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carbohydrates lipids nucleic acids proteins
Four types of organic molecules (biomolecules) exist in organisms:_________________________
Organic molecules are a ________group; even a simple bacterial cell contains some 5,000 organic molecules.
1. The chemistry of the carbon atom allows it to form covalent bonds with as many as _________other elements (generally with the CHNOPS elements).
_______--are chains of carbon atoms bonded exclusively to hydrogen atoms; hydrocarbons can be branched and they can form ringed (cyclic) compounds.
Functional groups are clusters of specific atoms bonded to the carbon skeleton with characteristic structure and functions.
As an example, the addition of an -OH (hydroxyl group) to a carbon skeleton turns the molecule into an alcohol.
Nonpolar organic molecules are hydrophobic (cannot dissolve in water) unless they contain a polar functional group (ex. ethane), while hydrophilic compounds (such as ethanol) can dissolve in water because the -OH functional group is polar.
Depending on its functional groups, an organic molecule may be both acidic and hydrophilic. An example is a hydrocarbon that contains a carboxyl group; carboxyl groups ionize in solution by releasing hydrogen ions, becoming both polar and acidic.
Isomers are molecules with identical molecular formulas but different arrangements of their atoms (e.g., glyceraldehyde and dihydroxyacetone).
Carbohydrates, lipids, proteins, and nucleic acids are called biomolecules because certain foods are known to be rich in them.
Cellular enzymes carry out dehydration reactions to synthesize biomolecules. In a dehydration reaction, a water molecule is removed and a covalent bond is made between two atoms of the monomers.
3. ___________("water breaking") reactions break down polymers in reverse of dehydration; a hydroxyl (— OH) group from water attaches to one monomer and hydrogen (— H) attaches to the other.
Enzymes are molecules that speed up chemical reactions by bringing reactants together; an enzyme may even participate in the reaction but is not changed by the reaction.
5. The largest biomolecules are called _________________, constructed by linking many of the same type of small subunits, called monomers. Examples: amino acids (monomers) are linked to form a protein (polymer); many nucleotides (monomers) are linked to form a nucleic acid (polymer).
In a dehydration reaction, a hydroxyl (— OH) group is removed from one monomer and a hydrogen (— H) is removed from the other.
This produces water, and, because the water is leaving the monomers, it is a dehydration reaction.
Glucose and fructose are hexoses, but are isomers of one another; each has the formula (C6H12O6) but they differ in arrangement of the atoms.
Glucose is found in the blood of animals; it is the source of biochemical energy (ATP) in nearly all organisms.
Ribose and deoxyribose are five carbon sugars (pentoses); they contribute to the backbones of RNA and DNA, respectively.
Maltose is composed of two glucose molecules; it forms in the digestive tract of humans during starch ____________
Sucrose (table sugar) is composed of glucose and fructose; it is used to sweeten food for human __________
Polysaccharides are polymers of monosaccharides. They are not soluble in water and do not pass through the plasma membrane of the cell.
Starch, found in many plants, is a straight chain of glucose molecules with relatively few side branches. Amylose and amylopectin are the two forms of starch found in plants.
Glycogen is a highly branched polymer of glucose with many side branches. It is the storage form of glucose in animals.
Cellulose is a polymer of glucose which forms microfibrils, the primary constituent of plant cell walls.
Chitin is the primary constituent of the exoskeleton of crabs and related animals (lobsters, insects, etc.).
Unsaturated fatty acids have double bonds in the carbon chain where there are less than two hydrogens per carbon atom.
Phospholipids are constructed like neutral fats except that the third fatty acid is replaced by a polar (hydrophilic) phosphate group; the phosphate group usually bonds to another organic group (designated by R).
Phospholipids arrange themselves in a double layer in water, so the polar heads face toward water molecules and nonpolar tails face toward one other, away from water molecules.
This property enables phospholipids to form an interface or separation between two solutions (e.g., the interior and exterior of a cell); the plasma membrane is a phospholipid bilayer.
Steroids have skeletons of four fused carbon rings and vary according to attached functional groups; these functional groups determine the biological functions of the various steroid molecules.
Cholesterol is a component of an animal cell's plasma membrane, and is the precursor of the steroid hormone (aldosterone, testosterone, estrogen, calcitriol, etc.).
Metabolic enzymes are proteins that act as organic catalysts to accelerate chemical reactions within cells.
Support proteins include keratin, which makes up hair and nails, and collagen fibers, which support many of the body's structures (e.g., ligaments, tendons, skin).
Transport functions include channel and carrier proteins in the plasma membrane, and hemoglobin that transports oxygen in red blood cells.
Hormones are regulatory proteins that influence the metabolism of cells. For example, insulin regulates glucose content of blood and within cells.
The polarity of the peptide bond permits hydrogen bonding between different amino acids in a polypeptide.
A protein may contain more than one polypeptide chain; it can thus have a very large number of amino acids.
The three-dimensional shape of a protein is critical; an abnormal sequence will have the wrong shape and will not function normally.
Amino acids differ according to their particular R group, ranging from single hydrogen to complicated ring compounds.
The R group of amino acid cystine ends with a sulfhydryl (— SH) that serves to connect one chain of amino acids to another by a disulfide bond (— S— S—).
Protein shape determines the function of the protein in the organism; proteins can have up to four levels of structure (but not all proteins have four levels).
Just as the English alphabet contains 26 letters, 20 amino acids can join to form a huge variety of "words."
Fibrous proteins (e.g. keratin) are structural proteins with helices and/or pleated sheets that hydrogen bond to one another.
Strong disulfide linkages maintain the tertiary shape; hydrogen, ionic, and covalent bonds also contribute.
Hemoglobin is globular protein with a quaternary structure of four polypeptides; each polypeptide has a primary, secondary, and tertiary structure.
As proteins are synthesized, chaperone proteins help them fold into their correct shapes; chaperone proteins may also correct misfolding of a new protein and prevent them from making incorrect shapes.
Certain diseases (e.g., the transmissible spongiform encephalopathies, or TSEs) are likely due to misfolded proteins, called prions.
DNA (deoxyribonucleic acid) stores the genetic code for its own replication and for the amino acid sequences in proteins.
RNA (ribonucleic acid) allows for translation of the genetic code of DNA into the amino acid sequence of proteins; other functions for RNA in the cell exist.
ATP (adenosine triphosphate) is a nucleotide used to supply energy for synthetic reactions and other energy-requiring metabolic activities in the cell.
Nucleotides are a molecular complex of three types of molecules: a phosphate (phosphoric acid), a pentose sugar, and a nitrogen containing base.
In RNA, the base uracil occurs instead of the base thymine. Both RNA and DNA contain adenine, guanine, and cytosine.
Complementary base pairing occurs where two strands of DNA are held together by hydrogen bonds between purine and pyrimidine bases.
In DNA, thymine is always paired with adenine; cytosine is always paired with guanine. Thus, in DNA: A + G = C + T.
ATP (adenosine triphosphate) is a nucleotide in which adenosine is composed of ribose and adenine.
In cells, the terminal phosphate bond is hydrolyzed, leaving ADP (adenosine diphosphate); energy is released when this occurs.
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