DNA Structure Flashcards
1
Q
What is the purpose of the major and minor grooves in DNA?
A
- contain receptors for drugs
- enable DNA to be read
2
Q
Describe the B-form structure of DNA
A
- very smooth
- sugars and phosphates on outside of helix
- different sized grooves
- most common form
- conformational state of DNA
3
Q
Describe the A-form structure of DNA
A
- generally more compressed but the same structure
- can go from A to B via elongation
- a conformational state of DNA
4
Q
Describe the Z-form of DNA
A
- helix twisted in opposite direction
- found in nucleus of cells
- present in very small amounts
5
Q
How do histones and DNA interact?
A
- DNA strands are anti-parallel and have a polarity
- the phosphate backbone is negatively charged
- histones are positively charged
- therefore can interact with DNA and DNA can wrap around it
6
Q
What are some examples of unusual DNA structures?
A
Left-handed/Z-DNA Four-stranded/holiday junction: -important in mitosis recombination Tetraplex DNA: -formed at telomeres -involved G-rich sequences -protects ends of chromosomes from being digested by nucleases
7
Q
What are the different levels of DNA structure and how can they be identified?
A
Primary: -sequence of bases -DNA sequencing used Secondary: -helical structures -X-ray and chemistry used Tertiary: -DNA supercoiling -coiled in space -electron microscopy used Quaternary: -interlocked chromosomes
8
Q
What is the structure of bacterial DNA?
A
- DNA ribbon is twisted in space, supercoiled
- supercoiling caused by enzyme- DNA gyrase
- chromosome is organised into approximately 50 independently supercoiled domains
9
Q
What is the ‘beads on a string’ structure?
A
- this is how nucleosomes were first seen in electron microscopy
- nucleosome= the basic building block of chromatin
- chromatin is DNA complexed with histones
10
Q
Examples of spontaneous mutations in DNA
A
- loss of bases
- hydrolysis of cytosine to uracil
11
Q
How do chemicals causes DNA mutations?
A
- change base structure
- insert between bases
- e.g. intercalators like doxorubicin
- widely used as anticancer drugs
12
Q
How does radiation cause DNA mutations?
A
- UV light produces thymine dimers which are formed from adjacent thymine molecules
- ionising radiation break DNA chromosomes which causes leukaemia
13
Q
What is the importance of DNA repair?
A
- maintains genome stability
- 50-100 different enzymes/proteins involved
- cancers have DNA repair defects
