Race to the Slopes #8

Hormones are chemical signals that are released by cells in one part of the body that travel through the bloodstream to signal cells in another part of the body. Insulin is a hormone that is released by the pancreas that induces the uptake of glucose molecules from the bloodstream into cells. In this way, insulin lowers the overall blood glucose levels of the body. Osteoblasts and osteoclasts are two types of bone cells that play a role in regulating blood glucose levels (Figure 1).

 

Binding of insulin to the insulin receptor on osteoblasts activates a signaling pathway that results in osteoblasts releasing a molecule, OPG, that binds to neighboring osteoclasts. In response, the osteoclasts release protons ( + H ) and create an area of lower pH outside the cell. This low pH activates osteocalcin, a protein secreted in an inactive form by osteoblasts.

 

The Esp gene encodes a protein that alters the structure of the insulin receptor on osteoblasts and interferes with the binding of insulin to the receptor. A researcher created a group of osteoblasts with an Esp mutation that prevented the production of a functional Esp product (mutant). The researcher then exposed the mutant strain and a normal strain that expresses Esp to glucose and compared the levels of insulin in the blood near the osteoblasts (Figure 2).

Which of the following best describes the effect of insulin binding to the receptor on the osteoblast cells?

• Insulin binding ultimately increases pancreatic secretion of additional insulin.

• Insulin binding blocks the release of osteocalcin from the osteoblasts.

• Insulin binding inhibits the expression of Esp.

• Insulin binding increases the pH of the extracellular matrix.

Answer explanation

Insulin binding increases the secretion of additional insulin via osteocalcin signaling

Hormones are chemical signals that are released by cells in one part of the body that travel through the bloodstream to signal cells in another part of the body. Insulin is a hormone that is released by the pancreas that induces the uptake of glucose molecules from the bloodstream into cells. In this way, insulin lowers the overall blood glucose levels of the body. Osteoblasts and osteoclasts are two types of bone cells that play a role in regulating blood glucose levels (Figure 1).

 

Binding of insulin to the insulin receptor on osteoblasts activates a signaling pathway that results in osteoblasts releasing a molecule, OPG, that binds to neighboring osteoclasts. In response, the osteoclasts release protons ( + H ) and create an area of lower pH outside the cell. This low pH activates osteocalcin, a protein secreted in an inactive form by osteoblasts.

 

The Esp gene encodes a protein that alters the structure of the insulin receptor on osteoblasts and interferes with the binding of insulin to the receptor. A researcher created a group of osteoblasts with an Esp mutation that prevented the production of a functional Esp product (mutant). The researcher then exposed the mutant strain and a normal strain that expresses Esp to glucose and compared the levels of insulin in the blood near the osteoblasts (Figure 2).

Which of the following was a positive control in the experiment?

• Minutes after glucose injection

• Blood insulin

• Mutant strain

• Normal strain

Answer explanation

Treatment of the normal strain of mouse has a known, expected result to ensure the experiment is functioning and is therefore the positive control

Hormones are chemical signals that are released by cells in one part of the body that travel through the bloodstream to signal cells in another part of the body. Insulin is a hormone that is released by the pancreas that induces the uptake of glucose molecules from the bloodstream into cells. In this way, insulin lowers the overall blood glucose levels of the body. Osteoblasts and osteoclasts are two types of bone cells that play a role in regulating blood glucose levels (Figure 1).

 

Binding of insulin to the insulin receptor on osteoblasts activates a signaling pathway that results in osteoblasts releasing a molecule, OPG, that binds to neighboring osteoclasts. In response, the osteoclasts release protons ( + H ) and create an area of lower pH outside the cell. This low pH activates osteocalcin, a protein secreted in an inactive form by osteoblasts.

 

The Esp gene encodes a protein that alters the structure of the insulin receptor on osteoblasts and interferes with the binding of insulin to the receptor. A researcher created a group of osteoblasts with an Esp mutation that prevented the production of a functional Esp product (mutant). The researcher then exposed the mutant strain and a normal strain that expresses Esp to glucose and compared the levels of insulin in the blood near the osteoblasts (Figure 2).

Based on the information provided, which of the following best justifies the claim that osteocalcin is a hormone?

• The phosphorylation of the insulin receptor causes a response in osteoblast bone cells.

• The osteoblasts in the bone secrete osteocalcin, which causes cells in the pancreas to change their activity.

• The change in expression of Esp changes the insulin receptor activity of the osteoblast.

• The activation of the osteocalcin by a bone cell is pH dependent.

Answer explanation

Hormones are signaling molecules that can be secreted from one part of the body and act on another part of the body.

Hormones are chemical signals that are released by cells in one part of the body that travel through the bloodstream to signal cells in another part of the body. Insulin is a hormone that is released by the pancreas that induces the uptake of glucose molecules from the bloodstream into cells. In this way, insulin lowers the overall blood glucose levels of the body. Osteoblasts and osteoclasts are two types of bone cells that play a role in regulating blood glucose levels (Figure 1).

 

Binding of insulin to the insulin receptor on osteoblasts activates a signaling pathway that results in osteoblasts releasing a molecule, OPG, that binds to neighboring osteoclasts. In response, the osteoclasts release protons ( + H ) and create an area of lower pH outside the cell. This low pH activates osteocalcin, a protein secreted in an inactive form by osteoblasts.

