Lecture 18: Energy Balance and Metabolism II Flashcards
What macromolecules is ATP generated from the combustion of?
- Carbohydrates
- Fatty Acids
- Proteins
What does ATP energize?
- Synthesis of cellular component.
- Muscle contraction.
- Active transport across membranes.
- Glandular secretion.
- Nerve conduction.
True or False:
Phosphocreatine functions as an accessory storage depot for energy and as an “ATP Buffer”.
True
Is phosphocreatine or ATP more abundant?
Phosphocreatine is 3-8x more abundant than ATP.
How many calories does the high energy phosphate bond in phosphocreatine have?
13,000 cal
True or False:
Phosphocreatine cannot transfer energy interchangeably with ATP.
False - phosphocreatine can transfer energy interchangeably with ATP.
What are essential amino acids?
Essential amino acids cannot be synthesized in the body or are not synthesized easily or in quantities.
What are non-essential amino acids?
Non-essential amino acid formation depends on alpha-keto acid precursors.
What is the definition of transamination?
The transfer of an amino group from one molecule to another, especially from an amino acid to a keto acid.
Could the synthesis of alanine from pyruvic acid by transamination be carried out if the patient had a deficiency in vitamin B6?
No - because the aminotransferaes, which is the enzyme for a transaminase reaction, are derivatives of pyridoxine (vitamin B6).
Why is glutamine important in the human body?
Present in the body in large quantities; serves as an amino radical storehouse to synthesis alanine from pyruvic acid by transamination.
The formation of which linkage is among the most important intracellular processes that require energy in the human body?
peptide linkages
How many high energy phosphate bonds are needed to form one peptide linkage?
4 high-energy phosphate bonds (48,000 cal).
List the steps in the formation of a peptide bond.
> AA + ATP -> AA-AMP + 2 Pi
> AA-AMP + tRNA -> AA-tRNA + AMP
> Attachment of tRNA to mRNA via condon-anticodon pairing
> Formation of peptide bond with second amino acid using peptidyl transferase + GTP
What is degraded in body fluids and used for energy?
Proteins (amino acids).
What does the first step in deamination involve?
transamination
2 molecules of what + 1 molecule of what are combined in the liver to form urea?
2 ammonia + 1 carbon dioxide = urea
In the degradation of proteins for energy, what pathway is utilized?
Urea (ornithine) Cycle
In the deamination of glutamic acid, what is released?
amino group
In the ornithine (urea) cycle, what steps occur in the mitochondria?
> ammonia + CO2 -> carbamoyl phosphate
> carbamoyl phosphate + ornithine -> citrulline
In the ornithine (urea) cycle, which steps occur in the cytoplasm?
> cirulline + aspartate -> argininosuccinate
> argininosuccinate -> arginine + fumarate
> arginine -> urea + ornithine
> fumarate can enter citric acid cycle (helps drive the cycle since this produce can enter the TCA cycle).
What is the rate of overall chemical reaction determined by?
- [enzyme]
- [substrate]
When the [substrate] is high, what is the reaction rate almost entirely determined by?
[enzyme]
When the [enzyme] is high, what is the reaction rate directly proportional to?
Directly proportional to [substrate] and [enzyme].
What is an example of the reaction rate becoming directly proportional to concentration of enzyme and substrate?
Absorption of substances from intestinal tract and renal tubules when concentrations of the substrate are low compared to transport enzymes.
What is an example of the reaction rate being determined almost entirely by concentration of enzyme?
Dabetes mellitus and glucose:
- Large quantities of glucose enter renal tubules.
- Glucose (substrate) is in great excess in the tubules.
- Transport enzymes become saturated.
- Further increases in glucose levels in tubules have little effect on glucose reabsorption.
- Glucose reabsorption rate is limited by concentration of transport enzymes.
The overall rate of a series of chemical reactions is determined by the rate of reaction of the slowest step in the series. What is this step called?
rate-limiting step
What molecule is the major rate-limiting factor for almost all energy metabolism in the body?
ADP
Give an example of a pathway that is ADP substrate dependent.
- All oxidative metabolic pathways.
- Other pathways for the release of energy.
What percentage of energy in foods becomes heat during ATP formation?
35%
List some factors that influence metabolic rate.
- Arousal vs. sleeping
- Skeletal muscle
- Age
- Thyroid activity
- Testosterone
- Growth hormone
- Fever
- Sleep
- Malnutrition
No more than what percentage of energy from food is used by the functional systems?
27%
most of this 27% is finally converted to heat
exception: energy transferred outside the body as potential energy (but eventually that will also become heat)
True or False:
Rate of the overall reaction is determined by both the concentration of the enzyme and the concentration of the substrate.
True
when substrate concentration is high, reaction rate is determined almost entirely by enzyme concentration
when substrate concentration is low, reaction rate is directly proportional to substrate concentration and enzyme concentration
Reaction Rate
ADP is the major rate-limiting factor for almost all energy metabolism in the body.
> Cellular concentrations of ADP are low.
> Chemical reactions that depend on ADP as one of the substrates are very slow.
> Examples of ADP substrate dependence:
- all oxidative metabolic pathways
- other pathways for the release of energy
> ATP is converted to ADP during cellular activity; therefore, ADP concentration increases during cellular activity.
> Increased concentration of ADP increases reaction rates.
What percentage of energy expended by the body is derived from oxidative phosphorylation involving different kinds of food?
95%
**Therefore, whole-body metabolic rate can be calculated from rate of oxygen utilization:
> metabolize 1 liter of oxygen with glucose = 5.01 Cal
> metabolize 1 liter of oxygen with fat = 4.7 Cal
> metabolize 1 liter of oxygen with protein = 4.6 Cal
How many calories of energy are liberated per liter of oxygen with an average diet?
4.825 Cal = energy equivalent of oxygen.
How many Cal per day does an average 70 kg man lying in bed all day use?
1650 Cal per day
How many Cal per day does an average 70 kg man lying in bed all day and eating a reasonable diet use?
1850 Cal per day
How many Cal per day does an average 70 kg man sitting in a chair all day without exercising use?
2000 Cal per day
True or False:
Walking upstairs requires 17x the energy as sleeping in bed all day.
True
BMR normally averages about how many Cal per hour?
65-70 Cal per hour.
What does thyroxine do?
Increases rate of chemical reactions in cells and increases metabolic rate.
What does the maximal secretion of thyroxine increase metabolic rate to?
50-100 percent above normal.
What does the loss of thyroid secretion decrease metabolic rate to?
40-60 percent decrease of normal.
How much does testosterone increase metabolic rate?
10-15 percent
mainly related to anabolic effect of increase in skeletal muscle mass
How does malnutrition affect basal metabolic rate?
> Malnutrition results in reduced food substances in the cells.
> This results in a marked reduction in metabolic rate.
> This process may accompany final stages of many disease conditions.
Why is BMR typically corrected for differences in body size?
Because skeletal muscle accounts for 20-30 % of BMR even at rest.
What is the decline in BMR with increasing age probably related to?
Loss of muscle mass and replacement with adipose tissue with a lower rate of metabolism.
What is glycogenolysis?
> Biochemical breakdown of glycogen to glucose.
> Takes place in the cells of muscle and liver tissues in response to hormonal and neural signals.
What is gluconeogenesis?
Is a metabolic pathway that results in the generation of glucose from certain non-carbohydrate carbon substrates.
