Ch 12 - Bioenergetics and Regulation of Metabolism

Question 1

What is the difference between an open and closed biological system and how is a system determined?

Answer 1

• open: matter and energy can be exchanged with the environment
• closed: only energy can be exchanged with the environment
• determined based on the examination of the entire organism or an isolated process

Question 2

How do enthalpy, internal energy, and heat exchange relate in an closed system?

Answer 2

changes in enthalpy are equal to changes in internal energy, which is equal to heat exchange within the environment

Question 3

Why is no work performed in a closed system?

Answer 3

because pressure and volume remain constant

Question 4

What is entropy?

Answer 4

a measure of energy dispersion in a system

Question 5

How do physiological concentrations relate to standard concentraitons?

Answer 5

physiological usually &laquo_space;standard

Question 6

How must free energy calculations be adjusted?

Answer 6

for pH (delta Go’), temperature (37 C = 98.6 C = 310 K), and concentrations

Question 7

What are the main roles of ATP??

Answer 7

• mid level energy molecule
• contains high energy phosphate bonds that are stabilized upon hydrolysis by resonance, ionization, and loss of charge repulsion
• provides energy through hydrolysis and coupling to energetically unfavorable reactions
• can participate in phosphoryl group transfers as a phosphate donor

Question 8

Why might redox reactions be broken down into half reactions?

Answer 8

half reactions provide useful information about stoichiometry and thermodynamics

Question 9

How do many redox reactions transport high energy electrons?

Answer 9

via electron carrier

Question 10

Where are electron carriers?

Answer 10

may be soluble or membrane bound

Question 11

What are flavoproteins?

Answer 11

one subclass of electron carriers that are derived from riboflavin (vitamin B2)

Question 12

Why is equilibrium an undesirable state for most biochemical reactions?

Answer 12

because need to harness free energy to survive

Question 13

What happens to insulin and metabolism in the postprandial/well fed (absorptive) state?

Answer 13

insulin secretion is high and anabolic metabolism prevails

Question 14

What happens to insulin and metabolism in the postabsorptive (fasting) state?

Answer 14

• insulin secretion decreases while glucagon and catecholamine secretion increases
• this state observed in short term fasting (overnight)
• there is a transition to catabolic metabolism

Question 15

What happens to metabolism in prolonged fasting (starvation)?

Answer 15

• dramatic increase in glucagon and catecholamine secretion
• most tissues rely on fatty acids
• at maximum, 2/3 of the brain’s energy can be derived from ketone bodies

Question 16

How do insulin and glucagon relate during most aspects of metabolism?

Answer 16

opposing activities

• insulin causes a decrease in blood glucose levels by increasing cellular uptake
• insulin increase the rate of anabolic metabolism
• insulin secretion by pancreatic beta-cells is regulated by blood glucose levels
• glucagon increases blood glucose levels by promoting gluconeogenesis and glycogenolysis in the liver
• glucagon secretion by pancreatic alpha-cells is stimulated by both low glucose and high amino acid levels

Question 17

What do glucocorticoids do in metabolism?

Answer 17

• increase blood glucose in response to stress by mobilizing fat stores and inhibiting glucose uptake
• increase the impact of glucagon and catecholamines

Question 18

What do catecholamines do in metabolism?

Answer 18

promote glycogenolysis and increases basal metabolic rate through their sympathetic nervous system activity

Question 19

What do thyroid hormones do in metabolism? What is the difference between T3 and T4?

Answer 19

• modulate the impact of other metabolic hormones and have a direct impact on basal metabolic rate
• T3 is more potent than T4, but has a shorter half-life and is available in lower concentrations in the blood
• T4 is converted to T3 at the tissues

Question 20

What are hepatocytes responsible for?

Answer 20

the maintenance of blood glucose levels by glycogenolysis and gluconeogenesis in response to pancreatic hormone stimulation

Question 21

How does the liver compare to other organs?

Answer 21

most metabolically diverse

Question 22

What does the liver participate in processing of?

Answer 22

lipids and cholesterol, bile, urea, and toxins

Question 23

What do adipose tissues do in metabolism?

Answer 23

stores lipids under the influence of insulin and releases them under the influence of epinephrine

Question 24

How does skeletal muscle metabolism differ based on the current activity level and fiber type?

Answer 24

• resting muscle conserves carbohydrates in glycogen stores and uses free fatty acids from the bloodstream, require insulin for glucose uptake
• active muscle may use anaerobic metabolism, oxidative phosphorylation of glucose, direct phosphorylation from creatine phosphate, or fatty acid oxidation, depending on fiber type and exercise duration

Question 25

What do cardiac muscles do in metabolism?

Answer 25

use fatty acid oxidation in both well fed and fasting states

Question 26

What metabolic states does the brain and other nervous tissue consume glucose?

Answer 26

they consume in all metabolic states, except for prolonged fast, where up to 2/3 of the brain's fuel may come from ketone bodies

Question 27

How can metabolic rates be measured?

Answer 27

by using calorimetry, respirometry, consumption tracking, or measurement of blood concentrations of substrates and hormones

Question 28

What does the respiratory quotient (RQ) estimate?

Answer 28

composition of fuel that is actively consumed by the body | RQ = CO2 produced/O2 consumed

Question 29

What hormones and their receptors play a role in body mass?

Answer 29

leptin, ghrelin, and orexin

Question 30

What do long term changes in body mass result from?

Answer 30

changes in lipid storage

Question 31

What threshold must be passed to cause weight change?

Answer 31

- changes in consumption or activity must surpass a threshold to cause weight change - the threshold is lower for weight gain than for weight loss

Question 32

How is body mass measured and tracked?

