Review for Lecture 4 1 Use the terms listed to fill in the blanks in Figure 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 6 Each DNA molecule is packaged in a separate and the total genetic information stored in the chromosomes of an organism is said to constitute its 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 The most important function of chromosomes is to A functional chromosome requires three DNA sequence elements at least one to permit the chromosome to be copied one to facilitate proper segregation of its two copies at mitosis and two to allow the chromosome to be maintained between cell generations 10 The five types of histones fall into two main groups the histones and the histones 11 Two copies of each of H2A H2B H3 and H4 form a around which the double stranded DNA helix is twice 12 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 13 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 14 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 15 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 16 Chromosomes from nearly all cells are visible during mitosis where they coil up to form much more condensed structures called 17 In eukaryotic DNA is complexed with proteins to form The paternal and maternal copies of human Chromosome 1 are whereas the paternal copy of Chromosome 1 and the maternal copy of Chromosome 3 are Cytogeneticists can determine large scale chromosomal abnormalities by looking at a patient s 18 The display of the 46 human chromosomes at mitosis is called the human 19 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 20 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 69 200 46 92 109 A How many centromeres are in each cell What is the main function of the centromere B How many telomeres are in each cell What is their main function C How many replication origins are in each cell What is their main function 21 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 chromosome mitosis cell cycle dynamic 100 different nuclear envelope proteins cell wall 1000 DNA nucleolus interphase interphase chromatin lipids static similar 22 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 23 The loosing of chromatin to a more decondensed state allows proteins involved in and to gain access to the necessary DNA sequences 24 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 and in the of interphase chromosomes 25 Interphase chromosomes contain both darkly staining and more lightly staining Genes that are being transcribed are thought to be packaged in a condensed type of euchromatin Nucleosome core particles are separated from each other by stretches of DNA A string of nucleosomes coils up with the help of to form the more compact structure of the A model describes the structure of the 30 nm fiber The 30 nm chromatin fiber is further compacted by the formation of that emanate from a central 30 nm fiber active chromatin axis beads on a string euchromatin heterochromatin histone H1 histone H3 histone H4 less linker loops more synaptic complex zigzag 26 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 27 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 lysine 9 methylation b lysine 4 methylation and lysine 9 acetylation c lysine 14 acetylation d lysine 9 acetylation and lysine 14 acetylation 28 The process of sorting human chromosome pairs by size and morphology is called karyotyping A modern method employed for karyotyping is called chromosome painting How are individual chromosomes painted Answer Chromosome painting relies on the specificity of DNA complementarity Because unique sequences for each chromosome are known short DNA molecules matching a set of these sites can be designed for each