Lecture 16 - Energy metabolism Flashcards
Hypoxia
Oxygen in limited supply
Anoxia
No oxygen in environment
Glycolysis
Key anaerobic pathway (especially in vertebrates)
Produces 2 ATP per glucose molecule
Lactate
The end product of anaerobic glycolysis
Pyruvate oxidized to lactate via enzyme lactate dehydrogenase.
What are the effects of lactic acid?
It dissociates and releases H+ ions which upset acid-base balance and has toxic effects
Goldfish vs Human anaerobic metabolism.
Goldfish use ethanol dehydrogenase, which produces ethanol (can be diffused out through gills)
Only suitable in <5 degree water.
Other less toxix end products than lactate
Alanine, succinate, octopine
Facultative anaerobes
Rely on anaerobic metabolism for extended periods
Intertidal vertebrates
Obligate anaerobes
Cannot survive in the presence of significant amounts of oxygen
Protozoans in termite guts and some parasites
Oysters and oxygen
Some oysters don’t need oxygen and can survive purely on anaerobic metabolism
Reasons to avoid anaerobic metabolism
- End products are usually toxic
2. Anaerobic metabolism is less efficient (2 ATP vs 38 ATP)
To maintain constant body temp
Heat production must be equal to heat loss
H = Q = C (Tb-Ta)
Heat production = Heat loss = Thermal conductance(Body temperature - ambient temperature)
BMR
Basal Metabolic Rate
Lowest rate of metabolism in an animal
What happens when Ta is below Tlc
Heat production at cost of ATP
What happens when Ta is above Tlc
Passive Decreasing Insulation until Tb=Ta
What happens when Ta is above Tuc
Active evaporative cooling
Endotherm vs Ectotherm Aerobic capacity
Endotherms have higher aerobic capacity
Why is Metabolism Important?
Converting energetic and material resources from the environment into energy for fitness-enhancing processes of survival (e.g. - growth and reproduction).
What are the Basic Requirements of Bomb Calorimetry?
- Sealed reaction vessel
- Sample ignited electrically in presence of pure oxygen
- Temperature rises of water expected
What are the 1st and 2nd Laws of Thermodynamics?
- Energy cannot be created or destroyed, but can be transformed from one form of energy into another.
- There is inevitable degradation of useful energy into heat.
What are the Features of ATP?
- Ubiquitous in living cells
- “Electricity” of cellular metabolism (chemical storage of energy)
- Can be cleaved from ATP -> ADP + P + energy
Name and Explain Both Metabolic Pathways:
Catabolic Metabolism:
Breakdown of complex molecules into simpler ones (produces “building block” molecules and ATP)
Anabolic Metabolism:
Synthesis of macromolecules - produces cellular components and uses ATP
Explain the Steps of Aerobic Metabolism:
- NAD+ (nicotine-adenine dinucleotide) reduced to NADH
- Glucose oxidised to pyruvate
- Complete oxidation to CO2 and H2O requires oxygen
Explain the Steps of Aerobic Metabolism:
- NAD+ (nicotine-adenine dinucleotide) reduced to NADH
- Glucose oxidised to pyruvate
- Complete oxidation to CO2 and H2O requires oxygen
Explain the Steps of Anaerobic Metabolism:
- NAD+ reduced to NADH and glucose becomes 2 pyruvate (2ADP -> 2ATP)
- 2 pyruvate becomes 2 lactate via NADH oxidation into NAD+.
- Overall output of 2 ATP per glucose molecule.
Note: Lactate can dissociate (if accumulated) and release H+ ions, upsetting the acid-base balance thus creating toxic effects.
What are the Two Types of Anaerobes?
Facultative Anaerobes:
Rely on anaerobic metabolism for extended periods
Obligate Anaerobes:
Cannot survive in the presence of significant amounts of oxygen (e.g. - protozoans)
What is Oxygen Debt?
The resynthesis of depleted ATP and phosphocreatine, replenishing myoglobin.
The Effect of Temperature on Metabolic Rate:
To maintain a constant body temperature, heat production (H) must equal heat loss (Q) -> H = Q = C(Tb - Ta)
- C = thermal conductance
- Tb = body temperature
- Ta = ambient temperature
What is Assimilation Efficiency?
Apparent assimilated energy (A) / Gross energy consumption (C)
A = C - Fecal energy
Which Food Has the Highest Assimilation Efficiency?
Highest to Lowest:
Nectar -> Vertebrate Tissue -> Grains and Seeds -> Herbivory
What are the Types of Urinary Energy Loss?
Endogenous:
Deamination and transamination of amino acids resulting from basal protein turnover.
Exogenous:
Deamination of amino acids ingested and absorbed in the food (depends on the feeding rate, food protein content and amino acid composition of the proteins)
Waste Products -> Ammonia (Fish), Urea (Mammals), Uric Acid (Birds and Reptiles)
What is Specific Dynamic Action (SDA)?
The heat increment of feeding:
- Depends on the size, composition and temperature of the meal.
- Depends on the animal’s body size, composition, sex and age
- Depends on the temperature, gas concentration and salinity of the environment.
What is the Mechanistic Basis of Specific Dynamic Action?
Pre-Absorptive Contributions:
- Occur prior to the passage of ingested nutrients into circulation
- Eating and swallowing (a few % for most species; more for herbivores)
- Gastric breakdown (cost depends on state of meal when entering stomach)
- Intestinal peristalsis and absorption.
Post-Absorptive Contributions:
- Occur once nutrients are circulating
- Substrate catabolism (major contributor)
- Biosynthesis (e.g. - protein synthesis, glycogen from glucose, etc.)
How do Animals Generate ATP When Oxygen is Limited or Unavailable? What are the Advantages and Disadvantages of This Pathway Compared to Pathways that Require Oxygen?
Animals generate ATP through anaerobic respiration when oxygen is limited.
Advantages:
- Produces ATP in absence of oxygen
- Rapid production of energy
Disadvantages:
- Lactic acid accumulation can be toxic to host organism
- Very inefficient process of producing ATP (2 ATP as opposed to aerobic respiration being 38 ATP).
