Lab Exam Flashcards
Describe the general structure of proteins
High molecular weight polymers of many amino acids linked by peptide bonds to form a linear chain (called polypeptide). In solution they take on a 3 dimensional shape
_____ proteins exhibit only a secondary structure brought about by H-bonding within or between polypeptide chains
Fibrous proteins
Describe the structure of globular proteins
form 3-dimensional shapes as a result of interactions between R-groups of constituent amino acids. Exhibit tertiary level of structure
Proteins that are globular with more than one polypeptide chain are referred to as having ____ structure
Quaternary level of structure
Why would one need to know the concentration of a protein in solution?
To measure enzyme activity, to figure out nutritional state of tissue, etc
Colorimetric tests are based on what feature of copper ions?
Based on the principle that copper ions in alkaline solutions form purple-coloured complex with 2 or more peptide bonds, detectable by spectrophotometer.
How does the colorimetric test give an estimate of ONLY protein in a sample?
Free amino acids do not have peptide bonds for the copper ions to bind to and will therefore produce no colorimetric change
Why is albumin usually used to construct standard curves?
It is cheap, abundant, and available in purified form
The higher the concentration of protein in a colorimetric test, the _____ the colour
deeper
Of the two colorimetric tests used in lab one, the ____ is more sensitive
Lowry test
In lab one, how many standard curves were constructed?
- One for Biuret test, one for Lowry, and one for UV
The Biuret test was done at a wavelength of ____nm using ___ reagent
540nm, Biuret reagent
Why did we do dilutions of the unknown sample in Lab 1? What dilutions were used?
We did dilutions just in case the unknown sample was “off scale” with respect to the concentration curve in some way. Two fold dilution (1:1), ten fold dilution (1:9), and undiluted
The Lowry test was done at a wavelength of ____nm using ___ reagent
500nm using Lowry reagent and Folin reagent
Which three amino acids are detected using the UV test? Are any less easily detectable?
Tryptophan, tyrosine, phenylalanine (slightly less than the other two)
The UV test was done at a wavelength of ____nm using ___ reagent
280nm using NO reagents
What test from lab 1 would you use for a sample that you are trying to keep for a future experiment with a protein concentration around 0.05mg/mL?
IF the sample must be kept for the future, then no reagents can be use. The UV test is the best option
What test from lab 1 would you use for a sample that is known to be deficient in tyrosine?
The UV test would not be accurate, as it detects tyrosine, tryptophan, and phenylalanine. Biuret test or Lowry test would be better
What test from lab 1 would you use for a sample with a high protein concentration (approx. 10mg/mL) that there is a lot of?
Any test is possible, as long as appropriate dilutions are prepared
What test from lab 1 would you use for a sample that is turbid with an approx. protein concentration of 1 mg/mL?
Not UV, because turbidity affects UV results. High turbidity likely means the concentration is high so the Biuret test is the best candidate, though Lowry is possible after more dilutions
If you need a final volume of 3 mls of the unknown solution in order to take an absorbance
reading in a spectrophotometer, how would you prepare the unknown dilutions? In other words, how
much water and how much of the unknown solution would you need to pipette into a test tube to end
up with the proper volume (3 mls) and proper dilution (2-fold and 10-fold)?
Tube 1 - 3mL unknown
Tube 2 - 1.5mL unknown, 1.5mL water
Tube 3 - 0.3mL unknown, 2.7mL water
DNA in the nucleus is in a long linear _____, sometimes called a _______
Polynucleotide, called deoxyribonucleoprotein (DNP)
What is a “wheat germ”?
The vitamin-rich embryo of the wheat kernel (separated before milling)
Describe the three main steps for isolation of DNA
Homogenization - Tissue is ground up, blended, crushed to release molecule in question.
Centrifugation - Homogenate is spun to sediment debris, unbroken cells, nuclei. Leaves soluble molecules in the supernatant.
Enrichment of Target Molecule - Either pellet or supernatant must be treated in some way to make DNA (molecule of interest) more accessible.