bio chapter 6

Living organisms constantly transform…

energy from one form to another

Adenosine triphosphate (ATP)

• nucleotide that stores chemical energy in the bonds between its phosphate groups

  • each PO4- group has a net negative charge

• breaking these bonds releases energy

• formed by adding a phosphate group to ADP

• In eukaryotic cells, mitochondria produce most _

• every cell requires _ to power reactions that require energy input

Macromolecules transformation

• carbohydrate → simple sugars (energy 4 calories/gram)

• protein → amino acids (energy 4 calories/gram)

• fat → fatty acids & glycerol (energy 9 calories/gram)

• nucleic acid → nucleotides (not a significant source of energy for cells)

How do cells use subunits that are broken down

• building blocks to make new macromolecules

• energy to fuel cellular work

Whats the most energy dense molecule

fats

Exergonic reaction examples

• cellular respiration

• catabolism (breakdown)

• electron transport chain (ETC)

breakdown of fuel, increases entropy

Endergonic reaction examples

• active transport

• cell movement

• anabolism (constructing)

• photosynthesis

build macromolecules, lowers entropy

Cellular respiration

• can be aerobic or anaerobic

• harvests the potential energy stored in food molecules & uses the energy to make ATP

• reactants: glucose & O2 consumed

• products: CO2, water, and energy (ATP) released

• 1 molecule of glucose is processed = 36-38 molecules of ATP

• formula: C6H12O6 + O2 → CO2 + H2O + ATP

  • aerobic formula: C6H12O6 + 6O2 + (36 ADP + 36 PO4) → 6CO2 + 6H2O + 36 ATP

    • necessary reactant: 6O2

    • waste products: 6CO2 + 6H2O

• location: cytoplasm and the mitochondria of eukaryotic cells

  • Glycolysis begins in the cytoplasm

  • Subsequent aerobic stages, the Krebs cycle and electron transport chain, occur within the mitochondria.

• series of redox reactions that release energy, which the cell uses to synthesize ATP

Glycogen carbohydrates provide

short-term energy storage

(excess simple sugars not immediately used for energy or cell structures are bound together in branching chains called _)

• location: muscle and liver tissue

• stores approx. 4 calories per gram

Triglyceride fats provide

long-term energy storage

(once glycogen stores have been filled, excess energy from dietary carbohydrates (simple suars), proteins (amino acids), and fats (fatty acids & glycerol) is stored as fat in the form of triglycerides)

• location: fat cells

• stores approx 9 calories per gram

Where does the energy to power formation of ATP from ADP come from?

breaking down glucose during cellular respiration or from sunlight during photosynthesis

The atp/adp cycle

the fundamental process cells use to store, transport, and release energy

Energy Release (Hydrolysis): When cells need energy, ATP loses a terminal phosphate group through hydrolysis, breaking down into ADP and inorganic phosphate (P), releasing energy for processes like muscle contraction or nerve impulses.

Energy Storage (Phosphorylation): Through cellular respiration or photosynthesis, energy is used to add an inorganic phosphate back onto ADP, reforming high-energy ATP.

Location: This cycle mainly occurs in the cytoplasm and mitochondria of cells.

The Cycle: ATP → ADP + P + Energy (used for work); then, ADP + P + Energy (from food/sun) → ATP

ATP synthesis

1. energy from food is required to push a 3rd phosphate group onto ADP (P + ADP)

2. energy from food is then stored as a phosphate bond in ATP

3. energy is then released when the phosphate bond is broken, and can be used to fuel our everyday activities (P + ADP)

Oxidation (-)

loss of electrons

Reduction (+)

gain of electrons

Redox reaction

combined reduction & oxidation

• cellular respiration is a series of ___

Electron transfer

electrons (e^-) from high energy molecules are transferred to low energy molecules

Electron carriers (coenzymes)

carry out the electron transfer process

Cellular respiration proceeds in 4 stages

• Glycolysis

• Pyruvate oxidation

• Krebs cycle (aka Citric Acid cycle)

• Electron Transport Chain (ETC)

