Introduction To Metabolism

Question 1

Metabolism

Answer 1

Sum total of the chemical processes that occur on living organisms,resulting in growth,production of energy,elimination of waste material etc

Question 2

Metabolic pathway

Answer 2

begins with a specific molecule and ends with a product. Each step is catalyzed by a specific enzyme

Question 3

Exergonic reactions

Answer 3

-result in a net release of free energy but require Activation energy (EA) to initiate the reaction
-don’t require energy beyond activation energy,often the reaction can be obtained environmentally from heat so reaction will occur spontaneously

Question 4

Endergonic reactions

Answer 4

-Endergonic reaction require relatively large amounts of energy to occur, so does not occur spontaneously.

Question 5

Catabolic pathways (mostly exergonic)

Answer 5

release energy by breaking down complex molecules into simpler compounds

Question 6

Anabolic pathways (endergonic)

Answer 6

consume energy to build complex molecules from simpler ones

Question 7

Enzyme characteristics

Answer 7

-Organic molecules (proteins or RNAs), which speed
up (catalyse) chemical reactions by up to 1012 -fold
-Highly specific – work only on a particular substrate
-Unaffected by the reaction they catalyse
-Can catalyse the same chemical reaction in the opposite direction
-The enzyme activity can be regulated

Question 8

Lock and Key (“rigid”) model

Answer 8

The lock is the enzyme and the key is the substrate
• Only the correctly sized key (substrate) fits into the key hole (active site) of the lock (enzyme)
(1852-1919)
• The active site in the enzyme has a fixed, rigid geometrical conformation

Question 9

Induced fit (“flexible”) model:

Answer 9

• Small changes in the shape or geometry of the active site of an enzyme (conformational changes) to accommodate a substrate

Question 10

How do enzymes work

Answer 10

-Substrates enter active site.

• Substrates are held in active site by
  weak interactions.

-Enzyme-substrate complex(this lowers the activation energy)

-subtracts are converted into products

-products are released

-active site is available for new substrates

Question 11

How does active site lower activation energy

Answer 11

• orienting substrates correctly
• straining substrate bonds
• providing a favorable microenvironment • covalently bonding to the substrate

Question 12

Enzyme cofactors

Answer 12

Cofactorsarenonprotein enzyme helpers
• Cofactors may be inorganic (such as a metal in ionic form) or organic
• An organic cofactor is called a coenzyme
• Coenzymes include vitamins

Question 13

Apoenzymes

Answer 13

Protein portion

Question 14

Holoenzyme

Answer 14

Combination of both apoenzyme and its cofactors

Question 15

What are coenzymes divided into

Answer 15

Co substrates
Prosthetic groups

Question 16

Importance of coenzymes

Answer 16

Deficiencies in enzyme cofactors can result in a number of different medical conditions.

Question 17

“rate of a chemical reaction

Answer 17

The concentration of a product that is formed in a unit of time or the concentration of a substrate that is consumed in a unit of time.

Question 18

Effect of v0 of enzyme catalysed reactions

Answer 18

Vo slows as enzyme loses activity or substrate [S] levels decrease

Question 19

Irreversible inhibitors

Answer 19

bind covalently to the active site of an enzyme (e.g. Aspirin irreversibly inhibits COX enzymes)

Question 20

Reversible inhibitors

Answer 20

form weak bonds with the enzyme → rapid dissociation of the enzyme: inhibitor complex

Question 21

• Competitive inhibitors

Answer 21

• resemble the substrate
• bind to the active site of an enzyme

Question 22

Noncompetitive inhibitors:

Answer 22

• bind at a site distinct (allosteric site) from the active site of an enzyme
• change the conformation of the enzyme and its active site

Question 23

Allosteric regulation

Answer 23

-Allosteric regulation may either inhibit or stimulate an enzyme’s activity
• Most 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 stabilizes the active form of the enzyme
• The binding of an inhibitor stabilizes the inactive form of the enzyme

Question 24

Cooperativity

Answer 24

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
• Cooperativity is allosteric because binding by a substrate to one active site affects catalysis in a different active sit

Question 25

feedback inhibition

Answer 25

-the end product of a metabolic pathway shuts down the pathway
-Feedback inhibition prevents a cell from wasting chemical resources by synthesizing more product than is needed

Question 26

Effect of competitive inhibitor on enzyme kinetics

Answer 26

• Feedback inhibition prevents a cell from wasting chemical resources by synthesizing more product than is needed

Question 27

Effect of non competitive inhibitors on enzyme kinetics

Answer 27

Vmax is reduced – but the Km is
unaltered