Introduction to Molecular Biology 1 Lecture

Question 1

Give 2 examples of nucleic acids

Answer 1

RNA and DNA

Question 2

What are the 2 types of nitrogenous bases, and list each

Answer 2

Purines: Adenine and Guanine
Pyrimidines: Cytosine and Thymine

Question 3

List the complementary base pairs and their corresponding number of bonds

Answer 3

Adenine to Thymine, forms 2 hydrogen bonds
Guanine to Cytosine, forms 3 hydrogen bonds

Question 4

What is epigenetics?

Answer 4

The inheritance of changes in the base sequence of DNA

Question 5

Explain the polarity of DNA

Answer 5

Both DNA strands are antiparallel to one another i.e. one side runs 5’ to 3’ and the other 3’ to 5’

Question 6

What happens to chromosomes during cell division?

Answer 6

They condense

Question 7

Describe the organisation of DNA during interphase

Answer 7

DNA is relaxed rather than tightly condensed. It is made of chromosomes associated with histone proteins, a complex known as chromatin. Euchromatin is the less condense form of DNA that is actively transcribed and heterochromatin is usually transcriptionally inactive

Question 8

Define telomere

Answer 8

A telomere is the end of a chromosome that shortens every cell division, that eventually leads to cellular aging and death

Question 9

What is a nucleosome?

Answer 9

147 base pairs of DNA wrapped around an octamer - made of 8 histone proteins (H2A, H2B, H3, H4). DNA wrapped by 1.7 left handed turns. This allows for compact packaging).

Question 10

Describe the structure of Histones

Answer 10

Histones have a +ve charge as they contain lots of basic amino acids.

The N-terminals are unstructured and flexible, and contain lysine residues which can be acetylated or methylated.

Question 11

What is Histone H1?

Answer 11

A type of Histone that forms the 30nm fibre.
It binds to DNA between nucleosomes to form the complex chromatin.

Question 12

What is euchromatin?

Answer 12

Actively transcribed form of chromatin that is less condense than its counterparts.

Question 13

What is heterochromatin?

Answer 13

More compact and generally transcriptionally inactive.

Question 14

Name 2 types of post-translational modifications

Answer 14

Acetylation - The addition of an acetyl group which causes the histones to “unwind”, allowing transcription factors to bind more readily.

Methylation - The addition of a methyl group to a CpG island, which prevents transcription factors from binding.

Question 15

How many genes code for proteins?

Answer 15

Less than than 5% of genes

Question 16

What is repetitive DNA?

Answer 16

Sequences in the genome that appear in multiple copies. They can be divided into 2 main types.

Question 17

What are Tandem repeats?

Answer 17

Microsatellites are short sequences (1-6 bps) repeated several times.
Minisatellites are larger repeats (10-60bps) often found in specific regions

Question 18

What are interspersed repeats?

Answer 18

Short Interspersed Nuclear Elements (SINEs) are short DNA sequences (100-400bps)

Long Interspersed Nuclear Elements (LINEs) are longer repeats (1000-10,000bps)

Question 19

What is the function of repetitive DNA?

Answer 19

Structurally, they help with chromosomal integrity and stability.

They also provide genetic diversity, which can have practical implications in forensics.