12.2. Aerobic Respiration Flashcards
Respiration (aerobic) definition
Enzymatic release of energy from organic compounds in living cells
(syllabus) the process whereby energy from complex organic molecules is transferred to ATP.
fuels for respiration
Mainly carbohydrates (glucose) as respiratory substrate - others break down fatty acids, glycerol and amino acids in respiration.
Aerobic respiration formula
Glucose + oxygen –> water + carbon dioxide
C6H12O6 + 6O2 –> 6H2O + 6CO2
Four stages of aerobic respiration (glucose breakdown) and where they take place
1) glycolysis - cytoplasm
2) link reaction - matrix of mitochondria
3) Krebs cycle - matrix of mitochondria
4) oxidative phosphorylation - inner mitochondrial membrane
Glycolysis definition
the splitting, or lysis, of glucose
- multi-step process
Glycolysis process
1) Glucose (6 Carbons) is phosphorylated by 2 ATP molecules as they donate phosphate to it
2) This produces a fructose biphosphate (6C) molecule
which splits into two molecules of triose phosphate.(3C)
3) Hydrogen is then removed from both triose phosphates (by dehydrogenase enzymes) and transferred to the carrier molecule NAD
4) Two molecules of reduced NAD are produced for each molecule of glucose entering glycolysis.
5) The hydrogens carried by reduced NAD can easily be
transferred to other molecules and are used in oxidative
phosphorylation to generate ATP
6) During this step, the phosphate groups from the triose phosphpates are added to ADP to form a small yield of ATP, in substrate-linked reactions - 4 ATPs
6) The end product of glycolysis is pyruvate and 2 molecules of pyruvate form which contain a great deal of chemical potential energy
Products gained and lost from Glycolysis
2ATP to breakdown glucose
4ATP generated by phosphorylation
= net total of + 2ATP
+ 2 reduced NAD
The Link reaction process
1) Pyruvate passes by active transport from the
cytoplasm, through the outer and inner membranes of
a mitochondrion and into the mitochondrial matrix.
2) Here it is decarboxylated (this means that carbon dioxide is removed)
3) It is also dehydrogenated, hydrogen is removed, and is picked up by NAD producing reduced NAD
4) This converts pyruvate into a 2C compound. The pyruvate combines with coenzyme A (CoA) to produce acetyl coenzyme A which is also a 2C compound
Link reaction formula
pyruvate + CoA + NAD –> acetyl CoA + CO2 + reduced NAD
Krebs cycle definition
The Krebs cycle is a closed pathway of enzyme-
controlled reactions.
Krebs cycle process
- Acetyl coenzyme A (2C) combines with a four-carbon
compound (oxaloacetate) to form a six-carbon
compound (citrate). - The citrate is decarboxylated and dehydrogenated in a
series of steps, to yield carbon dioxide, which is given
of as a waste gas, and hydrogens which are accepted by
the carriers NAD and FAD - Some ATP is produced from ADP, in substrate-linked reactions
- Oxaloacetate is regenerated to combine with another
acetyl coenzyme A.
For each turn of the cycle, two carbon dioxide molecules
are produced, one FAD and three NAD molecules are
reduced, and one ATP molecule is generated via an
intermediate compound.
oxidative phosphorylation meaning
the synthesis of ATP from ADP and Pi using energy from oxidation reactions in aerobic respiration (compare photophosphorylation)
electron transport chain meaning
chain of adjacently arranged carrier molecules in the inner mitochondrial membrane, along which electrons pass by redox reactions
oxidative phoshorylation process
1) the energy for the phosphorylation of ADP to ATP comes from the activity of the electron transport chain.
2) Reduced NAD and reduced FAD are passed to the
electron transport chain. Here, the hydrogens are removed from the two hydrogen carriers and each is split into its constituent proton (H+) and electron (e−).
3) The energetic electron is transferred to the first of a series of electron carriers, and goes down the respiratory complex (group of 4 membrane proteins)
4) As an electron moves from one carrier at a higher
energy level to another one at a lower level, energy is
released.
5) Some of this energy is used to move protons
from the matrix of the mitochondrion into the space between the inner and outer membranes of the mitochondrial envelope. This produces a higher
concentration of protons in the intermembrane space than in the matrix, setting up a concentration gradient.
6) The protons are allowed to move back by facilitated diffusion into the matrix through special channel proteins that work as ATP synthase. The movement of protons through the ATP synthase provides enough energy to cause ADP and inorganic phosphate to combine and make ATP
7) At the end of the chain, the electrons reunite with the protons from which they were originally split. They combine with oxygen to produce water. This is why oxygen is required in aerobic respiration - it acts as the final acceptor for the hydrogens removed from the respiratory substrate during glycolysis, the link reaction and the Krebs cycle
Relationship between mitochondria and its function
- mitochondria is surrounded by an envelope (two membranes) that separate it from cytoplasm, so that the reactions that take place inside of it are not affected by reactions elsewhere in the cell
- inner membrane is folded to form cristae, providing a large surface area in which the carriers of the electron transport chain, and ATP synthase, can be embedded
- The space between the two membranes (intermembrane space) allows high concentration of protons to build up
- matrix of the mitochondrion contains all the enzymes needed for Krebs cycle
- matrix of mitochondrion contains DNA and ribosomes, which are used to synthesise some of the proteins needed for the reactions of respiration
