Water is the only common substance that exists in nature in all three physical states (solid, liquid, gas).
Water's Importance for Habitability
Water is the main reason Earth is habitable.
Evolution occurred in water for approximately 3 billion years before spreading to land.
Terrestrial life is still tied to water.
Water and Survival
Humans can survive up to a week (around 3 days) without water, but a few weeks without food.
Water is required in many chemical reactions necessary to sustain life!
Origin of Water on Earth
Water was delivered to Earth by asteroids.
Evidence suggests heavy bombardment of Earth by asteroids during the first 100 million years brought water.
Earth retains water because:
Its distance from the sun ensures that water doesn't boil.
Its gravity (strong due to size) holds oceans near its surface and water vapor within its atmosphere.
Fun fact: Initial water on Mars disappeared when it reacted with minerals in Martian rock (less of these minerals on Earth).
Search for Extraterrestrial Life and Water
Goldilocks Zone: Habitable zone around a star ("just right").
Depends on the size of the star (energy emitted).
Depends on the size of the planet (strength of gravity).
If a planet is:
Too close: Water vaporizes.
Too far: Water freezes.
(Liquid water is essential to life).
Temperatures of planets in the Goldilocks Zone allow condensation of water (liquid form).
Estimated to be 40 billion planets with a Goldilocks Zone in our galaxy (Milky Way).
Unique Properties of Water
What properties of water make it unique?
Water as a Polar Molecule
Water is polar because it has a negative end and a positive end.
Water's polarity is due to:
Polar covalent bonds sharing electrons unequally.
Water's bent shape.
Polar Covalent Bonds in Water
Oxygen end of a water molecule is negative.
The oxygen atom is more "electronegative" and pulls bonded electrons closer to its nucleus.
Hydrogen end of water is positive.
Hydrogen atoms are less "electronegative" and therefore bonded electrons sit closer to oxygen, making hydrogen atoms less negative.
Consequences of Water's Polarity
Water's polarity leads to hydrogen bonding between water molecules.
Hydrogen bonds: Forces of attraction between water molecules.
Represented by dotted lines.
Intermolecular Forces: Hydrogen Bonds
Hydrogen bond intermolecular forces: Forces between molecules.
Example: Hydrogen bonds.
The positive region of one water molecule attracts the negative region of another water molecule!
Strength and Organization of Hydrogen Bonds
Groups of hydrogen bonds can be very strong!
Hydrogen bonding orders molecules into a higher level of structural organization.
One hydrogen bond is weaker than one covalent bond.
Do H bonds only occur in water molecules?
Intramolecular Forces
Intramolecular forces: Exist within a molecule.
Example: Covalent bonds between atoms.
Properties of Water Significant to Living Things
Several properties of water due to water's polarity and ability to hydrogen bond are significant to living things:
Cohesion
Adhesion
Solvent Properties
Physical Properties (buoyancy, viscosity, thermal conductivity, and specific heat capacity)
Cohesion
Cohesion: Ability of molecules of the same substance to stick together.
Hydrogen bonds between water molecules make water cohesive.
Surface Tension
Surface tension: Measure of how difficult it is to stretch or break the surface of a liquid (water molecules more attracted to each other than air molecules).
Cohesion gives water a high surface tension.
Surface tension allows:
Animals to live on the surface of water.
The maintenance of lung structure.
Water Properties and Living Things
Several properties of water due to water's polarity and ability to hydrogen bond are significant to living things:
Cohesion
Adhesion
Solvent Properties
Thermal Properties (ability to moderate temperature)
Adhesion
Adhesion: Ability of different types of molecules to stick to each other.
The polarity of water molecules allows them to be attracted to other polar molecules.
Examples: Water molecules are attracted to glass and cellulose molecules in the cell walls of plants.
Capillary Action
Capillary action: Spontaneous movement of liquid through a narrow passage (even against gravity).
Adhesion to walls is stronger than cohesive forces between molecules.
Capillary action is due to cohesion & adhesion.
The transport of water upwards in plants from roots to leaves requires capillary action.
Cohesion & Adhesion in Capillary Action
ADHESION: Adhesion of water to walls causes an upwards force on water at edges of narrow passages.
COHESION: Cohesion causes surface tension that holds the surface of water intact as it moves up a narrow passage.(Here, adhesion forces are stronger than cohesion forces)
Water: Solvent Properties
Several properties of water due to water's polarity and ability to hydrogen bond are significant to living things:
Cohesion
Adhesion
Solvent Properties
Physical Properties (buoyancy, viscosity, thermal conductivity and specific heat capacity)
Definitions Recap
Solution: Uniform mixture of two or more substances.
A solvent is…
A solute is…
A solution in which water is the solvent is an…
Water is the solvent of life.
