AP Biology Unit 1 Study Guide

Water

Water

a polar molecule composed of two hydrogen atoms covalently bonded to one oxygen atom (H₂O). Its polarity results from an uneven distribution of electron density, making the oxygen side slightly negative and the hydrogen side slightly positive. This polarity allows water to form hydrogen bonds, giving it unique properties essential to life,

Polarity

the distribution of electrical charge over the atoms in a molecule

Bent Shape

a molecular geometry where the atoms are arranged in a nonlinear configuration, forming an angle rather than a straight line. This shape typically occurs in molecules where a central atom is bonded to two other atoms, and there are lone pairs of electrons on the central atom, causing repulsion that "bends" the molecule.

Partially Negative

a region in a molecule where an atom has a slight negative charge due to an unequal sharing of electrons in a covalent bond

Partailly Positive

a region in a molecule where an atom has a slight positive charge due to the unequal sharing of electrons in a covalent bond

Hydrogen Bond

a weak, non-covalent interaction that occurs between a partially positive hydrogen atom, which is covalently bonded to an electronegative atom (such as oxygen, nitrogen, or fluorine), and another electronegative atom with a lone pair of electrons

Cohesion

the property of water molecules to stick to each other due to hydrogen bonding

Adhesion

the attraction between water molecules and other substances. This occurs because water molecules are polar, and they can form hydrogen bonds with other polar or charged surfaces

Capillarity

the ability of a liquid, such as water, to flow in narrow spaces without the assistance of external forces like gravity. This phenomenon occurs due to the combined effects of cohesion (the attraction between water molecules) and adhesion (the attraction between water molecules and the walls of the narrow space, such as the inside of a plant's xylem or a glass tube).

Surface Tension

the force that acts on the surface of a liquid, causing it to behave like a stretched elastic sheet. This occurs because of the cohesive forces between liquid molecules, particularly in water, where hydrogen bonding creates a high degree of cohesion.

Density of ice

how tightly its molecules are packed compared to liquid water. Uniquely, ice is less dense than liquid water. This happens because, as water freezes, its molecules form a crystalline structure maintained by hydrogen bonds, which spaces the molecules farther apart than in liquid water.

Solvent Properties

the ability of a substance, such as water, to dissolve other substances (solutes). Water is often called the "universal solvent" because of its ability to dissolve a wide variety of molecules, especially ionic compounds and polar molecules. This property arises from water's polarity, where the oxygen atom has a slight negative charge and the hydrogen atoms have slight positive charges.

Monomers

basic molecular unit that can join together with other similar molecules to form larger structures called polymers.

the building blocks of macromolecules like proteins, nucleic acids, and carbohydrates

Polymer

a large molecule made up of many repeating smaller units called monomers.

are essential macromolecules in living organisms, formed through processes like dehydration synthesis, where monomers are linked together by covalent bonds, releasing water in the process

Condensation Reactions

(also called dehydration synthesis) are chemical reactions where two molecules are covalently bonded together, and a molecule of water is released as a byproduct. These reactions are essential for building biological macromolecules, such as proteins, nucleic acids, and carbohydrates

Hydrolysis Reaction

a chemical process in which a polymer is broken down into its monomers by the addition of water. The word "hydrolysis" comes from "hydro" (water) and "lysis" (to break apart). In this reaction, water molecules break the bonds between monomers, reversing the process of condensation (dehydration synthesis)

Macromolecules

A giant molecule formed by the joining of smaller molecules. Polysacharides, proteins, and nucleic acids are macromolecules

Carbohydrates

A sugar(monosaccharide) or one of its dimers(dysaccarides) or polymers (polysaccharide)

Monosaccharides

The simplest carbohydrate, active alone or serving as a monomer for disaccharides and polysaccharides. Also called simeple sugars, they have molecular formulas that are generally some multiple of CH2O

Polysaccharides

They are long chains of carbohydrate molecules, composed of several smaller monosaccharides

Sugar

a general term for carbohydrates that are sweet and soluble in water. Sugars are classified as monosaccharides or disaccharides

Starch

A storage polysaccharide in plants, consisting entirley of glucose monomers joined by glycosidic linkages

Cellulose

A structural polysaccharide of plant cell walls, consiting of glucose monomers joined by B glycosidic linkages

Lipids

Any of a group of large biological molecules, including fats, phospholipids, and steroids, that mix poorly, if at all in water

Tryglycerides

a type of fat molecule composed of one glycerol molecule linked to three fatty acid chains, serving as the primary form of stored energy in the body and found circulating in the bloodstream; essentially, it's the most common type of fat found in the diet and stored in fat cells

Glycerol

a type of simple polyol compound. It is a three-carbon molecule with three hydroxyl (–OH) groups, making it a trihydroxy alcohol. Glycerol is a key component of lipids, including triglycerides and phospholipids, which are important in cell membranes and energy storage. It can also be metabolized to produce glucose and other substances through various biochemical pathways.

