Glossary
Chloroplasts
Membrane-bound organelles found in plant cells and other eukaryotic autotrophs, responsible for carrying out photosynthesis.
Example:
The vibrant green color of leaves comes from the numerous chloroplasts within their cells, efficiently capturing sunlight for energy conversion.
Common Ancestry
The evolutionary principle that all life on Earth shares a single origin, meaning all organisms are descended from a single ancestral species.
Example:
The universal genetic code, where the same codons specify the same amino acids across diverse species, is strong evidence for common ancestry among all living things.
Convergent Evolution
The independent evolution of similar features in species from different lineages, usually as a result of similar environmental pressures.
Example:
The streamlined body shapes of dolphins (mammals) and sharks (fish) are a classic example of convergent evolution, as both adapted to efficient movement in aquatic environments.
Endosymbiosis
The theory explaining the origin of eukaryotic cells, specifically how mitochondria and chloroplasts originated from ancient prokaryotic cells engulfed by another cell.
Example:
The presence of circular DNA and double membranes in mitochondria strongly supports the theory of endosymbiosis, suggesting they were once independent bacteria.
Eukaryotes
Organisms whose cells contain a nucleus and other organelles enclosed within membranes.
Example:
Humans, plants, fungi, and protists are all eukaryotes, showcasing complex cellular organization with specialized compartments.
Exons
Coding sequences of DNA within a gene that are expressed and remain in the mature mRNA molecule after splicing.
Example:
Different combinations of exons can be joined together from a single gene, leading to the production of multiple protein variants from a limited number of genes.
Introns
Non-coding sequences of DNA within a gene that are transcribed into mRNA but are subsequently removed before translation.
Example:
During gene expression, introns are precisely cut out of the pre-mRNA, allowing the remaining coding segments to be joined and creating diversity through alternative splicing.
Linear Chromosomes
Long, straight DNA molecules found in the nucleus of eukaryotic cells, typically associated with proteins like histones.
Example:
Humans have 46 linear chromosomes, each carrying a vast amount of genetic information organized into genes, allowing for greater genetic complexity.
Membrane-Bound Organelles
Specialized compartments within eukaryotic cells, each performing specific functions, enclosed by lipid membranes.
Example:
The Golgi apparatus, endoplasmic reticulum, and lysosomes are all examples of membrane-bound organelles that divide labor within a cell, improving efficiency.
Mitochondria
Membrane-bound organelles in eukaryotic cells responsible for cellular respiration and the production of ATP (adenosine triphosphate).
Example:
Muscle cells have a high density of mitochondria to provide the abundant energy needed for contraction, making them the 'powerhouses' of the cell.
Prokaryotes
Single-celled organisms that lack a membrane-bound nucleus and other membrane-bound organelles.
Example:
Bacteria and archaea are prokaryotes, characterized by their simpler cellular structure and circular chromosomes compared to eukaryotes.
Splicing
The process in which introns are removed from a pre-mRNA molecule and exons are joined together to form a mature mRNA.
Example:
Alternative splicing allows a single gene to produce multiple protein isoforms, greatly increasing the diversity of proteins an organism can make.