all the chemical reactions that occur within a cell

synthesize cellular components, involve increase in molecular order and thus a decrease in entropy, require energy (endergonic)

examples: polymer synthesis, biological reduction of carbon dioxide to sugar (gluconeogenesis)

involved in the breakdown of cellular constituents, involve decrease in molecular order and thus and increase in entropy (exergonic), release free energy needed to drive cellular functions

example: glycolysis

molecule most commonly used as an energy intermediate

contains 2 energy rich phosphoanhydride bonds

each phosphate group on ATP bears at least one negative charge due to its ionization at the near neutral pH of the cell

these charges repel each other thus straining the covalent bond linking the phosphate groups together

requires the joining of 2 negatively charged molecules that naturally repel each other

this requires an input of energy to overcome this repulsion

carboxylate group of ATP has one e- pair that is delocalized over both the C bonds to O

when e-s are delocalized in this way, the molecule in its most stable configuration

the reactions and pathways by which cells catabolize nutrients and conserve, as ATP, some of the free energy that is released in the breakdown

carbs, fats, and proteins

these are oxidizable organic compounds whose oxidation level is highly exergonic

removal of electrons

often seen as dehydrogenation

addition of electrons

endergonic process

an important way that cells store chemical energy as reducing power

oxidation-reduction reactions

electrons and hydrogens removed from substrate being oxidized are transferred to one of several...

not consumed, but recycled within the cell

most common involved in energy metabolism is NAD+

C₆H₁₂O₆

main sugar in blood and thus main energy source for most cells in the body

blood glucose comes from dietary carbs such as sucrose and starch and from breakdown of stored glycogen

important to plants since it is the monosaccharide released upon starch breakdown

glucose is a good potential source of energy because its oxidation is highly exergonic with a [image] of -686 kcal/mol for a complete conversion of glucose to carbon dioxide and water using oxygen as the final electron acceptor

in the absence or scarcity of oxygen, most organisms can still extract limited amounts of energy from partial oxidation of glucose but with lower energy yields per molecule of glucose

done via GLYCOLYSIS

electrons that are removed during glucose oxidation are returned to organic molecules later the same way

absolute requirement for oxygen

HUMANS

cannot use oxygen as an e- acceptor because O is toxic to such organisms

examples: bacteria found in wounds, sludge, ponds & organisms responsible for gangrene, food poisoning, and methane production

glycolysis

(glycolytic pathway)

10-step reaction sequence that converts 1 molecule of glucose into 2 molecules of pyruvate (a 3 carbon compound)

common to both aerobic and anaerobic glucose metabolism and present in almost all organisms

occurs in cytosol

in absence of O, it leads to fermentation

in presence of O, it leads to aerobic respiration

split into 3 phases

net result of the 1st 3 reactions is to convert an unphosphorylated molecule (glucose) into a doubly phosphorylated molecule called fructose 1, 6-bisphosphate

requires transfer of 2 phosphate groups from ATP to glucose, one on each terminal carbon

ATP hydrolysis provides driving force that renders phosphorylation rxn strongly exergonic making it irreversible

glucose is phosphorylated and phosphoester bond is formed

glyceraldehyde-3-phosphate oxidized to corresponding three-carbon acid

3-phosphoglycerate is highly exergonic and drives the next 2 steps

Glycolysis Phase 3: Pyruvate Formation and ATP Generation

phosphoester bond converted to phosphoenol bond

increase in amount of free energy release upon hydrolysis involves rearrangement of internal energy within molecule

2 molecules of ATP initially invested and 2 formed per molecule of glucose

glucose+2NAD⁺ + 2ADP +2Pi---->

2pyruvate +2NADH+2H+2ATP

dependent upon availability of oxygen

oxygen:undergoes further oxidation to a molecule called acetyl coenzyme A when oxygen is present which can be further oxidized to produce over 30 molecules of ATP per glucose

no oxygen: pyruvate is reduced and lactate/ethanol is formed

generate by direct transfer of electrons from NADH to carbonyl group of pyruvate reducing it to the hydroxyl group of lactate

reaction is reversible

major energy-yielding pathway in many anaerobic bacteria

used to produce cheese, yogurt, and muscles during periods of strenous exercise

glucose +2ADP +2Pi --> 2 lactate + 2ATP

pyruvate loses a carbon atom as carbon dioxide to form a 2 carbon compound called acetaldehyde

used by yeast cells in baking, brewing, and winemaking

2pyruvate + 2NADH + 4H--> 2ethanol +2CO₂+2NAD⁺

no external electron acceptor is involved and no net oxidation occurs

around 93% of free energy of glucose is still present in the 2 lactate molecules and only about 7% of the free energy potentially available from glucose was obtained during fermentation

sucrose(table sugar): disaccharide consisting of glucose and fructose

lactose (sugar in milk): consists of glucose and galactose

disaccharides are hydrolyzed into their component monosaccharides which are then converted to a glycolytic intermediate

phosphorylated pentoses are used in glycolytic pathways after being converted to hexose phosphates

process of glucose synthesis or the process by which cells synthesize glucose from 3-carbon and 4-carbon precursors that are usually not carbs

consumes 6 ATP molecules per glucose synthesized

Steps 1-3: bypassed by hydrolytic reaction that liberates inorganic phosphate

Step 10: bypassed by a two reaction sequence in which carbon dioxide is added to pyruvate and the carboxyl group is removed to form PEP

*consumes 6 ATP molecules per glucose synthesized

important to keep glycolysis and gluconeogenesis from proceeding simultaneously in the same cell

spatial regulation: pathways operate in separate cells

temporal regulation: operate at different times within the same cell

involves interconversion of an enzyme between 2 forms: 1 is catalytically active and the other 1 is catalytically inactive

activators indicated by +

inhibitors indicated by -

most important regulator

synthesis of F2,6BP is catalyzed by a separate form called phosphofructokinase-2 (PFK-2)

it activates glycolytic enzyme and inhibits gluconeogenic enzymes which in turn affects the F2,6BP concentration by inactivating the glycolytic activity and stimulating the gluconeogenic activity

regulation of apoptosis: process of programmed cell death

act as transcriptional regulators or transriptional activators