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Chemistry 2 > quiz 2 review ( enzymes) > Flashcards

quiz 2 review ( enzymes) Flashcards

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1
Q

What are isoenzymes?

A

Groups of related enzymes that have the same active site (can catalyze the same reaction) but have different properties

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2
Q

What does Q10 value refer to?

A

Q10 = difference in enzyme activity or reaction rate when performed at 2 temperature differing by 10oC. The rate of most enzyme-catalyzed reactions will double for an increase of 10oC

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3
Q

What does Km refer to in an enzyme catalyzed reaction?

A

Michaelis constant - the substrate concentration at ½ maximum velocity (rate). It is determined to ensure that the substrate concentration used is 10 - 100 times the Km. (to ensure zero order kinetics)

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4
Q

What does stereochemical specificity mean and give one example.

A

Enzymes that only catalyze reactions of one enantiomeric form of a substrate.
i.e. either D or L form.

Example: LD will only react with L-Lactate

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5
Q

What is the difference between an activator and a coenzyme?

A

Both are cofactors. An activator is inorganic. A coenzyme is organic

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6
Q

What does the term specificity mean in relation to enzyme catalyzed reactions?

A

That enzymes will only catalyze reactions of a specific substrate (or bond) or a small number of substrates (or bonds)

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7
Q

What is an I.U.?

A

The quantity of an enzyme that will catalyze the reaction of 1 μmol of substrate per minute per L (or mL) of serum.

Written as IU/L or mIU/mL

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8
Q

Explain the two general approaches used to measure the extent of an enzymatic reaction

A
  1. Fixed-time (endpoint)

2. Continuous monitoring (rate or kinetic)

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9
Q

Describe the type of reaction that a hydrolase catalyzes

A

Catalyzes breakdown of substrate by the addition of H2O

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10
Q

Why do we monitor the activity of an enzyme catalyzed reaction during zero-order kinetics?

A

Because we want the reaction rate to only depend upon the enzyme concentration. Then enzyme activity is proportional to enzyme concentration

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11
Q

What is the principle of the BLB method for measuring ALP?

A

p-nitrophenylphosphate + H2O −→−Mg2+ALP p-nitrophenol + inorganic phosphate
Alkaline buffer = AMP (amino methyl propanol)

Optimum pH = 9 - 10

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12
Q

In the BLB method, what is the purpose of serum blanks and how are they produced?

A

Produced by acidifying the reaction mixture. Acid converts the p-nitrophenol from yellow to colorless. Allows a correction for the color of serum

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13
Q

Which type of liver disease produces the highest levels of ALP in plasma or serum?

A

Extrahepatic obstruction

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14
Q

The highest levels of ALP are seen in which type of bone disease?

A

Paget’s Disease (bone resorption)

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15
Q

If Alkaline Phosphatase (ALP) and Acid Phosphatase (ACP) catalyze the same general type of reactions, what is the main difference between the two enzymes?

A

Their optimal pH.

ALP - pH 9 - 10
ACP - pH 4.9 - 5.0

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16
Q

Why are the BLB and Roy et al. methods for acid phosphatase (ACP) not preferred methods in a continuous monitoring system?

A

Because their products, p-nitrophenol (BLB) and thymolphthalein (Roy et al.), were colorless at the acid pH used. So the Hillman method is used because its product (α-napthol phosphate) gives a color.

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17
Q

Why would a hemolyzed sample not be used for measurement of acid phosphatase (ACP)?

A

There is a high level of ACP in red blood cells.

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18
Q

What is PAP?

A

Prostatic Acid Phosphatase - the isoenzyme that originates from the prostate

19
Q

Older methods employ tartrate as a means of differentiating prostatic ACP (PAP). What is an alternate approach?

A

Use the methods of either Hillman or Roy et al.

PAP hydrolyzes these substrates more readily than nonprostatic isoenzymes of ACP, so any reaction is due to PAP

20
Q

Very high elevations of acid phosphatase (ACP) are seen in which clinical condition?

A

Metastatic prostate cancer

So it is most useful to confirm metastatic prostate cancer and to stage prostate cancer.

21
Q

What is PSA and what is its clinical utility?

A

PSA = prostate specific antigen

Clinical use - monitoring of treatment for patients with known prostatic carcinoma. Also used in diagnosis along with rectal exam and ultrasound.

22
Q

Why is human amylase called alpha-amylase?

A

It hydrolyzes α 1,4-glucosidic linkages of polyglucans.

