The Eukaryotes

• The Eukaryotes are characterized by a nucleus, surrounded by a nuclear membrane, which encloses the cell’s DNA and holds the genome of an organism.
• The nucleus also contains the nucleolus, a structure involved in the production of ribosomes.
• A cell’s nucleus may contain one or more nucleoli.
• The nucleus is enclosed by a nuclear envelope, a double membrane, which separates its contents from the cytoplasm.
• The DNA is organized inside the nucleus into units called chromosomes, which carry the genetic information of the cell.
• Ribosomes carry out protein synthesis in the cell and are made of ribosomal RNA and protein.
• Ribosomes may be found suspended in the cytosol or bound to the endoplasmic reticulum or nuclear envelope.
• The ribosome is composed of two subunits, large and small, that assemble the amino acid molecules into proteins.
• The enzymes released by the smooth ER are important in the synthesis of lipids, metabolism of carbohydrates and detoxification of drugs and poisons.
• The Golgi manufactures some of the macromolecules needed by the cell such as polysaccharides.
• The ER has two distinct parts, the smooth ER and the rough ER, named because of the absence or presence of ribosomes on their surfaces, respectively.
• The enzymes of the lysosome can also be used to recycle the cell’s own organic material, a process known as autophagy wherein a damaged organelle is surrounded by a double membrane which then fuses with a lysosome.
• The endomembrane system consists of the endoplasmic reticulum (ER) and the Golgi apparatus.
• Plant cells have a central vacuole that is formed from the union of smaller vacuoles and enlarges when it absorbs water, allowing the plant cell to become larger without making too much new cytoplasm.
• Food vacuoles carry food obtained through phagocytosis.
• Peroxisomes are membrane bound organelles that play a role in lipid synthesis and produce hydrogen peroxide which helps break down compounds such as amino acids and fatty acids.
• The smooth ER also stores calcium ions.
• The Golgi apparatus consists of a complex of disc-like sacs of membrane structures that are stacked together and is located near the ER and the nucleus.
• The ER is part of the endomembrane system and is a network of sacs and tubes responsible for the synthesis of membranes and other metabolic processes.
• The endomembrane system also includes the Golgi apparatus, which is considered to be the warehouse of the cell; it receives, sorts, modifies, stores and ships products of the ER.
• The rough ER adds membrane proteins and phospholipids to its own membrane and transfers portions of it through transport vesicles to other parts of the cell.
• A lysosome is a membranous vesicle that contains hydrolytic enzymes and is responsible for the intracellular digestion in the cell.
• Vacuoles, large vesicles that form off from the ER and Golgi apparatus, serve many functions in the cell.
• Contractile vacuoles pump excess water out of the cell and are found in many freshwater protists.
• Food particles ingested by a cell through phagocytosis are contained in food vacuoles which fuse with lysosomes in order for the lysosmal enzymes to digest the food.
• The cytoskeleton, a network of tubes and filaments, provides structural support to eukaryotic cells and also functions for motility.
• The rough ER secretes proteins produced by the ribosomes attached to its membrane and synthesizes membranes.
• There are many species that are unicellular and there are also many species that are multicellular and possess cells that are of different types.
• Multicellular cells evolved due to the force of magnetic balls rolling individually on a table, which got close to each other and their magnetic force pulled them all together to become one unit.
• Multicellularity refers to the condition wherein an organism has more than one cell and has specialized cells grouped together to perform different functions.
• The theory of endosymbiotic theory states that the eukaryotic cell is a product of evolution and that the mitochondria and chloroplasts were originally bacteria that were engulfed by a bigger prokaryotic cell.
• The evolution of organisms to multicellularity is said to have happened many times.
• The chloroplasts possess the green pigment chlorophyll, enzymes and other molecules needed for photosynthesis to occur and can be found in plant cells, algal cells and other photosynthetic organisms.
• Over time, the cells merged into a single organism, the eukaryotic cell with a mitochondrion and chloroplast.
• The mitochondrial matrix contains DNA, ribosomes and many different enzymes which function in some of the steps of cellular respiration.
• The mitochondria and chloroplasts possess double membranes, DNA and ribosomes of their own and can grow and reproduce on their own within the cell.
• The mitochondrion has two compartments: the intermembrane space, the narrow space between the inner and outer membrane; and the mitochondrial matrix, the compartment enclosed by the inner membrane.
• The intermediate filaments help maintain the position of the nucleus and form the nuclear lamina just inside the nuclear envelope.
• The reproduction of the mitochondria and chloroplasts strongly resembles the binary fission of prokaryotic cells.
• The mitochondrion is a double-membrane bound structure in the eukaryotic cell that has invaginations (infoldings) in its inner membrane, called cristae, which increase the surface area on which biochemical reactions can occur.