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Cellular respiration overview

1. glucose enters glycolysis: broken into glucose derivatives, 2 ATP produced

2. glucose derivatives are broken down in pyruvate oxidation / citric acid cycle (CAC): CO2 and 2 ATP produced

3. electrons enter the electron transport chain (ETC) (O2 is required): H2O and ~32 ATP produced

Energy efficiency

• __ of cellular respiration is 37% - 37% of the energy stored in the bonds of a glucose molecule is stored in ATP, the rest goes to waste (as heat)

• Glycolysis alone is 2% efficient

• A typical car engine is 25% efficient (25% of the energy stored in the gasoline molecules is converted to mechanical energy)

Glycolysis “sugar-splitting” occurs in

cytosol

• First step of cellular respiration

  • least efficient (only 2 ATP/glucose)

• Oldest evolutionarily of the three steps

  • takes place in all living organisms

• Does NOT require oxygen

• Can occur in the presence or absence of oxygen

Glycolysis “sugar splitting”

Summary

• Location: cytosol

• Oxidized: the 6-carbon sugar glucose

• Reduced: NAD^+ → NADH

• Net Input: glucose (6 carbon molecule), 2 NAD^+, 2 ADP + 2P (so 2 ATP)

• Net Output: 2 pyruvates (two 3 carbon molecule), 2 NADH, 2 net ATP

  • “spend’ 2 ATP, synthesis 4 ATP: net gain of 2 ATP

Steps

1. 2 ATP donates 2 phosphates (one each) to a glucose, which then becomes 2 ADP

2. Glucose (6 carbon molecule) splits into two 3 carbon molecules each containing 1 phosphate group

3. Each phosphate group is removed from the 3 carbon molecules, which produces 2 ATP for each so 4 total

4. During the process of removing the phosphate group, an electron is stored in a molecule called NADH (2 of them), which was orginally NAD^+

• when NAD^+ takes on an electron (reduced), it becomes NADH

Extra notes

• initially “spend”/invest ATP to begin this (hydrolyzed to 2 ADPs)

• oxidation/reduction reactions

  • 3 carbon molecules are oxidized

  • 2 NAD^+ are reduced to 2 NADH

• energy harvest

  • 4 ADP are converted to 4 ATP

• doesnt require oxygen (can occur in aerobic + anaerobic conditions)

• glycolysis stores energy in the form of electrons inside NADH

How are evolutionary conservation and glycolysis connected

• Glycolysis is highly conserved across all domains of life because it is an ancient, fundamental metabolic pathway for anaerobic energy production (ATP) that evolved before oxygen was present in Earth's atmosphere

  • Glycolysis is used by nearly all organisms (bacteria, archaea, and eukaryotes), indicating it was present in a common ancestor

Aerobic (O2) respiration

• glucose + O2 = ATP

• extracts energy/complete oxidation of glucose to CO2 in the presence of O2, producing ATP / captures energy from the oxidation of glucose and reduction of oxygen & stores the captured energy in the bonds of ATP

  • electrons stripped from glucose are used to reduce O2

• formula: C6H12O6 + 6O2 → 6 CO2 + 6H2O + 36 ATP

  • products contain less potential energy than the reactants (exerogonic)

• autotrophs like plants use this to generate ATP as well

Pyruvate oxidation

Summary

• Pyruvate is oxidized → to acetyl-CoA (CO2 is waste)

• NAD^+ reduced → NADH

• location: mitochondrial matrix in eukaryotic cells & cytosol in prokaryotes

• Input: 2 pyruvates, 2 NAD^+, 2 Coenzyme A (CoA)

• Output: 2 Acetyl CoA, 2 CO2, 2 NADH

Steps

1. Decarboxylation (Remove CO2): A carboxyl group is removed from pyruvate, releasing CO2

2. Oxidation (Create NADH): The remaining two-carbon fragment is oxidized (acetate), and the electrons are transferred to NAD^+ forming NADH (reduced)

