4 - Enzymes Flashcards
1
Q
What are enzymes?
A
- they speed up chemical reactions by acting as biological catalysts.
- they catalyse metabolic reactions at cellular level and for organisms as a whole.
- They can affect structures and functions of an organism.
- enzyme action can be intracellular (inside cells) or extracellular (outside cells).
- globular proteins
- have an active site with a specific shape (determined by tertiary structure).
2
Q
intracellular enzymes? example?
A
- they are enzymes that work within cells.
- e.g catalase
- catalyses the breakdown of hydrogen peroxide (toxic by product of metabolic reactions) into oxygen and water.
3
Q
Extracellular enzymes? examples?
A
- enzymes that work outside cells.
- amylase
- found in saliva
- secreted by salivary glands in mouth.
- catalyses hydrolysis of starch into maltose.
- trypsin (a protease)
- catalyses digestion of proteins into smaller peptides. (further broken down into amino acids by other proteases).
- produced by cells in pancreas, secreted into small intestine.
4
Q
What are the two models for enzyme action?
A
- lock and key hypothesis
- induced fit hypothesis
5
Q
Lock and key hypothesis explained?
A
- substrate molecule binds to an enzyme with active site with complementary shape. Enzyme-substrate complex is formed.
- products are formed in an enzyme-product complex.
- products are released, enzyme is left unchanged.
6
Q
Induced fit hypothesis explained?
A
- active site is flexible
- substrate binds to active site of enzyme with complementary shape. Enzyme-substrate complex formed.
- enzyme’s tertiary structure changes shape slightly to strengthen binding, putting strain on the substrate molecule. Destabilises (weakens) bonds in substrate, lowering activation energy for the reaction.
- products formed in enzyme-product complex
- products released and enzyme returns to original shape.
7
Q
Enzymes reduce activation energy. How?
A
- they lower activation energy, increasing rate of reaction.
- substrate fitting into the active site destabilises the bonds in the substrate molecule, making it easier for the bonds to be broken.
8
Q
effect of temperature on enzyme activity?
A
- increase in temperature increases enzyme activity (frequency of collisions of particles increases).
- enzyme activity is highest at the optimum temperature.
- If temperature is greater than the optimum temperature, enzymes are denatured.
- If increase in temperature is too great, enzymes are denatured. Shape of active site changes, so enzyme-substrate complexes cannot form. Enzyme will no longer function as a catalyst.
9
Q
What is optimum temperature?
A
- temperature at which the enzyme has the highest rate of activity.
10
Q
How to calculate Q10 (temperature coefficient)?
A
Q10 = rate at (x+10)C / rate at xC
11
Q
Effect of pH on enzyme activity?
A
- all enzymes have an optimum pH value. Most human enzymes ph7. Pepsin pH2 found in stomach acid.
- above and below the optimum pH, H+ and OH- in acids and alkali can affect ionic and hydrogen bonds in enzyme tertiary structure. Enzyme is denatured (shape of active site is changed).
12
Q
Effect of substrate concentration on enzyme activity?
A
- increases
- Higher collision rate between active sites of enzymes and substrate molecules.
- rate increases up to Vmax.
- at this point all the enzyme active sites are occupied
- only way to increase rate is to increasing temp, or increase enzyme conc.
13
Q
Effect of substrate concentration on enzyme activity?
A
- Increase
- Higher collision rate between active sites of enzymes and substrate molecules.
- rate increases up to Vmax.
- at this point max amount of enzyme-substrate complexes have formed.
- only way to increase rate is to increase temp, increase substrate conc.
14
Q
What are cofactors?
A
non-protein substances bound to enzymes.
- loosely /temporarily bound to the enzyme
15
Q
What are coenzymes?
A
organic cofactors.
