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50 Cards in this Set
- Front
- Back
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Which of the following colonic polyps is not pre-malignant ?
A) Juvenile polyps B) Hamartomatous polyps associated with Peutz-Jeghers syndrome C) Villous adenomas D) Tubular adenomas |
A
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The most important prognostic factor in breast carcinoma is ?
A) Histological grade of the tumour B) Stage of the tumour at the time of diagnosis C) Status of estrogen and progesterone receptors D) Over expression of p-53 tumour suppressor gene |
B
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The tumour, which may occur in the residual breast or overlying skin following wide local excisionn and radiotherapy for mammary carcinoma, is ?
A) Leiomyosarcoma B) Squamous cell carcinoma C) Basal cell carcinoma D) Angiosarcoma |
D
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The type of mammary ductal carcinoma in situ (DCIS) most likely to result in a palpable abnormality in the breast is ?
A) Apocrine DCIS B) Neuroendocrine DCIS C) Well differentiated DCIS D) Comedo DCIS |
D
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Acinic cell carcinomas of the salivary gland arise most often in the ?
A) Parotid salivary gland B) Minor salivary glands C) Submandibular salivary gland D) Sublingual salivary gland |
A
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Which of the following is the most common presenting symptom of non-cirrhotic portal hypertension ?
A) Chronic liver failure B) Ascites C) Upper gastrointestinal bleeding D) Encephalopathy |
C
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All of the following are major complications of massive transfusion, except ?
A) Hypokalemia B) Hypothermia C) Hypomagnesemia D) Hypocalcemia |
A
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Which of the following statements is true regarding testicular tumours ?
A) Are embryonal cell carcinomas in 95% of cases B) Bilateral in upto 10 % cases C) Teratomas are more common than seminomas D) Usually present after 50 years of age |
B
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Mixed tumours of the salivary glands are ?
A) Most common in submandibular gland B) Usually malignant C) Most common in parotid gland D) Associated with calculi |
C
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In which of the following types of breast carcinoma, would you consider biopsy of opposite breast ?
A) Adenocarcinoma - poorly differentiated B) Medullary carcinoma C) Lobular carcinoma D) Comedo carcinoma |
C
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When carcinoma of stomach develops secondfarily to pernicious anemia, it is usually situated in the ?
A) Pre pyloric region B) PylorusC) Body D) Fundus |
B
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With regard to the malignant behaviour of leiomysarcoma, the most important criterion is ?
A) Blood vessel penetration by tumor cells B) Tumor cells in lymphatic channels C) Lymphocyte infiltration D) The number of mitoses per high power field |
D
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The treatment of choice for squamous cell anal cancer is ?
A) Abdomino perennial resection B) Laser fulgaration C) Chemoradiotherapy D) Platinum based chemotherapy |
C
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The most common malignancy found in Marjolin's ulcer is ?
A) Basal cell carcinoma B) Squamous cell carcinoma C) Malignant fibrous histiocytoma D) Neurotrophic malignant melanoma |
B
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Which one of the following statements is incorrect regarding stones in the common bile duct ?
A) Can present with Charcot's Triad B) Are suggested by a bile duct diameter > 6mm of ultrasound C) ERCP, sphincterotomy and balloon clearance is now the standard treatment D) When removed by exploration of the common bile duct the T -tube can be removed after 3 days |
D
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In a motor vehicle accident the seat belt leads to following EXCEPT ?
A) Reduced incidence of severe throracic injury B) Occurrence of small intestine and mesenteric injury C) Increased severity of decelerating head injury D) Trauma to major intra abdominal vessels |
A
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The most common cause of gastric outlet obstruction in India is ?
A) Tuberculosis B) Cancer of stomach C) Duodenal lymphoma D) Peptic ulcer disease |
D
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Treatment of choice for medullary carcinoma of thyroid is ?
A) Total Thyroidectomy B) Partial Thyroidectomy C) I131 ablation D) Hemithyroidectomy |
A
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Thoracic extension of cervical goiter is usually approached through ?
A) Neck B) Chest C) Combined cervico-thoracic route D) Thoracoscopic route |
A
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Which of the following is not an indication for cholecystectomy ?
A) 70 year old male with symptomatic gallstones B) 20 year old male with sickle cell anaemia and symptomatic gallstones C) 65 year old female with a large gallbladder polyp D) 55 year old with an asymptomatic gallstone |
D
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The initial investigation of choice for a post cholecystectomy biliary stricture is ?
