18 - Respiration Flashcards
What are the 4 stages of aerobic respiration?
- Glycolysis 2. Link Reaction 3. Krebs Cycle 4. Oxidative Phosphorylation
What is the primary substrate used in respiration?
Glucose
What are the 3 coenzymes used in respiration?
- CoA (Coenzyme A) 2. NAD (Nicotine Adenine Dinucleotide) 3. FAD (Flavine Adenine Dinucleotide)
What stage of respiration uses reduced coenzymes?
Oxidative phosphorylation
What is NAD derived from?
Vitamin B3
What is FAD derived from?
Vitamin B2
What is CoA derived from?
Vitamin B5
Where does glycolysis occur?
In the cytosol
What are the three products of glycolysis?
- Pyruvate 2. ATP 3. NADH
Briefly summarise the reactions of glycolysis
- Two Phosphate groups from ATP attach to glucose to form hexose bisphosphate 2. Hexose bisphosphate breaks down into 2 triose phosphate molecules because it is unstable 3. Each triose phosphate has a free Pi (inorganic phosphate ions) group attach to form triose bisphosphate 4. All Phosphate are removed by ADP to form ATP, and a H atom dissociates and forms NADH (dehydrogenation). Pyruvate is what is left behind
What is substrate level phosphorylation?
The formation of ATP without using electron transport chains
What is glycolysis an example of?
Substrate level phosphorylation
What is the net gain of glycolysis?
2 ATP, 2 NADH, 2 pyruvate
What is the function of cristae?
Increase the surface area of the inner mitochondrial membrane for oxidative phosphorylation
What is the function of the outer mitochondrial membrane?
Separates the contents of the mitochondrion from the rest of the cell to allow maintenance of conditions perfect for aerobic respiration
What does the matrix contain?
Enzymes for the Krebs cycle and Link Reaction, mitochondrial DNA
What does the inner mitochondrial membrane contain?
Electron transport chains and ATP synthase
What is an adaptation of the intermembrane space in mitochondria?
Is small so allows a quick buildup of protons when they are pumped in for chemiosmosis
How does pyruvate enter the mitochondria?
Via active transport
What is another name for the Link Reaction?
Oxidative decarboxylation
Briefly summarise what happens in the Link Reaction?
CO2 is removed from pyruvate. This forms a H+ ion which reduces NAD, and leaves an acetyl group which combines with CoA to form acetyl CoA
Where does the Krebs Cycle occur?
The matrix
What is the Krebs Cycle also known as?
The Citric Acid Cycle
What are the products of one turn of the Krebs cycle (i.e. after inputting one acetyl CoA)?
2 CO2, 3 NADH, 1 FADH and 1 ATP
What are the products of oxidative phosphorylation for one molecule of glucose?
10 NAD, 2 FAD, 6 H2O, 28 ATP
How does oxidative phosphorylation produce ATP?
Hydrogen atoms on reduced coenzymes dissociate to form H+ ions and high energy electrons. These high energy electrons enter an electron transport chain, with the energy thus provided used to produce ATP via chemiosmosis.
Where does oxidative phosphorylation occur?
The inner mitochondrial membrane and intermembrane space
How many electron carriers are involved in the electron transport chain of oxidative phosphorylation?
3
How is water formed during oxidative phosphorylation?
1/2 an O2 molecule and 2 H+ ions act as electron acceptors for two low energy electrons from the electron transport chain
How many ATP molecule can one NADH molecule synthesise?
2.5
How many ATP molecule can one FADH molecule synthesise?
1.5
How many ATP molecules are in theory produced by aerobic respiration and why is this not the true net gain?
32, but is lower in practice as active transport needed to transport pyruvate into the mitochondria
How does cyanide kill you?
It readily binds to a haem group in the last electron transport chain of oxidative phosphorylation, so electrons cannot bind and oxidative phosphorylation (and therefore ATP production) are inhibited
What type of molecule is cyanide?
