DNA Notes

GENOME The nucleus of a human cell contains to genes in the form of DNA called the GENOME.

CHROMOSOMES CHROMOSOMES are coiled DNA and proteins. Humans have 23 pairs of chromosomes in the NUCLEUS of any one of your cells

GENE Segment of DNA that codes for an organism’s trait.

DNA The genetic material found in the NUCLEUS of a cell. Carries the “code” to make proteins (expressed as traits). The unit of HEREDITY.

Frederick Griffith’s Experiment – Griffith wanted to find out how bacteria causes diseases. Do they release a toxin? – Is there some unit of HEREDITY in organisms?

Frederick Griffith’s Experiment – Mice with dead disease causing bacteria survived, but when that dead bacteria was combined with live, non-disease causing bacteria, the mouse died AND live disease causing bacteria was found in that mouse’s blood. – Is there some unit of HEREDITY in organisms?

Hershey & Chase’s Experiment – Bacteriophages cause diseases by passing on their genetic material – They are only made up of protein and DNA. – They used radioactive isotopes to label them and find out what the bacteriophage injects into the bacteria. – DNA is the unit of heredity!

Franklin & Wilkins Experiment – Took the first X-ray photograph of DNA

Watson and Crick – Used Franklin and Wilkin’s x-ray photograph and Chargaff’s data to determine the DOUBLE HELIX shape

Structure of DNA DNA is in the shape of a double helix, it looks like a twisted ladder. DNA is made up of 4 nucleotides that bond together, with hydrogen bonds. This forms the "rungs" of the ladder. Nucleotides are attached to a phosphate- sugar backbone.

NUCLEOTIDES 3 Parts: – Nitrogen bases Adenine Thymine Guanine Cytosine – Phosphate group – Sugar called deoxyribose

Chargaff’s Experiment Base Pairing Rule Nucleotides only pair with a specific nucleotide: Adenine - Thymine Cytosine – Guanine Adenine and Thymine are bonded by 2 hydrogen bonds. Cytosine and Guanine are bonded by 3 hydrogen bonds.

Base Pairing Rule Purines and Pyrimidines Pyrimidines have a single ring structure. Purines have a double ring structure.

What is a DNA Sequence? The particular order of the nitrogen bases is called the DNA SEQUENCE. The first letter of the base is used: Ex. A T G C C G A T C

DNA Replication

How does DNA Replication begin? Begins at Origins of Replication Two strands open forming Replication Forks (Y-shaped region) New strands grow at the forks

Enzymes in DNA replication HELICASE unwinds parental double helix DNA POLYMERASE binds nucleotides to form new strands LIGASE joins Okazaki fragments and seals other breaks in sugar-phosphate backbone

Replication Step 1: HELICASE unzips DNA down the middle by breaking Hydrogen bonds.

Step 2: DNA POLYMERASE moves along the 2 strands and base pairs nucleotides to each original parent strand.

Step 3: Replication moves in only in the 5’ to 3’ direction. So, small DNA segments called OKAZAKI FRAGMENTS are made on the other strand.

Step 4: DNA LIGASE seals up all of the gaps in the DNA molecule, like the Okazaki fragments.

Result: 2 identical DNA molecules are formed from the original.

Semi-conservative Model Idea presented by Watson & Crick The two strands of the parental molecule separate, and each acts as a template for a new complementary strand New DNA consists of 1 PARENTAL (original) and 1 NEW strand of DNA

Mutations DNA MUTATIONS can occur when a base (A, T, C or G) is accidentally changed. DNA Polymerase proofreads new DNA molecules to catch most of these mutations and fix them. OTHER CAUSESEFFECTS Environmental Agents: Genetic disorders UV raysCancer Chemicals X-rays