Chapter 8 DNA Structure ahd Formation

Watson and Crick

In the 1950's , they suspected that DNA was structured like a helix. To prove that DNA was a helix, they created models from scraps of metal connected by angled bonds of wire.

Model of DNA created by Watson and Crick

Chargaff Rule

In the 1950's, Erwin Chargaff created two rules about DNA. Chargaff's first rule said that the amounts of thymine and adenine in DNA are identical to each other. Also, the amounts of cytosine and guanine are identical. A simpler way to put this rule is A = T and G = C. Chargaff's second rule says two DNA of different species differ in proportions of adenine and guanine.

Chargaff's Rule

How do base pairs of DNA bind?

The two strands of DNA that bind together match. Their strands are complementary to each other because the base of each nucleotide one one strand of DNA pairs with a suitable partner base on the other nucleotide. The patterns of the binding are A pairs to T, and G pairs to C. In every single molecule of DNA, these binds will always be the same.

Base Pairs Bind Together

What is a Chromosome?

A chromosome is a structure that consists of DNA and associated proteins. It carries all or part of a cell's genetic information. During most of a cell's life, each chromosome consist of one DNA molecule. It will consist of two molecules of DNA after the cell divides. Each species has a specific chromosome number. A human cell has 46 chromsomes, or two sets of 23 chromosomes.


What is a Karyotype?

A Karyotype is an image of an individual's diploid set of chromosomes. Diploid means that cells have two sets of chromosomes.


How does DNA replicate?

The process by which a cell copies its DNA is called DNA replication. Before DNA replication, a chromosome consists of one molecule of DNA. As replication begins, enzymes break the hydrogen bonds that hold the double helix together, and the two DNA strands unwind and separate. Another enzyme constructs primers which serve as an attachment point for DNA polymerase, the enzyme that assembles new strands of DNA. A primer base-pairs with a complementary strand of DNA. DNA polymerase attach to the hybridized primers and begin DNA synthesis. The enzyme DNA ligase seals any gaps, so the new DNA strands are continuous. Both of the strands of the parent molecule are copied at the same time. As each new DNA strand lengthens, it winds up with its template strand into a double helix. Semiconservative replication produces two copies of a DNA molecule, one strand is new and the other is parental.

DNA Replication

What damages DNA?

Ionizing radiation from X-rays, most UV light, and gamma rays may cause DNA damage. It breaks down DNA, it causes covalent bonds to form between bases on opposite sides, it fatally alters nucleotide bonds, and it causes adjacent nucleotide dimers to form.

DNA Damage

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