Bio98 Lecture 11 (Fermentation & Gluconeogenesis)

Fermentation (lactate or alcohol) • How does it work? • When would a cell choose to do this? • Gluconeogenesis: the reverse of glycolysis • Steps that are different • Idea of compartmentalization • Definition of a futile cycle

Pyruvate in terms of Fermentation

1. Pyruvate → Reduction (lactate dehydrogenase) → lactate → transported from cell (fermentation for eukaryotes, bacteria)

2. Pyruvate → decarboxylation (pyruvate decarboxylase/ PDC) → acetaldehyde → alcohol dehydrogenase (ADH)→ ethanol (fermentation of yeast)

Pyruvate in terms of Gluconeogenesis (Anabolic)

Pyruvate → Carboxylation (pyruvate carboxylase) → oxaloacetate → glucose production

Explain Pyruvate Catabolism: Anaerobic (doesn’t need O2)

-Low energy yield per molecule of glucose

-Fermentation

-different modes in yeast and other organisms

-produces lactate or ethanol

Explain Pyruvate Catabolism: Aerobic (requires O2)

-high energy yield per molecule of glucose

-requires coupled use of the tricarboxylic acid cycle (TCA) & oxidative phosphorylation via the electron transport chain

Anaerobic Metabolism = ___?

NAD+ Regeneration.

-generates ATP/NAD+ in muscle without needing O2.

Yeast fermentation

-Pyruvate converted to acetaldehyde via Pyruvate decarboxylase (PDC)

-Acetaldehyde converted to ethanol by alcohol dehydrogenase (ADH)

Explain what the image is showing.

Yeast fermentation:

-Pyruvate converted to acetaldehyde via Pyruvate decarboxylase (PDC)

-Acetaldehyde converted to ethanol by alcohol dehydrogenase (ADH)

Pyruvate decarboxylase

-Thiamine disphosphate (TPP) cofactor

-Thiazole ring is important for catalysis (ylide)

-derived from vitamin B1 (essential)

-apart of yeast fermentation

Auto-Brewery Syndrome

-eat sugar, make alcohol → pt appears drunks

-caused by yeast infection

Ethanol detoxification is ___.

Yeast fermentation in reverse:

-ethanol converted to acetaldehyde (ethanal) by alcohol dehydrogenase (ADH) ; requires NAD+

-Acetaldehyde converted gto acetic acid by acetaldehyde dehydrogenase (ALDH)

Disfunction (mutation/genetic variation) of ADH or ALDH drives:

toxic buildup of acetaldehyde (hangover, flush)

Lactic acid fermentation

pryuvate converted to lactate via lactate dehydrogenase (LDH)

Example of anaerobic metabolism: alligator

-quick burst of energy by lactic acid fermentation

-generates ATP/NAD+ in muscle quickly w/o needing O2

-needs long recovery to clear excess lactate (source of sourness after exercise)

Gluconeogensis in terms of how much needed in body

-total need: ~160 g glucose/day

-brains and eyes alone: 120 g/day

-reserve: 190 g

When fasting or conducting extreme endurance exercise (marathon), need other source for glucose

Gluconeogenesis Definition

synthesis of 6 carbon glucose from 3-4 carbon precursors, normally non-carbohydrate sources

4 sources of precursors for gluconeogensis

Lactate: skeletal muscle, erythrocytes

Amino acids: dietary protein, muscle protein breakdown

Propionate: derived from fatty acids, amino acids

Glycerol and stored fats under starvation conditions

Gluconeogensis Purpose

- formation of glucose from NON-CARBOHYDRATE molecules

- mainly carried out in LIVER and KIDNEY

- another source for glucose

- similar to GLYCOLYSIS process except for 4 REACTIONS

Cori Cycle Purpose

turn lactate to glucose then transport it back to muscles

Cori Cycle After Exercise:

Lactate: transported from muscle to liver

Glucose: transported from liver to muscle

Anabolic Glucose Metabolism

-Glucose is made within most organisms

-Pathway is known as gluconeogenesis

-Process if strikingly simialr to glycolysis, with the exception of 4 reactions

GLUCONEOGENESIS STEP 1: Pyruvate cannot be ___.

directly converted to PEP; requires ATP.

