EONS LEARNING

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      • Study Skills
      • Periodic Table
      • Common Ion Sheet
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    • Unit 1: Beginning Chemistry >
      • Lesson 1: The Atom >
        • What is an Atom?
        • The Structure of Atoms
        • The Periodic Table
        • Modeling Atoms
      • Lesson 2: Chemical Bonding >
        • Why Do Atoms Form Bonds?
        • Ionic Bonding
        • Covalent Bonding
        • Intermolecular Attraction
      • Lesson 3: Chemical Nomenclature >
        • Octet Rule
        • Ionic Compounds
        • Covalent Molecules
      • Lesson 4: Molecular Molecules >
        • Modeling Ionic Compounds
        • Modeling Covalent Molecules
      • Lesson 5: States of Matter >
        • States of Matter
        • Phase Changes
      • Lesson 6: Density >
        • What is Density?
        • Calculating Density
      • Lesson 7: Thermodynamics >
        • Temperature
        • Heat
        • Gas Laws
      • Lesson 8: Solution Chemistry >
        • Diffusion
        • Solutions and Molarity
        • Semi-Permeable Membranes
      • Lesson 9: Thermal Expansion >
        • Thermal Expansion
    • Unit 2: Earth Science >
      • Lesson 10: Earth at a Glance >
        • Perspective
        • Maps
      • Lesson 11: Layers of the Earth >
        • Layers of the Earth
      • Lesson 12: Plate Tectonics >
        • Plate Tectonics
      • Lesson 13: Rocks and Minerals >
        • Rocks and Minerals
      • Lesson 14: Particle Sorting >
        • Differentiation
        • Deposition of Sediment
      • Lesson 15: The Atmosphere >
        • Composition of the Atmosphere
        • Layers of the Atmosphere
        • Change Over Time
        • Atmospheric Disruption
    • Unit 3: The Cell >
      • Lesson 16: Life >
        • What is Life?
        • Structural Hierarchy of Living Things
      • Lesson 17: Biochemistry >
        • Intro to Biochemistry
        • Water
        • Micromolecules
        • Energy, Carbohydrates, Lipids
        • Protein and Nucleic Acid
      • Lesson 18: Cells >
        • What are Cells?
        • Microscopy
        • Plant and Animal Cells
      • Lesson 19: Membrane Transport >
        • A Special Environment
        • The Structure of Membranes
        • Membrane Transport
      • Lesson 20: Energy and Cell Respiration >
        • Energy in Biology
        • Energy Diagrams
        • Glycolysis and Anaerobic Respiration
        • Aerobic Cellular Respiration
      • Lesson 21: Photosynthesis >
        • Plants Get Energy From The Sun
        • Photosynthesis Process
        • Energy, Ecosystems, and the Environment
    • Unit 4: Anatomy and Physiology >
      • Lesson 22: The Human Body >
        • What Are Bodies Made Of?
        • What Do Bodies Do?
      • Lesson 23: The Nervous System >
        • The Nervous System
        • Neuronal Communication
        • The Central Nervous System
      • Lesson 24: The Endocrine System >
        • The Endocrine System
        • Hormones
        • Hormones, Puberty, and Reproduction
      • Lesson 25: The Integumentary System >
        • The Integumentary System
      • Lesson 26: The Musculoskeletal System >
        • The Skeletal System
        • The Muscular System
        • Anatomy Of The Musculoskeletal System
      • Lesson 27: The Cardiovascular System >
        • Blood and Blood Vessels
        • The Heart
      • Lesson 28: The Respiratory System >
        • The Respiratory System
      • Lesson 29: The Digestive System >
        • The Digestive System
        • Nutrition
      • Lesson 30: The Excretory System >
        • The Excretory System
      • Lesson 31: The Immune System >
        • Disease and Infection
        • Immunity
    • Units 5-6 Coming Soon
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    • Unit 1 >
      • EIS >
        • Lesson 1: Atoms
        • Lesson 2: Chemical Bonding
        • Lesson 3: Chemical Nomenclature
        • Lesson 4: Molecular Models
        • Lesson 5: States of Matter
        • Lesson 6: Density
        • Lesson 7: Thermodynamics
        • Lesson 8: Solution Chemistry
        • Lesson 9: Thermal Expansion
      • Unit 1: Project
      • Unit 1: Exam Review
      • Unit 1: Exam
    • Unit 2 >
      • EIS >
        • Lesson 10: Earth at a Glance
        • Lesson 11: Layers of the Earth
        • Lesson 12: Plate Tectonics
        • Lesson 13: Rocks and Minerals
        • Lesson 14: Particle Sorting
        • Lesson 15: The Atmosphere
      • Unit 2: Project
      • Unit 2: Exam Review
      • Unit 2: Exam
    • Unit 3 >
      • EIS >
        • Lesson 16: Life
        • Lesson 17: Biochemsitry
        • Lesson 18: Cells
        • Lesson 19: Membrane Transport
        • Lesson 20: Energy and Cell Respiration
        • Lesson 21: Photosynthesis
      • Unit 3: Project
      • Unit 3: Exam Review
      • Unit 3: Exam
    • Unit 4 >
      • EIS >
        • 22: The Human Body
        • 23: The Nervous System
        • 24: The Endocrine System
        • 25: The Integumentary System
        • 26: The Musculoskeletal System
        • 27: The Cardiovascular System
        • 28: The Respiratory System
        • 29: The Digestive System
        • 30: The Excretory System
        • 31: The Immune System
      • Unit 4 Project
      • Unit 4 Exam Review
      • Unit 4 Exam
    • Units 5-6 Coming Soon
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  • Home
