The Krebs Cycle: Cellular Respiration Process

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.