Bioenergetics: Photosynthesis and Cellular Respiration

PHOTOSYNTHESIS: Capturing and Converting Energy

ENERGY Energy is the ability to do work. All living things depend on energy. Energy comes in the form of light, heat, electricity, or sound. Energy can be stored in chemical compounds.

ATP- Adenosine Triphosphate ATP is the cell’s energy currency. Energy is stored in the chemical bonds of ATP. ATP is made up of 3 parts: adenine base, ribose sugar, 3 phosphate groups

ATP Energy is released when the chemical bonds in ATP are broken. ATP can be broken down by breaking bonds with the phosphate molecules into ADP, and AMP. ADP- Adenosine Diphosphate (2 phosphate groups) AMP- Adenosine monophosphate (1 phosphate group) The energy released by breaking down ATP can be used for processes such as: Active Transport (ex: the sodium/potassium pump) Muscle contractions

Autotrophs and Heterotrophs Autotrophs are organisms that make their own food. Use light energy from the sun to produce food Ex: Plants Heterotrophs obtain energy from the food they consume. Unable to directly use the sun’s energy. Must consume other organisms either by ingesting (eating) them or decomposing them. Ex: Animals

The Photosynthesis Equation Photosynthesis is the process whereby plants use the energy of sunlight to convert water and carbon dioxide into oxygen and high-energy carbohydrates. Carbon dioxide +water  sugar and oxygen In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll, a molecule in chloroplasts.

The Photosynthesis Equation 3 Requirements for Photosynthesis: Sunlight Pigments Energy storing compounds

1. LIGHT Light travels to the Earth in the form of sunlight We perceive sunlight as white light Made of a mixture of many different wavelengths of light Wavelengths of light that are visible to us are known as the visible light spectrum

2. PIGMENTS Pigments are light absorbing molecules that help plants gather the sun’s energy The main pigment found in plants is chlorophyll Chlorophyll absorbs red and blue wavelengths of light, but it reflects green making the plant appear green When the pigments absorb light they are also absorbing the energy in that light, producing more energy for the cell

INSIDE A CHLOROPLAST Photosynthesis takes place in chloroplasts. Chloroplasts contain saclike photosynthetic membranes called thylakoids. Thylakoids contain clusters of chlorophyll and other pigments and proteins known as photosystems that are able to capture sunlight. The light reaction takes place in thylakoids Grana- stacks of thylakoids Stroma- the region outside the thylakoid membrane The dark reaction takes place in the stroma

3. Energy Storing Compounds Used to trap high energy electrons into chemical bonds. Occurs in 2 ways: 1. Electron carrier NADP+ accepts a pair of high energy electrons and gets converted to NADPH. 2. AMP is converted to ADP which is then converted to ATP. This requires light! Adenosine Triphosphate (ATP)- a molecule that provides energy for cellular reactions and processes. ATP releases energy when one of its high-energy bonds is broken to release a phosphate group. -the cell’s energy currency NOTE: The energy stored in these molecules is released by breaking chemical bonds to generate things the cell needs, like glucose!

Light Rxns - SUMMARY Take place in thylakoids The light reactions USE: water, light energy, chlorophyll pigments The light reactions PRODUCE: oxygen, NADPH, ATP Occurs by converting ADP and NADP+ into ATP and NADPH. These reactions REQUIRE light.

Dark Reactions/ Light Independent Reactions/ Calvin Cycle - SUMMARY Takes place in the stroma Calvin Cycle USES: NADPH, ATP ,CO2 Calvin cycle PRODUCES: glucose (C6H12O6) Glucose is more stable and can store up to 100 times more energy than NADPH and ATP. These reactions do not require light. Organisms that eat plants indirectly use the energy from glucose.