A) Ultrasound scan of the abdomen B) Endoscopic cholangiography C) Computed tomography D) Magnetic resonance cholangiography |
C
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The treatment of choice for an 8 mm retained common bile duct (CBD) stone is ?
A) Laparoscopic CBD exploration B) Percutaneous stone extraction C) Endoscopic stone extraction D) Extracorporeal shock wave lithotripsy |
C
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The direction of flow of venous blood in conditions of valve incompetence affecting perforating veins of lower limb is ?
A) along gravity B) superficial to deep C) along osmotic gradient D) deep to superficial |
D
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While doing thoracocentesis, it is advisable to introduce needle along ?
A) upper border of the rib B) lower border of the rib C) in the center of the intercostal space D) in anterior part of intercostal space |
A
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Abbey-Estlander flap is used in the reconstruction of ?
A) Buccal mucosa B) Lip C) Tongue D) Palate |
B
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In which one of the following conditions the Sialography is contraindicated ?
A) Ductal calculus B) Chronic parotitis C) Acute parotitis D) Recurrent sialadenitis |
C
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A 69 year old male patient having coronary artery disease was found to have gall bladder stones while undergoing a routine ultrasound of the abdomen. There was no history of biliary colic or jaundice at any time. What is the best treatment advice for such a patient for his gallbladder stones ?
A) Open cholecystectomy B) Laparoscopic cholecystectomy C) No surgery for gallbladder stones D) ERCP and removal of gallbladder stones |
C
Explanation:[Ref: Bailey & Love,23rd,Pg-975; Harrison,15th,Pg-1781][By - Dr. J.M.A. Bruno Mascarenhas, thanks...!!!] [Explanation - Presence of Gall stones per se is not an indication for Surgery in a normal patient. This patient is asymptomatic as well as having history of CAD Although laparoscopic cholecystectomy is the standard method for treating patients with symptomatic cholelithiasis or those with complications of cholelithiasis, other treatments may be useful in selected patients - Oral Dissolution Therapy - Agents used - Bile acids - chenodeoxycholic acid (CDCA) or ursodeoxycholic acid (UDCA) [dissolve predominantly cholesterol gallstones in selected patients] [At therapeutic dosages, CDCA causes diarrhea, induces transient abnormalities in liver function tests, and increases the concentration of serum low-density lipoprotein cholesterol in some patients, whereas UDCA is free of side effects and has therefore become the preferred oral agent] Prerequistes - Stones must be Radiolucent Gall bladder must be - fuctioning on oral cholecystography Results - are related to the initial size of the stones. Radiolucent gallstones less than 15 mm. in diameter will dissolve in up to 40% of patients within 2 years; longer therapy does not increase efficacy. Approximately 15% of patients will require cholecystectomy during therapy, and gallstones recur in approximately 50% of patients within 5 years without prophylaxis. Ideal candidate - The ideal candidate for oral dissolution is a thin, young female who has a small number of small, floating stones. Oral dissolution therapy may be useful in selected symptomatic patients who are unwilling to undergo laparoscopic cholecystectomy or who have precluding risk factors. Contact Dissolution Therapy - Methyl tert-butyl ether is a potent lipid solvent that dissolves gallstones within hours when introduced into the gallbladder through a pigtail catheter appropriately positioned under local anesthesia by an experienced radiologist. An automatic infusion-withdrawal device prevents overflow into the duodenum and washes the gallbladder free of debris as the stones disintegrate. Extracorporeal Shock Wave Lithotripsy - The procedure was less efficacious in patients who had larger or multiple stones] Your answer is correct.If you attempt these questions after logging in, then the responses will be used to compile your performance graph.You can later view your performance graph and assess your exam preparation progress and concentrate on weak areas.User Responses to This Mcq6.76%17.06%57.94%18.24% (Single Best Answer) |
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A 50 year old woman presented with history of recurrrent episodes of right upper abdominal pain for the last one year. She presented to casualty with history of jaundice and fever for 4 days. On examination, the patient appeared toxic and had a blood pressure of 90/60 mmHg. She was started on intravenous antibiotics. Ultrasound of the abdomen showed presence of stones in the common bile duct. What would be the best treatment option for her ?
