Enzymes Flashcards
Define what a catalyst is
- a substance that alters or speeds up a chemical reaction
- remains chemically unchanged at end of reaction
Define enzymes
- a protein (turn Biuret’s solution from blue to violet during Biuret’s test)
- functions as a biological catalyst
- alters or speeds up chemical reactions
- remains unchanged at the end of reaction
Enzymes lowers activation energy
-refers to energy needed to start a chemical reaction
Digestion
- some food molecules are large, insoluble in water
- these molecules cannot diffuse across the cell membrane
- have to be converted/digested into smaller, simpler molecules and soluble in water
Examples of digestive enzymes
- Amylase: Digest starch to maltose
- Maltase: Maltose to glucose
- Protease: Proteins to amino acids
- Lipase: digest fats into glycerol and fatty acids
Anabolic reactions
- building up of complex substances
- e.g. building proteins from amino acids, condensation reactions
Catabolic reactions
- break down of complex substances
- e.g. breakdown of glucose during respiration, hydrolysis
Characteristics of enzymes
- speed up chemical reactions
- required in minute amounts
- highly specific in action
Speeding up chemical reactions (Characteristic of enzymes)
-lowers activation energy needed to start reaction
Enzymes required in minute amounts (Characteristic of enzymes)
- same enzyme molecules can be used over and over again
- can catalyse large no of chemical reactions
Enzymes are highly specific in action (Characteristic of enzymes)
- enzyme specificity: each chemical reaction inside a cell is catalysed only by one unique enzyme
- e.g. amylase works on starch
- an enzyme specific due to its 3 dimensional shape
Lock and key hypothesis (Enzyme specificity)
- enzyme has a specific 3D shape containing an active site, substances that act on is known as substrate
- only substrate with 3D shape that is complementary to active site can fit into enzyme to form and enzyme-substrate complex
- chemical reaction occurs, substrate converted into products
- products detach from active site, enzyme remains unchanged at end of reaction
Define Denaturation
- since specificity of an enzyme due to 3D shape, any factor that causes enzyme to change shape will affect its function
- change in 3D shape of any enzyme or any protein is known as denaturation
Causes of denaturation
- Heat (extremely high temps)
- Chemicals e.g. acids, alkalis (pH level)
What happens during denaturation?
- loss or change in active site
- substrate can no longer fit enzyme’s active site (shape of active site no longer complementary to shape of substrate)
- no reaction take place, no longer act as a catalyst
How temperature affects enzymes (low temp)
- enzymes inactive at low temps
- kinetic energy low at low temps
- chances of substrate molecules successfully colliding with enzymes very low
How temperature affects enzymes (high temp)
- temp rises, enzyme activity increases
- increase in kinetic energy
- increase chances of successful collision between substrate and enzyme
- increases rate of formation of enzyme-substrate complex
How temperature affects enzymes (optimum temp)
- for every 10°c increase in temp, rate of enzyme reaction doubled until opt temp is reached
- optimum temp is the point when rate of reaction highest, enzyme most active (highest rate of product formation/no .of enzyme-substrate complexes formed)
- most enzymes opt temp is 40-45
How temperature affects enzymes (beyond optimum temp)
- enzyme activity decreases
- enzymes are proteins, high temp break bonds within the enzyme, changes 3D shape
- substrate no longer fit into active site
- enzyme now denatured
How pH affects enzymes
- diff enzymes, diff optimum pH values (most active)
- some work best in slightly acidic/alkaline
- extreme changes in pH result in denaturation, lose function
Examples of optimum pH values
- amylase in saliva: pH 7
- pepsin in stomach: pH 2
- trypsin in small intestine: pH 8
How enzyme-substrate concentration affects enzymes
- enzyme/substrate concentration is fixed
- at saturation pt, enzyme/substrate conc is limiting factor
- all enzymes occupied by a substrate(or the other way round), increasing conc does not affect reaction rate
Enzyme catalyse reversible reactions
- some reactions in living cells are reversible
- can proceed in forward or backward direction
- e.g. respiration
