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Cells and Molecules
Chapter 3
50
Biology
Undergraduate 3
07/05/2008

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Term
organic compounds
Definition
a chemical compound containing the element carbon and usually synthesized by cells.
Term
hydrocarbons
Definition
a chemical compound composed only of the elements carbon and hydrogen.
Term
carbon skeleton
Definition

the chain of carbon atoms that forms the structural backbone of an organic molecule.

Term
isomers
Definition
organic compounds with the same molecular formula but different structures and, therefore, different properties.
Term
functional groups
Definition
an assemblage of atoms that forms the chemically reactive part of an organic molecule.
Term
hydrophilic
Definition
"water-loving"; pertaining to polar, or charged, molecules (or parts of molecules) that are soluble in water.
Term
hydroxyl group
Definition
in an organic molecule, a functional group consisting of a hydrogen atom bonded to an oxygen atom.
Term
carbonyl group
Definition
in an organic molecule, a functional group consisting of a carbon atom linked by a double bond to an oxygen atom.
Term
carboxyl group
Definition
in an organic molecule, a functional group consisting of an oxygen atom double-bonded to a carbon atom that is also bonded to a hydroxyl group.
Term
amino group
Definition
in an organic molecule, a functional group consisting of a nitrogen atom bonded to two hydrogen atoms.
Term
amine
Definition
an organic compound with one or more amino groups.
Term
phosphate group
Definition
a functional group consisting of a phosphorus atom covalently bonded to four oxygen atoms.
Term
macromolecule
Definition
a giant molecule in a living organism: a protein, carbohydrate, lipid, or nucleic acid.
Term
polymers
Definition
a large molecule consisting of many identical or similar molecular units, called monomers, covalently joined together in a chain.
Term
monomer
Definition
a chemical subunit that serves as a building block of a polymer.
Term
dehydration reaction
Definition
a chemical process in which a polymer forms as monomers are linked by the removal of water molecules. One molecule of water is removed for each pair of monomers linked. Also called condensation.
Term
hydrolysis
Definition
a chemical process in which macromolecules are broken down by the chemical addition of water molecules to the bonds linking their monomers; an essential part of digestion.
Term
carbohydrate
Definition
member of the class of biological molecules consisting of simple single-monomer sugars (monosaccharides), two monomer sugars (disaccharides), and other multi-unit sugars (polysaccharides).
Term
monosaccharides
Definition
the smallest kind of sugar molecule; a single-unit sugar. Monosaccharides are the building blocks of more complex sugars and polysaccharides.
Term
disaccharide
Definition
a sugar molecule consisting of two monosaccharides linked by a dehydration reaction.
Term
polysaccharides
Definition
a carbohydrate polymer consisting of hundred to thousand of monosaccharides (sugars) linked by covalent bonds.
Term
starch
Definition
a storage polysaccharide found in the roots of plants and certain other cells; a polymer of glucose.
Term
glycogen
Definition
a complex, extensively branched polysaccharide of many glucose monomers; serves as an energy-storage molecule in liver and muscle cells.
Term
cellulose
Definition
a large polysaccharide composed of many glucose monomers linked into cable-like fibrils that provide structural support in plant cell walls.
Term
lipid
Definition

an organic compound consisting mainly of carbon and hydrogen atoms linked by nonpolar covalent bonds, making the compound mostly hydrophobic. Lipids include fats, waxes, phospholipids, and steroids and are insoluble in water.

Term
hydrophobic
Definition
"water-fearing"; pertaining to nonpolar molecules (or parts of molecules) that do not dissolve in water.
Term
triglyceride
Definition
a fat, which consists of a molecule of glycerol linked to three molecules of fatty acid.
Term

unsaturated

Definition
pertaining to fats and fatty acids whose hydrocarbon chains lack the maximum number of hydrogen atoms and therofre have one or more double covalent bonds. Unsaturated fats and fatty acids do not solidify at room temperature.
Term
saturated
Definition
pertaining to fats and fatty acids whose hydrocarbon chains contain the maximum number of hydrogens and therefore have no double covalent bonds. Saturated fats and fatty acids solidify at room temperature.
Term
phospholipid
Definition
a molecule that is a constituent of the inner bilayer of biological membranes, having a polar, hydrophilic head and a nonpolar, hydrophobic tail.
Term
steroids
Definition
a type of lipid whose carbon skeleton is in the form of four fused rings: three 6-sided rings and one 5-sided ring; examples are cholesterol, testosterone, and estrogen.
Term
anabolic steroids
Definition
a synthetic variant of the male hormone testosterone that mimics some of its effects.
Term
protein
Definition
a biological polymer constructed from amino acid monomers.
Term
enzyme
Definition
a protein that serves as a biological catalyst, changing the rate of a chemical reaction without itself being changed into a different molecule in the process.
Term
amino acids
Definition
an organic molecule containing a carboxyl group and an amino group; serves as the monomer of proteins.
Term
peptide bond
Definition
the covalent linkage between two amino acid units in a polypeptide; formed by a dehydration reaction.
Term
polypeptide
Definition
a chain of amino acids linked by peptide bonds.
Term
denaturation
Definition
a process in which a protein unravels, losing its specific conformation and hence function; can be caused by changes in ph or salt concentration or by high temperature; also refers to the separation of the two strands of the DNA double helix; caused by similar factors.
Term
primary structure
Definition
the first level of protein structure; the specific sequence of amino acids making up a polypeptide chain.
Term
secondary structure
Definition
the second level of protein structure; the regular patterns of coils or folds of a polypeptide chain.
Term
alpha helix
Definition
the spiral shape resulting from the coiling of a polypeptide in a protein's secondary structure.
Term
pleated sheet
Definition
the folded arrangement of a polypeptide in a protein's secondary structure.
Term
tertiary structure
Definition
the third level of protein structure; the overall, three-dimensional shape of a polypeptide in a protein.
Term
quaternary structure
Definition
the fourth level of protein structure; the shape resulting from the association of two or more polypeptide subunits.
Term
nucleic acid
Definition
a polymer consisting of many nucleotide monomers; serves as a blueprint for proteins and, through the actions of proteins, for all cellular structures and activites. The two types of nucleic acids are DNA and RNA.
Term
deoxyribonucleic acid (DNA)
Definition
the genetic material that organisms inherit from their parents; a double-stranded helical macromolecule consisting of nucleotide monomers with deoxyribose sugar and the nitrogenous bases adenine (A), cytosine (C), guanine (G), and thymine (T).
Term
ribonucleic acid (RNA)
Definition
a type of nucleic acid consisting of nucleotide monomers with a ribose sugar and the nitrogenous bases adenine (A), cytosine (C), guanine (G), and uracil (U); usually single-stranded; functions in protein synthesis and as the genome of some viruses.
Term
nucleotide
Definition
an organic monomer consisting of a five-carbon sugar covalently bonded to a nitrogenous base and a phosphate group. Nucleotides are the building blocks of nucleic acids.
Term
nitrogenous base
Definition
an organic molecule that is a base containing the element nitrogen.
Term
double helix
Definition
the form of native DNA, referring to its two adjacent polynucleotide strands wound into a psiral shape.
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