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UHS DES Entrance Exam study materials
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UHS DES Entrance Exam practice questions

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Question 1Anatomy

In the standard anatomical position, the plane that passes longitudinally through the midline of the body and divides it into equal right and left halves is the:

  1. Coronal (frontal) plane
  2. Median (midsagittal) plane Correct answer.
  3. Transverse (horizontal) plane
  4. Parasagittal plane

Explanation

The median or midsagittal plane runs vertically through the body's midline and divides it into equal right and left halves. A coronal plane separates anterior from posterior, a transverse plane separates superior from inferior, and a parasagittal plane lies parallel to the midline but off-centre, so the halves it creates are unequal.

Question 2Anatomy

Which of the following bones is classified as a sesamoid bone?

  1. Scaphoid
  2. Calcaneus
  3. Patella Correct answer.
  4. Talus

Explanation

Sesamoid bones are small bones that develop within a tendon where it crosses a joint; the patella is the largest sesamoid, embedded in the quadriceps femoris tendon. The scaphoid is a carpal bone, and the calcaneus and talus are tarsal bones, all of which develop in cartilage rather than within a tendon.

Question 3Anatomy

Which muscle acts as the prime mover of elbow flexion regardless of the position of the forearm?

  1. Brachioradialis
  2. Biceps brachii
  3. Brachialis Correct answer.
  4. Triceps brachii

Explanation

Brachialis arises from the distal half of the anterior humerus and inserts on the ulnar tuberosity, so it flexes the elbow equally well in the supinated, midprone and pronated positions. Biceps brachii also flexes the elbow but is chiefly a supinator, brachioradialis works best with the forearm midprone, and triceps brachii extends the joint.

Question 4Anatomy

A fracture through the surgical neck of the humerus most typically injures which nerve?

  1. Median nerve
  2. Musculocutaneous nerve
  3. Radial nerve
  4. Axillary nerve Correct answer.

Explanation

The axillary nerve winds around the surgical neck of the humerus accompanied by the posterior circumflex humeral artery before entering the quadrangular space. Injury paralyses deltoid and teres minor and produces numbness over the lateral aspect of the shoulder.

Question 5Anatomy

Which structure passes through the foramen ovale of the sphenoid bone?

  1. Optic nerve
  2. Middle meningeal artery
  3. Maxillary nerve
  4. Mandibular nerve Correct answer.

Explanation

The foramen ovale in the greater wing of the sphenoid transmits the mandibular division of the trigeminal nerve together with the accessory meningeal artery. The maxillary nerve uses the foramen rotundum, the middle meningeal artery the foramen spinosum, and the optic nerve the optic canal.

Question 6Anatomy

At which site is the mitral valve best auscultated?

  1. Left second intercostal space near the sternal edge
  2. Left lower sternal border at the fourth intercostal space
  3. Right second intercostal space near the sternal edge
  4. Left fifth intercostal space at the midclavicular line Correct answer.

Explanation

The mitral valve is heard at the cardiac apex, which lies in the left fifth intercostal space at the midclavicular line. The tricuspid valve is heard at the left lower sternal border, the pulmonary valve at the left second intercostal space, and the aortic valve at the right second intercostal space.

Question 7Anatomy

Within the femoral sheath, the structure lying immediately medial to the femoral artery is the:

  1. Deep inguinal lymph nodes
  2. Femoral vein Correct answer.
  3. Sartorius muscle
  4. Femoral nerve

Explanation

The femoral sheath has three compartments: the femoral artery laterally, the femoral vein in the intermediate compartment, and the femoral canal containing lymphatics medially. The femoral nerve lies outside the sheath and lateral to the artery, while sartorius forms the lateral border of the femoral triangle.

Question 8Anatomy

Motor supply to the muscles of facial expression is provided by which cranial nerve?

  1. Hypoglossal nerve (XII)
  2. Trigeminal nerve (V)
  3. Glossopharyngeal nerve (IX)
  4. Facial nerve (VII) Correct answer.

Explanation

Motor fibres of the facial nerve supply the muscles of facial expression through its posterior auricular, temporal, zygomatic, buccal, marginal mandibular and cervical branches. The trigeminal nerve supplies the muscles of mastication, the hypoglossal nerve supplies the tongue, and the glossopharyngeal nerve supplies stylopharyngeus.

Question 9Anatomy

Which structure forms the anterior boundary of the epiploic foramen (foramen of Winslow)?

