Biology IB HL: Enzymes - C1.1

metabolism

breakdown of complex molecules into smaller molecules; usually releases energy

transformation of polymers into monomers

catabolism

a reaction which releases energy; the breakdown of large molecules into smaller molecules

anabolism

synthesis of complex molecules from simple molecules; requires energy

formation of polymers from monomers by condensation reactions

The sequence of amino acids responsible for the catalytic activity of enzymes.

The active site is the sequence of amino acids responsible for the catalytic activity of the enzyme, and it is the region that binds to the substrate specifically.

substrate

reactants of a metabolic reaction which bind specifically to the active site

the induced fit model

when the substrate binds to the active site, it changes the 3D shape of the enzyme and allows it to change shape to have a tighter fit.

the tighter fit induces weakening in in the bonds of the substrate, reducing activation energy needed for reaction ( both catalysis and anabolism )

what to mention in enzyme questions

• active site

• subtrate ( complementary to active site )

• enzyme substrate complex

what can an active site bind to ?

a narrow range of specific substrates

what do enzymes do to lower activation energy ?

MODS

microenvironment

orientation

direct participation

straining bonds

intracellular enzyme-catalysed reactions; examples

• krebs cycle in mitochondria

• glycolysis

• helicase; unwinds DNA

• lysosomes; inside vesicles

  enzymes are synthesised by free ribosomes

extracellular enzyme-catalysed reactions

• saprotrophic nutrition=> funghi

• acetylcholinesterase; breaks down neurotransmitters

• insulin and glucagon; control glucose in blood and glycogen in liver

  excreted by cells

generation of heat energy in mammals

• heat generated my metabolism ( exothermic chemical reactions eg respiration )

• used to maintain body temperature above environment’s

• makes so enzymes are at optimal PH

methods to maintain body temperature

• brown fat in adipose tissue; fat with more mitochondria; more ATP can be released, increasing body temperature + insulating nature of lipids

• involuntary muscle contraction; results in shivers; generates heat

metabolic pathway

• series of chemical reactions occurring in a cel modifying a chemical

3 features of a metabolic pathway

1. most chemical changes happen not in a big jump, but in a sequence of small steps

2. most metabolic pathways involve a linear chain of reactions

3. some metabolic pathways form a cycle ( products are reused in reaction ) ( eg krebs cycle and calvin cycle )

competitive inhibition

• binding to active site, in direct competiton with substrate

• however, as substrate quantity increases, the inhibitors can be overcome

stations what type of inhibition

• competitive inhibition

• binds to enzyme catalysing one of the steps cholesterol formation

• similar in structure of HMGR, so can bind to enzyme HMG-Coa

non-competitive inhibition

• inhibitors bind to allosteric site

• this indirectly modifies active shape, leads to conformational changes preventing substrate from binding to enzyme

• so excess substrate does not overcome inhibition

• is reversible however.

immobilised enzymes

embedded in a membrane, usually for industrial use.

• facillates recycling of enzymes

• product is enzyme free

• enzyme is much more stable/ long lasting

why does heat increase reaction rate of enzymes

• molecules have more molecular kinetic energy

• thus move faster

• thus enzyme’s active site and substrate collide with each other more frequently

end product inhibition

products of chemical pathways work as inhibitors to the enzymes at the beginning of the pathway, preventing excess product from being produced

isoleucine end product/ non competitive inhibition

isoleucine ( amino acid ) can be synthesised from threonine

• isoleucine works as a non competitive inhibitor on threomine deaminase

• that enzyme is essential to first stages of metabolic pathway; if turned off when not needed, isoleucine production is regulated

• if isoleucine gets used up, it’s concentration falls and there wont be enough to stay binded to allosteric sites

mechanism based inhibition

• Molecules that are able to form covalent bonds with the active site of an enzyme are known as a substrate analogue

• The substrate analogue can now be changed by the enzyme to produce a reactive group: This reactive group leads to the formation of a stable inhibitor-enzyme complex

• This form of inhibition is called mechanism-based inhibition and it is irreversible

mechanism based inhibition pennicillin

it inhibits DDpeptidase

penicillin binds with ddpeptidase, forming an enzyme complex, which is inactive. this is irreversible

that is an enzyme which catalises repair of peptiglycan cell wall of bacteria

the walls cannot withstand the osmotic pressure that the bacteria takes up, and burst, leading to cell death.