  • About Us
  • Classroom
    • Resources >
      • Study Skills
      • Periodic Table
      • Common Ion Sheet
      • The Scientific Method
      • Doing Background Research
    • Introduction and Course Philosophy
    • Unit 1: Beginning Chemistry >
      • Lesson 1: The Atom >
        • What is an Atom?
        • The Structure of Atoms
        • The Periodic Table
        • Modeling Atoms
      • Lesson 2: Chemical Bonding >
        • Why Do Atoms Form Bonds?
        • Ionic Bonding
        • Covalent Bonding
        • Intermolecular Attraction
      • Lesson 3: Chemical Nomenclature >
        • Octet Rule
        • Ionic Compounds
        • Covalent Molecules
      • Lesson 4: Molecular Molecules >
        • Modeling Ionic Compounds
        • Modeling Covalent Molecules
      • Lesson 5: States of Matter >
        • States of Matter
        • Phase Changes
      • Lesson 6: Density >
        • What is Density?
        • Calculating Density
      • Lesson 7: Thermodynamics >
        • Temperature
        • Heat
        • Gas Laws
      • Lesson 8: Solution Chemistry >
        • Diffusion
        • Solutions and Molarity
        • Semi-Permeable Membranes
      • Lesson 9: Thermal Expansion >
        • Thermal Expansion
    • Unit 2: Earth Science >
      • Lesson 10: Earth at a Glance >
        • Perspective
        • Maps
      • Lesson 11: Layers of the Earth >
        • Layers of the Earth
      • Lesson 12: Plate Tectonics >
        • Plate Tectonics
      • Lesson 13: Rocks and Minerals >
        • Rocks and Minerals
      • Lesson 14: Particle Sorting >
        • Differentiation
        • Deposition of Sediment
      • Lesson 15: The Atmosphere >
        • Composition of the Atmosphere
        • Layers of the Atmosphere
        • Change Over Time
        • Atmospheric Disruption
    • Unit 3: The Cell >
      • Lesson 16: Life >
        • What is Life?
        • Structural Hierarchy of Living Things
      • Lesson 17: Biochemistry >
        • Intro to Biochemistry
        • Water
        • Micromolecules
        • Energy, Carbohydrates, Lipids
        • Protein and Nucleic Acid
      • Lesson 18: Cells >
        • What are Cells?
        • Microscopy
        • Plant and Animal Cells
      • Lesson 19: Membrane Transport >
        • A Special Environment
        • The Structure of Membranes
        • Membrane Transport
      • Lesson 20: Energy and Cell Respiration >
        • Energy in Biology
        • Energy Diagrams
        • Glycolysis and Anaerobic Respiration
        • Aerobic Cellular Respiration
      • Lesson 21: Photosynthesis >
        • Plants Get Energy From The Sun
        • Photosynthesis Process
        • Energy, Ecosystems, and the Environment
    • Unit 4: Anatomy and Physiology >
      • Lesson 22: The Human Body >
        • What Are Bodies Made Of?
        • What Do Bodies Do?
      • Lesson 23: The Nervous System >
        • The Nervous System
        • Neuronal Communication
        • The Central Nervous System
      • Lesson 24: The Endocrine System >
        • The Endocrine System
        • Hormones
        • Hormones, Puberty, and Reproduction
      • Lesson 25: The Integumentary System >
        • The Integumentary System
      • Lesson 26: The Musculoskeletal System >
        • The Skeletal System
        • The Muscular System
        • Anatomy Of The Musculoskeletal System
      • Lesson 27: The Cardiovascular System >
        • Blood and Blood Vessels
        • The Heart
      • Lesson 28: The Respiratory System >
        • The Respiratory System
      • Lesson 29: The Digestive System >
        • The Digestive System
        • Nutrition
      • Lesson 30: The Excretory System >
        • The Excretory System
      • Lesson 31: The Immune System >
        • Disease and Infection
        • Immunity
    • Units 5-6 Coming Soon
  • Workbench
    • Unit 1 >
      • EIS >
        • Lesson 1: Atoms
        • Lesson 2: Chemical Bonding
        • Lesson 3: Chemical Nomenclature
        • Lesson 4: Molecular Models
        • Lesson 5: States of Matter
        • Lesson 6: Density
        • Lesson 7: Thermodynamics
        • Lesson 8: Solution Chemistry
        • Lesson 9: Thermal Expansion
      • Unit 1: Project
      • Unit 1: Exam Review
      • Unit 1: Exam
    • Unit 2 >
      • EIS >
        • Lesson 10: Earth at a Glance
        • Lesson 11: Layers of the Earth
        • Lesson 12: Plate Tectonics
        • Lesson 13: Rocks and Minerals
        • Lesson 14: Particle Sorting
        • Lesson 15: The Atmosphere
      • Unit 2: Project
      • Unit 2: Exam Review
      • Unit 2: Exam
    • Unit 3 >
      • EIS >
        • Lesson 16: Life
        • Lesson 17: Biochemsitry
        • Lesson 18: Cells
        • Lesson 19: Membrane Transport
        • Lesson 20: Energy and Cell Respiration
        • Lesson 21: Photosynthesis
      • Unit 3: Project
      • Unit 3: Exam Review
      • Unit 3: Exam
    • Unit 4 >
      • EIS >
        • 22: The Human Body
        • 23: The Nervous System
        • 24: The Endocrine System
        • 25: The Integumentary System
        • 26: The Musculoskeletal System
        • 27: The Cardiovascular System
        • 28: The Respiratory System
        • 29: The Digestive System
        • 30: The Excretory System
        • 31: The Immune System
      • Unit 4 Project
      • Unit 4 Exam Review
      • Unit 4 Exam
    • Units 5-6 Coming Soon
  • Donate