A) ERCP and bile duct stone extraction B) Laparoscopic cholecystectomy C) Open surgery and bile duct stone extraction D) Lithotripsy |
A
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A blood stained discharge from the nipple indicates ?
A) Breast abscess B) Fibroadenoma C) Duct papilloma D) Fat necrosis of breast |
C
Explanation: [By - "Dr. Rohit Tekriwal", thanks...!!!] [Explanation - Discharge from single duct - Blood Stained - Intraductal Carcinoma, Intraductal papilloma, Duct ectasia Serous - Fibrocystic disease, Duct ectasia, Carcinoma Discharge from more than one duct - Blood stained - carcinoma, ectasia, fibrocystic disease Serous - Fibrocystic disease, Duct ectasia, Carcinoma Grumous - Duct ectasia Purulent - Infection Milk - Lactation, hypothyroidism, pituitary tumor Discharge from surface - Paget's Skin disease (Eczema, Psoriasis) Rare causes (e.g. Chancre)] Your answer is correct.If you attempt these questions after logging in, then the responses will be used to compile your performance graph.You can later view your performance graph and assess your exam preparation progress and concentrate on weak areas.User Responses to This Mcq8.1%8.1%80.48%3.33% (Single Best Answer) |
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Breast conservation surgery for breast cancer is indicated in one of the following conditions ?A) T1 breast tumor
B) Multicentric tumor C) Extensive in situ cancer D) T4b breast tumor |
A
Explanation: [By - "Dr. Rohit Tekriwal", thanks...!!!] [Explanation - Indications of Mastectomy - Large tumors (in relation of the size of breast) Central tumors beneath or involving the nipple Multifocal disease Local recurrence Patients preference T1 breast tumor - size of tumor is less than 2 cms in greatest dimension (ideal case for breast conservation surgery) Multicentric tumor - conservative surgery is not sufficient Extensive in situ cancer - conservative surgery is not sufficient T4b breast tumor - tumor of any size, with Edema (including peau d' orange) or ulceration of the skin of breast or satellite skin nodules confined to the same breast (here obviously conservative surgery cannot be done). So, A is the answer] [D) Schwartze Handbook Pg-543 - By Dr. Somnath Das]Your answer is correct.If you attempt these questions after logging in, then the responses will be used to compile your performance graph.You can later view your performance graph and assess your exam preparation progress and concentrate on weak areas.User Responses to This Mcq73.31%10.12%11.35%5.21% Recent Topicsactivation of adocuments to beTell me some benew mock test sNEET-PGPost New TopicMain Menu HomeBook Mark AdmissionsUpcat Dental 2016 COMEDKPGET 2016 Kerala PGDEE 2016 Kerala PGMEE 2016Gujarat PGMEE 2016 Recent UpdatesAverage Odds Ratio Distribution Symmetric DistributiPositively Skewed DiAdmin UpdatesMcqs Ranks Section UMocktest AIPGMEE 201Radiotherapy Mcqs UpOtorhinolaryngology Orthopaedics Mcqs UpNewest MemberKhalo Mcqs Toppers(This Month)abonada1972 (100.00 %)RMH (69.57 %)Raviprakash191518 (33.33 %)Netmedicos ExpertsAngelina (124)txguy (101)Karuna Mujalda (50)Netmedicos (43)Sandhya (42)Tanushree Pandi (21)sudipto (20)sanju5 (10)Jiss Joseph Pan (10)Smitha (10)All logos and trademarks at this site are the property of their respective owner(s). © 2008 by Netmedicos.com. All rights reserved.Any queries, feed back, suggestions, criticism, comments or clarifications may be submitted by the feedback form. By using this website you are agreeing to have read and accepted the Disclaimer & Privacy Policy and abide by our copyright laws. |
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Which of the following statement(s) is/are true concerning body fuel reserves?
