A coiled secondary structure of a polypeptide chain formed by hydrogen bonding between amino acids separated by four residues.
β-barrel
A transmembrane domain formed by the folding of β sheets into a barrel-like structure.
β sheet
A sheetlike secondary structure of a polypeptide chain, formed by hydrogen bonding between amino acids located in different regions of the polypeptide.
active transport
The transport of molecules in an energetically unfavorable direction across a membrane coupled to the hydrolysis ofATP or other source of energy.
adenine
A purine that base-pairs with either thymine or uracil.
amino acid
Monomeric building blocks of proteins, consisting of a carbon atom bound to a carboxyl group, an amino group, a hydrogen atom, and a distinctive side chain.
amphipathic
A molecule that has both hydrophobic and hydrophilic regions.
carbohydrate
A molecule with the formula (CH2O)n. Carbohydrates include both simple sugars and polysaccharides.
carrier protein
A protein that selectively binds and transports small molecules across a membrane.
cellulose
The principal structural component of the plant cell wall, a linear polymer of glucose residues linked by β(1→4) glycosidic bonds.
channel protein
A protein that forms pores through a membrane.
cholesterol
A lipid consisting of four hydrocarbon rings. Cholesterol is a major constituent of animal cell plasma membranes and the precursor of steroid hormones.
cytosine
A pyrimidine that base-pairs with guanine.
deoxyribonucleic acid (DNA)
The genetic material of the cell.
domain
A compact, globular region of a protein that forms the basic unit of tertiary structure.
fats
See triacylglycerols.
fatty acid
A long hydrocarbon chain usually linked to a carboxyl group (COO–).
fluid mosaic model
A model of membrane structure in which proteins are inserted in a fluid phospholipid bilayer.
genomics
The systematic analysis of entire cell genomes.
glycerol phospholipid
A phospholipid consisting of two fatty acids bound to a glycerol molecule.
glycogen
A polymer of glucose residues that is the principal storage form of carbohydrates in animals.
glycolipid
A lipid consisting of two hydrocarbon chains linked to a polar head group containing carbohydrates.
glycosidic bond
The bond formed between sugar residues in oligosaccharides or polysaccharides.
guanine
A purine that base-pairs with cytosine.
integral membrane protein
A protein embedded within the lipid bilayer of cell membranes.
lipid
Member of a group of hydrophobic molecules that function as energy storage molecules, signaling molecules, and the major components of cell membranes.
mass spectrometry
A method for identifying compounds based on accurate determination of their mass. Mass spectrometry is commonly used for protein identification.
messenger RNA (mRNA)
An RNA molecule that serves as a template for protein synthesis.
monosaccharide
A simple sugar with the basic formula of (CH2O)n.
nucleoside
A purine or pyrimidine base linked to a sugar (ribose or deoxyribose).
nucleotide
A phosphorylated nucleoside.
oligonucleotide
A short polymer of only a few nucleotides.
oligosaccharide
A short polymer of only a few sugars.
passive transport
The transport of molecules across a membrane in the energetically favorable direction.
peptide bond
The bond joining amino acids in polypeptide chains.
peripheral membrane protein
A protein that is indirectly associated with cell membranes by protein-protein interactions.
phosphodiester bond
A bond between the 5′-phosphate of one nucleotide and the 3′-hydroxyl of another.
phospholipid
One of a family of molecules that are the principal components of cell membranes, consisting of two hydrocarbon chains (usually fatty acids) joined to a polar head group containing phosphate.
phospholipid bilayer
The basic structure of biological membranes in which the hydrophobic tails of phospholipids are buried in the interior of the membrane and their polar head groups are exposed to the aqueous solution on either side.
polynucleotide
A polymer containing up to millions of nucleotides.
polypeptide
A polymer of amino acids.
polysaccharide
A polymer containing hundreds or thousands of sugars.
primary structure
The sequence of amino acids in a polypeptide chain.
protein
A polypeptide with a unique amino acid sequence.
proteome
All of the proteins expressed in a given cell.
proteomics
Large scale analysis of cell proteins.
purine
One of the types of bases present in nucleic acids. The purines are adenine and guanine.
pyrimidine
One of the types of bases present in nucleic acids. The pyrimidines are cytosine, thymine, and uracil.
quaternary structure
The interactions between polypeptide chains in proteins consisting of more than one polypeptide.
ribonucleic acid (RNA)
A polymer of ribonucleotides.
ribose
The five-carbon sugar found in RNA.
ribosomal RNA (rRNA)
The RNA component of ribosomes.
secondary structure
The regular arrangement of amino acids within localized regions of a polypeptide chain. See α helix and β sheet.
sphingomyelin
A phospholipid consisting of two hydrocarbon chains bound to a polar head group containing serine.
starch
A polymer of glucose residues that is the principal storage form of carbohydrates in plants.
steroid hormone
A member of a group of hydrophobic hormones, including estrogen and testosterone, that are derivatives of cholesterol.
tertiary structure
The three-dimensional folding of a polypeptide chain that gives the protein its functional form.
thymine
A pyrimidine found in DNA that base-pairs with adenine.
transfer RNA (tRNA)
An RNA molecule that functions as an adaptor between amino acids and mRNA during protein synthesis.
transmembrane protein
An integral membrane protein that spans the lipid bilayer and has portions exposed on both sides of the membrane.
triacylglycerol
Three fatty acids linked to a glycerol molecule.
two-dimensional gel electrophoresis
A method for separating cell proteins based on both charge and size.
uracil
A pyrimidine found in RNA that base-pairs with adenine.
X-ray crystallography
A method in which the diffraction pattern of X rays is used to determine the arrangement of individual atoms within a molecule.
