Respiration Flashcards
What are the four stages of respiration
Glycolysis
Link reaction
Krebs cycle
Electron transport chain
Is glycolysis aerobic or anaerobic?
Anaerobic
Where does glycolysis occur?
In the cytoplasm
Explain glycolysis in four steps
Phosphorylation - hexose sugar phosphorylated by 2 ATP molecules. Hesxose bisphosphate forms which is less stable / more reactive.
Lysis - hexose bis phosphate split and further phosphorylation occurs from inorganic phosphate ions in cytosol. Two TPs formed
Oxidation/dehydrogenation- hydrogen removed from the TP (3C) sugars via oxidation to reduce NAD to NADH. 2 lots of NADH form in total
ATP formation- some energy release from sugar intermediates directly used to synthesise ATP. In total 4 ATP form during glycolysis. (2x ATP per 3C sugar)
What are the end product of glycolysis?
Two molecules of pyruvate
Two molecules of NADH
A net gain of 2 a ATP
Is the link Reaction aerobic or anaerobic?
Aerobic
Where does the link reaction occur?
In the mitochondrial matrix
Explain the link reaction?
Pyruvate enters matrix by active transport via carrier proteins. Pyruvate then undergoes oxidative decarboxylation (carbon dioxide and hydrogen removed).
Hydrogen atoms accepted by NAD fo form NADH.
The left over 2c acetyl group is bound by coenzyme a forming acetyl coA.
Acetyl coA delivers the acetyl group to next stage of aerobic respiration.
What is NADH used for?
In oxidative phosphorylation to synthesise ATP.
Where does Krebs cycle occur?
Within matrix of mitochondria.
How many times to the link reaction occur per molecule of glucose
2x
What are the products of the link reaction per glucose?
2x CO2 and 2xNADH
Explain Krebs Cycle?
Acetyl coA delivers an acetyl group to the cycle. Here it combined with 4C OAA to form citrate (6C)
Citrate undergoes decarboxylation and dehydrogenation producing one NADH and carbon dioxide. A 5C compound forms.
The 5C compound undergoes further decarboxylation and dehydrogenation reactions, eventually regenerating OAA, so therefore the cycle continues.
What is produced at the end of Krebs cycle?
4x CO2
2x ATP
6x NADH
2x FADH
differences between NAD and FAD in respiration?
NAD involved in all stages of cellular respiration but FAD only accepts hydrogen in Krebs Cycle.
NAD accepts one hydrogen but FAD accepts 2.
NADH oxidised at beginning of ETC releasing protons and electrons etc while FAD oxidised further along the chain.
NADH = synthesis of 3x ATP FADH = synthesis of 2x ATP
Where are Coenzymes derived from?
Vitamins mostly
Explain oxidative phosphorylation?
Hydrogen ions collected by NAD and FAD are delivered to ETCs present in the cristae of mitochondria.
Hydrogen atoms dissociate into hydrogen ions and electrons.
The high energy electrons used in synthesis of ATP by chemiosmosis. Energy released during redox reactions as the electrons reduce and oxidise electron carriers as they flow along the ETC.
This energy from these reactions used to create proton gradient leading to proton diffusion through ATP Synthase channels = ATP produced.
At the end of ETC hydrogen ions and oxygen combine to form water. Oxygen is the final electron acceptor and ETC cannot operate unless oxygen is present.
What does oxidative phosphorylation of ADP to form ATP require?
It’s dependent on electrons moving along electron transport chains and requires the presence of oxygen
What is cytochrome C?
A component of the electron transport chain in mitochondria. The haem group of cytochrome c accepts electrons from the bc1 complex and transfers electrons to the complex IV
What does the complex IV do?
Large transmembrane protein found in bacteria and the mitochondrion of eukaryotes. It is the last enzyme in the respiratory electron transport chain of mitochondria (or bacteria) located in mitochondrial (or bacterial) membrane.
What is substrate level phosphorylation?
The production of ATP involving the transfer of a phosphate group from a short lived, highly reactive intermediate source called creatine phosphate.
What are obligate anaerobes?
Organisms that cannot survive in the presence of oxygen. Almost all are prokaryotes for example, Chlostridium, although there are some fungi as well.
What are facultative anaerobes?
They synthesise ATP by aerobic respiration if oxygen is present, but can switch to anaerobic respiration in the absence of oxygen, for example yeast.
What are obligate aerobes?
Can only synthesise ATP in the presence of oxygen. Eg mammals.
Why can some obligate aerobes be described as partly facultative anaerobes?
The individual cells of some organisms, eg muscle cells, can be described as facultative anaerobes as they can supplement ATP supplies by employing anaerobic respiration in addition to aerobic respiration when the oxygen concentration is low
What is fermentation?