a. The largest fuel reserve in the body is skeletal muscle b. Fat provides about 9 calories/gram c. Free glucose and glycogen stores are a trivial fuel reserve d. Body protein is a valuable storage form of energy |
Answer: b, c
The body contains fuel reserves which it can mobilize and utilize during times of starvation or stress. By far the greatest energy component is fat, which is calorically dense since it provides about 9 calories/gram. Body protein comprises the next largest mass of utilizable energy, but amino acids yield only about 4 kcal/gram. Unlike fat reserves, body protein is not a storage form of energy but rather serves as a structural functional component of the body; loss of body protein, if severe, is associated with functional consequences. Glycogen stored in muscle and liver and free glucose have a trivial caloric value of less than 1000 kcal for a 70 kg male. |
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Translocation is promoted in three general ways: 1) altered permeability of the intestinal mucosa as caused by shock, sepsis, distant injury, or cell toxins; 2) decreased host defense (secondary to glucocorticoid administration, immunosuppression, or protein depletion; and 3) an increased number of bacteria within the intestine. Because many factors that facilitate bacteria translocation occur simultaneously in surgical patients, these effects may be either additive or cumulative. In addition, many patients in Surgical Intensive Care Units do not generally receive enteral feedings and therefore current parenteral therapy results in gut atrophy which further promotes translocation.Which of the following statement(s) is/are true concerning nutritional support of the injured patient?
a. The goal of nutritional support is maintenance of body cell mass and limitation of weight loss to less than 25% of preinjury weight b. Under-nutrition may compromise the patient’s available defense mechanisms c. Nutritional support is an immediate priority for the trauma patient d. Fifty percent of non-nitrogen caloric requirements should be provided in the form of fat |
Answer: b
Metabolic response to injury results in increased energy expenditure. If energy intake is less than expenditure, oxidation of body fat stores and erosion of lean body mass will occur with resultant loss of weight. When weight loss exceeds 10–15% of body weight, the complications of malnutrition interact with disease processes, with increased morbidity and mortality rates. The goal of nutritional support is maintenance of body cell mass and limitation of weight loss to less than 10% preinjury. The major impact of nutritional support in the trauma patient is to aid host defense. Under-nutrition may compromise the available host defense mechanism and may thus increase the likelihood of invasive sepsis, multiple organ system failure, and death. Resuscitation, oxygenation and arrest of hemorrhage are immediate priorities for survival. Nutritional support is an essential part of the metabolic care of the critically ill patient and should be instituted after resuscitation before significant weight loss occurs. The nutritional requirements of a trauma patient can be determined by determining basal metabolic rate with appropriate increases based on extent of injury and hospital activity. After initial determination of nitrogen requirements, caloric requirements should be distributed at a ratio of 70% as glucose and 30% as fat. |
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Under certain circumstances, the gut may become a source of sepsis and serve as the motor of systemic inflammatory response syndrome. Microbial translocation is the process by which microorganisms migrate across the mucosal barrier to invade the host. Which of the following mechanisms can promote bacterial translocation?
a. An increased number of gut bacteria b. Altered intestinal mucosal permeability c. Decreased host defense mechanisms d. Lack of enteral feeding |
Answer: a, b, c, d
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Altering the amino acid profile in total parenteral nutrition solutions can be of benefit in certain conditions. Which of the following conditions are associated with a benefit by supplementation with the amino acid type listed?
a. Acute renal failure and essential amino acids b. Hepatic failure and aromatic amino acids c. Short gut syndrome and glutamine d. Chronic renal failure and essential amino acids |
Answer: a, c
In a number of conditions, altering the amino acid profile of the total parenteral nutrition solution can be of benefit. TPN with amino acids of high biologic value may decrease the mortality in patients with acute renal failure. These solutions, containing high quality amino acids, can improve nitrogen balance and diminish urea nitrogen. Provision of essential amino acids only allows the body to maximally utilize nitrogen for the synthesis of non-essential amino acids and thereby helps prevent rapid rises in blood urea nitrogen. There appears to be no advantages to using essential amino acids if the patient is already being dialyzed every other day and therefore a balanced standard amino acid solution is recommended. Because of liver damage and portasystemic shunting, patients with hepatic failure develop derangements in circulating levels of amino acids. The plasma aromatic/branch chain amino acid ratio is increased favoring the transport of aromatic amino acids across the blood brain barrier. These amino acids are precursors of false transmitters which contribute to lethargy and encephalopathy. Treatment of individuals with liver failure with solutions enriched in branch chain amino acids and deficient in aromatic amino acids results in improved tolerance to administration of protein and clinical improvement in encephalopathic states. Glutamine-enriched TPN partially attenuates villous atrophy and may be useful in treatment of short gut syndrome. |
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Most hormone receptors are localized on the cell membrane and transduce hormone binding into altered levels of intracellular messengers. A limited number of intracellular receptors do exist. Which of the following statement(s) is/are true concerning intracellular receptors?
