Cellular Respiration Quiz

Metabolic Pathways

• Biochemical reactions in living cells are organized into pathways, each with specific purposes
• These purposes include extracting energy, storing fuels, synthesizing essential building blocks, and eliminating waste materials
• Metabolic pathways can be visualized as maps, following the fate of metabolites, identifying enzymes, regulation points, and sources of metabolic diseases

Catabolic and Anabolic Pathways

• Catabolism (degradative phase) releases energy from nutrients
• Anabolism (biosynthetic phase) uses energy to synthesize biomolecules

Connection between Catabolic and Anabolic Pathways

• Catabolic pathways converge toward common intermediates
• Anabolic pathways diverge from these intermediates
• Some intermediates are recycled via cyclic pathways

Chemical Logic and Common Biochemical Reactions

• Biochemical reactions follow repeating patterns involving interactions between nucleophiles (electron-rich) and electrophiles (electron-deficient)
• Five general categories: reactions that make or break carbon-carbon bonds; internal rearrangements, isomerizations, and eliminations; free radical reactions; group transfers; redox reactions

Homolytic and Heterolytic Cleavage

• Homolytic cleavage: bond breaks evenly, each atom retains an unpaired electron (radical)
• Heterolytic cleavage: bond breaks unevenly, one atom retains both bonding electrons (carbocation or carbanion)

Kinases, Phosphorylases, and Phosphatases

• Kinases transfer a phosphoryl group from ATP to an acceptor molecule
• Phosphorylases catalyze the addition of a phosphate group (Pi + H) at a bond break.
• Phosphatases catalyze the removal of a phosphoryl group from a phosphate ester.

Phosphorylation

• Phosphoryl group transfer is a central reaction in metabolism, often involving phosphorylation of molecules
• ATP is typically involved in these transfers

Synthases, Synthetases, Ligases, and Lyases

• Synthases catalyze condensation reactions without needing nucleotides like ATP or GTP
• Synthetases catalyze condensation reactions requiring nucleotides such as ATP or GTP
• Ligases catalyze condensation reactions joining atoms using ATP or another energy source
• Lyases catalyze cleavages or additions involving electronic rearrangements

Oxidases and Oxygenases, Dehydrogenases

• Oxidases catalyze oxidation reactions where oxygen is the electron acceptor (oxygen not in product)
• Oxygenases catalyze oxidation reactions where oxygen is the electron acceptor (oxygen in product)
• Monooxygenases incorporate one O atom into the product
• Dioxygenases incorporate two O atoms into the product
• Dehydrogenases catalyze redox reactions involving NAD+ as the electron acceptor (no molecular oxygen involved)

Redox Reactions

• Redox reactions involve electron transfer between reactants
• Oxidation is the loss of electrons; reduction is the gain of electrons
• Conjugate redox pairs are components that participate in redox reactions

Oxidation of Organic Fuel Molecules During Cellular Respiration

• In cellular respiration, glucose is oxidized, and oxygen is reduced
• This process releases energy used to synthesize ATP

The Special Role of ATP

• ATP acts as a link between catabolism and anabolism.
• Energy from catabolism is used to convert ADP to ATP.
• ATP hydrolysis releases energy to make endergonic reactions possible

ATP Provides Energy by Group Transfers

• ATP transfers parts of the molecule, activating substrates, not direct hydrolysis

Phosphate Compounds with High Energy of Hydrolysis

• High-energy phosphate compounds, like PEP, have large, negative ΔG°' for hydrolysis, making them suitable for driving endergonic reactions

Assembly of Informational Macromolecules

• ATP provides energy for synthesis of macromolecules, transport, and muscle contraction processes, often using transfer reactions
• Adenylate kinase (AMPK): important for regulation and maintaining ATP levels

AMPK Enzyme

• AMPK regulates energy metabolism, typically activated by low ATP/high AMP ratio
• Largely for activating glucose and fatty acid uptake and oxidation

Cellular Respiration and Fermentation

• Living cells need outside energy sources for survival
• Some animals eat plants and other animals
• Cellular respiration and fermentation are processes for obtaining energy

Overview: Life is Work

• Energy flows into and out of ecosystems as sunlight, and heat.
• Photosynthesis generates organic molecules using sunlight, water, and carbon dioxide.
• Cells use energy from cellular respiration in organic molecules to regenerate ATP.

Stepwise Energy Harvest via NAD+ and Electron Transport Chain

• Energy is extracted from organic compounds in steps, often involving electron carriers like NAD+.
• NAD+ is an important coenzyme functioning as an oxidizing agent that picks up electrons in the reaction.

NADH passes electrons to the electron transport chain

• Electrons are transferred to the electron transport chain, to O2 in energy-yielding steps, regenerating ATP.

A Few Types of Coenzymes and Proteins Serve as Universal Electron Carriers

• Coenzymes like NAD and NADP+ and others, are derived from or with vitamins, often acting as water-soluble electron carriers.
• Coenzymes often act as enzyme-bound electron carrier, or freely diffusible
• Involved in redox reactions.

Oxidation is Often Synonymous with Dehydrogenation

• Oxidation is often synonymous with dehydrogenation; Dehydrogenation is a reaction where a compound loses two electrons and two hydrogen ions.
• Electrons are transferred directly or as hydrogen atoms.

Metabolism

• Metabolic pathways are regulated to maintain homeostasis, responding to changes in resource availability and needs.
• The quantities of metabolites must sometimes be altered rapidly.

ATP and AMP are Key Cellular Regulators

• ATP and AMP are part of processes regulating metabolic activity such as by adenylate kinase and AMPK(AMP-activated protein kinase).
• A 10% decline in ATP can cause dramatic AMP increases

Glycolysis

• Glycolysis ('splitting of sugar') is the breakdown of glucose into pyruvate. Glycolysis occurs in the cytoplasm and has two phases.
  • Some free energy is stored by converting ATP and NAD+ to ATP and NADH.

Importances of Phosphorylated Intermediates

• Phosphorylated intermediates are important because they prevent the intermediates from leaving the cell, serve as components in enzymatic energy conservation, and lower the activation energy of enzymatic reactions.

Investment and Payoff Phases of Glycolysis

• Glycolysis occurs in two major phases: investment and payoff.
• Investment phase requires energy and makes intermediate compounds for the payoff phase, which produces energy, and NADH and ATP.

The 10-step Summary of Glycolysis

• Summarized steps involved in glycolysis

Anaerobic Respiration and Fermentation

• Fermentation allows ATP production in the absence of oxygen.
• In the absence of oxygen, the electron transport chain will cease operations.
• Glycolysis couples with fermentation/ anaerobic respiration in the absence of oxygen.

Fermentation

• Fermentation is an alternative way of obtaining energy without oxygen.
• Uses substrate-level phosphorylation, not electron transport chains, to renew NAD+.
• Two common types of fermentation are alcohol and lactic acid fermentation

Types of Fermentation: alcohol and lactic acid fermentation

• In alcohol fermentation, pyruvate is converted to ethanol, releasing CO₂
• In lactic acid fermentation, pyruvate is reduced to lactate, preventing CO₂ release

NADH

• A crucial coenzyme that shuttles electrons during cellular respiration.

Test your knowledge on the key processes of cellular respiration. This quiz covers glycolysis, ATP role, and metabolic pathways, providing insights into energy harnessing from glucose. Perfect for biology students seeking to enhance their understanding of cellular metabolism.