Answer 32

body mass index (BMI) | BMI = mass /height^2

Question 33

What conditions does delta Go' adjust for that are not considered with delta Go?

Answer 33

- delta Go' adjusts only for the pH of the environment by fixing it at 7 - temperature and concentrations of all other reagents are still fixed at their values from standard conditions and must be adjusted for if they are not 1 M

Question 34

Why can heat be used as a measure of internal energy in living systems?

Answer 34

the cellular environment has a relatively fixed volume and pressure, which eliminates work from our calculations of internal energy - if delta U = Q - W and W = 0, delta U = Q

Question 35

How does entropy relate to enthalpy?

Answer 35

- when change in entropy (+): spontaneous at higher temperatures if delta H (+),; spontaneous if delta H (-) - when change in entropy (-): non spontaneous if delta H (+), spontaneous at low temperatures if delta H (-)

Question 36

How does coupling with ATP hydrolysis alter the energetics of a reaction?

Answer 36

- ATP hydrolysis yields about 30 kJ/mol of energy, which can be harnessed to drive other reactions forward - this may either allow a nonspontaneous reaction to occur or increase the rate of a spontaneous reaction

Question 37

Explain why ATP is an efficient molecule for long term energy storage.

Answer 37

- ATP is an intermediate energy storage molecules and is not energetically dense - the high energy bonds in ATP and the presence of a significant charge make it an inefficient molecule to pack into a small space - long term storage molecules are characterized by energy density and stable, non repulsive bonds, primarily seen in lipids

Question 38

What are the soluble electron carriers and their relevant metabolic pathways in the cells?

Answer 38

- NADH: glycolysis, fermentation, citric acid cycle, electron transport chain - NADPH: pentose phosphate pathway, lipid biosynthesis, bleach formation, oxidative stress, photosynthesis - Ubiquinone (CoQ): electron transport chain - cytochromes: electron transport chain - glutathione: oxidative stress

Question 39

What is an example of disequilibrium that is maintained at the expense of cellular energy?

Answer 39

- any excitable cell is maintained in a state of disequilibrium - classic examples include muscle tissues and neurons - in addition, cell volume and membrane transport are regulated by the action of the Na-K pump, which can maintain a stable disequilibrium state in most tissues

Question 40

What tissue is least able to change its fuel source in periods of prolonged starvation?

Answer 40

- cells that rely on anaerobic respiration are the least adaptable to different energy sources - therefore, RBCs are the least flexible during periods of prolonged starvation and stay reliant on glucose

Question 41

During what stage is there the greatest decrease in the circulating concentration of insulin?

Answer 41

- postabsorptive state - the concentrations of counterregulatory hormones (glucagon, cortisol, epinephrine, norepinephrine, and growth hormone) begin to rise

Question 42

Describe the primary function of insulin.

Answer 42

- promotes glucose uptake by adipose tissue and muscle - glucose utilization in muscle tissues - macromolecule storage (glycogenesis, lipogenesis)

Question 43

Describe the primary function of glucagon

Answer 43

- increase blood glucose levels by promoting glycogenolysis, gluconeogenesis, lipolysis, and ketogenesis

Question 44

Describe the primary function of cortisol

Answer 44

- increases lipolysis and amino acid mobilization, while decreasing glucose uptake in certain tissues and enhancing the activity of other counterregulatory hormones

Question 45

What is the preferred fuel for most cells in the well-fed state? What is the exception and its prefered fuel?

Answer 45

- glucose preferred | - exception is cardiac muscle which prefers fatty acid

Question 46

What organs consumes the greatest amount of glucose relative to its percentage of body mass?

Answer 46

brain

Question 47

Describe the major metabolic functions of the liver.

Answer 47

- responsible for maintaining a steady-state concentration of glucose in the blood through glucose uptake and storage, glycogenolysis, and gluconeogenesis - participates in cholesterol and fat metabolism, the urea cycle, bile synthesis, and the detoxification of foreign substances

Question 48

How is the respiratory quotient expected to change a person transitions from resting to brief exercise?

Answer 48

- as a person begins to exercise, the proportion of energy derived from glucose increases - this transition to almost exclusively carbohydrate metabolism will cause the RQ to approach 1

Question 49

Can body mass be predicted by the leptin receptor phenotype and caloric intake alone?

Answer 49

- no, energy expenditure, genetics, socioeconomic status, geography, and other hormones play a role in body mass regulation

Question 50

How do hormonal controls of glycogen metabolism differ from allosteric controls?

Answer 50

- hormonal controls are coordinated to regulate the metabolic activity of the entire organism, while allosteric controls can be local or systemic - the modification of the enzymes of glycogen metabolism by insulin and glucagon is either through phosphorylation or dephosphorylation, both of which modify covalent bonds

Question 51

Which tissue will experience damage most rapidly in the absence of oxygen?

Answer 51

- the brain uses aerobic metabolism of glucose exclusively and therefore is very sensitive to oxygen levels - the extremely high oxygen requirement of the brain (20% of the body's oxygen content) relative to its size (2% of total body weight) implies that the brain is the most sensitive organ to oxygen deprivation

Question 52

An RQ approaching 0.7 indicates metabolism primarily of which macromolecule?

Answer 52

- the RQ gives an indication of the primary fuel being utilized - an RQ around 0.7 indicates lipid metabolism, - 0.8-0.9 indicates amino acid metabolism - 1 indicates carbohydrate metabolism - nucleic acids do not contribute significantly to RQ

Question 53

What side effect would be anticipated in someone taking leptin to promote weight loss?

Answer 53

- leptin acts to decrease appetite by inhibiting the production of orexin - orexin is also associated with alertness, so decreasing the level of orexin in the body is expected to cause drowsiness