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7.1: DNA Structure and Replication

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Outline the features of DNA structure that suggested a mechanism for DNA replication.



Understanding: DNA structure suggested a mechanism for DNA replication.
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Outline the features of DNA structure that suggested a mechanism for DNA replication.



Understanding: DNA structure suggested a mechanism for DNA replication.
1. Complementary base pairing: A-T and C-G ensures that the sequence of the genetic code is conserved when each strand replicates.

2. Covalently bonded sugar-phosphate backbone: relatively strong bonds along the DNA backbone ensure the nucleotides of the parent strands remain in the same sequence during replication.

3. Hydrogen bonds between complementary strands: allow the parent DNA strands to easily separate to serve as templates for new strands during DNA replication.
Image: Outline the features of DNA structure that suggested a mechanism for DNA replication. Understanding: DNA structure suggested a mechanism for DNA replication.
Outline the mechanism of replication suggested by the structure of DNA.



Understanding: DNA structure suggested a mechanism for DNA replication.
Watson and Crick (1953) proposed that DNA was composed of two complementary strands hydrogen bonded together to form a double helix. Their model suggested a replication mechanism, later termed semiconservative replication.

According to Watson and Crick, the two strands of DNA first unwound and separated. Next, each DNA strand functioned as a template for a new DNA strand, with the bases on each parent strand dictating new bases on the new daughter strands based on complementary base pairing. Therefore, one parent double helix produced two new daughter double helices. Each daughter double helix contained one new strand and one parental strand, which was conserved from the parent double helix.

The semiconservative mechanism of DNA replication was confirmed by Meselson and Stahl in 1957.
Image: Outline the mechanism of replication suggested by the structure of DNA. Understanding: DNA structure suggested a mechanism for DNA replication.
Draw and label the structure of a nucleosome.



Understanding: Nucleosomes help to supercoil the DNA.
The nucleosome is the basic unit of DNA packaging in eukaryotes. Each nucleosome is composed of two turns of DNA wrapped around a group of eight histone proteins (called an octamer core). Each nucleosome connects to the adjacent nucleosomes through another type of histone protein (called the H1) and a region of "linker" DNA.
Image: Draw and label the structure of a nucleosome. Understanding: Nucleosomes help to supercoil the DNA.
State two roles of nucleosomes in eukaryotic cells.



Understanding: Nucleosomes help to supercoil the DNA.
To compact DNA while regulating gene accessibility for transcription, eukaryotic organisms organize their genomes using the nucleosome as a the fundamental unit of DNA packaging.
Image: State two roles of nucleosomes in eukaryotic cells. Understanding: Nucleosomes help to supercoil the DNA.
Define "supercoiling" as related to DNA structure.



Understanding: Nucleosomes help to supercoil the DNA.
Supercoiling refers to the repeated twisting and winding of the DNA strand. Supercoiling functions to reduce the space required for DNA packaging, allowing for more compact storage of DNA.
Image: Define "supercoiling" as related to DNA structure. Understanding: Nucleosomes help to supercoil the DNA.