A form of anaerobic respiration. The process by which complex organic compounds are broken down into simpler inorganic compounds without the use of oxygen or the involvement of an ETC.
Why does fermentation produce less ATP?
Because the organic compounds are not fully broken down so fermentation produced less ATP than aerobic respiration. Also small amount of ATP produced by substrate level phosphorylation alone.
What are the end products of alcoholic fermentation?
occurring in yeasts and plant root cells
Ethanol (an alcohol)
And
Carbon dioxide
End products of lactate fermentation?
Lactate and is carried out in animal cells
What happens when there is no oxygen to act as the final electron acceptor at the end of the ETC in oxidative phosphorylation?
The flow of electrons stops. Therefore the synthesis of ATP by chemiosmosis also stops.
NADH and FADH cannot be oxidised as there is no where for the electrons to go. As a result, NAD and FAD cannot be regenerated and so the decarboxylation and oxidation of pyruvate and the Krebs cycle come to a halt as there are no coenzymes to accept the removed hydrogens.
Without fermentation, glycolysis would also come to a halt due to the lack of NAD
Explain lactate fermentation in mammals?
Pyruvate can act as hydrogen acceptor taking in the hydrogen from reduced NAD, catalysed by the enzyme lactate dehydrogenase. Pyruvate is converted to lactate (lactic acid) and NAD is regenerated. This can keep glycolysis going so a small quantity of ATP is still synthesised.
Lactic acid is converted back to glucose in the liver but oxygen is needed to complete this process, leads to heavy breathing after exercise.
Why can lactate fermentation not occur indefinitely?
The reduced quantity of ATP produced would not be enough to maintain vital processes for a long period of time.
The accumulation of lactic acid causes a fall in pH leading to proteins denaturing. Respiratory enzymes and muscle filaments are made from proteins and will cease to function at low pH.
Explain alcoholic fermentation?
Not a reversible process like lactate fermentation.
Pyruvate is first converted into ethanal, catalysed by the enzyme pyruvate decarboxylase. Ethanal can then accept a hydrogen atom from reduced NAD, becoming ethanol. The regenerated NAD can then continue to act as a coenzyme and glycolysis can continue,
Not short term and can continue indefinitely In the absence of o2
Bacterial adaptations to low oxygen environments?
Some have evolved to use nitrate ions, sulphate ions and carbon dioxide as final electron acceptors.
Anaerobic bacteria present in digestive systems are essential to digestion, they digest cellulose from grass cells into products that can be used, their final electron acceptor is CO2. Water and methane produced.
Biochemical adaptions for mammals?
Greater conc. of Haemoglobin and myoglobin than land mammals particularly in muscle used in swimming.
This maximises oxygen stores, delaying the onset of anaerobic respiration. High tolerance to lactic acid, so can respite anaerobically for longer, and have a greater tolerance of CO2, effective buffer system that prevent rise in pH
Physiological adaptations of mammals to low oxygen environments?
Modified circulatory systems, when they dive they show peripheral vasoconstriction so blood is shunted to brain, heart and muscles. The heart slows by up to 85% - bradycardia.
Whales also exchange 80-95% of the air in the lungs when they breathe, it’s 15% in humans.
Physical adaptations in mammals to low oxygen environments?
Streamlining to reduce drag due to friction from water while swimming. This reduced the energy demand during a dive. Limbs are fin shaped to maximise the efficient use of energy in propulsion.
What is a respiratory substrate?
A molecule from which energy can be liberated to produce ATP in a living cell.
Examples of respiratory substrates?
All carbs, lipids, and proteins can be used, but they all have differing energy values.
What are carbs hydrolysed into?
Monosaccharides which enter glycolysis.
What are triglycerides hydrolysed into?
Glycerol and fatty acids which are able to be converted into Acetyl coA and used in Krebs cycle.
What are proteins hydrolysed into?
Amino acids and also enter Krebs cycle.
What is the respiratory quotient?
The ratio of carbon dioxide produced and oxygen consumed by an organism per unit time
How to calculate RQ?
RQ = vol of CO2 produced / vol of O2 consumed
What is the RQ of carbs?
1
What is the RQ of a fat and why?
Around 0.7 because they require more o2
RQ of proteins?
0.9, more o2 required to break them down.
Why do carbohydrates have the highest RQ?
Because it requires less o2 to be fully metabolised.
Why could an RQ be higher than 1?
If anaerobic respiration was also taking place.
Explain the metabolism of triglycerides as a respiratory substrate?
Glycerol is converted into pyruvate and can then undergo oxidative decarboxylation (link) to produce an acetyl group that can join with coA
Fatty acids- the High yielding components undergo a series of reactions called beta oxidation where carbon atoms are detached in pairs producing acetyl coA which is fed into Krebs cycle.
