DNA
Deoxyribonucleic acid
INTRODUCTION DNA is found in practically all living organisms, and it is now known to carry genetic information from one cell to the next, and from one generation to the next. The units of inheritance, called genes.
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CONTENTS
INTRODUCTION................................2 A CLOSER LOOK AT DNA..................4 THE DOUBLE HELIX...........................6 THE DNA LADDER EXPLAINED.........8 DNA IN SEX CELLS...........................10
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A CLOSER LOOK AT DNA What do a human, a rose, and a bacterium have in common? Each of these things along with every other organism on Earth contains the molecular instructions for life, called DNA. Encoded within this DNA are the directions for traits as diverse as the colour of a person’s eyes, the scent of a rose, and the way in which bacteria infect a lung cell.
Cell membrane
Cytoplasm Nucleus
Nuclear Membrane Vacuole
DNA is a very long molecule that can copy itself so that all the new cells produced by a plant or animal as it grows contain copies of the same set of genetic instructions, a genetic code.
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Plants and animals grow and function beacause of the amazingly complicated instructions in the genetic material inside their cells. Most DNA is found inside a cell’s nucleus. Some DNA DQG D GLÎ?HUHQW VRUW RI QXFOHLF acid called RNA (ribonucleic acid) are found outside the nucleus in the rest of the cell.
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THE DOUBLE HELIX Phosphate (chemical) Deoxyribose (sugar) Base (molecule)
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The double helix is made of billions of chemical units called nucleotides linked together like beads strung out along a string. Each nucleotide is made from three parts - a chemical called phosphate, a sugar called deoxyribose and a molecule called base. The phosphates
and sugars form the two long intertwined strands of the double helix and the bases link these two strands together.
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THE DNA LADDER EXPLAINED DNA can copy itself because of the way it’s two halves lock together like the two sides of a ladder. Each rung of a ladder is made from two molecules called bases. There are four GLÎ?HUHQW EDVHV NQRZQ DV 7K\PLQH Athenine, Guanine and Cysonine (T,A,C and G). T always connects to A, and C always connects G.
T
A
C
G
DNA copies itself to make more DNA IRU PRUH FHOOV E\ ȴUVW VSOLWWLQJ LQWR WZR halves. Then each half grows back it’s missing half, producing two sets of DNA where there was only one before.
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DNA IN SEX CELLS
There are two types of sex cells, the female ovum, (egg) and the male sperm. Both cells contain only half the DNA found in other cells. When an egg is fertilized by a sperm, they join together and their DNA combine. Together they form a new cell with the correct amount of DNA. 10
– Hagen Friend –