Cell Biology

• General characteristics of cells include:

  • Organizational complexity
  • Molecular components
  • Sizes and shapes
  • Specialization
• 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 eukaryotic cells
• 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-nucleated organisms 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 low concentration; larger molecules have slower diffusion rates
• 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 daughter cell
• 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