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Water As Medium Of Life
Charles Darwin made first statement saying that life came from water
Water Bonds
Covalent bonds between O & H atom, electronegativity means O has a slight negative charge and H is positive
Water molecules form hydrogen bonds (H can hydrogen bond to O, N or F)
Hydrogen bonds by themselves are weak, so there are multiple per unit volume of water
Cohesion with Xylem
Water molecules sticking together
Xylem: Cohesion allows water to be transported through tension in plants (attractions between soil and water occur as water is lost by evaporation and interactions between water molecules and cell walls
Cohesion with Water Surfaces
Surface tension: surface of pond or body of water acts like an elastic membrane that shrinks to the smallest possible area. Because of this, itâs possible to float objects on the surface because cohesion of water molecules is greater than the attractions between water and the floating object. Water striders are a good example.
Adhesion
Water sticks to the surface of a solid when hydrogen bonds between water and solids composed of polar molecules
This can be seen in capillary action, when water is drawn through narrow tubes. It occurs in plants when water adheres to the cellulose molecules, helping to keep cell walls moist.
Adhesion in Porous Solids
Porous solids such as paper have large surface areas attractive to water, allowing for extra suction forces
If soil is porous, water gets drawn by capillary action
Hydrophilic
Polar molecules (glucose), particles with + or - (Na or Cl ions). This describes substances that are chemically attracted to water, and also adheresHy
Hydrophobic
Non-polar, no + or - charges, all lipids. Describes substances that are not chemically attracted to water, but can dissolve in other solvents
Cytoplasm
Complex mixture of dissolved substances. Because itâs aqueous it allows itself to interact with other molecules.
Dissolved enzymes catalyze specific chemical reactions (known as metabolism)Cyt
Cytoplasm in Plants
Mineral ions transported in xylem sap
Sucrose & other particles of photosynthesis transported in phloem sap
Cytoplasm in Humans
In our cytoplasm we have:
Blood: NaCl dissolves and carries in blood plasma
Amino Acids: They get dissolved in blood plasma
Glucose: Gets carried in plasma
Oxygen: Dissolves sparingly & water gets saturated at low concentrations
Red blood cells have haemoglobin that include bonding sites for oxygen
Fat molecules are insoluble, but phospholipids coat the fat molecules to prevent large droplets
Air Vs Water
Air is less dense than water, so organisms need to generate lift
Pure water has a low viscosity, but sea water is higher than air
Water has a relatively high thermal conductivity. Air is about 5% of water
Heat capacity of water is high
Carbohydrates vs Lipids
Carbohydrates are in starch or glycogen form and are for short-term energy storage
Lipids are fats and oils and are for long-term energy storage
Both use oxidation in cell respiration to release energy
Importance of Carbon Atoms
Carbon atoms can form covalent bonds with other atoms (up to 4 with C, H, O, N, or P)
They can bond with 4 atoms of one element (CH4)
They can bond to more than one element (C-O-H)
They can make extremely long chains, such as fatty acids, which are branched by an oxygen. These chains can spread as far as a tetrahedral shape, but can only be as straight as a zig-zag
Carbons can form rings based on their bond angles
Macromolecules
Molecules with large number of atoms and a relative mass of 10,000 amu
Main classes are: polysaccharides, polypeptides and nucleic acids. They are linked by subunits (monomers)
Energy is required to make these macromolecules (usually ATP)
Condensation Reaction
Happens when a monomer links to a polymer
2 molecules link together and release a smaller molecule simultaneously (H2O). The hydroxyl (-OH) removes itself and links to another hydrogen
Polysaccharides
Made up of a chain of monosaccharides. Glucose is the mono used to make glycogen, starch and cellulose
Glucose molecules link up to glycosidic bonds (C-O-C), which are formed during condensation reactions
Monosaccharide Types
Glucose, Fructose, Galactose
Disaccharide Types
Sucrose, Maltose, Lactose
Deconstructing Polymers
Polymers are deconstructed so the monomers can be reused to make new polymers or as energy
This reaction is called hydrolysis. Polysaccharides deconstruct to monosaccharides, polypeptides deconstruct into amino acids, and nucleic acids deconstruct into nucleotides
Monosaccharide Properties
Between 3-7 carbon atoms, with each ring usually having one oxygen in them
Glucose properties
Glucose is soluble and small, allowing it to be easily transported. It circulates in blood and is dissolved in plasma
Glucose is chemically stable, which is helpful for food storage. Glucose can convert to starch or glycogen, but by itself it can release energy when oxidized
Starch
Found in plants, composed of large amounts of alpha-glucose molecules.
