Cell Bio Exam 2 - Cellular Energetics Pt1

aerobic oxidation - 30 ATP total

four-stage process to convert energy released by the of glucose/fatty acid oxidation into ATP terminal phosphoanhydride bond.

1. glycolysis

2. pyruvate oxidation

3. Krebs cycle

4. etc

if o2 is absent, fermentation instead of etc

glycolysis

• Cytosolic enzymes convert glucose to two molecules of pyruvate and generate two molecules each of NADH and ATP.

fermentation

• cells can metabolize pyruvate to lactic acid or ethanol and CO₂ to convert NADH back to NAD⁺ required for glycolysis. 

chemiosmosis

interconversion of 3 forms of biological pe

1. chemical bond energy

2. chemical gradients across membranes

3. voltage gradients across membranes

proton motive force

energy stored in the electrochemical gradient ; energy released as protons move down; powers ATP synthesis

metabolism

• collection of bio-chemical reactions that occur within a cell.

metabolic pathways

sequences of chemical reactions

• Each reaction in the sequence is catalyzed by a specific enzyme that produces metabolic intermediates that serve as substrate for downstream enzymes and ultimately leads to the formation of a final product

• Pathways are usually confined to specific locations.

• interconnected at various points so that a compound generated by one pathway may be shuttled in a number of directions, depending on cellular requirements.

aerobic oxidation location

glycolysis - cytosol

pyruvate oxidation, krebs cycle, and etc all happen in the mitochondrion

enzymes w pathway

help reduce loss of intermediates

substrate is sequentially modified as it is passes along from enzyme to enzyme

reside together as a membrane-bound system, the enzyme participants (and substrates) must diffuse in just the two dimensions of the membrane to interact with their neighbors.

oxidation

loss of e

reduction

gain of e

oxidizing agent

causes oxidation of another molecule by accepting e, so the oxidizing agent itself gets reduced

reducing agent

causes reduction of another molecule by donating e, so reducing agent itself gets oxidized

the more a substance is reduced

the more energy that can be released, the more pe to do work

Oxidation-reduction of organic compounds

Proton often picked up by molecule during reduction

hydrogenation reaction

gain of proton, type of reduction reaction

dehydrogenation reaction

loss of proton, type of oxidation reaction

energy released when carbon is oxidized

Carbohydrates and fats rich in energy because of numerous H-C bonds

Carbohydrates ready energy source

Enough energy released from 1 glucose molecule to generate large number of ATPs

catabolism of glucose occurs in

a series of small steps in order to capture energy, more efficient

atp is an ideal link btw pathways bc

any donor w a more - delta g value can be used to synthesize atp

transfer potential

any donor higher on the scale can be used to phosphorylate any molecule lower on the scale

Phase 1 of glycolysis

steps 1-5, energy investment, ATP used

Glucose → Glucose-6-phosphate

• step 1

• Enzyme: Hexokinase

• Uses 1 ATP

Glucose-6-phosphate → Fructose-6-phosphate

step 2

Enzyme: Phosphoglucose isomerase

Fructose-6-phosphate → Fructose-1,6-bisphosphate

• step 3

• Enzyme: Phosphofructokinase-1 (PFK-1)

• Uses 1 ATP

Fructose-1,6-bisphosphate → Glyceraldehyde-3-phosphate (G3P) + Dihydroxyacetone phosphate (DHAP)

step 4

Enzyme: Aldolase

DHAP ⇌ G3P

• step 5

• Enzyme: Triose phosphate isomerase

• Now 2 molecules of G3P continue forward.