  1. Inferior vena cava
  2. Hepatoduodenal ligament Correct answer.
  3. Caudate lobe of the liver
  4. Head of the pancreas

Explanation

The epiploic foramen is bounded in front by the free edge of the lesser omentum, the hepatoduodenal ligament, which carries the portal triad of portal vein, hepatic artery proper and bile duct. Behind it lie the inferior vena cava and right crus of the diaphragm, above it the caudate lobe, and below it the first part of the duodenum.

Question 10Anatomy

Avascular necrosis of the femoral head after a displaced intracapsular fracture of the femoral neck results mainly from interruption of the supply from which artery?

  1. Internal iliac artery
  2. Lateral circumflex femoral artery
  3. Obturator artery
  4. Medial circumflex femoral artery Correct answer.

Explanation

In adults the femoral head is nourished mainly by retinacular branches of the medial circumflex femoral artery that run along the femoral neck; these are torn in displaced intracapsular fractures, leading to avascular necrosis. The artery of the ligamentum teres, derived from the obturator artery, contributes only a small amount in adults.

Question 11Anatomy

The apex of the heart is formed mainly by which chamber?

  1. Right ventricle
  2. Left atrium
  3. Right atrium
  4. Left ventricle Correct answer.

Explanation

The left ventricle forms the apex because its thick wall extends to the left inferior border of the heart. The right ventricle contributes largely to the anterior surface but does not reach the true apex. The atria lie superior and posterior to the ventricles and do not form the apex.

Question 12Anatomy

Which nerve provides the principal motor innervation to the diaphragm?

  1. Intercostal nerves
  2. Vagus nerve
  3. Thoracic splanchnic nerves
  4. Phrenic nerve Correct answer.

Explanation

The phrenic nerve arises from cervical segments C3 to C5 and descends through the thorax to supply the diaphragm. Intercostal nerves supply the intercostal muscles and abdominal wall, while the vagus and splanchnic nerves are mainly autonomic. Diaphragmatic paralysis after phrenic injury therefore impairs ventilation.

Question 13Anatomy

The tracheal rings that keep the airway patent are made of which cartilage type?

  1. Hyaline cartilage Correct answer.
  2. Fibrocartilage
  3. Calcified cartilage
  4. Elastic cartilage

Explanation

The tracheal rings are composed of hyaline cartilage, which provides rigid support while allowing some flexibility. Elastic cartilage occurs in the epiglottis and external ear, and fibrocartilage occurs in intervertebral discs and the pubic symphysis. Calcified cartilage is a pathological or age-related finding, not the normal ring composition.

Question 14Anatomy

Which muscle of the rotator cuff is the main medial rotator of the humerus at the shoulder joint?

  1. Supraspinatus
  2. Subscapularis Correct answer.
  3. Teres minor
  4. Infraspinatus

Explanation

Subscapularis inserts on the lesser tubercle of the humerus and is the principal medial rotator of the shoulder. Infraspinatus and teres minor are lateral rotators, while supraspinatus initiates abduction. The rotator cuff stabilizes the glenohumeral joint during these movements.

Question 15Anatomy

Which structure passes through the carpal tunnel alongside the flexor tendons?

  1. Radial artery
  2. Ulnar nerve
  3. Median nerve Correct answer.
  4. Ulnar artery

Explanation

The carpal tunnel is bounded by the flexor retinaculum and the carpal bones, and the median nerve is its major nerve content. The ulnar nerve and ulnar artery pass superficial to the retinaculum in Guyon's canal. The radial artery passes dorsally around the wrist rather than through the carpal tunnel.

Question 16Anatomy

The posterior wall of the inguinal canal is formed mainly by which layer?

  1. Parietal peritoneum
  2. Internal oblique muscle
  3. External oblique aponeurosis
  4. Transversalis fascia Correct answer.

Explanation

The posterior wall of the inguinal canal is formed mainly by the transversalis fascia, reinforced medially by the conjoint tendon. The external oblique aponeurosis forms the anterior wall, and the internal oblique and transversus abdominis muscles form the roof. The inguinal ligament forms the floor of the canal.

Question 17Anatomy

Which nerve is at risk during ligation of the superior thyroid vessels and supplies the cricothyroid muscle?

  1. Hypoglossal nerve
  2. External laryngeal nerve Correct answer.
  3. Recurrent laryngeal nerve
  4. Glossopharyngeal nerve

Explanation

The external branch of the superior laryngeal nerve runs close to the superior thyroid vessels and supplies the cricothyroid muscle. Injury can impair production of high-pitched sounds while leaving most other laryngeal muscles intact. The recurrent laryngeal nerve supplies the remaining intrinsic laryngeal muscles and is at risk lower in the tracheoesophageal groove.

