Lecture 17: Chemistry Of DNA

Question 1

List the 5 pieces of evidence for DNA as genetic material

Answer 1

1. Bacterial transformation with purified DNA
2. Hershey-chase experiment with viruses
3. DNA of somatic cells is constant in amount for a given species. Germ cells (sperm and ova) contain only half amount
4. Various agents, which cause chemical alterations to DNA , are known to cause mutations
5. Recombinant DNA technology: human insulin gene, when inserted into bacteria, induces bacterium to synthesis human insulin (a proteins hormones)

Question 2

Chemistry and structure of DNA

Answer 2

DNA is a long polymer made up of 4 different types of nucleotides
-a nucleotide is the monomer is unit of DNA
-each nucleotide consists of:
Phosphate-sugar- nitrogen containing base

Question 3

The sugar of DNA

Answer 3

-nucleic acids consist if 5-carbon sugars
-general name is pentose sugar
-the pentose sugar in DNA is DEOXYRIBOSE (because there is an oxygen missing)
The bases attach to the deoxyribose by a covalent bond between the 1’ carbon of the sugar and the 9-position nitrogen of the purines or the 1-position of the pyrimidines

Question 4

Nitrogen-containing bases

What are the two types? Name all 4

Answer 4

There are 4 different N-bases of two types: 
1. Purines: 2 rings 
Adenine and guanine
2. Pyrimidines: 1 ring
Cytosine, thymine

Question 5

Watson and crick used models, describe them

1. Phosphodiester bonds
2. Hydrogen bonding
3. DNA strands are anti parallel
4. Complementary strands
5. The two strands form a double helix

Answer 5

1. Phosphodiester bonds: nucleotides are linked together by phosphodiester bonds, which link the sugar if one nucleotide to the sugar of another. Are the backbone of the molecule
2. Hydrogen bonding: DNA contains 2 polynucleotide strands, which are held together by hydrogen bonds
   - bonding only between A-T and G-C base pairs, which tells us something about the structure…
3. DNA strands are anti parallel: DNA is in a 5’ to 3’ direction
4. Complementary strands: one strand must be complementary to the other. For example refer to page 8
5. The two strands form a double helix

Question 6

Is a gene a section of one or both strands of DNA?

Answer 6

Only one of the two strands called the template strand, the other is called non-template strand.
The genetic information therefore lies in the sequence of bases in the template strand of the gene

Question 7

What is chargaffs rules?

Answer 7

Amount of adenine= amount of thymine
Amount of guanine = amount of cytosine
(A + T)/ (G + C) varies between species