Energy & Life: Cellular Respiration PART I: HARVESTING CHEMICAL ENERGY

Energy & Life: Cellular Respiration PART I: HARVESTING CHEMICAL ENERGY

Energy u Energy is not created or destroyed, it is transformed, changed. u E= ability to do work u Living things depend on energy to do work; carry out life processes such as: u Breathing, eating, sleeping, thinking u Obtain E through food u Break down food (specifically carbohydrates, in the form of glucose) into a useable form of E u Food provides building blocks necessary to grow and reproduce

Chemical Energy u Energy is found in many forms: light, thermal, mechanical, kinetic u E stored within the bonds of chemical compounds u As you break these bonds, chemical energy is released u Shifting of electrons, moving from a high state of energy to a lower, often more stable state of energy

ATP powers cellular work u Adenosine triphosphate (ATP): immediate source of energy that powers cellular work (currency of cell) This image cannot currently be displayed. u ATP + H2Oà ADP + P u Energy is stored in the phosphate bonds u Energy is released when the phosphate bonds are broken

u Storing Energy: Cell will store E by adding P group to ADP (adenosine diphosphate) to produce ATP (adenosine triphosphate) This image cannot currently be displayed.

u Releasing Energy: breaking chemical bond between P in ATP releases E to yield ADP u The release of E drives cellular processes such as: This image cannot currently be displayed.

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So how does the cell break down the food to release ATP?? u Cellular Respiration: process that releases energy by breaking down glucose (and other food molecules) in the presence of oxygen

Carbohydrate conversion done in stages u Complex sugars are broken down into simple sugars (monosacharide): glucose u Glucose molecule requires oxygen to give off carbon dioxide, water and energy in the form of ATP u Completed in 3 main stages: u Glycolosis u Krebs Cycle u Electron Transport Chain

3 main stages: u Stage 1 Glycolosis uglycolosis can be completed without oxygen uoccurs in cytoplasm, outside mitochondria ubreaks glucose molecule in half uyields a net gain of 2 ATP and 2 molecules of pyruvic acid

How? u 2 molecules of ATP used to start process u Removal of high E electrons through NAD + unad+ à NADH u This step helps pass energy from glucose to other pathways

If there is NO oxygen Present u If there is no oxygen present, glycolysis does not proceed to ETC u Instead, the pyruvic acid will be converted into: u Alcohol + CO 2 + NAD + = Alcholic Fermentation u Lactic acid + NAD + = Lactic Acid Fermentation u Combined process is called fermentation u Note that NADH transforms back into NAD + to keep the process of glycolysis to continue u No oxygen needed= anaerobic

Alcholic Fermentation

Lactic Acid Fermentation

If Glycolosis continues in presence of oxygen, process continues onto Kreb Cycle

3 main stages: u Stage 2: Krebs Cycle u Krebs cycle is completed in the presence of oxygen u Completed within the mitochondria u Yields a net gain of 2 ATP u CO2 is released in this stage u NADH u FADH 2

Citric Acid Production u Pyruvic acid (from glycolysis) enters mitochondria u Carbon atom from pyruvic acid à Carbon dioxide u Carbon atoms from pyruvic acid à citric acid

Energy Extraction u u u Citric acid (6 Carbon compound) further breaks down à more carbon dioxide + NADH + FADH 2 + ATP NAD+ and FAD are electron accepting molecules. Once a pair of electrons has been accepted: NAD+ à NADH u FAD à FADH 2 u Why should we care what happens to these electrons??

3 main stages: Stage 3: Electron Transport Chain uonly completed in presence of oxygen uuses high energy electrons from Krebs cycle to convert ADPà ATP ucompleted in the mitochondria uyields a net gain of 36 ATP

u u u u NADH and FADH2 pass through proteins in the inner membrane of the mitochondria. As electrons pass through proteins in membrane, H+ ions move across membrane and builds up creating a (+) charge building up inside making the outside of them membrane more (-) ATP synthase (an enzyme) uses the (+) ions to grab ADP and add a phosphate group, converting ADPà ATP Net gain of ATP: 34 (per glucose molecule)

Do some cells have more mitochondria that other cells?

Do some cells have more mitochondria that other cells u Unicellular organisms: u Usually 1 mitochondria u Human body: areas of a lot of active transport and active movement have more mitochondria in their cells.

Human body u Active transport u Liver cells (1000-2000 mitochondria per liver cell) u Kidney (fore extracting the urine) u Active movement u Muscles (cardiac muscles) usperm cells (for swimming)

Why cellular respiration? u The cell uses CR because the reactants are readily available in the environment (as long as the plants keep living humans are dependent on plants for life)

Key Ideas: u What is cellular respiration u Where does cellular respiration take place in the cell and human body? u Why does the cell use cellular respiration?

Key Ideas u CR is the chemical reaction which converts glucose to create energy for the cell u Location u Mitochondria in the cell through out the entire human body u Areas with mitochondria rich cells: liver, kidneys, muscles, sperm u The cell uses CR as its primary energy source because: u Reactants are easily obtained from plants by the human body u The energy produced from 1 ATP is just the correct amount for most reactions/activities