Notes

• Structure of ATP (Adenosine Triphosphate)

  A ribonucleotide consisting of an adenine base and three phosphate groups attached to the central ribose sugar
• ATP


  • Adenosine Triphosphate is a molecule that functions to distribute energy within cells (it is the 'energy currency' of the cell). Acts as an immediate source of chemical energy that is used to power cellular processes
  • Contains three covalently linked phosphate groups which store potential energy in their bonds
  • When hydrolysed, the energy stored in the phosphate bond is released to be used by the cell
  • The presence of adenine and ribose provides additional sites for attachment to enzymes, allowing ATP to fuel enzymatic activities.
• Structure of ATP (Adenosine Triphosphate)


  A ribonucleotide consisting of an adenine base and three phosphate groups attached to the central ribose sugar.

  
• Life processes within cells that ATP supplies with energy


  There are a wide range of biochemical processes that require the use of ATP as an energy source:

  • Biosynthesis, Active transport & Movement
• Biosynthesis


  The assembly of organic polymers (macromolecules) requires ATP hydrolysis

  • Anabolic reactions use ATP to construct complex molecules from simpler subunits
• Active transport


  ATP is required to move material against a concentration gradient

  • Nerves utilise ATP to establish a resting potential prior to generating an nervous impulse
  • Vesicular transport (endocytosis / exocytosis) requires ATP to break and reform membranes
• Movement


  The movement of cell components or the whole cell is dependent on ATP

  • Chromosomes are segregated during mitosis and meiosis in an energy-dependent process
  • The contraction of muscle cells (via the shortening of sarcomeres) involves the use of energy
• Coenzymes and their Role in Enzyme Reactions


  • Coenzymes are non-protein organic compounds that facilitate enzyme reactions.
  • They cycle between a loaded and unloaded form to support enzyme activity.
• ATP as a Loaded Coenzyme and Energy Transfer


  ATP is a loaded coenzyme that transfers chemical energy to enzymes.

  It enables the activation energy threshold to be reached, triggering catalysis.
• Energy Storage in ATP and Hydrolysis

  • ATP stores chemical energy in the covalent bonds between phosphate groups.
  • Phosphates are negatively charged and require high energy to keep in place.
  • Hydrolysis of ATP releases the terminal phosphate, converting it to ADP (adenosine diphosphate).

  
• Utilization of ATP's Chemical Energy


  The chemical energy released during ATP hydrolysis is used by enzymes.

  • Enzymes catalyze metabolic reactions within the cell, utilizing the energy from ATP.
• Cell Respiration and ATP Production


  • Cell respiration is a system for producing ATP within the cell using energy released from carbon compounds.
  • It involves the controlled release of energy through the breakdown of organic compounds to produce ATP.
  • ATP is produced from ADP as a result of the transfer of chemical energy from digested carbon compounds.
• Organic Compounds Used in Cell Respiration


  Carbohydrates, such as glucose, are the main organic compounds used in cell respiration.

  • Lipids (fatty acids) provide more energy per gram but are more challenging to digest and transport.
  • Proteins (amino acids) can yield a comparable amount of energy to carbohydrates but also produce toxic nitrogenous wastes (NH3).

  
• Types of Cell Respiration


  Cell respiration can be either anaerobic (does not require oxygen) or aerobic (requires oxygen)

  The two forms differ in the products that are formed, where the reactions occur and the overall ATP yield

  Not all respiratory substrates can undertake both forms or respiration (fatty acids are only digested aerobically)
• Anaerobic Respiration


  Anaerobic respiration begins with the process of glycolysis, whereby simple sugars (glucose) are partially broken down into two pyruvate molecules with a small yield of ATP

  • Certain amino acids and glycerol (from triglycerides) may also feed into the glycolytic pathway and produce pyruvate anaerobically

  In the absence of oxygen, the pyruvate molecules are fermented to form lactic acid (in animals) or ethanol and carbon dioxide (in plants and yeasts)

  • The anaerobic processes of glycolysis and fermentation both occur within the cytosol of the cell

  
• Aerobic Respiration


  Aerobic respiration begins with the process of glycolysis, but oxygen is then used to completely break down the pyruvate for a much larger ATP yield

  • The pyruvate is transported to the mitochondria and is broken down into carbon dioxide and water
  • The complete breakdown of pyruvate involves three key stages: the link reaction, the Krebs cycle and the electron transport chain

  
• Anaerobic versus Aerobic


  Both anaerobic and aerobic respiration use the digestion and oxidation of organic molecules to synthesise ATP

  • The process of glycolysis is common to both pathways, even though it is technically an anaerobic reaction
  • While sugars are the main respiratory substrate, lipids and proteins can both be converted into usable intermediaries

  
• Variables affecting the rate of cell respiration


  • Temperature
  • pH
  • Glucose
  • Oxygen
  • Inhibitors
• Numerous variables can potentially affect the rate of cell respiration within an organism.


