1 2 3 4 5 Bio 1101 Lec. 5, Part A (Guided Notes) Chapter 6: Cellular Respiration Energy is needed by cells to do work Chemical energy, a form of potential energy, is stored in bonds of food molecules (such as glucose) Energy from food is transferred in cellular respiration to high-energy molecules, which allow the cell to do work Cellular Respiration Multi-step chemical process (metabolic pathway) 2 of the 3 steps occur within the ; the first step occurs outside of the mitochondria, in the cytoplasm Both plant and animal cells use cellular respiration to obtain energy from food molecules Reaction occurs in the presence of C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + ATPs (energy) C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + ATPs (energy) In Cellular Respiration, are removed from sugar and transferred to Including their Reactions (aka Oxidation-Reduction Reactions) involve the transfer of electrons from one substance to another Cellular respiration is therefore a redox reaction Electrons (hydrogens) move from to C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + ATPs (energy) In a Redox Reaction: The molecule that loses an electron is said to be is oxidized in cellular respiration The molecule that gains electrons is said to be is reduced in cellular respiration Energy is generated because electrons fall from a level of higher energy to lower energy The oxygen has a greater affinity for the hydrogen electrons than did the glucose 1
molecule 6 7 How do the electrons get to oxygen? Via the electron acceptor (Nicotinamide Adenine Dinucleotide) Made from niacin (vitamin B3) When electrons (hydrogens) are transferred from food to NAD +, it becomes reduced to NADH NADH transports the electrons to the, which ultimately carries them to the final oxygen acceptor This is where most of the energy from food is captured to make The purpose of cellular respiration: to produce ATP s the high-energy molecules that do cellular work Cellular respiration is efficient and can produce up to approximately ATP s 8 9 10 11 12 Step 1: Glycolysis 1 molecule of Glucose is broken down into 2 molecules of pyruvic acid Glucose has carbons Pyruvic acid has carbons A net of 2 ATP molecules are created from ADPs Recall, 2 were used to split glucose 2 ATPs were then created from each pyruvic acid 2 NADH molecules are created from NAD+ molecules (one per molecule of pyruvic acid) NADHs carry electrons to the electron transport chain, where most of the ATPs are created Step 2: Krebs Cycle (aka Citric Acid Cycle) But first, pyruvic acid must be converted to Pyruvic acid from glycolysis is converted into acetic acid a 2-carbon compound In the process, 2 carbon dioxide molecules are given off The acetic acid combines with an enzyme called Co-a, making Acetyl-CoA 2
13 14 15 16 is the fuel of the Krebs cycle Krebs Cycle (aka Citric Acid Cycle) ATPs are generated directly in the Krebs cycle per glucose 6 NADHs and 2 FADH 2 s are also generated, per glucose These molecules carry electrons to the Step 3: Electron Transport Chain (ETC) The machinery of the ETC is built into the membranes of the mitochondria That s why there are so many inner-foldings of membrane in mitochondria 17 18 A series of molecules in the mitochondrial membranes accept electrons The first molecule in the chain accepts the electron from Passes it on to the next molecule, and so on At each step, energy is given up that is used to make ATPs ATPs produced here! Finally, the electrons (and the Hydrogen) are accepted by oxygen, making 19 20 21 How do organisms obtain energy from food when oxygen isn t available? Fermentation Ancient organisms likely used to make ATP No in the early Earth s atmosphere Today, glycolysis occurs in nearly all organisms Must be an ancient metabolic pathway 3
22 23 24 25 Today, with abundant oxygen, most organisms use However, a variety of organisms use anaerobic fermentation Fermentation is used by some organisms as their primary metabolic pathway (some bacteria and yeasts) Others switch between fermentation and aerobic respiration, depending on availability of In animals, some cells must function for short periods of time without oxygen i.e. when exercising strenuously Blood supplies your cells with oxygen for cellular respiration If you are consuming energy faster than oxygen, your muscle cells may resort to to obtain energy Very similar to glycolysis (first step of cellular respiration doesn t require oxygen) 26 27 28 29 30 Fermentation Much less efficient than cellular respiration, however Only ATPs produced, compared to for cellular respiration Consume more food molecules to obtain the same amount of energy using fermentation Also produces as a by-product, which accumulates and makes muscles ache Microbes that use fermentation as metabolic pathway are used in producing Cheeses Yogurt Bread Alcohol Soy sauce Pickled vegetables The produced by yeasts is also what makes bread rise Bonus Activity For an added biology lesson, let s look at the ingredients in chocolate 4
