Energy in Cells Objectives

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Energy in Cells


  • SWBAT:
  • Describe low of energy through living systems
  • Compare chemical processes of autotrophs and heterotrophs
  • Describe role of ATP in metabolism
  • Describe how energy released.


  • Metabolic activities alter molecules in a series of steps
  • Enzymes (proteins) accelerate each step
    • Enzymes regulated to maintain a balance of supply and demand

Catabolic and Anabolic Reactions

  • Catabolic-give off energy by breaking down molecules
  • Anabolic—use energy to build molecules
  • Energy released by catabolic pathways used to drive anabolic pathways
  • SWBAT:
  • Describe low of energy through living systems
  • Compare chemical processes of autotrophs and heterotrophs
  • Describe role of ATP in metabolism
  • Describe how energy released.

Autotrophs vs Heterotrophs

  • Autotrophs-Make own food through anabolic reactions
  • Heterotrophs-Can not make own food
    • Must eat other organisms to obtain energy from food through catabolic reactions
    • Utilize cellular respiration


  • Ability to do work


  • Study of the flow and transformation of energy in the universe.

1st Law of Thermodynamics

  • Law of conservation of energy
  • Energy can be converted but not created nor destroyed.
  • Example:Energy stored in food converted to chemical energy when we eat and mechanical energy when you run.

2nd Law of Thermodynamics.

  • Energy cannot be converted without the loss of usable energy.
  • (Energy “lost” is converted to thermal energy)


  • Measure of disorder, or usable energy, in a closed system (not available for useful work)
  • 2nd Law AKA “Entropy Increases”
  • Food Chain –Useful energy available to next level decreases

Cell Energy

  • All living organisms must
    • produce from environment
    • store for future use
    • Use in a controlled manner

Where does Cell Energy Come From?

  • Sun → Autotrophs → Food → ATP

Types of Energy Cells Use

  • Mechanical Work-moving cilia, contraction of muscle cells, movement of chromosomes
  • Transport Work-Pumping substances
  • Chemical Work-Synthesis of polymers, Bioluminescence

Adenosine Triphosphate (ATP)

  • Multipurpose chemical energy storage molecule

Objects compressed-store energy compressed object released- energy is released. Chemical bonds store energy, when bonds break energy is released.

Energy is stored in CHEMICAL BONDS of molecules.

ATP (Adenosine Triphosphate)

  • Adenine molecule
  • Ribose sugar
  • three phosphate groups

Forming and Breaking Down ATP

  • Law of electrical charges
  • Bonding phosphate groups to adenosine required considerable energy.


  • AMP
  • Adenosine Monophosphate
  • ADP
  • Adenosine Diphosphate
  • ATP
  • Adenosine Triphosphate-
  • Number of phosphate groups
  • 1
  • 2
  • 3
  • Energy to form bonds
  • Small Amount
  • More
  • Energy
  • Substantial Energy
  • Energy stored in chemical bonds
  • Minimal
  • Greater Amount
  • Greatest amount
  • 3rd Phos + ADP ATP,
  • Phos so eager to get away, bond is broken a great amount of energy is release.
  • Energy available when ATP loses phos

Bonds Broken by Hydrolysis

ATP Cycle

  • Doesn’t exist all the time as ATP.
  • Phosphate available--cell has an unlimited supply of energy.

Energy from Fuels

  • Digest large molecules into smaller ones
    • break bonds & move electrons from one molecule to another
      • as electrons move they “carry energy” with them
      • that energy is stored in another bond, released as heat or harvested to make ATP

Move electrons in Biology

  • “Glucose is like money in the bank; ATP is like money in your pocket”

We can write the overall reaction of this process as: 6H2O + 6CO2 ----------> C6H12O6+ 6O2 six molecules of water plus six molecules of carbon dioxide produce one molecule of sugar plus six molecules of oxygen Basically Opposite of Cellular Respiration

  • Photosynthesis

Two Reactions of Photosynthesis

  • Light Reaction ☼ – Light energy (sun) into chemical energy.
      • Thylakoid Disk
      • Produces ATP to power Light Independent Reaction.
      • Oxygen Released
  • Light Independent Reaction/Dark Reaction (Calvin Cycle) – Uses chemical energy to “Fix” Carbon dioxide into sugar.
      • Uses ATP and Electrons from Light Reaction
      • Stroma

Mesophyll Cells

  • Specialized cells in the middle of the leaf that contain a lot of chloroplast for photosynthesis

Chloroplast: Organelle where photosynthesis occurs Thylakoids-Site of light dependent reactions Grana: Stack of Thylakoids

  • Chloroplasts

Stomata (stoma) Pores in plant’s cuticles through which water vapor and gases are exchanged between the plant and atmosphere (underside of leaves)

  • Pigments: Molecules that absorb specific wavelengths of light (Plants: Chlorophyll-absorbs and transfers light energy)
  • **Chlorophyll forms a and b absorb most wavelengths except green. Because it doesn’t absorb it, it reflects it, hence green appearance.

