unit two

• catabolic pathways bring about the breakdown of complex molecules to simpler ones, releasing energy and providing building blocks.
• anabolic pathways bring about the biosynthesis of molecules from building blocks, requiring input of energy.
• catabolic and anabolic reactions are closely integrated and rely on eachother.
• the membrane system is selectively permeable and allows transport both within cells and between cells.

  membranes from surfaces and compartments for metabolic pathways allow for high concentrations and reaction rates.
• the membrane is made up of a bilayer of phospholipids with proteins embedded in it, and is described as the fluid mosaic level.
• protein pores (channels) allow specific molecules and ions to pass through the membrane, by passive transport.
• protein pumps (carriers) bind to specific molecules or ions temporarily, enabling them to cross the membrane, through active transport.
• some proteins in the membrane act as enzymes to catalyse a specific reaction.
• some proteins act as structural support to help shape the cell.
• metabolic pathways are controlled by the presence or absence of certain enzymes and the regulation of the rate of reaction of key enzymes.
• metabolic pathways are the sequence of reactions that are controlled by enzymes that change one metabolite into another.
• a metabolic pathway often contains both reversible and irreversible steps, allowing it to kept under precise control.
• problems occur in metabolic pathways if enzymes aren't synthesised properly due to mutations.
• the energy required to start a chemical reaction is activation energy.
• enzymes lower the activation energy needed for a reaction to take place.
• induced fit occurs when the active site changes shape to accommodate the substrate after it binds. this lowers activation energy.
• substrate molecules have a high affinity for the active site, when the reaction is complete, the products have a low affinity, allowing them to move away from the active site.
• enzyme inhibitors reduce the rate of enzyme-catalysed reactions by interfering with the enzyme in some way. this can be permanent or temporary.
• competitive inhibition occurs when the inhibitor binds to the active site to prevent the substrate from binding.

  this decreases the rate of reaction as less substrate molecules can bind to the enzymes.

  this is temporary, and can be reversed by increasing substrate concentration, which increases the chance of a substrate binding, overcoming competitive inhibition.
• non-competitive inhibition occurs when the inhibitor binds to another area in the enzyme, causing the active site to change its shape, making the substrate unable to bind.

  they don't compete with substrate molecules, so these inhibitors aren't affected by substrate concentration.

  can/can't be reversible.
• feedback inhibition occurs when the end-product of a metabolic pathway reaches a critical condition.

  the end-product inhibits an earlier allosteric enzyme at the allosteric site, blocking the pathway and preventing further synthesis of the end-product.
• atp is essential to biological systems as it's the link between reactions that release energy (catabolic) and those that use energy (anabolic).
• when glucose is broken down in a cell, it releases energy which is used to produce atp.

  atp is made from joining a phosphate to adp.

  the end phosphate bond contains a lot of energy which is released when broken off. this is used by cells to do work and carry out anabolic

  reactions.
• atp also carries out phosphorylation reactions in cells. it is an enzyme-controlled process.
• during respiration, glucose is gradually broken down and hydrogen released at various stages along the pathway. each of these stages is controlled by an enzyme called a dehydrogenase.
• if no oxygen is present, only glycolysis can take place, and pyruvate follows a fermentation pathway.
• you can measure respiration rate using a respirometer.
• metabolic rate is the quantity of energy used by the body over a given time and is measured in kilojoules.
• metabolic rate can be measured as oxygen consumption, carbon dioxide and energy production per unit time.
• you can measure metabolic rate by respirometers and calorimeters.
• respirometers measure the amount of oxygen uptake by an organism.

  these can be used in conjunction with oxygen or carbon dioxide probes.
• calorimeters measure the heat generated by an organism and calculates the metabolic rate from the results.
• at rest, the metabolic rate is known as the basal metabolic rate (bmr). the bmr is low compared to when the body is undergoing activities like exercise.
• high metabolic rates require efficient delivery of oxygen to cells.

  multicellular organisms need oxygen delivery systems such as cardiovascular systems.
• all vertebrates have closed circulatory systems.

  the blood is contained in a continuous circuit of blood vessels and is kept moving by a muscular pump (a heart).

  pressure drops in the capillary vessels as the narrow tubes offer resistance to the flow of blood.
• organisms with high metabolic rates require more efficient delivery of

  oxygen to cells.

  birds and mammals have higher metabolic rates than reptiles and

  amphibians, which in turn have higher metabolic rates than fish, resulting in different cardiovascular systems.
• fish have a single circulatory system as blood passes through the

  two-chambered heart once for each circuit of the body.

  fish have a two-chambered heart with an atrium and a ventricle, and valve in between.

  blood flows to the gills at high pressure but is delivered to the body capillaries at low pressure.

  it's a primitive and inefficient method.
• double circulatory systems allow blood to pass through the heart twice for each complete circuit of the body.

  blood is pumped to the lungs and the body at high pressure, ensuring vigorous flow.

  more efficient than single systems.
• amphibians and most reptiles circulatory systems are incomplete circulatory systems as there is only one ventricle.

  mixing of oxygenated blood from the lungs and deoxygenated

  blood from the body occurs.

  in amphibians the mixing is not a major problem as the blood returning from the body has been partially oxygenated through its moist skin.

  the amphibian and reptile heart are made of three chambers, two atria and one ventricle.

  in reptiles, little mixing occurs because the single ventricle is partly divided by a septum.
• birds and mammals have complete circulatory systems. they're complete because the heart has two ventricles completely seperated by a septum.

  complete double circulatory systems enable higher metabolic rates to be maintained.

  there is no mixing of oxygenated and deoxygenated blood.

  oxygenated blood is pumped out at a higher pressure.

  enabling more efficient oxygen delivery to the cells.