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EnergyLight to Life
Overview:• Energy from the sun is used to make ATP• ATP is used to activate molecular bonding• Energy is stored in bonds• Energy is released when bonds are broken
The structure of atoms
An atom is:
• The smallest unit of a pure substance (element) which cannot be broken down by ordinary chemical means
• Composed of protons, neutrons and electrons
The structure of atoms
• Protons: mass = 1, + charge, found in nucleus
• Neutrons: mass = 1, no charge, found in nucleus
• Electrons: mass negligible, - charge, orbit the nucleus
The structure of atoms
Chemical behavior is determined by electron number and arrangement :
• Electrons arranged in energy levels• Highest energy level electron shells are
farthest from nucleus • Octet Rule: atoms bond in ways to achieve 8
electrons in the highest energy level
The Structure of AtomsAn atom is made of negatively-charged electrons orbiting
around a positively-charged nucleus.
Biological molecules are organic (carbon-based) compounds
Common elements in living systems:
• C, O, H, N
• Important ions: Ca, K, P, Na, S, Cl, Mg
• Trace ions and minerals: I, Zn, Mn, Cu, and others
Carbon
• Basis of all organic compounds• Forms four bonds• Enables molecules to add backbone
length• Enables molecules to connect unique
side groups; provide character and informational value
• Forms bonds most often with O, H, or N
Example of an Organic CompoundLine structure and space-filling model of the dipeptide glycine-
serine
Making Bonds
Bonds:
• forces that hold atoms together
• form when atoms with correct fit collide with sufficient force
• store energy
Making Bonds
• Covalent bond: atoms collide and electrons rearrange so that some of the electrons are shared by the two atoms
Making Covalent BondsAtoms collide and electrons are rearranged and shared.
Two electron orbits are joined.
Molecular ChangesBreaking Bonds
• Bonds break when molecules collide with enough force and at appropriate angles
• Shared electrons return to their original orbits and release the stored energy in the bond
• Bond energy can be lost as heat or transferred to other molecules and preserved in a new bond
Transferring EnergyMolecules collide, bonds break, and energy is transferred to
the bonds of the new molecule.
Life and the Laws of Energy
All matter and energy in the universe follow the Laws of Thermodynamics:
• First Law: Energy can be gained or lost in chemical processes, but it can’t be created or destroyed.
• Second Law: Energy disperses and ordered structures become disordered (entropy increases).
Energy Flow and change in living systems
How the laws of thermodynamics apply to cells:
• Over time, all things in the universe tend toward disorder
• Cells need a continual, external source of useful energy to do work, overcome entropy and remain organized
Energy Flow and Equilibrium
• Equilibrium: energy flows as readily backwards as forwards in a chemical reaction
• Cells become inactive and die in equilibrium conditions
• Cells maintain far-from-equilibrium conditions by adding reactants and removing products
EquilibriumNO2 molecules collide to form N2O4. When sufficient N2O4 accumulates, the reverse reaction begins and N2O4 fragments into NO2. Equilibrium is reached when the forward and reverse reactions occur at the same rate.
ATP – The Energy Molecule
Each ATP molecule has three subunits:
• ribose sugar • adenine• three phosphate
groups (PO4) linked to form a triphosphate group
ATP – The Energy Molecule
• ATP is a high-energy donor molecule
• Energy is released by breaking ATP’s phosphate bonds (hydrolysis)
• ATP is reassembled by reattaching its phosphates with an input ? energy
Enzymes
Enzymes:• Catalysts that speed up and facilitate
chemical reactions• Molecules fit into active sites (docking
sites)• Chemically interact with molecules and
force them to react in aided collisions• Large protein molecules
Enzymes bind substrates at active sites
Active site:
• groove or cleft on enzyme formed by tertiary structure of protein
• binds, orients, strains substrate
• has shape specific for substrate
Energy Flow Through LifeMacro View
Food Chain:• Primary Producers: convert energy from sun
into chemical bonds of sugar (photosynthesis)• Herbivores: obtain energy directly from plants• Carnivores: obtain energy from flesh of
herbivores• Decomposers: obtain energy by breaking down
waste and dead bodies of above groups
Energy Flow Through LifeMacro View
Plants play an important role:
• produce fuel (sugar)
• produce oxygen to burn fuel
• consume carbon dioxide waste
Energy Flow Through LifeMicro View
Sugar (glucose)
• energy source
• building material for other molecules such as amino acids and nucleotides
Glucose
Glucose is a small carbohydrate called a monosaccharide (mono = “one”, saccharide is from saccharum = “sugar”)
Starch
Glucose molecules link together to form
starch, a polysaccharide
(“many sugar units”). Amylopectin is a type
of plant starch.