Phase 2 of glycolysis

energy payoff phase

make ATP + NADH

G3P → 1,3-bisphosphoglycerate

• step 6

• Enzyme: Glyceraldehyde-3-phosphate dehydrogenase

• Produces NADH

• NADH will be used to power the electron transport chain in the synthesis of ATP

1,3-bisphosphoglycerate → 3-phosphoglycerate

• step 7

• Enzyme: Phosphoglycerate kinase

• Substrate-level phosphorylation: makes 1 ATP per G3P (so 2 total)

3-phosphoglycerate → 2-phosphoglycerate

step 8

Enzyme: Phosphoglycerate mutase

2-phosphoglycerate → Phosphoenolpyruvate (PEP)

step 9

Enzyme: Enolase
phosphate transfer

removal of water 

created high energy enol phosphate linkage

PEP → Pyruvate

• step 10

• Enzyme: Pyruvate kinase

• Substrate-level phosphorylation: makes 1 ATP per PEP (so 2 total)

• ATP formed by transfer of high-energy phosphate from phosphoenolpyruvate to ADP

glycolysis equation

• 2 ATP + 2 ADP in → 4 ATP out = net 2 ATP per glucose

regulation of metabolic pathways

availability of substrate

concentration of rate limiting enzymes in the pathway

allosteric regulation of enzymes - activate or inactivated by small molecules binding at sites other than the active site

covalent modification of enzymes - Enzymes are regulated by reversible covalent changes, especially phosphorylation/dephosphorylation.

glycolysis regulated by

energy needs of the cell

concentration of key substrates

rate at which ATP is hydrolyzed to drive endergonic reactions

major form of regulation is regulating rate of key enzymes - hexokinase, phosphofructokinase, pyruvate kinase

main form of glycolosis regulation is regulating the rate of key enzymes

hexokinase, phosphofructokinase, pyruvate kinase - irreversible steps in glycolysis

Concentration of these enzymes is regulated by hormones that regulate their rates of transcription

low km

high affinity for glucose

Since normal blood glucose is around 5 mM (much higher than their KM), these transporters are always basically “saturated.”

That means they pull in glucose at a steady rate no matter what, even if blood sugar drops a little

high km transporters

low affinity for glucose.

Normal blood glucose (5 mM) is well below their KM, so they don’t work much unless blood sugar rises high (like after a meal).

Uptake rate rises proportionally with blood glucose concentration.

km is determined by

vmax BUT is not a direct reflection of how fast a reaction can proceed

insulin

hormone that upregulates transcription of hexo phospho and pyruvate

glucagon

downregulates the transcription of big 3

phosphofructokinase

most important rate limiting step in glycolysis

inhibited by ATP 

activated my amp

covalent modification of enzymes

phosphorylation of pyruvate kinase can regulate in specific tissues (e.g., liver vs muscle) by blood glucose levels

Phosphorylated pyruvate kinase is less active (e.g., liver), blood glucose levels fall (fasting)

Dephosphorylated pyruvate kinase is more active, blood glucose levels increase

aerobic pathway

transfer to mito and Krebs cycle and etc happen there

anaerobic pathway

fermentation

fermentation

• Glycolysis needs NAD⁺, but under anaerobic conditions NAD⁺ is depleted as it’s reduced to NADH.

• Fermentation regenerates NAD⁺ by oxidizing NADH while reducing pyruvate.

• Lactic acid fermentation: pyruvate → lactate (muscles, tumor cells, some microbes).

• Alcoholic fermentation: pyruvate → ethanol + CO₂ (yeast, some microbes).

• Main purpose: restore NAD⁺ so glycolysis can continue producing ATP without oxygen.

intermembrane space of mito

enclosed by the inner 75% proteins and outer 50% proteins mito membranes

inner mito membrane has two interconnected domains

inner boundary membrane

cristae - where machinery for ATP is located; inc surface are for ATP production

mito matrix

• Contains a circular DNA molecule, ribosomes, and enzymes.

• RNA and proteins can be synthesized in the matrix.

• nec machinery for synthesis of proteins

• new mito produced by fission

inner membrane

75% protein

contains cardiolipin but not cholesterol

impermeable to even small molecules

uptake and release of calcium ions

ATP gen

etc for oxidative phosphorylation

outer membrane

50% protein

contains large pore forming protein called porin

permeable to even some proteins

helps generate proton motive force