Cell Metabolism

Metabolic pathways can be “swiched on and off” in three main ways

1. controlling the amount of enzymes

2. allosteric control of the enzyme (binding other than active site)

3. covelent modifcation of the enzyme

controlling the amount of enzymes

depends on its particular rate of synthesis and rate of degradation usualy adjusted by changing the rate of transcription of the gene coding for the enzyme

Allosteric control of the enzyme

Binding of a metabolite to the allosteric site of some enzymes can lead to allosteric activation which increases enzyme activity.

Binding of a metabolite to the allosteric site of other enzymes can lead to allosteric inhibition which decreases enzyme activity.

feed-forward activation

where a metabolite early in the pathway activates an enzyme further down the pathway.

feedback inhibition

where the product of a pathway inhibits the rate of its own synthesis by inhibiting an early step in the pathway

Revesable covelant modifaction

is a regulatory mechanism where the activity of an enzyme is altered by the addition or removal of a chemical group, such as a phosphate group, which can activate or deactivate the enzyme.

Phosphorylation

carried out by the enzyme kinases

dephosphorylation

carried out by the enzyme phosphates

reasons why ATP has a high phosphoryl transfer potential

1. Respnance stabalization

2. electrostatic repulsion

3. stabilization due to hydration

stage 1 of glycolysis

energy investment phase of glycolysis

stage 2

energy yeilding phase of glycolysis where ATP is produced.

kinases

adds or removes phosphoryl groupto a molecule.

Hextokinase

Adds phosphoryl group to glucose

Isomerases

Rearranges atoms in the molecule without altering its molecular formulato create different isomers.

Aldolase

make or break carbon-carbon bonds

Dehydrogenases

transfers of hydride ion to an electron acceptor nad+ in glycolysis

Enolase

Adds double bond by dehydration reaction

Mutase

Catalzes intramolecular shift of a group