Plant Cell

• Plant Cell Cycle (Mitosis and Meiosis)
• The Plant Cell is Earth’s primary producers, solar harvesters, light energy converters, and are non-motile.
• Plant Cells are structurally reinforced to grow towards sunlight and against gravity.
• Plant Cells lose water continuously and evolve mechanisms to avoid desiccation.
• Plant Cells have mechanisms to move water and minerals to sites of photosynthesis and growth, and also to move the products of photosynthesis to non-photosynthetic organs and tissues.
• New cells in plants are produced by dividing tissues called meristems.
• Each plant cell is surrounded by a rigid cellulosic cell wall and each walled cell is cemented together by a middle lamella.
• The cell wall determines the mechanical strength of plant structures, controls the cell’s shape, allows high turgor pressures to develop, and determines cell turgor pressure and cell volume.
• The cell wall acts as a major structural barrier to pathogen invasion.
• According to the Fluid-Mosaic Model, all biological membranes have the same basic molecular organization: in the case of plasma membranes, a bilayer of phospholipids and various transport proteins, with chloroplasts, glycosyl glycerides.
• Membrane fluidity is controlled by transport proteins in the lipid bilayer.
• Anchored Proteins are bound to the membrane via lipid molecules like fatty acids.
• The nucleus contains most genetic material of the cell, is surrounded by a nuclear envelope with nuclear pores, and is the site of storage and replication of the chromosomes composed of DNA and proteins (histones) - Chromatin.
• The nucleolus is a densely granular region within the nucleus which is the site of ribosome synthesis.
• The Endoplasmic Reticulum is a network of internal membranes made of lipid bilayers and associated proteins, forming flattened or tubular sacs known as cisternae, continuous to the outer membrane of the nucleus.
• The Rough ER is the site of synthesis of membrane proteins and proteins secreted outside of the cell or into the vacuoles.
• The Smooth ER is the site of lipid synthesis and membrane assembly.
• The Golgi Apparatus processes proteins and polysaccharides for secretion, consists of one or more stacks of three to ten flattened membrane sacs or cisternae, and an irregular network of tubules and vesicles called the trans-Golgi Network (TGN), each individual stack is called a Golgi body or dictyosome.
• Secretory vesicles carry the polysaccharides and glycoproteins to the plasma membrane by fusion and emptying their contents to the cell wall.
• Mitochondria are the cellular site of respiration, from spherical to tubular, with a smooth outer membrane and convoluted inner membrane called cristae, and the compartment enclosed by cristae is the mitochondrial matrix containing the enzymes needed for Krebs Cycle.
• Lytic vacuoles contain hydrolytic enzymes that fuse with protein bodies to initiate the breakdown of stored food in seeds.
• Endocytosis is a process that brings soluble and membrane-bound proteins into the cell.
• Other plastids include chromoplasts (with carotenoids), leucoplasts (non-pigmented), and amyloplasts (starch-storing plastid).
• Mitochondria and chloroplasts both contain DNA and machinery to synthesize protein.
• Mitochondria and chloroplasts are believed to have evolved from endosymbiotic bacteria, they divide by fission, and they have circular chromosomes instead of linear which are located in the mitochondrial matrix or plastid stroma called nucleiods.
• The large central vacuole is surrounded by a vacuolar membrane or tonoplast, contains water and dissolved inorganic ions, organic acids, sugars, enzymes, and a variety of secondary metabolites.
• Like animal lysosomes, plant vacuoles contain hydrolytic enzymes.
• The fluid compartment surrounding the thylakoid is the stroma which is analogous to the mitochondrial matrix.
• Microtubules are an integral part of mitosis, form the Preprophase Band (PPB), a ring of microtubules encircling the nucleus before the start of prophase, form the prophase spindle (during prophase, analogous to centrosomes of animal cells) and mitotic spindle (during metaphase), and along with ER, form phragmoplast (during late anaphase or early telophase).
• Microfilaments guide in cytoplasmic streaming (a coordinated movement of particles and organelles in the cytosol) involving actin and myosin proteins, and guide vesicles of Golgi bodies with wall precursors which fuse to the plasma membrane and are deposited and assembled as cell wall material.
• Plasmodesmata are tubular extensions of the plasma membrane that traverse cell walls connecting cytoplasms of adjacent cells, forming a continuum known as the symplast.
• Protein bodies are specialized protein-storing vacuoles abundant in seeds.
• Chloroplasts belong to a group called plastids that contain chlorophyll, its membranes are known as thylakoids, and a stack of it is a granum.
• Three cytoskeletal types found in plants are microtubules, microfilaments, and intermediate filaments.
• The cytoskeleton serves as a scaffolding for the movement of organelles and other cytoskeletal components.
• The cytosol of a plant cell is organized by a 3-dimensional network of filamentous proteins which provides spatial organization of the organelles.
• Although they have their own genomes and can divide independently, majority of the proteins of these organelles still depend on the nucleus hence the word “semiautonomous”.