Energy Flow Through LifeProducing Sugar - Photosynthesis
Chloroplasts:
• organelle found in plant cells
• produces sugar using energy from sunlight
Energy Flow Through LifeBreaking Down Sugar - Respiration
Mitochondria:
• organelles found in both plant and animal cells
• break down sugar and produce ATP
Energy Flow Through LifeMicro View
Life’s molecules are continuously recycled:
• Chloroplasts:
carbon dioxide + water sugar + oxygen
• Mitochondria:
sugar + oxygen carbon dioxide + water
Capturing Light Energy
• Light: electromagnetic energy that travels in waves of varying lengths
• Photons: packets of light• Pigments: molecules which absorb some
light wavelengths and reflect others• The colors we observe correspond to the
wavelengths that are reflected by the pigment
Capturing light energy in chemical bonds
Photosynthetic pigments:
• Chlorophylls: primary pigments· Absorb photons of violet-blue and red
• Antenna pigments (carotenoids) · Absorb photons of green, blue, violet · Increase range of energy absorption
Chlorplast
• Double outer membrane• Stroma: inner chamber• Thylakoids: flattened sacs• Grana: stacks of thylakoids
PhotosynthesisLight-Dependent Reactions
(“Electron Bounce”)1. Photons hit
chlorophyll molecules (photosytem II) in leaves, exciting electrons to higher-energy orbits.
PhotosynthesisLight-Dependent Reactions
(“Electron Bounce”)• 2. Electrons
bounce along chlorophyll molecules and onto small carrier molecules (an electron transport chain) in the thylakoid membrane.
PhotosynthesisLight-Dependent Reactions
(“Electron Bounce”)
• 3. Electrons lost from chlorophyll are replaced by electrons from water. Oxygen atoms from the water pair up with hydrogen and are released as an important byproduct.
PhotosynthesisLight-Dependent Reactions
(“Ion Shuffle”)
• 4. Electrons on carrier molecules attract hydrogen ions from the stroma.
PhotosynthesisLight-Dependent Reactions
(“Ion Shuffle”)
• 5. Carrier molecules bring hydrogen ions to an enzyme which ejects them into the thylakoid sac.
PhotosynthesisLight-Dependent Reactions
(“Ion Shuffle”)
• 6. Hydrogen ions exit the thylakoid sac through a channel in an ATP-producing enzyme (ATP synthase).
PhotosynthesisLight-Dependent Reactions
(“Ion Shuffle”)• 7. Spent
electrons replace electrons bouncing off a new set of energized chlorophyll molecules (photosystem I).
PhotosynthesisLight-Dependent Reactions
(“Ion Shuffle”)
• 8. Energized electrons unite with hydrogen ions on NADP to form reactive “hot” hydrogens (NADPH).
PhotosynthesisLight-Independent Reactions – Calvin Cycle
Overview:• Team of five
enzymes uses ATP, carbon dioxide, and “hot” hydrogens from NADPH to produce half-molecules of sugar in the stroma of the chloroplast (carbon fixation or Calvin Cycle).
Calvin Cycle
• Three 6-C sugars break into six 3-C sugars
• Enzyme B: energizes 3-C sugar fragments with ATP
Calvin Cycle
• Enzyme C: attaches hydrogens from NADPH to six 3-C sugars and releases one
• Released 3-C sugars (half-sugars) exit chloroplast and pair up to form 6-C glucose in cytoplasm
Respiration Overview
Three main stages:
• Glycolysis: cytosol
• Krebs Cycle: mitochondrial matrix
• Electron Transport Chain: mitochondrial inner membrane
Glycolysis
• From greek: lysis = “to break apart”, glyco = “sugar”
• Glucose is broken into smaller fragments by a series of enzymes
• Generates two ATP• Requires no oxygen (anaerobic)• Prepares glucose for Krebs Cycle• Emergency energy source• Early metabolic pathway
RespirationKrebs Cycle
• Enzymes extract energetic hydrogens from 2-C sugar fragments (from glycolysis of glucose) [1]
• Carbon and oxygen combine and are discarded as carbon dioxide (animals exhale)
RespirationElectron Transport Chain
• “Hot” hydrogens (from NADPH) give up their electrons to an enzyme in the mitochondrion inner membrane.
• Electrons pass along carriers in the inner membrane, picking up hydrogen ions [2]
RespirationElectron Transport Chain
• Hydrogen ions force their way out through a channel in an ATP-producing enzyme [4] ATP is the end result
RespirationElectron Transport Chain
• Spent electrons combine with hydrogen ions and oxygen to form water – a waste product [5]