- An anaerobic process.
- The energy production is from glycolysis oxidation.
- In the absence of oxygen, no oxidative phosphorylation, no electron transport chain, no regeneration of NAD+ is expected to take place. Then, glycolysis would stop when NAD+ is depleted.
- However, in fermentation, additional reactions can occur, through which the NADH produced as a result of glycolysis is recycled back into NAD+. This allows for glycolysis to be sustained, as long as you have enough ATP around.
- Through this regeneration and oxidation of NADH, (animal) lactate or (yeast) ethanol is formed through the reduction of pyruvate.
- Involves electron transfer, but no electron transfer chain.
What is the process through which ATP is produced in fermentation?
Substrate level phosphorylation. This involves the transfer of phosphate to ADP from another compound that contains an energetic phosphate.
What is anaerobic respiration?
Respiration using a compound other than oxygen as the terminal electron acceptor.
When does fermentation occur?
When oxygen is limiting, NADH is limiting, and a need for ATP arises.
- Lactate is produced through anaerobic fermentation through the oxidation of pyruvate.
- Lactate exits the cell after its production and provides feedback inhibition for further glycolysis, even if the cell does need ATP and glucose is available.
- The heart and liver can convert lactate back to pyruvate.
Explain bacterial fermentation
- Perform glycolysis, as we do, in order to generate some ATP.
- They have an additional reaction, as well, that can regenerate NAD+ from NADH(2) through a slightly different reaction mechanism.
- This regeneration allows for continued glycolysis, enabling fermentation to continue.
Explain anaerobic respiration and differences with aerobic respiration
- With aerobic respiration, O2 is the final highly electronegative electron acceptor.
- However, less electronegative electron acceptor can also support respiration.
- Electrons from organic energy source gets oxidized (for example lactate). Electron is transported down a chain of electron transporters. This process is coupled to the generation of a proton gradient. The proton gradient is used for chemiosmosis and ATP production.
- However, in this example, the organic energy source is lactate instead of NADH (electron donor)
- There are related but distinct electron acceptors in this chain.
- Oxygen is not the final electron acceptor, (Could be sulfate)
Explain Photosynthesis shortly
- Light reaction: Harvest light energy and store it as ATP (photophosphorylation) and NADPH (reduction of NADP) through the oxidation of H2O (production of O2)
- Calvin cycle: Uses ATP and NADPH from light reaction to produce simple sugars from CO2.
What gets oxidized and reduced in photosynthesis?
Water is oxidized and CO2 is reduced.
Is photosynthesis endergonic or exergonic?
Endergonic. It harvests light energy.
Explain Light reaction
- Light energy is harvested in two photosystems.
- Different photosynthetic pigments absorb different wavelengths from the visible spectrum. (Leaves appear green because chlorophyll reflects green light) Maximum action occurs at 450 and 650 nm wavelength. (chlorophyll a, chlorophyll b, carotenoids all have maximum absorption at a characteristic wavelength)
- The absorbed energy is transferred between molecules by resonance. The energy is eventually transferred to the reaction center: photosystem 1 and photosystem 2 (linear in plants, cyclic in bacteria)
- ATP and NADPH are produced in reaction center through photophosphorylation.
Explain energy transfer by resonance in light reaction
- Begins with donor pigment, which absorbs the initial light.
- The donor pigment goes from low energy ground state (S0) to high energy excited state (S1)
- Some of the energy is lost by fluorescence (reemission of light). This, however, is slow.
- A faster process occurs when a donor pigment and acceptor pigment are close enough to be coupled and the energy is transferred to the acceptor by RESONANCE, with some efficiency loss.
- The acceptor then goes from a low energy ground state (S0) to a high energy excited state (S1)
- The electrons are not themselves transferred, their energy is transferred through RESONANCE.
Explain what happens at the reaction center in the Z scheme in plants
- Energy is transferred from pigments to P680, photosystem 2.
- P680+ now has an excited electron, which is transferred to the primary acceptor. (1st redox reaction)
- Without its electron, P680+ is a very powerful oxidizer. It oxidizes H2O into O2. The electrons from H2O restore P680+ back to P680.
