Chapter 5 Flashcards
What is metabolism? (3)
- metabolism refers to all chemical reactions that occur in a living organism
- involve the conversion of food into energy (ATP)
- involve formation of carbohydrate, protein, lipid & nucleic acid
What are the 2 types of metabolism in a cell?
- catabolism
- anabolism
What are the characteristics of catabolism? (3)
- process of breaking down complex substances into simple substances
- releases energy
- example: breakdown of glucose during cellular respiration
A (substrate) → B + C (products)
What are the characteristics of anabolism? ()
- process of synthesising complex molecules from simple molecules
- uses/absorbs energy
- example: formation of glucose during photosynthesis
A + B (substrate) → C (product)
What is an enzyme?
- an organic catalyst mostly made up of proteins & produced in living cell organism
- substrate is needed for enzyme reaction
- substrates bind to active site of enzyme & forms enzyme-substrate-complex
What are the general characteristics of enzyme? (8)
- biological catalysts that speed up biochemical reactions
- act rapidly
- required in small amounts & are reusable
- structure remains unchanged & not destroyed after reaction
- reactions are specific
- most reactions catalysed by enzymes are reversible
- enzyme activity can be slowed/stopped by enzyme inhibitors
- some enzymes need cofactors to work more efficiently
What are intracellular & extracellular enzymes? (2)
Intracellular enzyme
- enzymes synthesised in a cell for its own use (ex: hexokinase during glycolysis)
Extracellular enzymes
- enzymes secreted outside the cell (ex: trypsin from pancreatic cells used in duodenum)
How are extracellular enzyme produced? (6 steps)
1) ribosome synthesises proteins
2) the proteins enter the lumen of the rough ER and are transported through it
3) at the end of the rough ER, the membrane buds off to form transport vesicles
4) the transport vesicles containing proteins move towards & fuses with Golgi apparatus
5) in the Golgi apparatus, proteins are modified into enzymes, packaged into secretory vesicles that are formed at the tip of Golgi apparatus & transported to plasma membrane
6) secretory vesicles fuses with the plasma membrane to secrete extracellular enzymes
What is the mechanism of enzyme reaction?
The ‘lock and key’ hypothesis
- enzyme represents lock
- substrate represents key
Most reactions inside the cell require high activation energy. What is activation energy and how is it related to enzyme reaction?
- energy needed to break the bond in the substrate molecule before reaction can occur
- enzymes function by lowering the activation energy, thus rate if biochemical reactions in the cell is accelerated)
What are the factors that affect the mechanism of enzyme reaction? (4)
- temperature
- pH
- substrate concentration
- enzyme concentration
What are the effects of temperature on the rate of biochemical reaction controlled by enzymes? low temp (4), optimal (1), high (3)
low temperature
- rate of reaction catalysed by enzyme is low
- when temp rises, kinetic energy of enzyme & substrate increases - increases frequency of effective collision between substrate & enzyme molecules
- rate of reaction increases
- every rise of 10°C, rate of reaction by enzymes doubles till optimal temp reached
optimal temperature (37 °C) - enzyme reaction is at maximum
higher than optimal temperature
- enzyme activity reduces and stops at 60°C
- at 60°C enzymes are denatured (chemical bonds in enzyme broken)
- enzyme unable to retain 3D form, active site changes
What are the effects of pH on enzyme reaction? (5)
- most enzyme are most active in range pH 6 & 8 (ex: salivary amylase pH 6.8)
- there are some exceptions, (ex: pepsin in stomach optimal pH range between 1.5 & 2.5) (ex: trypsin in duodenum optimum in alkaline medium around pH 8.5)
- change in pH value changes the charge (H+ ion) of the active site & substrate surface, enzyme-substrate cannot be formed
- when pH return to optimum, charge on active site will be restored, enzyme function normally
- extreme change in pH value break the structural chemistry and change the active site (denatured)
What are the effect of substrate concentration on enzyme reaction [enzyme concentration fixed]? (4)
- when substrate concentration increases, chanced of effective collision between substrate & enzyme molecules increases
- reaction rate continues to increase until reaching maximum level, then rate of reaction becomes constant
At max level:
- concentration of enzymes becomes limiting factor [rate of reaction can only increase when concentration of enzymes increases]
- all active sites are saturated with substrate & involved in catalytic action
What are the effects of enzyme concentration on the enzyme reaction? (3)
- when enzyme concentration increases, rate of enzyme reaction increase because presence of more active sites that are ready for catalytic reaction
- if concentration of enzyme is doubled, amount of substrate converted to products per unit time is also doubled if there is excess supply of substrate
- at max rate: concentration of substrate becomes limiting factor [rate of reaction can only increase by adding more substrates]
