C1.1 - metabolism and enzyme action (2i) Flashcards
what is metabolism?
metabolism is the complex network of interdependent and interacting chemical reactions occurring in living organisms that are controlled by enzymes; this network is formed of chains of enzyme-catalysed reactions, linked into webs
what are the 2 categories of metabolic reactions?
what are some examples of each?
anabolism = the formation of macromolecules from monomers, often through condensation reactions
- protein synthesis and photosynthesis
catabolism = the breakdown of macromolecules into monomers, often using hydrolysis reactions
- digestion and respiration
what is the role of enzymes in metabolism?
control of metabolism occurs through enzymes, each of which catalyses a specific chemical reaction
- because of enzyme specificity, many different enzymes are required by living organisms
what are enzymes?
enzymes are biological catalysts and so increase the rate of reaction in cells
- enzymes have active sites that bind specific substrates
- enzymes speed up the reactions by lowering the activation energy
why do we need enzymes?
most reactions within a cell occur too slowly on their own to be able to sustain life, therefore enzymatic catalysis is required to maintain essential life functions
what is the structure of enzymes?
enzymes are proteins with specific 3D shape (conformation) and with an active site that binds with the substrate(s)
- enzymes are globular proteins, having spherical shape in general terms, but the precise shape of each enzyme is specific
the active site is the catalytic site on the surface of an enzyme, to which the substrate(s) bind
- the active site is composed of a few amino acids only
- interactions between amino acids within the overall three-dimensional structure of the enzyme ensure that the active site has the necessary properties for catalysis
–> these properties include shape, but also chemical properties such as hydrophobicity and charge
what is the role of molecular motion and substrate-active site collisions in enzyme catalysis?
movement is needed for a substrate molecule and an enzyme’s active site to come together
what is activation energy?
activation energy is the energy that must be put into destabilising the existing bonds in a substrate, so that the reaction can proceed
- this energy is provided by the kinetic energy, or rate of molecular motion, of the substrate and enzyme molecules
- there is an energy yield when bonds are made to form the products
what is the effect of enzymes on activation energy?
enzymes lower the activation energy of a reaction
- enzymes do not change the energy within the substrates or products, but lower the threshold that must be exceeded during a collision, to allow the reaction to proceed
- the activation energy is lowered because the interaction of chemical groups on the substrate(s) and active site lead to weakening of bonds in the substrate
why do substrate active site collisions allow for binding?
substrate-active site collisions allow for binding due to the complementary shapes of the active site and the enzyme’s specific substrate molecules
how does this binding between substrate and active site lead to weakening of bonds?
the binding occurs due to attractive chemical properties of the substrate and the active site, and brings the substrate(s) close together in the correct orientation within the active site
- this binding causes formation of an enzyme-substrate complex, in which the enzyme and substrate change shape slightly, putting strains on the chemical bonds of the substrate and weakening them
what determines whether a reaction can proceed after binding?
the reaction can only proceed and form a product if the activation energy is exceeded
- the energy is provided in the form of kinetic energy, or molecular motion, of the substrate and enzyme molecules
- if molecules do not have enough kinetic energy, the substrate may collide with the active site, but it will not be successful as the reaction will not occur
what happens after the products are formed from the enzyme?
once formed, the product is released from the active site, leaving the unchanged enzyme free to combine with other substrate molecules
how does immobilisation impact enzyme action?
sometimes large substrate molecules are immobilized, while sometimes enzymes can be immobilized by being embedded in membranes
- e.g) ATP synthase in mitochondrial membranes increases enzyme activity by making the formation of enzyme-substrate complexes more efficient
what is the relationships between the structure of the active site, enzyme-substrate specificity, and denaturation?
enzymes are proteins with specific 3D shape and an active site that binds with the substrate
- an enzyme active site’s shape only allows it to bind with specific substrates, which have the complementary shape to the active site
- the binding of the specific substrate into the active site forms an enzyme-substrate complex and allows the reaction to occur
- denaturation of an enzyme changes the shape of its active site, and so reduces the ability to bind with the substrate and catalyse that reaction