Fall Colors

  • Pigments other then chlorophyll
  • Chlorophyll reduced revealing other pigments (carotenoids that are red, orange or yellow)

Light Dependent Reaction —“photo” of photosynthesis

  • 1.)The light absorbed by chlorophyll causes a transfer of electrons and H+ from H20 molecules already present. This causes the H20 to split into molecular 0xygen (02) and a H+ ion (photolysis). 2.) The O2 is released (we breathe it) and the H+ bonds to NADP+ creating NADPH 3.)ATP is formed through photophosphorylation. (ADP gets a phosphate group added to it creating ATP) 4.) The NADPH and the ATP created here go on to fuel the reactions in the second part of photosynthesis - The Calvin Cycle
  • Photolysis: light causes water molecule split. Hydrogen to bind to an acceptor, subsequently releasing the oxygen.
  • Equation: H2O > 2H + O
  • Function:
    • Release O2 gas to the atmosphere
    • Replaces lost electrons

Calvin Cycle/Light Independent

  • “synthesis” of photosynthesis, making food, trapping CO2.
  • Rubisco (enzyme) brings together CO2 and sugar, carbon fixation
    • 3 CO2 (atmosphere) and 3, 5-carbon sugars (RuBP).
  • PGA Formation-Six-carbon product is unstable and splits into 3-carbon products (PGA).
  • ATP places a phosphate group on each PGA: NADPH donates a pair of electrons, yielding a high energy food, PGAL.

Calvin Cycle Completes

  • Glucose Production-After several rounds 2 PGAL leave to form glucose
  • Replenish RuBP (Ribose Biphosphate) Some PGAL reform 5-C Sugar-begin process again

Cellular Respiration

  • Mitochondria break down glucose to produce energy (ATP)


  • Every cell (plants and animals)
  • Exergonic Reaction(produces energy)
  • Equation-
  • C6H12O6 + ADP 6CO2 + 6H2O + ATP

Oxidation/Reduction Reactions

  • Oxidation
    • adding O
    • removing H
    • loss of electrons
    • releases energy
    • exergonic
  • Reduction
    • removing O
    • adding H
    • gain of electrons
    • stores energy
    • endergonic
  • C6H12O6
  • 6O2
  • 6CO2
  • 6H2O
  • ATP
  • +
  • +
  • +
  • oxidation
  • reduction

Cellular Respiration

  • Overview three stages:
    • Glycolysis
      • Cytoplasm
      • Glucose splits
      • Forms pyruvate (Intermediate-Acetyl CoA)
    • Citric acid cycle (Kreb Cycle)
      • Converts Acetyl CoA into CO2
      • Occurs in Mitochondrial Matrix
    • Electron transport chain
      • ATP Synthesized

Glycolysis— “Sugar” splitting

  • Yields little energy
  • No oxygen required (anaerobic)
  • Glucose (6 carbon sugar) → 2 Pyruvate and 2 ATP
  • Prokaryotes and single celled organisms-sole source of energy.

History of Energy Harvest

  • Energy transfer first evolved
  • transfer energy from organic molecules to ATP
  • still is starting point for ALL cellular respiration


  • Prokaryotes
    • first cells had no organelles
  • Anaerobic atmosphere
    • life on Earth first evolved without free oxygen (O2) in atmosphere
    • energy had to be captured from organic molecules in absence of O2
  • Prokaryotes that evolved glycolysis are ancestors of all modern life
    • ALL cells still utilize glycolysis

Glycolysis Reactants and Products

  • 1 glucose
  • Enzymes
  • 2 ATP are needed
  • 2 Pyruvates
  • 4 ATP (net gain 2)
  • 2 NADH (go to Electron Transport Chain (ETC))

Pyruvic acid forms Acetyl CoA

  • Mitochondrion
  • Pyruvic Acid combines with Coenzyme A to form acetyl CoA

Intermediate step Reactants and Products

  • 2 pyruvates (glycolysis)
  • 2 Acetyl CoA (Go to Kreb Cycle)
  • 2 CO2 (released as waste)
  • 2 NADH (ETC)

Citric Acid Cycle (Kreb Cycle)

