Watson and Crick

The thing he is pointing to in this picture is his model of the Helix.

In the 1950s James Watson and Francis Crick, believed that DNA is a helix. They made models from scraps of metal connected by specific angled “bonds” of wire

Chargaff Rule

Erwin Chargaff found two influential things about DNA: 1. (aka Chargaff's first rule)- the amounts of Thymine and Adenine are identical, as are the amounts of Cytosine and Guanine. A=T, G=C

Chargaff's 2nd rule is the following: 2. DNA of different species differs in its proportions of adenine and guanine.

How do the base pairs bind?

Hydrogen bonds between the internally positioned bases hold the two strands together. The only two kinds of base pairings are the ones from Chargaff's first rule.


Chromosome: structure that consists of DNA and associated proteins. Carries a piece or all of a cells genetic info. Each chromosome consists of one DNA molecule, that divides itself during DNA Replication.


Karyotype: an image of an individual’s diploid(Both Parents) set of chromosomes.

How does DNA replicate?

DNA REPLICATION: The process by which a cellcopies its DNA

The Steps:

1. enzymes break the hydrogen bonds that hold the double helix together, the 2 remaining strands unwind and separate. Another enzyme constructs primers: short, single strands of nucleotides.

2. nucleic acid hybridization occurs: base paring between two strands of DNA

3. DNA polymerases attach to the hybridized primers and begin DNA synthesis

4. The enzyme DNA ligase seals any gaps, so the new DNA strands are continuous

5. Both of the two strands of the parent molecule are copied at the same time, As each new DNA strand lengthens, it winds up with its template strand into a double helix

What damages DNA?

Radiation from X-rays, most UV light, and Gamma Rays may cause damage to DNA.

Created By
Jack Santini


Created with images by Can H. - "Karyotype"

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