I used to use Nutella instead of regular chocolate squares, to make gourmet s mores, BUT: Recently learned Nutella and many other chocolate products contain Palm Oil is most commonly produced by palm plantations growing in tropical areas; tropical rainforest is cut down to grow these plants; orangutans and tigers are two endangered species that are especially threatened by palm oil plantations So, now I look for palm-oil free products http://www.youtube.com/watch?v=3i-dxfcaqlu http://www.youtube.com/watch?v=orqwj4h9nh0 31 32 33 5-minute break Next, Photosynthesis Photosynthesis Plants are photosynthetic autotrophs Generate own food from ingredients Process of photosynthesis is essentially the reverse of cellular respiration: 6CO 2 + 6H 2 O energy C 6 H 12 O 6 + 6O 2 (recall cellular respiration: C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + energy) 34 35 36 37 Besides plants, many protists (such as algae, seaweed, microscopic protists like Euglena) and bacteria are also photosynthetic In bacteria, photosynthesis doesn t occur in chloroplasts (recall, prokaryotes do not have membrane-bound organelles) In eukaryotes, photosynthesis occurs in is the pigment in chloroplasts that give them their color, and absorbs light energy from the In plants, leaves are the structures that contain the most chloroplasts 5
Mostly in the ( the green tissue in the interior of the leaf ) 38 Chloroplasts are surrounded by a double membrane Inside, filled with thick fluid called Suspended in that fluid are stacks of disks called ; a stack of thylakoids is called a Photosynthetic pigments (such as chlorophyll) are built into the 39 40 Photosynthesis consists of two, multi-step processes: the, and the Light Reactions use sunlight to build and Calvin Cycle uses the energy from the light reactions to build Although doesn t need sunlight directly, can t synthesize sugar without the ATPs generated in the light reactions If runs out of ATPs, can t build more sugars until sunlight is available to begin the light reactions again 41 42 How is the energy from sunlight captured by plants? Sunlight is a type of energy Light travels in waves Different colors of light have different There are also wavelengths of light that are outside of the visible spectrum 43 44 45 Pigments are visible as different colors because they reflect certain wavelengths and absorb others Example: the feathers of a cardinal look red because the pigment in them reflects light with a red wavelength, and absorbs the other wavelengths of visible light Likewise, leaves of plants appear green because chlorophyll reflects green light So which wavelengths of light are best used by plants to do photosynthesis? Not, because it is reflected Other colors, like,,, and can be absorbed 6
Study of bacteria growing in water with algae and seeking oxygen 46 47 48 49 There are different types of pigments in plants Chlorphyll a reflects green light, and participates directly in the light reactions Chlorophyll b reflects yellow-green light; may participate indirectly in the light reactions Carotenoids reflect yellow/orange/ light; may pass energy to chlorophyll a, or may protect plant cells by absorbing excess light energy Fall colors due to decreases in green chlorophyll, making visible the effects of the carotenoids The Light Reactions 50 51 52 Light Reactions in a nutshell Light energy (photons) are absorbed by pigments and used to excite electrons in the water-splitting photosystem Excited electrons are accepted by molecules in the (built into the membranes of the thylakoids); is given off as a by-product Energy from the ETC is used to make (same concept as the ETC in cellular respiration) The electrons then pass to the NADPH-producing photosystem, where they are reexcited by light absorbed by pigment The electron is then used to produce NADPH, which is used in the Calvin Cycle The Calvin Cycle Where is Made Also called the Don t need light directly, but require the products of the light reactions ATP and NADPH generated in the light reactions are used to build molecules of sugar using carbon dioxide (CO 2 ) in the atmosphere 53 54 Starting materials: 3 molecules of carbon dioxide, 12 ATPs, and 6 NADPHs The product: one -carbon sugar (glyceraldehyde 3-phosphate), which the plant can use to build glucose or other organic molecules These products may be used later for cellular respiration in the plant, or for building cell 7
structures 55 56 Environmental Impact of Photosynthesis Interaction between cellular respiration and photosynthesis Food Oxygen The Greenhouse Effect Carbon Dioxide is a gas Traps heat energy in atmosphere Without a Greenhouse Effect, earth would be too cold for life Levels of greenhouse gases (like carbon dioxide) have increased since industrial revolution 57 58 59 Considering the process of photosynthesis, how might plants be able to moderate the greenhouse effect? 60 All for today 8