- The electron transport chain afterwards creates a proton gradient, just like in respiration
- This proton gradient drives chemiosmosis for the production of ATP through photophosphorylation.
- The electron is then accepted by P700, which further excites the electron using light.
- and P700 photosystem 2 and photosystem 1.
- The transfer of this electron to the primary acceptor, and further electron transport chain, gives electrons to NAD+, reducing it to NADH
What does photosystem 1 produce?
What does photosystem 2 produce
Explain cyclic photosynthesis
- Involves only photosystem 1.
- There is no terminal electron acceptor.
- NADPH is NOT produced. Only ATP is produced.
- This suggests that photosystem 1 and photosystem 2 probably evolved from a common ancestor. Cyanobacteria was the first to combine the two into a single system.
Explain Calvin Cycle
- Can occur in the dark, but not necessarily.
- Make sugars from CO2 using the products of the light reaction.
- Has three phases:
- Carbon fixation (using rubisco)
- Regeneration of the CO2 acceptor (RuBP)
What are the key inputs and outputs of the Calvin cycle?
- Inputs: ATP, NADPH, CO2
- Outputs: ADP, NADP, G3P (simple carbohydrate used to build glucose)
What is the relationship between calvin cycles and light reaction?
Depend on the products of each other but can occur independently.
Explain carbon fixation in calvin cycle
- Rubisco fixes CO2 to 5 sugar compound RuBP using water, producing 2 3-phosphoglycerate.
- 3-Phosphoglycerate (3PG) is also produced during glycolysis.
Explain reduction in calvin cycle
- Generates more complex sugars using energy from ATP and NADPH from light reaction.
- As a result, G3P is produced. G3P can later on be used in the production of 5,6,7 carbon compounds (such as RuBP or glucose)
Explain regeneration in calvin cycle
More ATP is used to regenerate 5 carbon compound RuBP from G3P.
Provides photoprotection by absorbing excessive light that would damage chlorophyll.
What is temperature?
A measure of the speed of the random motions of the atoms or molecules in a substance.
What is heat?
The total energy that a substance possesses by virtue of the sum of random motions of its atoms or molecules.
Why is body temperature important?
- Most biochemical and physiological processes are temperature sensitive.
- Functional proteins may denature.
- A quotient describing the sensitivity of a process to temperature.
- Q10 = R(T+10)/R(T)
- Use mostly metabolic heat to maintain internal temperatures.
- Thermoregulating endotherms are called homeotherms.
- But there are also non-thermoregulating endotherms such as naked mole rats.
- Use mostly environmental heat to maintain internal temperatures.
- Some are behavioral thermoregulators.
- Some are non-thermoregulating ectotherms called poikilotherms. Most ectotherms fall under this category as herps, fish, bugs etc.
How do we define homeostasis for heat balance?
For homeostasis to occur, the heat input and heat output must balance each other out.
What are poikilotherms and homeotherms and heterotherms?
Poikilotherms are organisms whose body temperature fluctuate. Ectotherms tend to be poikilotherms. Homeotherms are organisms with constant and stable body temperatures. Heterothermy are organisms that maintain a constant body temperature but sometimes allow it to fluctuate (such as animals who hibernate).
How do organisms acquire or lose the heat that they have.
T(body) = T(ambient) + H(metabolism) +/-H(radiation) +/-H(conduction) +/-H(convection) -H(evaporation)
Explain metabolic heat
- Metabolic heat is always positive due to the inefficiency of metabolic processes leading to heat release.
- In endotherms, basal and active metabolisms contribute (exercise)
- In ectotherms, muscular contraction is the first metabolic heat source. However, this differs with amount and nature of activity.
- Radiative heat can be gained or lost.
- Energy is lost or gained as infrared electromagnetic waves.
- All objects warmer than absolute zero emit radiation and lose energy.
- Think of a fireplace.
- Also think of an infrared filter from snipers.
- Radiation depends on difference in temperature between two surfaces and the surface area of the objects (huge for small animals)
- Can be gained or lost.
- The direct transfer of kinetic energy.
- Requires physical contact of the object with either a solid, a liquid, or a gas.
- Depends on thermal conductivity, area of contact and difference in temperature between the two things.
