Chapter 8 By Paul Ferguson

Watson and Crick

James Watson and Francis Crick

In 1950 two scientists made a discovery that changed the study of life forever. Shown above, James Watson and Francis Crick were the first people to suggest that DNA consists in the form of a helix. They made the first models of DNA from scrap metal that was bonded by pieces of wire.

Chargaff Rule

Chargaff Rule

Erwin Chargaff discovered the founding principles of DNA. Chargaff is most noteworthy for his two rules, but primarily his first one. Chargaff's first rule is that DNA from any organism should have a 1:1 ratio of pyrimidine and purine bases and, that the amount of guanine is equal to cytosine and the amount of adenine is equal to thymine. This first rule makes up the DNA double helix.

How do the base pairs bind?

The base pairs of DNA bond in a very special way. The two strands of DNA are complementary. The base of each nucleotide on one strand pairs with a suitable partner base on the other. The base patterns of pairing are adenine to thymine and guanine to cytosine. This pairing is the same in all the molecules of DNA.

What is a chromosome?

A chromosome is a structure that consists of DNA and associated proteins. Chromosomes part or all of the cell's genetic information. There is a protein that structurally organizes eukaryotic chromosomes named Histone. A nucleosome is a length of DNA wound twice around a spool of his histone proteins. Every chromosome consists of only one DNA molecule. The cell duplicates its chromosomes when it prepares to divide. Every species has a characteristic chromosome number. The human body has two sets of 23 chromosomes. This means the cells are diploid.

What is a karyotype?

A karyotype is an image of an individual's diploid set of chromosomes. An autosome is a chromosome that is the same in males and females. Two autosomes of pair have the same shape, length, and centromere location. They hold information about the same trait.

How does DNA replicate?

A cells copies its chromosomes so it contains two sets in preparation for divison. The process by which gen cell copies its chromosomes is called DNA replication. A chromosome consist of one molecule of DNA before DNA replication. During replication the DNA strands unwind and separate enzymes breaks the hydrogen bonds that hold the double helix together. A different enzyme creates primers. Primers are short single strands of nucleotides. Polymerase is the enzyme that assembles new strands of DNA. Primers are attachment points for these enzymes. A primer base pairs with a complementary strand of DNA. The establishment of base-pairing between two strands of DNA is called nucleic acid hybridization. DNA polymerase attach to hybridized primers and begin DNA synthesis. Both two strands parent molecule are copied at the same time. Semiconservative replication produces two copies of a DNA molecule: one strand of each copy is new, and the other is parental.

What Damages DNA?

A few factors can damage DNA. The main factors of DNA damage are Ionizing radiation from x-rays, most UV light, and gamma rays. This damage made include: Breaks in DNA, causes covalent bonds to form between bases of opposite strands, fatally laters nucleotide bases, and lastly causes adjacent nucleotide dimers to form.

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