Question

In: Chemistry

1 a. What is meant by “energy charge” of a cell? b. Describe two conditions that...

1 a. What is meant by “energy charge” of a cell?

b. Describe two conditions that would indicate a low cell energy charge?

c. What effect does a low energy charge have on cellular metabolism? Explain.

d. How many ATP are produced from the complete oxidation of pyruvate?

2. Glucose and fructose are both carbohydrates. Discuss the similarities and differences between them. What is their isomeric relationship? What type of ring structures does each tend to form? What is sucrose? How does sucrose differ from lactose? Include structures where necessary.

3. Glycolysis is a series of reactions that converts one molecule of glucose to two molecules of pyruvate and two molecules of ATP. The ∆G0’ for the set of reactions is -35.6 kJ/mol (-8.5 kcal/mol) whereas the ∆G is -76.6 kJ/mol (-18.3 kcal/mol). Explain why the free energy release differs under actual cellular conditions as compared to standard conditions.

4. a. Pyruvate dehydrogenase (the complex) catalyzes which reaction? Show the substrates and products. b.Name the coenzymes required and explain the function of each one. c.List one positive and one negative allosteric modulator. d.Where in the cell does this reaction take place

5. a. NAD+ participates in three steps of the citric acid cycle. Show the reactions and the enzymes involved in each step. b.In which reaction is FAD generated (include the enzyme)?

6. Name the citric acid cycle enzymes that are subject to allosteric modulation.               Name one positive and one negative allosteric modulator for each enzyme.

Solutions

Expert Solution

Energy charge is an index used to measure the energy status of biological cells.It is related to ATP, ADP and AMP concentrations. It is given as -

Biology textbooks often state that 38 ATP molecules can be made per oxidised glucose molecule during cellular respiration (2 from glycolysis, 2 from the Krebs cycle, and about 34 from the electron transport system).[2] However, this maximum yield is never quite reached because of losses due to leaky membranes as well as the cost of moving pyruvate and ADP into the mitochondrial matrix, and current estimates range around 29 to 30 ATP per glucose.

Sucrose, glucose and fructose are important carbohydrates, commonly referred to as simple sugars. Sugar is found naturally in whole foods and is often added to processed foods to sweeten them and increase flavor. Your tongue can't quite distinguish between these sugars, but your body can tell the difference. They all provide the same amount of energy per gram, but are processed and used differently throughout the body.

Structure

Simple carbohydrates are classified as either monosaccharides or disaccharides. Monosaccharides are the simplest, most basic units of carbohydrates and are made up of only one sugar unit. Glucose and fructose are monosaccharides and are the building blocks of sucrose, a disaccharide. Thus, disaccharides are just a pair of linked sugar molecules. They are formed when two monosaccharides are joined together and a molecule of water is removed -- a dehydration reaction.

Glucose

The most important monosaccharide is glucose, the body’s preferred energy source. Glucose is also called blood sugar, as it circulates in the blood, and relies on the enzymes glucokinase or hexokinase to initiate metabolism. Your body processes most carbohydrates you eat into glucose, either to be used immediately for energy or to be stored in muscle cells or the liver as glycogen for later use. Unlike fructose, insulin is secreted primarily in response to elevated blood concentrations of glucose, and insulin facilitates the entry of glucose into cells.

Fructose

Fructose is a sugar found naturally in many fruits and vegetables, and added to various beverages such as soda and fruit-flavored drinks. However, it is very different from other sugars because it has a different metabolic pathway and is not the preferred energy source for muscles or the brain. Fructose is only metabolized in the liver and relies on fructokinase to initiate metabolism. It is also more lipogenic, or fat-producing, than glucose. Unlike glucose, too, it does not cause insulin to be released or stimulate production of leptin, a key hormone for regulating energy intake and expenditure. These factors raise concerns about chronically high intakes of dietary fructose, because it appears to behave more like fat in the body than like other carbohydrates.

Sucrose

Sucrose is commonly known as table sugar, and is obtained from sugar cane or sugar beets. Fruits and vegetables also naturally contain sucrose. When sucrose is consumed, the enzyme beta-fructosidase separates sucrose into its individual sugar units of glucose and fructose. Both sugars are then taken up by their specific transport mechanisms. The body responds to the glucose content of the meal in its usual manner; however, fructose uptake occurs at the same time. The body will use glucose as its main energy source and the excess energy from fructose, if not needed, will be poured into fat synthesis, which is stimulated by the insulin released in response to glucose.


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