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TRANSCRIPT
Chemistry of Life
Chapter 2
PROPERTIES OF WATER 2.2
Key Concept
• Water’s unique properties allow life to exist on Earth.
Water
• Polar molecule – has slightly charged
regions
O
H H
_
+ +
Hydrogen Bonds
• Form between slightly positive hydrogen atoms and slightly negative oxygen atoms
Properties of Water
• Due to hydrogen bonds
Cohesive Behavior
– Cohesion • attraction of
molecules of a similar substance
– Adhesion • attraction of
molecules of different substances
Ability to Moderate Temperature
• Water resists changes in temperature
Expansion Upon Freezing
• Most (all?) substances are more dense when they are solid, but not water…
• Ice floats!!! – H-bonds form a crystal
Versatility as a Solvent
• Solvent – The dissolving agent
• Solute – The substance that is
dissolved
• Solution – A liquid that is a
homogenous mixture of substances
Water as a Solvent
• Polarity makes H2O a good solvent – Polar H2O molecules surround + and – ions
CARBON-BASED MOLECULES 2.3
Key Concept
• Carbon-based molecules are the foundation of life.
Carbon Atoms
• Can form bonds with up to 4 other atoms
Carbon-Based Molecules
• Have 3 general types of structures: – Straight chain
– Branched chain
– Ring
Subunits
• Many carbon-based molecules are made of many small subunits bonded together – subunit: monomer
– many monomers = a polymer
Macromolecules
• 4 main types found in living things: – carbohydrates
– lipids
– proteins
– nucleic acids
Carbohydrates
• Elements: – carbon
– hydrogen
– oxygen
– 1:2:1 ratio
• Building block: – monosaccharide
Carbohydrates
• Examples: – sugars
• monosaccharides
– starches, cellulose, glycogen • polysaccharides
Glucose
Carbohydrates
• Function: – energy reserve
– structure
Lipids
• Elements: – carbon (lots!)
– hydrogen (lots!)
Lipids
• Examples: – fats
– oils
– cholesterol
Lipids
• Function: – energy source
– make up cell membranes
– used to make hormones
Saturated vs. Unsaturated
• Saturated fatty acids: – all carbons are full,
lots of H-atoms – solid at room temp
• Unsaturated fatty
acids: – some double bonds
present – liquid at room temp
Proteins
• Elements: – carbon
– hydrogen
– nitrogen
– oxygen
– other
• Building block: – amino acid (20 different ones)
Proteins
• Functions: – antibodies
– muscle contraction
– enzymes
– hormones
– cell structure
Nucleic Acids
• Elements: – C, H, O, N, P
• Building block: – nucleotides
Nucleic Acids
• Examples: – DNA
• double stranded
• stores genetic info
– RNA • single stranded
• builds proteins
CHEMICAL REACTIONS 2.4
Key Concept
• Life depends on chemical reactions.
Chemical Reactions
• Bonds break and form during rxns
Bond Energy
• Energy is needed to start a rxn – activation energy
Exothermic Reactions
• Release more energy than they absorb
• Heat is released
Endothermic Reactions
• Absorb more energy than they release
• Heat is absorbed
ENZYMES 2.5
Key Concept
• Enzymes are catalysts for chemical reactions in living things.
Catalysts
• Enzymes are catalysts
• They lower the activation energy of a rxn – rxns are sped up
– increase rxn rate
Enzymes and Reactions
• Enzymes allow chemical rxns to occur
• Needed for almost all processes
• Most enzymes are proteins
Altering Enzymes
• Changing an enzyme changes its function
• Factors that can change an enzyme: – pH
– temperature
– concentration
STRUCTURE = FUNCTION