Explain adaptation against conduction loss: insulation
- The insulation strategy.
- Animals may evolutionarily modify conductivity and/or distance to vital organs. (build up fat)
Explain adaptation against conduction loss: countercurrent exchange
- Regional heterothermy: different regions of the body have different temperatures. This allows the core of the body to be kept more stable.
- Simple vascular loops on limbs lose heat all the way around. The temperature gradient is steep.
- However, countercurrent systems in mammals and birds have vessels that are very close to each other, thereby reducing heat loss from the body. The limbs will still be colder, but more heat will be retained.
- Transfer of heat by mass flow within a fluid medium, such as air or water.
- In practice, however the vast majority of cases involve convective cooling by the organism losing heat to a medium moving past it.
- Convection depends on surface area of contact, temperature difference between object and the medium, and the rate of flow of the medium.
- Think of humans fanning and a lizard raising itself.
- Always takes heat away from the body.
- Heat of vaporization is removed from the object from which the liquid leaves because phase change from liquid to gas requires energy.
- Depends on ambient temperature at which the phase change takes place, the volume of water evaporated and the relative humidity of the ambient air.
Why bother being mammals? Why did mammals diverge from reptiles 200 million years ago?
Maintaining constant body temperature allowed for mammals to forage at night. (nocturnal / btw diurnal is the exact opposite of that) Most mammals have a body temperature just above average daytime temperatures in order to be active at night.
What does conductivity depend on?
Heat exchange between ground and organism. (direct contact) Surface area making contact with the ground, the conductivity of the ground, and the temperature difference between the organism and the ground.
What does convection depend on?
Heat exchange between air / water and organism. Depends on wind / water speed, temperature difference and surface area of organism.
Explain adaptations with regard to solar radiation in order to maintain homeostasis
- Changing behaviour
- Insulation (layer with low thermal conductivity)
- Smaller leaves (higher wind speed on the boundary levels of the leaf, leading to higher convection)
- Smaller surface area is preferred in deserts. Another preventive strategy is to make the surface body more likely to reflect / absorb incoming radiation. Some adaptations are more complicated because of competing functions. Example: Polar bears. Although one might expect the bear to have black fur to absorb solar radiation, this color would make them a much less effective predator in the white environment. Thus, despite having white fur, polar bears have black skin. Additionally, animals may forage at night and sit out the sun.
Explain surface area to volume ratio with regard to maintaining heat
- As the organism increases in size, surface area to volume ratio decreases.
- Small animals lose heat well due to higher ratio and do well in hot habitats.
- Large animals retain heat well due to lower ratio and do well in cold habitats.
Explain the relationship between metabolic rate and body size
- Animals show a direct correlation between body size and resting metabolic rate.
- Basal metabolic rate is calculated by using mass. Lower mass leads to less heat generated by metabolism.
- Does not increase 1:1
- Some ectotherms are so big that the ratio of surface area to volume is really small.
- Thus, once the animal gets got, it doesn’t lose heat fats and becomes essentially endothermic.
- Sea turtle, T-rex
How is body temperature regulated? Heat gain
- Basal metabolic rate does most of the work.
- Exercise also contributes.
- Brown fat adipose tissue
How is body temperature regulated? Heat loss
- Evaporative cooling (sweating)
- Radiation (capillary opening increases radiation)
Explain brown fat thermogenesis
- Thermogenin uncouples electron transport from chemiosmosis and very little ATP is formed.
- Protons leak back through inner mitochondrial membrane instead of shuttling through ATP synthase.
Explain vasodilation and vasoconstriction
- Increased flow in distal loop through vasodilation increases radiation by exposing blood to the exterior.
- Decreased blood flow through vasoconstriction limits flow to inside the insulating subcutaneous fat, decreasing radiation.
How is Tb monitored?
“Thermostat” in hypothalamus initiates negative feedback mechanisms to maintain Tb at a set point.
When will evaporative cooling be the major process through which Tb is maintained at a set point?
When the temperature is hotter than Tb and there is relatively low humidity in the air.
Why does metal and wood feel different when touched?
They have the same temperature, but different thermal conductivity.