Enzymes, Metabolism, & Cellular Respiration

Photosynthesis & Global Warming

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Photosynthesis - Capturing the Energy in Light

All Organisms Use Energy to Carry Out the Functions of Life

• Plants are the primary producers

• The use direct sunlight for energy through a process called photosynthesis

• Autotrophic vs. Heterotrophic

• What is the difference?

Photosynthesis - Involves a complex set of chemical reactions that form a biochemical pathway.

Why are plants green?

• Chlorophyll– Two types:

• Chlorophylla and Chlorophyllb

Accessory pigments

• Carotenoids

• Xanthophylls– Pigments seen in FALL!!!

The Balance Sheet for Photosynthesis

• Light Reaction– Produces stored energy

in the form of ATP and NADPH from light energy.

• Calvin Cycle– Produces organic

compounds, using the energy stored in ATP and NADPH during the light reactions.

The Simplest Chemical Equation for Photosynthesis:

CO2 + H2O + light energy -> (CH2O) + O2

The Balanced Chemical Equation for Photosynthesis:

6CO2 + 6H2O+ light energy -> C6H12O6 + 6O2

Alternative Pathways

• C3 plants fix carbon exclusively through the Calvin Cycle, because the three carbon PGA is formed.

• Plants that do not produce the three carbon PGA live in hot or dry climates and utilize alternative pathways.– C4 pathway enables plants to fix into four carbon

compounds. Examples include: corn, sugar cane, and crabgrass.

– Cactuses, pineapples, and certain other plants that live in hot, dry climates fix carbon through the CAM pathway.

Summing it up…

• A plant’s environment can effect its rate of photosynthesis.

• Light intensity can also be a factor.

• As well as, CO2 levels and temperature.

Photosynthesis

Cellular

Respiration

Cellular Respiration

Cellular Respiration

C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy (ATP)

How are Photosynthesis and Cellular Respiration Related?

Photosynthesis– Uses Light Energy

– Uses Carbon Dioxide

– Uses Water

– Makes Glucose

– Makes Oxygen

– Happens in the Chloroplasts

6CO2 + 6H2O + light energy -> C6H12O6 + 6O2

Cellular Respiration– Makes Energy (ATP)– Makes Carbon Dioxide– Makes Water– Uses Glucose– Uses Oxygen

– Happens in the Mitochondria

C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy (ATP)

Cellular Respiration

• The food (glucose) is broken down into CO2 and H2O, and energy (ATP) is released.

• C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy (ATP)

• Cellular respiration takes place in the mitochondria. © The Virtual Cell

Textbook

1st Step in Cellular Respiration – Glycolysis

• Breakdown or splitting of glucose (6 carbons) into two 3-carbon molecules called pyruvic acid

• Does not need oxygen in any of its chemical reactions• Serves as the first step in a variety of anaerobic and

aerobic reactions• Happens in the cytoplasm of cells• FYI: The one metabolic pathway found in all living

organisms • Net yield of two ATP molecules for every molecule of

glucose that is converted into pyruvic acid

Molecular Pictures

Glucose

2 molecules of Pyruvic Acid

Images taken from: http://biology.clc.uc.edu/courses/bio104/cellresp.htm

2 ATP molecules

Fermentation

• Pyruvic acid molecules are turned into some “waste” product

• Occurs in anaerobic situations

• Two of the most common types of fermentation are:– lactic acid and alcoholic fermentation

Lactic Acid Fermentation

• Done by some fungi, some bacteria like the Lactobacillus acidophilus in yogurt, and sometimes by our muscles.

• The 3-carbon pyruvic acid molecules are turned into lactic acid

• This process is used in making cheese and yogurt. • Once our muscles form lactic acid, they can’t do anything

else with it, so until it is gradually washed away by the blood stream and carried to the liver (which is able to get rid of it) until it is converted back to pyruvic acid when oxygen becomes available

Alcoholic Fermentation

• Done by yeast and some kinds of bacteria.

• The “waste” products of this process are ethanol and carbon dioxide (CO2).

• This process is used in making bread, beer, and wine.

Fermentation – Two Major Types

Lactic Acid Fermentation

• Muscles produce lactic acid

• Causes muscles to become tired

• Occurs after exercise

• Why does this happen?– Your muscle cells can’t get

the oxygen they need to produce ATP by cellular respiration.

Alcoholic Fermentation• Yeast cells produce carbon

dioxide and alcohol• Example: carbon dioxide

causes bubbles to form in bread

• Why does this happen?– Yeast cells eat sugar and

expel carbon dioxide, which causes bubbles to form in bread.

Anaerobic Pathways as the oldest known way of producing ATP???

• Glycolysis is probably the oldest known way of producing ATP. There is evidence that the process of glycolysis predates the existence of O2 in the Earth’s atmosphere and organelles in cells: – Glycolysis does not need oxygen as part of any of its chemical

reactions. It serves as a first step in a variety of both aerobic and anaerobic energy-harvesting reactions.

– Glycolysis happens in the cytoplasm of cells, not in some specialized organelle.

– Glycolysis is the one metabolic pathway found in all living organisms.

– Total Efficiency of Glycolysis 3.5%

2nd Step of Cellular Respiration – Krebs Cycle

• In prokaryotes, the reactions of the Krebs Cycle take place in the cytosol of the cell.

• In eukaryotes, the reactions take place in the mitochondrial matrix

• The pyruvic acid produced in glycolyis diffuses across the double membrane of the mitochondria into the mitochondrial matrix where it reacts with a molecule called coenzyme A to form acetyl CoA, which then enters the Krebs Cycle

• In short…the Krebs Cycle breaks down acetyl CoA, produces CO2, hydrogen atoms, and ATP

Krebs Cycle Cont…

• Recall that…in glycolysis one glucose molecule produced two pyruvic acid molecules, which can then form two molecules of acetyl CoA.

• Thus…one glucose molecule causes two turns of the Krebs Cycle.

• The two turns produce:– Six molecules of NADH -> electron transport chain– Two molecules of FADH2 -> electron transport chain– Two molecules of ATP -> can be used as energy– Four CO2 molecules -> released by the organism

3rd Step in Cellular Respiration – The Electron Transport Chain

• The concentration gradient drives the synthesis of ATP by chemiosmosis, the same process that generates ATP in photosynthesis!!!

• ATP is produced when NADH and FADH2 release hydrogen atoms

• By combining with both electrons and protons (H+), oxygen forms water!!!Here is the formula: O2 + 4e- + 4H+ -> 2H2O

How many ATP molecules are made in aerobic respiration?

• 38 ATP per one glucose molecule!!! WOW!!!

• FYI: the actual number of ATP molecules generated through aerobic respiration varies from cell to cell. Most produce 36 ATP molecules per glucose molecule.

How efficient is aerobic respiration?

• 66% compared to 3.5% of glycolysis.

• This means that aerobic respiration is 20 times more efficient than anaerobic!!!

• It is even more efficient than a car engine which is only 25%!!!

Summing Up Cellular Respiration…• Cellular respiration provides the ATP that all cells

need to support the activities of life.• Cells also need specific organic compounds (sugars

and starches) from which to build macromolecules, which not always come from the food we eat.

• That is why Glycolysis and the Krebs Cycle are used by cells to make the compounds that are missing in food.

C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy (ATP)

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