Enzymes Flashcards
define an enzyme
Enzymes are globular proteins that act as catalysts.
they alter the rate of a chemical reaction without undergoing permanent changes themseves.
what is required for reactions like sucrose + water= glucose to take place naturally
the sucrose water molecules must collide with sufficient energy to alter the arrangement of their atoms to form glucose and fructose
the free energy of the products must be less than that of the substrates sucrose and water
many reactions require an activation energy
what must happen before a reaction can proceed
there is an activaion energy level, like an energy barrier which must initially be overcome before the reaction can proceed
explain how enzymes help reactions proceed
enzymes work by lowering this activation energy level
in this way enzymes allow reactions to take place at lower temperature than normal
this enables some metabolic processes to occur rapidly at the human body temperature of 37 degrees Celsius
what would happen without enzymes
these reactions would proceed too slowly to sustain life as we know it
what region of the enzyme is functional
active site
describe the active site
the active site is made up of a relatively small number of amino acids
he active site forms a small depression within the much larger enzyme molecule
what is the molecule on which the enzyme acts called
the substrate
explain the role of a substrate
fits neatly into this depression and forms an enzyme-substrate complex.
the substrate molecule is held within the active site by bonds that temporarily form between certain amino acids of the active site and group of the substrate molecule
describe the induced fit model of enzyme action
the induced fit model of enzyme action proposes that the active site forms as the enzyme and substrate interact
the enzyme is flexible and can mould itself around the substrate
the enzyme has a certain general shape but this alters in the presence of a substrate
As it changes shape, the enzyme puts a strain on the substrate molecule.
the strain distorts particular bonds in the substrate and consequently lowers the activation energy needed to break the bond
explain the induced fit concept
any change in an enzymes environment is likely to change its shape.
the very act of colliding with its substrate is a change in its environment and so its shape changes- induced fit
explain the mechanism of enzyme action
Substrates collide with the enzyme’s active site and this must happen at the correct orientation and speed in order for a reaction to occur
An enzyme-substrate complex forms when an enzyme and its substrate join together
The enzyme-substrate complex is only formed temporarily before the enzyme catalyzes the reaction and the product(s) are released
explain the specificity of an enzyme
The specificity of an enzyme is a result of the complementary nature between the shape of the active site on the enzyme and its substrate(s)
what determines the shape of the active site
The shape of the active site (and therefore the specificity of the enzyme) is determined by the complex tertiary structure of the protein that makes up the enzyme
what forms when an enzyme and substrate join together
an enzyme-substrate complex
what are the two types of enzyme reactions
Enzyme reactions can either be catabolic or anabolic
explain catabolic reactions
Catabolic reactions involve the breakdown of complex molecules into simpler products, which happens when a single substrate is drawn into the active site and broken apart into two or more distinct molecules (products)
give two examples of catabolic reactions
cellular respiration and hydrolysis
explain anabolic reactions
Anabolic reactions involve the building of more complex molecules from simpler ones by drawing two or more substrates into the active site, forming bonds between them and releasing a single product
give two examples of anabolic reactions
protein synthesis
photosynthesis
what type of protein are enzymes
globular proteins
what can enzymes be
Enzymes can be intracellular or extracellular referring to whether they are active inside or outside the cell respectively
define intracellular enzymes
Intracellular enzymes are produced and function inside the cell
define extracellular enzymes
Extracellular enzymes are secreted by cells and catalyse reactions outside cells (eg. digestive enzymes in the gut)
explain the effect of a rise in temperature on enzyme action
a rise in temperature increases the kinetic energy of molecules.
as a result, the molecules move around more rapidly and collide with each other more often
in an enzyme catalysed reaction, this means that the enzyme and substrate molecules come together more often in a given time
there are more effective collisions resulting in more enzyme-substrate complexes being formed and so the rate of reaction increases
what happens when the temperature exceeds 37 degrees celsius
it causes the hydrogen and other bonds in the enzyme molecule to break
this results in the enzyme, including its active site changing shape, slowing the rate of reaction
explain when denaturation occurs and define it
usually, around 60 degrees the enzyme is so disrupted that it stops working altogether. it is said to be denatured
denaturation is a permanent change and once it has occurred, the enzyme does not function again
why have our bodies evolved to be 37 degrees celsius
althougher higher body temperatures would increase te metabolic rate slightly, the advantages are offset by the additional energy that would be needed to maintain the higher temperature
other proteins, apart from enzymes, may be denatured at higher temperatures
at higher temperatures any further rise in temperature, for example, during illness, might denature the enzymes
