lecture 3 Flashcards
which important amino acids have nonpolar side chains?
- phenylalnine
- tryptophan
- proline
WHich important amino acids have polar side chains?
- tyrosine
- asparagine
- glutamine
which important amino acids have electrically charged side chains?
- lysine
- arginine
- histidine
What are albumins, globulins, prolamins and glutelins soluble, insoluble and percipitated by?
- Albumins:
- soluble: water, dilute salt and acid/base solutions
- percipitated: saturated salt solution
- Globulins:
- soluble: dilute salt solution
- insoluble: distilled water
- perciptated: half saturated salt solution
- Prolamins:
- soluble: 70-80% alcohol
- insoluble: water and absolute alcohol
- glutelins:
- soluble: dilute acids and alkalis
- insoluble: distiled water, dilute salt solutions and alcohol
what are the two protiens in wheat, and which categorgies do they belong to? And which is responsible for allergy?
The two protiens are gliadin (prolamin) and glutenin (glutelins). Gliadin is the one responsible for allergy.
what is a phosphoprotien and give an example
Is a protien that has a phosphoric acid conjugated to the protien via an ester linkage. An example would be casein in milk.
why is it important to measure protien content in food?
Health:
- nutritional balance: ensuring getting enough protien for nutritional goals
- dietary planning: helps to accurately plan meals to meet specific dietary needs
Food processing/industry:
- food labeling
- quality control: consitency in nutrional value
- affect organlopetic properties
- price
in the kjedal metho why are catalysts like copper or selenium used during the digestion step?
A catalyst, such as copper, selenium, or a mercury compound, can improve digestion
efficiency and reduce the need for excessively high temperatures.
why is the conversion factor 6.25 used when calculating percent protien
Because most protiens contain about 16% nitrogen→ N% x 100/16= N% x 6.25 which is the equation for percent protien
what are the advantages vs disadvantages of the kjedal method?
✅ Advantage
- ## AOAC Official Method – Used worldwide for food protein analysis.
❌ Disadvantages
- Time-consuming – Takes several hours to complete.
- Requires hazardous chemicals– Sulfuric acid, strong alkalis, toxic catalysts.
- Measures total nitrogen, not just protein – Can overestimate protein if other nitrogen-containing compounds (e.g., nitrates, urea) are presen
what are the advantages/disadvantges of the dumas method?
Advantages of the Dumas Method
- Much faster than Kjeldahl (a few minutes per sample vs. hours).
- No hazardous chemicals (no sulfuric acid or alkali required).
- Environmentally friendly (no toxic waste).
- Highly automated, requiring minimal manual handling.
- Can analyze multiple samples continuously.
❌ Disadvantages of the Dumas Method
- Expensive – Requires costly equipment and maintenance.
- Not selective – Measures all nitrogen, including non-protein nitrogen (e.g., nitrates, urea), which can overestimate protein content.
- Requires trained personnel to operate and maintain equipment.
differentiate between Dumas and kjedahl method
Nitrogen: dumas measures total nitrogen as gas and kjedahl as ammonium sulfate
Speed: dumas is way faster than kjedahl
Hazard: kjedahl uses hazardous chemicals wherase dumas does not
Price: dumas is more expensive due to the equipemnt price
Toxic waste: dumas does not produce toxic waste and kjedahl does
why is phenalynine discluded from direct measuremtn at 280 nm?
because it absorbs at around 275
what are the advantages/disadvantages of using direct measurement in terms of protien determenation
advantages:
- simple
- non destructuve
- does not require special reagents
Disadvantages:
- low or uneven levels of tryptophan and tyrosine can give innacurate results
- interfenance from nucelic acids as they also absorb at 280 nm and can lead to an overestimation
- interfernce from un bound tryptophan/tryosine
what is done to account for the nucleic acid interfernce
measure at two different wavelentghs and then measure a A280/A260 ratio and then use a specific correction factor. A higher ratio means less contamination from nucleic acid
what are the advantages/disadvantages of the buriet method>
Advantages of the Biuret Method
- Simple and Rapid: Can be completed in under 30 minutes.
- Specific to Proteins: Few non-protein substances interfere with the reaction.
- No Nitrogen Interference: Does not detect nitrogen from non-protein sources like urea or ammonia.
- Cost-Effective: Reagents are inexpensive and widely available.
Disadadvantegs:
- low sensitivity: requires at least 2-4 mg protien to test
what are the advantages/disadvantages of the lowry method?
advantages:
- more sensitive, especially in comparison to the biuret method
- less affected by turbidity of sample
- relatviley simple and can be done in a short amount of time 1-1.5 h
- more specific
Disadvantges:
- susceptible to interfence by reducing agents
what are the advantages/disadvantages of the BCA assay method
advantages:
- highly sensitive so can be used for low protien content samples
- only one reagent
- simple and convenient protocal
- one step process as it is more stable under alkaline conditions
Disadvantages:
- interfence from reducing agents
- time sensitive when done at high temperatures
what is the principle behind dye binding methos?
The dye will be mixed with sample, and there will be some binding to the protien, but not all the dye will be bound. So the idea here is that you measure the unbound die. The amount of unbound dye is inversely related to protien content
what are the advantages/disadvantages of the bradford assay method
advantages:
- inexpensive
- rapid: done in 15 minutes or less
- simple
- stable dye protien complex
Disadvanyages:
- not sensitive
- not suitable for hydrozlyed protiens because of N-terminal amino acids as you keep getting binding reactions making it look like you have more protien than you actually have
what are the advantages/disadvantages of infared spectroscopy?
- Advantages:
- Rapid and non-destructive method.
- Suitable for direct protein measurement in various sample types.
- Limitations:
- Complex mathematical processing is needed.
- Requires specialized equipment and calibration.
what are the advantages/disadvantages of ELISA
Advantages:
- highly specific: only the target protien is measured
-can detect low concentrations of protiens
- widely used in clinical and research applications
disadvantages:
- requires specilized kits and specific antibodies
- can be time consuming
whats the equation to calculate N% (kjedahl)
N%= moles of HCl x 14/ sample mass (g) x 100
