respiration Flashcards
where does glycolysis occur?and does it require oxygen
Occurs in the cytosol. Glycolysis occurs in anaerobic and aerobic respiration (doesn’t need O2).
describe how glycolysis occur
- Phosphorylation of glucose to hexose bisphosphate:
- 2 molecules of ATP are hydrolysed (used), and the
released phosphoryl groups are added to glucose to form
hexose bisphosphate. This molecule has phosphate
groups at C1 an C6.
- The energy from hydrolysed ATP activates the hexose
sugar and prevents it being transported out the cell. - Splitting each hexose bisphosphate molecule into 2 triose
phosphate molecules:
- Each molecule of hexose bisphosphate is split into 2
triose-phosphate molecules (3C – TP), each with a
phosphate group attached. - Oxidation of triose phosphate to pyruvate.
This process is anaerobic but is oxidation as it involved removal of
H atoms from substrate molecules.
- Dehydrogenase enzymes, aided by 2 NAD coenzymes, remove hydrogen from triose phosphate.
- The 2 molecules of NAD accept the hydrogen atoms and become reduced NAD.
- The triose phosphate is converted to pyruvate by a series of enzyme-controlled reactions, this
releases energy used to produce 4 ATP by substrate-level phosphorylation.
whats the net gain in glycolysis
Per molecule of glucose: net gain of 2 ATP (4 made but 2 used to phosphorylate glucose), 2 red NAD, 2
pyruvates produced. The 2 reduced NAD go to the cristae of mitochondria for oxidative phosphorylation.
The 2 pyruvate molecules are actively transported into the mitochondrial matrix for the link reaction (in
aerobic)
what and where does the link reaction occur
Occurs in the mitochondrial matrix. Pyruvate produced in glycolysis is actively transported across outer and
inner mitochondrial membranes into the mitochondrial matrix via specific pyruvate-proton symporter – a
transport protein that transports pyruvate and H in same direction
what and where does the link reaction occur
Occurs in the mitochondrial matrix. Pyruvate produced in glycolysis is actively transported across outer and
inner mitochondrial membranes into the mitochondrial matrix via specific pyruvate-proton symporter – a
transport protein that transports pyruvate and H in same direction
what is pyruvate converted to in the link reaction
Pyruvate is converted to 2C acetyl group (combined with CoA) in link reaction, which reacts in Krebs cycle.
1 Acetyl CoA, 1 red NAD and 1 CO2 produced in reaction. No ATP is produced. Red NAD go to oxidative
phosphorylation.
2 pyruvate produced per glucose in glycolysis, so link reaction happens 2 times per glucose molecule.
2 pyruvate + 2NAD + 2CoA -> 2CO2 + 2 reduced NAD + 2 acetyl CoA
describe what happend in the link reaction
- Pyruvate is decarboxylated (carboxyl group removed) producing CO2 (1C)
– catalysed by pyruvate dehydrogenase complex - Product is dehydrogenated, forming reduced NAD (from NAD), this
produces acetate (2C) – catalysed by pyruvate dehydrogenase complex. - Acetate combines with coenzyme A to form acetyl coenzyme A (CoA).
where does the krebs cycle occurs and what does it produce
Also occurs in mitochondrial matrix. It is a series of enzymecatalysed reactions that oxidise the acetate from the link reaction.
Produces 2 CO2, 1 ATP, 3 red NAD and 1 red FAD. Krebs cycle
happens 2 times per glucose molecule.
describe what happends in the krebs cycle
- The acetate from Acetyl CoA from the link reaction combines
with oxaloacetate (4C) to form citrate – a 6C compound.
- This is catalysed by citrate synthase.
- Coenzyme A released and is reused in the link
reaction. - 6C Citrate is decarboxylated and dehydrogenated, producing
a 5C compound,
- Decarboxylation produces 1 molecule of CO2
- Dehydrogenation removes hydrogen producing 1 molecule of reduced NAD. - This 5C compound is further decarboxylated and dehydrogenated, producing a 4C compound.
- A series of decarboxylation and dehydrogenation reactions produce 1 red FAD and 2 red NAD
and 1 more CO2.
