MCAT Biology : Systems Biology and Tissue Types
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Example Questions
Example Question #701 : Systems Biology And Tissue Types
Calcitonin, secreted from the thyroid gland, is responsible for which of the following actions?
Decrease blood calcium
Increase blood phosphate
Decrease blood phosphate
Increase blood calcium
Decrease blood calcium
Calcitonin generally antagonizes the effect of parathyroid hormone (PTH). When the c-cells of the thyroid sense a high calcium level, they will secrete calcitonin. Calcitonin then serves to inhibit osteoclasts and stimulate osteoblasts, promoting osteogenesis and sequestration of blood calcium into the bone matrix.
In contrast, parathyroid hormone stimulated osteoclasts and inhibits osteoblasts, causing degeneration of the bone matrix and increase in blood calcium levels.
Example Question #702 : Systems Biology And Tissue Types
Which hormone is secreted by the developing placenta and stimulates the corpus luteum to grow and release estrogen and progesterone?
Luteinizing hormone
Human chorionic gonadotropin
Follicle-stimulating hormone
Testosterone
Human chorionic gonadotropin
Human chorionic gonadotropin is a water-soluble hormone that is secreted from the placenta, and stimulates the corpus luteum to grow and release estrogen and progesterone. It is vital for the maintenance of the uterine environment for the fetus to grow and develop.
Luteinizing hormone and follicle-stimulating hormone regulate ovulation and the menstrual cycle, while testosterone is responsible for development of male secondary sex characteristics.
Example Question #98 : Endocrine System
Which steroid hormone, produced in the male testes, is responsible for the development of secondary sexual characteristics in males?
Estrogen
Testosterone
Adrenocorticotropic hormone
Cortisol
Testosterone
Testosterone is produced by the Leydig cells of the testes after stimulation by luteinizing hormone. Testosterone is responsible for the development of male secondary sexual characteristics such as deeper voices, increased muscle mass, testicular development, and pubic hair.
Adrenocorticotropic hormone promotes release of cortisol in response to prolonged stressors, and estrogen is responsible for the development of sexondary sex characteristics in females.
Example Question #703 : Systems Biology And Tissue Types
A scientist created a new drug that was found to have very similar chemical properties to testosterone. What is the most likely mechanism of action of this drug?
The drug is most likely ineffective
The drug binds to the plasma membrane or to receptors in the cytosol
The drug binds to a receptor on the cell membrane and triggers secondary messengers
The drug passes through the plasma membrane and elicits effects inside the cell
The drug binds to extracellular receptors on the surface of organs
The drug passes through the plasma membrane and elicits effects inside the cell
There are three main classes of hormones: peptide hormones, steroid hormones, and tyrosine-derivatives. Peptide hormones act by binding to plasma membrane receptors. They are large and polar, preventing them from crossing the plasma membrane. Steroid hormones and tyrosine-derivatives, on the other hand, are lipid soluble and are able to cross through the plasma membrane and bind to receptors in the cytosol.
We know from the base of the question that this drug has similar chemical properties to testosterone. Testosterone is a steroid hormone; thus, our drug likely acts in a similar manner to steroid hormones by crossing the membrane and entering the cell to elicit its effects.
Example Question #63 : Hormones
Type II diabetes results from defective pancreatic beta cells and increased insulin resistance, indicating that peripheral tissues (such as skeletal muscle) do not properly respond to insulin.
Mouse models have been developed to model type II diabetes. In addition to global mutations, tissue-specific mutations can be used to delete genes of interest in precise regions of the body. A group of investigators is interested in characterizing the role of the gene Dia in the onset of diabetes.
Four groups of male mice are compared. Group A is a control group, group B has a global deletion of Dia, group C has a beta cell-specific Dia mutation, and group D has a skeletal muscle-specific Dia mutation.
In order to measure the ability of these mice to respond to a glucose challenge, the mice are fasted overnight. Following the fast, their blood glucose levels are measured (in mg/dL). The mice are then injected with two grams of glucose, and blood glucose levels are measured at 30, 60, 90, and 120 minutes post-injection.
|
|
0 min |
30 min |
60 min |
90 min |
120 min |
|
Group A |
80 |
150 |
120 |
90 |
80 |
|
Group B |
90 |
220 |
180 |
160 |
140 |
|
Group C |
100 |
260 |
190 |
150 |
135 |
|
Group D |
75 |
145 |
110 |
90 |
75 |
Diabetes is indicated by increased fasting blood glucose levels, while glucose intolerance is defined by elevated blood glucose levels following a glucose challenge. Assuming proper experimental design, which groups can be diagnosed with diabetes?
Elevated levels are accepted as being above 120mg/dL.
None of the groups
Groups A and D
Groups B and C
Group C
None of the groups
None of the groups have a pre-injection blood glucose level greater than 120mg/dL, indicating that none of the groups have diabetes.
