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MCAT Biochem > Ch 12 - Bioenergetics and Regulation of Metabolism > Flashcards

Ch 12 - Bioenergetics and Regulation of Metabolism Flashcards

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MCAT flashcards
1
Q

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

A
  • 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
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2
Q

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

A

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

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3
Q

Why is no work performed in a closed system?

A

because pressure and volume remain constant

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4
Q

What is entropy?

A

a measure of energy dispersion in a system

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5
Q

How do physiological concentrations relate to standard concentraitons?

A

physiological usually &laquo_space;standard

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6
Q

How must free energy calculations be adjusted?

A

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

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7
Q

What are the main roles of ATP??

A
  • 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
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8
Q

Why might redox reactions be broken down into half reactions?

A

half reactions provide useful information about stoichiometry and thermodynamics

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9
Q

How do many redox reactions transport high energy electrons?

A

via electron carrier

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10
Q

Where are electron carriers?

A

may be soluble or membrane bound

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11
Q

What are flavoproteins?

A

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

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12
Q

Why is equilibrium an undesirable state for most biochemical reactions?

A

because need to harness free energy to survive

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13
Q

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

A

insulin secretion is high and anabolic metabolism prevails

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14
Q

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

A
  • insulin secretion decreases while glucagon and catecholamine secretion increases
  • this state observed in short term fasting (overnight)
  • there is a transition to catabolic metabolism
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15
Q

What happens to metabolism in prolonged fasting (starvation)?

A
  • 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
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16
Q

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

A

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
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17
Q

What do glucocorticoids do in metabolism?

A
  • increase blood glucose in response to stress by mobilizing fat stores and inhibiting glucose uptake
  • increase the impact of glucagon and catecholamines
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18
Q

What do catecholamines do in metabolism?

A

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

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19
Q

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

A
  • 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
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20
Q

What are hepatocytes responsible for?

A

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

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21
Q

How does the liver compare to other organs?

A

most metabolically diverse

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22
Q

What does the liver participate in processing of?

A

lipids and cholesterol, bile, urea, and toxins

23
Q

What do adipose tissues do in metabolism?

A

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

24
Q

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

A
  • 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
25
Q

What do cardiac muscles do in metabolism?

A

use fatty acid oxidation in both well fed and fasting states

26
Q

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

A

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

27
Q

How can metabolic rates be measured?

A

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

28
Q

What does the respiratory quotient (RQ) estimate?

A

composition of fuel that is actively consumed by the body

RQ = CO2 produced/O2 consumed

29
Q

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

A

leptin, ghrelin, and orexin

30
Q

What do long term changes in body mass result from?

A

changes in lipid storage

31
Q

What threshold must be passed to cause weight change?

A
  • changes in consumption or activity must surpass a threshold to cause weight change
  • the threshold is lower for weight gain than for weight loss
32
Q

How is body mass measured and tracked?

A

body mass index (BMI)

BMI = mass /height^2

33
Q

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

A
  • 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
34
Q

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

A

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

35
Q

How does entropy relate to enthalpy?

A
  • 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 (-)
36
Q

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

A
  • 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
37
Q

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

A
  • 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
38
Q

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

A
  • 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
39
Q

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

A
  • 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
40
Q

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

A
  • 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
41
Q

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

A
  • postabsorptive state
  • the concentrations of counterregulatory hormones (glucagon, cortisol, epinephrine, norepinephrine, and growth hormone) begin to rise
42
Q

Describe the primary function of insulin.

A
  • promotes glucose uptake by adipose tissue and muscle
  • glucose utilization in muscle tissues
  • macromolecule storage (glycogenesis, lipogenesis)
43
Q

Describe the primary function of glucagon

A
  • increase blood glucose levels by promoting glycogenolysis, gluconeogenesis, lipolysis, and ketogenesis
44
Q

Describe the primary function of cortisol

A
  • increases lipolysis and amino acid mobilization, while decreasing glucose uptake in certain tissues and enhancing the activity of other counterregulatory hormones
45
Q

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

A
  • glucose preferred

- exception is cardiac muscle which prefers fatty acid

46
Q

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

A

brain

47
Q

Describe the major metabolic functions of the liver.

A
  • 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
48
Q

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

A
  • 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
49
Q

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

A
  • no, energy expenditure, genetics, socioeconomic status, geography, and other hormones play a role in body mass regulation
50
Q

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

A
  • 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
51
Q

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

A
  • 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
52
Q

An RQ approaching 0.7 indicates metabolism primarily of which macromolecule?

A
  • 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
53
Q

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

A
  • 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

MCAT Biochem (12 decks)

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