DNA

Question 1

What is transformation?

Answer 1

A change in genotype and phenotype due to assimilation of external DNA by a cell

Question 2

What did experiments of M end el led to? (1860s)

Answer 2

The idea of ‘units of inheritance’ - later termed genes

Question 3

Miescher (1860s) isolated?

Answer 3

An unusual acidic, phosphorus-containing substance “nuclein” (DNA) from pus cells from discarded surgical bandages

Question 4

What did Morgan study? (1900s)

Answer 4

Drosphila. Genes were located on chromosomes in the nucleus. He examined characteristics such as eye colour and wing size.

Question 5

What were chromosomes known to contain?

Answer 5

DNA and proteins. Many suspected proteins to be “inheritance factor”

Question 6

What experiments did Griffith (1928) carry out?

Answer 6

A experiments on strains of streptococcus is pneumonia, a bacterium that causes pneumonia in mice and other mammals.

Question 7

What was the first indication that DNA was the inheritance factor?

Answer 7

When Avery used deoxyribonuclease to destroy DNA that blocked transformation

Question 8

What did Erwin Chargaff discover about the composition of DNA?

Answer 8

It different between species. Within a species, the DNA from all cells had the same composition.

Question 9

In 1947, what was DNA known to be?

Answer 9

A polymer of nucleotides (base-deoxyribose sugar-phosphate)

Question 10

What did X-Ray diffraction experiments discover? (Wilkins and Franklin, early 1950s)

Answer 10

DNA was helical in shape. Allowed Watson to deduce width of helix and spacing of nitrogenous bases along it.

Question 11

Structure of DNA?

Answer 11

Sugar-phosphate backbone
Anti-parallel strands
10 base pairs per turn of double helix
Bases on the inside, phosphate on outside
Space filling models show a major and minor groove in the double helix

Question 12

Where/how does DNA replication start?

Answer 12

At specific origins of replication. Proteins recognise the DNA sequence and bind to it, opening up the double helix. In the replication bubble, there are Y-shaped replication forms where new strands are being elongated.

Question 13

What carries out elongation?

Answer 13

Enzymes known as DNA polymerases. They use triphosphates as the sources of nucleotide units to add to growing chain.

Question 14

What is spit out of the chain?

Answer 14

A two-phosphate unit as the chain is extended by each nucleotide.