Glossary
Amino Acids
The monomers of proteins, each containing an amino group, a carboxyl group, a hydrogen atom, and a variable R-group, all attached to a central carbon atom.
Example:
There are 20 common types of amino acids, and their specific sequence determines the unique structure and function of a protein.
Antiparallel Strands
Describes the two strands of a DNA double helix that run in opposite 5' to 3' directions relative to each other.
Example:
The antiparallel strands of DNA are essential for proper base pairing and for the enzymes involved in DNA replication to function correctly.
Base Pairing
The specific hydrogen bonding between nitrogenous bases in nucleic acids: adenine (A) with thymine (T) or uracil (U), and guanine (G) with cytosine (C).
Example:
Accurate base pairing is vital during DNA replication to ensure that the genetic information is copied without errors.
Carbohydrates
Macromolecules composed of carbon, hydrogen, and oxygen, serving as primary energy sources and structural components.
Example:
Pasta and bread are rich in carbohydrates, providing quick energy for cellular activities.
Cellulose
A structural polysaccharide found in the cell walls of plants, providing rigidity and support.
Example:
Wood and cotton are primarily composed of cellulose, which gives them their strength and fibrous nature.
Chitin
A structural polysaccharide found in the exoskeletons of arthropods (like insects and crustaceans) and in the cell walls of fungi.
Example:
The hard outer shell of a crab is made of chitin, providing protection and structural support.
DNA
Deoxyribonucleic acid; a type of nucleic acid that stores and transmits genetic information in most living organisms.
Example:
The DNA in a single human cell, if uncoiled, would stretch for about 2 meters, containing all the instructions for building and maintaining an organism.
Denaturation
The process by which a protein loses its specific three-dimensional shape (tertiary and sometimes secondary structure) due to changes in environmental conditions like heat or pH, leading to loss of function.
Example:
When you cook an egg, the clear liquid egg white turns opaque because the proteins undergo denaturation due to heat.
Directionality (5' to 3')
Refers to the orientation of a nucleic acid strand, where the 5' end has a phosphate group and the 3' end has a hydroxyl group, crucial for synthesis.
Example:
During DNA replication, new nucleotides are always added to the 3' end of the growing strand, ensuring synthesis proceeds in a specific directionality.
Disaccharide
A carbohydrate formed from two monosaccharides linked together by a glycosidic bond.
Example:
Lactose, the sugar found in milk, is a disaccharide made of glucose and galactose.
Double Helix
The characteristic twisted-ladder shape of a DNA molecule, formed by two antiparallel polynucleotide strands.
Example:
Rosalind Franklin's X-ray diffraction images were crucial in revealing the iconic double helix structure of DNA.
Fats
Lipids primarily used for long-term energy storage, composed of a glycerol molecule linked to three fatty acid chains.
Example:
Animals store excess energy as fats in adipose tissue, providing insulation and a concentrated energy reserve.
Glycogen
A branched polysaccharide that serves as the primary form of glucose storage in animals, mainly in the liver and muscles.
Example:
After a large meal, excess glucose is converted into glycogen and stored in the liver for later use.
Glycosidic Bond
A covalent bond that joins a carbohydrate (sugar) molecule to another group, particularly linking monosaccharides to form disaccharides and polysaccharides.
Example:
The formation of a glycosidic bond between two glucose molecules creates maltose, a disaccharide.
Hydrogen Bonds
Weak intermolecular forces that form between a hydrogen atom covalently bonded to a highly electronegative atom and another electronegative atom.
Example:
The relatively weak hydrogen bonds between DNA base pairs allow the strands to separate easily during replication and transcription, yet provide overall stability.
Hydrolysis
A chemical reaction that breaks down a polymer into its monomers by adding a water molecule.
Example:
Our digestive system uses hydrolysis to break down complex carbohydrates like starch into simpler sugars that can be absorbed.
Lipids
A diverse group of hydrophobic macromolecules, primarily involved in energy storage, membrane structure, and signaling.