Groups B and C, however, have elevated final blood glucose levels after the glucose challenge, indicating that these groups have glucose intolerance.
Example Question #704 : Systems Biology And Tissue Types
Type II diabetes results from defective pancreatic beta cells and increased insulin resistance, indicating that peripheral tissues (such as skeletal muscle) do not properly respond to insulin.
Mouse models have been developed to model type II diabetes. In addition to global mutations, tissue-specific mutations can be used to delete genes of interest in precise regions of the body. A group of investigators is interested in characterizing the role of the gene Dia in the onset of diabetes.
Four groups of male mice are compared. Group A is a control group, group B has a global deletion of Dia, group C has a beta cell-specific Dia mutation, and group D has a skeletal muscle-specific Dia mutation.
In order to measure the ability of these mice to respond to a glucose challenge, the mice are fasted overnight. Following the fast, their blood glucose levels are measured (in mg/dL). The mice are then injected with two grams of glucose, and blood glucose levels are measured at 30, 60, 90, and 120 minutes post-injection.
|
|
0 min |
30 min |
60 min |
90 min |
120 min |
|
Group A |
80 |
150 |
120 |
90 |
80 |
|
Group B |
90 |
220 |
180 |
160 |
140 |
|
Group C |
100 |
260 |
190 |
150 |
135 |
|
Group D |
75 |
145 |
110 |
90 |
75 |
Why is it important that the mice were fasted?
To control for altered blood glucose levels due to uncontrolled meal consumption
To ensure the mice are hungry enough to consume glucose
The mice should not be fasted
To ensure that the full dose of glucose will enter the blood stream
To ensure that initial insulin levels are low
To control for altered blood glucose levels due to uncontrolled meal consumption
The mice need to be fasted to control for consuming meals at irregular times. For example, if one mouse ate shortly before the test, it would have higher blood glucose levels than a mouse that did not, which would complicate the results. Fasting ensures that the mice have a controlled base blood glucose level before the injection.
Because the mice are injected with glucose, the mice do not need to orally consume the glucose for the test. While low blood glucose after a fast will also lower insulin levels, the insulin levels are never measured in the experiment and would not be a good explanation for fasting the mice.
Example Question #705 : Systems Biology And Tissue Types
Type II diabetes results from defective pancreatic beta cells and increased insulin resistance, indicating that peripheral tissues (such as skeletal muscle) do not properly respond to insulin.
Mouse models have been developed to model type II diabetes. In addition to global mutations, tissue-specific mutations can be used to delete genes of interest in precise regions of the body. A group of investigators is interested in characterizing the role of the gene Dia in the onset of diabetes.
Four groups of male mice are compared. Group A is a control group, group B has a global deletion of Dia, group C has a beta cell-specific Dia mutation, and group D has a skeletal muscle-specific Dia mutation.
In order to measure the ability of these mice to respond to a glucose challenge, the mice are fasted overnight. Following the fast, their blood glucose levels are measured (in mg/dL). The mice are then injected with two grams of glucose, and blood glucose levels are measured at 30, 60, 90, and 120 minutes post-injection.
|
|
0 min |
30 min |
60 min |
90 min |
120 min |
|
Group A |
80 |
150 |
120 |
90 |
80 |
|
Group B |
90 |
220 |
180 |
160 |
140 |
|
Group C |
100 |
260 |
190 |
150 |
135 |
|
Group D |
75 |
145 |
110 |
90 |
75 |
Insulin production can be altered due to reduced numbers of beta cells or due to less efficient beta cells. Which of the following methods cannot be used to distinguish between these two defects?
Calculating the rate of beta cell death
Calculating the total mass of beta cells
Any of these methods could be used
Measuring the amount of insulin in the pancreas
Measuring insulin secretion in response to glucose from equal-sized cell samples
Measuring the amount of insulin in the pancreas
The total amount of pancreatic insulin is affected by the number of beta cells and the amount of insulin produced by each beta cell; therefore, an increase or reduction of pancreatic insulin cannot be used to distinguish the two possibilities. Insulin levels in the pancreas could be reduced due to lower cell numbers or due to less production from a large number of cells. There is no way to differentiate these two causes.
Measuring the mass of beta cells, and to an extent calculating the amount of beta cell death, can determine if there are fewer beta cells in the pancreas. Additionally, using an equal number of beta cells and measuring insulin secretion can determine if beta cell function is impaired.
Example Question #706 : Systems Biology And Tissue Types
Type II diabetes results from defective pancreatic beta cells and increased insulin resistance, indicating that peripheral tissues (such as skeletal muscle) do not properly respond to insulin.
Mouse models have been developed to model type II diabetes. In addition to global mutations, tissue-specific mutations can be used to delete genes of interest in precise regions of the body. A group of investigators is interested in characterizing the role of the gene Dia in the onset of diabetes.
