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Biochemistry final > Enzymes > Flashcards

Enzymes Flashcards

1
Q

What is an isoenzyme form?

A
  1. different form of an enzyme due to differing arrangements of the polypeptide units in the quaternary structure
  2. maintains specificity for the same chemical reaction
  3. possess unique diagnostic value: show specificity to certain organ systems
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2
Q

List isoenzymes of creatine kinase

A

CK-MM to skeletal muscle
CK-MB to cardiac tissue
CK-BB brain, GIT, genital tract

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3
Q

List isoenzymes of lactate dehydrogenase

A

LD1 and LD2 to cardiac tissue
LD4 and LD5 to liver and skeletal muscle

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4
Q

What is function of enyzmes?

A

to catalyze chemical reactions: accelerates specific chemical reactions toward equilibirum

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5
Q

List 5 properties of enzymes

A
  1. effective in small concentrations
  2. remain unchanged in the reaction, not consumed in the reaction
  3. affect the speed of reaction (not the final concentration of substrate or products)
  4. show a greater degree of specificity than chemical catalysts
  5. unstable and easily destroyed
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6
Q

what are cofactors

A

substances associated with some enzymes that are needed for maximal enzyme activity

  1. coenzyme: organic cofactors (NAD, NADH) serve as second substrates for enzyme reaction
  2. activators: inorganic cofactors (Ca2+, Fe2+, Zn2+, K+, Mg2+)
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7
Q

Where are enzymes found (intra or extracellular)?

A

intracellular,

their concentration differs dependent upon type of tissue

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8
Q

where is AST found

A

in liver

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9
Q

where is amylase found

A

in pancreas and salivary glands

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10
Q

difference between enzymes and isoenzymes

A

there are genetically determined differences in primary structure, but both catalyze the same reaction

these may have different subcellular distribution (cytoplasm x mitochondria)

may have different tissue distribution

isoenzymes can be combined from more subunits and can differ in kinetic properties

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11
Q

what are elevated blood values of isonezymes indication of?

A

specific markers of tissue damages

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12
Q

what are some factors tat affect results of plasma enzyme assays? (6)

A
  1. substrate concentration
  2. product concentration
  3. enzyme concentration
  4. reaction temperature
  5. reaction pH
  6. presence of activatios or inhibitors

!!! not pathological facotrs: age, race/ethnicity, physiological factors e.g. pregnancy!!!!

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13
Q

What is the total concentration of all plasma enzyme proteins?

A

less than 1g/L

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14
Q

what is the function of lactate dehydrogenase? where is it found and what does it measuremnt tell us?

A

it catalyzes the reversible interconversion of lactate and pyruvate

this enzyme is widely distributed in the body, high concentrations in cells of cardiac and skeletal muscle, liver ,kidney, brain and erythrocytes

non specific marker of cell damage

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15
Q

What does raised plasma total lactate dehydrogenase activity indicate?

A

we have to have a marked increse (5-10x)

  • ciruclatory failure with shock and hypoxia
  • myiocardial infarction
    -some hematological disorders in blood such as megaloblastic anemia, acute leukemias, lymphomas (20x)
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16
Q

in cases of lymphoma, what tumor marker is used?

A

LDH

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17
Q

what is LDH5

A

it is the slowest moving isoenzyme, and is the most abundant form in the liver and in skeletal muscle

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18
Q

what does predominant elevation of LDH1 and LDH2 (LDH1 more than LDH2) mean?