a. The messengers or hormones must by lipophilic b. These intracellular receptors generally regulate protein synthesis c. The intracellular receptors are located entirely in the nucleus of the cell d. A heat-shock protein serves as an inhibitor protein blocking the DNA-binding domain of the steroid receptor |
Answer: a, d
Although most hormone and other messenger receptors are extracellular, intracellular receptors have been identified. The hormone messengers involved for these receptors are primarily steroid and thyroid hormones and are lipophilic. By virtue of their hydrophobic nature, they are able to readily penetrate the lipid portion of the cell membrane. Receptors for these hormones exist intracellularly in the cytoplasm or in the nucleus and generally act as regulators of gene expression. These hydrophobic signaling molecules exist in plasma bound to protein, so that the concentration of this class of regulators does not fluctuate rapidly in plasma and their actions are generally slower in onset and more prolonged than those of water-soluble class. Some types of steroid receptors, particularly for glucocorticoids, are located in the cytosol in the inactive state. Once the ligand binds, the receptor undergoes a conformational change, termed activation. This allows cytoplasmic receptors to move into the nucleus and bind to DNA. Receptors already in the nucleus increase their affinity for DNA. In the case of glucocorticoid receptors and probably others of this class, the inactive receptor is associated with another protein, the heat-shock protein. They block the DNA-binding domain of the receptor. Activation involves the dissociation of the inhibitor protein. |
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Examples of ion channel blockers include:
a. Tetrodotoxin b. Amiloride c. Xylocaine d. None of the above |
Answer: a, b, c
Channel blockade is an important mechanism of action for toxins and some therapeutic agents. The deadly toxin of the puffer fish, tetrodotoxin, acts by blocking the Na+ channels that are responsible for the conduction of nerve impulse. The diuretic, amiloride, acts by blocking the Na+ channels that inhabit the apical membrane of the epithelial cells of the distal nephron. Local anesthetics such xylocaine also act by blocking ion channels. |
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Which of the following statement(s) is/are correct concerning cell junctions?
a. The major occluding junction is the tight junction or zonula occludens b. Tight junctions are usually located near the basal pole of the cell c. Desmosomes are button-like points of attachment which serve to weld together adjacent cells d. Gap junctions are a type of cell junction specialized for cell communication |
Answer: a, c, d
Cell junctions are classified as occluding, anchoring, and communicating. The major occluding junction is the tight junction or zonula occludens which connects cells in epithelia and thereby allows epithelia to serve as selective permeability barriers. Tight junctions are normally located near the apical pool of the cell and form a belt that completely encircles the cell. Anchoring junctions connect the cytoskeleton of the cell to the extracellular matrix or neighboring cells. Morphologically these are adherens junctions or desmosomes. Desmosomes are button-like points of attachment with a prominent intracellular plaque that serves to weld together adjacent cells by serving as anchoring sites for intermediate filaments within the cell. The third functional type of cell junction is a gap junction which is specialized for communication. This junction mediates both electrical and chemical coupling. |
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There are two properties of the cell necessary to maintain nonequilibrium cellular composition; the first is selectivity and the second is energy conversion. Which of the following statement(s) is/are true concerning energy converting transport?
a. The site of energy conversion and transport in the plasma membrane involves the phospholipid component b. The Na+-K++-ATPase derives energy from hydrolysis of extracellular ATP c. In some systems, energy inherent in the transmembrane ion gradient can be used to drive transport of a second species d. Examples of species transported via secondary active transport include hydrogen ions, calcium, amino acids and glucose |
Answer: c, d
The selectivity of the plasma membrane, although impressive, cannot account for the nonequilibrium composition of living cells. A cell can be maintained in a nonequilibrium state only by continual expenditure of energy. The maintenance of a steady-state, nonequilibrium cellular composition is possible because the plasma membrane is the site of energy converters, membrane proteins that function as biologic transport machines using energy derived from metabolic processes to perform transport work. The archetype for the biologic transport machine is the Na+-K+-ATPase, a membrane protein that hydrolyses cytosolic ATP and couples the resulting free energy to transport of Na+ and K+. A second equally important type of energy-converting transporter is one in which the energy inherent in a transmembrane ion gradient, usually that of Na+ can be used to drive the transport of a second species such as protons, calcium, amino acids, or glucose. |
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An important step in protein synthesis is transcription. Which of the following statement(s) is/are true concerning this process?