Glycolysis and Anaerobic Respiration

Making ATP

We’ve talked a lot about a molecule called ATP. ATP is the molecule that makes it possible to do all kinds of difficult, crazy reactions in the cell. It makes reactions that wouldn’t normally want to happen happen really easily, by providing an energy incentive. In the simplest possible terms, you can think of ATP like a biochemical deus ex machina that just makes life happen by throwing in some hand-wavy, magicky energy. Like Doctor Who’s sonic screwdriver. Or Gandalf.
Picture
Because ATP’s magic third phosphate makes the molecule very unstable (which is how it can power chemical reactions), ATP must be constantly produced by the cell. It can’t be stored. This happens through a process called cellular respiration. The main goal of this process is to get the energy out of sugar. But, instead of just letting this energy escape in the form of heat and light, like in a standard combustion reaction, we have to break down glucose one step at a time and collect the energy as we go, in a way that can be used to make ATP.
Picture

Let’s take a closer look at how our cells
very carefully “explode” sugar.

Glycolysis

The first step of cellular respiration (of glucose) is glycolysis. Glycolysis literally means “breaking apart sugar” (glyco = “sugar,” lysis = “breaking apart”). 

Glycolysis takes glucose, which is made up of 6 carbons, and breaks it into 2 pyruvate molecules, which are 3 carbons each. 

Overall, energy is released when you turn glucose into pyruvate. Since the main goal is to capture that energy, that must mean some new energy-storing molecules were made. In this case, the energy “reward” for turning glucose into 2 pyruvate is 2 ATP plus 2 NADH. You don’t need to memorize these numbers for this class.