Definitions: Solution Components
Solution: Uniform mixture of two or more substances.
Solvent: Dissolver in a solution.
Solute: What is being dissolved.
Aqueous solution: Solution in which water is the solvent.
What is a solvent?
Water as a Versatile Solvent
Water is a versatile solvent because its fluidity at body temperature allows it to dissolve many solutes.
Water can transport materials around organisms.
Blood can move heat for cooling.
Water can act as a solvent for chemical reactions in living things.
Body Fluids and Water as a Solvent
All body fluids used for carrying nutrients, waste, and chemical signals use water as a solvent.
Interstitial fluid: Surrounds most cells/provides nutrients and waste removal (≈17% of body weight).
Blood plasma: Suspends blood cells and contains dissolved proteins, glucose, clotting factors, electrolytes, and hormones (≈5% of body weight).
Other body fluids in lesser amounts are: Urine, lymph, cerebrospinal fluid, aqueous humor (supports lens of eye), and synovial fluid (joints reduce friction).
Water's Polarity and Solvent Versatility
Water's Polarity makes it a valuable solvent
Water can dissolve polar (charged) solutes such as:
Salts.
Sugars.
Proteins.
Nucleic acids.
Water transports:
Nutrients & waste.
Blood cells.
Gases.
Hormones.
Water Dissolving Substances: Hydration Shells
Hydration shell: Water molecules around a solute due to the attraction between water and solute particles.
Hydration shells spread out/dissolve solutes in water.
Even large molecules can dissolve in water if they have charged regions on their surface!
Hydrophilic vs. Hydrophobic Substances
Hydrophilic substances: Dissolve in water.
Polar substances are hydrophilic.
Hydrophobic substances: Do not dissolve in water.
Nonpolar substances don't dissolve in water, they dissolve in nonpolar solvents.
Blood Transport of Polar and Nonpolar Molecules
Blood transports polar molecules such as:
Glucose.
Amino acids (building blocks of proteins).
Sodium chloride and other salts.
Blood transports nonpolar molecules such as:
Cholesterol.
Fats.
Nonpolar molecules are transported in blood using lipoprotein molecules that have nonpolar and polar regions.
Importance of Hydrophobic Substances in Biological Systems
Why are hydrophobic substances important to biological systems?
Role of Hydrophobic Substances
Forces nonpolar molecules to associate together.
EX: Phospholipids form bilayers for cell membranes.
Shapes molecules with nonpolar regions.
EX: 3D structure of proteins.
Forms important interfaces with non-polar substances.
EX: Cell membranes act as a barrier to separate internal/external environments.
Hydrophobic exclusion = "oil and water don't mix".
Properties of Water and Living Things
Several properties of water due to water's polarity and ability to hydrogen bond are significant to living things:
Cohesion
Adhesion
Solvent Properties
Physical Properties (buoyancy, viscosity, thermal conductivity and specific heat capacity)
Evaporative Cooling
Why does rubbing alcohol feel cool when it is placed on the hand?
Organic Molecules and Carbon
Molecules containing carbon are organic (organism / life).
Carbon atoms can form 4 covalent bonds, allowing a diversity of stable molecules to exist.
Organic Molecules: Monomers, Polymers, and Macromolecules
Molecules containing carbon are organic (organism / life).
Monomers: Simple organic molecules.
Polymers: Made of monomers arranged in a simple repeating structure.
Macromolecules: Large, complex molecules made from thousands of atoms.
Does not have to be a polymer.
Condensation Reactions
Condensation reactions: Link monomers to form polymers.
One molecule of water is removed for each covalent bond formed.
Condensation reactions form bonds.
Hydrolysis Reactions
Hydrolysis reactions: Break down polymers into smaller molecules.
One molecule of water is added for each covalent bond broken.
Hydrolysis reactions break bonds.
Macromolecules Necessary for Life
Many macromolecules are necessary for life.
There are four classes of macromolecules found in living things:
Carbohydrates
Lipids
Proteins
Nucleic acids
Carbohydrates
Carbohydrates contain carbon, hydrogen, and oxygen atoms.
Energy source/storage.
Structural molecules that give cells shape.
Recognition or signaling molecules.
Monosaccharides
Carbohydrate monomers = monosaccharides.
Most end in -ose.
Typically have a formula that's a multiple of CH_2O.
Monosaccharides can be:
Used for fuel.
Combined into polymers.
Noteworthy Monosaccharides
Pentoses (5-carbon sugars):
Ribose and deoxyribose are found in RNA and DNA.
Hexoses (6-carbon sugars):
Glucose:
Yields energy when oxidized via respiration.
Soluble in water and easily transported.
Stable & good for energy storage in small amounts (stored as glycogen or starch to avoid too much water uptake).
