Questions and Answers of Biochemistry Concepts And Connections

How is carbamoyl-phosphate synthetase I (CPS-I) controlled?
What is the logic behind high levels of arginine positively regulating N-acetylglutamate synthase?
How does the level of glutamic acid affect the urea cycle?
When amino acids are catabolized, what are the end products of the carbon skeletons for glucogenic amino acids? For ketogenic amino acids?
What species excrete excess nitrogen as ammonia? Which ones excrete it as uric acid?
Why is arginine an essential amino acid, when it is made in the urea cycle?
People on high-protein diets are advised to drink lots of water. Why?
Why is it better, when running a marathon, to drink a beverage with sugar for energy rather than one with amino acids?
How is the importance of folic acid related to chemotherapy?
What is the structural difference between inosine and adenosine?
How is tetrahydrofolate important to purine synthesis?
How many high-energy phosphate bonds must be hydrolyzed in the pathway that produces GMP from guanine and PRPP by the PRPP salvage reaction, compared with the number of such bonds hydrolyzed in the
Why do most mammals, other than primates, not suffer from gout?
What is an important difference between the biosynthesis of purine nucleotides and that of pyrimidine nucleotides?
Suggest a mode of action for fluorouracil in cancer chemotherapy.
Chemotherapy patients receiving cytotoxic (cell-killing) agents such as FdUMP (the UMP analogue that contains fluorouracil) and methotrexate temporarily go bald. Why does this take place?
What are the two primary molecules that link anabolic and catabolic reactions?
Name some of the key metabolic intermediates that are seen in more than one pathway.
People who begin to lose weight often have a rapid weight loss in the first few days. Common knowledge says that this is “just” because of a loss of water from the body. Why might this be true?
Why is it advantageous for a metabolic pathway to have a large number of steps?
If you had your choice of doing research on any topic in this book, which would you choose? Why do you consider that topic to be interesting and important?
What is the relationship between saturated fatty acids and LDL?
What is leptin, and how does it work?
Many have suggested that vitamin D could be more appropriately called a hormone than a vitamin. Is this correct?
Recent recommendations on diet suggest that the sources of calories should be distributed as follows: 50%–55% carbohydrate, 25%–30% fats, and 20% protein. Suggest some reasons for these
It has been suggested that limits be put on the dose in vitamin A supplements sold in stores. What is a possible reason for this limitation?
In the early 20th century, goiter was relatively common in the Midwest. Why was this so? How has it been eliminated?
Immature rats are fed all the essential amino acids but one. Six hours later they are fed the missing amino acid.The rats fail to grow. Explain this observation.
Kwashiorkor is a protein-deficiency disease that occurs most commonly in small children, who characteristically have thin arms and legs and bloated, distended abdomens due to fluid imbalance. When
Biologically and nutritionally important trace elements tend to be metals. What is their likely biochemical function?
Over a period of several decades, an adult human consumes tons of nutrients and more than 20,000 L of water without significant weight gain. How is this possible? Is it an example of chemical
Are all hormones closely related in their chemical structure?
How do the actions of the hypothalamus and the pituitary gland affect the workings of endocrine glands?
The hormone thyroxine is given as an oral dose, but insulin needs to be injected into the body. Why?
Give three examples of second messengers.
The average male with a computer hooked up to the Internet receives thousands of spam e-mails for all kinds of things, such as Viagra, weight-loss pills, and others not fit to print.Among the spam,
List two hormones that work through the cAMP second messenger.
How does glucagon affect the following enzymes:(a) Glycogen phosphorylase(b) Glycogen synthase(c) Phosphofructokinase I
How does epinephrine affect the enzymes listed in Question 39?Question 39How does glucagon affect the following enzymes:(a) Glycogen phosphorylase(b) Glycogen synthase(c) Phosphofructokinase I
For each of three hormones discussed in this chapter, give its source and chemical nature; also discuss the mode of action of each hormone.
When PIP2 is hydrolyzed, why does IP3 diffuse into the cytosol while DAG remains in the membrane?
Cholera harms the body by its effect on a second messenger. Describe how this takes place.
What is the primary function of insulin?
What is the second messenger for the insulin response?
What is the link between insulin binding to the receptor and the eventual second messenger?
What types of normal cells typically have insulin receptors?
What is the relationship between obesity and cancer?
In what way can some cancers be thought of as a lifestyle disease?
What is PTEN and what is its relationship to cancer?
What is the natural function of PTEN?
What is the subunit composition of E. coli RNA polymerase?
How do the sites of cleavage of starch differ from one another when the cleavage reaction is catalyzed by α-amylase and β-amylase?
