Chp. 3 Molecules of Cells

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alpha helix

The spiral shape resulting from the coiling of a polypeptide in a protein's secondary structure.

amino acid

An organic molecule containing a carboxyl group and an amino group; serves as the monomer of proteins.

amino group

In an organic molecule, a functional group consisting of a nitrogen atom bonded to two hydrogen atoms.

anabolic steroid

A synthetic variant of the male hormone testosterone that mimics some of its effects.

carbohydrate

Member of the class of biological molecules consisting of simple single-monomer sugars (monosaccharides), two-monomer sugars (disaccharides), and other multiunit sugars (polysaccharides).

carbon skeleton

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

carbonyl group

In an organic molecule, a functional group consisting of a carbon atom linked by a double bond to an oxygen atom.

carboxyl group

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.

cellulose

A large polysaccharide composed of many glucose monomers linked into cable-like fibrils that provide structural support in plant cell walls.

chitin

A structural polysaccharide found in many fungal cell walls and in the exoskeletons of arthropods

cholesterol

A steroid that is an important component of animal cell membranes and that acts as a precursor molecule for the synthesis of other steroids such as hormones.

dehydration reaction

A chemical process in which two molecules become covalently bonded to each other with the removal of a water molecule. Also called condensation.

denaturation

A process in which a protein unravels, losing its specific structure 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.

deoxyribonucleic acid (DNA)

A double-stranded helical nucleic acid molecule consisting of nucleotide monomers with deoxyribose sugar and the nitrogenous bases adenine (A), cytosine (C), guanine (G), and thymine (T). Capable of replicating, is an organism's genetic material. See also gene.

disaccharide

A sugar molecule consisting of two monosaccharides linked by a dehydration reaction.

double helix

The form of native DNA, referring to its two adjacent polynucleotide strands wound into a spiral shape.

enzyme

A protein (or RNA molecule) that serves as a biological catalyst, changing the rate of a chemical reaction without itself being changed into a different molecule in the process.

fat

A large lipid molecule made from an alcohol called glycerol and three fatty acids; a triglyceride. Most fats function as energy-storage molecules.

functional group

An assemblage of atoms commonly attached to the carbon skeletons of organic molecules and usually involved in chemical reactions.

gene

A discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA, in some viruses). Most of the genes of a eukaryote are located in its chromosomal DNA; a few are carried by the DNA of mitochondria and chloroplasts.

glycogen

An extensively branched polysaccharide of many glucose monomers; serves as an energy-storage molecule in liver and muscle cells; the animal equivalent of starch.

hydrocarbon

A chemical compound composed only of the elements carbon and hydrogen.

hydrolysis

A chemical process in which polymers are broken down by the chemical addition of water molecules to the bonds linking their monomers; an essential part of digestion.

hydrophilic

"Water-loving"; pertaining to polar, or charged, molecules (or parts of molecules) that are soluble in water.

hydrophobic

"Water-fearing"; pertaining to nonpolar molecules (or parts of molecules) that do not dissolve in water

hydroxyl group

In an organic molecule, a functional group consisting of a hydrogen atom bonded to an oxygen atom.

isomer

Organic compounds with the same molecular formula but different structures and, therefore, different properties.

lipid

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

methyl group

In an organic molecule, a carbon bonded to three hydrogens.

monomer

A chemical subunit that serves as a building block of a polymer.

monosaccharide

The simplest carbohydrate; a simple sugar with a molecular formula that is generally some multiple of CH2O. Monosaccharides are the building blocks of disaccharides and polysaccharides.

nucleic acid

A polymer consisting of many nucleotide monomers; serves as a blueprint for proteins and, through the actions of proteins, for all cellular structures and activities. The two types of nucleic acids are DNA and RNA.

nucleotide

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.

organic compound

A chemical compound containing the element carbon and usually synthesized by cells

peptide bond

The covalent linkage between two amino acid units in a polypeptide; formed by a dehydration reaction.

phosphate group

A functional group consisting of a phosphorus atom covalently bonded to four oxygen atoms.

phospholipid

A lipid made up of glycerol joined to two fatty acids and a phosphate group, giving the molecule a nonpolar hydrophobic tail and a polar hydrophilic head. Phospholipids form bilayers that function as biological membranes.

polymer

A large molecule consisting of many identical or similar molecular units, called monomers, covalently joined together in a chain.

polypeptide

A polymer (chain) of amino acids linked by peptide bonds.

polysaccharide

A carbohydrate polymer consisting of hundreds to thousands of monosaccharides (sugars) linked by dehydration synthesis.

primary structure

The first level of protein structure; the specific sequence of amino acids making up a polypeptide chain.

protein

A functional biological molecule consisting of one or more polypeptides folded into a specific three-dimensional structure.

quaternary structure

The fourth level of protein structure; the shape resulting from the association of two or more polypeptide subunits

RNA

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.

saturated

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.

secondary structure

The second level of protein structure; the regular local patterns of coils or folds of a polypeptide chain.

starch

A storage polysaccharide found in the roots of plants and certain other cells; a polymer of glucose.

steroid

A type of lipid whose carbon skeleton is in the form of four fused rings with various chemical groups attached; examples are cholesterol, testosterone, and estrogen.

tertiary structure

The third level of protein structure; the overall, three-dimensional shape of a polypeptide due to interactions of the R groups of the amino acids making up the chain.

unsaturated

Pertaining to fats and fatty acids whose hydrocarbon chains lack the maximum number of hydrogen atoms and therefore have one or more double covalent bonds. Unsaturated fats and fatty acids do not solidify at room temperature

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