Module 1 - Metabolism

Question 1

Metabolism

Answer 1

refers to the enzyme-catalyzed chemical reactions that occur in a cell to either breakdown biomolecules to obtain energy in a form that can be used by the body (ATP), or reactions that synthesize biomolecules that our bodies need.

the sum total of Catabolism and Anabolism

Question 2

Catabolism

Answer 2

refers to those chemical reactions that breakdown biomolecules to produce energy

Question 3

Anabolism

Answer 3

refers to chemical reactions that lead to the synthesis of biomolecules that require the input of energy

Question 4

The primary functions of metabolism are:

Answer 4

To obtain chemical energy in the form of ATP from the degradation of energy-rich nutrients from the environment or from captured solar energy. For example, some of the food you eat is used to move your muscles or use your brain, both of which require energy.

To convert molecules that we ingest as food into the building blocks of larger molecules needed in the body

To assemble these small building block molecules into larger molecules such as proteins, nucleic acids, lipids, polysaccharides

To synthesize and degrade biomolecules that have specialized functions in cells

Question 5

A metabolic pathway

Answer 5

a term used to describe a series of linked reactions that begins with a particular biomolecule and converts it into another biomolecule in a carefully defined fashion and one that is regulated.

can be linear, branched, or circular

metabolic pathways can be interconnected; that is, an intermediate of one pathway can also be an intermediate in one or more other pathways

Question 6

amphibolic pathways

Answer 6

pathways that can function anabolically and catabolically, depending on the energy conditions in the cell

Question 7

Rate-limiting

Answer 7

An important concept is that the first committed step, which is often the first reaction in the pathway, is usually a point of regulation for that pathway.

It is also important to note that reactions that are regulated in a pathway are often rate-limiting steps i.e. slow reactions that can be increased by a variety of mechanisms.

Question 8

Living organisms require a continual input of free energy for three major purposes:

Answer 8

(1) the performance of mechanical work, such as muscle contraction and cellular movement;

(2) the active transport of biomolecules and ions; and

(3) the synthesis of macromolecules from simple precursors.

Question 9

Enzymes

Answer 9

enzymes only speed up the rate of a chemical reaction, but do not change the equilibrium constant for reactions and thus cannot make a thermodynamically unfavorable reaction proceed.

Question 10

There are only two thermodynamic properties of a reaction that one needs to consider in order to understand how enzymes work

Answer 10

the free energy difference (ΔG) between the products and the reactants,

the free energy required to initiate the conversion of reactants to products.

Question 11

free energy difference (ΔG)

Answer 11

determines whether a reaction will take place spontaneously i.e. whether it is possible

Question 12

free energy

Answer 12

determines the rate at which the reaction will proceed

Question 13

if ΔG is negative

Answer 13

Reactions can take place spontaneously

Question 14

Exergonic

Answer 14

reactions that release energy

Question 15

positive ΔG

Answer 15

Reactions that cannot proceed unless there is an input of energy, often involving ATP cleavage

Question 16

Endergonic

Answer 16

reactions that require energy

Question 17

What is so special about ATP that it is used as the carrier of energy in the cell?

Answer 17

It has high phosphoryl-transfer potential, meaning that it readily transfers its phosphate group to water.

the standard free energy of hydrolysis of ATP, where the terminal phosphate group is cleaved off to yield ADP and inorganic phosphate (Pi), is very negative at -30.5 kJ/mol.

Question 18

ATP + H2O ←—→ ADP + Pi
ΔG°’ = - 30.5 kJ/mol

there are four reasons for the large standard free energy change

Answer 18

Electrostatic repulsion - at pH 7, ATP carries four negative charges which repel one another when they are in close proximity

Resonance stabilization - Pi, one of the products of ATP hydrolysis, has a greater resonance stabilization than any of the phosphates in ATP

Increase in Entropy - hydrolysis of ATP results in two molecules instead of a single ATP molecule

Stabilization by hydration -water binds to ADP and Pi which stabilizes these molecules and makes the reverse reaction less favorable

Question 19

where does the energy that ATP possesses come from?

Answer 19

The carbon in the fuels we eat (primarily glucose and fats) is oxidized to CO2 and the energy released is used to regenerate ATP from ADP and Pi.

Question 20

substrate-level phosphorylation

Answer 20

ATP synthesis that results from the transfer of a phosphate group from one high phosphoryl-transfer potential compound to ADP

Question 21

Activated carriers

Answer 21

Many activated carriers are small organic molecules that function as coenzymes.

Question 22

Activated carriers of electrons for fuel oxidation

Answer 22

electrons released from oxidation of fuels are transferred to special carriers, and the reduced forms of these carriers then transfer the electrons to oxygen.

One of these carriers is NAD+.

The second activated carrier for fuel oxidation is FAD.

Question 23

Activated carriers of electrons for biosynthesis

Answer 23

In many biosynthetic reactions, the precursor molecules are more oxidized than the final product, so there is a need for electrons as well as for ATP.

In biological systems, the primary electron donor used in biosynthetic processes is NADPH

NADH is used primarily for the generation of ATP, while NADPH is used for reductive biosynthesis

Question 24

Activated carrier of two-carbon fragments

Answer 24

Another central molecule in metabolism is Coenzyme A (or simply CoA), which is a carrier of 2-carbon units termed acetyl groups as well as longer carbon units referred to as acyl groups.

Acetyl groups are attached to CoA through the reactive sulfhydryl group, to form the molecule acetyl CoA

most activated carriers that act as coenzymes are derived from vitamins, particularly the B vitamins

Question 25

Metabolic Pathways are Regulated in Three Principle Ways

Answer 25

The amount or abundance

The catalytic activity of the enzyme

Controlling the availability of substrates