THE DNA STRAND

1. THE DNA STRAND Deoxyribonucleic Acid (DNA) is a nucleic acid that contains the genetic info used in the development and functions of all known living things. Genes are the DNA segments that carry this genetic info. Other DNA sequences have structural purposes or are involved in regulating the use of this genetic info. Along with RNA and proteins, DNA is one of the three major macromolecules that are essential for all known forms of life. DNA consists of two long polymers of simple units called nucleotides, with backbones made of sugars and phosphate groups joined by ester bonds. These two strands run in opposite directions to each other and are therefore anti-parallel. Four nucleotide bases are attached to each sugar. The sequence of the nucleotide bases encodes this information.

2. WHAT IS THE GENETIC CODE? • The Genetic Code is the set of rules by which info that’s encoded in genetic material is translated into proteins by living cells. • The code defines how sequences of codons ( the 3 nucleotides) specify which amino acids will be added next during protein synthesis. In some exceptions a three-nucleotide codon in a nucleic acid sequence specifies a single amino acid. • Because the vast majority of genes are encoded with the same exact code, this particular code is often referred to as the canonical or standard genetic code (simply the genetic code). In fact, some variant codes have evolved over time. • Example: Protein synthesis in human mitochondria relies on a genetic code that differs from the standard genetic code.

3. HOW DO CELLS MAKE PROTEINS? • Inside every living cell, the DNA directs all the main functions, such as growth, division, movement, respiration, and even death! It does this by providing the instructions cells use to build proteins. • The chemical language for this code is stunningly simple. It consists of just four letters, which correspond to the four functional molecules (called nucleotides) that, in addition to sugar and phosphate molecules, form DNA. These nucleotides are adenine (A), thymine (T), cytosine (C), and guanine (G). Various combinations of these four molecules make up genes, the discrete sequences of DNA that provide instructions for one or more proteins. Human cells are thought to contain between 20,000 and 25,000 genes that provide the code to build many more different types of proteins.

4. WHAT ARE MUTATIONS ? • A gene mutation is a permanent change in the DNA sequence. • Gene mutations can be inherited from your parents or they can be acquired during an individual’s lifetime. • Mutations that are passed from parent to offspring are known as hereditary mutations. • Acquired mutations are caused by environmental factors or DNA replication errors.

5. EFFECTS OF MUTATIONS • Most genetic mutations have no impact on an organism’s health or development. • Enzymes can repair genetic mutations before gene expression creates a particular protein. • Some mutations are actually beneficial to an organism. If the mutation helps the organism better adapt to its environment, then it will have an increased chance to survive and pass the new gene on to the next generation.

6. DNA REPLICATION • The structure of DNA resembles that of a twisted ladder. • The DNA molecule “unzips” by separating the base pairs {A-T} and {C-G}. • When both halves of the molecule are completely separated, free nucleotide bases present in the cell’s nucleus chemically bind to their complimentary base. • In this way, the DNA molecule creates an exact duplicate of itself. • This process takes place during cell division.

7. WORKS CITED • Life Science • http://ghr.nlm.hih.gov • www.pbs.org/wnet/dna • http://en.wikipedia.org/wiki/DNA