Photoautotrophs – capture solar energyChemoautotrphs – use inorganic molecules to produce storable chemical energy
Energy transformations in cells
Ian Anderson (2013)Saint Ignatius College Geelong06. Energy transformations.
Energy. All living organisms require a constant supply ofenergy to survive e.g. for cellular processes (incl.protein synthesis, active transport, digestionetc.), growth, movement, reproduction, etc. Energy = capacity to do work.
Energy. In plants and animals glucose is the main source ofchemical energy. If there is insufficient glucose available, fatty acids andamino acids can be used instead. Chemical energy is present in the chemical bonds. When the bonds break, energy is released (i.e. exergonicreaction).
ATP – ADP cycle. Adenosine triphosphate (ATP) is the energy currencyof a cell. ATP is needed for every activity that requires energy. ATP structure – adenosine attached to a sugar group(ribose), which is bound to a chain of three phosphategroups. = nucleotide (sugar, N containing base and a phosphategroup). Immediate energy source lies in the energy rich bondholding the third phosphate to the rest of themolecule.
ATP – ADP cycle. Cells make their own ATP in a cyclic process. When energy is used ATP is broken down intoAdenosine diphosphate (ADP) and inorganicphosphate, with energy released. ATP is then reformed during cellular respiration.
Cellular respiration. The process that releases energy from glucosemolecules in the form of ATP. Cellular respiration is the most important andcommon catabolic reaction to all living organisms. Occurs in several stages [Biochemical/metabolic pathway = each step beginswith a substrate, which is then converted to aproduct, which then becomes the substrate for anotherchemical reaction (each enzyme controlled)].Source: Campbell et al. (2011)
Cellular respiration. First stage = Glycolysis. Occurs in cytosol. Anaerobic (without oxygen) pathway. Glucose is broken down into two pyruvatemolecules, with a net production of two ATP molecules. H+ and e- are released as glucose is split and collected byelectron carrier molecule (nictoninamide adeninedinucleotide).Glucose 2 pyruvate + 2H2O + 2NADH + 2ATP(6 carbon sugar) (2 x 3 carbon sugar)
Electron carrier molecule. H+ and e- are not stable and are quickly picked up byNAD (nictoninamide adenine dinucleotide) whichacts as an electron carrier.NAD+ NADHSource: Russell et al. (2011)
Cellular respiration.Next stage of cellular respiration depends on whether ornot oxygen is available. Oxygen available aerobic pathway. Oxygen not available anaerobic pathway.
Cellular respiration– aerobic pathway. Most efficient way of producing ATP. Occurs in mitochondria in eukaryotes. Pyruvate enters via active transport. (Occurs in cytoplasm of prokaryotes). Involves two steps Krebs cycle (Citric acid cycle). Electron-transport chain.
Cellular respiration– aerobic pathway.Krebs cycle. Occurs in fluid matrix of mitochondria. Pyruvate molecules converted to two molecules ofacetyl CoA, one molecule of CO2 and 2 H+. Acetyl CoA then enters Krebs Cycle where eachmolecule is converted into 2 CO2, 4 H+ & 1 ATP. H+ are picked up by electron carriers (NAD & FADH). A total of 2 ATP molecules produced per initial glucosemolecule.
Cellular respiration– aerobic pathway.Electron-transport chain. Occurs on the cristae (inner membrane) ofmitochondria. Energy from the NADH and FADH2 produced inglycolysis and Krebs cycle used to produce ATP. H+ combine with O2 to form H2O. A total of 32-34 ATP from each original glucosemolecule. 34 ATP in prokaryotes & 32 ATP in eukaryotes (2 ATPused as as NADH produced via glycolysis pass acrossmitochondrial membrane).
