Respiration

• What do living cells need in order to survive?

  All living cells need a constant supply of energy to ensure their survival.
• What occurs in respiration?

  The conversion of the chemical energy contained in complex organic molecules into energy-rich chemicals like ATP, which can be used by cells occurs in respiration.
• What is aerobic respiration?

  Mostly respiration involves the oxidation of glucose into carbon dioxide and water, with the release of energy.
• Give the word + symbol equation for aerobic respiration.

  
• What happens to energy in respiration?

  Energy is released or transferred - NOT produced.
• What does respiration occur in + how does it differ from combustion? (2)

  - Respiration occurs in a series of enzyme controlled steps - this means that the release of energy is controlled.

  
  

  - This is unlike combustion where the energy is released in 1 step.

  
• What is ATP? (3)

  - ATP is the nucleotide adenosine triphosphate.

  
  

  - It consists of 3 phosphate groups combined with the nucleotide base, adenine, and the pentose sugar, ribose.

  
  

  - It is the immediate, but short term energy store of all cells.

  
• What is ATP synthesised from, how + what property does this give it? (2)

  - ATP is synthesised from ADP (adenosine diphosphate) and inorganic phosphate (Pi) during the process of phosphorylation.

  
  

  - This makes ATP energy rich (as it has an extra phosphate group)
• What does ATP have in relation to hydrolysis?

  - ATP has a high free energy of hydrolysis.

  
• What does 'high free energy of hydrolysis' mean? (2)

  - This means that when ATP is hydrolysed (when the 3rd terminal phosphate group is removed) a relatively large amount of energy is released.

  
  

  - This is catalysed by the enzyme ATPase.
• What does the conversion of ATP to ADP yield in comparison to the conversion of ADP to AMP?

  The conversion of ATP to ADP yields energy and the conversion of ADP to AMP alsoyields the same amount(the breakage of the bond between the single remaining phosphate and the sugar yields very little energy).
• What are the conversions carried out by?

  These conversions are carried out by a group of enzymes called ATPases.
• What can be determined about the reactions?

  The reactions are also reversible - that is to say that the conversion ADP back into ATP is possible but will require the input of energy.
• How much ATP do cells store + what compensates for this? (2)

  - Cells do not store large amounts of ATP: there may be as little as 5g of ATP in the body at any one time.

  
  

  - However, it can be rapidly built up form ADP and Pi, and in cells there is a continual cycling between ADP & Pi and ATP.
• Why is ATP a suitable energy store? (3)

  - Hydrolysis of ATP molecules releases a small amount of energy (compared to glucose), so energy can be released in small manageable steps.

  
  

  - ATP hydrolysis is a single reaction (only one bond broken) releasing immediate energy and providing the cell with fine control over its energy.

  
  

  - ATP is small & soluble so can be transported around the cell easily which enables it to be transported from the mitochondria to any part of the cell.
• What are the 4 uses of ATP?

  - Energy for metabolic processes including synthesis of larger molecules (anabolism)

  
  

  - Movement - muscle contraction, ciliary action, spindle fibre action in cell division

  
  

  - Active transport

  
  

  - Activates molecules (via phosphorylation) e.g. in glycolysis.
• Describe the structure of mitochondria - membranes.


  It is surrounded by a double membrane separated by an inter-membrane space.
• Describe the structure of mitochondria - outer membrane.


  Outer membrane is permeable to most small molecules involved in cellular respiration.
• Describe the structure of mitochondria - inner membrane. (3)

  - Inner membrane is highly folded forming cristae which increase the surface area enabling more ATP to be produced.

  
  

  - The enzymes needed for the ETC are located on this membrane.

  
  

  - The more cristae, the more ATP produced, and the more metabolically active is the cell.
• Describe the structure of mitochondria - the matrix.


  The matrix contains many chemical compounds and some respiration reactions occur here.

  
• How is ATP produced during respiration? (2)

  - Substrate level phosphorylation : the direct transfer of a phosphorylated substance to ADP.

  
  

  - Oxidative phosphorylation: ATP produced form ADP and Pi as electrons are transferred along a series of carries - the ETC.
• What are the 4 stages of aerobic respiration?

  1. Glycolysis

  2. Pyruvate Oxidation (link reaction)

  3. Kreb's Cycle

  4. The Electron Transport Chain (ETC)

  
• What is glycolysis?


  Glycolysis is the splitting of a hexose sugar (glucose) into two 3-carbon pyruvate molecules.

  
• What type of respiration does glycolysis occur in?

  This is the only stage of respiration that occurs in both aerobically + anaerobically respiring organisms (i.e. it does not require oxygen).
• Where does glycolysis happen?