Question 18Anatomy

Sensation from the skin around the umbilicus is carried by which spinal dermatome?

  1. T8
  2. T6
  3. T10 Correct answer.
  4. L1

Explanation

The umbilicus is the classic surface landmark for the T10 dermatome. T4 corresponds roughly to the nipple level, and L1 corresponds to the groin and inguinal region. These dermatome landmarks are useful for localizing spinal cord lesions.

Question 19Anatomy

Which cranial nerve leaves the skull through the jugular foramen?

  1. Facial nerve
  2. Vestibulocochlear nerve
  3. Glossopharyngeal nerve Correct answer.
  4. Optic nerve

Explanation

The glossopharyngeal nerve, along with the vagus and accessory nerves, exits the skull through the jugular foramen. The facial and vestibulocochlear nerves pass through the internal acoustic meatus, and the optic nerve passes through the optic canal. The trochlear nerve reaches the orbit through the superior orbital fissure.

Question 20Anatomy

Which structure lies immediately anterior to the left kidney?

  1. Pancreas Correct answer.
  2. Gallbladder
  3. Duodenum
  4. Liver

Explanation

The left kidney is related anteriorly to the pancreas, stomach, spleen, jejunum, and descending colon. The liver, gallbladder, and duodenum lie anterior to the right kidney. This asymmetric visceral relationship helps distinguish right-sided from left-sided renal anatomy.

Question 21Anatomy

A young man develops prominent winging of the scapula when he pushes his hands against a wall. Paralysis of which muscle is responsible for this finding?

  1. Latissimus dorsi
  2. Rhomboid major
  3. Trapezius
  4. Serratus anterior Correct answer.

Explanation

The long thoracic nerve (roots C5–C7) supplies serratus anterior, which holds the medial border of the scapula firmly against the rib cage. When this muscle is paralysed the medial border lifts away from the thorax, and the winging becomes most obvious when the patient pushes forward against resistance.

Question 22Anatomy

Which structure leaves the pelvis through the greater sciatic foramen above the piriformis muscle?

  1. Sciatic nerve
  2. Pudendal nerve
  3. Superior gluteal nerve Correct answer.
  4. Inferior gluteal nerve

Explanation

The superior gluteal nerve and vessels are the only structures that pass through the greater sciatic foramen above the upper border of piriformis, after which they run between gluteus medius and minimus. All other nerves and vessels in this region emerge below the muscle.

Question 23Anatomy

A 24-year-old man is diagnosed with a malignant tumour of the testis. To which lymph node group does the testis primarily drain?

  1. Superficial inguinal nodes
  2. External iliac nodes
  3. Para-aortic nodes Correct answer.
  4. Deep inguinal nodes

Explanation

The testis develops on the posterior abdominal wall and carries its lymphatic supply with it during descent, so lymph drains along the testicular vessels to the para-aortic (lumbar) nodes near the level of L2. The scrotal skin, by contrast, drains to the superficial inguinal nodes, which is why the two must be distinguished clinically.

Question 24Anatomy

In the male pelvis, the ductus deferens crosses anterior to which structure on its course towards the prostate?

  1. Ureter Correct answer.
  2. Rectum
  3. Obturator internus muscle
  4. External iliac vein

Explanation

After entering the pelvis at the deep inguinal ring, the ductus deferens runs medially and crosses anterior to the ureter before descending medial to the seminal vesicle to form the ejaculatory duct. At this crossing the ureter lies behind the vas, a relationship surgeons must appreciate during pelvic dissection.

Question 25Physiology

The sodium–potassium ATPase pump of the cell membrane transports ions in which ratio per molecule of ATP hydrolysed?

  1. 1 Na+ out of the cell and 1 K+ into the cell
  2. 3 Na+ into the cell and 2 K+ out of the cell
  3. 3 Na+ out of the cell and 2 K+ into the cell Correct answer.
  4. 2 Na+ out of the cell and 3 K+ into the cell

Explanation

Each cycle of the Na+/K+-ATPase moves three sodium ions out of the cell and two potassium ions into it while consuming one ATP. Because the pump is electrogenic, it contributes to the negative resting membrane potential and keeps intracellular sodium low.

Question 26Physiology

During the absolute refractory period of a neuron, a second action potential cannot be triggered mainly because:

  1. chloride conductance is increased
  2. voltage-gated calcium channels are blocked
  3. potassium channels remain closed
  4. voltage-gated sodium channels are in the inactivated state Correct answer.

