Photosynthesis Light-Dependent Reactions.docx

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Integrative Biology
IB 103

Energy Part 1, Lecture 2: Photosynthesis: Light-Dependent Reactions Pgs 25-27, 38-41, 66-76 Chemical Background Information (pgs 25-27) Electrons move around nucleus, but their exact positions are uncertain - The electron configuration of an atom is the way electrons are arranged around nucleus - Electrons are negatively charged; nucleus is positive - Electrons and nucleus attract each other while electrons vs electrons repel each other - Energy levels: o 1: closest to nucleus, 2 electrons to be „complete‟ o 2: max.of 8 electrons, 8 to be „complete‟ o 3: more than 8 electrons, 8 to be „complete‟ o 4: more than 8 electrons, 8 to be „complete‟ - Electron with more energy (ex:light energy) allows it to move farther from nucleus; giving up energy allows it to drop to lower energy level) Chemical bonds hold atoms together - Compounds are fixed ratios of united elements (H2O) - Chemical bond is the force holding 2+ atoms together in a compound - Main point: if atom‟s outer energy level is less than 8 electrons, it gains, loses, or shares them to reach 8 (except hydrogen and helium) - This is done through ionic and covalent chemical bonds Atoms gain or lose electrons to form ionic bonds - ion is a gain or loss of electrons in an atom - an ionic bond is the force of attraction between 2 oppositely charged ions - ex: NaCl (sodium chloride) Atoms share electrons to form covalent bonds - covalent bond is when 2 atoms share electrons to complete outer energy levels - molecules are formed by 2 or more covalent bonds - example: methane (CH4) - sharing one pair of electrons= single bond; sharing two pairs =double bonds - nonpolar covalent bonds are covalent bonds which equally share electrons (ex:H2), and unequally shared is polar covalent bonds Hydrogen bonds are attractions between adjacent molecules - hydrogen bond= positively charged H atom in one polar molecule and a negatively charged O or N atom in another polar molecule - Weak bonds compared to covalent - Form and break easily - Affects shape and function of protein and nucleic acid molecules - Determines properties of water Biological Background Information (pgs 38-41) Enzymes and Activation energy - Enzymes catalyze reactions, therefore less activation energy needed - Enzyme performs reaction on substrate, increasing rate of reaction Enzyme+ substrate(s)enzyme-substrate complexenzyme + product(s) Substrates find active sites on enzyme and react with each other, and products separate from enzyme so enzyme is used for other substrates DNA and RNA are nucleic acids - Nucleic acids are macromolecules containing O, H, N, and P elements - DNA (deoxyribonucleic acid) contains instructions for making necessary proteins; instructions are written in genes, the unit of hereditary info - DNA molecule is a double helix - RNA helps for protein synthesis - Nucleotides are the repeating units in nucleic acids - One nucleotide= nitrogenous base, 5-carbon sugar, and phosphate molecule Energy is temporarily stored in ATP - Nucleotides don‟t just build nucleic acids: some serve other functions - ATP (Adenosine triphosphate) is a nucleotide containing: base adenine, sugar ribose, and 3 phosphate molecules - “energy currency” present in all living cells - Transfers energy Energy and Biological Work - Energy is the ability to do work - Different forms: chemical (in molecular bonds), heat, radiant (sun), mechanical, electrical - Stored energy= potential energy - Energy in motion = kinetic energy The laws of thermodynamics govern energy transformations - thermodynamics is the study of energy and its transformations - Law 1: First Law—energy cannot be created or destroyed - Plants can‟t simply create energy to live, but must capture from the environment - Law 2: Second Law—when energy is converted from one form to another, some of it is degraded into a lower-quality, less useful form - Entropy is a measure of the disorder in energy. - Organized/usable energy (electrical, chemical) have low entropy (disorder) - Heat= disorganized energy, so high entropy Chapter 4:Metabolism in Cells, Photosynthesis (pgs 66-76) Metabolism - Metabolism is known as the chemical processes occurring in the cell - 2 kinds of chemical rxns in cell‟s metabolism: 1. Anabolic reactions (anabolism)—energy stored in molecules - Large molecules synthesized from simpler molecules - „building-up‟ process - In photosynthesis, CO2 and H2O creae glucose 2. Catabolic reactions (catabolism)—energy is released from molecules - Break down process - Large molecules split apart into simpler ones to release energy - In cellular respiration of glucose, it is broken down to CO2 and H2O with the release of energy Oxidation-reduction reactions occur in metabolism - Electrons are the means of transferring energy in cells Oxidation—chemical process where substance loses electrons Reduction—chemical process reaction where substance gains electrons - Both rxns accompany each other - If substance gains electron (through reduction), the electron had to have been lost in oxidation rxn - O-R rxns are in photosynthesis - Electrons associated with hydrogen are transferred to electron acceptor molecules - In cells, oxidation involves removal of H atom - when H atoms are removed from organic compound and take energy to store in electrons, called Electron acceptor molecules - electron transport chain moves electrons from one acceptor to another Photosynthesis - plants, algae, and certain prokaryotes can absorb and convert light energy from sun into chemical energy in photosynthesis - end products= carbs and oxygen - biomass is organic material used as fuel; wood, agricultural waste, which contains chemical energy traced back to solar energy Light exhibits properties of both waves and particles - light makes up portion of electromagnetic spectrum—the range of radiations through space and matter - gamma rays are short in wavelengths, as opposed to radio waves, which are longest - visible spectrum is the portion of the spectrum humans can see (includes colors) - UV radiation is invisible to human eye, and is shorter in wavelength than visible light - Photons—the small particles of energy that make up light - Shorter wavelength of light=more energy per photon, so inversely proportional - *photosynthesis depends on visible light because it is the perfect length to excite biological molecules. Long waves (ex:microwaves) don‟t have enough energy, and short waves (UV) have too much energy - The ground state is the lowest energy state an electron possesses, but energy can make it higher, so the electron is energized by energy - Molecules are energized when they
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