Genetics

Cell Divsion

DNA- A genetic code, deoxyribonucleic acid; a nucleic acid that is the main constituent of the chromosomes of all organisms (except some viruses). The DNA molecule consists of two polynucleotide chains in the form of a double helix, containing phosphate and the sugar deoxyribose and linked by hydrogen bonds between the complementary bases adenine and thymine or cytosine and guanine.

Chromosomes- Several threadlike bodies, consisting of chromatin, that carry the genes in a linear order: the human species has 23 pairs, designated 1 to 22 in order of decreasing size and X and Y for the female and male sex chromosomes respectively.

Genes- The basic physical unit of heredity; a linear sequence of nucleotides along a segment of DNA that provides the coded instructions for synthesis of RNA, which, when translated into protein, leads to the expression of hereditary character.

How these three terms are related: DNA is the molecule which codes for polypeptides when read in triplets. When DNA is organized into units in which the code specifies a specific polypeptide, with a start and a stop, this is a gene. Several genes are packed together in a single unit called a chromosome.

Meiosis- A type of cell division in which a nucleus divides into four daughter nuclei, each containing half the chromosome number of the parent nucleus: occurs in all sexually reproducing organisms in which haploid gametes or spores are produced

Mitosis- the usual method of cell division, characterized typically by the resolving of the chromatin of the nucleus into a threadlike form, which condenses into chromosomes, each of which separates longitudinally into two parts, one part of each chromosome being retained in each of two new cells resulting from the original cell.

What happens when Mitosis and Meiosis goes wrong?

Mitosis: involves the replication of every other type of cell beyond a sex cells. One example of things going awry is when the checkpoint of mitosis are passed prematurely or are shut off by various pro cancer mechanisms the cell will continually divide. Uncontrolled cellular growth characterizes cancer. Another example could be if mitosis does not get out of control with growth rate the cell can divide improperly and the cell can have an unusually number of chromosomes. Then, if this cell replicates, more and more cells from it will have this odd number of chromosomes and a number of problems can ensue.

Meiosis: involves the replication of sex cells. If this process goes awry the sex cell can have an odd number of chromosomes and this can lead to numerous genetic disorders. For examples, three number 21 chromosomes yields Down Syndrome and an extra X chromosome for a male can make him sterile.

What happens when the DNA sequence is mutated?

The nucleotide sequence is altered, thus changing the sequence of the mRNA codons. This causes the wrong amino acid to be produced resulting in a non-functional polypeptide. Occasionally, there is no effect or the protein is actually improved.

Sickle-cell disease and Cancer are both results of mutations.

Cell Division