Chapter 2: Molecules and Membranes

organic molecules

carbohydrates, lipids, proteins, nucleic acids

most abundant molecule in cells

water

polarity of water

polar

hydrogen bonds

bond that forms between polar organic molecules

polar molecule interactions with water

hydrophilic

nonpolar molecule interactions with water

hydrophobic

ΔG < 0

reaction proceeds in forward direction, builds energy

ΔG > 0

reaction proceeds in reverse, consumes energy

location where energy is stored in ATP

bonds between the phosphates

result of ATP hydrolysis

large decrease in free energy

ATP synthesis

coupled to energy-yielding reactions

ATP hydrolysis

coupled to energy-requiring reactions

molecule that provides the principle source of cellular energy

glucose

structure of glucose

ring formed by 6 carbon sugar

polymers of a few sugars

oligosaccharides

polymers of 100s or 1000s of sugars

polysaccharides

polysaccharide bond

α (1→4) glycosidic bond

glycogen

storage of glucose in animal cells

starch

storage of glucose in plant cells

molecules that contain α (1→6) glycosidic bonds

glycogen, amylopectin

cellulose

main structural component of plant cell walls; glucose in ß configuration

roles of lipids

energy storage, major component of cell membranes, cell signaling

fatty acids

long hydrophobic hydrocarbon chains (16 or 18 carbons) with a carboxyl group (COO^-) at one end

unsaturated fatty acids

one or more double bonds

saturated fatty acids

no double bonds, only nonpolar C-H bonds

triacylglycerols (fats)

3 fatty acids linked to a glycerol molecule; insoluble in water

phospholipid

2 fatty acids (hydrophilic tails) joined to a phosphate group with a polar attachment (hydrophilic head); amphipathic

glycerol phospholipids

2 fatty acids bound to 2 carbons in glycerol

sphingomyelin

the only nonglycerol phospholipid in cell membranes

glycolipids

2 hydrocarbon chains and a carbohydrate polar head group (amphipathic)

cholesterol

4 hydrophobic hydrocarbon rings and a polar hydroxyl (OH) group (amphipathic)

derivatives of cholesterol

steroid hormones

function of steroid hormones

act as chemical messengers

structure of steroid hormones

contain 4 hydrocarbon rings

purines

adenine and guanine

pyrimidines

cytosine, thymine, uracil

nucleotide replaced by uracil in RNA

thymine

mRNA

carries info from DNA to the ribosomes

rRNA, tRNA

involved in protein synthesis

nucleotides

one or more phosphate groups linked to 5’ carbon of sugars

phosphodiester bond

bond between the 5’ phosphate of one nucleotide and the 3’ hydroxyl of another

direction of polynucleotide synthesis

5’ to 3’

guanine pairs with

cytosine

thymine pairs with

adenine

bond between complementary base pairs

hydrogen bonds

amino acid structure

core α-carbon bonded to a carboxyl group (COO^-), an amino group (NH₃⁺), a hydrogen, and a distinctive side chain

number of amino acids

20

bond that joins amino acids

peptide bonds

polypeptide

chain of 100s or 1000s of amino acids

polypeptide structure

one end terminates in an α amino group (N terminus) and the other terminates in an α carboxyl group (C terminus)

denaturation

disruption of the 3D protein shape by breaking non-covalent bonds

primary structure of a protein

the sequence of amino acids in a polypeptide chain

secondary structure of a protein

α-helix and ß-sheet arrangements, held together by hydrogen bonds

tertiary structure of a protein

folded 3D structures due to interactions between amino acid side chains

quaternary structure of a protein

interactions between multiple polypeptide chains

enzymes

catalysts that increase the rate of all cellular chemical reactions without being consumed or altered

transition state

higher energy state

activation energy

energy required to reach the transition state

active site

specific region on an enzyme for substrate binding

induced fit

substrate and enzyme are both distorted to the transition state conformation

serine protease

enzymes that cleave peptide bonds adjacent to specific types of amino acids

chymotrypsin

cleaves bonds adjacent to hydrophobic amino acids

trypsin

cleaves bonds next to basic (ionic) amino acids

coenzyme

small organic molecule that participates in specific types of enzymatic reactions

NAD⁺

can accept H⁺ and 2 electrons to form NADH

NADH

can donate 2 electrons to form NAD⁺

allosteric regulation

the binding of small molecules to enzyme regulatory sites changes the enzyme conformation and alters the active site

feedback inhibition

the product of a metabolic pathway inhibits an enzyme involved in its synthesis

phosphorylation

common mechanism of enzyme regulation in which phosphate groups are added to the side-chain OH groups of serine, threonine, or tyrosine residues