Example:
Fats, oils, and phospholipids are all types of lipids crucial for various biological processes.
Macromolecules
Large organic molecules essential for life, built from smaller organic subunits. They include carbohydrates, lipids, proteins, and nucleic acids.
Example:
The human body relies on various macromolecules, such as the proteins in muscles and the DNA in our cells, to function correctly.
Monomers
The individual building blocks or repeating units that link together to form polymers.
Example:
Glucose is a monomer that can be linked repeatedly to form complex carbohydrates like starch or cellulose.
Monosaccharides
The simplest form of carbohydrates, also known as simple sugars, which are the monomers of larger carbohydrates.
Example:
Glucose, fructose, and galactose are common monosaccharides that serve as immediate energy sources for cells.
Nucleic Acids
Macromolecules that carry genetic information, primarily DNA and RNA.
Example:
Forensic scientists often analyze nucleic acids from a crime scene to identify individuals based on their unique genetic code.
Nucleotides
The monomers of nucleic acids, each composed of a five-carbon sugar, a phosphate group, and a nitrogenous base.
Example:
ATP, the energy currency of the cell, is a modified nucleotide that powers many cellular processes.
Oils
Lipids that are liquid at room temperature, typically derived from plants, and composed of unsaturated fatty acids.
Example:
Olive oil is a healthy source of dietary lipids, rich in unsaturated fatty acids.
Peptide Bonds
Covalent bonds that link amino acids together to form polypeptide chains, formed by dehydration synthesis.
Example:
During protein synthesis, ribosomes catalyze the formation of peptide bonds between incoming amino acids.
Phospholipids
Lipids that are a major component of cell membranes, characterized by a hydrophilic (water-loving) head and two hydrophobic (water-fearing) tails.
Example:
The phospholipids in the cell membrane spontaneously arrange into a bilayer, forming a barrier that separates the cell's interior from its external environment.
Polysaccharides
Complex carbohydrates formed from many monosaccharides linked together, serving roles in energy storage or structural support.
Example:
Starch, glycogen, and cellulose are all examples of polysaccharides with distinct functions in plants and animals.
Primary Structure
The unique linear sequence of amino acids in a polypeptide chain, determined by the genetic code.
Example:
A change in just one amino acid in the primary structure of hemoglobin can lead to sickle-cell disease.
Proteins
Complex macromolecules made of amino acids, performing a vast array of functions including structural support, catalysis, transport, and defense.
Example:
Enzymes, which speed up chemical reactions in the body, are a critical type of protein.
Quaternary Structure
The arrangement of multiple polypeptide chains (subunits) in a multi-subunit protein complex.
Example:
Hemoglobin, which carries oxygen in red blood cells, exhibits quaternary structure as it is composed of four separate polypeptide chains.
RNA
Ribonucleic acid; a type of nucleic acid involved in gene expression, carrying out the instructions encoded in DNA.
Example:
Messenger RNA (mRNA) acts as a temporary blueprint, carrying genetic information from the nucleus to the ribosomes for protein synthesis.
Secondary Structure
Local folded structures that form within a polypeptide due to hydrogen bonding between atoms of the polypeptide backbone, commonly alpha helices and beta-pleated sheets.
Example:
The spiral shape of an alpha helix, a common secondary structure, provides flexibility and strength to many fibrous proteins.
Starch
A polysaccharide used for energy storage in plants, composed of many glucose units.
Example:
Potatoes and rice are staple foods because they are rich in starch, providing a readily available energy source.
Structure Determines Function
A fundamental principle in biology stating that the specific shape and arrangement of a molecule or organelle dictates its biological role.
Example:
The unique folded shape of an enzyme, a perfect fit for its substrate, exemplifies how structure determines function in biological catalysis.
Tertiary Structure
The overall three-dimensional shape of a single polypeptide chain, resulting from interactions between the R-groups of its amino acids.
Example:
The specific active site of an enzyme is formed by its unique tertiary structure, allowing it to bind to a particular substrate.