a. The first step in gene transcription involves separating the double helix of DNA by an enzyme known as DNA polymerase b. The initial product of DNA transcription is called heterogeneous nuclear RNA which codes directly for proteins c. After processing is complete, the mRNA is exported from the nucleus to the cytoplasm d. Only one protein can be produced from an initial mRNA strand |
Answer: c
Transcription of a gene begins at an initiation site associated with a specific DNA sequence, termed a promoter region. After binding to DNA, the RNA polymerase opens up a short region of the double helix to expose the nucleotides. Once the two strands of DNA are separated, the strand containing the promoter acts as a template to which ribonucleoside triphosphates base pair by hydrogen bonds. The initial products of transcription are known as heterogeneous nuclear RNA because of their large size variation. These primary transcripts are then processed to form mRNA. RNA splicing accounts for mature RNA being much shorter than nuclear RNA. Moreover, alternative splicing can lead to the production of different mRNA molecules and in some cases different proteins from the same gene. mRNA is exported from the nucleus only after processing is complete. |
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Intracellular organelles involved with protein synthesis include
a. Mitochondria b. Endoplasmic reticulum c. Golgi complex d. Lysosomes |
Answer: b, c
Mitochondria are the major source of energy production in eukaryotic cells. The endoplasmic reticulum is the network of interconnected membranes forming closed vesicles, tubules, and saccules. The endoplasmic reticulum has a number of functions and is primarily involved in the synthesis of proteins and lipids. Adjacent to the rough endoplasmic reticulum and functionally involved in the sorting and package of secreted protein is the Golgi complex. Lysosomes are membrane-limited organelles containing acid hydrolytic enzymes that degrade polymers such as proteins, carbohydrates, and nucleic acids. |
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The activities of the cytoskeleton is dependent on which of the following types of filaments?
a. Microtubules b. Intermediate filaments c. Actin filaments d. None of the above |
Answer: a, b, c
The cytoskeleton is a collection of filamentous protein structures that allow cells to assume and maintain a variety of shapes, to produce directed movement of organelles within the cell, and to affect movement of the entire cell relative to other cells. These multiple activities depend upon three main types of filaments: actin filaments, intermediate filaments, and microtubules. |
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The best understood intracellular messenger is cyclic AMP (cAMP). Which of the following statement(s) concerning this intracellular messenger is/are correct?
a. Intracellular cyclic AMP is constantly degraded by a specific enzyme, cAMP phosphodiesterase b. Most of the actions of cAMP are mediated by activation of protein kinase A c. Intracellular levels of cAMP are relatively stable and change solely in response to activation of adenylate cyclase d. cAMP is the only cyclic nucleotide active as an intracellular messenger |
Answer: a, b
The prototypic intracellular messenger is cAMP. To function as a mediator, the concentration of cAMP must change rapidly. In resting cells, cAMP is continuously being degraded by a specific enzyme, cAMP phosphodiesterase. cAMP levels can increase 10-fold or more within seconds of receptor binding through activation of adenylate cyclase. cAMP acts as an allosteric regulator, and most, if not all, of its actions are mediated by activation of cAMP-dependent protein kinase A. cAMP is not the only cyclic nucleotide active as an intracellular messenger. Most animal cells also produce cGMP. Intracellular calcium ions also serve as second messengers in a large number of cells. |
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Proteins that are destined to be secreted from the cells must pass through a series of organelles. These organelles include:
a. Endoplasmic reticulum b. Golgi apparatus c. Mitochondria d. Lysosomes |
Answer: a, b, d
Proteins targeted for the secretory pathway most commonly begin with translocation from the cytoplasm across the lipid bilayer into the lumen of the endoplasmic reticulum. It must then pass through a number of compartments including the Golgi apparatus where they are further processed and sorted and end up in a secretory vesicle or lysosome. |
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Cell regulation can be thought of as the effector side of cell communication. Most commonly cell regulation occurs by means of extracellular chemical messengers. Which of the following statement(s) is/are true concerning these messengers?