23
Q

Why were defined substrate methods introduced to measure amylase?

A

Because of problems with older starch based methods. i.e. variability of starch substrate and inconsistency of hydrolysis conditions.

24
Q

How can amylase be measured by O2 consumption?

A

Starch −→−−−−− (Amylase) maltose, maltotriose →GlucoseGlucose + O2 −→−−−−−−−−(Gluose, Oxidase) H2O2 + gluconolactone
Decrease in O2 measured.

25
Q

Why is amylase the only enzyme that is routinely measured in urine as well as serum?

A

Because it appears in urine due to its small size

26
Q

What is the systematic name, practical name and abbreviation for the enzyme that catalyzes the following reaction?

L-lactate + NAD+ ⇄ ? Pyruvate + NADH + H+

A

Systematic name: L-Lactate:NADoxidoreductase

Practical name: Lactate Dehydrogenase

Abbreviation: LD

27
Q

Why do most methods for aspartate aminotransferase (AST) now incorporate P-5-P in the test procedure?

A

Because it is a prosthetic group for AST and it increases the rate of the reaction

28
Q

Why is aspartate aminotransferase (AST) used as an aid in the diagnosis of myocardial infarctions?

A

It begins to rise in the blood about 8 hours after AMI.
Peaks about 24 hours.
Remains elevated for about 5 days.
Can be used to confirm diagnosis of AMI.

29
Q

Why is Gamma-glutamyltransferase (GGT) referred to as a transferase?

A

Because it transfers glutamate from one peptide to another

30
Q

Highest levels of gamma-glutamyltransferase (GGT) are seen in which clinical conditions?

A

30 times normal elevation in intrahepatic or posthepatic biliary obstruction and in liver cancer.

31
Q

Why is a wavelength of 340 nm used in NAD/NADH reactions?

A

Because of the difference in absorbance of NAD+ and NADH at 340 nm.

NADH absorbs at 340 nm, so an increase in absorbance can be read.

NAD+ doesn’t absorb light at 340 nm, so a decrease in absorbance can be read.

32
Q

What is the basic principle for measurement of lactate dehydrogenase (LD) using a method based upon the P → L reaction? What is the optimum pH?

A

Pyruvate + NADH −→−− ( LD ) Lactate + NAD+
Measure decrease in absorbance at 340 nm

Optimum pH 7.1 - 7.4

33
Q

a) Lactate Dehydrogenase (LD) isoenzymes are made up of how many peptide chains?
b) What kind of chains are they?
c) This gives rise to how many LD isoenzymes?

A

a) Four peptide chains
b) M (muscle) and H (heart) chains
c) 5 isoenzymes (LD-1 to LD-5)

34
Q

What is the predominant LD isoenzyme(s) found in:

a) the heart
b) the liver
c) skeletal muscle

A

a) *LD-1, LD-2
b) LD-4, *LD-5
c) LD-4, LD-5`

35
Q

Why will hemolysis increase serum LD values?

A

RBCs have a high concentration of LD

36
Q

How long will serum lactate dehydrogenase (LD) levels remain elevated after AMI?

A

7 - 12 days post-infarct.

37
Q

What is the reverse reaction for measuring serum creatine kinase (CK) and why is it the preferred method?

A

Phosphocreatine + ADP →Creatine + ATP

It occurs faster than the forward reaction.

38
Q

Why should hemolyzed serum samples not be used for the measurement of creatine kinase (CK) activity?

A

Because RBCs have a high level of the enzyme AK (adenylate kinase) which catalyzes a reaction to produce ATP.

Since the CK reaction also measure ATP, it can give a falsely increased result

39
Q

Why are CK isoenzymes called dimers?

A

They contain two subunits, M and/or B.

Di = 2

40
Q

What is the predominant creatine kinase (CK) isoenzyme found in the serum of healthy individuals?

A

CK-MM (CK-3) is the major isoenzyme and makes up 94 - 100% of the total CK.

41
Q

What can be considered one of the most specific indicators of AMI?

A

Increased CK-MB (>6% of total CK)

42
Q

Name two instances when creatine kinase (CK) activity could be elevated in the serum of healthy individuals?

A

After strenuous muscular activity - up to 48 hours.

After intramuscular injections - up to 1 week.

43
Q

What enzymes/isoenzymes are important in the investigation of suspected AMI?

A

CK (CK-MB)

LD (LD-1 & LD-2)

AST`

Chemistry 2 (30 decks)

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