eukaryotic cellA cell that containsmembrane-boundcompartments in whichspecific metabolicactivities take place. Mostimportant among thesecompartments is thenucleus, which houses theeukaryotic cells DNA. It isthis nucleus that gives theeukaryote – literally, "true Comparison of a typical eukaryotic cell with a typical prokaryotic cell (bacterium).nucleus" – its name. The drawing on the left highlights the internal structures of eukaryotic cells,Eukaryotic organisms also including the nucleus (light blue), the nucleolus (intermediate blue), mitochondriahave other specialized, (orange), and ribosomes (dark blue). The drawing on the right demonstrates howmembrane-bounded bacterial DNA is housed in a structure called the nucleoid (very light blue), as wellstructures, called as other structures normally found in a prokaryotic cell, including the cellorganelles, which are membrane (black), the cell wall (intermediate blue), the capsule (orange),small structures within ribosomes (dark blue), and a flagellum (also black).cells that performdedicated functions.Eukaryotic cells aretypically 10 to 100 micrometers across, or about 10 times the size of prokaryotic cells.Origin of eukaryotic cellsThe set of ideas most favored by biologists to explain how eukaryotic cells first came about is called theendosymbiotic theory. This theory is able to account well for the fact that two of the organelles found ineukaryotic cells, mitochondria and chloroplasts, have their own DNA that is completely distinct from theDNA housed in the nucleus. According to the endosymbiotic theory, the eukaryotic cell evolved from asymbiotic community of prokaryotic cells. Specifically, the mitochondria and the chloroplasts are whatremains of ancient symbiotic oxygen-breathing bacteria and cyanobacteria, respectively, whereas therest of the cell seems to be derived from an ancestral archaean prokaryote cell.The origin of the eukaryotic cell was a milestone in the evolution of life. Although eukaryotes use thesame genetic code and metabolic processes as prokaryotes, their higher level of organizational
complexity has permitted the development of truly multicellular organisms. Without eukaryotes, the world would lack mammals, birds, fish, invertebrates, fungi, plants, and complex single-celled organisms. Comparison of eukaryotic and prokaryotic cells feature eukaryotic cells prokaryotic cells Found in "simple" organisms,types of Found in "complex" organisms, including all plants and animals including bacteria andorganism cyanobacteria Can specialize for certain functions, such as absorbing nutrients from food or Usually exist as single, virtuallyspecialization transmitting nerve impulses; groups cells can form large, multicellular organs and identical cells organisms Most animal cells are 10–30 micrometers across; most plant cells are 10–100size Most are 1–10 micrometers across micrometers across Contain a nucleus and many other organelles, each surrounded by a membrane (the Lack a nucleus and othernucleus nucleus and mitochondrion have two membranes) membrane-encased organellesnucleolus One (or more) present in each nucleus Absent Simple duplex not associated withDNA DNA always in combination with histone proteins histones (i.e. basic proteins)Absentspindle Present temporarily during mitosis and meiosis Absent Complete nuclear fusion between gametes, with equal contributions from both Unidirectional transfer of genessexual system genomes from donor to recipient Present, but chemically differentcell wall Present in plant cells, but never contain muramic acid in many respects from eukaryotes (e.g. presence of muramic acid)internal Complex compartmentalization into endoplasmic reticulum, Golgi bodies, Usually simple and oftenmembranes lysosomes, etc transient, if present at allribosomes 80 S with subunits (60 S + 40 S) 70 S* with subunits (30 S + 50 S)photosynthesis Complex chloroplasts (membrane-bounded organelles) Simple chromatophores Virtually all forms are aerobic, though a few are faculatively anaerobic (e.g. yeasts);respiration Simple chromatophores and, uniquely, the trichomonads are obligate anerobeselectron Found on the inner membrane of special membrane-bound organelles: mitochondriatransport (oxidative phosphorylation) and chloroplasts (photophosphorylation). Virtually all Localized on the cell membranesystem & ATP forms are aerobic, though a few are faculatively anaerobic (e.g. yeasts); and,synthesis uniquely, the trichomonads are obligate anerobes
metabolic functions. For example, someProkaryotic Cells bacteria use sulfur instead of oxygen in theirCells that lack a membrane-bound nucleus are metabolism.called prokaryotes (from the Greek meaningbefore nuclei). These cells have few internalstructures that are distinguishable under amicroscope. Cells in the monera kingdom suchas bacteria and cyanobacteria (also known as Examples of Prokaryotic Cellsblue-green algae) are prokaryotes.Prokaryotic cells differ significantly fromeukaryotic cells. They dont have a membrane-bound nucleus and instead of havingchromosomal DNA, their genetic information isin a circular loop called a plasmid. Bacterial cellsare very small, roughly the size of an animalmitochondrion (about 1-2µm in diameter and10 µm long). Prokaryotic cells feature threemajor shapes: rod shaped, spherical, and spiral.Instead of going through elaborate replicationprocesses like eukaryotes, bacterial cells divideby binary fission.Bacteria perform many important functions onearth. They serve as decomposers, agents offermentation, and play an important role in ourown digestive system. Also, bacteria areinvolved in many nutrient cycles such as thenitrogen cycle, which restores nitrate into thesoil for plants. Unlike eukaryotic cells thatdepend on oxygen for their metabolism,prokaryotic cells enjoy a diverse array of
Plant cells are eukaryotic cells that differ in several key respects from the cells of othereukaryotic organisms. Their distinctive features include: A large central vacuole, a water-filled volume enclosed by a membrane known as the tonoplast maintains the cells turgor, controls movement of molecules between the cytosol and sap, stores useful material and digests waste proteins and organelles. A cell wall composed of cellulose and hemicellulose, pectin and in many cases lignin, is secreted by the protoplast on the outside of the cell membrane. This contrasts with the cell walls of fungi (which are made of chitin), and of bacteria, which are made of peptidoglycan. Specialised cell–cell communication pathways known as plasmodesmata, pores in the primary cell wall through which the plasmalemma and endoplasmic reticulum of adjacent cells are continuous. Plastids, the most notable being the chloroplasts, which contain chlorophyll a green coloured pigment which is used for absorbing sunlight and is used by a plant to make its own food in the process is known as photosynthesis. Other types of plastid are the amyloplasts, specialized for starch storage, elaioplasts specialized for fat storage, and chromoplasts specialized for synthesis and storage of pigments. As in mitochondria, which have a genome encoding 37 genes, plastids have their own genomes of about 100–120 unique genes and, it is presumed, arose as prokaryotic endosymbionts living in the cells of an early eukaryotic ancestor of the land plants and algae. Cell division by construction of a phragmoplast as a template for building a cell plate late in cytokinesis is characteristic of land plants and a few groups of algae, notably the Charophytes and the Order Trentepohliales The sperm of bryophytes and pteridophytes have flagellae similar to those in animals, but higher plants, (including Gymnosperms and flowering plants) lack the flagellae and centrioles that are present in animal cells.