a. Paracrine regulation involves a messenger which is produced and acts systemically b. The extracellular signal or stimulus is received by a receptor on or in the target cell c. Neurocrine regulation depends on a physical connection between the neuron and the target cell d. Most hormones, local mediators, and neurotransmitters readily cross the cell plasma membrane |
Answer: b, c
Depending on how the extracellular messenger arrives, cell regulation can be classified as paracrine, endocrine, or neurocrine. In paracrine regulation, a chemical messenger or mediator is produced and acts locally. In endocrine regulation, the extracellular messengers (hormones) are released into the blood and act on target cells anywhere on the body that has appropriate receptors. In neurocrine regulation, neurons secrete transmitters into highly localized regions, the synaptic cleft, so that the regulation depends on a physical connection between the neuron and the target cell as well as the presence of a specific receptor. In almost all cases of cell regulation, the extracellular signal or stimulus is restricted to being an informational molecule. This information is received by receptor on or in the target cell, which generally has an affinity for the signal molecule. Most hormones, local mediators, and neurotransmitters are water-soluble and cannot readily cross the plasma membrane. |
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Which of the following statement(s) is/are true concerning translation of the mRNA message to protein synthesis?
a. An adaptor molecule, tRNA, recognizes specific nucleic acid bases and unites them with specific amino acids b. Covalent attachment of tRNA to amino acids is energy dependent c. The formation of a peptide bond between the growing peptide chain and the free amino acid occurs in the free cytoplasm d. Complete protein synthesis takes hours |
Answer: a, b
The synthesis of protein involves conversion from a four-letter nucleotide language to one of 20 chemically distinct amino acids. This process is referred to as translation. There is no mechanism for direct chemical recognition between specific nucleic acid bases and specific amino acids. Instead, an adaptor molecule, tRNA, is used. Each tRNA carries only one amino acid and must be recognized by a distinct enzyme which catalyzes the covalent attachment of the carboxyl end of the amino acid to the end of the tRNA in a process using ATP. Protein synthesis occurs by the formation of a peptide bond between the carboxyl terminal of the growing peptide chain and the free amino acid of deactivated amino acid tRNA. This event does not occur in free solution, but within ribosomes. Ribosomes are protein synthesizing machines that bring all of the necessary components together in the correct sequence and spacial orientation. Protein synthesis consumes a great deal of energy because four high-energy phosphate bonds must be split to make each peptide bond. Complete synthesis of a single protein takes 30 seconds to a few minutes, but multiple ribosomes can initiate translation and be moving down the mRNA molecules simultaneously, thus increasing the rate of protein synthesis. |
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Which of the following statement(s) is/are true concerning carrier proteins?
a. Carrier proteins are distinguished by three types of mechanisms: carrier-type, channel-type, and conduction-type b. Conformational changes in the membrane protein occur between the conducting and the nonconducting states c. A channel-type carrier protein has two states—closed and open d. Carrier-type transport proteins are equally accessible from either side of the membrane |
Answer: b, c
Most transport proteins appear to function as carriers, rather than channels. Important distinctions can be made between types of carrier proteins on the basis of transport kinetics. Two primary types can be distinctly identified based on carrier-type and channel-type mechanisms. The most important difference between the channel mechanism and the carrier mechanism is the role in the transport event played by conformational changes in the membrane protein. The channel is depicted as having two states, closed and open, so that it operates like a switch. In contrast, carrier transport is envisioned as requiring a cycle of conformational changes. The transport of one molecule of substrate requires one complete cycle of the protein. In a channel mechanism, binding sites within the open pore are equally accessible from either side of the membrane, whereas in a carrier mechanism, the binding site is available only one side of the membrane at any instant. |
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Which of the following statement(s) is/are true concerning cellular ion channels?
a. Ion channels are transmembrane proteins that form pores that can conduct ions across the plasma membrane b. Ion channels are formed by membrane-spanning peptides that are arranged so that polar moieties line a central core c. Ion channel proteins undergo conformational changes between open states and closed states d. Ion channels can be blocked |
Answer: a, b, c, d
Ion channels are transmembrane proteins that form pores that can conduct ions across the plasma membrane. Ion channels are formed by membrane-spanning peptides that are arranged so that polar moieties line a central pore. These polar groups take the place of the water of hydration, which stabilizes an ion in an aqueous solution creating, in essence, a water-like environment into which the ion can partition and move in the presence of the appropriate driving force. Ion channels are permissive transport elements. Ions flow through a channel only through the presence of an appropriate driving force. Ion channels do not conduct all the time, rather the channel protein undergoes conformational changes between a conducting (open) state and nonconducting (closed) state. These conformational changes are collectively referred to as gating. The conduction process can also be blocked by ions or organic compounds that enter the channel, bind there, and occlude the pore. |
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Which of the following statement(s) is/are true concerning cell membrane receptors?
