推 crazycrab:Ch2的第3題有寫過了對不對 220.138.252.202 10/25
推 bryan648:是阿~~應該不用再寫一遍吧XD 218.166.208.146 10/25
Chapter 2
3. Measurement of Acetylcholine Levels by pH Changes
The concentration of acetylcholine (a neurotransmitter) in a sample can be
determined from the pH changes that accompany its hydrolysis. When the sample
is incubated with the enzyme acetylcholinesterase, acetylcholine is
quantitatively to yield acetate and a hydrogen ion: (有圖)
In a typical analysis, 15mL of an aqueous solution containing an unknown
amount of acetylcholine had a pH of 7.65. When incubated with
acetylcholinesterase, the pH of the solution decreased to 6.87. Assuming that
there was no buffer in the assay mixture, determine the number of moles of
acetylcholine in the 15mL sample.
8. pH and drug absorption
Aspirin is a weak acid with a pKa of 3.5
It is absorbed into the blood through the cells lining the stomach and the
intestine. Absorption requires passage through the plasma membrane, the rate
of which is determined by the polarity of the molecule: charged and highly
polar molecules pass slowly, whereas neutral hydrophobic ones pass rapidly.
The pH of the stomach contents is about 6. Is more aspirin absorbed into the
bloodstream from the stomach or from the small intestine?
Clearly justify your choice.
16. Control of Blood pH by Respiration Rate
(a) The partial pressure of CO2 in the lungs can be varied rapidly by
the rate and depth of breathing. For example, a common remedy to alleviate
hiccups is to increase the concentration of CO2 in the lungs. This can be
achieved by holding one's breath, by very slow and shallow breathing
(hypoventilation), or by breathing in and out of a paper bag. Under such
conditions, the partial pressure of CO2 in the air space of the lungs rises
above normal. Qualitatively explain the effect on the blood pH.
(b) A common practice of competitive short-distance runners is to breathe
rapidly and deeply (hyperventilate) for about half a minute to remove CO2
from their lungs just before running in, say, a 100m dash. Blood pH may rise
to 7.60. Explain why the blood pH increases.
(c) During a short-distance run the muscles produce a large amount of
lactic acid (CH3CH(OH)COOH, Ka=1.38*10^(-4)) from their glucose stores.
In view of this fact, why might hyperventilation before a dash be useful?
Chapter 3
10. Net Electric Charge of Peptide
A peptide has the sequence Glu-His-Trp-Ser-Gly-Leu-Arg-Pro-Gly
(a) What is the net charge of the molecule at pH 3,8, and 11?
(Use pKa values for side chains and terminal amino and carboxyl groups as
given in Table 3-1.)
(b) Estimate the pI for this peptide.
12. The Isoelectric Point of Histones
Histones are proteins found in eukaryotic cell nuclei, tightly bound to DNA,
which has many phosphate groups. The pI of histones is very high, about 10.8.
What amino acid residues must be present in relatively large numbers in
histones? In what way do these residues contribute to the strong binding of
histones to DNA?
14. Purification of an Enzyme
A biochemist discovers and purifies a new enzyme, generating the
purification table below.
Total
protein Activity
Procedure (mg) (units)
______________________________________________________________________
1.Crude extract 20.000 4.000.000
2.Precipitation(salt) 5.000 3.000.000
3.Precipitation(pH) 4.000 1.000.000
4.Ion-exchange chromatography 200 800.000
5.Affinity chromatography 50 750.000
6.Size-exclusion chromatography 45 675.000
(a) From the information given in the table, calculate the specific
activity of the enzyme solution after each purification procedure.
(b) Which of the purification procedures used for this enzyme is most
effective (i.e., gives the greatest relative increase in purity)?
(c) Which of the purification procedures is least effective?
(d) Is there any indication based on the results shown in the table that the
enzyme after step 6 is now pure? What else could be done to estimate the
purity of the enzyme preparation?
很高興
終於學會轉寄信件了
以後就可以把批萬和批兔的東西互相傳送了
--
當我們以為地球不轉時
其實是我們自己的心停止了
只要我們讓心動起來
你會發現地球隨時都在跳舞
by 623
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