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
