A1.2 nucleic acids

What are the 4 nitrogenous bases

Adenine, thymine, cytosine, guanine

Purines

Adenine, guanine

Pyrimidines

Cytosine, uracil and thymine

How many bonds do cytosine and guanine form

3

What are the differences between RNA and DNA

DNA - deoxyribose, double stranded, ATCG, one type

RNA - ribose, single stranded, AUCG, 3 types

Helicase

Unwinds DNA, breaks H bonds

DNA polymerase

Joins free nucleotides

Semi-conservative theory

DNA replication - one strand of original DNA is kept

What direction is the new strand formed in DNA replication

5’ to 3’

What direction is DNA copied

3’ to 5’

Structure of a nucleosome

8 histone proteins that the DNA is wrapped around and a 9th protein holding the structure together

Explain the Hershey chase experiment method

Labelled DNA with radioactive phosphorus-32 and protein coats with radioactive sulfur-35

Allowed bacteriophages to infect E. coli bacteria.

Used a blender to detach viral protein coats from bacteria.

Centrifuged the mixture to separate bacteria (pellet) from viral coats (supernatant).

Hershey chase conclusion

Phosphorous was mainly found in the pellet (made of bacteria) and sulfur in the supernatant, showing that DNA is what enters the bacteria and carries the genetic information

What did Chargaff’s research show

% of adenine = % of Thymine, % of guanine = % of cytosine, all four bases add to 100%, applies to double stranded DNA