All organisms are categorized as bacteria, archaea, or eukaryotes
The main distinction between prokaryotic (bacteria) and eukaryotic cells is the presence of a membrane-bounded nucleus in eukaryoticcells
Prokaryotic cells can be divided into bacteria and archaea based on rRNA sequence analysis
Biologists recognize three domains: archaea, bacteria, and eukarya (eukaryotes)
Bacteria include commonly encountered single-celled, non-nucleatedorganisms like Escherichia coli, Pseudomonas, and Streptococcus
Archaea include species that live in extreme habitats and have diverse metabolic strategies, such as Methanogens, Halophiles, and Thermacidophiles
Cell size is limited by the need for adequate surface area relative to volume, rates of diffusion, and maintaining adequate local concentrations of substances
The major limit on cell size is maintaining an adequate surface area/volume ratio for efficient exchange with the surroundings
Cells specialized for absorption maximize surface area/volume ratio, like cells lining the small intestine with microvilli
Diffusion is the unassisted movement of substances from high to lowconcentration; larger molecules have slowerdiffusionrates
Eukaryotic cells use carrier proteins, cytoplasmic streaming, and vesicles for active transport to overcome slow diffusion rates
For reactions to occur, cells need adequate concentrations of reactants and catalysts, which increase with cell size
Eukaryotic cells compartmentalize cellular functions using organelles like chloroplasts for photosynthesis
Eukaryotic cells have a true, membrane-bound nucleus, while bacterial or archaeal cells have a nucleoid attached to the cell membrane
Eukaryotes use organelles like endoplasmic reticulum, Golgi complex, mitochondria, and lysosomes for specific functions
The cytoskeleton in eukaryotic cells includes microtubules, microfilaments, and intermediate filaments for structure, elasticity, and transport
Eukaryotic cells exchange materials through endocytosis and exocytosis, unique membrane fusion processes
Bacterial DNA is circular and associated with few proteins, while eukaryotic DNA is linear and complexed with histones
Archaeal DNA is circular and complexes with proteins similar to eukaryotic histones
Bacterial or archaeal DNA must be tightly packed, while eukaryotic DNA is organized into chromosomes containing equal amounts of histones and DNA
Eukaryotes organize DNA into chromosomes to solve the problem of DNA packaging
Prokaryotes and eukaryotes differ in how genetic information is allocated to daughter cells
Chromosomes contain equal amounts of histones and DNA
Prokaryotes and Eukaryotes differ in how genetic information is allocated to daughter cells upon division
Bacterial and archaeal cells replicate their DNA and divide by binary fission with one molecule of the replicated DNA and the cytoplasm going into each daughtercell
Eukaryotic cells replicate DNA and distribute their chromosomes into daughter cells by mitosis and meiosis, followed by cytokinesis, division of the cytoplasm
Eukaryotic cells transcribe genetic information in the nucleus into large RNA molecules which are processed and transported into the cytoplasm for protein synthesis
Each RNA molecule typically encodes one polypeptide
Bacteria transcribe genetic information into RNA, and the RNA molecules produced may contain information for several polypeptides
In both bacteria and archaea, RNA molecules become involved in protein synthesis before transcription is complete
All cells resemble one another in fundamental ways
Cells differ from one another in important aspects
Unicellular organisms must carry out all the necessary functions in one cell
Multicellular organisms have cells which are specialized for particular functions
The structural complexity of eukaryotic cells is illustrated by the typical animal and plant cells
A typical eukaryotic cell has a plasma membrane, a nucleus, membrane-bound organelles, and the cytosol interlaced by a cytoskeleton
Plant and fungal cells have a rigid cell wall, surrounded by an extracellular matrix
The plasma membrane surrounds every cell and ensures that the cell's contents are retained
The plasma membrane consists of lipids including phospholipids and proteins and is organized into two layers