9) Cellular Respiration Pt1

Glucose

• Energy rich b/c it contains many C-H bonds

C-H Bonds

• Share electrons relatively equally

• Represent reduced carbon

• Store high potential energy

CO₂ and C=O bonds

• Electrons pulled toward oxygen

  • has greater EN

• Carbon fully oxidized

• Low potential energy

Respiration

• Conversion of reduced carbon into oxidize carbon

Glucose Oxidation and Free Energy

• The oxidation of glucose to CO₂ releases about

  • ΔG ≈ - 686 kcal/mol

  • 233 kcal/mol is stored in ATP

  • 30-34% efficiency

    • The remaining energy is released as heat (body temp regulation)

Oxidation and Reduction in cellular respiration

• Oxidation

  • The loss of electrons

  • Glucose is oxidized

• Reduction

  • Gain of electrons

  • Oxygen is reduced

Electrons in Oxidation

• Electrons don’t disappear they are transferred

• This flow in a central theme of respiration

Electron Movement and energy release

• e^- spontaneously move towards HIGH EN

• Oxygen is highly EN!

• As electrons move toward oxygen

  • Free energy drops

    • (Electron move to stability)

  • Energy is released

    • (Ball rolls from high to low PE)

• Cells use that released energy for ATP and heat

ΔG Free energy

• Free energy is how much energy is available to do work

  • High G = electron in high-energy, unstable position

  • Low G = electron is a low-energy, stable position

Electronegativity

• How strongly an atom pulls on electrons

  • Usually smaller atoms

• Oxygen has one the strongest strongest pulls

NAD⁺ becoming NADH

• NAD+ (Oxidized form)

  • Primary electron carrier

  • Becomes NADH when it picks up high energy electrons

• NADH (Reduced form)

  • like a charged battery

  • Stores e^- from broken down glucose

  • The electrons that release energy used for ATP

No NAD+ = No ____

• No NAD+ = No Glycolysis

• Glycolysis the first step of breaking down glucose and produces NADH.

• This can only continue if there is fresh NAD+ available to pick up more electrons.

• SO REDOX is essential for metabolism

Cellular Respiration

• Cellular respiration breaks glucose apart into CO2 while sending its electrons to oxygen

• The energy release along the way is used to make ATP

3 major stages of Cellular Respiration

1. Glycolysis (cytoplasm)

2. Pyruvate oxidation + Citric acid cycle (matrix)

3. Oxidative phosphorylation (inner membrane)

Carbon Flow

• Glucose → CO2

• The 6 carbon on glucose are broken down and release as CO2

• The carbon leaves your body as carbon dioxide.

Electron Flow

• Glucose → NADH/FADH₂ → Oxygen

Mitochondrial Structure (4 major compondents)

• Outer membrane

• Intermembrane space

• Inner membrane (Cristae folds)

• Matrix

Cristae

• The inner membrane is highly folded into cristae

• They increase surface area for

  • Electron transport chain

  • ATP synthase

Endosymbiosis Evidence

• Mitochondria evolved from aerobic bacteria through endosymbiosis

  • Double Membrane

  • Circular DNA

  • 70S ribosomes

  • Binary fission

Endosymbiosis Benefits

• Endosymbiosis allowed eukaryotic cells to

  • Efficiently use oxygen

  • Dramatically increase ATP production

Glycolysis

Glucose + 2ADP + 2Pi + 2NAD⁺ → 2 Pyruvate + 2ATP + 2NADH + 2H⁺

• In the Cytoplasm

• Anaerobic

  • (Muscles with no oxygen still make a little ATP)

• No CO2 released

• All 6 carbons are retained in 2 pyruvate

Glycolysis Equation Breakdown

Glucose + 2ADP + 2Pi + 2NAD⁺ → 2 Pyruvate + 2ATP + 2NADH + 2H⁺

Goes in

• Glucose (sugar)

• ASP + Pi (empty ATP parts)

• NAD+ (empty electron carrier)

Comes out

• 2 pyruvates (half glucose pieces)

• 2 ATP (small amount of energy you get right away)

• 2 NADH ( charged electron carriers that are used later)

• H

Energy Investment

• 2 ATP molecule are consumed (energy investment)

• When consumed

  • ATP → ADP (hydrolysis)

• This phosphate is added to glucose and…

  • Negative charge traps glucose inside the cell

    • charged ions cant pass through cell membrane.

  • Increase glucose chemical instability

    • raises ΔG

  • Prepare for cleavage

Phosphorylation in Energy Investments

• Adds phosphate group to glucose from ATP

  • INCREASE ΔG

    • Less stable

    • More reactive

    • Easier to break apart in later steps.

Hexokinase Reaction

• Glucose → Glucose-6-phosphate

• ATP → ADP

• Phosphorylation

  • Adds negative charge

  • Prevents glucose from leaving the cell

• IRREVERSIBLE

Phosphofructokinase (PFK)

• Fructorse-6-phosphate → Fructorse-1, 6-bisphosphate

• ATP → ADP

• Phosphorylation

  • Increases instability

• IRREVERSIBLE

PFK Importance

• Commits glucose to energy extraction

• Links glucose to overall metabolic demand

  • Inhibitors and Activators

PFK Inhibitors

• Signal of low metabolism

• High ATP = Cell already has enough energy

• High Citrate = Mitochondria are back up with fuel.

  • So stop sending more sugar down glycolysis.

Citrate Inhibitor and AMP Activators explanation

• Comes from the citric acid cycle

• AMP = ATP releases 2 phosphate groups

PFK Activators

• Signal of high metabolism

• High AMP = Cell needs more energy

Cleavage Phase

• Fructose-1, 6-bisphophate → two glyceraldehyde-3-phosphate

• these two (G3P) proceed independently

  • why glycolysis produces (ATP and NADH) x2

Oxidation Step

• glyceraldehyde-3-phosphate → 1,2-bisphospoglycerate

• Critical REDOX event

  • G3P is oxidized → 1,2-bisphosphoglycerate (high energy intermediate)

  • NAD+ is reduced → NADH

• e^- FINALLY removed from the carbon backbone and energy is captured in NADH.

Where does the energy from oxidation step go

• G3P oxidation = energy release

• NAD+ reduction quickly catches energy release.

• NADH: stored a LOT of energy

  • e^- more stable = releases a bit of energy

• 1,3-bisphosphoglycerate: high-energy Intermediate

Phosphorylated intermediate

• A molecule with a high-energy phosphate

Substrate level Phosphorylation

• The simplest way to make ATP

• An enzyme transfers a phosphate from high energy intermediate directly to ADP forming ATP

  • No electron transport chain

  • Uses direct phosphate transfer

• Requires no…

  • ATP synthase

  • Membrane

  • Oxygen

  • Proton gradient

Phosphoglycerate Kinases

• Enzyme

• Takes phosphate group from high energy intermediate to form ATP

• Removes 1st phosphate from glucose

Pyruvate kinases

• Enzyme

• Takes phosphate group from high energy intermediate to form ATP

• Removes 2nd and last phosphate from glucose

• Creates pyruvate

End Products of Glycolysis

• Per glucose

  • 2 pyruvate

  • 2 NADH

  • 2 ATP (net gain)

• NO CARBON LOST (6-C)

• Glycolysis produces only a small fraction of total ATP

• Its main purpose is to create reduced electron carriers (NADH)