Biology - Enzymes Flashcards
What are biological catalysts?
Large biological molecules called enzymes.
- substance that can speed up/catalyse the rate of a chemical reaction and remain chemically unchanged at the end
Types of reactions
Enzymes are used in all metabolic reactions in cells
- Anabolic reactions: synthesizing complex molecules
- Catabolic reactions: breaking of complex molecules
What is the structure of enzymes and what do they do?
Made up of protein molecules folded into three-dimensional globular shapes.
Enzymes lower activation energy (energy needed to start chemical reaction). They speed up the rate of chemical reactions by lowering activation energy.
What is the limiting factor?
A limiting factor directly affects the rate of a chemical reaction.
Why and what reactions do enzymes catalyse?
During digestion, enzymes break large molecules that cannot diffuse through cell membranes so that they are more soluble and smaller.
Enzymes involved in digestion are digestion enzymes.
e.g.
amylase - starch into maltose
maltase - maltose into glucose
protease - proteins to polypeptides then to amino acids
lipase - fats to fatty acids and glycerol
How are enzymes classified?
carbohydrases - carbohydrates
proteases - proteins
lipases - fats (lipids)
What is enzyme specificity?
Each chemical reaction inside a cell is catalysed by a unique enzyme. (due to its three-dimensional shape)
What is the lock-and-key hypothesis?
The substances on which enzymes act are called substrates. Enzyme reactions depend on the presence of their active sites (grooves/depressions on the surface where the substrate molecule(s) with a complementary shape can fit)
How does the enzyme catalyse?
Substrate binds to active site –> enzyme-substrate complex (temporary molecule substance)
Reactions take place in the active site to convert the substrate molecule(s) into product molecule(s), which separates from the enzyme when finished. The enzyme remains unchanged and can combine with more substrates.
Equation: E + S –> ES –> E + P
What are the characteristics of enzymes?
- Speed of chemical reactions
- Specific in action
- Required in minute amounts (small amt of enzymes for large amt of substrates) and remain unchanged at the end of reaction
- Affected by temperature, pH, enzyme concentration and substrate concentration
What is denaturation?
Denaturation is the change in the three-dimensional structure of an enzyme or any other soluble protein, caused by heat or chemicals such as acids or alkalis. Results in the loss or alteration of the active site so that the substrate can no longer fit, and the enzyme can no longer catalyse.
How are enzymes affected by temperature?
Based on a graph.
1. Less active at low temp: low kinetic energy, enzyme and substrates move slowly, rate of collision low
2. Temp increases, rate of enzyme reaction increases: increased kinetic energy, rate of effective collision (colliding and fitting), increased rate of enzyme-substrate complex formation
3. Optimum temp, enzyme most active: optimum temp for human enzymes is 40-45 degrees Celsius.
4. Increasing temp after optimum causes rapid decrease in rate: enzymes lose original shape, no longer complementary to substrate molecule
5. Higher temp: most enzymes have denatured
How are enzymes affected by pH?
Different enzymes work best in different pH (protease in acidic solutions, intestinal enzymes in alkaline conditions) They denature when pH varies from optimum and changes extremely.
e.g. amylase at maximum activity at optimum pH of 7, solution becomes acidic (pH 7 to 5) or alkaline (pH 7 to 9), the enzyme is completely denatured.
How are enzymes affected by substrate concentration?
(Graph is increasing)
Low concentration of substrate –> enzyme occurs in excess
Hence more active sites available –> all can bind immediately
Substrate conc increases –> frequency of effective collisions increases, more enzyme-substrate complexes formed –> more products formed per unit time –> rate of enzyme reaction increases
(Graph plateaus)
High conc of substrate –> rate of enzyme plateaus (remains at maximum). All active sites are occupied, enzymes are saturated. More substrate molecules than enzyme molecules. Enzyme concentration is the limiting factor.
How are enzymes affected by enzyme concentration?
(Increasing graph)
Low enzyme conc –> rate of reaction increases as enzyme conc increases due to more active sites being available to bind. Frequency of effective collisions increases. More enzyme-substrate complexes formed.
(Graphs plateaus)
Enzyme conc increases to higher conc –> rate of reaction plateaus because the number of substrate molecules is fixed –> excess of enzyme molecules present. All of the substrate molecules are bound to an enzyme’s active site. Substrate concentration is the limiting factor.
