Lecture 6 (Chris Allen) Flashcards
1
Q
What is the range for UV-visible light
A
200-800nm
2
Q
What determines the specific wavelength at which a biological molecule absorbs UV light
A
It’s covalent structure
3
Q
When is the molar extinction coefficient a constant
A
At a particular wavelength for a specific compound
4
Q
What is the molar extinction coefficient related to
A
The absorbance at a specific wavelength.
5
Q
Do absorbance and wavelength have a directly or inversely proportional relationship
A
Directly proportional.
6
Q
What type of molecules are UV chromaphores
A
- Molecules containing double bonds (aliens such as beta-carotene)
- Aromatic compounds such as benzene
- Contain a carboxylate group or ketone (carbonyl group) such as benzoin acid
- Heterocyclic compounds such as indigo
7
Q
How does conjugation affect absorption of UV light
A
- Increases the absorption of UV light and shifts absorption toward the visible region.
- Therefore, unsaturated bond conjugation (alkenes/aromatics) increase the extinction coefficient for particular molecules and shift the absorption maxima toward the visible (higher wavelengths) region.
8
Q
How can UV spectroscopy be used to estimate the GC content of DNA
A
- GC pairs are linked with three hydrogen bonds and AT pairs are linked with two hydrogen bonds.
- Therefore the temperature at which DNA becomes single stranded will reflect the GC content.
9
Q
How can UV Vis spectroscopy be used in enzyme assays
A
- Many enzymes catalyse reactions with intermediates that can readily absorb light of these wavelengths.
- By comparing the concentration of reactants/products in a spectrophotometer during a reaction, we can determine the rate of the reaction under certain conditions.
- For example, consider: A + B ➡️ C + D
- If D is the only chromaphore at a specific wavelength, then the rate of the reaction (and enzyme activity) can be measured by monitoring the concentration of D.