Cellular respiration– aerobic pathway. Total ATP produced via aerobic pathway Glycolysis = 2 ATP Krebs cycle = 2 ATP Electron transport chain = 32-34 ATP = total 36-38ATPSummary reaction of cellular respiration via aerobicpathwayC6H12O6 + 6O2 6CO2 + 6 H2O + 36-38 ATP
Cellular respiration– aerobic pathway.Source: Raven et al. (2011)
Cellular respiration– anaerobic pathway. Occurs in the cytoplasm of cells. No further ATP is produced during the anaerobicpathway. i.e. only 2 ATP produced as a result of glycolysis. Anaerobic pathway known as fermentation.
Cellular respiration– anaerobic pathway. In animals Pyruvate produced by glycolysis is converted to lacticacid. NADH (produced during glycolysis) converted back toNAD+ (thus allowing it to be reused).Pyruvate + NADH lactic acid + NAD+Source: Campbell et al. (2011)
Cellular respiration– anaerobic pathway. In most plants, yeast & bacteria Pyruvate is converted to ethanol and carbon dioxide. NADH (produced during glycolysis) converted back toNAD+ (thus allowing it to be reused).Source: Campbell et al. (2011)Pyruvate + NADH ethanol + CO2 + NAD+
Energy. The sun provides this energy either directly orindirectly for nearly all life forms. Autotrophs – manufacture organic material frominorganic material [self feeding] e.g. plants, algae &cyanobacteria. Heterotrophs – obtain organic material by feeding onother organisms (or their products) [feed on others] e.g.animals, fungi, most bacteria & some protists.
Photosynthesis. Autotrophs (photoautotrophs) capture solar energy tohelp drive the reactions that convert inorganic C toorganic C. Overall process = photosynthesis6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O
Photosynthesis.6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O Reaction is anabolic Larger molecules made from smaller molecules & endergonic Needs energy to proceed. Equation is a summary of 100’s of reactions that makeup photosynthesis (i.e. it is a biochemical pathway).
Photosynthesis. Occurs in the chloroplasts Membrane bound organelles – inner & outer membrane. Stroma – gel-like matrix that fills the interior of achloroplast. Rich in enzymes. Thylakoid membranes – suspended in the stroma.Flat, sac-like structures that are stacked like pancakesknown collectively as grana.
Photosynthesis. Two main stages Light dependent reactions. Light independent reactions. Each stage confined to specific sites within thechloroplast.
Photosynthesis- Light dependent reactions. Light is essential for these reactions to occur. Occurs on the thylakoid membranes of thechloroplast. Chlorophyl absorbs light energy, which is then used toproduce ATP and split water molecules into H+ ionsand O2 gas. O2 gas is a waste product. ATP, H+ ions and electrons are used in the lightindependent reactions.
Photosynthesis- Light independent reactions. Also know as the Calvin Cycle. Occurs in the stroma of the chloroplast. Carbon dioxide is combined with the H+ ions usingenergy provided by ATP, to form glucose and water.
Photosynthesis.Factors that affect the rate of photosynthesis. Light intensity CO2 availability Temperature Indirect factors Lacking nitrogen/magnesium reduces the amount ofchlorophyll produced. Dehydration causes stomata to close.
Variations in photosynthesis.Plants adapt to their environment C3 plants C4 plants CAM plants‘the norm’Adapted to arid conditions
C3 plants. Called C3 because the CO2 is first incorporated into a3-carbon compound. Stomata are open during the day. Photosynthesis takes place throughout the leaf. Adaptive value = more efficient than C4 and CAMplants under cool and moist conditions and undernormal light because requires less machinery (fewerenzymes and no specialized anatomy).. Most plants are C3.
C4 plants. Called C4 because the CO2 is first incorporated into a4-carbon compound. Use a different enzyme to capture & convert CO2. Adaptive value = reduces the time the stomates areopen and therefore reduces water loss. C4 plants include several thousand species in at least19 plant families. E.g. fourwing saltbush, corn, andmany of our summer annual plants.
CAM plants. Open their stomates at night. Convert the CO2 to an acid that is stored. During the day the acid is broken down back into CO2and used during photosynthesis. Adaptive value = stomates are not open during day andtherefore reduces water loss. CAM plants include succulents, some orchids andsome bromeliads.