The Krebs Cycle: Cellular Respiration Process

Study Notes

Krebs Cycle (Citric Acid Cycle or TCA Cycle)

Critical metabolic pathway that generates energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins.
Occurs in the mitochondria of eukaryotic cells.

Overview of the Krebs Cycle

Series of enzymatic reactions that play a central role in cellular respiration.
Process by which cells harvest energy from organic molecules.
Cycle begins with the condensation of acetyl-CoA with oxaloacetate to form citrate.
Oxaloacetate is regenerated, enabling the cycle to continue.

Key Steps and Enzymes

Formation of Citrate: Acetyl-CoA combines with oxaloacetate to form citrate, catalyzed by citrate synthase.
Isomerization to Isocitrate: Citrate is converted to isocitrate via cis-aconitate intermediate, catalyzed by aconitase.
Oxidative Decarboxylation: Isocitrate is oxidized and decarboxylated to alpha-ketoglutarate by isocitrate dehydrogenase, producing NADH.
Formation of Succinyl-CoA: Alpha-ketoglutarate undergoes oxidative decarboxylation to form succinyl-CoA, catalyzed by alpha-ketoglutarate dehydrogenase, producing NADH.
Conversion to Succinate: Succinyl-CoA is converted to succinate by succinyl-CoA synthetase, generating GTP (or ATP).
Oxidation to Fumarate: Succinate is oxidized to fumarate by succinate dehydrogenase, producing FADH2.
Hydration to Malate: Fumarate is hydrated to malate by fumarase.
Regeneration of Oxaloacetate: Malate is oxidized to oxaloacetate by malate dehydrogenase, producing NADH.

Energy Yield

Three molecules of NADH are produced per cycle.
One molecule of FADH2 is produced per cycle.
One molecule of GTP (or ATP) is produced per cycle.
High-energy electron carriers (NADH and FADH2) proceed to the electron transport chain (ETC), where their energy is used to produce ATP through oxidative phosphorylation.

Regulation of the Krebs Cycle

Tightly regulated by several factors.
Substrate Availability: Availability of acetyl-CoA and oxaloacetate.
Allosteric Enzymes: Key enzymes such as citrate synthase, isocitrate dehydrogenase, and alpha-ketoglutarate dehydrogenase are regulated by allosteric effects.

Weather and Climate

Weather

Weather is the day-to-day condition of the atmosphere at a specific place and time.
Weather can be described by:
- Temperature (hot or cold)
- Humidity (amount of water vapor in the air)
- Cloudiness (clear, cloudy, sunny)
- Wind direction and speed
- Precipitation (rain, snow, sleet, hail)
Weather can change quickly, from day to day or even within a day.

Climate

Climate refers to the long-term average atmospheric conditions in a specific region.
Climate is determined by:
- Latitude (distance from the equator)
- Altitude (height above sea level)
- Proximity to large bodies of water
- Land use patterns
Climate can be classified into different types, such as:
- Tropical
- Desert
- Temperate
- Polar

Differences between Weather and Climate

Weather is short-term, while climate is long-term.
Weather can change quickly, while climate changes slowly over time.
Weather is local, while climate is regional or global.

Tools Used to Study Weather and Climate

Thermometers measure temperature.
Barometers measure air pressure.
Hygrometers measure humidity.
Anemometers measure wind speed and direction.
Rain gauges measure precipitation.
Weather vanes show wind direction.

Importance of Understanding Weather and Climate

Helps prepare for and respond to natural disasters (e.g. hurricanes, droughts).
Influences agriculture and food production.
Affects human health and comfort.
Impacts transportation and recreation activities.

Description

Explore the Krebs Cycle, a critical metabolic pathway that generates energy through the oxidation of acetyl-CoA. Learn about its role in cellular respiration and the enzymatic reactions that occur in the mitochondria.