Four groups of male mice are compared. Group A is a control group, group B has a global deletion of Dia, group C has a beta cell-specific Dia mutation, and group D has a skeletal muscle-specific Dia mutation.
In order to measure the ability of these mice to respond to a glucose challenge, the mice are fasted overnight. Following the fast, their blood glucose levels are measured (in mg/dL). The mice are then injected with two grams of glucose, and blood glucose levels are measured at 30, 60, 90, and 120 minutes post-injection.
|
|
0 min |
30 min |
60 min |
90 min |
120 min |
|
Group A |
80 |
150 |
120 |
90 |
80 |
|
Group B |
90 |
220 |
180 |
160 |
140 |
|
Group C |
100 |
260 |
190 |
150 |
135 |
|
Group D |
75 |
145 |
110 |
90 |
75 |
Assuming proper experimental design, which groups have impaired glucose clearance?
Groups A and D
Group B
Group D
Groups B and C
Group C
Groups B and C
Assuming proper experimental design, group A should be used as a baseline for "normal" glucose clearance rate. Any groups showing glucose levels higher than group A demonstrate impaired clearance.
Group A and group D show similar trends, with similar values for the initial and final blood glucose samples. This indicates that the injection was cleared from the blood completely over the 2-hour sample period.
Group B and C, however, show higher blood glucose levels after two hours than their initial levels, indicating that they were unable to completely clear the injected glucose from the blood during this period. Although, the glucose levels decrease after the injection, the glucose levels after two hours are still greatly elevated compared to fasting levels, suggesting a defect in glucose tolerance.
Example Question #707 : Systems Biology And Tissue Types
Type II diabetes results from defective pancreatic beta cells and increased insulin resistance, indicating that peripheral tissues (such as skeletal muscle) do not properly respond to insulin.
Mouse models have been developed to model type II diabetes. In addition to global mutations, tissue-specific mutations can be used to delete genes of interest in precise regions of the body. A group of investigators is interested in characterizing the role of the gene Dia in the onset of diabetes.
Four groups of male mice are compared. Group A is a control group, group B has a global deletion of Dia, group C has a beta cell-specific Dia mutation, and group D has a skeletal muscle-specific Dia mutation.
In order to measure the ability of these mice to respond to a glucose challenge, the mice are fasted overnight. Following the fast, their blood glucose levels are measured (in mg/dL). The mice are then injected with two grams of glucose, and blood glucose levels are measured at 30, 60, 90, and 120 minutes post-injection.
|
|
0 min |
30 min |
60 min |
90 min |
120 min |
|
Group A |
80 |
150 |
120 |
90 |
80 |
|
Group B |
90 |
220 |
180 |
160 |
140 |
|
Group C |
100 |
260 |
190 |
150 |
135 |
|
Group D |
75 |
145 |
110 |
90 |
75 |
What flaws exist in the experimental design?
The amount of glucose injected should have been adjusted according to mouse weight
The mice should have been injected both before and after fasting
Blood glucose levels should have been measured every 15 minutes
Both males and females should have been included to get accurate results
The mice should not have been fasted
The amount of glucose injected should have been adjusted according to mouse weight
The investigators are measuring for a relationship between blood glucose level and genetic mutation. They must isolate the variation between samples to only the genetic mutation in order to get accurate results. Variation in weight will alter the blood volume and metabolism of glucose in the blood, resulting in an uncontrolled variable. The investigators needed to weigh the mice, and provide different injection amounts based on the different mouse weights. As the experiment currently stands, heavier mice will metabolize the glucose injection faster than lighter mice.
While it may be important to eventually analyze the Dia gene in females, they should not be included in the same study as males because males and females can have different rates of clearing blood glucose. The exclusion of females limits the data, but does not result in a design flaw. Similarly, sampling data every 15 minutes would give more data points (more information), but sampling every 30 minutes does not represent a design flaw. Finally, the mice need to be fasted to eliminate the possibility of a mouse eating shortly before the test, complicating the results. Injecting the mice before and after fasting would neither increase, nor decrease the validity of the results, and does not represent a design flaw.
Example Question #71 : Hormones
Gigantism is a rare condition that is the result of hypersecretion of growth hormone from the anterior pituitary during childhood. Symptoms of gigantism include abnormal height (several standard deviations above average) and abnormal growth of the face, hands, and feet.
Functions of growth hormone are best decribed by which of the following?
Increased liver uptake of glucose and decreased lipolysis
Increased protein synthesis and decreased mineralization of bone
Increased calcium retention and stimulation of the immune system
Increased glyconeogenesis in the liver and increased muscle mass
Increased calcium retention and stimulation of the immune system
Growth hormone (GH) causes increased calcium retention and stimulation of the immune system. It reduces liver uptake of glucose and increases lipolysis. Growth hormone also causes increased protein synthesis, muscle mass, bone mineralization, and gluconeogenesis.
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