Energy for Life

• Plants, caterpillars, and birds, like all living things, require energy to live.
• Organisms need energy for activities like running or sleeping, with every cell requiring energy for its processes.

Energy for Life

• Energy enables work.
• Energy is evident in living organisms through activities such as running, flying, and eating, alongside internal bodily functions.
• All life forms require energy for metabolism.
• Energy capture starts the energy flow, it is transformed, utilized, and dissipated as heat.
• As energy cannot be recycled, continuous input is essential for all organisms.

How Organisms Obtain Energy

• Organisms typically obtain chemical energy from food, which comprises organic molecules that store energy.
• Animals obtain food in varied ways to acquire energy.
• Autotrophs create their own nourishment and are often called producers.
• Most autotrophs, including plants, algae, and photosynthetic bacteria, use sunlight to produce food via photosynthesis.
• Food produced by autotrophs sustains not only themselves but also other organisms, marking them as vital starting points in food chains.
• Heterotrophs are organisms that cannot produce their own food so they consume autotrophs or other heterotrophs, this includes animals, fungi and single-celled organisms.

Energy-Giving Molecules: Glucose and ATP

• All living organisms use glucose & ATP as energy-giving molecules.
• Plants synthesize glucose during photosynthesis: this process uses light, water, and carbon dioxide, with the chemical energy being stored.
• Glucose is transported via blood and absorbed by cells as an energy source in humans.
• Cellular respiration, a reverse reaction of photosynthesis, releases the stored energy in glucose.
• ATP molecules store smaller energy amounts but release sufficient energy for cellular work and serves as the cell's energy carrier.
• ATP is produced during the initial phase of photosynthesis and used during the second, it also provides energy for cellular processes.
• Energy from ATP is discharged through the release of one of its three phosphates, transforming it from ATP to ADP (adenosine diphosphate).

Photosynthesis in Producers

• Energy flow in living organisms starts with photosynthesis in producers.
• This process stores solar energy within the chemical bonds of glucose.
• Cellular respiration breaks these bonds, releasing ATP.
• Photosynthesis and cellular respiration are complementary processes, with the products of one being the reactants of the other.
• Both processes are vital for energy storage, release in living things, and oxygen recycling on Earth.

Photosynthetic Organelles

• Photosynthetic pigments are in photosynthetic organisms.
• These pigments capture light for photosynthesis.
• Plants have two pigment categories, chlorophylls and carotenoids.
• Chlorophylls a and b are green, absorbing wavelengths of light of red, blue, and violet ranges.
• Carotenoids are yellow, orange, and red pigments, absorbing blue, green, and violet light.
• Phycobilins, in red algae makes them reddish and absorb blue and green light.
• Chloroplasts are cell organelles in plants and algae which contains grana (granum), where light reactions occur, being made of thylakoids.
• Thylakoids are the location of Photosystem I (PSI) & Photosystem II (PSII).
• Photosystems are groups of molecules that are part of photosynthesis, including chlorophyll.
• Light-dependent reactions of photosynthesis occur in thylakoid membranes.
• The stroma, outside the thylakoids, is where the Calvin cycle happens.
• Photosystems act as the thylakoid membrane's light-harvesting complexes.
• Each thylakoid contains hundreds of photosystems each having a reaction center with chlorophyll a and other pigments which direct energy to chlorophyll a.
• Photosystems are named in order of discovery although PSII operates before PSI.
• PSI absorbs light optimally at 680 nm (P680).
• PSII absorbs best at 700 nm (P700).

Significance of Photosynthesis

• Photosynthesis is seen as Earth's most vital life process.
• It provides over 99% of the energy for living things by converting light energy into chemical energy and releasing oxygen.
• Photosynthesis involves many reactions, summarized as: 6CO2 + 12H2O → C6H12O6 + 6H2O + 6O2

Stages of Photosynthesis

• Photosynthesis occurs in two stages: light-dependent reactions (Stage I) & light-independent reactions (Stage II).

• Stage I utilizes light energy to produce ATP and NADPH which power Stage II and also releases oxygen as a waste product.

• During Stage II, also known as the Calvin cycle, ATP and NADPH are used to create glucose, simple sugars, starch, sucrose, fructose, and other carbohydrates.