Explanation

After depolarisation, voltage-gated sodium channels pass into an inactivated state from which they cannot reopen until the membrane repolarises. This inactivation is the basis of the absolute refractory period, which limits the maximum firing frequency of the neuron.

Question 27Physiology

Which coagulation factor depends on vitamin K for gamma-carboxylation of its glutamate residues?

  1. Factor I
  2. Factor VIII
  3. Factor VII Correct answer.
  4. Factor V

Explanation

Vitamin K is the cofactor for gamma-carboxylation of factors II, VII, IX and X, as well as proteins C and S. This modification allows these factors to bind calcium and phospholipid membranes during coagulation.

Question 28Physiology

The first heart sound is produced by:

  1. rapid ventricular filling during early diastole
  2. atrial contraction at the end of diastole
  3. AV valve closure at the onset of systole Correct answer.
  4. semilunar valve closure at the end of ejection

Explanation

The first heart sound coincides with closure of the atrioventricular valves as ventricular pressure rises above atrial pressure at the start of systole. The second sound is produced later by closure of the aortic and pulmonary valves.

Question 29Physiology

Which of the following is normally retained in plasma by the glomerular filtration barrier?

  1. Albumin Correct answer.
  2. Glucose
  3. Creatinine
  4. Urea

Explanation

The filtration barrier restricts large, negatively charged proteins, so albumin is largely retained in plasma while small solutes pass freely. Glucose, urea and creatinine are all small enough to be filtered at the glomerulus.

Question 30Physiology

The largest fraction of carbon dioxide in arterial blood is transported:

  1. as carbonic acid
  2. as bicarbonate ions Correct answer.
  3. dissolved in plasma
  4. bound to haemoglobin as carbamino compounds

Explanation

About 70 per cent of carbon dioxide is carried as bicarbonate after carbonic anhydrase converts CO2 and water inside red cells. The bicarbonate then leaves the red cell in exchange for chloride, which is known as the chloride shift.

Question 31Physiology

Intrinsic factor, secreted by gastric parietal cells, is required for the absorption of which nutrient?

  1. Iron
  2. Vitamin B12 Correct answer.
  3. Calcium
  4. Folate

Explanation

Intrinsic factor binds vitamin B12 in the small intestine and the complex is absorbed through receptors in the terminal ileum. Loss of parietal cells therefore causes B12 deficiency with megaloblastic anaemia and neurological features.

Question 32Physiology

The principal stimulus for aldosterone secretion by the adrenal cortex is:

  1. ACTH
  2. angiotensin II Correct answer.
  3. atrial natriuretic peptide
  4. hypernatraemia

Explanation

Aldosterone release is driven mainly by angiotensin II acting on the zona glomerulosa, with hyperkalaemia as a second strong stimulus. ACTH has only a minor trophic effect, and atrial natriuretic peptide inhibits rather than stimulates aldosterone.

Question 33Physiology

In skeletal muscle, after calcium binds to troponin C, the immediate next event is:

  1. tropomyosin shifts, exposing actin's myosin-binding sites Correct answer.
  2. calcium is pumped into the sarcoplasmic reticulum
  3. the A band shortens
  4. the myosin head hydrolyses ATP

Explanation

Calcium binding to troponin C pulls tropomyosin away from the actin filament, uncovering the sites where myosin heads can attach. Cross-bridge cycling with ATP hydrolysis follows this exposure, and the I band and H zone shorten while the A band stays constant.

Question 34Physiology

If a substance has a renal clearance greater than inulin clearance, it must be:

  1. secreted by the tubules Correct answer.
  2. reabsorbed by the tubules
  3. filtered only
  4. neither filtered nor secreted

Explanation

Inulin is filtered but neither reabsorbed nor secreted, so its clearance equals the glomerular filtration rate. A clearance above this value means the tubules add the substance to the urine by secretion, as happens with para-aminohippurate.

Question 35Physiology

The resting membrane potential of a typical neuron lies closest to the equilibrium potential of which ion?

  1. Sodium (Na+)
  2. Calcium (Ca2+)
  3. Potassium (K+) Correct answer.
  4. Chloride (Cl−)

Explanation

The resting membrane is much more permeable to K+ than to other ions because of open K+ leak channels, so the resting potential approaches the K+ equilibrium potential. Na+ permeability is low at rest, while Ca2+ and Cl− contribute comparatively little to the resting value.

