Nucleic Acids Stores information Two types: DNA (deoxyribonucleic acid) RNA (ribonucleic acid)

Nitrogenous base (adenine) Phosphate group Sugar Nucleotides are the building blocks of Nucleic acids. Have 3 parts: * 5 carbon sugar   * phosphate group * nitrogenous base group The sugar is either: deoxyribose (DNA) ribose (RNA)

Dehydration synthesis Polynucleotides are formed from its monomers bonding together through dehydration synthesis. The phosphate group of one nucleotide bonds to the sugar of the next. The result is a repeating sugar phosphate backbone. Covalent bond   Hydrogen bond

4 base pairs DNA nitrogenous bases are adenine (A) thymine (T) cytosine (C) guanine (G) RNA has A, C, and G as well, but has U (Uracil) instead of T DNA molecules have thousands or even millions of base pairs.

Double helix Two DNA strands wrap around each other to form a double helix The two strands are connected by a hydrogen bond between the base pairs. A pairs with T C pairs with G RNA is usually a single strand

Important DNA terms These terms are often used interchangeably. Make sure you understand the differences between them. DNA – organic compound that serves as the hereditary material for all living things (the rest of these terms simply refer to different forms / amounts of DNA) Genes – a segment of DNA that codes for 1 polypeptide Chromosomes - DNA in a dividing cell (DNA is wrapped around histone proteins) Chromatin – DNA in a non-dividing cell (DNA is not wrapped around histone proteins)

Genes (enough DNA to code for one polypeptide) codes for the sequence in which the amino acids are arranged (primary structure of proteins). Genes (DNA) DO NOT code directly. Genes use an intermediary (RNA). The DNA is transcribed into RNA, which is then translated into the amino acid sequence. Flow of information: DNA  RNA  Proteins

DNA usage DNA is read in groups of 3 bases. As stated earlier, DNA does not directly code for proteins themselves. DNA uses RNA as an intermediate. DNA is used as a template to make messenger RNA This mRNA is read by ribosomes in groups of 3 bases called codons. Each codon codes for 1 amino acid (remember than amino acids are the monomers for proteins).

Differences in DNA and mRNA Both DNA and RNA are nucleic acids; therefore, they have similarities (both are made of nucleotides [sugar, phosphate, and base], both are used in the passage of hereditary information, etc. Even so, there are 3 major differences in DNA and mRNA (there are other types of RNA that will be discussed later. DNA mRNA Pyrimidine bases C, T C, U Sugar Deoxyribose Ribose Size Double stranded Single strand

Mutations – any change in DNA sequence Any change in DNA sequence is considered a mutation because changing DNA sequence will change amino acid sequence (and thus the physical appearance of the organism) Mutagenesis – production of mutations Mutagen – chemical or physical agent causing mutation 2 major kinds: Base substitution – Sub 1 nucleotide for another Not as bad because only 1 codon is changed (which may mean 1 amino acid change or possibly no amino acid change at all) We will study how amino acids are coded for later Insertion or deletion – insert or delete a base Alters the entire reading frame (triplet grouping) This type of mutation is very bad because it changes the entire DNA sequence and thus the entire polypeptide that is being coded for ** Note: Although mutations are almost always harmful, they are also very important. This is because mutations can on rare occasions be beneficial. Mutations provide the diversity of life that evolution can then act upon.