Unit 6: Carbohydrate Metabolism and Adenosine Triphosphate (ATP)

Under anaerobic conditions in humans, which molecule is formed in the cytosol by fermentation?

a. Lactate'. Fructose is a simple sugar, similar to glucose. Fructose is metabolized through glycolysis. Lactate is formed from pyruvate under anaerobic conditions by the process of fermentation

Starting with one molecule of glucose, compare the amount of ATP made in aerobic vs anaerobic respiration.

b. Aerobic respiration creates 30 ATP while anaerobic respiration creates 2 ATP'. Aerobic metabolism of glucose creates 30 ATP after glycolysis and oxidative phosphorylation. Anaerobic metabolism only creates 2 ATP from glycolysis.

Glycolysis produces two ATP molecules. Through what process are these ATP molecules made?

b. Substrate level phosphorylation'. Oxidative phosphorylation is the process in which ATP is made aerobically. Substrate-level phosphorylation is the only way ATP can be made without oxygen.

Jason is a 17-year-old male with a glycogen storage disease. He is also planning on running the high school marathon. Should Jason consume a diet that is low in a) fats, b) protein/amino acids, or c) carbohydrates/glucose? Explain.

B Jason is unable to store glycogen which is a stored form of glucose that is used as a quick source of energy when glucose is not readily available in the diet. This means that he needs to compensate in other ways to have enough stored energy. If he were to go on a low fat diet, he would not have any form of stored fat(triglycerides) to meet his needs. Glucose, fatty acids, and amino acids that are not broken down for energy are used in anabolic pathways to synthesize structural, regulatory, or storage molecules. Glucose molecules can be used to synthesize glycogen, a storage form of carbohydrate. If the body has enough glycogen, glucose can also be used to synthesize fatty acids. Fatty acids can be used to synthesize triglycerides that are stored as body fat. Amino acids can be used to synthesize the various proteins that the body needs, such as muscle proteins, enzymes, protein hormones, and blood proteins. Excess amino acids can be converted into fatty acids and stored as body fat.

There is no energy gained (and in fact energy is required) when converting pyruvate to lactate. Why is this a necessary step?

B. NAD+ is required for glycolysis to occur'. Fermentation does not create ATP. Lactate fermentation regenerates NAD+ from NADH. NAD+ is essential for glycolysis to occur, which is the step where the 2 ATP of anaerobic metabolism are made.

Which of the following occur during aerobic respiration? Water donates electrons to the ETC, producing oxygen.

B. NADH and FADH2 are produced from NAD+ and FAD during the citric acid cycle'. Water does not donate electrons to the ETC. Water is produced when O2 accepts electrons at the end of the ETC.

Glycolysis produces two ATP molecules through which process?

B. Substrate level phosphorylation.' Beta Oxidation is the pathway in which we break down fatty acids to make Acetyl CoA. During glycolysis, substrate level phosphorylation transfers a phosphate group from an intermediate of glycolysis directly to ADP to create ATP.

What happens in the muscle cells when they respond to insulin?

GLUT4 transporters move to the surface of the cell.' Glycogenolysis will decrease as a result of insulin release. Glycogenolysis breaks down glycogen into glucose. Insulin is released in response to high blood sugar and additional glucose is not needed.

A woman is about to begin her ascent of Mount Everest and is preparing for Day 1 of the climb. Approximately 6 hours before the hike begins, she and her climbing team eat a meal containing 80% complex carbohydrates. What is the physiological benefit of this approach?

Glucagon is a hormone that is normally secreted in response to the low glucose levels. Eating complex carbohydrates does not increase the glucagon levels. Glycogen is a stored form of glucose. Individual glucose units are polymerized to form glycogen and is stored in liver and muscle. People who partake in endurance sports consume complex carbohydrate meals right before the activity or sport in order to improve their glycogen stores in liver and muscle. During the activity, the stored glycogen is then broken down to supply the much needed glucose to sustain the athlete.

What are advanced glycation end products (AGEs)? The end products of glycogenolysis

Glucose molecules linked to lipids or proteins without the need for enzymes.' The end product of glycogenolysis is glucose.

What happens to glucose under anaerobic conditions?

Glucose undergoes glycolysis to produce pyruvate'. This is the first step of glucose metabolism in anaerobic and aerobic conditions. The citric acid cycle only occurs during aerobic conditions and acetyl-CoA, not glucose, enters into the citric acid cycle.

During gluconeogenesis, how many ATP molecules are consumed for each glucose molecule produced?

It takes 6 ATP molecules to produce glucose through gluconeogenesis.

Katrina is an 18-year-old female at Southwest High. Her high school is raising money by hosting a marathon pledge drive. She was advised to carb load before the big race. Why would this be recommended?

