2ND EXAM Flashcards
(110 cards)
An object appears colored because it
absorbs part of the visible spectrum and reflects or transmits light of other wavelengths.
A solution will only absorb light energy at wavelengths corresponding to those energy levels which cause __________ within the molecules contained in the solution.
electronic excitation
the absorbance of light of a solution can be used in the
identification of its component or in the determination of the concentration of component molecules.
The absorption of light of a particular wavelength and energy by a solution is measured with a _________.
spectrophotometer
the ratio of the intensity of light emerging from a solution, I, to the intensity of light entering the solution, Io. (It is often expressed in percentage).
= I/Io
Transmittance (T)
the negative logarithms of transmittance
= -log t = log lo / I
Absorbance (A)
The absorbance of a solution is proportional to:
The relationship is given by _______ expressed as:
A = abc,
where a is a constant known as the extinction coefficient
- the concentration, c, of absorbing material
- the length of the light path through the cell, b (cm)
Beer-Lambert Law
From the Beer-Lambert Law it is apparent that a plot of absorbance against concentration will yield a straight line. If the solutions used to construct the straight line are of accurately known concentrations (standards), then the straight line is referred to as the_____________.
The Standard Curve
the concentration of a substance in solution can be determined from
the standard curve.
At low concentrations, standard curves are usually ________. But at higher concentrations, the curve ________. Consequently, the linear section of the curve must not be _______ beyond the highest absorbance measured.
linear, flattens off, extrapolated
A “______” tube, in which water (or the appropriate solvent) replaces standard or unknown solutions, should also be assayed simultaneously with standards and unknowns. The absorbance of the _____ is then subtracted from the absorbance of all tubes. Thus, the standard curve always passes through the origin, i.e. through zero.
“blank”
may be used as a general test for peptide chains of at least three amino acids (i.e.,t wo peptide bonds).
positive: purple color
The Biuret Reaction
is reproducible for a given protein but requires relatively large amounts of protein for detectable color formation.
The Biuret assay
All peptides, the amino acids histidine, serine and threonine and a number of small molecules give a _______ Biuret reaction
positive
When interfering substances are present for the Biuret assay, the protein can be precipitated with _______ prior to its estimation. The _________ carries a negative charge which neutralizes positive charges on proteins to form an insoluble protein (denatured) - __________ complex at low pH.
trichloroacetic acid, trichloroacetate ion , trichloroacetate
Why are samples and standards assayed simultaneously?
to obtain accurate results since it ensures that the absorbance readings fall in the desired range
- is a mixed secretion of several glands and has a pH of 6.4 to 6.9.
- contains ptyalin and amylase
Saliva
a carbohydrase that catalyzes the digestion of starch and glycogen, producing dextrins and limited quantities of maltose.
ptyalin and amylase
The action of salivary amylase is _______ since the food remains in the mouth for a short time then goes to the stomach where the enzyme amylase is quickly inactivated by the gastric juice which has a pH of 1.0 - 2.0.
brief
The hydrolytic action of ptyalin involves the random cleavage of _________at any interior point of the polysaccharide chain
alpha-glycosidic linkages
Digestion of starch sequentially yields
amylodextrin, erythrodextrin, achroodextrin, and maltose.
Maltose is then finally hydrolyzed to glucose by another enzyme, ________, when it reaches the ______.
maltase, small intestine
Starch gives ___________with I
blue-colored complex
amylodextrin gives _____ color
purple
