4. RNA是由核糖核苷酸通过 键连接而成的一种 。几乎所有的RNA都是由 DNA 而来，因此，序列和其中一条链 。
5. 大肠杆菌的染色体配对需要 ；它与单链DNA结合并使同源双链DNA与之配对。染色体参与复制的活性区呈Y形结构，称为 。
四、问答题：
1. Draw the general structure of an amino acid and a peptide bond.
2. Draw a typical DNA melting curve. Label the axes and point out the melting temperature.
3. Draw the structure of a cruciform DNA and an RNA hairpin with an 8-bp stem and a 5-bp loop.
4. Briefly describe the different levels of DNA organization in chromosome.
5. DNA's B Form和A Form与and Z Form最主要的结构不同点是什么？
6. 碱基对间在生化和信息方面有什么区别?
7. 反向重复序列在DNA和RNA上会产生什么结构?
8. 简述染色质的结构。
9. 论述tRNA二级和三级结构。
习题四
一、名词解释：
replicon，origin，ARS， primosome， telomere，Replisome, Lagging strand of DNA
二、选择题：
1. Which of the following statements is FALSE regarding eukaryotic chromosomes?（ ）
a) Because they are larger than prokaryotic chromosomes and have a single ori, replication in eukaryotes is much faster than in prokaryotes.
b) They are linear with a centromere and two telomeres.
c) They are larger and contain many more genes than prokaryotic chromosomes.
d) They contain many repetitive sequences.
e) Because they contain genes with introns, the DNA of a gene is actually much longer than the mature mRNA that is produced from that gene.
2. All replicons must: （ ）
a) be contained within the nucleus of a cell
b) be composed of circular DNA or RNA
c) be composed of DNA
d) have an origin of replication
e) carry a gene for DNA polymerase
3. SSB protein （ ）
a) unwinds the double helix in front of the replication fork
b) attaches the synthetic subunit of DNA polymerase to the DNA
c) inserts the primer for DNA synthesis
d) keeps the DNA single stranded at the replication fork
e) seals the nicks between Okazaki fragments
4. During rolling circle replication: （ ）
a) Many interlocking circles of DNA are made
b) Two origins of replication are used
c) A single strand is nicked when replication starts
d) A circular RNA primer is used
e) None of the above is true
5. During rolling circle replication, which of the following is false? （ ）
a) There is no RNA primer synthesis required for synthesis of the leading strand.
b) The leading strand is covalently linked to the parental template used for lagging strand synthesis.
c) No .lagging strand is synthesized.
d) The template used for synthesis of the lagging strand remains intact.
6. In eukaryotes, the lagging strand DNA is synthesized by DNA polymerse-（ ）
(a) α.(b)β.(c)γ.(d)δ.(e)ε.
7. Telomerase is a ribonucleoprotein complex that（ ）
a) synthesizes DNA in the absence of a DNA or RNA template.
b) synthesizes DNA use a DNA template that is part of the ribonucleoprotein complex.
c) synthesizes DNA use a RNA template that is part of the ribonucleoprotein complex.
d) synthesizes DNA using ribosomal RNA as template.
8. Telomeres are shortened slightly after every round of replication because: （ ）
a) Telomerase cuts off several 6-bp repeats.
b) The gap created by removal of the RNA primer at the very end of the chromosome cannot be filled in.
c) The gap created by removal of the RNA primer in the center of the chromosome cannot be filled in.
d) Older chromosomes are more fragile and the ends break off more frequently.
e) Telomerase is only functional in cancer cells.
