cell respiration hl Flashcards
Role of NAD as a carrier of hydrogen and oxidation by removal of hydrogen during cell respiration
- compare oxidation and reduction w/ e-, hydrogen, oxygen, and energy
- Students should understand that oxidation is a process of electron loss, so when hydrogen with an electron is removed from a substrate (dehydrogenation) the substrate has been oxidized. They should appreciate that redox reactions involve both oxidation and reduction, and that NAD is reduced when it accepts hydrogen.
- Respiration is a series of oxidation and reduction (redox) processes which occur together. These reactions involve the transfer of electrons and hydrogens from one substance to another. Electron carriers such as NAD support the transport of electrons and hydrogens.
- Electron carriers such as NAD are substances that can accept and give up eleconts as required.
NOTE: Reactions involving NAD show that reduction can also be achieved by accepting atoms of hydrogen. This is because subsances (e.g. glucose) are oxidized in respiration by removing two hydrogen atoms. Each hydrogen atom consist of an electron and a proton, so NAD+ accepts 2H+ + 2e- and is reduced.
Conversion of glucose to pyruvate by stepwise reactions in glycolysis with a net yield of ATP and reduced NAD
- what is preparatory and payoff phase?
- why add phosphate to glucose?
- Include phosphorylation, lysis (when F1,6 bisphophgylcerate splits), oxidation and ATP formation. Students are not required to know the names of the intermediates, but students should know that each step in the pathway is catalysed by a different enzyme.
Preparatory phase: Phosphorylation of glucose and its conversion to glyceraldehyde 3-phosphate
Payoff phase: Oxidative conversion of glyceraldehyde 3-phosphate to pyruvate and the coupled formation of ATP & NADH
- It makes the molecule less stable and lowers the activation energy for the subsequent splitting
- To prevent the phosphorylated molecule from being transported through the cell membrane (protein pumps don`t recognize it)
Conversion of pyruvate to lactate as a means of regenerating NAD in anaerobic cell respiration
- Regeneration of NAD allows glycolysis to continue, with a net yield of two ATP molecules per molecule of glucose.
- Location: Cytoplasm of the cell
Substrate: Glucose
Product: 2 Lactate, 2 ATP, 2 NADH - In this pathway reduced NAD transfers its hydrogens to pyruvate to form lactate.
This allows NAD to be reoxidised in the absence of oxygen, so glycolysis can continue/pyruvate formation can continue - used in food preservation b/c lots of lactic acid lowers pH and prevents decomposition of bacteria
Anaerobic cell respiration in yeast and its use in brewing and baking
- Students should understand that the pathways of anaerobic respiration are the same in humans and yeasts apart from the regeneration of NAD using pyruvate and therefore the final products.
- Yeast is a unicellular fungus that occurs naturally in habitats where glucose or other sugars are available
- Yeast is a facultative anaerobe single-celled fungus which can respire aerobically or anaerobically. Yeast acts on starch and sugars in the dough, breaking them down by alcoholic fermentation to make carbon dioxide and ethanol.
- The CO2 released in fermentation is trapped in the sticky dough, causing the bread to rise. When the bread has risen to a desired height, the bread is baked in an oven to kill the yeast and evaporate the ethanol.
- In wine production, yeast is added to crushed grapes and put into a tank, when the oxygen is consumed aerobically, fermentation occurs.
Carbon dioxide escapes from the tank while the ethanol stays behind
beer
- Barley grains are wetted in order to cause germination, which triggers the breakdown of starch to maltose – making a liquid called malt.
- More water is added to make a sweeter-tasting liquid called wort, and then hops are added to give the liquid a bitter taste
The mixture is boiled and cooled before yeast is added, which breaks down the maltose into glucose. - Fermentation by yeast produces ethanol and carbon dioxide, and the beer is finally pasteurised (heated) to kill any remaining yeast cells
Oxidation and decarboxylation of pyruvate as a link reaction in aerobic cell respiration
- Students should understand that lipids and carbohydrates are metabolized to form acetyl groups (2C), which are transferred by coenzyme A to the Krebs cycle.
- Pyruvate (pyruvic acid) enters the mitochondrial matrix by facilitated diffusion, where it will be processed further.
- Decarboxylation of pyruvate to acetate
Binding of the enzyme CoA to acetate
Oxidation of acetate
Acetyl CoA is transported to the matrix of the mitochondrion, where it participates in the Krebs cycle. - Acetyl groups can be produced from most carbohydrates and fats. Once acetyl groups are formed, they can be transferred by CoA into the Krebs cycle.
Oxidation and decarboxylation of acetyl groups in the Krebs cycle with a yield of ATP and reduced NAD
- Students are required to name only the intermediates citrate (6C) and oxaloacetate (4C).