  • Mitochondria
  • Series of reactions
  • Generates electrons for ETC
  • Aerobic- Needs Oxygen

The Krebs cycle has five main steps. It starts with one molecule of Acetyl CoA (formed at end of glycolosis)

  • The Krebs cycle has five main steps. It starts with one molecule of Acetyl CoA (formed at end of glycolosis)
  • Step 1: Acetyl CoA, a two-carbon molecule, bonds with four-carbon oxaloacetic acid to form six-carbon citric acid.
  • Step 2:Citric acid releases a molecule of CO2 and a hydrogen atom, becoming a five-carbon compound. The hydrogen atom bonds with NAD+, reducing it to NADH.
  • Step 3: The five-carbon compound releases another CO2 molecule and a hydrogen atom, which again bonds with NAD+, producing NADH. This step is the same as step 2, except in this step one molecule of ATP is formed from an ADP and a phosphate.
  • Step 4: The new four-carbon compound releases another hydrogen atom. This time, the atom reduces a molecule of FAD to FADH2.
  • Step 5: The four-carbon molecule formed in step 4 releases a hydrogen atom, reforming oxaloacetic acid. hydrogen atom reduces another molecule of NAD+ to NADH.
  • Since one glucose molecule is converted into two pyruvic acid molecules by glycolysis, the Krebs cycle completes two turns for every molecule of glucose. This makes it produce 6 NADH molecules, 2 FADH, 2 ATP molecules, and 4 CO2 molecules.

Citric Acid cycle

  • 2 Acetyl CoA
    • 4 CO2 (waste)
    • 6 NADH (ETC)
    • 2 ATP
    • 2 FADH2 (ETC)

Citric Acid Cycle/Kreb Cycle

Electron Transport Chain:

  • Mitochondria
  • Series of reactions-electrons transported through chain
  • NADH and FADH2 from Krebs Cycle carry electrons
  • Electron route: food---> NADH ---> electron transport chain ---> oxygen
  • Oxygen used
  • Water released

Electron Carriers Move electrons by shuffling H+ around

  • NAD+ → NADH
  • FAD+ → FADH2
  • like $$ in the bank
  • reducing power!

Steps of Electron Transport Chain

  • Carrier molecules arrives, bumps the ETC’s first carrier, which accepts the electrons, then passes them on along the chain (like a hot potato).
  • Movement of electrons releases enough energy to power the movement of H+ ions from the inner compartment into the outer compartment (like heat of a hot potato dissipating as it is passed). The ions are being pumped against their concentration gradient.
  • Hydrogen ions flow downhill through an enzyme called ATP synthase, like a water wheel spinning; as the ions pass, energy is used to transfer phosphate onto ADP to make ATP.

Electron Transport Chain

  • Greatest amount of energy is made in this stage (32-34 ATP per glucose)

Cellular Respiration

  • Glycolysis: 2 ATP
  • Krebs: 2 ATP
  • Electron Transport: 32 for Eukaryotes, and 34 for prokaryotes.
  • Total 36 for eukaryotes, and 38 for prokaryotes.

Anaerobic Respiration (fermentation)

  • Cytoplasm
  • Regenerates the cells supply of NAD+ (electron carriers)
  • 2 Pyruvate and ONLY 2 ATP (glycolysis)
  • Oxygen not being available as the final receptor in the ETC.
  • Lactic Acid Fermentation and Alcohol Fermentation

Lactic Acid Fermentation

  • Converts pyruvate to lactic acid.
  • Transfers high energy electron and proteins from NADH.
  • Strenuous exercise—muscle not supplied with enough oxygen.
    • LA builds up; muscles become sore, cramps and fatigued
    • Panting helps provide extra O2; return to aerobic conditions

Alcohol Fermentation

  • Yeast and bacteria
  • Pyruvate forms Ethyl Alcohol and CO2
  • NADH donates electrons; NAD+ is generated.
  • Baking---CO2 provides bubbles (dough rise)
  • Alcohol—Consumable and ethanol

Comparison of Photosynthesis and Cellular Respiration

  • Photosynthesis
  • Cellular Respiration
  • Food broken down
  • Energy from sun stored in glucose
  • Energy of glucose released
  • Carbon dioxide taken in
  • Carbon dioxide given off
  • Oxygen given off
  • Oxygen taken in
  • Produces glucose from PGAL
  • Produces CO2 and H2O
  • Goes on only in light
  • Goes on day and night
  • Only in presence of chlorophyll
  • All living cells

Alternative to Cellular Respiration: Fermentation

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