3. Formation of Acetyl CoA: The oxidized two-carbon acetyl group attaches to Coenzyme A, forming Acetyl CoA.

Krebs cycle (Citric Acid Cycle)

• Captures/extracts the high energy electrons of acetyl CoA by oxidizing it / citrate → 2 CO2

• Electron carriers NAD+ and FAD and reduced → NADH and FADH2

• 2 ATP

• location: mitochondrial matrix in eukaryotic cells and cytosol in prokarytoic cells

• does not directly use oxygen but it is an aerobic process that stops without it

Steps

• Oxaloacetate (OAA) is a vital 4-carbon molecule (C4H4O5) reacts with acetyl-CoA to initiate energy production and creates citrate (6 carbon)

• Coenzyme A is released and recycled to deliver more acetate

• the acetyl group's two carbon atoms is oxidized to two molecules of carbon dioxide (CO2)

• the electron carriers 3 NAD^+ and 1 FAD are reduced (gain electron) to 3 NADH and 1 FADH2 (per turn of the cycle)

  • Each molecule in the CAC is less energetic than its predecessor

Key Byproducts Per Cycle (One Turn/One Acetyl-CoA):

• CO2: 2 molecules (waste product)

• NADH: 3 molecules

• FADH2: 1 molecule

• ATP: 1 molecule

Key inputs per Glucose (Two Turns):

• Acetyl-CoA: 2 molecules

• NAD^+: 6 molecules

• FAD: 2 mollecules

• ADP: 2 molecules

  • + Phosphate: 2

Key Byproducts Per Glucose (Two Turns):

• CO2: 4 molecules (waste product, contains remaining carbon atoms from the og 6 carbon glucose molecule)

• NADH: 6 molecules

• FADH2: 2 molecules

• ATP: 2 molecules

  • since 1 molecule of glucose produces 2 Acetyl-CoA molecules, the cycle turns twice per glucose, resulting in a total of 2 ATP molecules

For every glucose molecule that enters glycolysis, 2 citric acid cycles must take place bc…

• glycolysis produces two molecules of pyruvate, which are then converted into two molecules of acetyl-CoA.

• Each acetyl-CoA molecule enters the cycle separately, requiring two turns to process the full energy potential of one glucose molecule

Purpose of NADH and FADH2

carrying electrons to the electron transport chain

Proton gradient (H^+ gradient)

• established by the ETC

• an electrochemical difference in hydrogen ion concentration across a membrane, creating potential energy (proton-motive force) essential for powering cellular processes

• primarily formed by proton pumps (ETC) in mitochondria, chloroplasts, and bacteria, driving ATP synthesis via ATP synthase

ATP synthase

• enzyme that uses the potential energy in a proton (H^+) gradient to produce ATP

• enzyme complex that admits protons through a membrane, triggering the production of ATP

• uses the energy of a proton gradient to add a phosphate to ADP

Electron transport chain (ETC)

Summary

• Active transport of H^+

  • Proton gradient drives ATP synthesis via ATP synthase

• Oxidized: NADH → NAD^+ and FAD → FADH2

• Reduced: O2 → H2O

• Location: inner mitochondrial membrane (cristae) in eukaryotes and the plasma membrane in prokaryotes

• Inputs: NADH, FADH2, O2, ADP + P

• Outputs: NAD+, FAD, H2O (waste), ATP (~32 to 34)

Extra

• Membrane bound molecular complex that shuttles electrons to slowly extract their energy

  • harnesses the potential energy of NADH & FADH2, which donate electrons to proteins in this chain

• The final step in cellular respiration, a series of redox reactions

Steps

• NADH and FADH2 bring electrons harvested glycolysis, pyruvate oxidation and the CAC are oxidized: give their electrons to Enzyme Complexes. By accepting the electrons, Enzyme Complexes are reduced.

