Energy in a Cell

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Energy in a Cell : 

Energy in a Cell By: Mr. B. del Rosario 2nd Quarter BIOLOGY Paref-Southridge School

All organisms need energy. : 

All organisms need energy. Energy from the sun is the major source and is trapped by green organisms. This energy is used in cell processes like: active transport, mobility (cilia and flagella), cell division, protein production, etc.



Charged molecules behave like magnets. : 

Charged molecules behave like magnets. Will energy be required to put like poles together?

ATP (Adenosine Triphosphate) : 

ATP (Adenosine Triphosphate)

ATP : 

ATP has phosphate groups and these are charged molecules is the energy-rich molecule that is primarily used in cellular and other biological processes holds energy between the 2nd and 3rd phosphate groups. ATP>ADP>AMP

ATP : 

ATP is similar to rechargeable batteries wherein energy can be stored again after use. (by adding another phosphate to ADP) ATP : battery protein : electronic device


PHOTOSYNTHESIS 6CO2 + 6H2O C6H12O6 + 6O2 Carbon Dioxide + Water = Glucose + Oxygen process that uses the sun’s energy to make simple sugars represented by the chemical equation:


PHOTOSYNTHESIS converts simple sugars into complex carbohydrates that store energy. (ex: starch) Since dependent on sunlight, it must have a means of continuing even at night when sunlight is not available. has 2 phases: light-dependent reactions light-independent reactions


PHOTOSYNTHESIS occurs in the chloroplast, specifically in the thylakoid membranes.

Thylakoid Membranes : 

Thylakoid Membranes have light-absorbing pigments (most common of which is chlorophyll) Wavelength for green light is reflected (not absorbed), thus, leaves are green.

Photosystems : 

Photosystems refer to the cluster of pigments in the thylakoid membranes

Light-Dependent Reactions : 

Light-Dependent Reactions Sunlight strikes chlorophyll in a photosystem. This light energy “excites”/energizes electrons. Electrons are passed from chlorophyll to an electron transport chain embedded in the thylakoid membrane.

“Lost” or “spilled” energy is used for : 

“Lost” or “spilled” energy is used for forming ATP from ADP pumping hydrogen ions into the thylakoid (a gradient is formed, therefore…) stroma thylakoid

Light-Dependent Reactions : 

Light-Dependent Reactions 4. Electrons get re-energized in a second photosystem. 5. At the end of another ETC, electrons are carried to the stroma for later use. 6. NADP+ (an electron carrier) becomes NADPH+ as it transfers the electrons to the stroma. NADP+ can combine with 2 electrons and a H+.

Electrons may run out… : 

Electrons may run out… This is solved by photolysis which also occurs in the first photosystem. Light breaks down H2O into ½ O2, 2 H+, and 2 electrons.

Light-Independent Reactions : 

Light-Independent Reactions series of reactions that use CO2 to form sugars (called “carbon fixation”) take place in the stroma also produces PGAL (phosphoglyceraldehyde), a molecule that is essential during cellular respiration * PGAL a.k.a. G3P (glyceraldehyde-3-phosphate)

The Calvin-Benson Cycle : 

The Calvin-Benson Cycle

PHOTOSYNTHESIS (simplified) : 


Cellular Respiration : 

Cellular Respiration involves breakdown of food molecules by mitochondria to produce ATP has 3 stages: glycolysis, the citric acid cycle, and the electron transport chain Glycolysis is an anaerobic process, does not require oxygen. The citric acid cycle and the electron transport chain are both aerobic.

Glycolysis : 

Glycolysis also refer to page 232

Glycolysis : 

Glycolysis Glyco (sweet/sugar/glucose) + lysis (to split) Glucose (6-carbon compound) is split into 2 molecules of pyruvic acid (3-carbon compound), occurs in the cytoplasm. not very efficient in terms of energy production as it produces only 4 molecules of ATP after starting the process with 2 ATP molecules (net gain of 2 ATP molecules)

Glycolysis : 

Glycolysis uses NAD as its electron carriers; each molecule can carry 2 electrons PGAL from the Calvin cycle may also enter this chemical process. If O2 is present, the pyruvic acid transfers to the mitochondria to begin the aerobic reactions. *Refer to page 232 for the diagram.

The Citric Acid Cycle : 

The Citric Acid Cycle a.k.a. Krebs cycle uses the electron carriers NAD+ and FAD Each electron carrier transfers 2 electrons to the inner membrane of the mitochondrion. (Remember, the mitochondrion has an inner and outer membrane.)

The Citric Acid Cycle : 

The Citric Acid Cycle every turn of the cycle produces: 1 ATP molecule 2 Carbon Dioxide molecules 3 NADH 3 Hydrogen ions 1 FADH 2

The Citric Acid Cycle : 

The Citric Acid Cycle Refer to page 233 for the diagram.

Electron Transport Chain : 

Electron Transport Chain ATP Production during Aerobic Respiration by Oxidative Phosphorylation involving an Electron Transport System and Chemiosmosis

The Electron Transport Chain : 

The Electron Transport Chain occurs in the inner membrane of the mitochondrion very similar to the ETC in the thylakoid H+ ions are pumped continuously, making the inner membrane positively charged. Oxygen is the final electron acceptor at the end of the chain.

Why oxygen is important as the final electron acceptor… : 

Why oxygen is important as the final electron acceptor… It reacts with 4H+ ions and 4 electrons to form 2 H2O molecules. Proteins in the ETC cannot accept electrons unless they are passed on to oxygen. If these proteins cannot accept electrons, the entire chain is blocked, and ATP production stops. ETC adds 32 ATP molecules to the 4 from glycolysis and Krebs cycle.

Total ATP Production : 

Total ATP Production

Cellular Respiration (simplified) : 

Cellular Respiration (simplified)

Fermentation : 

Fermentation provides ATP supply in the absence of O2 2 major types: lactic acid fermentation & alcoholic fermentation happens after glycolysis * NADH and FADH2 cannot continue accepting electrons if O2 is unavailable. Therefore…

Lactic Acid Fermentation : 

Lactic Acid Fermentation FAD cannot be replaced by the cell; however, NAD can be replaced through lactic acid fermentation. 2 molecules of pyruvic acid produced in glycolysis use NADH to form 2 molecules of lactic acid. THIS RELEASES NAD TO BE USED IN GLYCOLYSIS AND FORM 2 ATP MOLECULES. Lactic acid is brought to the liver and converts it into pyruvic acid.

Alcoholic Fermentation : 

Alcoholic Fermentation used by yeast cells and some bacteria produces CO2 and ethyl alcohol also produces 2 ATP molecules * Refer to page 235 for the comparison of fermentaion to cellular respiration.

References : 


References : 

References 7. 8. 9. 10. 11. 12. 13.

References : 

References 14. 15. 16. 17.

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