5/4 Biochemistry/ Mixed

Question 1

Short non-coding RNA sequences (micro RNA and small interfering RNA) role in gene silencing

Answer 1

Induce posttranscriptional gene silencing by base-pairing with complementary sequences within target mRNA molecules

Question 2

Hormone-sensitive lipase

Answer 2

Found in adipose tissue

Functions to drive the breakdown of stored triglycerides into free fatty acids and glycerol

During times of starvation, this enzyme provides substrated for hepatic gluconeogenesis and ketone body formation

Stimulated in response to stress hormone (catecholamines, glucagon, ACTH), inhibited by insulin

NOTE: brain can only use ketone bodies/glucose (FFA do not cross BBB), RBC only use glucose (no mitochondria

Question 3

Hereditary fructose intolerance

Answer 3

Aldolase B deficiency

Failure to thrive, jaundice, hepatomegaly

Question 4

Lynch syndrome (hereditary nonpolyposis colon cancer)

Answer 4

Autosomal Dominant

Defective DNA mismatch repair (MSH2, MLH1 mutations) > MutS and MutL homologs

Question 5

Acetyl-CoA’s role in gluconeogenesis

Answer 5

Acts as an allosteric activator by increasing the activity of pyruvate carboxylase (pyruvate to oxaloacetate). Note, this only occurs when Acetyl-CoA levels are high. When Acetyl-CoA is low, pyruvate is shunted toward Acetyl-CoA production, preventing the cell from becoming energy depleted

Question 6

Sucrose

Answer 6

Fructose + Glucose

Avoid in aldolase B deficiency (hereditary fructose intolerance)

Question 7

Most common genetic cause of hyperhomocysteinemia (increased thrombotic events)

Answer 7

MTHFR deficiency (methylene tetrahydrofolate reductase)

also deficiencies of Vit B12, 6, and folate

Question 8

More than one codon can code for a particular amino acid

Answer 8

Genetic code is degenerate

Wobble

Question 9

Secondary lactate deficiency

Answer 9

Can occur after inflammatory (celiac disease) or infectious (giardiasis) processes damage the microvilli of the small intestines

Abdominal distension, cramping, flatulence, diarrhea

Question 10

Conversion of norepinephrine to epinephrine

Answer 10

Phenylethanolamine-N-methyltransferase

Adrenal medulla

Cortisol increases converstion
(no pituitary= no ACTH= no cortisol)

Question 11

Galactosemia

Answer 11

Impaired galactose-1-phosphate metabolism

Deficiency of galactose-1-phosphate uridyl transferase

Vomiting, lethagy, failure to thrive soon after breastfeeding

Question 12

Scurvy (vit C deficiency)

Answer 12

perifollicular hemorrhages, myalgias, subperiosteal hematoma, gingivitis, hemarthrosis, petechial hemorrhages, impaired wound healing, weakened immune responses

Question 13

Base excision repair

Answer 13

Repairs non-bulky DNA base alterations (depurination, alkylationmoxidation, deamination)

Excessive consumption of dietary nutrutes can promote deamination

Glycosylases, endonuclease, lyase DNA polymerase, ligase

Question 14

Cofactor for oxaloacetate to phosphoenolpyruvate during gluconeogenesis

Answer 14

GTP (synthesized by succinyl-CoA synthetase during the conversion of succinyl-CoA to succinate in the Citric acid cycle)

During gluconeogenesis, phosphoenolpyruvate carboxykinases uses GTP to synthesize phosphoenolpyruvate from oxaloacetate

Question 15

Wernicke encephalopathy

Answer 15

Opthalmoplegia, ataxia, confusion (coma, death)

Foci of hemorrhage/necrosis in mammillary bodies

Chronic thiamine (B1) deficiency

Dx: baseline erythrocyte tranketolast activity is low but increases with addition of thiamine pyrophosphate

Treat with thiamine supplementation and glucose infusion

Question 16

Smooth ER

Answer 16

Contains enzymes for steroid and phopholipid biosynthesis

All steroid producing cells (e.g. cells in the adrenals, gonads, and liver) contains a well developed smooth ER

Question 17

Methylmalonic acidemia

Answer 17

AR, organic acidemia
Deficiency of methylmalonyl-CoA mutase

Metabolic acidosis, hypoglycemia, ketones, hyperammonemia

Elevated urine methylmalonic acid and propionic acid

Lethargy, vomiting, tachypnea

Question 18

Pompe disease

Answer 18

Deficiency of acid-a-glucosidase

Infancy, cardiomegaly, macroglossia, muscular hypotonia

Question 19

Glucose-6-phosphate dehydrogenase (G6PD deficiency)