L.oading on carbohydrates will increase glucose levels. Under high glucose conditions, cells perform glycogenesis, a process of building glycogen from glucose molecules. Glycogen can then be broken down rapidly into individual glucose units when glucose is low, such as during a marathon.

Which molecule is regenerated with the production of lactate during anaerobic metabolism?

NAD+ Fermentation regenerates NAD+ so that it can be used by glycolysis.

Fill in the missing numbers of ATP molecules in the diagram of the Cori Cycle shown. A=2 ATP; B=6 ATP

The Cori cycle has a net loss of 4 ATP: 2 made during glycolysis and 6 used during gluconeogenesis.

Which molecules undergo anaerobic metabolism?

a. Only molecules that can enter glycolysis can be used in anaerobic metabolism. Fatty acids cannot enter into glycolysis.

Which of the following is expected to occur when oxygen is not present?

The proton gradient dissipates, resulting in a dramatic reduction in ATP production that can lead to cell death. The proton gradient will dissipate when oxygen is not present because the electron transport chain will no longer be able to transport electrons. The proton gradient is necessary for the aerobic production of ATP.

Why would a marathon runner consume a large meal full of complex carbohydrates the night before her run?

To replenish cellular stores of glycogen A large amount of carbohydrates can be stored as glycogen and used during exercise.

Which of the following is incorrectly paired?

c. 'Lactic acid fermentation - mitochondrial matrix'. Lactic acid fermentation occurs during anaerobic metabolism and therefore occurs in the cytosol, not the mitochondria. During aerobic metabolism, ATP is created during the Electron transport chain in the inner mitochondrial membrane.

Glucose that is phosphorylated after entering the cell cannot move through GluT transporters. True False

true > Glucose that is phosphorylated after entering the cell cannot move through GluT transporters.

Why must red blood cells rely solely on glycolysis to make ATP?

'Red blood cells lack mitochondria.' Red blood cells transport oxygen by hemoglobin but lack mitochondria.

Which molecule signals the liver to release glucose by breaking down glycogen?

'glucagon'. High levels of glucose stimulate insulin which increases glycogen formation.

During aerobic metabolism, acetyl-CoA is produced from which molecule?

'pyruvate'. Lactate is produced during anaerobic metabolism.

If a patient is healthy and has a normal oxygen concentration in her blood, approximately how many ATP are produced for every molecule of glucose that enters the process of metabolism?

30 Since the patient has normal oxygen levels, their cells will undergo aerobic respiration. 30 ATP is generated per 1 glucose molecule as a result of aerobic respiration. 6 ATP are used (not made) in gluconeogenesis to regenerate glucose from 2 lactates. The Cori Cycle utilizes gluconeogenesis to convert the products of fermentation back into glucose, which occurs during anaerobic respiration. Oxygen levels are normal, so most likely aerobic respiration is being utilized by the cells.

What kind of molecule is glycogen?

A complex carbohydrate

Billy is a 26-year-old male currently on his 12th day of a hunger strike to protest "government stuff." How can Billy keep going long after his glycogen supply has been used up? (Note: The brain requires a constant supply of glucose to function.)

A. Fatty acids are not used to create new glucose. Instead they are used to build triglyceride a stored form of fat. The glycerol part of triglycerides (more on this in the next module on lipids), lactate (recall the Cori cycle), and certain amino acids can be converted in the liver to glucose. The process by which glucose is formed from these noncarbohydrate sources is called gluconeogenesis (gluco = glucose, neo = new, genesis = make). About 60% of the amino acids in the body can be used for gluconeogenesis. Lactate and amino acids such as alanine and serine are converted to pyruvate, which then may be synthesized into glucose or enter the citric acid cycle. Glycerol may be converted into glyceraldehyde 3-phosphate, which may continue on in glycolysis to make pyruvate or be used to synthesize glucose via gluconeogenesis.

What is the function of fermentation during anaerobic metabolism?

A. Fermentation regenerates the NAD+ needed for glycolysis. Fermentation produces NAD+. NAD+ is needed as a substrate for glycolysis.

During the reactions of the Electron Transport Chain, hydrogens are pumped by complexes _________ and move from the matrix to the _________.

A. I, III, & IV; intermembrane space During the reactions of the Electron Transport Chain, hydrogens are pumped by complexes I, III, & IV and move from the matrix to the intermembrane space.

During periods of strenuous exercise, the muscle cells can become anaerobic. Without oxygen, the electron transport chain cannot continue and the citric acid cycle slows down. When this occurs, how do cells make ATP?

A. In order for the glycolysis portion of anaerobic metabolism to continue, pyruvate is converted to lactate during fermentation. This process regenerates the NAD+ needed for glycolysis.