Fatty acids

A carboxylic acid with long carbon chain. Fatty acids vary in length and in the number and location of double bonds; three fatty acids linked to glycerol molecule form a fat molecule, also called triacylglycerol or tryglyceride

Phospholipids

A lipid made up of glycerol joined to two fatty acids and a phosphate group. The hydrocarbon chains of the fatty acids act as nonpolar, hydrophobic tails, while the rest of the molecule acts as a polar, hydrophilic head. They form bilayers that function as biological membranes

Phosphate group

a chemical group consisting of a phosphorus atom bonded to four oxygen atoms; important in energy transfer

Hydrocarbon

an organic molecule consisting of only of carbon and hydrogen

Hydrophobic

having no affinity for water; tending to coalesce and form droplets in water

Proteins

a biologically functional molecule consisting of one or more polypeptides folded and coiled into a specific three-dimensional structure

Amino acids

an organic molecule with both a carboxyl and an amino group, serve as the monomers of polypeptides

Amino group

a chemical group with a nitrogen atom bonded to two hydrogen atoms; can act as a base in a solution, accepting a hydrogen ion and acquiring a charge of 1+

Carboxyl group

a chemical group present in organic acids and consisting of one carbon atom doubled bonded to an oxygen atom and also bonded to a hydroxyl group

R group

a specific group of atoms attached to the central carbon atom of an amino acid, which is the building block of proteins. Each amino acid has a distinct R group, which varies in size, shape, and chemical properties

Polypeptide

a polymer of many amino acids linked together by peptide bonds

Primary Structure

the level of protein structure referring to the specific linear sequence of amino acids

Secondary Structure

regions of repetitive coiling or folding of the polypeptide backbone of a protein due to hydrogen bonding between constituents of the backbone (not the side chains)

Alpha helix (a helix)

a coiled region constituting one form of of the secondary structure of proteins, arising from a specific pattern of hydrogen bonding between atoms of the polypeptide backbone (not the side chains)

Beta pleated sheet (B pleated sheet)

one form of the secondary structure of proteins in which the polypeptide chain folds back and forth. Two regions of the chain lie parallel to each other and are held together by hydrogen bonds between atoms of the polypeptide backbone (not the side chains)

Tertiary Structure

The overall shape of the protein molecule due to interactions amino acids side chains, including hydrophobic interactions, ionic bonds, hydrogen bonds, and disulfide bridges

Quaternary Structure

the particular shape of a complex, aggregate protein, defined by the characteristics three-dimensional arrangement of its constituent subunits, each a polypeptide

Nucleic Acids

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

Nucleotides

the building block of nucleic acid, consisting of a five-carbon sugar covalently bonded to a nitrogenous base and one to three phosphate groups

DNA (deoxyribonucleic acid)

a nucleic acid molecule, usually a double-stranded helix, in which each polynucleotide strand consists of nucleotide monomers with deoxyribose sugar and the nitrogenous bases (A), cytosine (C), guanine (G), and thymine (T); capable of being replicate and determining the inherited structure of a cell’s protein

RNA (ribonucleic acid)

A type of nucleic acid consisting of a polynucleotide made up of nucleotide monomers with ribose sugar and nitrogenous bases adenine (A), cytosine (C), guanine (G), and uracil (U); usually single-stranded; functions in protein synthesis, in gene regulation, and as the genome of some viruses

Ribose

the sugar component of RNA nucleotides

Deoxyribose

the sugar component of DNA nucleotides, having one or fewer hydroxyl groups than ribose, the sugar component of RNA nucleotides

Adenine

one of the four nitrogenous bases found in the nucleic acids DNA and RNA

Thymine

one of the four nitrogenous bases found in the nucleic acids DNA

Cystosine

one of the four nitrogenous bases found in the nucleic acids DNA and RNA

Guanine

one of the four nitrogenous bases found in the nucleic acids DNA and RNA

Uracil

one of the four nitrogenous bases found in the nucleic acids RNA

Double Helix

the from of native DNA, referring to its 2 adjacent antiparallel polynucleotide strands wound around an imaginary axis into a spiral shape

Sugar-phosphate backbone

the structural framework of DNA and RNA molecules. It consists of alternating sugar and phosphate groups that form the sides of the "ladder" in the double helix of DNA (or single-stranded RNA)

antiparallel

referring to the arrangement of the sugar-phosphate backbones in a DNA double helix (they run in oppisode 5’—>3’ directions)

genetic code

the set of rules by which information encoded within DNA or RNA sequences is translated into proteins by living cells. It defines how sequences of three nucleotides, called codons, correspond to specific amino acids, which are the building blocks of proteins.

codon chart

a reference tool that shows the relationship between codons (three-nucleotide sequences of mRNA) and the amino acids they encode during the process of translation in protein synthesis

base-pairing rules

Key base-pairing rules:

1. In DNA:

   • Adenine (A) pairs with Thymine (T) using two hydrogen bonds.

   • Cytosine (C) pairs with Guanine (G) using three hydrogen bonds.

2. In RNA:

   • Adenine (A) pairs with Uracil (U) (instead of thymine).

   • Cytosine (C) still pairs with Guanine (G).