Endosymbiotic Theory

Evolution of Prokaryotes 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 Photosynthetic Organisms 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 Eukaryotes Eukaryotic cells differ from and are much more complex than prokaryotes Fossil evidence suggests that eukaryotic cells may have been present 2.7 bya

Eukaryotes Arose from Endosymbiosis 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.

What Exactly Happened? Chloroplast Heterotrophic bacteria Ancient Prokaryotes Nuclear envelope evolving Photosynthetic bacteria Mitochondrion Plants and plant-like protists Primitive Autotrophic (Photosynthetic) Eukaryote Ancient Heterotrophic Prokaryote Primitive Heterotrophic Eukaryote Animals, fungi, and animal-like protists

Origin of Eukaryotes 1 Endosymbiosis to explain the origin of mitochondria and chloroplasts 2 Invagination of the plasma membrane to form the endomembrane system

Origin of Eukaryotes 1 Endosymbiosis to explain the origin of mitochondria and chloroplasts 2 Invagination of the plasma membrane to form the endomembrane system Mitochondria

Origin of Eukaryotes 1 Endosymbiosis to explain the origin of mitochondria and chloroplasts 2 Invagination of the plasma membrane to form the endomembrane system Mitochondria Endoplasmic Reticulum Nucleus Chloroplast Golgi Body

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

Evidence for Endosymbiosis 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.

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?

When you exercise, your body uses oxygen to get energy from glucose, a 6-carbon sugar. 1. How does your body feel at the start of exercise, such at a long slow run? How do you feel 1 minute into the run; 10 minutes into the run? 2. What do you think is happening in your cells to cause the changes in how you feel? 3. Think about running as fast as you can for 100 meters. Could you keep up this pace for a much longer distance? Explain your answer.

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 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) energy?

Cellular Respiration Overview Transformation of chemical energy in food into chemical energy cells can use: ATP à cellular respiration Overall Reaction: C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O Glucose + Oxygen à Carbon dioxide + Water + Energy

Stages of Cellular 1) Glycolysis 2) Krebs cycle 3) Electron transport chain Respiration

Stages of Cellular 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 Respiration

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 The 36 ATP molecules the cell makes per glucose represents only about 38% of the total energy that was in the glucose molecule. The rest of the energy is released as heat.

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 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. Respiration

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 Stored ATP can support only a few seconds of intense exercise ( ex: 50 meters in a race) Lactic acid fermentation can usually supply enough ATP to last about 90 seconds (ex: 200 meter sprint) Cellular respiration is necessary for sustained exercise

Role of cellular respiration in exercise Cellular respiration produces ATP more slowly than fermentation Glycogen stored in muscles is broken down into glucose for cellular respiration Usually the amount of stored glycogen is enough to last for about 15 to 20 minutes of activity To continue exercising the body will break down other stored molecules including fats.