What is the fate of pyruvate when oxygen is absent?

A. Pyruvate is converted to lactate and enters the Cori cycle. During anaerobic conditions the pyruvate will be converted to lactate to allow glycolysis to continue and produce ATP. Gluconeogenesis can be used to convert pyruvate to glucose when there is low blood sugar.

A two year old boy is found to have an autosomal recessive glycogen storage disease that prevents him from being able to fully metabolize glucose. On examination, he has an enlarged liver and bulky appearing muscles. Biopsy of both the liver and the muscles shows markedly increased amounts of glycogen compared to normal. Which of the following is TRUE?

A. Since glucose can be partially but not fully metabolized, there is an increased concentration of the intermediate compounds and this causes a shift in enzymatic reactions, favoring the production of glycogen. The selected answer choice is not related to glycogen storage or glucose metabolism. If glucose can be absorbed by the liver and muscles cells but not be fully metabolized to make ATP, then the intermediate compounds will be converted into glycogen AND the child will need to rely on alternative nutritional sources for ATP production. Excessive glycogen will accumulate in the liver/muscles, increasing their size while worsening their function.

How does the proton gradient affect the pH of the mitochondrial matrix and the intermembrane space?

A. The concentration of protons in the intermembrane space is higher than the concentration in the matrix. The intermembrane space of mitochondria has a high concentration of protons (H+) compared to the matrix.

GluT transporters aid in glucose transport into a cell __________

A. by acting as a channel to allow transport of glucose into the cell'. Glut4 is a transporter and not an enzyme that has a role in phosphorylating glucose. Typically, a kinase is an enzyme that would phosphorylate the glucose to glucose-6-phosphate. Glut4 is a channel which transports glucose into the cell and is regulated by the insulin. Insulin, which is secreted by the pancreas in response to elevated glucose levels in the blood, increases the insertion of one type of GluT, called GluT4, into the plasma membranes of most body cells, thereby increasing the rate of facilitated diffusion of glucose into those cells. This is especially evident in muscle and adipose cells. The GluT4 proteins are located on intracellular vesicles that fuse with the membrane and quickly increase the number of GluT4 transporters. This process is known as translocation of GluT4.

Insulin signaling results in an increased transport of ________ into cells, which allows the cell to subsequently increase ______ synthesis and store energy in the form of ______ in the liver and ______ in the adipose.

A. glucose, protein, glycogen,triglycerides'. Insulin has several effects on metabolism. It stimulates uptake of glucose into the cell. It also increases protein synthesis, glycogen synthesis and fatty acid synthesis and storage in the form of triglycerides.

Cyanide binds to complex IV of the electron transport chain, preventing electron transport. Which of the following would be the most immediate effect of cyanide consumption?

ADP will build-up. Since the electron transport chain can no longer function because the electrons are blocked at complex IV, the protons cannot be pumped into the intermembrane space. As a result, ATP synthesis will drastically decrease.

Which of the following best describes the role of ATP synthase?

ATP synthase allows protons to flow down their concentration gradient into the matrix and generates ATP'. Protons flow down their concentration gradient through ATP synthase, from the intermembrane space into the matrix.

the Cori Cycle demonstrates how glucose is consumed in the muscle cell and regenerated in the liver. How many ATP are produced in the muscle cell when glucose is broken down and how many ATP are consumed in the liver when glucose is regenerated?

C. 2 ATP are generated when glucose is broken down in the muscle cell (through glycolysis) and 6 ATP are consumed when ATP is regenerated in the liver (through gluconeogenesis).

Which of the following is an accurate statement about glycolysis?

C. The final products of glycolysis are two molecules of pyruvate'. While glycolysis does break down glucose, this process can occur independently of oxygen. The electron transport chain requires oxygen. Additionally, glycolysis results in the net production of 2 ATP. So these two answers would not be correct.

Glycolysis is the conversion of glucose to pyruvate. Is this a catabolic process or an anabolic process?

Catabolic'. Anabolic reactions created bonds and build molecules. In glycolysis, glucose is being broken down. This process is catabolic.

Why are blood glucose levels high in patients with unmanaged Diabetes Mellitus?

Cells do not move enough GLUT4 transporters to their cell membranes.' GLUT4 transporters allow blood glucose to enter cells which then lowers blood glucose levels.

What is anaerobic metabolism?

D. ATP production using only substrate-level phosphorylation'. Substrate level phosphorylation is responsible for ATP production during glycolysis. Anabolic reactions require energy to build larger molecules from smaller molecules.

A patient with advanced cancer has not been able to eat a full meal for the past three months, and his intake has gradually diminished over the last month such that his entire intake in the prior three days consists solely of water. Which of the following is most likely?