- Substrate-level phosphorylation takes place, a phosphate ion group combines with ADP,
forming 1 molecule of ATP. - Rearrangement of atoms in a 4C intermediate, followed by a final dehydrogenation reaction,
regenerates oxaloacetate, so the cycle can continue.
where does all the reduce FAD and FAD go
All red NAD and FAD produced in glycolysis, Link
reaction and Krebs cycle go to oxidative
phosphorylation. They carry H atoms to the ETC
on the cristae, where they will be involved in
producing many more ATP molecules.
where does the oxidative phosphorylation takes place
Takes place in the inner mitochondrial membrane (cristae). It involves electron carrier proteins, arranged in
ETCs, embedded in the cristae, and chemiosmosis.
describe what happends in the oxidative phosphorylation
Hydrogen atoms are released from reduced NAD and reduced FAD (coenzymes oxidised to NAD and
FAD). The H atoms split into protons (H+
) and electrons. The protons go into solution in the matrix.
- The electrons pass along the electron transport chain (in the inner mitochondrial membrane)
between electron carriers.
- Electron carriers get reduced as they accept electrons and oxidised as electron pass to the
next carrier).
- Electrons lose energy at each carrier as they pass along the ETC.
- This energy released by electrons is used by electron carriers to actively pump protons from the
mitochondrial matrix across the inner mitochondrial membrane into the intermembrane space.
Product per 1
glucose
Glycolysis Link reaction
(x2)
Krebs
cycle (x2)
Reduced NAD 2 2 6
Reduced FAD 0 0 2
CO2 0 2 4
ATP 2 (4-2) 0 2
- As protons accumulate in the
intermembrane space, H+ conc in the
intermembrane space increases, forming a
proton gradient (electrochemical gradient).
- This generates a chemiosmotic
potential (/proton motive force).
- Protons cannot easily diffuse through the
lipid bilayer of the mitochondrial
membranes; the inner membrane is
impermeable to protons.
- Protons flow into the matrix (by facilitated diffusion) through channel proteins associated with ATP
synthase enzymes in the inner membrane.
- The flow of protons causes a conformational change in the ATP synthase enzyme allowing
ADP and Pi to combine to form ATP.
- This process is called chemiosmosis. The formation of ATP in this way, in the presence of O2 is
called oxidative phosphorylation.
- In the mitochondrial matrix, oxygen (the final electron acceptor), combines with electrons coming off
the end of the ETC and with protons diffusing through the ATP synthase channel proteins, forming
water:
- 4H+ + 4e- + O2 -> 2H2O
why is that the Theoretical yield is rarely achieved, (28 ATP) but the actual yield is closer to 30 or less because
Some ATP is used to actively transport pyruvate into the mitochondrial matrix (between glycolysis
and link reaction).
- Some ATP is used to transport red NAD (made in glycolysis) into mitochondrial matrix.
- Some protons may leak out through outer mitochondrial membrane in oxidative phosphorylation
describe what happens to the eukaryotesif anaerobic respiration takes place (oxygen is not present)
If oxygen is absent:
1. O2 cannot act as final electron acceptor at the end of oxidative phosphorylation. Protons diffusing
through channels associated with ATP synthase can’t combine with electrons and O2 to form water.
2. Proton conc increases in matrix and reducing proton gradient across inner mitochondrial membrane.
3. Protons stop diffusing through channels associated with ATP synthase enzymes.
4. Oxidative phosphorylation stops.
5. Reduced NAD and reduced FAD cannot release their H atoms and cannot be reoxidised.
6. Krebs cycle stops, as does the link reaction (as no source of (oxidised) NAD and FAD).
Product per 1
glucose
Glycolysis Link reaction
(x2)
Krebs
cycle (x2)
Reduced NAD 2 2 6
Reduced FAD 0 0 2
CO2 0 2 4
ATP 2 (4-2) 0 2
Glycolysis can take place, but the red NAD generated in the oxidation of TP to pyruvate has to be reoxidised
so glycolysis can continue. Another metabolic pathway must run to reoxidise them as the ETC has stopped.
