02 Energiestoffwechsel Flashcards
Metabolism
- Metabolic reactions are coupled together to form metabolic pathways (glycolysis, lipolysis….), where one substance is transformed, through a series of reactions, into another one.
- This process produces various intermediates, which can act as an initial substrate for other metabolic pathways.
- For example pyruvate can be converted to lactate, or it can form an amino acid alanine, participate in the formation of glucose in the process of gluconeogenesis or be converted to acetyl-CoA and act as an energy source.
- We call this interconversion of nutrients with various intermediate products an intermediary (or intermediate) metabolism.
Metabolism
Metabolic reactions in general can be divided into anabolic and catabolic:
1) Anabolic reactions: Synthesis, construction of complex substances from simpler one (i.e. protein synthesis from amino acids, gluconeogenesis, lipogenesis....). Require energy (endergonic reactions)
2) Catabolic reactions: breaking down, degradation or decomposition of complex substances into simpler ones (i.e. glycolysis, lipolysis, beta-oxidation….).
The energy is released during this process.
Basics of (food) energy
Institute of Biological Chemistry and Nutritional Science (140a) Basics of (food) energy
- Joule (J) is the energy expended in applying a force of one Newton (N) through a distance of one meter (m)
- Energy= force x distance = J = N x m = W x s =
(kg x m^2) / s^2
- Joule (J); 1 kcal = 4,184 kJ or 1kJ = 0,239 kcal
- One calorie (cal) is the heat energy required to increase the temperature of 1 gram of water by one degree Celsius (°C).
- Forms of energy: mechanical/ chemical/ electrical/ thermal…
1 Joule (J) represents approximately:
- The energy required to lift a medium-sized potato up 1 m
- The heat required to raise the temperature of 1 g of water by 0.24 °C
- The typical energy released as heat by a person at rest every 1/60 s
- The kinetic energy of a 50 kg human moving very slowly (0.2 m/s or 0.72 km/h)
- The kinetic energy of an object with mass 2 kg moving at 1 m/s
• The amount of electricity required to light a 1 W LED for 1 s
Energy needs
a
Control of energy balance
Physiological energy value ~ Physical energy value
Power supply
Ø 2000kcal
Carbohydrates (55-60%) Fats (30%)
Proteins (10-15%) Alcohol (max 20g)
Power consumption
Ø 2000kcal
Basal metabolim Job Thermogenesis
(Tabellen)
Physical and physiological energy values of the energy-supplying nutrients
- Physical energy value: is the energy released from the nutrient, if it is completelly burned and broken down. Measured in a calorimeter.
- Physiological calorific value: how much energy is released during metabolism per unit of weight (g) of a food during metabolism (catabolism).
- The organism never fully breaks down the material it took in. Physical energy value > physiological energy value.
Energy Balance
Physiological energy value of fats and carbohydrates
Physiological energy value ~ Physical energy value
- Almost complete combustion; Products: CO2, H2O
- Physiological energy value ~ Physical energy value
• Digestibiliy carbohydrates: max 98%
Loss due to accompanying substances (fiber)
• Digestibility fats: ~97%
Energy balance
Physiological energy value of proteins
Physical energy value > Physiological
- Incompletecombustion;Synthesisofanenergy-richmetabolit(urea)
- Energy loss: 3 ATP / Mol urea
- Physical energy value > Physiological
- The energy (calorific) value varies depending on the amino acids composition
• VariableDigestion:
Animal protein 98% > Vegetal Protein 95%
Energy balance – Efficiency of energy yield
Electrochemical gradient
• Mitochondria uses fuels to produce energy in the form of ATP
• Cells store the energy as a proton gradient across the
mitochondrial inner membrane
• To keep T constant, body heat is maintained by signalling the
mitochondria to allow protons to run back along the gradient
without producing ATP
• Alternative return route for the protons through an uncopling
protein in the inner membrane (UCP1 or thermogenin)
Regulation of food intake
- The sensation of hunger is associated with a craving for food and several other physiologic effects (eg, rhythmical contractions of the stomach).
- Appetite is a desire for food, often of a particular type.
- Satiety is the inhibition of hunger and eating, arising from the eating of sufficient food.
Regulation of hunger and satiety:
• Periphery adipose tissue (leptin) gastrointestinal tract
• Central Nervous system
cerebral cortex, limbic system
• Central nervous system, Hypothalamus (swticthing point)
Regulation of food intake and energy storage
The hypothalamus receives neural signals from the GI tract that provide:
.
