Metabolism, Cellular Respiration, and Photosynthesis: Study Guide for BIO 1111 Exam 3

Metabolism

Catabolism vs. Anabolism

Metabolism encompasses all chemical reactions in a cell, divided into two main types: catabolism and anabolism.

• Catabolism: Breakdown of complex molecules into simpler ones, releasing energy (e.g., cellular respiration).

• Anabolism: Synthesis of complex molecules from simpler ones, requiring energy input (e.g., protein synthesis).

• Comparison: Catabolic pathways are exergonic (energy-releasing), while anabolic pathways are endergonic (energy-consuming).

Thermophilic Bacteria in Hot Springs

• Some bacteria are active in hot springs due to specialized enzymes and membrane structures that remain stable and functional at high temperatures.

• These adaptations prevent denaturation and allow metabolic processes to continue efficiently.

Exergonic Reactions

• Exergonic reactions release free energy (ΔG < 0), are spontaneous, and often drive cellular work.

• Example: Hydrolysis of ATP.

ATP Structure and Comparison

• ATP (Adenosine Triphosphate): Consists of adenine, ribose, and three phosphate groups.

• High-energy phosphate bonds store potential energy.

• Compared to ADP (adenosine diphosphate) and AMP (adenosine monophosphate), ATP has more phosphate groups and higher energy content.

Key Definitions

• Entropy: Measure of disorder or randomness in a system.

• Energy Coupling: Use of exergonic process to drive an endergonic one.

• Bioenergetics: Study of how organisms manage energy resources.

• Feedback Regulation: Process where the end product of a pathway regulates its own production.

• Catalyst: Substance that increases reaction rate without being consumed.

• Enzyme: Biological catalyst, usually a protein, that speeds up reactions by lowering activation energy.

• Thermodynamics: Study of energy transformations.

Increasing Reaction Rate

• Increase temperature (within limits), substrate concentration, or enzyme concentration.

• Use of catalysts (enzymes).

Chemical Energy and Laws of Thermodynamics

• Chemical Energy: Potential energy stored in chemical bonds.

• First Law (Conservation of Energy): Energy cannot be created or destroyed, only transformed.

• Second Law (Increasing Entropy): Every energy transfer increases the entropy of the universe.

ATP Hydrolysis

• Breaking bonds between phosphate groups in ATP is a hydrolysis reaction.

• When ATP is hydrolyzed, the released phosphate can be transferred to another molecule (phosphorylation) or remain inorganic (Pi).

Cellular Respiration

Oxidative Phosphorylation

• Direct energy source for ATP synthase: Proton (H+) gradient across the inner mitochondrial membrane.

• Final electron acceptor in aerobic respiration: Oxygen (O2).

Fermentation vs. Cellular Respiration

• Fermentation: Anaerobic process, produces less ATP, end products include lactate or ethanol.

• Cellular Respiration: Aerobic, produces more ATP, end products are CO2 and H2O.

Redox Reactions

• Redox reactions transfer electrons, releasing energy to establish a proton gradient.

• Oxidation: Loss of electrons.

• Reduction: Gain of electrons.

• Reducing Agent: Donates electrons.

• Oxidizing Agent: Accepts electrons.

Stages of Cellular Respiration

• Glycolysis: Occurs in cytosol; glucose (6C) → 2 pyruvate (3C), produces 2 ATP (substrate-level), 2 NADH.

• Citric Acid Cycle (Krebs Cycle): Occurs in mitochondrial matrix; acetyl-CoA (2C) enters, cycle regenerates oxaloacetate, produces 2 ATP, 6 NADH, 2 FADH2 per glucose, CO2 released.

• Oxidative Phosphorylation: Occurs in inner mitochondrial membrane; electron transport chain and chemiosmosis, produces ~26-28 ATP per glucose.

ATP Production

• Substrate-level phosphorylation: Direct transfer of phosphate to ADP (glycolysis, citric acid cycle).