Question 36Physiology

A rise in which substance shifts the oxyhaemoglobin dissociation curve to the right and reduces haemoglobin's affinity for oxygen?

  1. Fetal haemoglobin
  2. Carbon monoxide
  3. 2,3-Bisphosphoglycerate Correct answer.
  4. Methaemoglobin

Explanation

2,3-Bisphosphoglycerate binds to deoxyhaemoglobin and stabilises the T state, shifting the curve right and promoting oxygen unloading at the tissues. Fetal haemoglobin and carbon monoxide instead shift the curve left, while methaemoglobin cannot carry oxygen normally.

Question 37Physiology

Erythropoietin, the main hormone controlling red blood cell production, is produced predominantly by which cells?

  1. Renal peritubular interstitial cells Correct answer.
  2. Hepatic Kupffer cells
  3. Bone marrow megakaryocytes
  4. Gastric parietal cells

Explanation

The kidney senses tissue hypoxia and increases erythropoietin secretion mainly from peritubular interstitial fibroblast-like cells in the renal cortex. This hormone then stimulates erythroid progenitor proliferation and differentiation in the bone marrow.

Question 38Physiology

A patient has an end-diastolic volume of 120 mL and an end-systolic volume of 50 mL. If the heart rate is 70 beats per minute, what is the cardiac output?

  1. 7.0 L/min
  2. 3.5 L/min
  3. 8.4 L/min
  4. 4.9 L/min Correct answer.

Explanation

Stroke volume equals end-diastolic volume minus end-systolic volume, or 120 − 50 = 70 mL. Cardiac output is stroke volume multiplied by heart rate, so 70 mL × 70 beats/min = 4900 mL/min, or 4.9 L/min.

Question 39Physiology

In the glomerular capillary, which change would increase net filtration pressure and tend to raise glomerular filtration rate?

  1. Increased Bowman's capsule hydrostatic pressure
  2. Decreased efferent arteriolar resistance
  3. Decreased afferent arteriolar resistance Correct answer.
  4. Increased plasma oncotic pressure

Explanation

Decreased afferent arteriolar resistance increases renal blood flow and raises glomerular capillary hydrostatic pressure, which increases net filtration pressure and GFR. Capsular hydrostatic pressure and plasma oncotic pressure oppose filtration, so increases in either would lower GFR.

Question 40Physiology

Pulmonary surfactant reduces alveolar surface tension mainly by which mechanism?

  1. Increasing the viscosity of alveolar mucus
  2. Increasing the solubility of alveolar gas in plasma
  3. Reducing cohesive forces between water molecules at the air–liquid interface Correct answer.
  4. Promoting contraction of bronchial smooth muscle

Explanation

Surfactant phospholipids interpose between water molecules at the alveolar air–liquid interface, reducing cohesive forces and thereby lowering surface tension. This stabilises alveoli of different sizes and reduces the work of breathing.

Question 41Physiology

Gastric parietal cells secrete hydrogen ions into the canaliculus by which apical membrane mechanism?

  1. Carbonic anhydrase
  2. H+/K+ ATPase Correct answer.
  3. Cl−/HCO3− exchanger
  4. Na+/H+ exchanger

Explanation

The parietal cell apical membrane uses an H+/K+ ATPase that pumps H+ into the canaliculus in exchange for K+, generating the low luminal pH of gastric juice. Carbonic anhydrase supplies H+ intracellularly, but it is not the apical export pump.

Question 42Physiology

In the thick ascending limb of the loop of Henle, NaCl is reabsorbed while water remains behind. This segment is best described as:

  1. Impermeable to solute and permeable to water
  2. Freely water permeable and actively transports water
  3. The principal site of glucose reabsorption
  4. Impermeable to water but active in NaCl reabsorption Correct answer.

Explanation

The thick ascending limb is impermeable to water but actively reabsorbs NaCl via the Na+–K+–2Cl− cotransporter, which dilutes the tubular fluid and contributes to the medullary osmotic gradient. This water impermeability is essential for the countercurrent multiplier system.

Question 43Physiology

A patient with diabetic ketoacidosis has plasma Na+ 140 mEq/L, Cl− 100 mEq/L, and HCO3− 12 mEq/L. What is the anion gap and its interpretation?

  1. 28 mEq/L, indicating high-anion-gap metabolic acidosis Correct answer.
  2. 40 mEq/L, indicating high-anion-gap respiratory acidosis
  3. 16 mEq/L, indicating normal-anion-gap metabolic acidosis
  4. 12 mEq/L, indicating a normal anion gap

Explanation

The anion gap is calculated as Na+ − (Cl− + HCO3−), which is 140 − (100 + 12) = 28 mEq/L. A value above the normal range of roughly 8–12 mEq/L indicates high-anion-gap metabolic acidosis, consistent with ketoacid accumulation.