 

The Esp gene encodes a protein that alters the structure of the insulin receptor on osteoblasts and interferes with the binding of insulin to the receptor. A researcher created a group of osteoblasts with an Esp mutation that prevented the production of a functional Esp product (mutant). The researcher then exposed the mutant strain and a normal strain that expresses Esp to glucose and compared the levels of insulin in the blood near the osteoblasts (Figure 2).

A researcher observes that mice from the mutant strain experience low blood sugar. Which of the following best describes the feedback mechanism in the pathway (Figure 1) causing the low blood sugar in the mutant strain?

• The positive feedback of insulin production

• The negative feedback of inactive osteocalcin production

• The positive feedback of the Esp protein

• The negative feedback of insulin-secreting pancreatic cell proliferation

Answer explanation

The release of insulin from the pancreas ultimately leads to more insulin being released. The excess insulin production results in too much sugar being removed from the bloodstream and the low blood sugar seen in the mutant mice.

Hormones are chemical signals that are released by cells in one part of the body that travel through the bloodstream to signal cells in another part of the body. Insulin is a hormone that is released by the pancreas that induces the uptake of glucose molecules from the bloodstream into cells. In this way, insulin lowers the overall blood glucose levels of the body. Osteoblasts and osteoclasts are two types of bone cells that play a role in regulating blood glucose levels (Figure 1).

 

Binding of insulin to the insulin receptor on osteoblasts activates a signaling pathway that results in osteoblasts releasing a molecule, OPG, that binds to neighboring osteoclasts. In response, the osteoclasts release protons ( + H ) and create an area of lower pH outside the cell. This low pH activates osteocalcin, a protein secreted in an inactive form by osteoblasts.

 

The Esp gene encodes a protein that alters the structure of the insulin receptor on osteoblasts and interferes with the binding of insulin to the receptor. A researcher created a group of osteoblasts with an Esp mutation that prevented the production of a functional Esp product (mutant). The researcher then exposed the mutant strain and a normal strain that expresses Esp to glucose and compared the levels of insulin in the blood near the osteoblasts (Figure 2).

Which of the following claims is most consistent with the data shown in Figure 2 ?

• Esp expression is necessary to prevent the overproduction of insulin

• Esp protein does not regulate blood-sugar levels in normal mice.

• Normal mice require a higher blood concentration of insulin than mutant mice do.

• Mutant mice have a cyclical pattern of insulin secretio

Answer explanation

Mutant mice that do not express Esp have a higher blood insulin level twenty minutes after injection and beyond.

Researchers studying the bacterium Escherichia coli split a population of the bacteria into two samples. Sample 1 was transformed with a plasmid containing a gene that makes the bacteria resistant to the antibiotic kanamycin. Sample 2 was transformed with a plasmid lacking the antibiotic resistance gene. A portion of each sample was then added to growth plates containing just nutrients or growth plates containing nutrients and kanamycin.

After being allowed to grow for 24 hours at 37˜ C, the number of colonies on each growth plate was counted (Table 1).

Which of the following claims is best supported by the data in Table 1 ?

• The transformation procedure killed all the bacteria that were added to plate 3.

• More bacteria on plates 1 and 2 were successfully transformed than on any other plate.

• None of the bacteria on plate 2 were successfully transformed with the kanamycin resistance gene.

• Only the bacteria that were successfully transformed with the kanamycin resistance gene grew on plate 4.

Answer explanation

Plate 4 contains kanamycin, which will kill any bacteria that do not contain the kanamycin resistance gene. The bacteria that grew are expected to contain the gene.

Carbon dioxide most likely enters a cell through which of the following processes?

• Simple diffusion through the membrane

• Facilitated diffusion through membrane proteins

• Active transport through membrane proteins

• Active transport through aquaporins

Answer explanation

Carbon dioxide is a small molecule without a charge and so can pass through a cell membrane by simple diffusion.

The cladogram shows shared traits among four plant taxa. Based on the cladogram, which of the following are the traits shared between ferns and pines?

• Xylem only

• Seeds and wood only

• Embryo and xylem only

• Embryo, xylem, wood, and seeds only

Answer explanation

The cladogram shows that ferns and pines have two shared characteristics: embryos and xylem tissue.

Mosquitoes are frequently a target of insect control strategies because of their ability to spread disease. One strategy is to introduce guppies, a type of freshwater fish, into areas where mosquitoes are a problem. Guppies can consume large numbers of mosquito larvae, which cuts down on the number of mosquitoes living to adulthood.

Researchers assessing the effectiveness of the guppy solution are concerned that the introduction of guppies might cause more problems than it is fixing. Guppies are hardy, tolerant of a wide range of environmental conditions, and fast-reproducing.

Which of the following predicts the most likely ecological problem that would occur if guppies are introduced into new areas to control the mosquito population?

• The guppies might have no natural predators, which will result in a dramatic increase in the guppy population and an increase in competition for other native species.

• The guppy population will likely evolve to consume another food source instead of the mosquito larvae.

• The larvae will evolve a mechanism that will enable them to avoid predation from the guppies

• Predators in the area will consume the guppies, requiring the addition of more guppies on a regular basis

Answer explanation

Guppies are strong and fertile. If they have ample resources and few predators, their population could grow unchecked and create problems for native species.