Cellular Respiration: An Overview

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My AP Biology Thoughts

Unit 3 Cellular Energetics

Welcome to My AP Biology Thoughts podcast, my name is Nidhi and I am your host for episode #71 called Unit 3 Cellular Energetics: Cellular Respiration:An overview. Today we will be discussing what cellular respiration is,who uses it, and why it's important.

Segment 1: Introduction to Cellular Respiration

  • All organisms perform cellular respiration. The reactants of cellular respiration are glucose, which is oxidized, and oxygen which is reduced and they both produce carbon dioxide, water, and ATP. The purpose of cellular respiration is to make energy for cell work in the form of ATP. This occurs in a series of metabolic reactions. The reactions involved are catabolic reactions, which break down large molecules into smaller ones, releasing energy in the process which is supported by the overall reactions negative delta G. The ATP produced is eventually recycled and used to make more ATP. Most of the energy is released when reduced molecules are fully oxidized to create CO2. The oxidation occurs in a series of small steps allowing the cell to harvest 34% of the energy released. The rest of the energy is lost as heat.

Segment 2: More About Cellular Respiration

  • The two types of cellular respiration are anaerobic and aerobic. Anaerobic respiration can occur without oxygen while aerobic respiration requires oxygen to be present. Anaerobic respiration does not release enough energy to power human cells for long. It primarily occurs in muscle cells during hard exercise, after the oxygen has been used up. It also occurs in yeast during fermentation. Many prokaryotes perform anaerobic respiration.Through Anaerobic respiration, glucose is broken down to form 2 pyruvates. The purpose is to regenerate NAD plus for glycolysis, which is a part of aerobic respiration. Anaerobic respiration also keeps the pyruvate produced in the cytoplasm and uses it there. The main reactants are glucose, ADP, and Pi. This then produces ethanol, carbon dioxide and 2 atp. Anaerobic respiration has different products in animals. In animals instead of ethanol being produced, lactic acid is produced.
  • Aerobic respiration has 4 steps, glycolysis, pyruvate oxidation, the krebs cycle also known as the citric acid cycle, and the electron transport system. Glycolysis occurs in the cytoplasm, pyruvate oxidation and the citric acid cycle occur in the mitochondrial matrix, and the electron transport system occurs in the cristae of the mitochondria. In glycolysis, glucose is converted to pyruvate, ATP is produced, and NADH is produced. The energy transfers include 2 ATP used to produce 4 ATP ,NAD+ being reduced, Glucose being oxidized, and energy lost as heat. Overall, 2 net ATP are produced and no oxygen is used. Next, in pyruvate oxidation, Pyruvate is oxidized which reduces NAD+ to NADH. Coenzyme A reacts with the decarboxylated pyruvate to create acetyl CoA. This process occurs two times per glucose molecule. Again, energy is lost as heat is released. This time, CO2 is produced as a waste product. In the citric acid cycle, Acetyl CoA reacts with oxaloacetic acid to form citric acid . Citrate gets oxidized and loses carbons in the form of CO2. In that process, NAD+ and FAD are reduced into NADH and FADH2. Oxaloacetate is also regenerated since the process is a cycle. ADP+Pi makes ATP and total of 2 ATP is produced. Acetyl COA from the pyruvate oxidation and Pyruvate is needed for the reaction and CO2 is produced and heat is released. Lastly, in the electron transport system, Cells transfer energy from NADH and FADH2 to ATP by oxidative phosphorylation. NADH oxidation is used to actively transport H plus across the inner mitochondrial membrane, resulting in a proton gradient. Electrons from the oxidation of NADH and FADH2 pass from one carrier to the next in the chain. The oxidation reactions are exergonic and the energy released is used to actively transport H+ ions across the membrane.This Diffusion of protons back across the membrane then drives the synthesis of ATP. There is the potential to make 34 molecules of ATP from the electron transport chain but the number in real life is closer to 29. The entire process of aerobic cellular respiration has the potential to produce 36 ATP while anaerobic respiration alone can only produce 2 ATP per glucose molecule.

Segment 3: Connection to the Course

  • The process of cellular respiration has many connections to AP Biology in general. Cellular respiration is essential to produce ATP which is used by cells to power their metabolism and all their activities. The energy stored in food is broken down into a usable form. Cellular respiration can also connect to the theory of evolution and the theory that all organism evolved from a common ancestor. The fact that all living organisms perform anaerobic cellular respiration also supports this hypothesis because the common ancestor most likely performed anaerobic respiration meaning aerobic respiration evolved later since only some organisms can perform aerobic respiration.

Thank you for listening to this episode of My AP Biology Thoughts. For more student-ran podcasts and digital content, make sure that you visit www.hvspn.com.

Music Credits:

  • "Ice Flow" Kevin MacLeod (incompetech.com)
  • Licensed under Creative Commons: By Attribution 4.0 License
  • http://creativecommons.org/licenses/by/4.0/

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