  It occurs in the fluid part of the cytoplasm - i.e. outside the mitochondria.
• What is the first step of glycolysis? (3)

  - The first step in the process is the activation of glucose phosphorylating it.

  
  

  - This makes the glucose more reactive and uses up ATP, as the 2 phosphates come from the hydrolysis of 2 ATP molecules.

  
  

  - The resulting molecule is fructose 1,6 bisphosphate.
• What is the second step in glycolysis? (4)

  - This 6 carbon molecule fructose 1,6 bisphosphate then

  splits into two 3 carbon molecules of triose phosphate.

  
  

  - The triose phosphate is oxidised through the loss of

  hydrogen atoms to eventually form pyruvate, with the

  production of 2x ATP molecules.

  
  

  - The Hydrogen atoms are collected by the hydrogen carrier molecule NAD (nicotinamide adenine dinucleotide), a coenzyme which becomes reduced to form reduced NAD (NADH).

  
  

  - The removal of hydrogen involves dehydrogenase

  enzymes in a process called dehydrogenation.
• What is the net gain of ATP in glycolysis?

  Overall the process from glucose to 2x pyruvate molecules, results in the formation of 4 ATP and 2NADH + H+, however 2 ATP are used up in the process of glucose activation, so the net gain of ATP is only 2.
• What must happen before the Krebs cycle can take place + why (2)

  - Before Krebs cycle can take place the link reaction must be used to form a molecule called acetyl coenzyme A (acetyl CoA).

  
  

  - This is necessary to allow the entry of a 2 carbon molecule into the mitochondrial matrix.
• Stage 2 - The Link Reaction

  - Before Krebs cycle can take place the link reaction must be used to form a molecule called acetyl coenzyme A (acetyl CoA).

  
  

  - This is necessary to allow the entry of a 2 carbon molecule into the mitochondrial matrix.
• Describe the process of the link reaction. (3)

  - Pyruvate is decarboxylated with the removal of one molecule of CO2.

  
  

  - Dehydrogenations occurs with the removal of hydrogen leading to the formation of NADH.

  
  

  - The resulting 2 carbon (acetyl) group then combines with coenzyme A (CoA) forming acetyl CoA.

  
• What happens to the 2 carbon acetyl group + the CoA?

  The 2 carbon acetyl group enters the Krebs cycle and the CoA is recycled to be combined with another acetyl group.
• What happens to the pyruvate if oxygen is present>

  If oxygen is present the pyruvate formed, will proceed through the link reaction and enter the Krebs cycle.
• What is the Krebs cycle named after + what are its alternate names?

  The cycle is named after Sir Hans Krebs - the man who discovered it, but you should be aware that it has alternative names: the tricarboxylic acid cycle (TCA) and the citric acid cycle.
• How much energy does glycolysis release from the glucose molecule - relatively (small amount or large amount)?

  Although glycolysis releases a little of the energy from the glucose molecule the majority still remain locked up in the pyruvate.
• What is the first step in the Krebs cycle?

  
  

  HINT: Acetyl CoA


  The 2 carbon (2C) acetyl Co A produced from the link reaction enters the Krebs cycle and combines with a four carbon (4C) compound called oxaloacetate forming a six carbon compound (6C) citric acid or citrate.
• What is the second step in the Krebs cycle? (2)

  
  

  HINT: Citrate


  - Citrate (6C) then undergoes decarboxylation resulting in the formation of the 5 C compound, oxoglutarate, with the loss of a molecule of CO2.

  
  

  - Dehydrogenation also occurs at this step, and hydrogen is released that subsequently reduces NAD to NADH.
• What is the third step in the Krebs cycle?

  
  

  HINT: Oxoglutarate


  Oxoglutarate is also decarboxylated resulting in the formation of a 4C oxaloacetate, with the loss of CO2 and the cycle continues.
• What is the fourth step in the Krebs cycle? (3)

  
  

  HINT: Dehydrogenation

  The reactions involved in the conversion of 5C oxoglutarate to 4C oxaloacetate also involve dehydrogenation (using dehydrogenase enzymes).

  
  

  => At 2 points, hydrogen is released that subsequently reduces NAD to NADH - therefore producing 2 molecules of NADH.

  
  

  => At 1 point, hydrogen is released and is used by a different hydrogen carrier, FAD (Flavin adenine dinucleotide) and reduces FAD to FADH2.
• What is the fifth step in the Krebs cycle? (2)

  
  

  HINT: Type of phosphorylation


  - 1 molecule of ATP is produced from the transfer of a phosphate group from an intermediate compound to ADP.

  
  

  - ATP produced in this way is referred to as substrate level phosphorylation.