- Students should appreciate that citrate is produced by transfer of an acetyl group to oxaloacetate and that oxaloacetate is regenerated by the reactions of the Krebs cycle, including four oxidations and two decarboxylations.
- They should also appreciate that the oxidations are dehydrogenation reactions.
Transfer of energy by reduced NAD to the electron transport chain in the mitochondrion
- Energy is transferred when a pair of electrons is passed to the first carrier in the chain, converting reduced NAD (NADH) back to NAD.
- Students should understand that reduced NAD comes from glycolysis, the link reaction and the Krebs cycle.
- The energy contained in glucose is gradually transferred into specific carrier molecules (ATP, NADH, FADH2), which in the later step of aerobic respiration will become oxidized again.
The energy given out in these oxidation reaction is used to make ATP. - see taxi image
- The electrons and the hydrogen ions (H+, protons), which have taken a ride with the energy carrier NADH and FADH2, are dropped off at the electron transport chain in the cristae of the mitochondria.
- Electrons and H+ are transported to the cristae where they are offloaded by NADH and FADH.
Generation of a proton gradient by flow of electrons along the electron transport chain
- Students are not required to know the names of protein complexes.
- NADH delivers its’ electrons to NADH dehydrogenase, releasing energy that is used to pump H+ from the matrix into the intermembrane space
- The e- are then transported by UBIQUINONE to their next destination/also picks up electrons from FADH2
- This next destination is cytochrome BC 1 complex, where electron energy is again used to transport H+ from the matrix into the intermembrane space
- Electrons are then transported by CYTOCHROME C to the cytochrome oxidase complex, where electron energy is again used to transport H+ from the matrix into the intermembrane space
- Oxygen accepts e- from inner mitochondrial membrane and H+ from matrix to make water
- The reduced molecules (NADH and FADH2) from glycolysis and Krebs cycle will become oxidized again in the electron transport chain – and the energy released during these redox reactions will be used to establish a proton gradient (Chemiosmosis). The proton gradient is used to phosphorylate ADP to produce ATP (Oxidative phosphorylation).
- The electron transport chain is established by the inner mitochondrial membrane and carrier proteins that easily undergo redox reactions. Each carrier in the chain has a slightly higher electronegativity and therefore a stronger attraction for electrons than the previous carrier so electrons are passed down an energy gradient.
- The purpose of the ETC is to establish a proton gradient to facilitate the production of ATP.
- NADH and FADH2 are oxidized to form NAD+ and FAD, respectively. By this they lose electrons and hydrogen ions (H+).
- The carrier molecules embedded within the membrane of the cristae accept the protons, while electrons pass along the chain from carrier to carrier.
- This process releases energy, as the electrons “fall” from higher levels to lower ones. The energy given out is used to pump protons (H+) from the matrix into the intermembrane space against the concentration gradient.
Chemiosmosis and the synthesis of ATP in the mitochondrion
- Students should understand how ATP synthase couples release of energy from the proton gradient with phosphorylation of ADP.
- pumped H+, leads to concentration gradient/H+ flows down ATP synthase, forming water/This process releasesw energy, so allows phosphorylation of ADP to ATP
- Oxidative phosphorylation = forming ATP from recuded hydrogen carriers
ATP synthase is a complex of integral proteins located in the mitochondrial inner membrane where it catalyses the synthesis of ATP from ADP and phosphate, driven by a flow of protons.
Role of oxygen as terminal electron acceptor in aerobic cell respiration
- Oxygen accepts electrons from the electron transport chain and protons from the matrix of the mitochondrion, producing metabolic water and allowing continued flow of electrons along the chain.
- Oxygen is the final electron acceptor in the mitochondrial electron transport chain. The reduction of the oxygen molecule involves both accepting electrons and forming a covalent bond with hydrogen to produce H2O.
Differences between lipids and carbohydrates as respiratory substrates
- Include the higher yield of energy per gram of lipids, due to less oxygen and more oxidizable hydrogen and carbon.
- Also include glycolysis and anaerobic respiration occurring only if carbohydrate is the substrate, with 2C acetyl groups from the breakdown of fatty acids entering the pathway via acetyl-CoA (acetyl coenzyme A).
- Simple sugars (glucose or fructose) of carbohydrates can be used straight away in glycolysis and anaerobic respiration, while lipids have to be broken down into glycerol & fatty acids beforehand.
- The fatty acids are converted into acetyl groups and then can then be used in the Krebs cycle, but not in glycolysis and anaerobic respiration.
- Because lipids include a high percentage of C-H bonds, which store chemical potential energy more effectively than other molecules,
