DNA Structure and Function

DNA Structure and Function KEY CONCEPTS VOCABULARY Who helped discover DNA? What does DNA do for us? What is the structure of DNA? What is DNA made of? DNA Adenine Guanine Cytosine Thymine Purines Pyrimidines Nucleotide

DNA DNA stands for deoxyribonucleic acid Large molecule that contains all genetic information Functions of DNA: Directs the activities of cells Contains the instructions cells use to make proteins What kinds of things do living organisms use proteins for?

History Rosalind Franklin took the first x-ray pictures of DNA molecules The x-ray pictures helped scientists to determine the shape of DNA. What is the shape of a DNA molecule?

History James Watson and Francis Crick built the first DNA model They are given credit for first determining the double helix shape

Structure A strand of DNA is made of monomers called nucleotides Each nucleotide has three parts: Sugar (deoxyribose) Phosphate Nitrogen base The nitrogen base always binds to the sugar of a nucleotide

Structure There are four different DNA nitrogen bases: Adenine Guanine Cytosine Thymine Adenine and guanine are single-ringed purines Cytosine and thymine are double-ringed pyrimidines

Structure Label the following parts of the DNA nucleotides below: adenine, thymine, guanine, cytosine, purines, pyrimidines, phosphate, and sugar

Structure Nucleotides bond together to form a double stranded DNA molecule DNA’s structure looks like a twisted ladder This structure is called the double helix The deoxyribose and phosphate form the “sidepieces,” of the ladder. Nitrogen bases bond together to form the “rungs,” of the ladder.

Structure

Structure Label the following parts of the DNA molecule below: nucleotide, hydrogen bonds, sugar-phosphate backbone Nucleotide Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G)

Chargaff’s Base Pairing Rules Adenine always bonds to thymine Cytosine always bonds to guanine The nitrogen bases are bonded with weak hydrogen bonds Why do only certain nitrogen bases bind to each other?

Chargaff’s Base Pairing Rules Complete the other half of the DNA molecule below using Chargaff’s base pairing rules: A T G A A C G T C A C C G T A C A T C G T

DNA and Chromosomes In eukaryotic cells, DNA molecules are tightly wound into chromosomes Where are chromosomes located in eukaryotic cells? Chromosomes contain all the DNA needed to carry out cellular functions

DNA and Chromosomes Label the following parts of the diagram below: double helix, chromosome, supercoils, coils, histones, proteins Histones