Monosaccharides in Aqueous Solutions
In aqueous solutions, monosaccharides form rings.
Sugar rings are planar (flat) with -H and -OH groups above and below the plane of the ring.
-OH: Hydroxyl group.
Isomers
Isomers: Compounds with the same formula but a different arrangement of atoms.
Alpha and Beta Glucose Isomers
When writing the –OH on carbon 1…
down for the α form.
up for the β form.
trans configuration (opposite).
cis configuration (both on the same side).
Disaccharides
Consist of two monosaccharides.
Examples: Sucrose, lactose, and maltose.
The covalent bonds joining monosaccharides are called glycosidic linkages.
Maltose Formation
The bonding of two glucose units forms maltose.
α-(1, 4) glycosidic linkage
Polysaccharides
Polysaccharides are carbohydrates made from long chains of monosaccharides (hundreds) and can be:
Storage molecules.
Structural compounds.
Storage Polysaccharides
Starch - plants
Glycogen - animals
Starch
Starch - plants
Major storage form of energy/glucose in plants.
Polymer made from alpha-glucose monomers.
Starch contains: Amylose and amylopectin
Amylose
Made from α-glucose monomers.
Linked by α-(1,4) glycosidic linkages.
Helical structure (coils) stabilized by hydrogen bonds.
Amylopectin
Made from: α-glucose joined by α-(1,4) and α–(1,6) glycosidic linkages.
α–(1,6) glycosidic linkages form branches.
Amylose vs. Amylopectin
Amylose is:
Helical in structure
Tightly packed
Good for storage
Amylopectin is:
Helical w/ branches
Takes up more space
Easier to digest
Glycogen
Major storage form of glucose (energy) in animals.
Polymer made from ɑ-glucose monomers.
Found in muscles and the liver.
Joined by α-(1,4) and α-(1,6) linkages.
Has more branches than amylopectin in starch (easier to hydrolyse for quicker energy).
Glycogen and Glucose Storage
During a meal, your liver stores glucose as glycogen.
Both glycogen and starch are very large molecules and have low solubility in water.
Can store large amounts of glucose without the cell filling up with water due to osmosis.
Can be built up or broken down via condensation & hydrolysis reactions to store or release energy.
Structural Polysaccharides
Cellulose
Cellulose
The most abundant natural polymer.
Provides strength and support in plant cell walls.
A polymer made from β-glucose monomers.
Beta Glucose Molecules
To form glycosidic links, each β-glucose molecule is rotated 180° compared to the one next to it.
β (1,4) glycosidic linkages
Cellulose: Structure & Function
Has straight, unbranched chains that run parallel.
Has hydrogen bonds linking cellulose chains to provide strength.
Provides rigidity to cell walls to prevent cells from bursting when full with water.
Biological Macromolecules
Four main classes of biological macromolecules:
Carbohydrates
Lipids
Proteins
Nucleic acids
Lipids
Contain nonpolar hydrocarbons (hydrocarbon=C and H atoms).
Insoluble in water due to hydrocarbons.
Are not true polymers
Lipids: Substances in living things that dissolve in non-polar solvents and only sparingly in water.
Include fats, oils, waxes and steroids.
Functions of Lipids
Energy source
Energy storage
Organ padding
Structural role in cell membranes & maintains fluidity
Hormone synthesis
Fat in animal bodies serves as thermal insulation
Fatty Acids
Fatty acids consist of a carboxyl group (-COOH) with a hydrocarbon chain attached.
Fatty acids can vary in length due to the # carbons in the hydrocarbon tail.
Fatty acids are insoluble in water due to the nonpolar hydrocarbon tail.
Fatty Acids
Fatty acids are carboxylic acids (COOH & hydrocarbon tail)
Classifying Fatty Acids
Fatty acids can be classified by whether they have double bonds present in the hydrocarbon tail:
Saturated fatty acids have only single bonds in the hydrocarbon tail.
Unsaturated fatty acids have one or more double bonds in the hydrocarbon tail.
Unsaturated Fatty Acids
Unsaturated fatty acids can be monounsaturated or polyunsaturated:
Monounsaturated fatty acids have one double bond in the hydrocarbon tail.
Polyunsaturated fatty acids have two or more double bonds in the hydrocarbon tail.
Cis and Trans Isomers
Cis isomer-hydrogens on same side of double bond
Nearly all unsaturated fatty acids in life are cis
Trans isomer-hydrogens on opposite side of double bond
Cis isomer: kinked chain, liquid
Trans isomer: straight chain, solid
Variations in Fatty Acids
Fatty acids can…
vary in length/ be short or long carbon chain
be saturated or unsaturated
Unsaturated fatty acids can…
vary in the location of the double bond
be monounsaturated or polyunsaturated
Be cis or trans isomers
Phospholipids
Phospholipids consist of:
One glycerol (alcohol)
Two fatty acids (nonpolar)
One phosphate group (negative & polar)
ester bond: linkage between glycerol and fatty acid
Phospholipids: Function
Phospholipids arrange in lipid bilayers.
