DNA Basics

[Anonymous]

What is DNA and where is it stored?

http://www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/graphics/nuc_to_bp.gif

The nucleus is a membrane bound organelle that contains the genetic information in the form of chromatin, highly folded ribbon-like complexes of deoxyribonucleic acid (DNA) and a class of proteins called histones.

When a cell divides, chromatin fibers are very highly folded, and become visible in the light microscope as chromosomes. During interphase (between divisions), chromatin is more extended, a form used for expression genetic information.

The DNA of chromatin is wrapped around a complex of histones making what can appear in the electron microscope as "beads on a string" or nucleosomes. Changes in folding between chromatin and the mitotic chromosomes is controlled by the packing of the nucleosome complexes.

DNA or deoxyribonucleic acid is a large molecule structured from chains of repeating units of the sugar deoxyribose and phosphate linked to four different bases abbreviated A, T, G, and C. We will later show how the simple structure of DNA contains the information for specifying the proteins that allow life. The process of mitosis is designed to insure that exact copies of the DNA in chromosomes are passed on to daughter cells.


ref: biology.arizona.edu

[Anonymous]

The Cell Cycle

Stages of the cell cycle


http://www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/graphics/cellcycle.gif

The cell cycle is an ordered set of events, culminating in cell growth and division into two daughter cells. Non-dividing cells not considered to be in the cell cycle. The stages, pictured above, are G1-S-G2-M. The G1 stage stands for "GAP 1". The S stage stands for "Synthesis". This is the stage when DNA replication occurs. The G2 stage stands for "GAP 2". The M stage stands for "mitosis", and is when nuclear (chromosomes separate) and cytoplasmic (cytokinesis) division occur. Mitosis is further divided into 4 phases.


Regulation of the cell cycle

How cell division (and thus tissue growth) is controlled is very complex. The following terms are some of the features that are important in regulation, and places where errors can lead to cancer. Cancer is a disease where regulation of the cell cycle goes awry and normal cell growth and behavior is lost.

Cdk (cyclin dependent kinase, adds phosphate to a protein), along with cyclins, are major control switches for the cell cycle, causing the cell to move from G1 to S or G2 to M.

MPF (Maturation Promoting Factor) includes the CdK and cyclins that triggers progression through the cell cycle.

p53 is a protein that functions to block the cell cycle if the DNA is damaged. If the damage is severe this protein can cause apoptosis (cell death).

1. p53 levels are increased in damaged cells. This allows time to repair DNA by blocking the cell cycle.

2. A p53 mutation is the most frequent mutation leading to cancer. An extreme case of this is Li Fraumeni syndrome, where a genetic a defect in
p53 leads to a high frequency of cancer in affected individuals.
p27 is a protein that binds to cyclin and CdK blocking entry into S phase. Recent research (Nat. Med.3, 152 (97)) suggests that breast cancer prognosis is determined by p27 levels. Reduced levels of p27 predict a poor outcome for breast cancer patients.


ref: biology.arizona.edu

[adam]

Amazing Step 1. God Bless ya!