Endosymbiotic Theory - WordPress.com · Endosymbiotic Theory-suggests that mitochondria and...
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Endosymbiotic Theory
� The oldest known fossils are 3.5 bya = stromatolites which are rock like layers of bacteria and sediment.
� Earliest life forms may have emerged as early as 3.9 bya.
� Earliest prokaryotes were chemoheterotrophs� Used chemicals in the environment
for food and energy� There was still little oxygen in the
atmosphere and so they must have been anaerobic
Evolution of Prokaryotes
� Some prokaryotes developed the ability to convert light energy into chemical energy = photosynthesis
� These organisms released oxygen as a product of photosynthesis� Oxygen gas accumulated in the atmosphere
� Increase in oxygen created a “crisis”� Some organisms died
� Other organisms evolved more efficient metabolic pathways that used oxygen for respiration
Evolution of Photosynthetic Organisms
� Eukaryotic cells differ from and are much more complex than prokaryotes
� Fossil evidence suggests that eukaryotic cells may have been present 2.7 bya
Evolution of Eukaryotes
� Endosymbiotic Theory - suggests that mitochondria and chloroplasts were formerly small prokaryotes living within larger cells
� Prokaryotic ancestors of organelles probably lived as internal parasites within a larger prokaryotic host cell.
Eukaryotes Arose from Endosymbiosis
What Exactly Happened?
Heterotrophic bacteria
Ancient Prokaryotes
Ancient Heterotrophic Prokaryote
Primitive Heterotrophic Eukaryote
Primitive Autotrophic (Photosynthetic) Eukaryote
Chloroplast
Photosynthetic bacteria
Nuclear envelope evolving Mitochondrion
Plants and plant-like protists
Animals, fungi, and animal-like protists
Origin of Eukaryotes1 Endosymbiosis to explain the origin of mitochondria
and chloroplasts2 Invagination of the plasma membrane to form the
endomembrane system
Origin of Eukaryotes1 Endosymbiosis to explain the origin of mitochondria
and chloroplasts2 Invagination of the plasma membrane to form the
endomembrane system
Mitochondria
Origin of Eukaryotes1 Endosymbiosis to explain the origin of mitochondria
and chloroplasts2 Invagination of the plasma membrane to form the
endomembrane system
Nucleus
Endoplasmic Reticulum
Golgi Body
Mitochondria
Chloroplast
Origin of Eukaryotes1 Endosymbiosis to explain the origin of mitochondria
and chloroplasts2 Invagination of the plasma membrane to form the
endomembrane system
Chloroplast
Endoplasmic Reticulum
Nucleus
Golgi Body
Mitochondria
Membrane-Bound Organelles
� Mitochondria = membrane-bound organelle that produces energy for the cell
� Chloroplast = membrane-bound organelle that captures sunlight and uses it to make food for the cell
� Inner membranes of both organelles have enzymes and transport systems that are homologous to those in the plasma membranes of modern prokaryotes
� Both organelles replicate by a process similar to binary fission
� Each organelle has a single circular chromosome similar to prokaryotes
� Ribosomes of both organelles are similar to prokaryotic ribosomes in terms of size and nucleotide sequence.
Evidence for Endosymbiosis
Cellular Respiration
You feel weak when you are hungry because food serves as a source of energy. How does the food you eat get converted
into a usable form of energy for your cells?
Whenyouexercise,yourbodyusesoxygentogetenergyfromglucose,a6-carbonsugar.
1.Howdoesyourbodyfeelatthestartofexercise,suchatalongslowrun?Howdoyoufeel1minuteintotherun;10minutesintotherun?
2.Whatdoyouthinkishappeninginyourcellstocausethechangesinhowyoufeel?
3.Thinkaboutrunningasfastasyoucanfor100meters.Couldyoukeepupthispaceforamuchlongerdistance?Explainyouranswer.
Chemical Energy and Food
� Calorie – amount of energy needed to raise a temperature of 1 gram of water by 1 degree Celsius
� Cells use all sorts of molecules for food, including fats, proteins, and carbohydrates. The energy stored in each of these molecules varies because their chemical structures, and therefore their energy-storing bonds, differ.
� Cells break down food molecules gradually and use the energy stored in the chemical bonds to produce compounds such as ATP that power the activities of the cell.
Where do organisms get energy?
� Food = chemical energy� It provides living
organisms with chemical building blocks they need to grow and reproduce
� ATP = organic molecule containing high energy bonds -powers most cell activities (cell energy)
Cellular Respiration Overview
� Transformation of chemical energy in food into chemical energy cells can use: ATP à cellular respiration
� Overall Reaction:� C6H12O6 + 6O2 → 6CO2 + 6H2O
Glucose + Oxygen à Carbon dioxide + Water + Energy
Stages of Cellular Respiration
1) Glycolysis2) Krebs cycle3) Electron transport chain
Stages of Cellular Respiration
1) Glycolysis – produces small amount energy� Glucose is broken down to
pyruvate acid during glycolysis making some ATP
� Most of the glucose’s energy (90%) remains locked in the chemical bonds of pyruvic acid at the end of glycolysis
Stages of Cellular Respiration
2) Krebs Cycle – little more energy is generated from pyruvic acid
Stages of Cellular Respiration
3) Electron transport chain–produces a bulk of the energy in cellular respiration by using oxygen, a powerful electron acceptor
Energy Totals
Efficiency of Cellular Respiration
� The36ATPmoleculesthecellmakesperglucoserepresentsonlyabout38%ofthetotalenergythatwasintheglucosemolecule.
� Therestoftheenergyisreleasedasheat.
Oxygen and Energy� Aerobic- process that
requires oxygen� Krebs cycle and electron
transport chain are aerobic
� Both take place in mitochondria
� Anaerobic- process that does not require oxygen� Glycolysis is anaerobic� Takes place in cytoplasm
Photosynthesis vs. Cellular Respiration
� The reactants of cellular respiration are the products of photosynthesis and vice versa.
� The release of energy by cellular respiration takes place in plants, animals, fungi, protists, and most bacteria.
� Energy capture by photosynthesis occurs only in plants, algae, and some bacteria.
Fermentation
We are air-breathing organisms, and we use oxygen to release chemical energy from the food we eat. But what if oxygen isn’t around? What happens when you hold your breath and dive under water, or use up
oxygen so quickly that you cannot replace it fast enough?
Fermentation� Fermentation - in the absence
of oxygen, fermentation releases energy from food molecules by producing ATP
� Electron transport chain doesn’t run à WHY?
� Alcoholic Fermentation –yeasts are other organisms use alcoholic fermentation produces ethyl alcohol and carbon dioxide
� Lactic Fermentation – MOST organisms carry out fermentation using a chemical reaction that converts pyruvic acid to lactic acid
Energy and Exercise• To obtain energy for
exercise the body uses:
• Stored ATP• ATP formed
through lactic acid fermentation
• ATP formed through cellular respiration
Energy use during intense exercise
� StoredATPcansupportonlyafewsecondsofintenseexercise(ex:50metersinarace)
� LacticacidfermentationcanusuallysupplyenoughATPtolastabout90seconds(ex:200metersprint)
� Cellularrespirationisnecessaryforsustainedexercise
Role of cellular respiration inexercise
� CellularrespirationproducesATPmoreslowlythanfermentation
� Glycogen storedinmusclesisbrokendownintoglucose forcellularrespiration
� Usuallytheamountofstoredglycogenisenoughtolastforabout15to20minutesofactivity
� Tocontinueexercisingthebodywillbreakdownotherstoredmoleculesincludingfats.