Chapter 4 - Enzymes Flashcards
globular proteins, specificity, enzyme-substrate complex
what are enzymes?
enzymes are biological catalysts.
GLOBULAR proteins that interact with substrate molecules to lower reactions activation energy.
which reactions do enzymes catalyse in cells?
metabolic reactions
what is metabolism?
the sum of all reactions occurring within an organism or cell.
types of metabolic reactions?
ANABOLIC- chemical reactions needed for growth (smaller to bigger), energy required
CATABOLIC- breaking down reactions, release energy
what is Vmax?
the maximum initial velocity or rate of the enzyme-catalysed reaction
what is the specificity of an enzyme?
a molecular recognition system which allows an enzyme to choose one specific substrate between many.
what is activation energy?
minimum energy needed for a reaction to start
what are the two hypotheses for how enzymes work?
lock and key
induced-fit
what is the active site?
the small region of the enzyme’s tertiary structure that is COMPLEMENTARY to the shape of the specific substrate molecule
describe the lock and key hypothesis
when the specific substrate fits exactly into the enzyme
what forms when an enzyme and substrate bind? what forms when the substrates react to form the product?
an enzyme-substrate complex
an enzyme-product complex
what changes and what remains unchanged during catalysis?
substrate changes (to form product) enzyme remains unchanged and can cary on forming ESC’s
enzyme + substrate —> enzyme substrate complex —> enzyme product complex
yes
which model has more recently been more accepted than the lock and key model? why?
induced fit
- more evidence to prove
describe the induced fit model of enzyme action
the enzymes active site changes shape slightly as the substrate enters
describe how the induced fit model lowers activation energy of a reaction
interactions between the enzymes active site and substrate are weak but then cause the tertiary structure to change, strengthen binding IN THE ACTIVE SITE and put strain on the substrate and weaken bonds IN THE SUBSTRATE.
describe how lock and key model lowers activation energy of a reaction
the R groups within the active site react with the substrate forming temporary binds and put strain in bonds within the substrate.
why are extracellular enzymes needed?
to break down larger molecules to smaller ones to be transported inside cells
where are intracellular enzymes made?
in the cell, ribosome (site of protein synthesis)
give examples of extracellular enzymes and state what they are involved in?
amylase, trypsin - digestion
give examples of intracellular enzymes and state what they are involved in?
DNA polymerase, DNA ligase, ATP synthetase - DNA replication
process of digestion of starch step 1
starch first broken down into maltose by _____ which is released into the _____ and ______
amylase, salivary glands and pancreatic juice in small intestine
process of digestion of starch step 2
maltose is broken down into _____ which is a ______ by _______ which is present in the ______
glucose, monosaccharide, maltase, small intestine
process of digestion of proteins
the protease enzyme that breaks down proteins into ______ in the small intestine is called _____. this enzyme is produced in the ______ and carried to the small intensities via _____ _____. amino acids which are produced by digestion if proteins are _____ into the ________ by the cells lining the _____ _____
smaller peptides, trypsin, pancreas, pancreatic juice, absorbed, bloodstream, digestive system
What is an enzyme?
A biological catalyst that speeds up the rate of a biochemical reaction by lowering the activation energy.
Structure of enzymes?
Globular protein with a helical secondary structure
What are the two types of enzymes?
Intracellular and extracellular
What are intracellular enzymes?
Function/have effect within the cell
What are extracellular enzymes?
Function/ have effect outside the cell
What factors affect the rate of reaction/action of enzyme-assisted reactions?
enzyme concentration, substrate concentration, temperature, pH
What is the substrate?
The substance on which the enzyme acts.
what is a cofactor
- a component necessary for the function of the enzyme,
- inorganic
- not permanently attached
- e.g. chloride ions for amylase function
what is a coenzyme
- a component necessary for the function of a specific enzyme
- organic
- TEMPORARILY attached
what is a prosthetic group
- a non protein component necessary for the function of an enzyme
- PERMAMENTLY attached
what is precursor activation
some enzymes produced in an inactive form, must have e.g. cofactor added to them to work
what is an enzyme called before the cofactor is added
apoenzyme
what is an enzyme called after the cofactor is added
holoenzyme
what is a enzyme which needs an environment change to work called?
a zymogen or proenzyme
what does the change in temperature/pH do in precursor activation?
changes the tertiary structure so enzyme can function
give and example of a zymogen activation
inactivated pepsinogen becomes activated by the acidic conditions in the stomach
what is the turnover number?
the number of reactions an enzyme can catalyze per second
what happens if the enzyme that catalyses a reaction is deficient?
metabolic disorder results
example of an intracellular enzyme? where is it found?
catalase breaks down hydrogen peroxide, found in vesicles called peroxisomes
example of an extracellular enzyme? where is it found?
amylase digests starch, produced in salivary glands
example of prosthetic group?