Amylose is a type of starch thatâs unbranched linked by 1â4 glycosidic bonds. Usually chain is helical'
Amylopectin has a similar structure but there are some 1â6 bonds making it branched. They can contain up to a 100,000 glucose subunits
In both, hydrolysis releases a glucose molecule by breaking the 1â4 bond
Glycogen
Found in animals, also composed of large amounts of alpha-glucose molecules. They usually have tens of thousands of glucose subunits
Similar to amylopectinâs structure, with glycosidic bonds between 1â4 and branched by 1â6
Cellulose
Composed of beta-glucose. All links are 1â4 so the entire molecule is unbranched
C1âs OH is angled up while C4âs OH is angled down, meaning the subunits must be inverted to join
Chains allow the cellulose to be in parallel formation. These bundles are called microfibrils and are the basis of plant cell walls. They have high tensile strength
Glycoproteins
Composed of polypeptides with carbohydrate attached (usually an oligosaccharide, which is a short chain of monosaccharides linked by glycosidic bonds)
Component of plasma membranes in animal cells and position with the carbohydrate facing outwards. This allows cells to recognize each other via receptors, allowing them to organize tissues or identify and kill foreign or infected cells
Red Blood Cells
Red blood cells have glycoproteins, with the oligosaccharides either O, A, or B. One or two can be present, but not all three
If blood glycoprotein A is injected into someone who doesnât produce it, it will be rejected (same as B). However, O doesnât have rejection problems because it has the same structure minus one monosaccharide
Lipids
In living organisms that dissolve in non-polar solvents, but they are sparingly soluble in aqueous solvents.
Oils (melt under 20C), Fats (melt between 20-37C), Waxes (melt above 37C), Steroids
Triglyceride
3 fatty acids linked to one glycerol via condensation reaction (3 H2O molecules are formed)
The bond between the acid and glycerol is called an ester bond, and forms between the acid and the hydroxyl group.
Triglyceride Properties
Chemically very stable, allows to keep energy
Immiscible in water, meaning it naturally forms harmless droplets in the cytoplasm
Release 2x the energy per gram in cell respiration compared to carbohydrates, but they take longer to build up
Can be used as a thermal insulator (located in adipose tissue)
Liquid at room temperature, allowing it to act as a shock absorber
Phospholipids
2 fatty acids plus a phosphate group linked to a glycerol
Phosphate group is hydrophilic, hydrocarbons are hydrophobic, giving it a unique property: amphipathic
When phospholipids mix with H2O, phosphate heads attract to water but hydrocarbon tails attract to each other. These form phospholipid bilayers, which are the basis of cell membranes
Fatty Acids
Unbranched chain of C atoms, with H atoms covalently bonded
Acid part is carboxyl (-COOH), Methyl is on other end (CH3)
Fatty acids with all single bonds are saturated (usually fats from animal sources)
Fatty acids with one double bond is monounsaturated, & multiple double is polyunsaturated. Unsaturated fats are oils, and are mainly from (but not always) plants)
Types of Unsaturated Fatty Acids
H atoms on double bonds all on same side mean that the fatty acid is cis-unsaturated (these are found in nature)
Alternating sides means itâs trans-unsaturated (these are only made through food processing)
Steroids
Group of lipids similar to sterol (4 fused rings of carbon)
3 cyclohexane rings, 1 cyclopentane ring (17 total carbon atoms)
Hundreds of different types of steroids, but all are made from hydrocarbon and are hydrophobic, allowing it to pass through phospholipid bilayers and enter or leave cells
Cholesterol is the precursor to all other steroids. Itâs found in animal cell membranes, keeping them fluid and flexible.