Answer 19

Hemolytic anemia after infections (pneumonia, viral hepatitis), consumption of fava beans, meds (primaquine, sulfa drugs)

G6PD converts glucose 6-phosphate to ribulose-5-phosphate, 2 NADPH are produced (pentose phosphate pathway)

Major source for cellular NADPH
Necessary for reducing glutathione (preventing oxidative damage), biosynthesis of cholesterol, fatty acids, steroids

Question 20

Spinal muscular atrophy

Answer 20

Mutation in SMN1 gene

impaired assembly of snRNPs in lower motor neurons

Flaccid paralysis dye to degeneration of anterior horn cells

Question 21

Familial erythrocytosis

Answer 21

B-globin mutation > reduced binding of 2,3-BPG, results in loss of positive charge in pocket, causes hemoglobin A to resembled fetal hemoglobin (binds oxygen with a higher affinity, due to inability to interact with 2,3-BPG

Question 22

GLUT-4

Answer 22

Skeletal muscles, adipocytes

Insulin-sensitive

Question 23

What causes cataract formation in a patient with galactosemia

Answer 23

(Galactokinase deficiency)

Galactitol accumulates in lens of patients with galactosemia and causes osmotic damage leading to cataract formation.

Galactitol is formed from excess circulation galactose in galactosemia by aldose reductase

Question 24

Glucagon second messenger system mechanism

Answer 24

Exerts it effects via G-protein coupled receptors using adenylate cylase second messenger system, cAMP, protein kinase A

TSH, glucagon, PTH receptors all use this system!

Question 25

Lesch-Nyhan syndrome

Answer 25

- deficiency of HGPRT - increases the demand for de novo purine synthesis - activity of PRPP aminotransferase must increase to supply a sufficient quantity of purine nucleotides

Question 26

Cofactor for transaminases

Answer 26

Pyridoxine (Vit B6) Transamination reactions (N) typically occur between an amino acid and an a-keto acid Amino group is transferred to a-keto acid from amino acid and the a-keto acid thereby becomes an amino acid Glutamate reacts with oxaloacetate to form asparate and a-ketoglutarate

Question 27

Ataxia-telangiectasia

Answer 27

AR, defect in DNA-repair genes DNA is hypersensitive to ionizing radiation Cerebellar ataxia, oculocutaneous telangiectasias, repeated sinopulmonary infections, increased incidence of malignancy

Question 28

Rx of moderate-severe allergic asthma

Answer 28

Anti-IgE antibodies given as SQ injection (Omalizumab) Helps to reduce dependency on both oral and inhaled steroids

Question 29

Most important mediator of sepsis

Answer 29

TNF-a (produced by activated macrophages), induces a systemic inflammatory response (IL-1 and IL-6 are also involved)

Question 30

Theophylline intoxication

Answer 30

Seizures, tachyarrhythmias, nausea/vomiting, abdominal pain, diarrhea Rx: activated charcoal, B-blockers, benzodiazepines/barbituates (seizures)

Question 31

Best indicator of severity of mitral regurgitation?

Answer 31

Presence of audible S3 Indicates a high regurgitant volume and severe mitral regurg, left ventricular volume overload (reflects increased rate of left ventricular filling due to a large volume of regurgitant flow-reentering the ventricle during mid diastole)

Question 32

Pulsus paradoxus

Answer 32

decrease in systolic blood pressure of >10 mm Hg with inspiration seen in patients with cardiac tamponade (pericardial dx), severe asthma, COPD, constrictive pericarditis Quanitified by the difference between systolic pressure at which Korotkoff sounds first become audible during expiration and the pressure at which they are head throughout all the phases of respiration

Question 33

How do beta-adrenergic agonists control acute asthma/COPD?

Answer 33

Cause bronchial smooth muscle relaxation via increased intracellular cAMP

Question 34

Drugs that have been shown to improve long-term survival in patients with heart failure due to left ventricular systolic dysfunction

Answer 34

Beta blockers, ACE inhibitors, angiotensin II receptor blockers, aldosterone antagonists

Question 35

Stop codons

Answer 35

UAA, UAG, UGA Cause releasing factor proteins to bind the ribosome and stimulate release of the formed polypeptide chain Note: START = AUG

Question 36

Colchicine

Answer 36

Inhibits tubulin polymerization into microtubules (cytoskeleton) Used for acute Rx and prophylaxis of gout SE: nausea, abdominal pain, diarrhea

Question 37

Which artery supplies Broca's area and Wernicke's area

Answer 37

Middle cerebral artery Broca= superior division Wernicke= inferior division