- e.g. Zinc ions for carbonic anhydrase
found in erythrocytes, catalyses conversion of CO2 to water and carbonic acid
example of coenzyme?
- e.g. Vitamin B5 for Coenzyme A
what is Q10?
the increase in the rate when the temp. increases by 10 degrees
= rate of reaction at T + 10
————————————–
rate of reaction at T
what does a Q10 of 2 mean? what is the Q10 for most reations in a test tube?
for every 10 degrees increase, the rate is DOUBLED.
it is 2
how can u find the rate from just one point? (as there is no gradient)
1
—————–
time/value
how does heat denature an enzyme?
molecules vibrate faster, weaker bonds like ionic and hydrogen bonds break, tertiary structure breaks, the active site DENATURED.
why doesn’t heat change the primary structure?
peptide bonds are covalent and so very strong
how does temperature increase rate of reaction?
- enzyme and substrate have more KE
- collide more often and more successfully
- more enzyme-substrate complexes formed
- more enzyme-product complexes formed
what does the rate of reaction against pH graph look like?
bell-shaped
how does pH increase rate of reaction? then lower it?
excess DO
explain how enzymes lower the activation energy of reactions
Because they bring the substrate molecules close together, as the substrate molecules fit into the enzyme’s active site, and form S–E complexes, and stay there long enough to react.
how do the enzymes of organisms that live in extreme conditions vary from others, that allow them to withstand
These proteins may have many disulfide bridges as these bonds are heat stable.
why do enzymes only work within narrow ranges of pH?
Because changes in pH change the balance of hydrogen ions/protons, and these interfere with the hydrogen bonds that hold the shape of the enzyme’s active site. If the shape of the active site changes slightly, the substrate molecules do not fit in so well.
why is the enzyme added last during an experiment?
so the reaction doesn’t start before we start timing
why are some enzymes produced in an inactive form?
so they don’t digest/harm cells or tissue where they were made and only work where needed
(imagine a graph of substrate conc. to rate of reaction)
(increases, then plateaus)
explain the shape of the graph
Between A and B, the concentration of SUBSTRATE is the LIMITING FACTOR. As substrate concentration increases, rate of reaction increases. At point B the maximum rate of reaction is reached, because there are NO MORE ACTICE SITES available for substrate molecules to form ES complexes. Between B and C, the substrate concentration is no longer the limiting factor. Something else is limiting the reaction – the availability of enzyme active sites, in other words the enzyme concentration. Adding more substrate molecules does not increase the rate of reaction as the number of enzyme active sites is limited.
e. g. why do some plants have the enzyme urease?
- how would u tackle this question?
- urease … UREA
- breaks down urea
- why would u break down urea
- to make ammonia which is a source of nitrogen so can be absorbed by soil and make new proteins
explain how competitive inhibitors reduce enzyme activity
Competitive inhibitors have a similar shape to those of the enzyme’s substrate, so they may attach to the active site when enzyme and inhibitor molecules collide; they form enzyme–inhibitor complexes; they compete with the substrate for the enzyme’s active site; because the active site is occupied, the substrate molecules cannot fit into it, so there are fewer ES complexes, fewer catalysed reactions, and fewer product molecules are made.
explain how non-competitive inhibitors reduce enzyme activity
They attach to a part of the enzyme molecule, other than the active site ALLOSTERIC SITE, and cause the enzyme to change shape. This distorts the shape of the active site, so it is no longer complementary to the substrate; substrate cannot fit into the active site and fewer ES complexes form.
explain how end-product inhibition may regulate metabolic pathways
The product molecules may remain bound to the enzyme/regulatory subunits of enzyme, keeping the enzyme in
its inactive form (the active site may not be exposed). Many metabolic pathways are regulated by different
enzymes that form a large multi-enzyme complex. The end product may bind to an enzyme early in the pathway.
graph for competitive inhibition?
compared to no inhibitor
lower gradient, reaches same max initial rate as no competitor
graph for non-competitive inhibition?
compared to no inhibitor
max initial rate much lower than with no competitor