These processes occur in the cytoplasm.
- Anaerobic respiration consists of glycolysis and one of these pathways
how does fungi and plants produce ethanol
- Each molecule of pyruvate produced in glycolysis is
decarboxylated (CO2 produced) forming ethanal –
catalysed by pyruvate decarboxylase. - Ethanal accepts hydrogen atoms from reduced NAD
(from glycolysis), forming ethanol – catalysed by ethanol dehydrogenase.
- This reoxidises the reduced NAD to NAD so it can be used in glycolysis (to accept H atoms from TP).
Produces ethanol & CO2 (2 NAD, 2ATP – from glycolysis).
how do mammals lactate fermentation
. Pyruvate from glycolysis accepts hydrogen atoms from reduced NAD forming lactate and (reoxidised)
NAD – catalysed by lactate dehydrogenase.
- The reoxidised NAD can accept hydrogen from TP during glycolysis, so glycolysis can continue to
produce enough ATP to sustain muscle contraction for a short period.
Produces lactate (2 NAD, 2ATP – from glycolysis) NO CO2 produced.. Pyruvate from glycolysis accepts hydrogen atoms from reduced NAD forming lactate and (reoxidised)
NAD – catalysed by lactate dehydrogenase.
- The reoxidised NAD can accept hydrogen from TP during glycolysis, so glycolysis can continue to
produce enough ATP to sustain muscle contraction for a short period.
Produces lactate (2 NAD, 2ATP – from glycolysis) NO CO2 produced.
name and explain the 3 respiratory substrate
Carbohydrates:
The monosaccharide glucose is the main respiratory substrate. Some mammalian cells (brain/red blood) can
only use glucose. Animals and some bacteria store carbs as glycogen, plants as starch.
Lipids:
Important for many tissues, including muscle tissue. Triglycerides are hydrolysed by lipase to fatty acids and
glycerol. Glycerol is then converted to pyruvate and enter the Krebs cycle via the link reaction.
Fatty acids are long-chain hydrocarbons (carboxylic acids). So, each molecule has many carbons, many
hydrogens and few oxygen atoms. Hydrogen is the source of protons for chemiosmosis in oxidative
phosphorylation, so fats produce more ATP than equivalent mass of carbohydrate.
1. Using the energy from hydrolysis of ATP, each fatty acid is combines with CoA.
2. The fatty acid-CoA complex is transported to the mitochondrial matrix, where it is broken down into
2C acetyl CoA groups which can enter the Krebs cycle. This is called the beta-oxidation pathway
whats deamination
Excess amino acids, released after digestion of proteins, are deaminated in the liver. Deamination of an
amino acids involves removal of the amino (-NH2) group forming a keto acid that enters Krebs cycle or Link
reaction as pyruvate or acetyl CoA.
what happends when we start having insufficient amount of glucose or lipid
During fasting, starvation or prolonged exercise, when insufficient glucose or lipid are available for
respiration, protein from muscle can be hydrolysed to amino acids which are then respirated.
why does the number of hydrogen affects the reactions during chemiosmosis
The greater availability of protons (H+
) for chemiosmosis (oxidative phosphorylation), the more ATP can be
produced. As most ATP is produced by chemiosmosis in oxidative phosphorylation, the greater proportion of
H atoms (most H atoms per unit mass) there are in the respiratory substrate, the more ATP is produced.
- As protons eventually combine with O2 to form water, the more H atoms a substrate has, the more
O2 will be needed for its respiration.
which out of the 3 contains the most hydrogen number
Lipids contain the most H atoms per unit mass, followed by proteins then carbs. Lipids produce most
ATP per unit mass, then protein, then carbs.
Respiratory quotient:
RQ = volume of CO2 produced/volume of O2 consumed
- (no units)
why are lipids and proteins less than one in the RQ values
Lipids and proteins are less than 1 because more O2 is needed to oxidise them.
what happens if the RQ value is more than 1
If the RQ value is greater than 1, this indicates some anaerobic respiration is taking place, as more CO2 is being produced than O2 consumed. Plants have very low RQ as CO2 released is used in photosynthesis
