respiration- chapter 12 Flashcards
what are the 4 stages of aerobic respiration
- Glycolysis- the splitting of the 6-carbon glucose molecules into two 3-carbon pyruvate molecules.
- Link reaction- the 3-carbon pyruvate molecules enter into a series of reaction which lead to the formation of acetylcoenzyme A, a two carbon molecule.
- Krebs Cycle- 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- 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.
what are the two forms of cellular respiration
-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 and carbon dioxide (in plants and fungi) but only a little ATP in both cases.
what are the 4 stages of glycolysis
- Phosphorylation of glucose to glucose phosphate=
Glucosemust first be 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=
Each glucose molecule is split into two 3-carbon molecules known as triose phosphate. - Oxidation of triose phosphate=
Hydrogen is removed from each of the two triose phosphate molecules and transferred to a hydrogen-carrier molecule known as NAD to form reduced NAD - Production of ATP=
Enzyme-controlled reactions convert each triose phosphate into another 3-carbon molecule called pyruvate.
In the process, two molecules of ATP are regenerated from ADP.
what is glycolysis
- Initial stage of both aerobic and anaerobic respiration.
- Occurs in the cytoplasm of all living cells
- Is the process where a hexose (6-carbon) sugar, usually glucose, is split into two molecules of the 3-carbon molecules, pyruvate.
what are the energy yields of glycolysis
Two molecules of ATP
Two molecules of reduced NAD
Two molecules of pyruvate.
what is the 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.
what are the three steps of the link reaction
- The 3-carbon pyruvate loses a carbon dioxide molecule and two hydrogens.
- The hydrogens are accepted by NAD to form reduced NAD
- The 2-carbon acetate combined with a molecule called coenzyme A (CoA) to produce a compound called acetylcoenzyme A.
Pyruvate + NAD + CoA 🡪 acetyl CoA + reduced NAD + CO2
what is the krebs cycle
Involves a series of oxidation and reduction reactions that take place in the matrix of mitochondria.
what are the three steps of the krebs cycle
- The 2-carbon acetylcoenzyme A from the link reaction combines with a 4-carbon molecule to produce a 6-carbon molecule.
- In a series of reactions this 6-carbon molecule loses carbon dioxide and hydrogen to give a 4-carbon molecule and a single molecule of ATP produced as a result of substrate-level phosphorylation.
- The 4-carbon molecule can now combine with a new molecule of acetylcoenzyme A to begin to cycle again.
how do the krebs cycle and link reaction link
For each molecule of pyruvate, the link reaction and the Krebs cycle therefore produce:
- Reduced coenzymes (NAD and FAD). These have the potential to provide energy to produce ATP molecules by oxidative phosphorylation.
- One molecule of ATP
- Three molecules of carbon dioxide.
what are coenzymes
- Coenzymes are not enzymes but molecules that some enzymes require in order to function.
- Coenzymes play a major role in photosynthesis and respiration where they carry hydrogen atoms from one molecule to another.
what are 3 examples of coenzymes
- NAD, important throughout respiration
- FAD, which is important in the Krebs cycle.
- NADP, which is important in photosynthesis.
what coenzyme is the most important in respiration
- In respiration, NAD is the most important carrier, it works with dehydrogenase enzymes that catalyse the removal of hydrogen atoms from substrates and transfer them to other molecules involved in oxidative phosphorylation.
what is the significance of the krebs cycle (4)
- Breaks down macromolecules into smaller ones.
- Produces hydrogen atoms that are carried by NAD to the electron transfer chain and provide energy for oxidative phosphorylation. This leads to the production of ATP that provides metabolic energy for the cell.
- Regenerates the 4-carbon molecule that combines with acetylcoenzyme A.
- Source of intermediate compounds used by cells in the manufacture of substances i.e. fatty acids, amino acids and chlorophyll
explain oxidative phosphorylation
- Hydrogen atoms from the previous stages are carried by the coenzymes NAD and FAD into this stage.
- This is the mechanism by which some of the energy of the electrons within the hydrogen atoms are conserved in the formation of ATP.
- Mitochondria are the site of oxidative phosphorylation.
- Within the inner folded membrane (cristae) are the enzymes and other proteins involved in oxidative phosphorylation.
- Mitochondria is found in greater numbers in metabolically active cells.
- The mitochondria in these cells also have more densely packed cristae which provide a greater surface area of membrane.
what does the synthesis of ATP by oxidative phosphorylation involve
the transfer of electrons down a series of electron carrier molecules which form a electron transfer chain
exaplain the electron transfer chain with the synthesis of ATP
-The hydrogen atoms produced during glycolysis and the Krebs cycle combine with the coenzymes NAD and FAD.
-The reduced NAD and FAD donate the electrons of the hydrogen atoms they are carrying to the first molecule in the electron transfer chain.
-The electrons pass along a chain of electron transfer 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 channels embedded in the inner mitochondrial membrane.
-At the end of the chain the electrons combine with these protons and oxygen to form water. Oxygen is therefore the final acceptor of electrons in the electron transfer chain.
what is the importance of oxygen in respiration
to act as the final acceptor of the hydrogen atoms produced in glycolysis and the Krebs cycle
explain the respiration of lipids
- Lipids are hydrolysed to glycerol and fatty acids.
- The glycerol is then phosphorylated and converted to triose phosphate which enters the glycolysis pathway and subsequently the Krebs cycle.
- The fatty acid component is broken down into 2-carbon fragments which are converted to acetyl coenzyme A. This then enters the Krebs cycle.
- The oxidation of lipids produces 2-carbon fragments of carbohydrate and many hydrogen atoms.
- The hydrogen atoms are used to produce ATP during oxidative phosphorylation.
- Lipids release more than double the energy of the same mass of carbohydrate.
explain the respiration of proteins
- It is hydrolysed to amino acids.
- These have their amino group removed (deamination) before entering the respiratory pathway at different points depending on the number of carbon atoms they contain.
- 3-carbon compounds are converted to pyruvate, which 4- and 5- carbon compounds are converted to intermediates in the Krebs cycle.
what is anaerobic respiration
- In plants and in microorganisms such as yeast, the pyruvate is converted to ethanol and carbon dioxide.
- In animals, the pyruvate is converted to lactate.
explain the production of ethanol in plants and some microorganisms
- This happens in certain bacteria and fungi (yeast) as well as in some cells of higher plants i.e. root cells under waterlogged conditions.
- The pyruvate molecule formed at the end of glycolysis loses and molecule of carbon dioxide and accepts hydrogen from reduced NAD to produce ethanol.
Pyruvate + reduced NAD 🡪 Ethanol + carbon dioxide + oxidised NAD
- This has been exploited by humans for thousands of years in the brewing industry. Yeast ferments natural carbohydrates in plant products such as grapes (wine production) or barley seeds (beer production) into ethanol.
explain the production of lactate in animals
- The production of lactate occurs in animals as a means of overcoming a temporary shortage of oxygen.
- During strenuous exercise, oxygen may be used up more rapidly than it can be supplied and therefore an oxygen debt occurs.
- When oxygen is in short supply, NADH from glycolysis can accumulate and must be removed.
- So, each pyruvate molecule produced takes up the two hydrogen atoms from the reduced NAD produced in glycolysis to form lactate.
Pyruvate + Reduced NAD 🡪 Lactate + oxidised NAD
- When oxygen is once again available lactate is oxidised back into pyruvate to either be further oxidised to release energy or converted into glycogen.
- Lactate will cause cramp and muscle fatigue if allowed to accumulate. It is also an acid so affects enzymes.