Question 44Physiology

During a marathon, a runner's skeletal muscles rely increasingly on slow-twitch fibers. Which characteristic best distinguishes slow-twitch (type I) fibers from fast-twitch (type II) fibers?

  1. High capillary density and high mitochondrial content Correct answer.
  2. Large fiber diameter and low oxidative capacity
  3. High myosin ATPase activity and rapid fatigue
  4. Predominance of white glycolytic metabolism

Explanation

Type I fibers are adapted for endurance: they have a rich capillary supply, many mitochondria, and high oxidative enzyme content, which supports sustained aerobic ATP production. Type II fibers generally have higher myosin ATPase activity and greater glycolytic capacity but fatigue more quickly.

Question 45Physiology

Which plasma protein is the principal determinant of plasma oncotic (colloid osmotic) pressure?

  1. Gamma globulin
  2. Transferrin
  3. Albumin Correct answer.
  4. Fibrinogen

Explanation

Albumin is the most abundant plasma protein and, because of its high concentration and relatively small molecular size, accounts for roughly three-quarters of plasma oncotic pressure. This oncotic pressure opposes capillary hydrostatic pressure and helps hold fluid within the vascular compartment. Fibrinogen and the globulins are present at much lower concentrations and contribute far less.

Question 46Physiology

A 58-year-old smoker has spirometry showing an FEV1/FVC ratio of 0.55 with an increased total lung capacity. Which pattern does this most likely represent?

  1. An obstructive ventilatory defect Correct answer.
  2. A pure diffusion defect
  3. A normal ventilatory pattern
  4. A restrictive ventilatory defect

Explanation

An FEV1/FVC ratio below the lower limit of normal (commonly less than 0.70) defines airflow obstruction, and the increased total lung capacity indicates hyperinflation, as seen in COPD. Restrictive disease instead reduces total lung capacity and usually preserves or raises the FEV1/FVC ratio. A diffusion defect alone does not produce this spirometric pattern.

Question 47Physiology

Which enzyme secreted by the duodenal mucosa converts pancreatic trypsinogen to active trypsin?

  1. Salivary amylase
  2. Pepsinogen
  3. Carboxypeptidase A
  4. Enteropeptidase Correct answer.

Explanation

Enteropeptidase (enterokinase), a brush-border enzyme of the duodenal mucosa, cleaves trypsinogen to form active trypsin. Trypsin then activates the remaining pancreatic zymogens, including chymotrypsinogen and procarboxypeptidase. This cascade is essential for protein digestion in the small intestine.

Question 48Physiology

A drug selectively blocks the rapid delayed rectifier potassium current (IKr) in ventricular myocytes. What is the most likely consequence for the ventricular action potential?

  1. Shortening of the phase 2 plateau
  2. Faster phase 0 depolarization
  3. Hyperpolarization of the resting membrane potential
  4. Prolonged phase 3 repolarization with a longer QT interval Correct answer.

Explanation

IKr is an outward potassium current that contributes importantly to phase 3 repolarization. Blocking it slows the return of the membrane potential to rest, prolonging action potential duration and the QT interval. This delayed repolarization predisposes to early afterdepolarizations and torsades de pointes.

Question 49Biochemistry

Which amino acid commonly found in proteins has an achiral α-carbon?

  1. Glycine Correct answer.
  2. Valine
  3. Alanine
  4. Threonine

Explanation

Glycine has a single hydrogen atom as its side chain, so its α-carbon carries two identical hydrogen substituents and is therefore achiral. Every other standard amino acid has four different groups on the α-carbon and is chiral; threonine and isoleucine actually possess two stereocentres each.

Question 50Biochemistry

Thiamine pyrophosphate serves as the coenzyme for which of the following reactions of carbohydrate oxidation?

  1. Phosphofructokinase-1
  2. Glucokinase
  3. Pyruvate dehydrogenase complex Correct answer.
  4. Hexokinase

Explanation

The pyruvate dehydrogenase complex requires thiamine pyrophosphate to decarboxylate pyruvate and transfer the two-carbon fragment to lipoate, linking glycolysis to the citric acid cycle. The kinases listed simply transfer phosphate from ATP to glucose or fructose-6-phosphate and require magnesium ions, not thiamine.