Waxes
Hydrophobic and are used to create waterproof structures and coatings
Amino Acids
Building blocks of proteins, amphiprotic
Central carbon is called alpha-carbon, and has covalent bonds to 4 other subunits
Covalently bonded to N atom of amine group (H2N) (acid)
Covalently bonded to C atom of carboxyl group (COOH) (base)
Covalently bonded to H atom
Covalently bonded to R-Group (20 different kinds)
Multiple Amino Acids
2 amino acids join via condensation reaction to form a dipeptide. Oligopeptides are less than 20 amino acids together, while polypeptides are 20 or more
Once the condensation reaction finishes, the amino acids join via peptide bonds (C-N). This is catalyzed in cells by ribosomes
Free amino acid uses amine group to link to carboxyl of growing chain. All bonds are the same
Multiple Amino Acids (cont.)
20 different amino acids are used by ribosomes to make polypeptides
Plants make all of these via photosynthesis, but animals need to obtain some of these through food
Essential vs Non-essential Amino Acids
Non-essential amino acids means that they can be synthesized by an animal through metabolic pathways
Essential amino acids means that they cannot be synthesized, therefore they must be ingested into diet
Animal-based foods (milk, fish, meat, eggs) provide a balance of amino acids
Plant-based foods may lack a balance, but traditional plant-based diets provide sufficient amounts
Linking Amino Acids
Ribosomes link amino acids one at a time until a polypeptide is formed.
Even though they can link as many as they want, genetic code gives information to the ribosomes as to what they need to create
For a polypeptide of n amino acids, there are 20^n possible sequences
The polypeptide sequences are called your proteome
Bonds & Interactions
When bonds and interactions break, there is a change in the structure, called denaturation
Denaturation is permanent, and sometimes soluble proteins become insoluble & form precipitates because hydrophobic R-groups are exposed to H2O
Heat can cause denaturation because vibrations can break intermolecular bonds. Each protein has a different heat tolerance
Extreme pH can cause denaturation because the positive or negative charges can change the R-groups
Genetic Material
Store of information. If copied it can pass cell to cell or parent to offspring
Usually called hereditary info because itâs inherited
DNA Properties
All living organisms use DNA to store hereditary info
2 polynucleotide strands, Nucleotides (pentose, phosphate, base), Antiparallel orientation, Hydrogen bond between bases, Covalent bond between other subunits (called phosphodiester bonds)
All nucleotides link phosphate to pentose, forming a strong sugar-phosphate backbone in DNA & RNA molecules that conserve the sequence of bases
If the strands were not antiparallel, no hydrogen bonds would form
DNA & RNA Bases
Adenine, Thymine, Guanine & Cytosine
Adenine, Uracil, Guanine, & Cytosine
These are called complementary base pairings (Chargaffâs Rule)RNA
RNA Properties
Single unbranched polymer of nucleotides. All nucleotides are linked via condensation reaction (hydroxyl group of phosphate and on pentose sugar)
DNA Replication
Two strands of the double helix separate, with the original strands serving as a template to build the new strand. The new strands form by adding nucleotides one by one and linking them together
Gene
Genetic info consisting of sections of DNA to code for proteins
Gene Expression
When info on a gene has an effect on the cellT
Transcription
Copies base sequence out of DNA. One of 2 strands used as a template. The adenine pairs with the uracil
RNA made by transcription is either used for regulatory or structural role in a cell, or it could be used for protein synthesis
Decoding DNA
Info in DNA & RNA is decoded during protein synthesis
Groups of 3 bases are called codons are have meaning
Most codons specify a particular amino acid, but one codon signals to start protein synthesis while 3 signals to stop
Purines & Pyrimidines
Purines are double-ringed nitrogenous bases (Adenine & Guanine)
Pyrimidines are single-ringed nitrogenous bases (Thymine, Cytosine, Uracil)