• Enzyme Complex I gives up its electrons (becomes oxidized) to the next molecule in the ETC (Mobile protein I)

  • Each molecule in the ETC is lower in energy than its predecessor

• As electrons move along a series of proteins, energy is released at each step (exergonic)

• This energy is used to maintain proton gradient (that holds potential energy)

  • Pumps hydrogen ions from the matrix across the inner membrane of mitochondria against their concentration gradient (active transport)

  • Hydrogen ions are pumped from the inside to the outside, even though there are more hydrogen ions on the outside (going against the concentration gradient) (matrix → intermembrane compartment)

• ATP synthesis using ATP synthase

  • the H^+ ions then spontaneously flow back across the membrane but only though a protein channel called ATP synthase (facilitated diffusion)

  • the passage of hydrogen ions through ATP synthase causes it to spin very rapidly

  • the kinetic energy from the spinning ATP synthase is used to attach a phosphate group to ADP, forming ATP

• Oxygen is the final electron receptor in the ETC

  • Electrons from the ETC combine with H^+ and oxygen to form water, a byproduct of the ETC

    • if there is no oxygen, electrons have nowhere to go, ETC gets backed up and the whole process grinds to a halt. Long term results would result in no ATP molecules produced, and cells die

Once 1 molecule of glucose is processed, how many molecules of ATP are produced?

• theoretically yields ~36 molecules

• actual yield is abt 30 ATPs per glucose

Importance of respiration/breathing/oxygen

• the O2 we breath is needed for the ETC to function

• when we breathe, the oxygen enters the blood, and the blood takes it to all cells in the body

• cells use the oxygen to synthesize ATP, producing CO2, and water as waste products, which are picked up by the blood

  • blood enters the lungs again, CO2 is expelled

What if oxygen is not around?

glycolysis is folllowed by fermentation

Fermentation

• glycolysis occurs before this

• produces significantly less ATP

  • 2 ATP molecules per molecule of glucose

• NADH transfers electrons to pyruvate and is oxidized to NAD^+, which can then be used in glycolysis

  • * remember, we normally recycle NADH to NAD^+ using the ETC

  • no oxygen = we dont use ETC

Alcoholic fermentation

• metabolic pathway in which NADH reduces the pyruvate from glycolysis, producing ethanol and CO2

Input: 2 pyruvates, 2 NADH

Output: 2 ethanol, 2 CO2, 2 NAD^+

Lactic acid fermentation

• metabolic pathway in which NADH from glycolysis reduces pyruvate, producing lactic acid or lactate

Input: 2 pyruvates, 2 NADH

Output: 2 lactic acid/lactate (waste), 2 NAD^+

Photosynthesis comparison

Food: produced

Energy: stored as glucose & other sugars

Light: required

H2O: consumed

CO2: consumed

O2: released

Equation: 6CO2 + 6H2O + Light Energy → C6H12O6 + 6O2

Respiration comparison

Food: consumed

Energy: released from glucose & other food molecules

Light: not required

H2O: released

CO2: released
O2: consumed

Equation: C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP

Mitochondria

• powerhouse of the cell

  • converts the energy in food into a form that the cell can use to power its normal activites

• contain own DNA

• generate most chemical energy (ATP) for eukaryotic cells

• each _ has 2 membranes enclosing a central matrix (the inner compartment of a _)

Intermembrane compartment

the space between a mitochondrion’s two membranes (between the outer & inner membrane)

Cristae

• folds of the inner membrane & they greatly increase the surface area of the inner membrane

• house electron transport chain proteins

  • these proteins pump protons into the intermembrane compartment, ATP synthase also spans the inner membrane

How does other food molecules (proteins, fats, carbohydrates) enter the energy extracting pathways?

