Chapter 12 DNA

Ch. 16 - DNA DNA Model Rosalind Franklin was able to produce a picture of DNA using a procedure called X-ray crystallography

Ch. 16 - DNA DNA Model (cont.) From this image, James Watson and Francis Crick were able to generate a model of DNA In their model: 1) DNA was a helix 2) DNA was made of two strands that went in opposite directions 3) the two strands were held together by chemical bonding between nitrogenous bases The later determined that adenine (A) always bound to thymine (T) and cytosine (C) always bound to guanine (G)

DNA and Chromosomes Eukaryotic Chromosome Structure Chromosome Nucleosome DNA double helix Coils Supercoils Eukaryotic chromosomes contain DNA wrapped around proteins called histones. The strands of nucleosomes are tightly coiled and supercoiled to form chromosomes. Histones

DNA Located on chromosomes in the nucleus. Chromosomes have DNA and protein tightly packed together called chromatin. Chromatin consists of DNA tightly coiled around proteins called histones. DNA and histones together form nucleosomes.

Ch. 16 - DNA DNA holds the genetic material of living organisms Sugar–phosphate backbone Nitrogenous bases DNA holds the genetic material of living organisms DNA is a polymer made of several nucleotides Each nucleotide consists of 1) Sugar 2) Phosphate group 3) Nitrogenous base Thymine (T) Adenine (A) Cytosine (C) DNA nucleotide Guanine (G)

DNA 4 types of bases Adenine (A) Guanine (G) Thymine (T) Cytosine (C)

5 end Hydrogen bond 3 end 1 nm 3.4 nm 3 end 0.34 nm 5 end Key features of DNA structure Partial chemical structure Space-filling model

Ch. 16 - DNA DNA Replication Watson and Crick suggested that the double helix structure of DNA provides a copying mechanism for DNA They suggested that since each strand of the helix is complementary, they could be used as a template for new DNA Therefore, when new DNA is made, each new strand of DNA consists of ½ “old” DNA and ½ “new” DNA