Small and non-polar, so can pass through membranes
Why does cyanide inhibit the Krebs Cycle and Link Reaction?
Lots of NADH and FADH would stockpile as they couldn’t be oxidised, so there wouldn’t be enough NAD and FAD.
What are the three categories that organisms can be grouped into based on their dependence on oxygen?
- Obligate anaerobe 2. Facultative anaerobe 3.Obligate aerobe
What are obligate anaerobes?
Organisms which cannot survive in the presence of oxygen.
What type of organism are obligate anaerobes?
Mostly prokaryotes, some fungi
What are facultative anaerobes?
Organisms which synthesise ATP by aerobic respiration if oxygen is present, but can switch to anaerobic respiration if necessary
What is an example of a facultative anaerobe?
Yeast
What are obligate aerobes?
Can only synthesise ATP in the presence of oxygen
What is an example of a class of obligate aerobes?
Mammals
Why are humans obligate aerobes even though some cells in them can be facultative anaerobes?
The compounds produced by anaerobic respiration in those cells must be broken down by oxygen, so the organism as a whole is an obligate aerobe
What type of cell does lactate fermentation occur in?
Animal cells
What type of cells does alcoholic fermentation occur in?
Yeast and some plant root cells
Why is fermentation of pyruvate necessary in anaerobic respiration?
To ensure that NAD can cycle between its reduced and oxidised states, so that glycolysis can continue occurring
Where does lactate oxidation occur in humans?
The liver
What are two reasons that anaerobic respiration is not sustainable in mammals?
- It does not produce enough ATP 2. Lactate is a toxin (due to the pH change it causes which affects enzymes) and needs oxygen to break it down
What is the word equation for anaerobic respiration involving lactate fermentation?
Glucose —-> Lactic Acid + Water
What happens to NADH during fermentation?
It is oxidised to NAD, which is one of the molecules necessary for glycolysis
Is lactate fermentation reversible?
Yes
Is alcoholic fermentation reversible?
No
What are the two stages of anaerobic respiration?
- Glycolysis 2. Fermentation
Which enzyme catalyses the conversion of pyruvate to ethanal?
Pyruvate decarboxylase
What is pyruvate converted to in alcoholic fermentation? (2 steps)
First ethanal, then ethanol
What happens to ethanal in alcoholic fermentation?
It accepts a H atom from NADH, forming ethanol and NAD.
Why can’t ethanolic fermentation continue indefinitely?
Due to the buildup of ethanol, which is a toxin as it damages plasma membranes and kills yeast if concentrations reach above about 15%
How is respiratory quotient calculated?
CO2 produced/O2 consumed
What can respiratory quotient be measured using?
A respirometer
What is the approximate respiratory quotient of carbohydrates?
1
What is the approximate respiratory quotient of proteins?
0.9
What is the approximate respiratory quotient of lipids?
0.7
Why is the RQ of lipids lower than that of glucose?
Because of the increased number of C-H bonds in lipids
Why can lipids produce lots more ATP than carbohydrates per molecule?
Because the long fatty acid chains have lots of C-H bonds and can lead to the formation of lots of acetyl CoA, and in turn lots of ATP
How are lipids respired?
Lipids are hydrolysed into fatty acids and glycerol. Glycerol can be converted to pyruvate, whilst the fatty acids can be converted to many CoA molecules
How are proteins respired?
They are metabolised into amino acids, then deaminated, and can then enter the respiratory pathway (usually as pyruvate)
Why are proteins usually only used as a respiratory substrate as a last resort?
They are less efficient than other substrates,this reduces the number of amino acids available to synthesise proteins, damages muscles and causes urea buildup
What is RQ during anaerobic respiration?
Above 1, although this is difficult to measure
What is human RQ during normal activity?
0.8-0.9
What does the human RQ during normal activity show?
Shows that both lipids and carbohydrates are being used
