In 1953 Watson and Crick recognize that DNA

In 1953, Watson and Crick recognize that DNA is a double-helix. X-ray crystallography image from Franklin that provides clue to DNA structure

The Components and Structure of DNA • DNA is in the shape of a twisted ladder, called a double helix. – The sides of the DNA are made up of 1. Deoxyribose (sugar) 2. Phosphate group (links the deoxyribose together) – The “rungs” of DNA are made up of bases 1. 2. 3. 4. Adenine Cytosine Guanine Thymine

Nucleotides always “Base Pairs” pair together. Purines Pyrimidines In 1949, Chargaff determined that their were equal parts A and T, and equal parts of G and C Adenine Guanine Thymine Cytosine

Base Pairing

DNA Replication • Helicase “Hacks” the two strands open at the hydrogen bonds. • The DNA molecule separates into two strands • DNA Polymerase “pastes” matching nucleotides on each half of the “unzipped” DNA.

2. DNA Polymerase “reads” the nucleotide base sequence and “pastes” the correct nucleotide to the growing strand. 1. Helicase “Hacks” the DNA strands apart by breaking the hydrogen bonds between the nitrogen bases. Old Strand DNA replication is “Semi. Conservative. ” DNA has one old strand one new strand after replication is complete. New Strands

• Amount of DNA varies per organism – Bacteria have ~600, 000 base pairs their genomes. (A genome is an organism’s complete set of DNA. ) – Humans have ~3, 000, 000 base pairs in our genome. – http: //en. wikipedia. org/wiki/Genome • Each human chromosome contains 50250 million base pairs. This single-celled organism, Amoeba dubia, has a larger genome than you do.

Chromosome Structure • DNA is long. – E. coli bacterium is about 2 μm length, yet it contains about DNA. – A single human cell contains ~1. 8 m of DNA! (There is enough DNA in your body to stretch from here to the moon and 70 times!!) in 1. 6 m of back • Chromosomes are supercoils of DNA – Double-stranded DNA coils around histone proteins, called chromatin – Chromatin forms coils, and then those coils form coils again - supercoils

Genes • Genes are the regions of DNA that are instructions for making proteins (a few make RNA). • Humans have 20, 000 -25, 000 genes. • Only about 2% of our DNA is genes – The noncoding regions function to provide chromosomal structural integrity and to regulate where, when, and in what quantity proteins are made. • Compare genes: http: //en. wikipedia. org/wiki/Gene