• Oxidative phosphorylation: ATP synthesis powered by proton gradient (electron transport chain and chemiosmosis).

Fermentation Types

• Alcohol fermentation: Produces ethanol and CO2.

• Lactic acid fermentation: Produces lactate, no CO2 released.

Electron Carriers

• NAD+ and FAD: Electron acceptors.

• NADH and FADH2: Electron donors to the electron transport chain.

Electron Transport Chain and Chemiosmosis

• As electrons move down the chain, protons are pumped from the matrix to the intermembrane space, creating a gradient.

• Chemiosmosis: Flow of protons back into the matrix through ATP synthase, driving ATP production.

• Links to oxidative phosphorylation and energy storage.

Citric Acid Cycle Details

• Called a cycle because the starting molecule (oxaloacetate) is regenerated.

• Substrate: Acetyl-CoA.

• Per glucose, 2 acetyl-CoA enter the cycle.

Products of Cellular Respiration (per glucose)

Stage	ATP	NADH	FADH2	CO2
Glycolysis	2	2	0	0
Citric Acid Cycle	2	6	2	4
Oxidative Phosphorylation	~26-28	0	0	0

Fermentation Products

• Alcohol fermentation: Ethanol, CO2.

• Lactic acid fermentation: Lactate.

Photosynthesis

Light Reactions

• Occur in the thylakoid membrane.

• Light energy excites electrons in pigment molecules, powering the electron transport chain.

• Produce ATP and NADPH via chemiosmosis (H+ gradient from stroma to thylakoid space).

• Light-dependent.

Synthesis (Calvin Cycle) Reactions

• Occur in the stroma.

• Light-independent (do not require light directly).

• Require CO2, ATP, and NADPH.

• Fix CO2 into simple sugars.

Electron Flow in Photosynthesis

• Electrons flow from water → Photosystem II → Photosystem I → NADP+ (forming NADPH) → Calvin Cycle.

C4 vs. CAM Plants

Feature	C4 Plants	CAM Plants
Carbon Fixation Enzyme	PEP carboxylase	PEP carboxylase
Rubisco Role	Not used for initial fixation	Not used for initial fixation
Separation	Spatial (different cells)	Temporal (same cell, different times)
Example	Corn	Cacti

Photophosphorylation vs. Oxidative Phosphorylation

• Both use chemiosmosis to generate ATP.

• Photophosphorylation: Driven by light energy in chloroplasts.

• Oxidative phosphorylation: Driven by energy from electron transfer in mitochondria.

Role of Antennae Pigment Molecules

• Harvest photons and transfer light energy to chlorophyll reaction centers in the thylakoid membrane.

Photosystem II vs. Photosystem I

Feature	Photosystem II	Photosystem I
Order in Pathway	First	Second
Primary Function	Splits water, releases O2, generates ATP	Produces NADPH
Electron Source	Water	Electron transport chain

Photosynthesis vs. Respiration

• Both use chemiosmotic mechanisms for ATP synthesis.

• Photosynthesis stores energy in glucose; respiration releases energy from glucose.

Electron Acceptors and Donors in Photosynthesis

• NADP+: Electron acceptor.

• NADPH: Electron donor in the Calvin Cycle.

Light Wavelength and Energy

• Shorter wavelength = higher energy; longer wavelength = lower energy.

• Blue/violet light has more energy than red light.

Photorespiration

• Occurs when rubisco uses O2 instead of CO2.

• Consumes ATP, releases CO2, does not produce sugar.

Additional info:

• ATP hydrolysis equation: $\mathrm{ATP} + \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{ADP} + \mathrm{P}_i + \text{energy}$

• Overall cellular respiration equation: $\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 + 6\mathrm{O}_2 \rightarrow 6\mathrm{CO}_2 + 6\mathrm{H}_2\mathrm{O} + \text{energy}$

• Overall photosynthesis equation: $6\mathrm{CO}_2 + 6\mathrm{H}_2\mathrm{O} + \text{light energy} \rightarrow \mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 + 6\mathrm{O}_2$