AP Biology Unit 2: Cellular Structures, Biomolecules, Enzymes, and Energetics

Comprehensive vocabulary flashcards covering cell types, biomolecules, protein structure, enzyme kinetics, cellular energy transformations, and polymerization mechanisms.

Prokaryotic Cells

First life forms on Earth that generally measure $< 6\,\text{microns}$ in size, lack well-defined membrane-bound organelles, contain simple duplex DNA in a loop, and reproduce by binary fission.

Prokaryote (Etymology)

Derived from the Greek words 'pro' meaning 'before' and 'keryon' meaning 'kernel' or 'nucleus'.

Eukaryotic Cells

Complex cells that generally measure $7-10\,\text{microns}$ (or $> 10\,\text{microns}$) in size, containing a well-defined membrane-bound nucleus, a nucleolus, and specialized membrane-bound organelles.

Eukaryote (Etymology)

Derived from the Greek words 'eu' meaning 'true' and 'keryon' meaning 'kernel' or 'nucleus', together meaning 'true nucleus'.

Monosaccharides

The simplest form of carbohydrates, consisting of a single sugar molecule made of carbon, hydrogen, and oxygen in a $1:2:1$ ratio, such as glucose, fructose, and galactose.

Disaccharides

Double sugar molecules formed from two monosaccharides connected by covalent bonds, such as sucrose ($\text{glucose} + \text{fructose}$) and lactose ($\text{glucose} + \text{galactose}$).

Polysaccharides

Carbohydrate polymers consisting of three or more sugar molecules joined by covalent bonds, serving structural or storage functions.

Starch

A storage polysaccharide in plants containing multiple glucose units that break down into glucose when instant energy is needed for functions such as respiration.

Cellulose

A structural polysaccharide in plants composed of multiple glucose units linked by strong covalent bonds.

Glycogen

A storage polysaccharide in animals stored in muscle and liver cells that breaks down into glucose when instant energy is needed.

Chitin

A structural polysaccharide mainly found in arthropods.

Triglycerides

Primary fat molecules composed of one glycerol and three fatty acids.

Saturated Fats

Triglycerides with no double bonds in the hydrocarbon structure of their fatty acids, predominantly found in animal fats such as lard and butter.

Unsaturated Fats

Triglycerides containing one or more double bonds in their fatty acid hydrocarbon chain, predominantly found in plant and fish fats such as olive oil and cod liver oil.

Phospholipids

Lipids composed of one glycerol, a hydrophilic phosphate group end, and two hydrophobic fatty acid ends, which provide fluidity to the cell membrane.

Steroids

Powerful lipid chemicals found in hormones and cell membranes, such as cholesterol, estrogen, and testosterone, which act to reduce swelling and pain.

Nucleic Acids

Organic molecules (DNA and RNA) composed of nucleotides joined by covalent bonds that preserve and express genetic information within cells.

DNA

Double-stranded nucleic acid containing deoxyribose sugar (having one less oxygen atom than ribose), which serves as the material of heredity responsible for its own replication and directing cellular activities.

RNA

Single-stranded nucleic acid containing ribose sugar involved in protein synthesis, existing as tRNA, mRNA, and rRNA.

Peptide Bond

A rigid covalent bond formed between the amine group ($-\text{NH}_2$) of one amino acid and the carboxyl group ($-\text{COOH}$) of an adjacent amino acid, releasing a $\text{H}_2\text{O}$ molecule.

Primary Structure

The most basic protein structure consisting of a single linear sequence of amino acids (polypeptide chain) representing its exact atomic composition.

Secondary Structure

Protein structure produced by the coiling and folding of a polypeptide chain through hydrogen bonds between amine and carboxyl groups.

Alpha Helix

A delicate coil in a protein's secondary structure held together by hydrogen bonding every 4th amino acid, typically $10\,\text{amino acids}$ long, found in keratin.

Beta Sheet

A secondary protein structure formed when a polypeptide chain folds back on itself with two or more adjacent regions connected by hydrogen bonds, found in spider web silk protein.

Tertiary Structure

The 3D spatial arrangement of a single completely folded and compact protein molecule, held together by hydrophobic interactions, van der Waals forces, hydrogen bonds, ionic interactions, and disulfide bridges.

Disulfide Bridges

Strong covalent bonds ($-\text{S}-\text{S}-$) formed between the sulfhydryl ($-\text{SH}$) groups of two cystines during protein folding.

Quaternary Structure

A functional macromolecule formed when several peptide chains cluster together in a specific shape, such as collagen ($3\,\text{helical subunits}$) or hemoglobin ($4\,\text{subunits}$).

