Cells are the building blocks of life, with intricate structures that enable them to function. This section explores the components of eukaryotic and , highlighting their unique features and roles in cellular processes.
The cytoskeleton, plasma membrane, and organelles work together to maintain cell shape, facilitate movement, and carry out essential functions. Understanding these structures is key to grasping how cells operate and interact within living organisms.
Eukaryotic Cell Organelles and Functions
Membrane-bound Organelles and their Roles
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contain specialized structures called organelles, each surrounded by a membrane and performing specific functions that contribute to the overall functioning of the cell
The is the control center of the cell, housing the genetic material (DNA) and serving as the site of DNA replication and transcription into RNA
The (ER) is a network of membranous channels and sacs involved in the synthesis, modification, and transport of proteins and lipids
The rough ER is studded with ribosomes and is the site of protein synthesis
The lacks ribosomes and is involved in lipid synthesis and detoxification
The is a stack of flattened membrane sacs that modifies, packages, and sorts proteins and lipids for transport to various destinations (, plasma membrane, or secretion)
Lysosomes are membrane-bound sacs containing digestive enzymes that break down and recycle damaged organelles, macromolecules, and foreign particles (bacteria, cellular debris)
Energy Production and Cellular Respiration
are the powerhouses of the cell, generating through the process of
The inner membrane of mitochondria is highly folded, forming that increase the surface area for energy production
The , the innermost compartment of mitochondria, contains enzymes involved in the citric acid cycle and oxidative phosphorylation
are small, membrane-bound organelles involved in the breakdown of fatty acids and the detoxification of harmful substances (hydrogen peroxide, alcohol)
Peroxisomes contain enzymes such as and that neutralize toxic compounds
Prokaryotic vs Eukaryotic Cells
Structural Differences
Prokaryotic cells (bacteria, archaea) lack membrane-bound organelles and a true nucleus, while eukaryotic cells (plants, animals, fungi) possess these structures
The genetic material in prokaryotic cells is a single, circular DNA molecule located in the nucleoid region, whereas eukaryotic cells have multiple linear DNA molecules housed within a membrane-bound nucleus
Prokaryotic cells are generally smaller (1-5 μm) than eukaryotic cells (10-100 μm) and have a higher surface area-to-volume ratio
Prokaryotic cells have a composed of , while eukaryotic cells may have a cell wall made of (plants) or lack a cell wall entirely (animals)
Functional Differences
Prokaryotic cells have ribosomes (70S) that are smaller than those found in eukaryotic cells (80S), reflecting differences in protein synthesis
Eukaryotic cells have a more complex cytoskeleton, which includes , , and , while prokaryotic cells have a simpler cytoskeleton (FtsZ rings, MreB filaments)
Prokaryotic cells lack membrane-bound organelles, so cellular processes (DNA replication, transcription, translation) occur in the cytoplasm, while in eukaryotic cells, these processes are compartmentalized within organelles
Structure and Function of Cells
Plasma Membrane and Cell Surface
The plasma membrane is a selectively permeable barrier that controls the exchange of materials between the cell and its environment
The large surface area-to-volume ratio of the plasma membrane facilitates efficient exchange of nutrients, waste products, and signaling molecules
The describes the plasma membrane as a fluid phospholipid bilayer with embedded proteins that can move laterally within the membrane
Membrane proteins perform various functions, such as transport (channels, carriers), enzymatic activity, cell signaling (receptors), and cell adhesion
Compartmentalization and Organelle Function
The compartmentalization provided by membrane-bound organelles allows for the spatial separation of different cellular processes, enhancing efficiency and preventing interference between incompatible reactions
The specific shapes and structures of organelles optimize their functions
The cristae in mitochondria increase the surface area for energy production through cellular respiration
The flattened sacs of the Golgi apparatus enable efficient modification, sorting, and packaging of proteins and lipids
The arrangement and composition of the cytoskeleton provide structural support, enable cell movement, and facilitate the transport of organelles and macromolecules within the cell
The Cytoskeleton: Shape, Movement, and Organization
Components of the Cytoskeleton
The cytoskeleton is a dynamic network of protein filaments that provides structural support, enables cell movement, and organizes the internal components of the cell
Microfilaments are thin, flexible filaments composed of actin monomers
Microfilaments are involved in cell motility (pseudopodia formation, cytoplasmic streaming), muscle contraction, and the maintenance of cell shape
Intermediate filaments are rope-like fibers that provide mechanical strength and resistance to shear stress
Intermediate filaments help maintain cell shape and organize the internal structure of the cell (nuclear lamina, keratin filaments in epithelial cells)
Microtubules are hollow, cylindrical tubes composed of α- and β-tubulin dimers
Microtubules are involved in cell division (mitotic spindle), intracellular transport, and the maintenance of cell shape and polarity (centrioles, cilia, flagella)
Motor Proteins and Cellular Movement
use ATP to drive the movement of organelles and macromolecules along the cytoskeleton
motors are associated with microfilaments and are responsible for muscle contraction and cell movement (cytokinesis, phagocytosis)
and motors are associated with microtubules and transport cargo (vesicles, organelles) within the cell
Kinesin moves cargo towards the plus end of microtubules (cell periphery), while dynein moves cargo towards the minus end (centrosome)
The cytoskeleton plays a crucial role in cell migration, allowing cells to move and change shape in response to external stimuli or during processes such as wound healing and embryonic development
Actin polymerization drives the formation of protrusions (lamellipodia, filopodia) at the leading edge of migrating cells
Myosin-mediated contraction of actin filaments at the rear of the cell propels the cell forward