a. The largest family of cell surface receptors are the G-protein-linked receptors b. Activities of the G-protein involve binding and hydrolysis of ATP c. The G protein receptor generates an intracellular messenger commonly through the use adenylate cyclase d. Tyrosine kinase receptors are considered G-protein-linked receptors |
Answer: a, c
All water-soluble regulatory molecules bind to the cell surface receptor proteins. Binding of the appropriate ligand evokes an intracellular signal which usually regulates enzyme activity, membrane transport, or in some cases gene expression. Most cell surface receptors belong to one of three functional classes—these are ion channel receptors, catalytic receptors, and G-protein-linked receptors. Ion channel receptors are multisubunit assemblies which, with each subunit, have a multiple membrane spanning segment. Together these subunits form an ion-selected pore that can be gated by a change in transmembrane electrical potential or binding of a ligand to one of the subunits. Catalytic receptors are membrane proteins that possess enzymatic activity. The best understood receptors of this class are the tyrosine kinases. The largest family of cell surface receptors are the G-protein-linked receptors. G-proteins are a family of proteins that bind and hydrolyze GTP. The final component of single transduction by G-protein-linked cell surface receptors is the effector that generates the intracellular messenger. The two best understood effectors are adenylate cyclase, which converts ATP to cAMP, and the polyphosphoinositide-specific phospholipase C. |
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Which of the following statement(s) is/are true concerning DNA?
a. DNA is contained only in the nucleus of the cell b. DNA strands are encoded by the sequence of four bases—adenine, guanine, cytosine and uridine c. The basic unit of information of DNA is the intron, a sequence of three bases d. There are an infinite number of possible codons |
Answer: a
The genetic blueprint of an organism is carried in the nucleus of every cell, encoded by the sequence of four bases—adenine, guanine, cytosine and thymine, which together make up two long chains bound together by hydrogen bonds to form a DNA double helix. A gene is a segment of DNA that is transcribed into a corresponding RNA molecule that either codes for a protein or forms a structural RNA molecule. Genes are commonly between 10,000 and 100,000 base pairs in length and include, in addition to the coding sequence, flanking regions and intervening sequences, termed introns. Introns are removed from the primary RNA transcript by a process called splicing. The basic unit of information is the codon, a sequence of three bases or triplet. The four nucleotide bases arranged as triplets lead to 64 possible codons. Sixty-one of these code for amino acids and three are termination signals called stop codons. |
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A striking feature of living cells is a marked difference between the composition of the cytosol and the extracellular milieu. Which of the following statement(s) concerning the mechanisms of maintenance of these differences is/are true?
a. The cell membrane is able to maintain a 10,000 fold gradient between the extracellular concentration of ionized calcium and the intracellular concentration b. The key to these differences is the fact that the plasma membrane is normally impermeable to sodium, potassium and calcium c. The selectivity of biologic membranes is highly consistent and seldom changes d. The selectivity of cell membranes relates only to ions and not organic compounds |
Answer: a
The survival of the cell requires that cytosolic composition be maintained within narrow limits, despite the constant influx of nutrients and the simultaneous outflow of waste. A familiar example of the distribution of ions across the cell membrane is that of sodium and potassium. Cells are typically rich in potassium and contain very little sodium. Despite the fact that they are constantly bathed by fluid that is precisely the opposite composition. Even more impressive is the distribution of ionized calcium. The extracellular concentration of this ion is typically of the order of 10–3M, whereas that of cytosol is typically 10–7M, a 10,000-fold gradient. Such nonequilibrium ion distributions are even more remarkable in light of the fact that the plasma membrane is, to varying degrees, leaky to ions such as sodium, potassium and calcium. The plasma membrane is leaky to a variety of substances, but it exhibits an astonishing ability to discriminate or select one substance over another. This selectivity relates to not only ions but also for organic compounds such as glucose. Finally, the selectivity of biologic membranes can be altered drastically as a result of regulatory or signaling processes that occur within the cell. |
