5 Respiration Flashcards
aerobic respiration
requires oxygen and produces carbon dioxide, water and much ATP
anaerobic respiration
takes place in the absence of oxygen and produces lactate (in animals) or ethanol (in plants and fungi) but only as little ATP in both cases
four stages of aerobic respiration
glycolysis
link reaction
krebs cycle
oxidative phosphorlyation
glycolysis brief description
the splitting of the 6-carbon glucose molecule into two 3-carbon pyruvate molecules
link reaction brief description
the 3-carbon pyruvate molecules enter onto a series of reactions which lead to the formation of acetylcoenzyme A, a 2-carbon molecule
krebs cycle brief description
the introduction of acetylcoenzyme A into a cycle of oxidation-reduction reactions that yield some ATP and a large quantity of reduced NAD and FAD
oxidative phosphorylation brief description
the use of the electrons, associated with reduced NAD and FAD, released from the krebs cycle to synthesise ATP with water produced as a by-product
four stages of glycolysis
- phosphorylation of glucose to glucose phosphate
- splitting of the phosphorylated glucose
- oxidation of triose phosphate
- the production of ATP
phosphorylation of glucose to glucose phosphate in glycolysis
glucose is made more reactive by the addition of two phosphate molecules (phosphorylation)
the phosphate molecules come from the hydrolysis of two ATP molecules to ADP.
this provides the energy to activate glucose and lowers the activation energy for the enzyme-controlled reactions that follow
splitting of the phosphorylated glucose in glycolysis
each glucose molecule is split into two 3-carbon molecules known as triose phosphate
oxidation of triose phosphate in glycolysis
hydrogen is removed from each of the two TP molecules and transferred to a hydrogen-carrier molecule known as NAD to form NADH
the production of ATP in glycolysis
enzyme-controlled reactions convert each TP into another 3-carbon molecule called pyruvate
in the process, two molecules of ATP are regenerated from ADP
the overall yield from one glucose molecule undergoing glycolysis is..
- 2 molecules of ATP (4 molecules are produced but 2 were used up in the initial phosphorylation of glucose and so the net increase is 2 molecules)
- 2 molecules of NADH
- 2 molecules of pyruvate
where does glycolysis take place?
cytoplasm
the enzymes for the glycolytic pathway are found in the cytoplasm of cells and so glycolysis does not require any organelle or membrane for it to take place
it doesn’t require oxygen and therefore it can take place whether or not it is present
how is glycolysis indirect evidence for evolution?
glycolysis is an universal feature of every living organism
link reaction
the pyruvate molecules produced in the cytoplasm during glycolysis are actively transported into the matrix of mitochondria
- the pyruvate is oxidised to acetate. the 3-C pyruvate loses a CO2 molecule and two hydrogens. these Hs are accepted by NAD to form NADH, which is later used to produce ATP
- the 2-carbon acetate combines with a molecule called coenzyme A (CoA) to produce acetylcoenzyme A
link reaction equation
pyruvate + NAD + CoA –> acetyl CoA + NADH + CO2
where does the link reaction occur?
matrix of mitochondria
krebs cycle
- the 2-C acetylcoenzyme A from LR combines a 4-C molecule to produce a 6-C molecule
- in a series of reactions this 6-C molecule loses CO2 and H (NAD is reduced) to give a 5-C molecule
- then 5-C molecule loses CO2 and H (NAD is reduced) to give a 4-C molecule and a single ATP molecule as a result of substrate-level phosphorylation
- another NAD molecule and a FAD molecule is reduced
- the 4-C molecule can now combine with a new molecule of acetylCoA to begin the cycle again
for each pyruvate molecule, the link reaction and krebs cycle produces…
- reduced coenzymes such as NAD and FAD. these have the potential to provide energy to produce ATP molecules by oxidative phosphorylation and are therefore the important products of krebs cycle
- one molecule of ATP
- 3 molecules of CO2
as 2 pyruvate molecules are produced from each original glucose molecule, the yield from a single glucose molecule is double the quantities above
coenzymes
molecule that some enzymes require in order to function
they play a major role in PS and resp where they carry H atoms from one molecule to another
e.g. NAD, FAD and NADP
significance of the krebs cycle
- breaks down macromolecules into smaller ones- pyruvate to CO2
- produced H atoms that are carried by NAD to the electron transfer chain and provide energy for oxidative phosphorylation. his leads to the production of ATP that provides metabolic energy for the cell
- it regenerates the 4-C molecule that combines with acetyl CoA, which would otherwise accumulate.
