Biology

DNA DNA stands for DeoxyriboNucleic Acid DNA has the shape of a double helix (like a twisted ladder) The DNA molecule is made up of repeating components called NUCLEOTIDES Nucleotides consist of three components: A Sugar A Phosphate One of 4 Nitrogenous Bases: Adenine (A) Thymine (T) Guanine (G) Cytosine (C) NOTE: You only need to know the letters, not the full names Adenine can only pair with Thymine, while Guanine can only pair with Cytosine Nitrogenous bases pair through Hydrogen bonds DNA contains all the instructions to create an organism Key term: POLYPEPTIDE, also known as a protein DNA is read in groups of three, called a CODON or a triplet Mutations A MUTATION is the alteration of the nucleotide sequence in the genome of an organism A MUTAGEN is a physical or chemical agent that changes the genetic material of an organism, increasing the frequency of mutations in an organism Most mutations are harmless (NEUTRAL) Mutations that improve survivability are called BENEFICIAL mutations Mutations that decrease survivability are called DETRIMENTAL mutations Examples of mutations Beneficial:

Fossils A fossil is evidence of past life. Fossils can be part of an organism, such as its bones, teeth, feathers, scales, branches or leaves. Fossils can also be traces, such as footprints, burrows and other evidence that an organism existed in an area.

Mitosis Mitosis is the process by which one parent cell splits into two identical daughter cells. Mitosis is the most common method of reproduction for single-celled organisms. There are 5 main stages of mitosis: Prophase: number of chromosomes in the cell double up Metaphase: chromosomes wind up and align along the equator of the cells Anaphase: Chromatids (Not Chromosomes, this is explained later) are drawn towards the ends of the cell by spindle fibers Telophase: Cell nuclei forms, chromosomes form and unwind Cytokinesis: Cell splits into two, completing the process of mitosis In the human body, all cells other than sex cells (sperm and ova) are generated through mitosis.