GLUCONEOGENESIS STEP 1: involves…

turning pyruvate to oxaloacetate

-how? take CO2 from molecule of bicarbonate and link it onto a molecule of pyruvate through the action of an enzyme (pyruvate carboxylase), ATP (putting energy to remake glucose), a cofactor (biotin), and magnesium (Mg2+) = oxaloacetate

Glycolyis happens in the ___ while pyruvate carboxylase is in the ___ for glucogenesis (step 1).

cytosol, mitochondria

GLUCONEOGENESIS STEP 1: compartmentalization is an issue why?

Pyruvate is funneled into mitochondria, meaning it’s compartmentalized or sequestered away; the enzyme pyruvate carboxylase is also in the mitochondria, which is an added issue.

GLUCONEOGENESIS STEP 1 & 2: COMPARTMENTALIZATION (pathway)

1) -Pyruvate carboxylase @ mitochondria.

-pyruvate transported to mitochondria → turned into oxaloacetate (OAA), an important precursor

-OAA can’t cross mitochondrial membrane → converted to malate

-Malate transported to cytosol, then converted back to OAA

2) -Cytosolic OAA is converted to PEP by PEP carboxykinase (PEPCK)

-Uses GTP - another energy currency

-Purpose: to get pyruvate out of mitochondria and back in cytoplasm for gluconeogenesis.

REMIND: 2 DIFFERENCES FROM GLYCOLYSIS

Gluconeogenesis uses how many ATP, GTP, and NADH total?

6 ATP (4 ATP + 2 GTP, which are equivalent) and 2 NADH ( 2 pyruvate → 1 molecule of glucose conversion)

remind: breaking down a molecule of glucose = 2 ATP

GLUCONEOGENESIS: 1st 6 Steps

1) Pyruvate (in mitochondria) → use pyruvate carboxylase + ATP (and etc.) = oxaloacetate (OAA)

2) (Cytosolic) OAA → PEPCK (PEP carboxykinase) + GTP = Phophoenolpyruvate (PEP)

3) PEP → enolase = 2-phosphoglycerate (2PG) + loss of H2O

4) 2PG → phosphoglycerate mutase (PGM) = 3-phosphoglycerate (3PG)

5) 3PG → phosphoglycerate kinase (PGK) + ATP = 1,3-bisphosphoglycerate (1,3-bPG)

6) 1,3-bPG → glyceraldehyde-3-phosphate dehydrogenase (GADPH) & regenerates NAD+ = Glyceraldehyde 3-phosphate

REMIND: done 2Xs so 2 of everything (excluding the enzymes)

GLUCONEOGENSIS: FRUCTOSE BISPHOSPHATASE (Step 9)

-removes one of the phosphates on F-1,6-bP

-removes 1 x Pi while using H2O

REMIND: GLUCOSE HAS 6 CARBONS

-3rd difference

GLUCONEOGENSIS: GLUCOSE 6-PHOSPHATASE (final step 11)

-removes the last Pi

-allows glucose to leave the cell

GLUCONEOGENESIS: STEPS 7-11

7) Glyceraldehyde 3-phosphate → triose phosphate isomerase (TMI) = 2 products. Glyceraldehyde 3-phosphate & Dihydroxyacetone phosphate

8) 2 products → aldolase = Fructose 1,6-bisphosphate (F-1,6-bP)

9) F-1,6-bP → fructose bisphosphatase removes one of the phosphates on F-1,6-bP & 1 x Pi = Fructose-6-phosphate (F6P)

10) F6P → phosphoglucose isomerase (PG) = Glucose-6-phosphate (G6P)

11) G6P → glucose-6-phosphatase removes the last Pi using H2O & allows glucose to leave the cell (GLUCOSE IS MADE!)

How do we keep cells from spending all the energy they make from glycolysis doing gluconeogensis?

Futile cycle: pathways running in opposite directions resulting in loss of energy.

COMPARTMENTALIZATION (extra)

-Not just about organellar separation of pathways, tissue too!

-Not all the organs have the same metabolic needs

-Gene expression in different tissues, or different cells within different tissues allows for the use of one pathway or another

Other cells can feed cancer cells what?

alanine and glucose