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Chapter 7

DNA is wrapped around histone proteins to form nucleosomes. Nucleosomes are joined together by another histone to form supercoiled structures. Telomeres are repetitive base sequences that are found at the ends of chromosomes. DNA replication occurs during S phase and results in two identical DNA molecules through a semi-conservative process where the parental strands serve as templates for new complementary strands to be synthesized in the 5' to 3' direction.

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Chapter 7

DNA is wrapped around histone proteins to form nucleosomes. Nucleosomes are joined together by another histone to form supercoiled structures. Telomeres are repetitive base sequences that are found at the ends of chromosomes. DNA replication occurs during S phase and results in two identical DNA molecules through a semi-conservative process where the parental strands serve as templates for new complementary strands to be synthesized in the 5' to 3' direction.

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Term Definition

Nucleosome DNA wrapped around 8 histone proteins, another histone holds nucleosomes
together for supercoiling

Telomeres Repetitive base sequences at the ends of chromosomes

Explain the process of DNA replication


- DNA replication occurs during S phase of interphase in preparation for mitosis
- DNA replication is semi-conservative, with an old strand from parent molecule and a new strand
- Helicase unwinds the DNA double helix and separate the two strands by breaking hydrogen
bonds between bases. Each strand of parent DNA is used as template for synthesis
- DNA primes adds NTPs on each template strands to form a short length of RNA primer
- DNA polymerase III binds to RNA primer and adds dNTPs in the 5’ to 3’ direction according to
complementary base pairing. Adenine with Thymine and Guanine with Cytosine
- Two phosphate groups in NTPs and dNTPs are removed to provide energy for forming
phosphodiester bond
- Synthesis is in 5’ to 3’ direction. It is continuous on the leading strand but discontinuous on the
lagging strand, resulting in the formation of Okazaki fragments on the lagging strand
- DNA ligase joins Okazaki fragments together by forming sugar-phosphate bond


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