Lipid bilayers are major component in cell membranes
Polar “heads” face outward to interact with water
Hydrophobic “tails” pack together inward
Triglycerides
Triglycerides consist of:
Three fatty acids -nonpolar hydrocarbon chain attached to a polar carboxyl group (-COOH) (carboxylic acid)
One glycerol -an alcohol with 3 hydroxyl (—OH) groups
Synthesis of a triglyceride involves:
condensation reactions.
Triglycerides: Function
Triglycerides are used by plants and animals to store energy.
In animals, triglycerides/fats are stored in adipose cells
Adipose tissue also functions to cushion vital organs (kidneys) and provide insulation
Triglycerides: Energy Storage & Insulation
Chemically stable, so energy is not lost over time
Immiscible with water, so fat droplets don’t draw in water or affect cells
Release 2x as much energy per gram than carbs (energy stored in ½ body mass)
Poor conductors of heat, used as insulators in body
Liquid at body temperature, good shock absorption
Triglycerides and Thermal Insulation
Insulation is needed by animals that live in cold habitats (maintain body temps ↑than environment)
Blubber: Thick layers of subcutaneous (under skin) adipose tissue in marine mammals.
fun fact: Adipose tissue is such good insulation that sea lions can overheat when they come onto land to breed. Blubber prevents the release of heat needed in the warmer air.
Fats vs Oils
At room temperature triglycerides can be:
Fats (solid) -made with saturated and trans-unsaturated fatty acids
Oils (liquid) -made with cis-unsaturated fatty acids -lower melting point
Sources of Fats
Saturated & Cis-Unsaturated fats occur naturally in food
Saturated fats-most come from animal sources like meat and dairy products.
Cis-Unsaturated fats-most come from plant sources, including nuts, oils, fish and vegetables.
Trans Fats
Trans unsaturated fats are mostly man-made.
Trans fats are formed by adding hydrogen to unsaturated vegetable oils under pressure.
This process increases the spreadability of vegetable oils and extends the shelf life of processed foods.
Methods that do not produce trans fats are being developed due to health risks.
Health Effects of Fats
Positive health effects
Negative health effects
Saturated fats
trans unsaturated fats
cis-unsaturated fats
Steroids
Have 4 fused rings of carbon atoms (3 cyclohexane rings and 1 cyclopentane ring)
Differ in double bonds and functional groups
Are nonpolar and can enter & exit cells through phospholipid bilayers
Biological Macromolecules
Four main classes of biological macromolecules:
Carbohydrates
Lipids
Proteins
Nucleic acids
Proteins
Make up 50% or more of dry mass of most cells
Humans have tens of thousands of different proteins
Proteins have many structures, resulting in a wide range of functions
Most structurally and functionally diverse of life’s molecules
Proteins are Essential to Life
Proteins are essential to the structures and activities of life
Amino Acids
Each amino acid contains:
An amine group
A carboxyl group
R group, which distinguishes each of the different amino acids
H
Peptide Bonds
Condensation reactions form peptide bonds
Remove one H_2O to form one bond
Peptide bonds form betw/amine and carboxyl groups
Amino Acids
Most proteins built by living things use 20 amino acids!
Plants make all 20 amino acids by photosynthesis and animals obtain them from their diet.
non-essesntial amino acid: Can be synthesized in animals using chemical reactions that transform amino acids
essential amino acid: Obtained from diet
Animal based foods have a balance of aa we need, plant based foods have different balance.
Peptide Chains
Ribosomes link amino acids together to form polypeptide chains based on genes in DNA (genes code aa sequences).
Most polypeptides then fold to form functional protein.
A polypeptide with n amino acids has 20^n possible sequences
400 amino acid chain= 20^{400} sequences
10,000 amino acid chain= infinite sequences
β-endorphin (pain killer)=31 aa
ɑ-amylase (digests starch)=496 aa
titin (part of muscle)=35,213 aa
Protein Functions
A protein’s specific shape determines its function
Polypeptides fold to give four levels of protein structure:
Primary
Secondary
Tertiary
Quaternary
Primary Structure
The unique sequence of amino acids in a polypeptide
Secondary Structure
The folding or coiling of the polypeptide into a repeating configuration.
Types include…
α helix: helical shape
β pleated sheet: 2 or more sections of chain arranged in parallel
Hydrogen Bonds
Hydrogen bonds stabilize secondary structure due to attractions between amine and carboxyl groups.