A

myocardial infarction, megaloblastic anaemia, after reanl infarction

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19
Q

predoominant elevation of LDH2 and LDH3 occurs in …

A

acute leukemia

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20
Q

LDH3 is the main isoenzyme elevated as a result of …

A

malignancy of many tissues

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21
Q

elevation of LDH5 occurs after…

A

damage to the liver or skeletal muscle

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22
Q

function of CK

A

reversible phsophorylation of creatine by ATP

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23
Q

what are 2 protein subunits of CK

A

M and B

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24
Q

CK-MB accounts for about —% of the total CK activity in cardiac muscle and less than – % in skeletal muscle

A

35% cardiac, 5% skeletal

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25
Q

in malignant disease, plasma total CK activity is usually _______

A

normal

26
Q

specimens or CK analysis include : (2)

A

heparinize serum and heparinize plasma

27
Q

what should no be used in collection tubes because it inhibits CK activity?

A

anticoagulant ants other than heparin

28
Q

what is CK activity in serum like?

A

relatively unstable and is rapidly lost during storage

29
Q

average stabilities of CK in storage are
____ at room temp, ____ at 4C, and ____ at -20C

A

Average stabilities are less than 8 hours at room
temperature, 48 hours at 4 °C, an 1 month at −20 °C.

30
Q

CK raised in physiological situations:

A
  • neonatal period (slightly raised above the adult)
  • during and for a few days after parturition, (higher in Africans than in Caucasians)
31
Q

list scenarios when there is marked increase of CK (5-10x UL) (6)

A
  1. dermatomyositis and polymyositis
  2. shock and circulatory failure
  3. myocardial infarction
  4. muscular infarction
  5. rhabdomyolysis
  6. necrotizing fascitis
32
Q

Define rhabdomyolysis

A

acute increase in plasma CK concenration greater than 10 times the upper limit of normal

33
Q

what can lead to grossly elevated plasma CK concentrations, sometimes up to 100 000 u/l

A

severe muscle breakdown: trauma, severe exertion, alcohol, heat, electrolyte disturbance, drugs such as statins

34
Q

decision limits of creatine kinase-MB mass peak for infarct sze definition

A

microscopic <10ug/L
small MI 10-60 ug/L
medium MI 60-225 ug/L
large MI >225 ug/L

35
Q

function of amylase, where is it found, excretion

A

Amylase breaks down starch and glycogen to maltose.
* It is present at a high concentration in pancreatic juice and in
saliva and may be extracted from other tissues, such as the
gonads, Fallopian tubes, skeletal muscle and adipose tissue.
* Being of relatively low molecular weight, it is excreted in the
urine

36
Q

estimation of plasma amylase activiy is mainly requested to help in the diagnosis of____

A

acute pancreatitis, but a high result is not a specific diagnostic marker for acute pancreatitis

37
Q

marked increase of plasma amylase activity is seen in (4)

A
  1. acute pacreatitis
  2. severe glomerular impairment
  3. diabetic ketoacidosis
  4. perforated peptic ulcer
38
Q

In acute pancreatitis, what test should we run?

A
  • lipase measuremnt is superior to P-AMY in terms of diagnostic performance
  • it is recommended that lipase replace P-AMY as initial test for acute pancreatitis, measuring both serum P-AMY and lipase is not warranted
  • the measurment of total AMY shoud be considered obsolete
39
Q

Lipase measurment in serum is used to diagnose…

A

acute pancreatitis with a clinical sensitivity and specificity 80-100%

40
Q

after an attack of acute pancreatitis, serum lipase activity increases within ___ to ___ hours, peaks at about ___ hours and decreases within ____.

A

After an attack of acute pancreatitis, serum LPS activity
increases within 4 to 8 hours, peaks at about 24 hours,
and decreases within 7 to 14 days.

41
Q

Lipase clinical significance

A

LIP is among the more poorly standardized laboratory tests, so misdiagnosing acute pancreatitis is a real possibility, especially if clinicians receive results from different analytical systems

42
Q

what are two aminotransferases? what do they do?

A

ALT and AST involved in the transfer of an amino group from a 2-amino acid to 2-oxoacid

43
Q

what is aspartate aminotransferase?

A

it is a lliver enzyme present in high concentrations in cells of cardiac and skeletal muscle, liver, kidney, erythrocytes.. damage to any of these results in high levels

44
Q

is AST specific for hepatic disease?

