Chemical Structures and Properties of Biologically Important Molecules Flashcards
What are key characteristics of organic molecules?
- have C-H bonds
- generally have covalent bonds
What are key characteristics of inorganic molecules?
- may contain C, but lack H
- usually contain metals
- generally have ionic bonds
When do covalent bonds form?
- covalent bonds form when electrons are shared
What are the two types of covalent bonds?
- Nonpolar (pure) covalent bonds: electrons are shared equally
- Polar covalent bonds: electrons are shared unequally
When do ionic bonds form?
- form when electrons are transferred
What is the distinction between a cation and an anion?
- cations lose electrons and are positively-charged
- anions gain electrons and are negatively-charged
What elements can participate in hydrogen bonding?
- Occurs only between polar molecules with hydrogen atoms bonded directly to F, O, or N
Why is carbon such an important element for biological molecules? Why are carbon-containing compounds so diverse and stable?
- valence of four - carbon forms four covalent bonds w/other atoms, which gives it diversity in structure and function
- covalent bonds - carbon covalent bonds have high bond energies, which makes them stable
- diverse - carbon-containing compounds are extremely diverse (ie many functional groups)
- tetrahedral - b/c carbon has a tetrahedral geometry, it can form stereoisomers
What are key characteristics of water?
- polar
- excellent solvent
- high specific heat
- high heat of evaporation
- strong cohesive/adhesive forces
- less dense as solid than liquid
What is the most important characteristic of water?
- its polarity, b/c this accounts for all of its other characteristics
How is water polar?
- water has a bent geometry (104.50)
- oxygen = highly electronegative = draws electrons towards it = partial negative charge
- hydrogen = electropositive = electrons are drawn from it = partial positive charge
Why is water considered an excellent solvent?
- b/c it is polar, it can dissolve many polar/ionic solutes
Why is the high specific heat of water important?
- it takes a lot of energy to raise the temperature of water by a degree
- this helps keep the surrounding environment temperature regulated/consistent
Why is the high heat of vaporization of water important?
- it takes a lot of energy to change water from liquid to a gas
- this helps cool down organisms via evaporative cooling
Why are the strong cohesive forces of water important?
- water molecules have a strong attraction to other water molecules b/c H-bonds
- this creates surface tension and enables fluid transport of substances
Why are the strong adhesive forces of water important?
- water molecules have a strong attraction to other non-water molecules because of partial charges
- this allows it to stick to other substances besides itself and enables fluid transport of substances
Why is it important that water is less dense as a solid than as a liquid?
- this causes ice to float and keeps ponds/lakes/oceans from freezing solid during the winter, which allows life to continue below the surface
What are the 4 macromolecules?
- proteins
- carbohydrates
- nucleic acids
- lipids
What is the basic structure of an amino acid?
- an alpha carbon surrounded by:
- carboxyl group (-COOH)
- amino group (-NH2)
- hydrogen atom
- side-chain (r-group)
What determines the chemical characteristics of a specific AA?
- the side-chain chemistry
How do peptide bonds form?
- peptide bonds form between adjacent AA in a chain via a dehydration synthesis reaction between the carboxyl group of one AA and the amino group of the second AA, releasing water
- this reaction is not easily reversible b/c it is catalyzed by enzymes and the peptide bond is extremely stable
What determines the primary structure of a protein?
- the linear sequence of the AA in a polypeptide chain
What determines the secondary structure of a protein?
- local interactions between AAs via hydrogen bonds between the carbonyl oxygen and the amino nitrogen
When do alpha helices form?
- secondary structures that form via hydrogen bond interactions between AAs four residues apart on the same chain
When do beta-sheets form?
- form via hydrogen bond interactions between AAs on separate chains
What determines the tertiary structure of proteins?
- determined by long-range hydrophobic/hydrophilic interactions between the R-groups of AAs on separate
When do proteins have quaternary structure?
- only when the protein contains more than one subunit
What is the general structure of a monosaccharide?
- general formula = (CH2O)n [n determines the specific type]
- ~3-7 carbons
- carbonyl group
- hydroxyl group
How are glycosidic bonds formed?
- glycosidic bonds are formed between two monosaccharides via an oxygen atom after a dehydration reaction that releases water
What are the two most abundant storage polysaccharides?
- starch (plant cells)
- glycogen (animal cells)
What are the two types of starch?
- amylose: straight-chain polymer of glucose, ~20% of starch content
- amylopectin: branched-chain polymer of glucose, ~80% of starch content
What are the two most abundant structural polysaccharides? What are the differences between the two?
- Cellulose:
- Polymer of glucose
- Plant/algae cell walls
- Chitin:
- Polymer of glucosamine (contains N)
- Arthropod exoskeletons and fungi cell walls
What is the basic structure of a fatty acid? What is the most key characteristic of fatty acids?
- long hydrocarbon chain (non-polar)
- carboxyl group at one end (polar)
Amphipathic: both polar and nonpolar
What is the distinction between saturated fatty acids and unsaturated fatty acids?
- Saturated fatty acids: no double-bonds in tails; long, straight chains that pack together well
- Unsaturated fatty acids: one or more double-bonds; result in a kink in a chain that prevents tight packing
What is a triacylglycerol?
- Composed of a glycerol molecule with 3 fatty acids linked to it
- Ester bonds link fatty acids to glycerol
- Main function = store energy
What is a phospholipid?
- Composed of one glycerol, two fatty acids, and phosphorus
- Main function = bilayer of membrane
What is the basic structure of nucleotides?
- Nitrogen-containing base
- Pentose
- One or more phosphate groups
What are the two types of nucleotide bases?
- pyrimidine: one-carbon/nitrogen ring: uracil, cytosine, thymine
- purine: two-carbon/nitrogen rings: guanine, adenine
What are the two types of pentose sugars?
- ribose: has a hydroxyl group on 2’C
- deoxyribose: lacks a hydroxyl group on 2’C
How are nucleotides linked to one another?
- phosphodiester (covalent) bonds between the phosphate group of one nucleotide and the C’3 of the pentose sugar
- creates an alternating backbone of sugar-phosphate-sugar
How do bases pair?
- purines and pyrimidines pair up
- A forms two H-bonds w/T (or U)
- G forms three H-bonds with C