• Sensory information about stomach filling.
• Chemical signals from nutrients in the blood (glucosa, aa
and FAs).
- Signals from gastrointestinal hormones.
- Signals from hormones released by adipose tissue (leptin).
- The Hypothalamus contains hunger and satiety centers
- The lateral nuclei of the hypothalamus serve as a feeding center → stimulation causes to eat in excess (hyperphagia). Destruction causes lack of desire for food → inanition
- The ventromedial nuclei of the hypothalamus serve as satiety center. Inhibits the feeding center. Stimulation of this region → complete satiety. Destruction of this region → voracious and continued eating
• Signals from the cerebral cortex (sight, smell and taste) that
CCK, GLP-1, PYY influence feeding behaviour.
• The hypothalamic feeding and satiety centers have a high density of receptors for neurotransmitters and hormones that influence feeding behavior.
• Substances that alter appetitite and feding bahaviour are:
-orexigenic (stimulate feeding) -anorexigenic (inhibit feeding)
Long-term regulatory mechanisms:
• Leptin, formed in adipose tissue
• Anorexigenic effect
• Leptin Serum levels correlate closely with adipose
Regulation of hunger and satiety
- Regulation of hunger and satiety to keep energy balance constant.
- Complex regulation of food intake through peripheral and central mechanisms.
- There are multiple short- and long-term control systems that regulate not only food intake but also energy expenditure and energy stored.
Genetic factors
Why do metabolism, nutrition and disease risk differ between people?
Energy requirements are influenced by:
1) Environmental factors (intra-individual differences)
2) Genetic factors (inter-individual differences)
• The optimization of energy use through genetic variants led to the survival advantage of these individuals in times of energy deficiency („Thrifty Phenotype“).
Polygenetic forms of obesity
- About 70% of variance in the BMI is caused by genetic factors;
- Genetic Disposition impacts basal metabolic rate, respiratory quotent, acitivity, hyperphagia, etc..
Genetic factors
When different people consume the same meal, the impact on each person’s blood sugar and fat formation will vary by their genes, lifestyles and unique mix of gut bacteria.
Nutritional genomics (nutrigenomics): the study of how different foods can interact with particular genes to ↑ the risk of disease (eg. T2D, obesity) (diet → genotype → phenotype).
Nutrigenetics: identifies how genetic makeup of a subjec coordinates his or her response to various dietary nutrients (genotype → diet).
Also both known as nutrigenomics.
Bioenergetics
Study of energy transformation that accompanies biochemical reactions
All living organisms are open systems
they exchange matter & energy with the environment.
All organism exist in a steady (equilibrium) state
rate of transfer in and out of the system is constant.
Living organisms are essentially isothermal.
1st Law of Thermodynamics: Energy can be transferred and converted; but cannot be generated or destroyed
2nd Law of thermodynamics: spontaneous processes are associated with an increase in entropy (ΔG’).
Classes of reactions:
Reaction with negative ΔG ́ < 0: exothermic (release heat)
Reaction with positive ΔG‘ > 0: endothermic (need heat)
Individual reactions must be specific.
The sequence of the reactions must be termodynamically favoured (ΔG0‘ < 0).
A thermodynamically unfavoured reaction can be made possible by a favoured reaction which is coupled to it.
A ⟷ B + C
ΔG01‘= + 21 kJ/mol
B ⟷ D
ΔG02‘= - 34 kJ/mol
A ⟷ C + D
ΔG0‘ = 13 kJ/mol
(∆G total = ∆G1 + ∆G2)
(Bsp. S 17)
High energy substrate – Adenosine triphosphate (ATP)
- ATP (adenosine triphosphate) is a complex organic chemical that provides energy to drive many processes in living cells
- ATP is the chemical link between catabolism and anabolism
- ATP is the “energy currency” of living cells
• The exergonic conversion of ATP to ADP or AMP is coupled to many
endergonic reactions and processes
Energy consumption – basal metabolic rate
The basal metabolic rate (BMR) is the resting metabolic rate at rest.
Calories spent with NO activity.
Amount of energy needed to sustain life ́s processes.
Average BMR: 70 cal / hr
Basal metabolic rate corresponds to Basal Energy Expenditure (BEE) Rate of energy consumption : Calories/unit of time or watts.
