24 Key Terms

active site
location on an enzyme configured to bind a substrate
alpha-helix structure (α-helix)
type of secondary protein structure formed by folding the polypeptide into a helix shape with hydrogen bonds stabilizing the structure
amino acid
a protein’s monomer; has a central carbon or alpha carbon to which an amino group, a carboxyl group, a hydrogen, and an R group or side chain are attached; the R group is different for all 20 common amino acids
beta-pleated sheet (β-pleated)
secondary structure in proteins in which hydrogen bonding forms “pleats” between atoms on the polypeptide chain’s backbone
biological macromolecule
large molecule necessary for life that is built from smaller organic molecules
carbohydrate
biological macromolecule in which the ratio of carbon to hydrogen and to oxygen is 1:2:1; carbohydrates serve as energy sources and structural support in cells and form arthropods’ exoskeleton
cellulose
polysaccharide that comprises the plant’s cell wall; provides structural support to the cell
chaperone
(also, chaperonin) protein that helps nascent protein in the folding process
chitin
type of carbohydrate that forms the outer skeleton of all arthropods including crustaceans and insects; it also forms fungi cell walls
chromatin
complex of histone proteins and DNA, the substance of eukaryotic chromosomes
chromosome
structure composed of DNA and histone proteins, containing genetic information
dehydration synthesis
(also, condensation) reaction that links monomer molecules, releasing a water molecule for each bond formed
denaturation
loss of shape in a protein as a result of changes in temperature, pH, or chemical exposure
deoxyribonucleic acid (DNA)
double-helical molecule that carries the cell’s hereditary information
disaccharide
two sugar monomers that a glycosidic bond links
enzyme
catalyst in a biochemical reaction that is usually a complex or conjugated protein
genome
a cell or organism’s entire genetic content
glycogen
storage carbohydrate in animals
glycosidic bond
bond formed by a dehydration reaction between two monosaccharides, involving   eliminating a water molecule
hormone
chemical signaling molecule, usually protein or steroid, secreted by endocrine cells that act to control or regulate specific physiological processes
hydrolysis
reaction that causes breakdown of larger molecules into smaller molecules by utilizing water
hydrolysis reactions
breaking a large molecule into smaller molecules by adding and splitting a water molecule
lipid
macromolecule that is nonpolar and insoluble in water
messenger RNA (mRNA)
RNA that carries information from DNA to ribosomes during protein synthesis
monomer
smallest unit of larger molecules that are polymers
monosaccharide
single unit or monomer of carbohydrates
nucleic acid
biological macromolecule that carries the cell’s genetic blueprint and carries instructions for the cell’s functioning
nucleotide
monomer of nucleic acids; contains a pentose sugar, one or more phosphate groups, and a nitrogenous base
omega fat
type of polyunsaturated fat that the body requires; numbering the carbon, omega starts from the methyl end, or the end that is farthest from the carboxylic end
peptide bond
bond formed between two amino acids by a dehydration reaction
phosphodiester
linkage covalent chemical bond that holds together the polynucleotide chains with a phosphate group linking neighboring nucleotides’ two pentose sugars
phospholipid
membranes’ major constituent; comprised of two fatty acids and a phosphate-containing group attached to a glycerol backbone
polymer
chain of monomers that covalent bonds link; polymerization is the process of polymer formation from monomers by condensation
polynucleotide
long chain of nucleotides
polypeptide
long chain of amino acids that peptide bonds link
polysaccharide
long chain of monosaccharides; may be branched or unbranched
primary structure
linear sequence of amino acids in a protein
protein
biological macromolecule comprised of one or more amino acid chains
purine
type of nitrogenous base in DNA and RNA; adenine and guanine are purines
pyrimidine
type of nitrogenous base in DNA and RNA; cytosine, thymine, and uracil are pyrimidines
quaternary structure
arrangement of polypeptide subunits within a protein that has multiple subunits
ribonucleic acid (RNA)
single-stranded, often internally base paired, molecule that is involved in protein synthesis
ribosomal RNA (rRNA)
RNA that ensures the proper alignment of mRNA and ribosomes during protein synthesis and catalyzes formation of the peptide linkage
saturated fatty acid
long-chain hydrocarbon with single covalent bonds in the carbon chain; the number of hydrogen atoms attached to the carbon skeleton is maximized
secondary structure
regular structure that proteins form by intramolecular hydrogen bonding between the oxygen atom of one amino acid and the hydrogen attached to the nitrogen atom of another  
starch
storage carbohydrate in plants
steroid
type of lipid comprised of four fused hydrocarbon rings forming a planar structure
tertiary structure
a protein’s three-dimensional conformation, including interactions between secondary structural elements; formed from interactions between amino acid side chains
trans fat
fat formed artificially by hydrogenating oils, leading to a different arrangement of double bond(s) than those in naturally occurring lipids
transcription
process through which messenger RNA forms on a template of DNA
transfer RNA (tRNA)
RNA that carries activated amino acids to the site of protein synthesis on the ribosome
translation
process through which RNA directs the protein’s formation
triacylglycerol (also, triglyceride)
fat molecule; consists of three fatty acids linked to a glycerol molecule
unsaturated fatty acid
long-chain hydrocarbon that has one or more double bonds in the hydrocarbon chain
wax
lipid comprised of a long-chain fatty acid that is esterified to a long-chain alcohol; serves as a protective coating on some feathers, aquatic mammal fur, and leaves

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Biology 2e Part I, 2nd edition Copyright © 2022 by LOUIS: The Louisiana Library Network is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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