Review for Lecture 4 1. Use the terms listed to fill in the blanks in Figure. 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. A. A-T base pair B. G-C base pair C. deoxyribose D. phosphodiester bonds E. purine base F. pyrimidine base10. 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 heterochromatin linker active chromatin histone H1 loops axis histone H3 more beads-on-a-string histone H4 synaptic complex euchromatin less zigzag26. 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