Biology in a Minute: Photosynthesis http://www.youtube.com/watch?v=BeUmj8d6Mag

Photosynthesis Summary Chart

CELLULAR RESPIRATION

Photosynthesis vs. Respiration - almost opposite processes -equations are opposites Photosynthesis- deposits energy -occurs only in plants, algae, and some bacteria Respiration withdraws energy -takes place in all eukaryotes and some prokaryotes

Chemical Energy In Food Purpose of food: Source of raw materials used to make new molecules Source of energy calorie – the amount of energy needed to raise the temperature of one gram of water one degree Celsius. Cells gradually release the energy from glucose.

Cellular Respiration Overview Cellular Respiration – the process that releases energy by breaking down food molecules in the presence of oxygen. Contains 3 Pathways: Glycolysis Krebs cycle Electron transport

Cellular Respiration overview The equation for cellular respiration is: 6O2 + C6H12O6  6CO2 + 6H2O + ATP (energy) If cellular respiration took place in one step, all the energy would be released at once and most would be lost as heat. SOLUTION: Each of the three stages of cellular respiration captures some of the chemical energy available in food molecules and uses it to produce ATP or energy.

Step 1: Glycolysis -process in which 1 molecule of glucose is broken in half, producing 2 molecules of pyruvic acid -does NOT require oxygen location: cytoplasm Uses: 2 stored ATP, 1 molecule of glucose Produces: 4 ATP molecules, 2 molecules of pyruvic acid NET GAIN: 2 ATP (2% of the total chemical energy in glucose), 2 molecules pyruvic acid

OXIDATIVE (AEROBIC) RESPIRATION Respiration - process that involves oxygen and breaks down food molecules to release energy. To get the rest of the energy from the food molecules, the cell uses oxygen. Aerobic – requires oxygen. the reason we need to breathe, to respire.

Step 2: Krebs Cycle location: mitochondria Uses: the carbon from pyruvic acid (made in glycolysis) is broken down Produces: CO2 (waste product, released when you exhale) NADH FADH2

Step 3: Electron Transport location: mitochondria Uses: NADH and FADH2 (from the Krebs Cycle) - passed from one carrier protein to the next - uses the high energy electrons Produces: converts ADP  ATP, H20

ENERGY AND EXERCISE Aerobic cellular respiration produces 36 total ATP molecules from each glucose molecule (37% efficient). Remainder of energy from glucose is released as heat (body feels warm after exercise). Eating food: Complex carbs are broken down into simple sugars that are converted to glucose. Lipids and proteins broken down into molecules that enter glycolysis or Krebs cycle. Breathing and respiration: Oxygen is needed to produce ATP in mitochondria Without oxygen, the body tries to make ATP by glycolysis alone (not sufficient for most cells). Relationship between photosynthesis and cellular respiration: Photosynthesis produces glucose and oxygen Cellular Respiration breaks down glucose using oxygen, to produce ATP

Fermentation anaerobic- does not require oxygen fermentation -process of breaking down glucose in the absence of oxygen -cells perform glycolysis followed by fermentation (this means Krebs cycle and electron transport DO NOT occur) Uses: 1 glucose molecule Produces: CO2, NAD+ 2 main types: 1. Alcoholic Fermentation 2. Lactic Acid Fermentation

Alcoholic Fermentation Pyruvic Acid + NADH  ethyl alcohol + CO2 + NAD+ -used by yeast -(facultative anaerobes- will use aerobic respiration when oxygen is present, but if not they will use fermentation) Products: ethyl alcohol, CO2, and NAD+ -CO2 production causes bread dough to rise, bubbles in beer, etc.

Lactic acid fermentation Pyruvic Acid + NADH  lactic acid + NAD+ -occurs during rapid exercise - not enough oxygen to continue oxidative respiration (through Krebs Cycle and Electron Transport Chain) -lactic acid buildup causes the painful, burning sensation in muscles after intense activity - bacteria use this process to make foods like sour cream, yogurt, buttermilk, and sauerkraut Why is fermentation useful? -produces NAD+ that is used in glycolysis so that it can continue to make small amounts of ATP

A Guide to Cellular Respiration: http://www. youtube. com/watch