Structure of Eukaryotes
Eukaryotes have a distinct nucleus with a nuclear membrane and other membrane bound organelles. Almost all species of large organisms are eukaryotes, including animals, plants and fungi. The organelles found in eukaryotes are plasma membrane, golgi complex, mitochondria, ribosomes, nucleus, and endoplasmic reticulum. Plant cells have additional components like cell wall, vacuoles and chloroplast.
Plasma membrane is a lipid bilayer found in all cells. It separates the interior of the cell with exterior environment. It is composed of lipids and proteins. It is a semi-permeable membrane allowing the passage of substances through it. Protein receptors are present on plasma membrane which communicate with other cells.
Golgi apparatus
Golgi apparatus is a single membrane bound organelle named after its discoverer, Camillo Golgi, an Italian physician. It is composed of stacks of membrane bound vesicles called cisternae. The main function of Golgi apparatus is to process and package biomolecules like proteins and lipids. The substances are modified by the enzymes present in cisternae by combining with carbohydrates and phosphates. The vesicles that leave the endoplasmic reticulum are transported to cis face and empty their contents in to lumen. Then the contents are moved to trans face where they are sorted and transported to their respective destinations.
Mitochondria
Mitochondria are a double membrane bound organelle. The outer membrane is smooth but inner membrane is convoluted into folds called cristae which increase its surface area. These folds are studded with small round bodies known as F1 particles or oxysomes. Matrix is a space enclosed by inner membrane. It is important in the production of ATP with the help of ATPase present in inner membrane. Mitochondria are known as power house of the cell as ATP is produced in it. It has its own genetic material and also manufactures its own RNAs and proteins.
Chloroplast
Chloroplasts are found in plants and some protists. Chloroplasts contain chlorophyll, a green pigment that traps solar energy and gives plants their green color. They transform light energy into chemical energy that is stored in food molecules.
Nucleus
Nucleus is also called control center of cell. It is enveloped by double layered nuclear membrane. Nuclear membrane is impermeable to most substances so it has nuclear pores to transport small molecules and ions. Proteins are transported with the help of carrier proteins. Nuclear transport is crucial to cell function, as movement through the pores is required for both gene expression and chromosomal maintenance. Inside the nucleus is nucleolus which is mainly involved in the assembly of ribosomes. After being produced in the nucleolus, ribosomes are exported to the cytoplasm where they translate mRNA.
The cell nucleus contains the majority of the cell's genetic material, in the form of multiple linear DNA molecules organized into structures called chromosomes. During most of the cell cycle these are organized in a DNA-protein complex known as chromatin, and during cell division the chromatin can be seen to form the well defined chromosomes familiar from a karyotype. A small fraction of the cell's genes are located instead in the mitochondria.
The main function of the cell nucleus is to control gene expression and mediate the replication of DNA during the cell cycle. The nucleus provides a site for genetic transcription that is segregated from the location of translation in the cytoplasm, allowing levels of gene regulation that are not available to prokaryotes.
Endoplasmic reticulum
It forms the interconnected network in cells. The general structure of the endoplasmic reticulum is an extensive membrane network of cisternae held together by the cytoskeleton. The functions of the endoplasmic reticulum vary greatly depending on the exact type of endoplasmic reticulum and the type of cell in which it resides. The three varieties are called rough endoplasmic reticulum, smooth endoplasmic reticulum and sarcoplasmic reticulum.
The surface of the rough endoplasmic reticulum(RER) is studded with protein-manufacturing ribosomes giving it a "rough" appearance.The membrane of the RER is continuous with the outer layer of the nuclear envelop.The smooth endoplasmic reticulum (SER) has functions in several metabolic processes.The sarcoplasmic reticulum (SR) is a special type of smooth ER found in smooth and striated muscle.This fundamental difference is indicative of their functions: the SER synthesizes molecules while the SR stores and pumps calcium ions.The SR contains large stores of calcium, which it sequesters and then releases when the muscle cell is stimulated.
Cytoskeleton
Cytoskeleton is the skeletal system present within the cytoplasm. It maintains the cell’s shape, protects it and helps in its motion. It plays role in cell division and intra cellular transport. Eukaryotic cells contain three main kinds of filaments. They are microfilaments, intermediate filaments and microtubules.
Microfilaments are concentrated just beneath the cell membrane. This filament type is composed of two intertwined chains. These are responsible for resisting tension and maintaining cellular shape and participation in some cell-to-cell or cell-to-matrix junction. They are also important for cytokinesis and, along with myosin, muscular contraction.
Intermediate filaments are more stable than actin filaments. Their function is to maintain cell shape.
Microtubules are hollow cylinders most commonly comprised of 13 protofilaments which, in turn, are polymers of alpha and beta tubulin. They have a very dynamic behavior, binding GTP for polymerization. They are commonly organized by the centrosome.
STORAGE ORGANELLES
Vacuoles are a sac of fluid surrounded by a membrane used to store food, fluid or waste products. Lysosymes are membrane bound organelles that contain digestive enzymes. They fuse with vacuoles to digest food or worn out cell parts. Lysozymes are also called ‘suicide sacs’ because they can destroy the whole cell.
Centrioles are membrane bound organelle made of protein. They are found in animals and fungi. They play a role in splitting of the cells into two cells.
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