• Polysaccharides (starch/glycogen)→ glucose

• Amino acids → pyruvate, acetyl CoA, or an intermediate of the Krebs cycle

• Fatty acids → acetyl CoA

• Glycerol → pyruvate

Anaerobic respiration

• the process of breaking down sugars to generate energy (2 ATP per glucose) without oxygen

• occurring in the cytoplasm

• essential for organisms in low-oxygen environments and provides quick energy during intense exercise, yielding products like lactic acid in humans or ethanol/CO₂ in yeast

• it does not use oxygen as the final electron acceptor, relying instead on inorganic molecules (like sulfate or nitrate) or fermentation to produce energy

• final electron acceptors: NO3-, SO4²-, CO2

Mitochondrial matrix

the fluid enclosed by the inner membrane of a mitochondrion

Before the NADH and FADH2 produced during glycolysis & the krebs cycle enter the ETC, the net number of ATP molecules produced per glucose molecule is…

4 molecules

Energy pathways that do not require O2 to generate ATP

• fermentation (with glycolysis)

• anaerobic respiration

What has been produced from the og gluclose molecule after glycolysis, oxidation of pyruvate, & the krebs cycle, but before molecules enter the electron transport chain

• CO2

• NADH

• FADH2

• ATP

Aerobic cellular respiration requires that organisms need to acquire _ that can diffuse into their cells & need to eliminate _ that diffuses out of their cells

O2; CO2

The rearrangement and oxidation of intermediates in the Krebs cycle transfer electrons to form __ and eventually recreate a 4-carbon molecule that allows the cycle to repeat

NADH and FADH2

How much ATP is generated/used during the passage of 1 molecule of glucose (net theoretical total production)?

36 ATP

How much ATP is generated/used during the passage of 1 molecule of glucose (glycolysis)?

produces 4 ATP but also uses 2 ATP; so net 2 ATP are produced

How much ATP is generated/used during the passage of 1 molecule of glucose (Krebs cycle)?

2 ATP generated

How much ATP is generated/used during the passage of 1 molecule of glucose (electron transport)?

34 ATP generated

How much ATP is generated/used during the passage of 1 molecule of glucose (moving NADH from glycolysis into mitochondrion)?

2 ATP used

What causes the difference between the theoretical & actual yields of ATP in aerobic respiration?

• protons leak across the inner mitochondrial membrane without using ATP synthase

• ATP is spent transporting ADP & pyruvate into the mitochondrial matrix

  • 2 molecules ATP must be used to transport NADH produced in glycolysis into the mitochondrion, the net theoretical yield of aerobic respiration is 36 ATP molecules

When carbohydrate supplies are depleted in cells, amino acids from proteins can enter aerobic respiration after _ is removed from the amino acids and excreted

nitrogen

What can be a final electron acceptor in anaerobic respiration

• NO3-

• SO4²-

• CO2

What are the products of glycolysis?

• 2 NADH

• 2 ATP

• 2 pyruvates (two 3 carbon molecule)

What are the products of pyruvate oxidation?

• 2 NADH

• 2 Acetyl CoA

• 2 CO2 (waste)

  • releasing one CO2 per pyruvate

What are the products of the Krebs cycle?

• 6 NADH

• 2 FADH2

• 2 ATP

• 4 CO2

  • waste product, contains remaining carbon atoms from the og 6 carbon glucose molecule

What are the products of the Electron Transport Chain?

• ATP (~34)

• NAD+

• FAD

• H2O (waste),

Amount that energy yield is lowered due to leaking protons & shuttling pyruvate

6 ATP molecules

What is NADH oxidized?

• NAD^+

• looses electrons

What is NAD^+ reduced?

• NADH

• gains electrons

What is FADH2 oxidized?

• FAD

• looses electrons

What is FAD reduced?

• FADH2

• gains electrons

What is oxidized/reduced in glycolysis?

Oxidized: the 6-carbon sugar glucose

Reduced: NAD^+ → NADH

Location: Cytosol

What is oxidized/reduced in pyruvate oxidation?

Oxidized: 3-carbon molecule pyruvate

Reduced: NAD^+ → NADH

Location: Mitochondrial matrix

What is oxidized/reduced in Krebs cycle?

Oxidized: Acetyl-CoA (into 2 molecules of CO2)
Reduced: NAD^+ → NADH and FAD → FADH2

Location: Mitochondrial matrix

What is oxidized/reduced in Electron Transport Chain (ETC)?

Oxidized: NADH → NAD^+ and FADH2 → FAD

Reduced: O2 → H2O

Location: Cristae (inner mitochondrial membrane)