Regulatory mechanisms for glycolysis include 1 Allosteric regulation

Regulatory mechanisms for glycolysis include 1. Allosteric regulation 2. Hormonal control (via enzyme phosphorylation) 3. Substrate level control 4. Covalent modification (phosphorylation via the kinase cascade)

Key regulatory enzymes in the glycolytic pathway include: 1. Hexokinase substrate-level regulation by glucose-6 -phosphate 2. Phosphofructokinase allosteric regulation by AMP, ADP, ATP, citrate, and fructose-2, 6 bisphosphate 3. Pyruvate kinase allosteric regulation by D-fructose 1, 6 -bisphosphate, ATP, acetyl-Co. A, and phosphorylation

Three common fates of pyruvate

What happens to the end products of Glycolysis if O 2 is present for the completion of cell respiration? Formation of acetyl Co. A: NADH forms, is used at ETC, then oxidized back to NAD+ CO 2 is formed as a waste product

Formation of acetyl Co. A Catalyzed by an enzyme complex: pyruvate dehydrogenase • First the carboxyl group is split off of the 2 pyruvates as carbon dioxide • Then remaining two-carbon acetyl fragment is oxidized and electrons transferred to NAD+ making NADH • Finally, the oxidized two-carbon acetyl group is attached to coenzyme A • Creates acetyl Co. A

In the absence of O 2 Glycolysis alone will still produce some ATP. Lactic acid (lactate) fermentation Different organisms follow 1 of 2 different metabolic pathways: each will regenerate NAD+ Ethanol fermentation

Fermentation: Yeasts (single-celled eukaryotic fungi) and some bacteria can also do a different type of anaerobic respiration when O 2 isn’t readily available. Not very efficient: it’s just glycolysis with an extra bit added to recycle the NADH back to NAD+.

Alcoholic fermentation Yeast excretions! Yum! Yeasts are facultative anaerobes: they switch to fermentation when O 2 levels are low.

• In alcoholic fermentation, 3 C pyruvic acid is converted to CO 2 and ethanol (C 2 H 5 OH) – This recycles NAD+ to keep glycolysis working 2 Ethanol 2 Pyruvic acid Glucose released GLYCOLYSIS Pyruvic acid decarboxylated forming CO 2 and ethanol NADH molecules oxidized back into NAD+. Ethanol is the oxidizing agent helping NADH get oxidized back to NAD+.

Alcoholic fermentation Yeast is allowed to do anaerobic alcohol fermentation to produce ethyl alcohol. Above ~17% alcohol content the yeast die off.

• In lactic acid fermentation, pyruvic acid is converted to lactic acid – As in alcoholic fermentation, NADH is recycled by oxidation back to NAD+ • Lactic acid fermentation is used to make cheese, yogurt, kefir, sauerkraut, pickles, poi, & wine Glucose GLYCOLYSIS 2 Pyruvic acid 2 Lactic acid Our muscle cells do this if needed.

Skeletal muscle tissue is composed of 2 general types of muscle fibers: fast-twitch and slow-twitch • Slow -twitch muscle fibers used for: - steady, low-intensity, repetitive contraction. • Do not tire easily – used for endurance. • Used for low-intensity, high-endurance activities: - long distance running.

Fast-twitch muscle fibers used for: - heavy work, strength and power. Contract quickly, providing short bursts of energy. High-intensity, low-endurance activities: - sprinting, weightlifting, or shot-putting. Fast-twitch muscle fibers become exhausted quickly.

White meat and dark meat? Chicken or turkey: White meat is fast twitch muscle. Dark meat is slow twitch muscle. It is dark because it contains myoglobin. Slow twitch muscles: wing & leg - long term endurance. Breast is usually fast twitch - quick response. Wild animals tend to have more slow twitch muscle.

Why do athletes breath heavily before an event? Strenuous bursts of muscle activity produce high levels of lactic acid as glucose is broken down for energy anaerobically. Causes muscle cramp/fatigue. To counteract this, rapidly deep breathing for 30 -40 seconds will – introduce temporary alkaline condition – helps to neutralize the acidity arising from lactic acid.

Lactic acid fermentation Running from danger, pushing beyond body’s ability to provide O 2 to muscles – must switch to anaerobic fermentation

CH 3 CHOHCOOH During Fast-twitch muscular exercise: • Increase O 2 supply by dilating blood vessels in muscles – increases blood flow • Running from danger pushes beyond bodies’ability to provide O 2 • Muscles kick over to anaerobic fermentation. • Muscles continue to break down glucose to liberate some energy for a short time • This partial breakdown produces lactic acid • When lactic acid reaches certain levels in the muscles and blood - fatigue occurs

Oxygen debt: waste not, want not! Why do you keep breathing hard after you stop exercising?

Huffing & puffing after exercise helps repay the “oxygen debt” • Break down the lactic acid – get the rest of the energy out of the molecules • Once adequate O 2 is available, lactic acid must be catabolized – Broken down into CO 2 and H 2 O • Pay back any oxygen that has been borrowed from hemoglobin, myoglobin, air in the lungs, and body fluids • Hard breathing and sufficient discomfort stops muscle activity until homeostasis is restored

All 3 fates of pyruvate from glycolysis provide for the regeneration of NAD+ from NADH.