Energy in Living Organisms

• All living organisms need energy to stay alive
• This energy comes from the Sun (or chemicals)
• Plants use photosynthesis to make organic molecules
• Plants and animals break down these molecules into ATP
• ATP is the energy source for life processes

What is energy?

• Energy is the ability to do work
• Kinetic energy is the energy of motion
• Potential energy is stored energy

Other facts about energy

• Energy takes forms like light, heat, sound, and electricity, and can change forms
• Energy cannot be created or destroyed
• Energy is measured in joules (J)

Why organisms need energy

• Organisms need energy to maintain order

Specifically, energy is needed for

• Anabolism: Building larger molecules
• Movement: Internal (e.g., blood circulation) and external (e.g., locomotion)
• Active transport: Moving ions and molecules against concentration gradients
• Maintenance and repair of cells and organelles
• Maintaining body temperature (in endothermic animals)

Energy and metabolism

• Energy flow in living systems:
  • Plants convert sunlight into chemical energy
  • Chemical energy is converted into ATP
  • Cells use ATP to do work

Metabolism

• All reactions within organisms
  • Anabolism is building complex molecules (requires energy)
  • Catabolism is breaking down molecules (releases energy)

Free energy

• Not all energy is converted, some is lost as heat
• Free energy is available at constant temperature and pressure

Endergonic reaction

• Products have more energy than reactants and require energy input

Exergonic reaction

• Products have less energy than reactants and release energy

Activation energy

• Energy is needed to start a chemical reaction
• Catalysts (e.g. enzymes) lower activation energy
• Reactions can be reversible

Energy input

• External energy is needed to continue the process
• The Sun is the ultimate energy source

Adenosine triphosphate (ATP)

• ATP is the universal energy currency of cells

ATP's features

• One-step reaction for immediate energy
• Easily hydrolysed to release energy
• Recycled from ADP
• Small and mobile
• Water-soluble
• The released ATP has a recyclable efficiency

Structure of ATP

• Adenine is a nitrogen-containing organic base
• Ribose is a 5-carbon sugar molecule
• There are three phosphate groups
• The three phosphate groups are key, the bonds are unstable due to negative charges

Synthesis of ATP

• ATP can be reformed by adding inorganic phosphate to ADP, catalysed by ATP synthase
• Photophosphorylation happens in chloroplasts
• Oxidative phosphorylation happens in mitochondria
• Substrate-level phosphorylation happens during glycolysis

Chemiosmotic Theory

• Process of ATP synthesis
• Hydrogen atoms are split into protons and electrons
• Electrons pass along the electron transport chain and release energy
• Protons are pumped into the intermembrane space

Accumulation

• Protons accumulate in the inter-membranal space, creating an electrochemical gradient

Inner Mitochondrial membrane properties

• The inner mitochondrial membrane is impermeable to protons

Protons return

• Protons diffuse through chemiosmotic channels in ATP synthase

Phosphorylation reaction

• The phosphorylation reaction combines ADP with inorganic phosphate
• The phosphorylation reaction is catalysed by ATP synthase
• Protons recombine with electrons to form hydrogen and then water

Role of ATP

• ATP is the immediate energy source of a cell

The role of ATP in

• Anabolic processes
• Movement (muscle contraction, etc.)
• Active transport
• Secretion
• Activation of chemicals

Respiration - Glycolysis

• Cellular respiration
• Converts food energy for biological work
• Glucose is the main fuel

Respiration

• C6H12O6 + 6O2 —> 6CO2 + 6H2O + energy

Aerobic respiration process

• Glycolysis: Glucose to pyruvate
• Link reaction: Pyruvate to acetyl coenzyme A and carbon dioxide
• Krebs cycle: Acetyl coenzyme A into a cycle, producing reduced coenzymes and some ATP
• Oxidative phosphorylation: Oxidation of reduced coenzymes, ATP synthesis, oxygen as final electron acceptor

Anaerobic Respiration

• Respiration involves gylcolysis, creating pyruvate, but the pyruvate is further metabolized to ethanol or lactate

Glycolysis

• Glycolysis occurs in the cytoplasm
• Glycolysis converts glucose into two molecules of pyruvate

