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Thursday, 15/11/2018, 2:11:51 PM
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Biochemistry


 
 
A 50-year-old homeless man was brought to the emergency room in a stuporous state. Blood pressure is 100/50 mmHg, heart rate 120 beats/min, respiratory rate 35/min, and his temperature is 104F (40C). He was found to have cellulitis of his left foot. Below are his lab results: Sodium 150mEq/L (135-145), Potassium 2.5mEq/L (3.5-5.0), Chloride 107mEq/L (95-105),Bicarbonate 10mEq/L (24-26), pH 7.2 (7.35-7.45), PCO2 25mmHg (35-45), Alcohol 40mmol/L (0), Osmolality 370mOsm/L (280-295), Glucose 50mg/dl (60-110) BUN 40mg/dl (5-22). What is the acid-base status?
 
a. metabolic acidosis and metabolic alkalosis
b. metabolic acidosis with partial respiratory compensation
c. respiratory acidosis and partial metabolic compensation
d. respiratory acidosis
 
The correct answer is: b
 
A 44-year-old man is brought to the emergency room stuporous and obtunded. He has not seen a physician previously and he takes no medication. Physical examination reveals BP 120/70 and pulse 90 (supine); and BP 90/50 and pulse 120 (standing). Serum chemistries are: Na+ = 140 mEq/L; Cl = 86 mEq/L; K+ = 2.9 mEq/L; HCO3 = 42 mEq/L; arterial pH = 7.5; PCO2 = 50mmHg. The disease process that best accounts for this problem
 
a. chronic obstructive pulmonary disease
b. congestive heart failure
c. protracted vomiting
d. renal failure
 
The correct answer is: c
 
The medical student next to you, realizing that there is an examination question on acid base balance, begins nervously hyperventilating and then faints. You make him breathe into a paper bag and he recovers. If you had drawn and analysed his blood when he fainted you would have expected to see

a. decreased pH, decreased pCO2
b. decreased pH, decreased pCO2
c. elevated pH, decreased pCO2
d. elevated pH, elevated pCO2
 
The correct answer is: c

 
A hospital patient with AIDS has large amount of diarrhea over the past 4 hours. He becomes hypovolemic over a short period of time. Which of the following lab results would best fit this clinical history?
 
a. pH: 7.15, pCO2: 55 mmHg, HCO3: 40 mEq/L
b. pH: 7.25, pCO2: 36 mmHg, HCO3: 15 mEq/L
c. pH: 7.40, pCO2: 40 mmHg, HCO3: 24 mEq/L
d. pH: 7.50, pCO2: 28 mmHg, HCO3: 24 mEq/L
 
The correct answer is: b
 
A 28-year-old man with bronchiectasis presents to the hospital emergency room with 3 days of increasing cough, sputum, and dyspnea despite maximizing his bronchodilators. About 1 month ago, an outpatient stable room arterial blood gas showed pH 7.38, PaO2 55 mmHg, PaCO2 65 mmHg, and HCO3- 32 mEq/L. His current vital signs are BP 117/65 mmHg, P 123/min, T 100°F. His room air ABG in the ER is pH 7.28, PaCO2 70 mmHg, PaO2 50 mmHg, and HCO3- 23 mEq/L. Which of the following best characterizes the current acid-base status?
 
a. compensated metabolic acidosis
b. compensated metabolic alkalosis
c. uncompensated metabolic acidosis
d. uncompensated respiratory acidosis
 
The correct answer is: d

 
The anion gap is calculated as follows:
 
a. [K+] + [HCO3- + Cl-]
b. [Na+] + [Cl- + HCO3-]
c. [Na+] – [HCO3- + Cl-]
d. This is typically machine derived so I will not have to calculate it.

The correct answer is: c

 
The bicarbonate gap, calculated as Delta AG – Delta HCO3-, is a useful tool with mixed acid-base disorders because
 
a. If it is a positive a number it clearly indicates two respiratory problems.
b. If it’s negative, it clearly indicates one of the conditions is renal in origin.
c. If it’s positive or negative, it simply indicates I am dealing with a mixed problem.
d. It’s of no value at all and was simply cooked up to make my life miserable.
 
The correct answer is: c

 
The so called proximal type of renal tubular acidosis, type 2 RTA, is characterized by
 
a. Reduced carbonate reabsorption and plasma bicarbonate levels between 12 and 20 mEq/L
b. Impaired renal tubular acidification and serum bicarbonate levels often below 10 mEq/L
c. High serum K+ levels
d. The loss of large amounts of protein and glucose.
 
The correct answer is: a
 
The so called distal type of renal tubular acidosis, type 1 RTA, is characterized by
 
a. Reduced carbonate reabsorption and plasma bicarbonate levels between 12 and 20 mEq/L
b. Impaired renal tubular acidification and serum bicarbonate levels often below 10 mEq/L
c. High serum Na+ levels
d. Lack of response to aldosterone
 
The correct answer is: b
 
Bob is a 64 year-old man who develops acute renal failure while recovering from a particularly bad MI. His labs are Na+ 140 mEq/L, K+ 4 mEq/L, Cl- 115 mEq/L, CO2 5 mEq/L, pH = 7.12, PaCO2 13 mmHg, and HCO3- 4 mEq/L. Calculate his bicarbonate gap and then choose the best answer that explains Bob's acid-base problem.
 
a. His bicarbonate gap of 14 indicates he has more than one reason for his acidosis.
b. His anion gap of 20 is conclusive evidence of a respiratory acidosis.
c. His delta bicarbonate of 22 strongly suggests an underlying GI problem.
d. None of this makes the remotest sense to me and I think Bob is malingering.
 