Denaturation

The process where changes in pH, temperature, salt concentration, or addition of alcohol, acids, urea, or heavy metals cause a protein to unfold and lose its original shape, rendering it biologically inactive.

Enzymes

Proteins made by cells consisting of long chains of amino acids that act as biological catalysts to regulate metabolic pathways without being used up.

Activation Energy ($E_a$)

The energy barrier that reactants must meet for a chemical reaction to proceed.

Active Site

A specific region formed by the folding of an enzyme molecule, lined with specific amino acids from its tertiary structure, where the substrate temporarily binds.

Induced Fit Model

A model proposed by Daniel Koshland stating that an enzyme is flexible and reshapes its active site to accommodate the substrate.

Michaelis-Menten Curve

A graphical representation showing that enzyme activity increases as substrate concentration increases until all active sites reach saturation.

Metabolism

A constant cycle of chemical reactions in the body that transforms energy through ordered catabolic and anabolic pathways.

Catabolic Pathways

Metabolic pathways that release energy by breaking down complex molecules into simpler compounds, such as cellular respiration.

Anabolic Pathways

Metabolic pathways that consume or absorb energy to build complex molecules from simpler ones, such as forming proteins from amino acids.

Gibbs Free Energy ($\Delta G$)

A calculation defined by J. Willard Gibs that measures the portion of a system's energy available to perform work at constant temperature and pressure.

Exergonic Reactions

Reactions that lose free energy ($\Delta G < 0$) and occur spontaneously, such as cellular respiration ($\Delta G = -686\,\text{kcal/mol}$).

Endergonic Reactions

Reactions that absorb free energy ($\Delta G > 0$) and require external energy input, such as photosynthesis ($\Delta G = +686\,\text{kcal/mol}$).

Energy Coupling

The transfer of energy from an exergonic process to drive an endergonic reaction, primarily helped along by ATP.

ATP (Adenosine Triphosphate)

A multifunctional molecule consisting of adenosine and three phosphate groups that releases $-7.3\,\text{kcal/mol}$ of free energy when hydrolyzed into ADP.

Linear Polymers

Polymers in which monomer units form a long chain backbone with one starting point and one ending point.

Branched Polymers

Polymers featuring tree-like branches with more than one starting point and many ending points.

Dehydration Synthesis

The process of joining monomers together with a covalent bond through the loss of a water molecule.

Hydrolysis

The chemical process of breaking covalent bonds between monomers in a polymer through the addition of a water molecule.

Amino Acid Structure

Consists of a central alpha carbon attached to an amine group ($-\text{NH}_2$), a carboxyl group ($-\text{COOH}$), a solitary hydrogen atom, and a unique R group.

Prokaryotic Cells

Simple, early life forms generally $<6\,\text{microns}$ in size that lack a well-defined membrane-bound nucleus and organelles, reproducing via binary fission.

Eukaryotic Cells

Complex cells generally $7-10\,\text{microns}$ (or $>10\,\text{microns}$) in size that contain a well-defined membrane-bound nucleus, nucleolus, and specialized membrane-bound organelles.

Nucleoid

The region in a prokaryotic cell containing its simple duplex DNA loop, serving as the functional equivalent of a nucleus.

Monosaccharides

The simplest form of carbohydrates, consisting of single sugar molecules with a carbon, hydrogen, and oxygen atom ratio of $1:2:1$ (e.g., glucose, fructose, galactose).

Disaccharides

Double sugar molecules formed from two monosaccharides joined by covalent bonds (e.g., sucrose and lactose).

Polysaccharides

Carbohydrate polymers composed of three or more monosaccharide units covalently bonded, functioning in energy storage and structural support.

Starch

A storage polysaccharide in plants composed of multiple glucose units that breaks down into glucose for instant energy.

Cellulose

A structural polysaccharide in plants composed of multiple glucose units linked by strong covalent bonds.

Glycogen

A storage polysaccharide in animals stored in muscle and liver cells that breaks down into glucose when instant energy is required.

Chitin

A structural polysaccharide found mainly in arthropods.

Triglycerides

Lipid molecules composed of one glycerol molecule attached to three fatty acid chains.

Saturated Fats

Fats lacking double bonds in the hydrocarbon structure of their fatty acid chains, predominantly found in animal fats such as lard and butter.

Unsaturated Fats

Fats containing one or more double bonds in their hydrocarbon fatty acid chains, predominantly found in plant and fish fats like olive oil and cod liver oil.

Phospholipids

Lipid molecules composed of one glycerol, a hydrophilic phosphate group end, and two hydrophobic fatty acid ends, forming key structural parts of cell membranes.

Steroids

Lipids consisting of complex chemical structures that act in cell membranes and as hormones (e.g., cholesterol, estrogen, and testosterone).