Would you expect cross-linking to play a role in the structure of polysaccharides? If so, how would the cross-links be formed?
Compare the information in the sequence of monomers in a polysaccharide with that in the sequence of amino acid residues in a protein.
Could bacterial cell walls consist largely of protein? Why or why not?
Some athletes eat diets high in carbohydrates before an event. Suggest a biochemical basis for this practice.
You are a teaching assistant in a general chemistry lab. The next experiment is to be an oxidation–reduction titration involving iodine. You get a starch indicator from the stockroom. Why do you
Blood samples for research or medical tests sometimes have heparin added. Why is this done?
What are glycoproteins? What are some of their biochemical roles?
Briefly indicate the role of glycoproteins as antigenic determinants for blood groups.
What are the possible metabolic fates of pyruvate?
Explain the origin of the name of the enzyme aldolase.
Define isozymes and give an example from the material discussed in this chapter.
Why is the formation of fructose-1,6-bisphosphate the committed step in glycolysis?
What are the metabolic effects of not being able to produce the M subunit of phosphofructokinase?
In what way is the observed mode of action of hexokinase consistent with the induced-fit theory of enzyme action?
How does ATP act as an allosteric effector in the mode of action of phosphofructokinase?
At what point in glycolysis are all the reactions considered doubled?
Which of the enzymes discussed in this chapter are NADH-linked dehydrogenases?
Define substrate-level phosphorylation and give an example from the reactions discussed in this chapter.
Which reactions are the control points in glycolysis?
Which molecules act as inhibitors of glycolysis? Which molecules act as activators?
Many NADH-linked dehydrogenases have similar active sites. Which part of glyceraldehyde-3-phosphate dehydrogenase would be the most conserved between other enzymes?
Is the reaction of 2-phosphoglycerate to phosphoenolpyruvate a redox reaction? Give the reason for your answer.
Show the carbon atom that changes oxidation state during the reaction catalyzed by glyceraldehyde-3-phosphate dehydrogenase. What is the functional group that changes during the reaction?
Most metabolic pathways are relatively long and appear to be very complex. For example, there are 10 individual chemical reactions in glycolysis, converting glucose to pyruvate.Suggest a reason for
What does the material of this chapter have to do with beer? What does it have to do with tired and aching muscles?
What is the metabolic purpose of lactic acid production?
Briefly discuss the role of thiamine pyrophosphate in enzymatic reactions, using material from this chapter to illustrate your points.
Most hunters know that meat from animals that have been run to death tastes sour. Suggest a reason for this observation.
What is the metabolic advantage in the conversion of glucose to lactate, in which there is no net oxidation or reduction?
Can modification of enzymes of aerobic glycolysis play a role in cancer treatment?
What is the net gain of ATP molecules derived from the reactions of glycolysis?
How does the result in Question 41 differ from the gross yield of ATP?Question 41What is the net gain of ATP molecules derived from the reactions of glycolysis?
Which reactions in glycolysis are coupled reactions?
Which steps in glycolysis are physiologically irreversible?
In the muscles, glycogen is broken down via the following reaction:What would be the ATP yield per molecule of glucose in the muscle if glycogen were the source of the glucose? (Glucose) + P₁ →
What should be the net ATP yield for glycolysis when fructose, mannose, and galactose are used as the starting compounds? Justify your answer.
Why is the formation of fructose-1,6-bisphosphate a step in which control is likely to be exercised in the glycolytic pathway?
High levels of glucose-6-phosphate inhibit glycolysis. If the concentration of glucose-6-phosphate decreases, activity is restored. Why?
Do hormones play a role in control of metabolism? Is glycolysis a possible pathway for such control?
Why is it reasonable to expect that control can be exerted near the end of a pathway as well as near the beginning?
Why is it essential that the mechanisms that activate glycogen synthesis also deactivate glycogen phosphorylase?
How does phosphorolysis differ from hydrolysis?
Why is it advantageous that breakdown of glycogen gives rise to glucose-6-phosphate rather than to glucose?
Briefly outline the role of UDPG in glycogen biosynthesis.
Name two control mechanisms that play a role in glycogen biosynthesis. Give an example of each.
Does the net gain of ATP in glycolysis differ when glycogen, rather than glucose, is the starting material? If so, what is the change?
How does the cost of storing glucose-6-phosphate (G6P) as glycogen differ from the answer you obtained in Question 7 if G6P were used for energy in aerobic metabolism?Question 7In metabolism,
You are planning to go on a strenuous hike and are advised to eat plenty of high-carbohydrate foods, such as bread and pasta, for several days beforehand. Suggest a reason for the advice.

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