  • Temperature and pH will alter the functionality of respiratory enzymes and hence influence reaction rates
  • Glucose and oxygen are respiratory substrates and their levels of availability will influence reaction rates
  • Certain inhibitors may also influence respiration rates by preventing necessary enzyme-substrate interactions
• Factors Affecting Enzyme Activity in Cell Respiration : Temperature 


  Temperature affects the rate of cell respiration by impacting the frequency of successful enzyme-substrate collisions.

  • Low temperatures result in low respiration rates due to insufficient kinetic energy for frequent collisions.
  • High temperatures lead to low respiration rates as enzymes begin to denature and lose functionality.
  • Respiration rates are highest at a temperature reflecting optimum physiological conditions (typically around 37ºC).

  
• Factors Affecting Enzyme Activity in Cell Respiration : pH


  pH affects the rate of cell respiration by changing the charge and solubility of the enzymes involved.

  • Respiration rates are highest at a pH reflecting optimum physiological conditions (typically around pH 7).
  • Any pH conditions outside the optimal range cause enzyme denaturation, reducing the respiration rate.

  
• Substrate and Oxygen Levels in Cell Respiration: Other Substrate & Glucose 


  
  

  Levels of other respiratory substrates, such as lipids and proteins, need to be controlled to avoid influencing the respiration rate.

  
  

  Glucose is the main respiratory substrate, and its levels determine the rate of cell respiration.

  • Increasing glucose concentrations lead to higher respiration rates until all glycolytic enzymes are saturated, resulting in a plateau.
• Substrate and Oxygen Levels in Cell Respiration : Oxygen


  Oxygen is required for aerobic respiration, and its levels determine the rate of this type of respiration.

  • However, using oxygen as an independent variable can be challenging since it is difficult to assess the concurrent occurrence of anaerobic respiration.
• Measuring Cell Respiration


  A respirometer is a device that determines an organism’s aerobic respiration rate by measuring the rate of oxygen consumption

  The living specimen (e.g. germinating seeds or invertebrate organism) is enclosed in a sealed container

  When an alkali is included to absorb CO2 (e.g. limewater), oxygen consumption can be measured as a change in pressure within the system

  The pressure change can be detected with a data logger or via the use of a U-tube manometer
• Inhibitors


  An enzyme inhibitor is a molecule that disrupts the normal reaction pathway between an enzyme and a substrate

  • Competitive inhibitors bind directly to the active site of the enzyme and prevent substrate interaction 
• Darkness Requirement for Plant Experiments

  As plants produce oxygen when they undertake photosynthesis, experiments involving plants must be conducted in darkness (no light = no photosynthesis)

  
• The ATP-ADP cycle 


  It's a fundamental process in cellular metabolism that is responsible for the production and utilization of the energy-carrying molecule, adenosine triphosphate (ATP).
• ATP Synthesis


  • Involves the conversion of adenosine diphosphate (ADP) and inorganic phosphate (Pi) into ATP.
  • Energy is typically derived from the oxidation of organic molecules, such as glucose, through metabolic pathways like cellular respiration or photosynthesis.
  • Catalyzed by the enzyme ATP synthase.
• ATP Utilization


  • The stored energy in the high-energy phosphate bonds of ATP is released and used to power various cellular processes, such as active transport, muscle contraction, protein synthesis, and cell signaling.
  • When ATP is used, it is converted back to ADP and Pi, which can then be used in the ATP synthesis stage.
• Life Processes Requiring ATP

  1. Muscle contraction: ATP provides the energy needed for muscle fibers to contract.
  2. Active transport: ATP supplies the energy for transport proteins to move molecules against their concentration gradient.
  3. Protein synthesis: ATP is used in the assembly of proteins from amino acids.
  4. Cell division: ATP powers the processes involved in cell replication and division, including the movement of chromosomes.
• Cell Respiration vs. Gas Exchange vs. Ventilation

  Cell respiration:

  • The process by which cells break down glucose and other molecules to produce ATP, involving glycolysis, the Krebs cycle, and the electron transport chain.

  Ventilation:

  • The physical process of moving air into and out of the lungs or respiratory structures to facilitate gas exchange.

  Gas exchange:

  • The biological process of exchanging oxygen and carbon dioxide between the bloodstream and the air in the lungs (or other respiratory surfaces).
• Properties of ATP

  1. High-energy bonds: The bonds between the phosphate groups in ATP store a large amount of energy, which can be released quickly and efficiently.
  2. Small and soluble: ATP is small and soluble in water which makes it easy to transport around the cell.
  3. Rapid regeneration: ATP can be quickly regenerated from ADP and inorganic phosphate (Pi) through cellular respiration.
• Limitations and Reliability


  Sensors used to measure ATP production have some limitations - name two:

  1. Sensitivity to environmental conditions such as temperature and pH.
  2. Potential interference from other cellular components or reactions.