Nucleotides & Nucleic Acids

Question 1

What happens during G1 of interphase?

Answer 1

Cellular contents excluding chromosomes are duplicted. mRNA and proteins needed for chromosome duplication are synthesised.

Question 2

What happens during G2 of interphase?

Answer 2

Organelles divide and energy is stored for mitosis.

Question 3

What happens at G0?

Answer 3

Cell cycle arrest: terminally differentiated

Question 4

What is the difference between ribose and deoxyribose?

Answer 4

ribose has a hydroxyl group below the plane of ring on carbon 2, whereas this is just a hydrogen atom on deoxyribose.

Question 5

How many hydrogen bonds are there between

a) A-T or A-U?
b) C-G?

Answer 5

a) 2

b) 3

Question 6

Which nitrogenous bases are purines and which are pyrimidines?
How many rings do each have?

Answer 6

Purines: 2 ring, A, T, U
Pyrimidines: 1 ring, C, G

Question 7

What is a phosphorylated nucleotide and where does it store energy?

Answer 7

e.g. ATP, ADP
have an extra phosphate group
In ATP, energy is stored in the extra phosphate bond

Question 8

What are the two bond types in a polynucleotide?

Answer 8

Phosphodiester on the sugar-phosphate backbone between the phosphate and hydroxyl groups of adjacent nucleotides.
Hydrogen between purine and pyrimidine bases holding the antiparallel strands together.

Question 9

What are the steps involved in a precipitation reaction for purifying DNA?

Answer 9

1- grind up tissue to break up cells
2- add detergent to break down cell membranes
3- add salt to break hydrogen bonds between bases
4- add protease to break down histones associated with DNA
5- add ethanol to precipitate DNA- should see white strands

Question 10

What are primers?

Answer 10

small pieces of RNA that bind to the DNA strand and serve as a starting pint for RNA polymerase to bind to. One on leading strand, many on lagging strand due to antiparallel nature of DNA and the enzyme only synthesizing 5’ to 3’.

Question 11

How many common start and stop codons are there?

Answer 11

1 start codon AUG, 3 stop codons

Question 12

How are Okazaki fragments joined together once synthesised?

Answer 12

By DNA ligase

Question 13

How does DNA helicase unwind and unzip DNA?

Answer 13

By breaking h bonds between bases

Question 14

What happens during prophase of mitosis?

Answer 14

chromosomes condense
nuclear envelope disintegrates
centrioles form

Question 15

Which stage of meiosis includes crossing over? Describe this.

Answer 15

Prophase I

Chiasmata occur between homologous chromosome pairs in bivalents.

Question 16

Name the 5 main processes that cause genetic diversity.

Answer 16

Crossing over during prophase I
Independent assortment (/random segregation) during metaphase I
Independent assortment during metaphase II
Random mating
Random fertilisation of gametes