C HAPTER 11: DNA AND G ENES 11-1 – DNA: The Molecule of Heredity

W HAT IS DNA? DNA ultimately determines an organism’s trait. Achieves control by producing proteins Example: Skin, muscle, bone, hair, enzymes, etc. Enzymes (protein) control the chemical reactions needed for life. DNA contains the information – the instructions for manufacturing all proteins.

T HE STRUCTURE OF DNA DNA = Deoxyribonucleic Acid VERY long molecule Polymer made of repeating subunits/nucleotides. Nucleotides have 3 parts: Sugar – Deoxyribose Phosphate Group Nitrogen Base 4 Types of Nitrogen Bases: Adenine (A) Cytosine (C ) Guanine (G) Thymine (T) DNA Backbone – Phosphate and Sugar Nitrogen bases stick out of the backbone like teeth on a zipper.

DNA S TRUCTURE C ONTINUED Chargoff’s Rule : The amount of Adenine (A) is always found in equal amounts to Thymine (T). The amount of Cytosine (C ) is always found in equal amounts to Guanine (G). Forming Complementary Base Pairs – Watson and Crick proposed that DNA is made of 2 chains of nucleotides joined together by Nitrogen bases that are held together by a hydrogen bond (weak bond). DNA’s shape is a double helix

W HAT ABOUT R OSLIND F RANKLIN ?

T HE I MPORTANCE OF N UCLEOTIDE S EQUENCES All organisms have DNA made of the same 4 Nitrogen bases. How can organisms be so different from each other if their genetic material is made of the same 4 nucleotides? Different sequences of nucleotides ATTGAC carries different information from a sequence that reads TCCAAA. The closer the relationship between 2 organisms the greater the similarity in their order of DNA nucleotides. Used to determine whether 2 people are related or if a blood sample matches the DNA of a suspected criminal.

DNA R EPLICATION Each cell has a copy of DNA. DNA is in the chromosomes and is copied during DNA Replication. Each strand of DNA serves as a pattern to make a new DNA molecule. Step by Step: An enzyme breaks the H bonds between N bases that are holding them together. (Unzipping the DNA) As the DNA unzips nucleotides that are floating free in the surrounding medium (cytoplasm) bond to the open single strand of DNA by base pairing. Another enzyme bonds to the newly made strand and “proof- reads” the nucleotides to make sure no mistakes were made. The process continues until the entire molecule has been unzipped and replicated. The new strand is formed and is the complement of the original “parent” DNA strand.

L ET ’ S P RACTICE DNA R EPLICATION ATT GAC CAT TAC AAC CGT GTA GGG AGC TAA CTG GTA ATG TTG GCA CAT CCC TCG TTA CGG ACC TCG ACG TAA CTC GTT AAA AAT GCC TGG AGC TGC ATT GAG CAA TTT