C1.2 Cell Respiration

• ATP stands for Adenosine TriPhosphate
• ATP is a nucleotide that provides activation energy for chemical reactions within cells
• ATP is composed of adenine, ribose and three phosphate groups
• the bond between the last two phosphates in ATP is unstable, when broken it releases energy which is used as activation energy
• ATP allows the following; Active transport across membranes, anabolism, movement of the whole cell and components within cells (mitosis and meiosis)
• ADP stands for Adenosine DiPhosphate
• energy is released by the hydrolysis of ATP into ADP and Phosphate but energy is required to synthesize ATP from ADP and Phosphate.
• the synthesis of ATP to ADP is by condensation reactions
• glucose and fatty acids are the principal substrates for cell respiration but a wide range of carbon/organic compounds can also be used
• cell respiration is the controlled release of ATP energy from organic compounds (food) within cells
• organic molecules are compounds that contain carbon but not oxides or carbonates
• gas exchange happens in the alveoli of the lungs and respiring tissues in humans (the gases move by diffusion). It is the process of exchanging carbon dioxide and oxygen in living cells and tissues
• oxygen is used during respiration
• carbon dioxide is produced by respiration
• respirometers are used to determine the rate of respiration in living organisms
• respiration is an enzyme catalyzed reaction
• factors that affect respiration in insects or seeds are; temperature and mass of the organism
• factors that affect respiration in yeast are; temperature, mass of yeast, pH, substrate types (food source) and concentration as well as chemical inhibitors for enzymes
• aerobic respiration includes; glycolysis, the link reaction, krebs cycle, electron transport chain and chemiosmosis
• Oxidation is the loss of an electron. This occurs by the addition of an oxygen and removal of a hydrogen.
• Reduction is the gaining of an electron. This occurs by the removal of an oxygen and addition of a hydrogen.
• NAD is an electron carrier that undergoes reduction in aerobic respiration. It removes of 2 electrons and a hydrogen from substrates (substrate becomes oxidized)

  When NAD gains those two, reduced NAD is formed. This carries the electrons and hydrogen to the electron transport chain (reduced NAD becomes oxidized and returned to NAD)
• Glycolysis converts glucose into pyruvate
• glycolysis occurs in the cytoplasm of the cell
• glycolysis requires a constant supply of NAD. When oxygen isn't present in human cells anaerobic respiration is used to generate that NAD.
• Anaerobic respiration produces a net gain of 2 ATP molecules, regenerates NAD, and produces the waste product lactate in humans
• pyruvate enters the mitochondrion and link reaction pathways
• The link reaction includes;

  Decarboxylation of pyruvate - loss of carbon dioxide, which is then released as a waste product, to produce a 2-carbon acetyl group.

  Reduction of NAD - pyruvate is oxidized and NAD is reduced

  Formation of acetyl coenzyme A by the combination of both substances (coenzyme A transports the acetyl group to the Krebs cycle)
• DNA is considered to be a nucleotide made up of three components:

  • a nitrogen containing base (adenine)
  • a five carbon sugar (ribose)
  • one or more phosphate groups (three groups)
• properties of DNA that make it suitable for temporary storage and transfer of energy between cells are:

  1. solubility - can move freely in the cytoplasm/aqueous solutions
  2. stable at pH levels close to cytoplasm's pH (7)
  3. cannot pass through phospholipid bilayer via diffusion hence its' movement is controlled and
  4. the third phosphate can easily undergo hydrolysis/condensation
  5. hydrolysis of ATP to ADP and phosphate releases low energy and reduces heat loss from reaction
• ATP supplies energy to cells for:

  • synthesis of macromolecules (anabolism): its' an endothermic process and need energy to initiate
  • active transport: movement against a conc gradient requires energy
  • movement of whole cell or cell components (mitosis)
• ATP contains more potential chemical energy than ADP
• when converting ATP to ADP and phosphate, the energy released is from the detachment of one phosphate
• the regeneration of ATP from ADP and phosphate requires energy which can come from:

  • cell respiration: energy released by oxidizing carbohydrates
  • photosynthesis: light energy converted to chemical energy
  • chemosynthesis: energy released by oxidizing inorganic substances i.e. sulfides
• glucose and fatty acids are the main substrates for cell respiration but a wide range of carbon/organic compounds can also be used
• gas exchange and cell respiration are interdependent processes as without gas exchange, cell respiration cannot occur due to lack of o2 and without cell respiration there's no concentration gradient for gases to diffuse across hence gas exchange can't occur
• cell respiration can be aerobic or anaerobic:

  aerobic respiration: glucose + oxygen -> carbon dioxide + water

  anaerobic (humans): glucose -> lactate

  anaerobic (yeast/fungi): glucose -> ethanol + carbon dioxide

  for each arrow, ADP is converted into ATP
• In aerobic respiration:

  • reactions initially occur in the cytoplasm, then they occur in the mitochondrial matrix as o2 gets introduced
  • yield of 36 ATP molecules per one glucose
  • waste products are water and carbon dioxide
  • o2 is used as an electron accepter in oxidation reactions
• in anaerobic respiration:

  • all reactions occur in the cytoplasm
  • yield of 2 ATP molecules per one glucose
  • waste products don't include water
  • o2 isn't used, so other substances act as electron acceptors in oxidation reactions
• respirometers are used to determine the rate of respiration