Introduction to Molecular Biology 1 Lecture Flashcards
28/11/24
Give 2 examples of nucleic acids
RNA and DNA
What are the 2 types of nitrogenous bases, and list each
Purines: Adenine and Guanine
Pyrimidines: Cytosine and Thymine
List the complementary base pairs and their corresponding number of bonds
Adenine to Thymine, forms 2 hydrogen bonds
Guanine to Cytosine, forms 3 hydrogen bonds
What is epigenetics?
The inheritance of changes in the base sequence of DNA
Explain the polarity of DNA
Both DNA strands are antiparallel to one another i.e. one side runs 5’ to 3’ and the other 3’ to 5’
What happens to chromosomes during cell division?
They condense
Describe the organisation of DNA during interphase
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
Define telomere
A telomere is the end of a chromosome that shortens every cell division, that eventually leads to cellular aging and death
What is a nucleosome?
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).
Describe the structure of Histones
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.
What is Histone H1?
A type of Histone that forms the 30nm fibre.
It binds to DNA between nucleosomes to form the complex chromatin.
What is euchromatin?
Actively transcribed form of chromatin that is less condense than its counterparts.
What is heterochromatin?
More compact and generally transcriptionally inactive.
Name 2 types of post-translational modifications
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.
How many genes code for proteins?
Less than than 5% of genes
What is repetitive DNA?
Sequences in the genome that appear in multiple copies. They can be divided into 2 main types.
What are Tandem repeats?
Microsatellites are short sequences (1-6 bps) repeated several times.
Minisatellites are larger repeats (10-60bps) often found in specific regions
What are interspersed repeats?
Short Interspersed Nuclear Elements (SINEs) are short DNA sequences (100-400bps)
Long Interspersed Nuclear Elements (LINEs) are longer repeats (1000-10,000bps)
What is the function of repetitive DNA?
Structurally, they help with chromosomal integrity and stability.
They also provide genetic diversity, which can have practical implications in forensics.
