Flashcards in enzymes Deck (37):
what are enzymes?
biological catalysts that speed up chemical reactions without being used up in the reaction itself. they are globular proteins that lower the activation energy needed to change the reactants into products.
what type of reactions can enzymes catalyse?
anabolic (building up) and catabolic (breaking down).
what type of reactions can't enzymes catalyse?
reactions that wouldn't naturally occur.
conditions for reactions to take place naturally
1. the substrates must collide with sufficient energy to alter the arrangement of their atoms to form the products.
2. the free energy of the products must be less than that of the substrates
3. activation energy - minimum amount of energy needed to activate reaction.
why are enzymes important?
they allow metabolic reactions to happen rapidly at much lower temperatures (37 degrees in humans). Without enzymes, these reactions would occur to slowly to sustain life as we know it.
what is the active site of an enzyme made up of?
region made up of relatively small number of amino acids.
what is an enzyme substrate complex?
the intermediate formed when a substrate molecule interacts with the active site of an enzyme - held by temporary bonds formed between amino acids of active site and groups on substrate.
Enzymes that catalyse chemical reactions outside of cells are called...
Describe the induced fit model of enzyme action
Substrate approaches active site
active site not complementary
active site changes shape and forms functional active site - as substrate binds - is complimentary
Enzyme moulds to substrate - forming enzyme-substrate complex.
Change in shape puts a strain on bonds of substrate, lowering activation energy.
product is released from enzyme
Describe the lock and key model of enzyme action
A substrate is complimentary to an enzyme.
A substrate binds to the active site of an enzyme, forming enzyme substrate complex.
This lowers the activation energy.
Product is released from enzyme.
what is the limitation of the lock and key model?
enzyme considered to be a rigid structure, but scientists observed that other molecules could bind to enzymes at other sites. Binding molecule alters shape of enzyme: not rigid but flexible.
Which have a higher energy level: substrates or products?
The specific 3D shaped active site of an enzyme is determined by..
its sequence of amino acids (primary structure)
Enzymes that catalyse reactions inside of cells are called...
Hormones are proteins that have a binding site so that they can switch on or off bodily processes. Are they enzymes?
No - many proteins have binding sites or receptor sites. These are not active sites.
Why are enzymes still effective even in small amounts?
Because they are not used up or changed so can be used again and again.
Why does formation of enzyme substrate complex increase rate of reaction?
Reduces activation energy
due to the bending/weakening of bonds
For an enzyme to work it must:
come into contact with its substrate.
have an active site which complements the substrate.
How can the progress of an enzyme controlled reaction be measured? (2 methods)
substrates used up/time
gas measured using...
inverted measuring cylinder
mmols/s^-1. mmols/hr^-1, mmols/g^-1
liquids/solids measured using...
describe rate of reaction graph
1. initially, there is a rapid increase in product produced.
2. the rate then gradually starts to decrease.
3. eventually, the graph "tails" off, no more product is released.
explain rate of reaction graph
1. rapid initial increase - lots of available/free active sites - lots of enzyme substrate complexes form so rate quick.
2. rate of reaction starts to decrease - less substrates (as broken down) and more products formed - product molecules start to "block"/prevent substrates reaching active site.
3. graph flattens, reaction stops - all substrates used up, no new product can be formed.
how to calculate ROR from linear graph?
how to calculate ROR from curve?
explain the effect of temperature on enzyme action
1. as the temp increases, the kinetic energy of the substrates and enzymes increases - more collisions = more enzyme substrate complexes form - ROR increases.
2. ROR reaches optimum temp - enzyme works best
3. as temp becomes too high, too much kinetic energy causes hydrogen bonds in tertiary structure (3D) of active site to break. Enzyme denatures so no longer complimentary - no enzyme substrate complexes form - reaction slows down until no more products formed.
why have our bodies evolved to around 37 degrees?
higher temperatures would increase the metabolic rate slightly but
1. more energy (food) needed to maintain the body temperature.
2. other proteins, apart from enzymes may be denatured at higher temperatures.
3. at higher temp, even higher temp (during illness) - denaturation of enzymes.
what is the Ph of a solution a measure of?
its hydrogen ion concentration (H+)
Why do birds have a body temperature of 40 °C?
They have a high metabolic rate in order to release the energy required for flight.
What is the equation for calculating the pH of a solution?
pH = -log10[H+]
explain the effect of PH on enzyme action
1. a change in PH away from the optimum pH alters the charges of the amino acids that make up the active site. Changes in tertiary structure - no longer complimentary - no enzyme substrate complexes form.
2. extremes of pH break ionic and hydrogen bonds between the amine and hydroxyl groups (polypeptide) of tertiary structure of the active site. Therefore, no enzyme substrate complexes form - as enzyme denatured.
A solution with a high H+ ion concentration is an...
A solution with a high OH- concentration is an...
pH fluctuations inside organisms...
are usually small. Far likely to reduce enzyme activity than denature it.
explain the effect of enzyme concentration on enzyme action
1. fewer enzyme substrate complexes formed as not enough enzyme molecules to allow substrates to find an AS at any time - ROR - half the maximum for substrate molecules available.
2. more enzyme substrate complexes formed - twice as many enzyme molecules available - all substrates can occupy AS at the same time - ROR doubled to maximum and increases.
3. all AS are filled if substrate not limiting, R increases proportionally forever.
4. addition of further enzyme molecules has no effect, as all AS occupied - levels out - no more enzyme substrate complexes form - no further increase in ROR.