A

NO

45
Q

AST: conditions with marked (3) VS slight/moderate increase (7)

A

marked increase is 5 and more times URL:
circulatory failure with shock and hypoxia
MI
acute viral or toxic hepatitis

moderate to slight increase in less than 5x URL
hepatic steatosis
infectious mononucelosis
cholestatic jaundice
skeletal muscle disease
after trauma or surgery
severe hemolytic episodes
certain drugs

46
Q

What is more specific for hepatic disease? AST or ALT?

A

ALT!!! AST is not specific for hepatic disease.
remember:
A L(iver) T

47
Q

ALT: conditions with marked (2) VS slight/moderate (8) increase

A

marked: ciriculatory failure with shock and hypoxia and acute viral or toxic hepatitis
moderate to sight:
1. hepatic steatosis
2. cirrhsis
3. infectious mononucelosis
4. liver congestion secondary to congestive cardiac failure
5. cholestatic jaundice
6. coeliac disease
7. surgery, extensive trauma and skeletal muscle disease
8. certain drugs

48
Q

when could we expect higher AST than ALT

A

in case of surgery, extensive trauma and skeletal muscle disease: ALT is much less affected than AST

49
Q

How do we differentiate hepatocellular vs cholestatic type of injury in case of drug-induced liver toxicity?

A

In hepatocellular injury, ALT/ALP equal/greater than 5

In cholestatic injury, ALT/ALP equal/less than 2

In mixed injury: ALT/ALP = 2-5

50
Q

Where is alkaline phosphatase found?

A

especially associated with cell surfaces
located in the mucosa of the small intestine and the proximal convoluted tubules of the kidney, in bone (osteoblasts), liver, and placenta, anchored on the cell membrane

51
Q

Assumed function of ALP and its inhibitors?

A

the exact metabolic function of the enzyme is not yet understood, it appears that ALP is associated with lipid transport in the intestine and with the calcification process in bone.

Phosphate, borate, oxalate, and cyanide ions are inhibitors of ALP activity.

52
Q

When should ALP be measured?

A

in fasting serum; its activity increases after a meal

53
Q

is ALP age dependent?

A

yes

54
Q

in what cases could we expect ALP to be minimal?

A

serum of individuals of blood group B or 0

55
Q

when will we order ALP?

A

to investigate hepatobiliary diseae and bone disease associated with increased osteoblastic acitvity

56
Q

is ALP reliable marker of hepatobiliary disease in pregnancy?

A

No:
An increase of up to two to three times URL is observed in women in the third trimester of pregnancy, with the additional enzyme being of placental origin.

57
Q

what speciemen is used to measure ALP?

A
  • Serum or heparinized plasma, free of hemolysis, should be used.
    Complexing anticoagulants—such as citrate, oxalate, and EDTA—must be avoided because they bind cations, such as Mg2+ and Zn2+, which are necessary cofactors for ALP activity measurement.
  • Blood transfusion (containing citrate) causes a transient decrease in serum ALP through a similar mechanism.
  • Freshly collected serum samples should be kept at room temperature and assayed as soon as possible but
    preferably within 4 hours after collection.
58
Q

Infants and peripubertal children show ___ ALPR activity than healthy adults

A

Infants and peripubertal children show higher ALP activity (up
to threefold) than healthy adults as a result of the leakage of
bone ALP from osteoblasts during bone growth.

59
Q

how does sex affect ALP

A

activities in growing children are highly variable and the decrease in ALP activity to typical adult ranges is known to differ from subject to subject, occurring on average 2 years earlier in females than in males.

60
Q

normal values of ALP

A

adult individuals: 33 to 98 U/L for premenopausal women(18–49 years)
* 43 to 115 U/L for men (≥20 years).
* For women, a progressive increase of both lower and URL after menopause is described.

Biochemistry final (7 decks)

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