Four stages of smaller groups

• Activation of Glucose
• Splitting of the phosphorylated hexose sugar
• Oxidation of triose phosphate
• The production of ATP

Outcome summary

• Two molecules of ATP
• Two molecules of reduced NAD
• Two molecules of pyruvate

Respiration Details

• Glycolysis is an early biochemical process, that occurs in the cytoplasm of cells
• Glycolysis does not require any organelle or membrane, and occurs in aerobic and anaerobic conditions
• In the absence of oxygen, pyruvate is fermented

Link Reaction and Krebs Cycle

• Pyruvate molecules need to be oxidized for the Krebs cycle

The Link Reaction

• Pyruvate from cytoplasm is transported into mitochondrial matrix

Pyruvate undergoes

• Decarboxylation: removal of carbon dioxide by pyruvate decarboxylase
• Oxidation: pyruvate oxidation reduces NAD
• Formation of acetyl coenzyme A

Importance of Acetyl Coenzyme A

• Most molecules used for energy are made into acetyl coenzyme A before entering the Krebs cycle

Krebs Cycle

• A series of eight enzyme-catalysed steps that take place in the matrix of mitochondria

Events can be summarised as:

• Acetyl coenzyme A combines with oxaloacetate to produce citrate
• Citrate loses CO₂ and hydrogen to produce a 5-carbon compound, carbon dioxide, and reduced NAD
• Decarboxylation and dehydrogenation produces oxaloacetate
• The 4-carbon molecule combines with acetyl coenzyme A to begin the cycle

Role of Coenzymes

• Coenzymes carry hydrogen atoms/electrons from one compound to another -NAD transports hydrogen -FAD transports hydrogen

Summary Of NAD and FAD reaction

• Hydrogen atoms dissociate into protons and electrons
• NAD+ combines with hydrogen ions and electrons to form NADH and a hydrogen ion

Respiration

• Coenzyme A carries an acetyl group in the formation of acetyl CoA from pyruvate
• Acetyl CoA the enters Kreb's Cylce

The Krebs cycle significance

• Krebs significances are:
• Breaks down macromolecules
• Produces hydrogen atoms
• Regenerate the starter material
• Source of intermediate compounds
• Produces hydrogen atoms needed for ATP

Oxidative Phosphorylation

• Converts pyruvate to carbon dioxide and hydrogen atoms, happens during Glycolysis
• Hydrogen (electrons) is a potential energy, most ATP is synthesised here

Mitochondria

• The Mitochondria are sites of the link reaction, Krebs cycle and oxidative phosphorylation
  • The inner folded membrane (cristae) enables to oxidative phosphorylation
  • The ATP synthase contains ATP synthase for synthesising ATP

Mitochondria structure

• the matrix contains enzymes needed for the link reaction and Krebs cycle
• Hydrogen (ph) gradient results in synthesising ATP.

Oxidative Phosphorylation process

• Hydrogen is produced in cell respirtation combines with special molecules, these molecule have hydrogen atom with split proton state

Carriers

• First carrier accepts electrons is NADH hydrogenase
• Passing of electrons is called electron transport chain
• Causes catalysis reactions that produce protons

ATP synthesis

• As protons pass through ATP synthase, ADP is combined with inorganic phosphate to produce ATP
• The molecule forms a diffusion force and its called chemiosmosis,
• The Oyxgen is combined with electrons, and with hydrogen to form water.

Importance

• Oxygen removes hydrogen atoms at the end of the chain.
• Cyanide poison inhabits this removal and causes the Krebs cycle to halt and the cell to die and accumulate.

Anaerobic Respiration and Energy Yields

• In the absence of oxygen, only the glycolysis process can be done for the potential source of ATP
• products of pyruvate and hydrogen must be constantly removed for glycosis to continue

Eukaryotic cells, the Ferementation process

• Alcoholic fermentation and Lactate fermentation are the processes

Alcoholic Fermentation

• Alcoholic fermentation: forms ethane
• Occurs in bacteria (e.g. yeast)
• Occurs in fungi
• Occurs in plant cells

Reaction summary:

Rice adaptation

• Tolerance to ethanol

Lactate Fermentation in animals

• Overcoming a temporary shortage of oxygen.
• Cori cycle: Converts to glycogen in the liver
• If oxygen isn't there individual builds an oxygen debt.