D.'He is likely to have lost adipose tissue and muscle mass'. Body only stores a glycogen supply to last 72 hours. Beyond that period, under long term starvation like conditions, the protein from the muscle and fats from the adipose tissue are utilized to provide energy in the form of ATP. As a result, the patient would have lost muscle mass and adipose tissue. Under long term starvation like conditions, the body would have already utilized any stored form of glycogen to produce glucose, in return ATP to meet the energy needs. Thus, the adipose tissue, and proteins from the muscle are catabolized to provide energy under such conditions.

A defect in an enzyme in the citric acid cycle causes the cycle to stop functioning. What is a possible consequence?

Decreased levels of ATP'. Since the citric acid cycle is no longer working, then there will be no production of NADH and FADH2. These molecules are required in order to generate ATP. Without these molecules transporting electrons to the electron transport chain, ATP levels will decrease.

A type II diabetes patient who has been on metformin treatment along with making some lifestyle changes for over two months now has a current A1C level reading of 7% . Which of the following statements best describes his response to the treatment and management of the condition? A Yes, he is responding to the treatment well since the normal range of A1C levels in healthy individuals is 0- 10% B. No, the patient is not responding to the treatment since the normal range of A1C levels in healthy individuals is 0-5%

No, the patient is not responding to the treatment since the normal range of A1C levels in healthy individuals is 0-5%'. The normal range of A1C levels in healthy individuals is anywhere from 0-5% and should be less than 5% and certainly not 0-10% like in this specific patient. A level anywhere above 6.5% indicates a high glucose concentration. Since the patient's A1C levels are at 7%, it is clearly indicating that his/her blood sugars levels are not in the normal range and is not responding to the treatment well. The glycated form of hemoglobin is called A1C (other names are hemoglobin A1c, HbA1c), and it serves as a helpful indicator of blood glucose levels. In healthy bodies, a small percentage of A1C exists at any given point in time, due to the slow, constant rate of glycation. The percentage of A1C under normal conditions is usually less than 5% of hemoglobin. However, when blood sugar levels are high for extended periods of time, the A1C levels go above this standard range. A diagnosis of diabetes is usually made when the levels of A1C are above 6.5%. A1C is a good indicator of how well the diabetes is being managed on a consistent basis since it is an average of glucose levels over a time range of 120 days (the average lifespan of an RBC) rather than simply the levels for that day.

Anabolic pathways result in larger molecules being made from smaller molecules and Catabolic pathways result in larger molecules being broken down into smaller molecules. True False

True. Anabolism creates larger molecules from smaller molecules and Catabolism breaks down larger molecules into smaller molecules.

There are two types of diabetes mellitus (DM) that lead to impairment in glucose utilization. Resistance to the effects of insulin leads to which type of DM?

Type II diabetes'. Type I diabetes is a result of decreased ability to produce the hormone insulin. Whereas, in the type II diabetes, the cells can produce insulin but the cells are resistant to the effects of insulin. Diabetes results from a decreased ability to produce insulin or a decreased sensitivity of cells to the insulin produced by the body (type I and type II, respectively). This leads to excessively high blood glucose levels that are damaging to various organs and systems in the body.

Why is the Cori Cycle important for red blood cells?

c. Red blood cells have no mitochondria'. Red blood cells contain no mitochondria and therefore cannot carry out aerobic respiration involving the citric acid cycle. The Cori Cycle involves the production of lactate during the anaerobic production of ATP. The Cori Cycle is not involved in oxygen binding to hemoglobin. Instead, oxygen affinity to hemoglobin is regulated by a change in pH.

In the absence of oxygen in the exercising muscle, why does the amount of lactate in the blood change?

c. The amount of lactate increases because lactate produced in muscles anaerobically must travel to the liver During anaerobic conditions, ATP is produced during glycolysis and lactate is produced as a product of fermentation. Lactate produced during anaerobic metabolism leaves the muscle cells and travels to the liver via the blood.

Which of the following differentiates aerobic from anaerobic cellular metabolism?

c. The utilization of O2 as an electron acceptor'. Only aerobic metabolism depends on oxygen as the terminal electron acceptor in the electron transport chain. Both aerobic and anaerobic metabolism use ingested nutrients to produce ATP.

When oxygen is low, muscle and liver cells can participate in the Cori Cycle in which the muscle cells produce _______ which is then converted to _______ in the liver.

c. lactate, glucose'. During anaerobic metabolism, muscles convert pyruvate to lactate and the liver uses this lactate to create glucose.

Which of the following best describes the purpose of fermentation?

d. Fermentation enables the regeneration of NAD+ so that glycolysis can still occur in anaerobic conditions'. Fermentation produces lactate, not acetyl CoA. Fermentation regenerates the NAD+ that is essential for glycolysis to occur.