clinical chemistry

Question 1

how is glucose measured?

Answer 1

not easy to measure glucose itself, so instead measure reduced product (NADPH)

Question 2

glucose + ATP –>

Answer 2

glucose-6-phosphate + ADP

enzyme = hexokinase

Question 3

glucose-6-P + NADP –>

Answer 3

glucono-lactone-6-P + NADPH

enzyme= G6P dehydrogenase

Question 4

when measuring serum enzymes, describe importance of Km

Answer 4

want [substrate] > km

Question 5

describe isozymes

Answer 5

closely related enzymes that catalyze the same reaction but have slightly different aa composition and come from different genes. usually have different charges (helps with electrophoresis) and different kinetics (vmax, Km), some are tissue specific

Question 6

describe the forms of LDH

Answer 6

tetramer, 5 forms Muscle (M) and heart (H) - HHHH, HHHM, HHMM, HMMM, MMMM

Question 7

elevation of which 2 forms of LDH indicate MI

Answer 7

elevation of LDH 1 (HHHH) and LDH2 (HHHM)

Question 8

where, besides the heart, is LDH1 and LDH2 found?

Answer 8

in RBCs, consequence that these levels can be increased with hemolysis

Question 9

which form is high in liver and skeletal mm?

Answer 9

MMMM (LDH5)

Question 10

how is LDH visualized?

Answer 10

redox mechanism that results in conversion of NBT from oxidized (colorless) to reduced (blue) form

Question 11

when does LDH increase after MI?

Answer 11

peaks at about 24 hours

Question 12

3 problems with using LDH for MI detection

Answer 12

• other conditions may also elevate LDH levels
• electrophoresis is labor intensive and slow
• takes 12-24 hrs to appear

Question 13

how is CPK measured?

Answer 13

couple with glucose reaction (common to both reactions is ATP), then measure NADPH

Question 14

what can interfere with CPK measurement?

Answer 14

adenylate kinase- which catalyzes 2 ADP –> ATP and AMP and will thus elevate ATP

Question 15

how can problem with adenylate kinase be avoided?

Answer 15

use a control that is run first without creatinine-P, this will yield the ATP that comes from the adenylate kinase run, then run the reaction with creatinine-P and take the difference

Question 16

isozymes of CPK

Answer 16

dimeric- Muscle (M), brain (B)

MM, MB, BB

Question 17

what increased CPK isozyme indicates MI

Answer 17

MB

Question 18

what are other reasons, aside from MI, that will increase MB?

Answer 18

previously damaged mm and regenerating mm (like that of athletes in training)

Question 19

describe the rise of CPK-MB vs. rise of LDH1/2 after MI

Answer 19

CPK-MB rises faster than LDH1/2

Question 20

preferred enzyme for detecting MI

Answer 20

Troponin (T and I forms)

Question 21

why are TnT and TnI good for detecting MI?

Answer 21

• low serum levels normally
• rise rapidly, can be measured early
• high specificity for cardiac tissue

Question 22

describe RIA process (4)

Answer 22

• attach antibody to polymer
• add sample, remove excess, protein of interest binds Ab
• add second radio labeled ab to protein of interest
• measure radioactivity present

Question 23

describe ELISA process (5)

Answer 23

• attach antibody to polymer
• add sample, remove excess, protein of interest binds Ab
• add second labeled Ab (with enzyme attached) to bind protein
• enzyme takes non-flourescent substrate and makes fluorescent product
• fluorescence is measured