• Stage 1 light-dependent reactions, occur in the thylakoid of the chloroplast, are shown in Figure 3, include several steps.

• Units of light (photons) impact a molecule of chlorophyll in PSII. The chlorophyll a absorbs and energizes two electrons, allowing them to leave.

• Water splits, replacing the lost electrons in chlorophyll a, releasing hydrogen ions into the thylakoid membrane.

• Oxygen atoms combine, generating oxygen molecules that are released.

• Two excited electrons go from PSII through an electron transport chain with plastoquinone (PQ), complexes of cytochromes, ending in PSI.

• Energy from the electron flow pumps hydrogen ions into the thylakoid membrane.

• This process of electron flow provides energy to produce ATP by chemiosmosis and a gradient forms that drives hydrogen ions back to the stroma through ATP synthase.

• ATP synthase acts as a channel protein that provides ADR another phosphate group (Pi), forming ATP.

• The Calvin cycle gains energy from this process.

• When electrons reach PSI, light energy is absorbed again, re-energizing chlorophyll a, before capture.

• Nicotinamide adenine dinucleotide phosphate (NADP+) gains 2 H ions via PS II forming NADPH.

• The newly formed cofactor carries the hydrogens, reducing and carrying them to the Calvin cycle to make glucose.

• Light-independent reactions take place in the stroma and do not need direct light.

• Melvin Calvin won a Nobel Prize in 1961, as the first scientist to map out the Calvin cycle reactions.

• The chemical energy from NADPH and ATP from the light-dependent reactions are used to make glucose, with three major steps: carbon fixation, reduction reactions, and regeneration.

Carbon Fixation

• Carbon dioxide (CO2) from the atmosphere joins with ribulose-1,5-biphosphate (RuBP), a five-carbon (5-C) sugar, to make RuBisCO.
• Ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO) breaks down to two molecules of 3-phosphoglycerate (3-PGA).

Reduction Reactions

• The 3-PGA molecules take in energy from ATP and rearrange to form glycerate-3-phosphate (G3P).
• A single G3P molecule becomes glyceraldehyde-3-phosphate (PGAL), the carbohydrate precursor to glucose and other sugars, while the remaining G3P regenerates.

Regeneration of RuBP

• Remaining G3P molecules use more ATP to revert back into RuBP, therefore finishing the cycle.

Cellular Respiration

• Cells retrieve stored energy in glucose to synthesize ATP through cellular respiration.
• This process aims to convert stored energy into a usable form, like ATP, for cells to carry out functions.
• C6H12O + 6O2 → 6CO2 + 6H2O + ATP

3 Stages of Cellular Respiration

• Glycolysis: initial stage.
• Krebs cycle: cyclical series of reactions.
• Electron transport chain (ETC): final stage.

Glycolysis: Stage 1

• Glycolysis involves one (1) molecule of 6-C glucose to be broken down into 3-C pyruvates or pyruvic acids along with the release of ATP.

• This step occurs in the cytosol.

• Glycolysis involves enzymes.

• This proceeds when two (2) ATP molecules donate energy: ATP molecules donate energy to the glucose with enzyme hexokinase produces glucose-6-phosphate.

• Enzyme phosphoglucose promotes the rearrangement: atoms producing isomer fructose-6-phosphate.

• Action of enzyme phosphofructokinase: promotes ATP molecule phosphate transfer, producing fructose-1,6-bisphosphate.

• Help of enzyme aldolase results molecules: splitting into two (2) molecules having three (3) carbon backbones.

• Molecules include dihydroxyacetone phosphate and glyceraldehyde-3-phosphate.

• Triosephosphate isomerase interconverts both molecules of dihydroxyacetone phosphate and glyceraldehyde-3-phosphate yielding two molecules of glyceraldehyde-3-phosphate or 3-phosphoglyceraldehyde (PGAL).

• In another step hydrogen (H) coming from PGAL is transferred to nicotinamide adenine dinucleotide (NAD+) which forms NADH.

• Phosphate (Pi) aids step is the cytosol of the cell to oxidize the two (2) molecules of PGAL yielding two (2) 1,3-bisphosphoglycerate.

• The enzyme involved is dehydrogenase.

• With the support of phosphoglycerate kinase: 1,3-bisphosphoglycerate is transferred to ADP produces ATP.