- it is a source of intermediate compounds used by cells in the manufacture of other important substances such as fatty acids, AAs and chlorophyll
mitochondria
organelles found in eukaryotic cells
each is bounded by a smooth outer membrane and an inner one that is folded into extensions called cristae
the matrix contains proteins, lipids and traces of DNA
chemiosmotic theory of oxidative phosphorylation
- hydrogen atoms produced during glycolysis and Krebs cycle combine with coenzymes NAD and FAD
- the NADH and FADH donate the electrons of the hydrogen atoms they are carrying to the first molecule in the elec trans chain
- the elecs pass along a chain of elec trans carrier molecules in a series of oxidation-reduction reactions. as the electrons flow along the chain, the energy they release causes the active transport of protons across the inner mitochondrial membrane and into inter-membranal space
- the protons accumulate in the inter-membranal space before they diffuse back into the mitochondrial matrix through ATP synthase channel embedded in the inner mitochondrial membrane
- at the end of the chain the elecs combine with these protons and oxygen to form water. oxygen is therefore the final acceptor of elecs in the elec trans chain
importance of oxygen in respiration
acts as final acceptor of the hydrogen atoms produced produced in glycolysis and the Krebs cycle
without its role in removing hydrogen atoms at the end of the chain, the hydrogen ions and elecs would ‘back up’ along the chain and the process of respiration would come to a halt
releasing energy in stages
the greater the energy that is released in a single step, the more of it is released as heat and less there is available for more useful purposes
when energy is released a little at a time, more of it can be harvested for the benefit of the organism
energy transfers in oxidative phosphorylation
elecs carried by NAD and FAD are not transferred in one explosive step
instead, they are passed along a series of electron trans chain molecules, each of which is at a slightly lower energy level
the elecs therefore move down an energy gradient
the transfer of elecs down this gradient allows their energy to be released gradually and therefore more usefully
alternative respiratory substrates
sugars are not the only substances which can be oxidised by cells to release energy
both lipids and protein may, in certain circumstances, be used as respiratory substrates, without first being converted to carbohydrate
what happens in absence of O2 - respiration
neither the krebs cycle nor the elec trans chain can continue because soon all the FAD and NAD will be reduced
no NAD or FAD will be available to take up the protons produced during the Krebs cycle and so the enzymes stop working
this leaves only the anaerobic process of glycolysis as a potential source of ATP
glycolysis in absence of O2
its products of pyruvate and hydrogen must constantly be removed. the H must be released from the NADH in order to regenerate NAD.
without this, the already tiny supply of NAD in cells will be entirely converted to NADH, leaving no NAD to take up the hydrogen newly produced from glycolysis
glycolysis will then grind to a halt
the replenishment of NAD is achieved by the pyruvate molecule from glycolysis accepting the hydrogen from reduced NAD
the oxidised NAD produced can then be used in further glycolysis
anaerobic respiration in plants and some microorganisms
produces ethanol
occurs in organisms such as certain bacteria and fungi (e.g. yeast) as well as in some cells of higher plants
the pyruvate molecule formed at the end of glycolysis loses a molecule of CO2 and accepts H from reduced NAD to produce ethanol
equation of anaerobic respiration in plants and MO
pyruvate + NADH –> ethanol + CO2 + NAD
anaerobic respiration in animals
produces lactate
occurs in animals as a means of overcoming a temporary shortage of oxygen
lactate production occurs most commonly in muscles as a result of strenuous exercise
in these conditions O2 may be used up more rapidly than it can be supplied and therefore an O2 debt occurs.
it is often essential, however, that the muscles continue to work despite the shortage of O2
when O2 is in short supply, ???NAD??? from glycolysis can accumulate and must be removed
to achieve this, each pyruvate molecule produced takes up the two hydrogen atoms from the NADH produced in glycolysis to form lactate
at some point the lactate produced is oxidised back to pyruvate
this can then be either further oxidised to release energy or converted into glycogen
this happens when O2 is once again available
lactate will cause cramp and muscle fatigue if ti is allowed to accumulate in the muscle tissue
as lactate is an acid it also causes pH changes which affects enzymes
its important that lactate is removed by the blood and taken to the liver to be converted to glycogen
anaerobic respiration in animals equation
pyruvate + NADH –> lactate + NAD
in what ways is energy derived from cellular respiration?
- substrate level phosphorylation in glycolysis and the krebs cycle. this is direct transfer of phosphate from a respiratory intermediate to ADP to produce ATP
- oxidative phosphorylation in the elec trans chain. this is the indirect linking of energy from phosphate to ADP to produce ATP involving energy from the hydrogen atoms that are carried on NAD and FAD. cells produce most of their ATP this way
where does each stage of respiration occur?
glycolysis- cytoplasm
link reaction- matrix of mitochondria
krebs cycle- matrix of mitochondria
oxidative phosphorylation- inner mitochondrial membrane
how does aerobic respiration differ from anaerobic?
Water is produced.
More ATP is produced.
Glucose is fully broken down.
After glycolysis, there are more steps (the link reaction, the Krebs cycle and oxidative phosphorylation).
Which enzyme catalyses the conversion of pyruvate to ethanal?
pyruvate decarboxylase
Which enzyme catalyses the conversion of pyruvate to lactate?
lactate dehydrogenase
Which enzyme catalyses the conversion of ethanal to ethanol?
ethanol dehydrogenase
Why does anaerobic respiration produce far less ATP than aerobic respiration?
Anaerobic respiration relies on substrate level phosphorylation in the glycolytic pathway to produce a net 2 ATP per glucose.
Aerobic respiration produces 2 ATP from substrate-level phosphorylation in glycolysis, 2 ATP from substrate-level phosphorylation in the Krebs cycle and around 32 ATP from oxidative phosphorylation.
