chapter 2 cell chemistry

element

composed of a single type of atom

atomic number

equal to the number of protons in the nucleus; atomic number determines the element

atomic mass

sum of masses of protons, neutrons, and electrons

electronegativity

attraction of atom for electrons

the more electronegative an atom, the greater the pull its nucleus exerts on electrons

when are atoms most stable

electrons in lowest possible energy levels

outermost energy level (valence shell or level) is filled to maximum (2 or 8)

chemical bonds

electrostatic forces between positively charged protons of one atom and negatively charged electrons of another atom that hold these atoms together within a molecule or between molecules

intramolecular bonds

hold atoms in the same molecule together

types of intramolecular bonds

ionic bonds

covalent bonds

hydrogen bonds

hydrophobic interactions

intermolecular bonds

form between two different molecules

types of intermolecular bonds

hydrogen bonds

hydrophobic interactions

electrostatic )ionic) forces

van der waals forces

ionic bonds

forms between oppositely charged ions

cations and anions

no electrons shared

covalent bonds

strong bond between where electrons are shared between atoms to fill valence shell

relationship between strength and number of bonds

as the number of bonds increase, the strength of the bond increases

relationship between movement and number of bonds

as the number of bonds increase, the movement of the bond decreases

electronegativity

the force of attraction of a nucleus on the electrons moving around it or for the electrons in a chemical bond

amphipathic

composed of part hydrophilic (ionic and/or polar) and part hydrophobic (non-polar_ regions; one part water soluble other part not

hydrophobic interactions

weak bonds occurring when non polar molecules, or non polar regions of molecules, associate tightly together in a polar solvent; non polar molecules disrupt hydrogen bonding among water molecules so they squeeze together to minimize their volume and the disruption of hydrogen bonds

hydrophobic interactions play important roles in

enzymes binding substrates

protein conformation

stabilization of RNA and cell membranes

van der waals forces

weak attractive forces that occur between atoms when they become close than 3-4 A

due to temporary polarities in atoms and molecules

play important roles in enzymes binding substrates and protein-nucleic acid interactions

play an important role in membrane fluidity

polar molecule

water is the major constituent of all microbial cells

can form hydrogen bonds and other bonds

good solvent for polar and ionic molecules

high specific heat

exhibits cohesion and adhesion

participates in many chemical reactions

salts

ionic compounds consisting of a cation and an anion held together by an ionic bond

salts often dissociate in water (a polar solvent) into their respective ions

cations and anions of salts are electrolytes that

create electrical differences between inside and outside cell

transfer electrons from one location to another

form important components

acids

proton donors; increase concentration of H+ ions in a solution

bases

proton acceptors; decrease the concentration of H+ ions in a solution

buffers

compounds that resist changes in pH by sometimes behaving like an acid, and sometimes like a base; found in all cells

carbohydrates

monosaccharides and polysaccharides

polymers of monosaccharides units bonded together by glycosidic bonds

play important roles in cell walls and as energy storage molecules

lipids

fats, oils, sterols

non polar

hydrophobic

play crucial roles in most membrane and as every storage molecules

proteins

polymers of amino acids

most abundant macromolecule in cells

important structural and enzymatic cells

nucleic acids

polymers of nucleotides

two forms: RNA and DNA

amount of RNA>amount of DNA

pentose

c5 sugars

structural backbones of nucleic acids

hexoses

c6 sugars

monomeric constituents of cell wall polymers and energy reserves

modified monosaccharides derivatives

when other chemical species replace one or more of the hydroxyl groups on the sugar, derivatives are formed

glycosidic bonds

covalent bonds linking adjacent sugars together

two geometric orientations: alpha and beta

configuration of bond imparts different functional properties to macromolecules composed of the same builidng blocks

starch

polysaccharide composed of glucose monomers joined to each other by alpha glycosidic bonds

tend to be hydrophobic

function is for energy storage

structural polysaccharide

ex. cellulose chitin

polisaccaride composed of glucose monomers joined to each other by beta glycosidic bonds

hydrophobic

function is for structural strength of cell walls

glycoproteins

polysaccharides and proteins

include eukaryotic cell-surface receptor molecules; typically reside on external surfaces of the membrane

glycolipids

polysaccharides and lipids

important in the cell walls of gram-negative bacteria

triglycerides

composed of three fatty acids bonded to a 3 carbon alcohol, glycerol

function is for energy storage

has ester bonds between glycerol and fatty acids

fatty acids consist carboxyl group and hydrocarbon chain

fatty acids

consist of carboxyl group and hydrocarbon chain

saturated fatty acids

no double bonds between Cs; straight, linear molecule

unsaturated fatty acids

one or more double bonds between the carbons; bent or kinked molecule

complex lipids

simple lipids that contain additional elements such as phosphorus, nitrogen, sulfur, or small hydrophilic organic compounds

phospholipids

complex lipids containing 2 fatty acids, glycerol, a phosphate group and something attached to phosphate play a major role in cytoplasmic membranes; amphipathic

sterols

structural lipids found in cell membranes

found in all eukaryotes and few prokaryotes

sterols

hopanoid

structural lipid found in cell membranes

found in many prokaryotes, but not in any eukaryotes

hopanoids

nucleic acid

polymer of nucleotides

DNA

polymer of deoxyribonucleic genetic material in all cells and some viruses

RNA

polymer of ribonucleotides; plays role in protein synthesis in all cells ; genetic material of most viruses

nucleotides composed of

~ c5 sugar (pentose) either robse (rna) or deoxyribose (DNA)

~nitrogen base

~phosphates

nucleotide

~nitrogen base attached to c5 sugar by N-glycosidic linkage and bonded to a phosphate

~carriers of sugar in biosynthesis of polysacchardides

~regulatory of molecules for certain enzymes or metabolic events

key forms of chemical energy

~main short term energy supply for cells

~energy is released when phosphate bonds of ATP are broken

~atp supply is limited and must be replenished

purine bases

double ring structure, adenine and guanine