DNA Structure and Replication

Review What organelle is the “control center” of the cell? The Nucleus What structures are found in the nucleus? Chromosomes What are located on chromosomes? Genes

Review What are chromosomes made of? DNA & proteins How do genes and chromosomes control the activity of a cell? By making proteins that regulate cellular functions or become part of the cell.

Frederick Griffith British scientist, 1928 Experiments with pneumonia bacteria & mice (page 287-288) He discovered “Transformation” Was this a gene?

Hershey-Chase 1952 by Alfred Hershey and Martha Chase Used radioactive Bacteriophages (viruses) to infect bacteria (page 289-290) Found the infecting agent to be DNA

Genes have to carry information from one generation to the next. DNA has 3 jobs to do… Genes have to carry information from one generation to the next. They have to use the information to determine characteristics of an organism. They have to be easily copied. Chargaff Rules Erwin Chargaff, American biochemist Discovered the same amount of Cytosine and Guanine in any DNA sample & the same amount of Adenine and Thymine in any DNA sample A = T G = C

Rosalind Franklin & X-ray diffraction 1950’s, British scientist: Rosalind Franklin took pictures of DNA using X-rays. Watson and Crick Francis Crick & James Watson were trying to discover the structure of DNA. Making a 3-D model They used Franklin’s photograph to determine that it was a double helix (2 strands of DNA wound around each other)

Watson & Crick Francis Crick & James Watson were trying to discover the structure of DNA. Making a 3-D model They used Franklin’s photograph to determine that it was a double helix (2 strands of DNA wound around each other)

DNA Structure A – T G - C DNA is made of units called “nucleotides” Nucleotide = Sugar (deoxyribose) + Phosphate group + Nitrogenous base A double helix looks like a twisted ladder. Four kinds of nitrogenous bases: Adenine Purines (2 rings) Guanine Cytosine Pyrimidines (1 ring) Thymine A – T G - C

The two parent stands separate. A new strand is made complimentary to each parent strand. At the end we have 4 DNA strands. Base pairing to original parent strands keeps the DNA the same.

DNA Storage DNA wraps around protein and coils into compact blobs! This allows a lot of DNA to fit in small area. During Mitosis the DNA coils into the chromosome shape that we are familiar with. Outside of mitosis the DNA is coiled but not as condensed as in Mitosis