Animal CellPublic Domain Image: National Human Genome Research InstituteAnimal cells are eukaryotic cells, or cells with a membrane-bound nucleus. Unlike prokaryotic cells, DNAin animal cells is housed within the nucleus. In addition to having a nucleus, animal cells also containother membrane-bound organelles, or tiny cellular structures, that carry out specific functions necessaryfor normal cellular operation. Organelles have a wide range of responsibilities that include everythingfrom producing hormones and enzymes to providing energy for animal cells.Animal Cells: Structures and OrganellesThe following are examples of structures and organelles that can be found in typical animal cells:Centrioles - organize the assembly of microtubules during cell division.Cytoplasm - gel-like substance within the cell.Endoplasmic Reticulum - extensive network of membranes composed of both regions with ribosomes(rough ER) and regions without ribosomes (smooth ER).Golgi Complex - responsible for manufacturing, storing and shipping certain cellular products.Lysosomes - sacs of enzymes that digest cellular macromolecules such as nucleic acids.Microtubules - hollow rods that function primarily to help support and shape the cell.Mitochondria - power producers and the sites of cellular respiration.Nucleus - membrane bound structure that contains the cells hereditary information.Nucleolus - structure within the nucleus that helps in the synthesis of ribosomes.Nucleopore - tiny hole within the nuclear membrane that allows nucleic acids and proteins to move intoand out of the nucleus.Ribosomes - consisting of RNA and proteins, ribosomes are responsible for protein assembly.Animal cells contain other cell structures that are not depicted in the illustration above. Some of thesestructures include the cytoskeleton, cilia and flagella and peroxisomes.
Parts of the Cell and Its DescriptionCell WallA rigid layer of nonliving material that surrounds the sells of plants and some other organisms; helps toprotect and support the cellCell Membrane Controls what substances come into and out of the cellNucleusThe cells control center; it directs all of the cells activitiesCytoplasm ContainsContains a gel-like material and cell organellesMitochondriaRod shaped cell structures that produce most of the energy needed to carry out the cells functionsEndoplasmic ReticulumA cell structure that forms a maze of passageways in which proteins and other materials are carriedfrom one part of the cell to anotherRibosomeA tony structure in the cytoplasm of a cell where proteins are madeGolgi BodyA structure in the cell that recieves proteins and other newly formed materials from the endoplasmicreticulum, packages them, and distributes them to other parts of the cellChloroplastA structure in the cells of plants and some other organisms that captures energy from sunlight and usesit to produce food. (This is when the plant bends toward the light).VacuoleA water-filled sac inside a cell that acts as a stoarge areaLysosomeA small round cell structure that contains chemicals that break down large food particles into smalleronesOrganelleA tiny sell structure that comes out a specific function within the cell
Cell Parts and Their FunctionsNucleus- Large Oval body near the centre of the cell.- The control centre for all activity.- Surrounded by a nuclear membrane.Nucleoplasm- is the protoplasm in the nucleus.- contains genetic material ---> CHROMOSOMES (DNA)Nucleolus- is found in the nucleus.- contains more genetic information (RNA)Cell Membrane- the outer boundary of the cell.- it separates the cell from other cells.- it is porous ---> allows molecules to pass through.Cell Wall ( Plant Cells Only )- non living structure that surrounds the plant cell.- protects + supports the cell.- made up of a tough fibre called cellulose.Cyto Plasm- cell material outside the nucleus but within the cell membrane.- clear thick fluid.- contains structures called organelles.Vacuoles- are clear fluid sacs that act as storage areas for food, minerals, and waste.- in plant cell the vacuoles are large and mostly filled with water. This gives the plant support.- in animal cells the vacuoles are much smaller.Mitochondria- power house of the cell.- centre of respiration of the cell.- they release energy for cell functions.Chloro Plasts ( Plant cells only )- contains a green pigment known as chlorophyll which is important for photosynthesis.
Ribosomes- tiny spherical bodies that help make proteins.- found in the cyto plasm or attached to the endo plasmic reticulum.Endo Plasmic Reticulum ( ER )- systems of membranes throughout the cyto plasm.- it connects the nuclear membrane to the cell membrane.- passageway for material moving though the cell.Golgi Bodies- tube like structures that have tiny sacs at their ends.- they help package protein.Lysosomes- " suicide sacs "- small structures that contain enzymes which are used in digestion.- if a lysosome were to burst it could destroy the cell.