The ATP that is made by glycolysis can immediately be used to power chemical reactions in the cell. NADH is also a high-energy molecule, but it isn’t used for energy right away. Instead, it holds onto that energy for now and can be used to make a lot more ATP later on in organisms that can do aerobic respiration, which is the type of respiration that uses oxygen (we do this!). We’ll continue our learning of cell respiration by going through aerobic respiration in more detail in the next part of this lesson.

There is an actual chemical reaction that explains just how ATP and NADH are made by breaking apart glucose--but you don’t have to worry about that for this class. It’s much more important for you to understand the main idea that we are gradually breaking down glucose, releasing energy along the way and storing that energy in ATP and NADH. If you just want to be convinced that cells do chemistry and not magic, here’s a picture of what the actual mechanism looks like:
Picture
If it’s helpful for your conceptual understanding to see how these steps fit together, you can watch this video. We’re mainly interested in you understanding the main idea of glycolysis, including the start and end products, than the process:
Glycolysis occurs in all living organisms (including bacteria) and does not require oxygen. All the other steps of aerobic respiration don’t happen in most types of bacteria, but do happen in all eukaryotes (plant and animal cells), and don’t happen unless oxygen is present.
Picture
This process happens in the main compartment of the cell, which is called the cytoplasm. The cytoplasm is all the goopy, gooey stuff that is inside of the cell membrane but isn’t inside of an organelle.
Picture

Anaerobic Respiration

After glycolysis, most eukaryotic cells continue to break down pyruvate from cellular respiration and release all the energy from it. This is called aerobic respiration, and it requires oxygen and specialized machinery found in organelles called mitochondria. In these cells, cell respiration starts with glycolysis and continues through both steps of aerobic respiration. For now, we mainly want you to focus on understanding glycolysis, which is the first step in this process and happens in all living things.

Living things that can’t do aerobic respiration, whether because they lack the machinery (as is the case with many bacteria) or because they don’t have enough oxygen (as is the case with, for example, our muscle cells when they’re working really hard), get all of their energy from glycolysis. This means they have to take up a lot of sugar to get proportionally less energy. It’s not that efficient, but it will do in a pinch. This is called anaerobic respiration, or respiration that does not require oxygen (“an-” as a prefix means “not”). 

But, glycolysis can’t just keep going on forever, because you’ll run out of the important, difficult-to-make-or-find molecule NAD⁺. NAD⁺ is the resource that gets turned into NADH. In aerobic respiration, we’ll never run out of NAD⁺ because, once NADH is used in the electron transport chain, we get our NAD⁺ back. In anaerobic respiration, we need a second step to recycle NAD⁺. This can happen one of two ways:

1. Alcoholic fermentation is done by yeast. It is how beer and bread is made. It recycles NADH by turning pyruvate (3 carbons) into CO₂ (1 carbon) and alcohol (2 carbons). 
Picture
2. Lactic acid fermentation is done by muscle cells during exercise. This type of fermentation is also present in the bacteria found in yogurt, which convert lactose into lactic acid. It recycles NADH by turning pyruvate (3 carbons) into lactic acid (3 carbons). No CO₂ is produced, since both pyruvate and lactic acid have 3 carbons.
Picture
Even though anaerobic respiration is inefficient, nearly all organisms show some form of anaerobic fermentation, indicating that this process likely occurred in early evolutionary history--perhaps in places where oxygen was hard to come by, like deep in the ocean or in thermal vents. And, even though it’s inefficient, anaerobic respiration is still better than no respiration at all—and it’s definitely great for fans of yogurt and bread.

This video gives a good overview of anaerobic respiration:

Summary

You should understand:
  • That cell respiration is the process of gradually breaking down glucose and collecting usable energy from it.
  • That glycolysis is the first step of aerobic respiration and is the only energy-producing step in anaerobic respiration.
  • That glycolysis breaks down glucose (6 carbons) into 2, 3-carbon pyruvate molecules, and that the energy “reward” for this is ATP and NADH. It happens in the cytoplasm.
  • That aerobic respiration is the preferred way of making energy, when it is possible, because it is more efficient (you get more ATP per glucose—by a lot).
  • That NAD⁺ must be recycled in anaerobic respiration, which happens through either alcoholic fermentation or lactic acid fermentation.

Learning Activity

Picture
Next: ​Aerobic Cellular Respiration

Content contributors: Kathleen Yu, Eli Levine, Emma Moulton
© COPYRIGHT 2020. ALL RIGHTS RESERVED.