DNA Overview Deoxyribonucleic Acid, or DNA, must be able to do 2 things: 1) give instructions for building and maintaining cells. 2) be copied each time a cell divides. DNA is made of subunits called nucleotides which have three parts: a sugar, a phosphate, and a base. There are 4 types of bases: Adenine (A),Thymine (T), Cytosine (C), and Guanine (G). Adenine pairs with Thymine (A & T) Cytosine pairs with Guanine (C & G) DNA s shape is a double helix. This means it looks like a long twisted ladder. The sides of the ladder are made from the sugar and the phosphate. The rungs of the ladder are made from the bases. The DNA is supercoiled into rod like structures called chromosomes. If you took all the DNA in one human cell, it would equal about 1.86 miles! These chromosomes (made of DNA) are copied when a cell goes through Meiosis or Mitosis.
Three scientists are given credit for having discovered the structure of DNA: 1) Rosalind Franklin, who found the spiral shape by x ray pictures. 2) James Watson and 3) Francis Crick, who were the first to built a model of what DNA looks like. Rosalind Franklin Francis Crick James Watson Each set of three base pairs is called a codon and codes for an amino acid. Amino acids are put together to form proteins. The proteins made by nucleotides are important because they act as chemical triggers and messengers for many of the things that happen in cells, and give the cell information about the organism's traits. (T) (T) Phe = Phenylalanine Leu = Leucine Ile = Isoleucine Met = Methionine Val = Valine Ser = Serine Pro = Proline Thr = Threonine Ala = Alanine Tyr = Tyrosine His = Histidine Gln = Glutamine Asn = Asparagine Lys = Lysine Asp = Aspartic acid Glu = Glutamic acid Cys = Cysteine Trp = Tryptophan Arg = Arginine Gly = Glycine
A gene is a string of nucleotides. Each gene makes proteins that gives the cell information about how to make a specific trait for that individual. If there is a change in a nucleotide base pair, it causes a change in the gene, called a mutation. The mutation in the base pair changes the gene code. The changed gene makes a different amino acid, which changes the protein, which causes a change in the trait. The change can be a deletion, a substitution, or an insertion, which can lead to different types of mutations. 1) A deletion is when a base pair is left out. Leaving out a base pair changes every codon after the deletion. 2) An insertion is when a base pair is added. Adding a base pair changes every codon after the insertion. How? Original DNA sequence: AGC TAT CCC GCA AAT GGG Deletion: Insertion:
3) A substitution is a mutation where the wrong base pair is used. * A missense mutation is where one nucleotide in a codon is changed. This can cause a completely different amino acid to be added to the protein. * A nonsense mutation changes the codon sequence for one amino to a STOP codon (TAA, TGA, TAG) that stops the cell from adding more amino acids to the protein. This shortens the protein. * A silent mutation changes the codon sequence for one amino acid to another codon for the same amino acid. Because it doesn't change how the protein turns out, it's called a silent mutation. Mighty Mutation Maker Any change in the gene is a mutation, but not all mutations are bad. Simple differences, such as in hair color or eye color, are from mutations. Other mutations can even be beneficial. If a mutation caused a plant to be more resistant to freezing, it could survive at colder temperatures. Other mutations, however, can cause problems. Mutations can cause non helpful changes in a trait or even genetic diseases.
Since genes are made of DNA, and are found on chromosomes, when a cell divides through Meiosis or Mitosis, DNA is copied and passed on from parent cells to daughter cells. This means the genes that a parent has can be passed on to their children, changes and all! DNA Replicating Itself old new new old