Lecture 17

Question 1

Exergonic reaction

Answer 1

proceeds with a net release of free energy is spontaneous

Question 2

Endergonic reaction

Answer 2

Absorbs free energy from its surrounding and is non-spontaneous

Question 3

free energy

Answer 3

a living systems free energy is energy that can do work when temperature and pressure are uniform as in a living cell

Question 4

Activation energy

Answer 4

the initial energy needed to start a chemical reaction is called the free energy of activation or activation energy

Question 5

how enzymes speed up reactions

Answer 5

in catalysis, enzymes of other catalysts speed up specific reactions by lowering the Ea barrier

enzymes do not affect the change in free energy; instead they hasten reactions that would occur eventually

Question 6

substrate specificity of enzymes

Answer 6

the reactant that an enzyme acts on is called the enzyme substrate

the enzyme binds to its substrate, forming an enzyme-substrate complex

while bound the activity of the enzyme coverts substrate to product

the reaction catalysed by each enzyme where the substrate binds

induced fit of a substrate bring chemical groups of the active site into positions that enhance their ability to catalyse the reaction

Question 7

How enzymes lower the Ea barrier

Answer 7

enzymes catalyse reactions by lowering the Ea barrier of a specific reaction pathways

enzymes do not affect the change in free energy: instead they hasten reactions that would occur eventually

Question 8

Catalysis in the enzymes active site

Answer 8

in an enzymatic reaction, the substrate binds to the active site of the enzyme

enzymes are extremely fast acting and emerge from reactions in their original form

very small amounts of enzyme can have substantial metabolic effects because they are used repeatedly in catalytic cycles

Question 9

The active site and catalytic cycle of an enzyme

Answer 9

1. substrate enter active site
2. substrates are held in active site by weak interactions forming enzyme substrate complex
3. the active site lowers Ea
4. substrates are converted to products
5. products are released
6. active site is available for new substrates

Question 10

The active site can lower Ea barrier by

Answer 10

-orientating substrates correctly
-straining substrate bonds
-providing a favourable microenvironment
-covalent bonding to the substrate

Question 11

Saturated enzyme

Answer 11

where active site is engaged

Question 12

Effects of local conditions on enzyme activity

Answer 12

an enzymes activity can be affected by:
- general environmental factors such as temperature and pH
- Chemicals that specifically influence the enzyme

Question 13

Effects of temperature and pH on enzyme

Answer 13

each enzyme can function over a fixed range of temperature and pH conditions

so each enzymes has an optimal pH and temperature at which it can function

optimal conditions favour the most active shape for the enzyme molecule

Question 14

Cofactors

Answer 14

non protein enzyme helpers
- may be inorganic (such as a metal in ionic form) or organic
- an organic cofactor is called a coenzyme
- coenzymes include vitamins

Question 15

Enzyme inhibitors

Answer 15

competitive inhibitors- binds to the active site of an enzyme, competing with the substrate

noncompetitive inhibitors- bind to another part of an enzyme =, causing the enzyme to change shape and making the active site less effective

Question 16

regulation of enzyme activity helps control metabolism

Answer 16

chemical chaos would result if a cells metabolic pathways were not tightly regulated

a cell does this by switching on or off the genes that encode specific enzymes or by regulating the activity of enzymes

Question 17

Allosteric regulation of enzymes

Answer 17

may either inhibit or stimulate an enzymes activity

allosteric regulation occurs when a regulatory molecules binds to a protein at one site and affects the proteins function at another site

Question 18

Allosteric activation and inhibition

Answer 18

mostly allosterically regulated enzymes are made from polypeptide subunits, each with its own active site

the enzyme complex has active and inactive forms

the binding of an activator stabilised the active form of the enzyme

the binding of an inhibitor stabilises the inactive form of the enzyme

Question 19

Allosteric enzyme structure

Answer 19

four subunits each with an active site and regulatory site

Question 20

Activation and inactivation of allosteric enzymes

Answer 20

oscillation changes an allosteric enzyme from active to inactive or vice versa

activators stabilise both active and inactive forms of allosteric enzymes

Question 21

Cooperativity

Answer 21

is a form of allosteric regulation that can amplify enzyme activity
- one substrate molecule primes an enzyme to act on additional substrate molecules more readily

allosteric because binding by a substrate to one active site affects catalysis in a different active site

Question 22

Feedback inhibition

Answer 22

in feedback inhibition, the end product of a metabolic pathway shuts down the pathway

feedback inhibition prevents a cell from wasting chemical resources by synthesising more product than is needed

Question 23

Localisation of enzymes within the cell

Answer 23

structure within the cell help bring order to metabolic pathways

some enzymes act as structural components of membranes

in eukaryotic cells, some enzymes reside in specific organelles