Essential Biology Terms and Concepts

Key Terms in Biology

Water and Macromolecules

• Hydrogen bonds: H2O molecules form these with each other or other polar molecules.
• Carbohydrates: Composed of C, H, and O. Include simple sugars and polysaccharides. Carbohydrate breakdown provides energy.
• Polysaccharides: Carbohydrates made up of 10+ monosaccharides, serving as storage forms of sugars.
• Glycosidic bonds: Bonds formed by a dehydration reaction between two monosaccharides.
• Glycogen/starch: Storage forms of carbohydrates for energy, composed of glucose in alpha configuration (two glucose molecules linked by bonds between C1 and C4).
• Cellulose: Structural component in plants, composed of glucose in beta configuration.
• Chitin: Polysaccharide found in exoskeletons.
• Lipids: Involved in energy storage, cell membranes, and cell signaling.
• Fatty acids: Long hydrocarbon chains (16-18 carbons) with a carboxyl group at one end. They have long hydrophobic chains. Saturated fatty acids have no double bonds (solid at room temperature), while unsaturated fatty acids have one or more double bonds (fluid at room temperature).
• Triglycerides: The storage form of fatty acids, consisting of three fatty acids linked to a glycerol molecule. They are insoluble in water and represent a more efficient form of energy storage.
• Phospholipids: Lipids with a glycerol bound to two fatty acids and a phosphate group.
• Glycolipids: Two hydrocarbon chains linked to phosphate head groups.
• Cholesterol: Composed of four hydrocarbon rings, highly hydrophobic.
• Steroid hormones: Hormones derived from cholesterol, acting as chemical messengers (e.g., estrogen and testosterone). They also consist of four hydrocarbon rings.

Nucleic Acids and Proteins

• Phosphodiester bond: Bond between nucleotides, formed by a phosphate group linking the sugar molecules of two nucleotides.
• Phosphoanhydride bond: Bond found in ATP, where three phosphate groups are linked. This is a high-energy bond because a significant amount of energy is released when it is broken.
• Polypeptides: Polymers of amino acids.
• Amino acids: Building blocks of proteins, each with a unique side chain. They have a central carbon atom bonded to a hydrogen atom, an amino group (NH3), a carboxyl group (COOH), and a variable side chain (R-group).
• Peptide bonds: Link amino acids between the carboxyl group of one amino acid and the amino group of another.

Protein Structure

• Primary structure: The linear sequence of amino acids in a polypeptide chain, determined by peptide bonds.
• Secondary structure: Local folding or twisting of the polypeptide chain into alpha helices and beta sheets, stabilized by hydrogen bonding.
• Tertiary structure: The overall three-dimensional structure of a polypeptide chain, which may include one or more secondary structures. It is stabilized by various interactions, including hydrogen bonding, ionic bonding, hydrophobic interactions, and disulfide bonds.
• Quaternary structure: The arrangement of multiple polypeptide chains (subunits) into a functional protein complex.
• Domains: Folded three-dimensional structures within a protein that often perform specific functions.

Enzymes and Membranes

• Enzymes: Biological catalysts that speed up chemical reactions by lowering the activation energy. They bring substrates together at their active sites.
• Active site: The specific region on an enzyme where the substrate binds and is converted into product.
• Allostery: The process of transmitting the effect of binding at one site on a protein to another site, often affecting the protein's activity.
• Diffusion: The passive movement of molecules from an area of high concentration to an area of low concentration. Only small, uncharged polar molecules can easily diffuse across cell membranes.
• Transport proteins: Facilitate the movement of most molecules across cell membranes.
• Channel proteins: Form open pores in the membrane, allowing the free passage of specific molecules.
• Carrier proteins: Selectively bind and transport specific small molecules. They undergo conformational changes that open and close channels for the passage of the bound molecule.
• Active transport: Uses energy (typically from ATP hydrolysis) to move molecules against their concentration gradient.
• Passive transport: The movement of molecules across membranes in the energetically favorable direction, often through channel or carrier proteins.

Cellular Processes and Genetics

• SDS-PAGE: (Sodium dodecyl sulfate-polyacrylamide gel electrophoresis) A technique that separates proteins based on their size.
• DTT: (Dithiothreitol) A reducing agent used in SDS-PAGE to break disulfide bonds within and between proteins, disrupting their tertiary and quaternary structures.
• Substrate-level phosphorylation: The direct phosphorylation of ADP with a phosphate group from a high-energy substrate molecule.
• Oxidative phosphorylation: The process in mitochondria where ATP is produced from the flow of electrons across the inner mitochondrial membrane.
• Splicing: The process of removing introns (non-coding sequences) and reconnecting exons (coding sequences) in pre-mRNA.
• Chromatin: The complex of DNA and proteins that packages DNA into a compact structure within the nucleus of a cell.
• Histones: Proteins around which DNA wraps to form nucleosomes.
• Nucleosomes: The basic structural units of chromatin, consisting of DNA wrapped around histone proteins.
• Euchromatin: A less condensed form of eukaryotic chromatin that is often transcriptionally active.
• Heterochromatin: A densely packed form of chromatin that is generally inaccessible to enzymes and is transcriptionally inactive.
• Centromere: The region of a chromosome where the two sister chromatids are attached.
• Kinetochore: A specialized protein structure on the centromere that links each sister chromatid to the microtubules of the mitotic spindle during cell division.
• Epigenetic inheritance: The inheritance of traits that are not directly encoded in the DNA sequence, often involving modifications to chromatin structure or DNA methylation patterns.