BIO 100 Ch 8 DNA

DNA Inheritance

Inherited characteristics are transmitted from parent genes to offspring. Genes are parts of the chromosomes. Genes provide the genetic instructions for every organism – contained in its DNA. DNA molecules direct the life & function of each cell. DNA is passed on from parents to the next generation

DNA structure – was determined by Watson and Crick. Originally discovered, studied and researched by Linus Pauling, but because of political set-backs. He was involved in peace movements and the time and accused of being a communist. He was never acknowledged or given credit. He probably would have been the one to receive the Nobel prize. Later, Franklin & Wilkins came along and determined the structure of the DNA molecule through x-ray studies; but it was Watson and Crick that were given the credit for discovering the DNA. They were not as knowledgeable as Pauling, but by studying his information and studying the x-rays works of Franklin & Wilkins, they were able to describe the DNA and formulate a model.

The DNA structure is a double helix

The DNA is composed of monomers called nucleotides. Each nucleotide has 3 parts:

1. Phosphoric acid (phosphate)2. deoxyribose sugar3. Nitrogen base- there are 4 possible nitrogen base molecules:

Adenine Thymine Guanine Cytosine

The DNA structure is arranged in a “ladder” configuration. DNA molecule consists of 2 chains of nucleotides and is held together by hydrogen bonds. It alternates phosphate and sugar groups to form the sides of ladder. The Rungs are composed of paired nitrogen bases which are complementary base pairing (purine with pyrimidine)

Adenine combines with Thymine (A-T) Guanine combines with Cytosine (G-C)

The “ladder” then coils to form a helix

DNA Replication

How then does DNA encode the amount of information required to build and operate an organism?

How are we determined our individual height, bone frame, color of eyes, hair, and tone of voice? What determines the variety in the species of dogs?

By the transmission of Genetic Information. This occurs during cell division

Cell Division

Cell division is required for growth & reproduction. The Cell cycle p.114

Dividing cells will have limited differentiation or permanent differentiation

Stem cells: are the 1st few newly divided cells of a fertilized egg. They are not fully programmed to be the specific cell they are going to be.

Cell Division – occurs in sexual reproduction in the eukaryotes cells – where fusion of 2 Gametes (egg & sperm) take place. The fertilized egg cell undergoes the process of mitosis.

Asexual reproduction of cells – the cell is formed by a single parent without fusion of gametes. This process produces offsprings genetically identical to the parent

Prokaryotes reproduce through binary fission – splitting in two

During DNA Replication – a variations in the organism’ characteristics is determined by the sequencing of the four simple parts of the molecule (the nucleotides in the DNA). The 4 nitrogen bases are arranged in any order. This occurs during the ‘S’ phase of the cell cycle (mitosis).. When cells divide, the DNA is copied with accuracy. Chromosomes carry the genes - a chromosomes consists of DNA and protein. Each double helix is the DNA components of a single chromosome. Therefore, the nitrogen base pairing is the foundation of DNA replication.

DNA Enzyme – Ligase is what Bonds the DNA together; completes it. It also is responsible for repairing any breaks in the sugar-phosphate backbone

Semi-conservative replication. Semiconservative = means that the two new DNA molecules will each contain half “old” and half “new” DNA strands.

When the DNA divides, one parent DNA strand and its complementary daughter DNA strand entwine into a helix formation

Each daughter DNA molecule consists of one new chain of nucleotides that has paired up with the parent DNA molecule

The 2 daughter DNA molecules will be identical to the parent molecule