The correct answer is: a

 
The following are true about calcium:
 
a. the extracellular calcium concentration is over 10,000
times that of intracellular calcium concentration
b. over 90% of intracellular calcium is protein-bound
c. cytosolic calcium is increased by the action of
phospholipase C
d. the effects of calcium are mainly mediated by
calmodulin
e. protein kinase C, an enzyme that phosphorylates
proteins requires calcium for maximum activity.
 
True statements include:
 
a. activation of a membrane receptor casues an exchange
of GTP for GDP
b. protein kinase is inactivated by cAMP
c. G-proteins that are bound to GTP are inactive
d. the a-subunite of G protein activates adenylate cyclase
e. G-proteins are made up of three subunits.
 
Glucogenesis:
 
a. maintains blood glucose druing overnight fast
b. occurs in both liver and muscles
c. is stimulated by elevated levels of acetyl CoA
d. is inhibited by fructose 2,6-biphosphate
e. uses carbon skeletons of amino acid
 
The following are true about cholesterol:
 
a. cholesterol is the most abundant sterol found in
human tissue
b. cholic acid is a precursor in the biosynthesis of
cholesterol
c. all the carbon atoms of cholesterol are derived
from acetyl CoA
d. HMG Co A reductase is the main regulator enzyme
of cholesterol synthesis
e. it is essential for the production of thyroxine
 
The following are true about blood glucose
 
a. muscle glycogen can not give rise to free
glucose because it lacks glucose 6-phospahte
b. liver glycogen is depleted after 12 hours of fasting
c. acetoacetate is an important source of carbon for
glucose synthesis
d. lactate dervied from red blood cells is an important
source of carbon for glucose synthesis.
e. after 48-hour of fasting, amino acid from the
breakdown of muscle protein is an important source
of carbon for gllucose synthesis
 
With regard to collagen molecule:
 
a. it is formed from trimers
b. it is formed from polypeptides containing a chains
c. glycine accounts for one-third of amino acids found
within collagens
d. it contains less hydroxyproline than elastin
e. ascorbate is essential for hydroxylation of proline
 
Type I collagen:
 
a. contains two a1 chains and one a2 chain
b. is the most common collagen
c. is the main type of collagen found in basement
membrane
d. is found in skin and bone
e. is found in cornea
 
Elastin:
 
a. is synthesized only by the liver
b. contains cross-linking polypeptides involving lysine
c. is the most common connective tissue in lungs
d. is digested by a1-antitrypsin
e. can be stretched to several times its length and can
still return to its original shape.
Vitamin B12:
 
a. is fat-soluble
b. requires a glycoprotein from absorption
c. contains a haeme ring
d. is required for the conversion of homocysteine to
methionine
e. is need for myelination of nerve fibres
 
In mucopolysaccharidoses:
 
a. the production of proteoglycan is increased
b. proteoglycan degradation is reduced
c. the lysosomal enzyme is defective
d. the urine excretes excess oligosaccharides
e. the body has an increased accumulation of
glycoaminoglycans
With regard to histones:
 
a. they are basic proteins
b. they are essential for the formation of stable DNA
c. mitochondria do not contain histones
d. in the chromosomes, the weight of the histones equal to that of the
DNA
e. the amino acid composition of histones show great variability
amongst different human races
 
In the regulation of genes:
 
a. more than 90% of the base sequences in human DNA have not
known function
b. extrons are the part of the gene that code for amino acids found in
the final proteins.
c. introns usually begins with the nucleotide sequence GT
d. splicing cut out the mRNA coded by introns.
e. promoters are responsible for initiating gene transcription
 
Thromboxane A2(TXA2):
 
a. is derived from the membrane phospholipid
b. requires lipoxygenase for its production
c. its production is decreased by non-steroidal anti-inflammatory
drugs
d. causes platelet aggregation
e. causes vasodilatation
 
In the lens:
 
a. the capsule is made up of type IV collagen
b. most metabolism is carried out in the anterior pole
c. hexokinase is a rate-limiting enzyme in carbohydrate metabolism
d. anaerobic glycolysis is the main source of energy
e. pentose phosphate pathway metabolizes 30% of the available
glucose
 
The following are true about the oxidation of glucose:
 
a. glycolysis produces 3% of the energy ultimately obtained from
glucose
b. the first stage of glycolysis involves phosphorylation of glucose to
1,6-fructose biphosphate.
c. glycolysis occurs within the mitochondria
d. glucose enters the Kreb's cycle as pyruvate
e. the Kreb's cycle generates 36 ATP molecules.
 
The following are true about DNA synthesis:
 
a. it requires DNA polymerase
b. reverse transcriptase enzymes are involved
c. moves in a 5'---> 3' direction
d. the rate of error in DNA synthesis is 1 in 105 base pairs
e. cytarabine inhibits DNA synthesis
 
With regard to DNA molecules:
 
a. they contain adenine, cytosine, guanine and uracil bases
b. they can be detected with Western blotting
c. they can be detected with Southern blotting
d. they are denatured at temperature of 1000C
e. they are denatured by pH of £ 7.14
 
G-proteins:
 
a. are activated by the binding of an extracellular ligand to a membrane receptor
b. can be mutated in tumour cells
c. mediate the action of glucocorticoid hormone
d. they are inactivated by cholera toxins.
e. bind to DNA to regulate gene transcription
 
The following is true about gluconeogenesis:
 
a. it occurs in liver
b. it occurs in kidney
c. it occurs in adipose tissue
d. it is inhibited by glucagon
e. it is stimulated by insulin
 
With regard to membrane receptors for hormones:
 
a. they are often glycoproteins
b. they are important for hormones made up of steroid
c. those for insulin exhibit an intrinsic protein kinase activity
d. glucagon uses calcium as a second messenger
e. catecholamines uses cyclic AMP as second messenger
 
 
 
 

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