many centromeres are in each cell What is the main function of the centromere How many telomeres are in each cell What is their main function How many replication origins are in each cell What is their main function 92 109 20 Each chromosome is a single molecule of whose extraordinarily long length can be compacted by as much as fold during and tenfold more during This is accomplished by binding to that help package the DNA in an orderly manner so it can fit in the small space delimited by the The structure of the DNA protein complex called is highly over time 10 000 100 1000 chromatin chromosome different DNA lipids mitosis cell cycle dynamic nuclear envelope proteins cell wall nucleolus interphase interphase static similar 21 A cell can regulate its chromatin structure temporarily decondensing or condensing particular regions of its chromosomes using and enzymes that histone tails in various ways 22 The loosing of chromatin to a more decondensed state allows proteins involved in and to gain access to the necessary DNA sequences 23 Some forms of chromatin have a pattern of histone tail modification that causes the DNA to become so highly condensed that its genes cannot be expressed to produce RNA such condensation occurs on all chromosomes during mitosis and in the of interphase chromosomes 24 Interphase chromosomes contain both darkly staining heterochromatin and more lightly staining euchromatin Genes that are being transcribed are thought to be packaged in a less condensed type of euchromatin Nucleosome core particles are separated from each other by stretches of linker DNA A string of nucleosomes coils up with the help of histone H1 to form the more compact structure of the 30 nm fiber A zigzag model describes the structure of the 30 nm fiber The 30 nm chromatin fiber is further compacted by the formation of loops that emanate from a central axis 30 nm fiber heterochromatin linker active chromatin axis beads on a string euchromatin histone H1 histone H3 histone H4 less loops more synaptic complex zigzag 25 Describe the mechanism by which heterochromatin can spread once it has been established in one region of the chromosome Answer Once the initial H3 lysine 9 methylation is established on core histone octamers in one region the modification attracts a specific set of proteins and other histone methylating enzymes These enzymes create the same modification on adjacent histone octamers which continue to recruit more heterochromatin specific proteins and enzymes creating a wave of heterochromatin spreading along the chromosome 26 Methylation and acetylation are common changes made to histone H3 and the specific combination of these changes is sometimes referred to as the histone code Which of the following patterns will probably lead to gene silencing a b c d lysine 9 methylation lysine 4 methylation and lysine 9 acetylation lysine 14 acetylation lysine 9