• Of each of 1,3-bisphosphoglycerate, which gives two (2) ATP with two (2) 3-phosphoglycerate molecules.

• Transfer of phosphate molecules from 3-phosphoglycerate with phosphoglyceromutase enzyme's support.

• Molecules formed from the third to the second carbon are 2-phosphoglycerate.

• A H2O molecule is released forming phosphoenolpyruvic acid (PEP).

• Phosphate is transferred from PEP aiding pyruvic acid creating pyruvic acid and ATP molecules.

Glycolysis Summary

• A single glucose molecule yields two 3-C pyruvates, four ATP, two NADH, and two water molecules. Yields just two ATP molecules, since two are spent, and so the real output is just two molecules.

Stage 2: Kreb's Cycle

• A cyclical series of reactions controlled by enzymes.
• Occurs in the matrix of the mitochondria.
• The Citric Acid Cycle (CAC) can also be referred to the Tricarboxylic Acid Cycle (TCA), as it yields citric acid. Pyruvic acids yielded during glycolysis are required.
• Its major role is to create molecules of NADH and FADH, later used within the process of chain transport.
• Coenzyme-A (CoA) combines resulting in A crucial preliminary reaction: pyruvate forming acetyl-CoA assisted through enzyme pyruvate dehydrogenase: conversion also yields CO2 and NADH.
• Then, Kreb cycle begins, with the Acetyl-CoA the 4-C molecule creates isocitrate.
• Citrate's aid now undergoes a series of reactions that releases energy -OH group citric acid.
• Water molecule is also returned to another position.
• Molecule forms with the help of dehydrogenase catalyst: - oxidation forming ketoglutarate. The byproducts of this reaction are NADH and CO2 gas.
• The - forms ketoglutarate molecule is added in its position. Then this decarboxylation happens and then becomes molecule is yielded after which loses and a coenzyme.

Kreb Cycle - CoA conversion to Succinate

• Acetyl-CoA by catalyst reaction that also yields a guanosine.
• Molecule is produced by a high-energy reaction and then is used by cells the molecule phosphate the then frees the yields as ATP reaction occurs with the same way.
• Two (2) removal of and the product called FAD by succinate's dehydrogenate the production is catalyzed is then aided hydrogen's from succinate enzyme.
• Water molecule aids it as fumarase that the production is malate's conversion from the addition of addition.
• During malate that catalyst by cycle the is aided in malate that aids regeneration, through oxolacetate.
• Pyruvate molecules were generated resulting twice as the the two of them occur: each process as high byproduct one ATP.

The Electron Transport Chain (ETC)

• A collection of photon pumps located on the inner mitochondrial membrane.
• Is the stage of cellular respiration.
• NADH's/from Krebs's are transferred for ADP in generating ATP.
• This process goes by the name of oxidative phosphorylation.
• Peter Mitchell termed it Chemiosmotic, an mechanism found in cells during This energy coupling.
• Stored energy comes from the addition gradient phosphate ATP is provided by a molecule's proton.
• When the concentration across inner levels membrane is higher then what there is available outside, This is due in helping gradients concentration, chemiosmotic and by ions which is lower membrane inner help.
• The gradients power synthesis when ions transport molecule by ATP which helps combine electrons forms water molecule.

Anaerobic Respiration

• Oxygen is present and aerobic respiration occurs.
• Muddy, harsh conditions that lacks O2 and thrives.
• Organism is exposed to anaerobic situations, it suffers and is called anaerobes that are obligate.
• Anaerobic is when cellular respiration has to occur without any O2 being involved.
• Aerobic cell does anaerobic when O2. There are two distinct fermentations: those are lactate and alcoholic fermentations.
• Ethanol and CO2 is also and then the arrangement: to produce alcohol fermentation releases the pyruvate to rearrange, then its CO2 that results.
• Is used for wide use industry: Saccharomyces is and under production by a CO2 gas bakers that rise the yeast.
• Juices and sugars forms beer and wine.

Additional Notes

• Pyruvate becomes of the electrons that the from produced: two NADH, lactate, ATP, in cells produced.
• Muscle cells goes fermentation can occur during that cant blood that results acids burns.
• With O2 as back from pyruvate in the liver.
• With turn bacteria makes lactate that turn milk sour yogurt by production cells.
• Do breakdown, only has used, or for single cellular energy.