respiration and biological processes Flashcards
Why is respiration a metabolic pathway?
It is a sequence of reactions controlled my enzymes
Why are respiration reactions catabolic?
They break down energy-rich macromolecules, such as glucose and fatty acids
What is oxidative phosphorylation and where does it occur?
- It occurs on the inner membrane of the mitochondria in aerobic respiration
- The energy for making ATP comes from oxidation-reduction reactions and is released in the transfer of electrons along a chain of electron carrier molecules
What is photophosphorylation and where does it occur?
- Occurs on the thylakoid membrane of the chloroplasts in the light-dependent stage of photosynthesis
- The energy for making the ATP comes from light and is released in the transfer of electrons along a chain of electron carrier molecules
What is substrate level phosphorylation?
- It occurs when phosphate groups are transferred from donor molecules, e.g. glycerate-3-phosphate to ADP to make ATP in glycolysis or when enough is released for a reaction to bind ADP to inorganic phosphate e.g. in the Krebs cycle
Three groups of organisms are recognised, depending on their respiration: Living organisms
Most living organisms use aerobic respiration, and break down substrate using oxygen, with the release of a relatively large amount of energy. These are obligate anaerobes.
Three groups of organisms are recognised, depending on their respiration: microorganisms
Some microorganisms including yeast and many bacteria, respire aerobically, but can also respire without oxygen; these are facultative anaerobes
Three groups of organisms are recognised, depending on their respiration: some species of bacteria
Some species of bacteria and archea use anaerobic respiration. They respire without oxygen and cannot grow in its presence. They are obligate anaerobes
Aerobic respiration can be divided into 4 distinct but linked stages
- Glycolysis which occurs in solution in the cytoplasm and generates pyruvate, ATP and reduced NAD
- The link reaction , in solution in the matrix of the mitochondrion. Pyruvate is converted into acetyl coenzyme A
- The Krebs cycle, in solution in the mitochondrial matrix generates carbon dioxide and reduced NAD and FAD
- The electron transport chain, on the cristae of the inner mitochondrial membrane, in which the energy from protons and electrons generates ATP from ADP and inorganic phosphate Pi
What is glycolysis?
Where does it occur and why?
- The initial stage of both anaerobic and aerobic respiration
- It occurs in the cytoplasm because glucose cannot pass through the mitochondrial membrane
Why can glucose not be broken down in the mitochondria?
- The enzymes for its breakdown are not present in the mitochondria and so it could not be metabolised there
Explain the process of glycolysis:
- A glucose molecule is phosphorylated by the addition of two phosphate groups , using two molecules of ATP, making a hexose phosphate called glucose diphosphate
- The glucose diphosphate splits into two molecules of a triose phosphate, a 3-carbon sugar, glyceraldehyde-3-phosphate
- The two triose phosphate molecules are dehydrogenated, i.e. hydrogen is removed from each of them, oxidising them to pyruvate, the hydrogen atoms are transferred NAD, a hydrogen carrier molecule, making reduced NAD.
- these steps release enough energy to synthesise 4 ATP molecules. The ATP is formed by substrate-level-phosphorylation
- The phosphate from the triose phosphate converts ADP to ATP, without the involvement of an electron transport chain producing pyruvate
- Of the 4 ATPs made by substrate-level-phosphorylation, 2 were used to phosphorylate the glucose molecule. Net production of 2 ATPSs
- 2 molecules of NADH is produced
What is the link reaction?
The link reaction links glycolysis to the Krebs cycle
Explain the process of the link reaction
NAD + CoA—> AcCoA + reduced NAD + CO2
- Pyruvate diffuses from the cytoplasm into the mitochondrial matrix
- The pyruvate is dehydrogenated and the hydrogen released is accepted by NAD to form NADH
- The pyruvate is decarboxylated i.e. a molecule of carbon dioxide is removed from it. All that remains of the original glucose molecule is a 2-carbon acetate group which combines with coenzyme A (CoA), making acetyl coenzyme A (AcCoA) which enters the krebs cycle
Describe the processes in the Krebs cycle
A means of liberating from C-C, C-H and C-OH bonds. It produces ATP, containing the energy which was held in the chemical bonds of the original glucose molecule
It also produces reduced NAD and reduced FAD which deliver hydrogen atoms to the electron transport chain on the inner mitochondrial membrane . Three molecules of water are used in reactions in the Krebs cycle. Carbon dioxide is released as a waste product
Explain the processes in the Krebs cycle
- Acetyl CoA enters the Krebs cycle by combining with a 4-carbon acid to form a 6-carbon compound and the CoA is regenerated
- The 6-carbon acid is dehydrogenated, making reduced NAD, and decarboxylated to make carbon dioxide and a 5-carbon chain
- The 5-carbon acid is dehydrogenated, making reduced NAD and FAD, and decarboxylated to make carbon dioxide and to regenerate the 4-carbon acid
- The 4-carbon acid can combine with more AcCoA and repeat the cycle
In the Krebs cycle, there are two significant types of reaction
- Decarboxylation happens twice. Decarboxylases remove carbon dioxide from the -COOH groups of Krebs cycle intermediates. They collected by hydrogen carriers giving three molecules of reduced NAD and one molecule of reduced FAD
- The acetate group from the original glucose molecule is now entirely broken down to carbon dioxide and water. The energy in the bonds of the glucose molecule is carried by electrons in the hydrogen atoms in the reduced NAD and FAD
The Krebs cycle: Summary
- One ATP produced by substrate-level-phosphorylation
- Three molecules of reduced NAD
- One molecule of reduced FAD
- Two molecules of carbon dioxide
The passage of electrons
2H+ + 2e- + 1/2 O2—-> H2O
- The reduced NAD donates the electrons of the hydrogen atoms to the first of a series of electron carriers in the electron transport chain
- The electrons from these atoms provide energy for the fist proton pump and protons from the hydrogen atoms are pumped into the inter-membrane space
- The electrons pass along the chain of carrier molecules providing energy to pump the hydrogen ions (protons) across to the intermembrane space
- This builds up a proton gradient, which is also a pH gradient and electrochemical gradient.
- At the end of the chain, the electrons combine with protons and oxygen to form water
2H+ + 2e- +1/2O2—>H2O
where is the electron transport chain located?
On the cristae of the inner mitochondrial membranes
What is the electron transport chain?
A series of protein molecules that are carriers and pumps, which are sometimes called ‘respiratory enzymes’
The carrier molecules include cytochromes and are proteins conjugated to iron or copper and the metal ions are oxidised and reduced by electron transport
What is the role of coenzymes?
NAD feeds electrons and protons into the electron transport chain earlier than FAD does
Each pair of hydrogen atoms carried by reduced NAD provides enough energy to synthesise how many molecules of ATP?
3 molecules of ATP
Each pair of hydrogen atoms carried by reduced FAD provides enough energy to synthesise how many molecules of ATP?
2 molecules of ATP
FAD passes hydrogen atoms directly to the second proton pump
