Lecture 3 Bio Sci

Carbon (as the backbone of biological molecules)

has 4 valance electrons, letting it form up to 4 covalent bonds with other atoms - this is why carbon skeletons can branch form rings, and build the enormous diversity of biological molecules

Polymer

a long molecule built from many similar repeating subunits (monomers) joined together by covalent bonds - e.g., a polysaccharide made of repeating sugar units

Monomer

the small, repeating building-block molecule that links together (via dehydration reactions) to build a polymer, such as a single glucose unit in starch

Dehydration reaction (synthesis)

joins two monomers by removing a water molecule (an -OH from one monomer and an -H from the other), forming a new covalent bond and building a longer polymer

Hydrolysis

breaks a covalent bond between two monomers by adding a water molecule back in - essentially the reverse of a dehydration reaction. This is how digestion breaks down polymers like starch or proteins

Carbohydrate

sugars and their polymers - ranging from single-unit monosaccharides to disaccharides to large polysaccharides - and serve as fuel and structural material in cells

Monosaccharide

simplest type of carbohydrate - a single sugar unit (like glucose, galactose, or fructose) that varies in the position of its carbonyl group and the length of its carbon skeleton

Disaccharide

ormed when two monosaccharides are joined together by a covalent glycosidic linkage, created through a dehydration reaction (e.g., glucose + fructose → sucrose)

Glycosidic linkage

covalent bond that joins two monosaccharides together, formed by a dehydration reaction that removes a water molecule

Polysaccharide

large polymer made of hundreds to thousands of monosaccharides joined together; examples include cellulose, starch, and glycogen

Cellulose

structural polysaccharide made of unbranched glucose chains linked by bonds that most animals cannot enzymatically break down; it forms the rigid cell walls of plants

Starch

storage polysaccharide made entirely of glucose monomers, stored in plant structures like tubers and seeds; unlike cellulose, animals have enzymes able to digest it

Glycogen

highly branched storage polysaccharide made of glucose, stored in animal liver and muscle tissue as a quick energy reserve - the animal equivalent of starch

Aldose

monosaccharide whose carbonyl group is located at the end of its carbon skeleton, forming an aldehyde group (e.g., glucose)

Ketose

monosaccharide whose carbonyl group is located within the carbon skeleton, forming a ketone group (e.g., fructose)

Functional group (chemical group)

group of atoms attached to a carbon skeleton that replaces one or more hydrogens and gives the molecule its unique chemical properties, often directly participating in reactions

Hydroxyl group

-OH; polar due to its electronegative oxygen, allowing it to form hydrogen bonds with water; a molecule with this group is called an alcohol (e.g., ethanol)

Carbonyl group

>C=O; found in sugars; when at the end of the carbon chain it's called an aldehyde (compound: aldehyde), and when within the chain it's a ketone (compound: ketone)

Carboxyl group

-COOH; acts as an acid, able to release its H+ to become a negatively charged carboxylate ion; a molecule with this group is a carboxylic acid (e.g., acetic acid in vinegar)

Amino group

-NH2; acts as a base, able to accept an H+ to become positively charged; a molecule with this group is called an amine. It's part of every amino acid (e.g., glycine)

Sulfhydryl group

-SH; can react with another sulfhydryl group to form a cross-link that helps stabilize a protein's 3D structure; a molecule with this group is called a thiol (e.g., cysteine)

Phosphate group

-OPO3^2-; contributes a negative charge to a molecule and, when attached, confers the ability to react with water and release energy - the basis of how ATP powers cells. It's found in organic phosphates

Methyl group

-CH3; can attach to molecules like DNA, affecting the expression of genes, and also affects the shape and function of molecules like sexhormones; molecules bearing it are called methylated compounds

Lipid

diverse group of hydrophobic molecules (due to nonpolar C-H bonds). Unlike carbohydrates or proteins, they are NOT true polymers - they're built from two or more different types of smaller subunits (e.g., glycerol + fatty acids). The three forms are fats, phospholipids, and steroids

Fatty acid

a long hydrocarbon chain with a carboxyl group at one end; the carboxyl group is what makes it an "acid." Fatty acids link to glycerol via ester linkages (dehydration reactions) to form fats

Fat (triacylglycerol)

forms when glycerol bonds to three fatty acid chains via three ester linkages (each formed by a dehydration reaction). Fats are used primarily for long-term energy storage

Saturated fat

has no C=C double bonds in its fatty acid chains, meaning each carbon is "saturated" with the maximum number of hydrogens. This lets the chains pack tightly, making them solid at room temperature (e.g., butter, lard)

Unsaturated fat

has one or more C=C double bonds, which create kinks (cis bonds) in the fatty acid chain. These kinks prevent tight packing, keeping the fat liquid at room temperature (e.g., vegetable oils)

Hydrogenated fat

unsaturated fats that have been synthetically converted to a more saturated form by adding hydrogen atoms, which allows a naturally liquid oil to become solid (e.g., some peanut butters and margarines)

Trans fat

produced during the hydrogenation of oils; the double bond takes on a "trans" configuration rather than the natural "cis" form. They are linked to coronary heart disease and are especially common in baked goods and processed foods

Phospholipid

made of glycerol, two fatty acids, a phosphate group, and (often) choline. It has a hydrophilic (polar) head and hydrophobic (nonpolar) tails, making it amphipathic - this is why phospholipids spontaneously form the bilayer of cell membranes

Steroid

lipid characterized by a carbon skeleton of four fused rings, with varying attached functional groups. Cholesterol is a key steroid: a component of cell membranes and the precursor to other steroids like testosterone and estrogen

Protein

polymer made of amino acid monomers linked together by peptide bonds, folded into a specific 3D shape that determines its function (e.g., enzymes, structural support, transport)

DNA

polymer made of nucleotide monomers, arranged as two strands twisted into a double helix, that stores an organism's hereditary (genetic) information