DNA (Deoxyribonucleic Acid)

A double-stranded nucleic acid containing deoxyribose sugar that stores genetic information, directs cellular activities, and mediates its own replication.

RNA (Ribonucleic Acid)

A single-stranded nucleic acid containing ribose sugar involved in protein synthesis, existing as mRNA, tRNA, and rRNA.

Purines

A category of nitrogenous bases found in nucleic acids that includes adenine and guanine.

Pyrimidines

A category of nitrogenous bases found in nucleic acids that includes cytosine, thymine (in DNA), and uracil (in RNA).

Peptide Bond

A covalent bond formed between the amine group ($\text{-NH}_2$) of one amino acid and the carboxyl group ($\text{-COOH}$) of an adjacent amino acid, releasing $\text{H}_2\text{O}$.

Primary Structure

The linear, specific sequence of amino acids linked by peptide bonds forming a single polypeptide chain.

Alpha Helix

A type of protein secondary structure featuring a delicate coil stabilized by hydrogen bonding every 4th amino acid, typically about 10 amino acids long (e.g., keratin).

Beta Sheet

A type of protein secondary structure where a polypeptide chain folds back on itself, connecting adjacent regions with hydrogen bonds (e.g., silk protein in spider webs).

Tertiary Structure

The overall 3D spatial arrangement of a single completely folded polypeptide chain, maintained by weak interactions and strong disulfide bridges.

Disulfide Bridges

Strong covalent bonds ($\text{-S-S-}$) formed between the sulfhydryl ($\text{-SH}$) R groups of cysteine amino acids in a protein's tertiary structure.

Quaternary Structure

A functional macromolecule formed by the clustering of two or more polypeptide chain subunits (e.g., collagen with 3 subunits, hemoglobin with 4 subunits).

Denaturation

The process where altered environmental conditions (such as changes in pH, temperature, or salt concentration) cause a protein to unfold and lose its structure, rendering it biologically inactive.

Enzymes

Proteins composed of amino acid chains that function as biological catalysts to regulate metabolic pathways without being consumed in the reaction.

Activation Energy ($E_a$)

The energy barrier required to trigger a chemical reaction by bringing reactants close enough together to proceed.

Active Site

A specific pocket formed by the tertiary structure of an enzyme, lined with specific amino acids, where the substrate binds to undergo catalysis.

Induced Fit Model

A model proposed by Daniel Koshland stating that an enzyme is flexible and reshapes its active site around the substrate upon binding.

Michaelis-Menten Curve

A graph illustrating how enzyme activity increases with rising substrate concentration until reaching a constant rate due to active site saturation.

Metabolism

The total set of energy-transforming chemical reactions occurring within an organism through ordered metabolic pathways.

Catabolic Pathways

Downward metabolic pathways that release energy by breaking down complex molecules into simpler compounds (e.g., cellular respiration).

Anabolic Pathways

Upward metabolic pathways that consume energy to synthesize complex molecules from simpler compounds (e.g., building proteins from amino acids).

Gibbs Free Energy ($\Delta G$)

A quantitative measurement defined by J. Willard Gibbs that calculates the portion of a system's energy available to perform work under constant temperature and pressure.

Exergonic Reactions

Chemical reactions that result in a net loss of free energy (negative $\Delta G$) and occur spontaneously (e.g., cellular respiration with $\Delta G = -686\,\text{kcal/mol}$).

Endergonic Reactions

Non-spontaneous chemical reactions that absorb and store free energy (positive $\Delta G$) from an outside source (e.g., photosynthesis with $\Delta G = +686\,\text{kcal/mol}$).

Energy Coupling

The cellular strategy of using energy released from an exergonic process to directly drive an endergonic reaction, primarily mediated by ATP.

ATP (Adenosine Triphosphate)

A multifunctional nucleotide composed of adenine, ribose, and three phosphate groups that provides energy for cellular work via the exergonic removal of its terminal phosphate (releasing $-7.3\,\text{kcal/mol}$).

Polymerization

The chemical process in which monomer units join together via covalent bonds to form macromolecules known as polymers.

Linear Polymers

Polymers where monomers are linked in a single continuous chain backbone with exactly one starting point and one ending point.

Branched Polymers

Polymers structured with tree-like extensions, possessing multiple starting and ending points.

Dehydration Synthesis

A polymerization reaction where a covalent bond is formed between two monomers through the removal of a water molecule ($\text{H}_2\text{O}$).

Hydrolysis

A reaction that breaks covalent bonds within polymers into individual monomers by the chemical addition of a water molecule ($\text{H}_2\text{O}$).