All About Cell and Tissues

The basic membrane-bound unit that contains the fundamental molecules of life and of which all living things are composed. A single cell is often a complete organism in itself, such as a bacterium or yeast. Although cells are much larger than atoms, they are still very small. The smallest known cells are a group of tiny bacteria called mycoplasmas.
Different Parts of Cell
Cell/Plasma Membrane
Cell Membrane also known as Plasma Membrane
It has three primary functions:
·        To keep toxic substances out of the cell
·         To allow specific molecules, such as ions, nutrients, wastes, and metabolic products, that mediate cellular and extracellular activities to pass between organelles and between the cell and the outside environment
·         It separate vital but incompatible metabolic processes conducted within organelles.
The Cell Membrane is primarily composed of a mix of proteins and lipids. Depending on the membrane’s location and role in the body, lipids can make up anywhere from 20% to 80% of the membrane, with the remainder being proteins. While lipids help to give membranes their flexibility, proteins monitor and maintain the cell's chemical climate and assist in the transfer of molecules across the membrane.
Cell Wall
The cell wall is the rigid, semi-permeable protective layer in some cell types. This outer covering is positioned next to the Cell membrane in most plant cells, fungi, bacteria, algae and some archaea. Animal cells however, do not have a cell wall. The cell wall conducts many important functions in a cell including protection, structure, and support.
The composition of cell walls varies between species and may depend on cell type and developmental stage.
·        The primary cell wall of land plants is composed of the polysaccharides cellulose, hemicellulose and pectin. Often, other polymers such as lignin, suberin or cutin are anchored to or embedded in plant cell walls.
·        Algae possess cell walls made of glycoproteins and polysaccharides such as carrageenan and agar that are absent from land plants.
·         In bacteria, the cell wall is composed of peptidoglycan.
·        The cell walls of archaea have various compositions, and may be formed of glycoprotein S-layers, pseudo peptidoglycan, or polysaccharides.
·         Fungi possess cell walls made of the glucosamine polymer chitin.
·        Unusually, diatoms (A group of Micro-Algae) have a cell wall composed of biogenic silica
The cell nucleus is a membrane bound structure that contains the cell's hereditary information and controls the cell's growth and reproduction. It is the command centre of a eukaryotic cell and is commonly the most prominent organelle in a cell. The nucleus is the organelle which houses chromosomes.
Chromosomes consist of DNA, which contains heredity information and instructions for cell growth, development, and reproduction. When a cell is "resting" i.e. not dividing, the chromosomes are organized into long entangled structures called chromatin and not into individual chromosomes as we typically think of them.
Nuclear envelope
The cell nucleus is bound by a double membrane called the nuclear envelope. This membrane separates the contents of the nucleus from the cytoplasm.
Like the cell membrane, the nuclear envelope consists of phospholipids that form a lipid bilayer. The envelope helps to maintain the shape of the nucleus and assists in regulating the flow of molecules in and out of the nucleus through nuclear pores. The nuclear envelope is connected with the endoplasmic reticulum (ER) in such a way that the internal compartment of the nuclear envelope is continuous with the lumen of the ER.
Nucleoplasm is the gelatinous substance within the nuclear envelope. Also called karyoplasm, this semi-aqueous material is similar to cytoplasm and is composed mainly of water with dissolved salts, enzymes, and organic molecules suspended within.
The nucleolus and chromosomes are surrounded by nucleoplasm, which functions to cushion and protect the contents of the nucleus. Nucleoplasm also supports the nucleus by helping to maintain its shape. Additionally, nucleoplasm provides a medium by which materials, such as enzymes and nucleotides (DNA and RNA subunits), can be transported throughout the nucleus.
Substances are exchanged between the cytoplasm and nucleoplasm through nuclear pores.
The Nucleolus
Contained within the nucleus is a dense, membrane-less structure composed of RNA and proteins called the nucleolus. The nucleolus contains nucleolar organizers, which are parts of chromosomes with the genes for ribosome synthesis on them. The nucleolus helps to synthesize ribosomes by transcribing and assembling ribosomal RNA subunits. These subunits join together to form a ribosome during protein synthesis.
Protein synthesis
The nucleus regulates the synthesis of proteins in the cytoplasm through the use of messenger RNA (mRNA). Messenger RNA is a transcribed DNA segment that serves as a template for protein production. It is produced in the nucleus and travels to the cytoplasm through the nuclear pores of the nuclear envelope. Once in the cytoplasm, ribosomes and another RNA molecule called transfer RNA work together to translate mRNA to produce proteins.
The cytoplasm consists of all of the contents outside of the nucleus and enclosed within the cell membrane of a cell. It is clear in colour and has a gel-like appearance. The cytoplasm is composed mainly of water and also contains enzymes, salts, organelles, and various organic molecules.
The cytoplasm functions to support and suspend organelles and cellular molecules. Many cellular processes also occur in the cytoplasm.
Some of these processes include protein synthesis, the first stage of cellular respiration known as glycolysis, mitosis, and meiosis. In addition, the cytoplasm helps to move materials, such as hormones, around the cell and also dissolves cellular waste.
Endoplasmic Reticulum
The endoplasmic reticulum (ER) is an important organelle in eukaryotic cells. It plays a major role in the production, processing, and transport of proteins and lipids. The ER produces Trans membrane proteins and lipids for its membrane and for many other cell components including lysosomes, secretory vesicles, the Golgi apparatus, the cell membrane, and plant cell vacuoles.
There are two regions of the ER that differ in structure and function.
Rough Endoplasmic Reticulum
The rough endoplasmic reticulum manufactures membranes and secretory proteins. The ribosomes attached to the rough ER synthesize proteins by the process of translation.
·        In certain leukocytes (white blood cells), the rough ER produces antibodies.
·        In pancreatic cells, the rough ER produces insulin.
The rough and smooth ER are usually interconnected and the proteins made by the rough ER move into the smooth ER to be transferred to other locations. Some proteins are sent to the Golgi apparatus by special transport vesicles. After the proteins have been modified in the Golgi, they are transported to their proper destinations within the cell or exported from the cell by exocytosis.
Smooth Endoplasmic Reticulum
The smooth ER has a wide range of functions including carbohydrate and lipid synthesis. Lipids such as phospholipids and cholesterol are necessary for the construction of cell membranes. Smooth ER also serves as a transitional area for vesicles that transport ER products to various destinations.
·        In liver cells the smooth ER produces enzymes that help to detoxify certain compounds.
·         In muscles the smooth ER assists in the contraction of muscle cells, and
·        In brain cells it synthesizes male and female hormones.
Golgi Apparatus
 The Golgi apparatus is the "manufacturing and shipping centre" of a eukaryotic cell.
The Golgi apparatus, sometimes called the Golgi complex or Golgi body, is responsible for manufacturing, warehousing, and shipping certain cellular products, particularly those from the endoplasmic reticulum (ER). Depending on the type of cell, there can be just a few complexes or there can be hundreds. Cells that specialize in secreting various substances typically have a high number of Golgi.
Molecules synthesized in the ER exit via special transport vesicles which carry their contents to the Golgi apparatus
The Golgi apparatus modifies many products from the ER including proteins and phospholipids. The complex also manufactures certain biological polymers of its own. The Golgi apparatus contains processing enzymes, which alter molecules by adding or removing carbohydrate subunits. Once modifications have been made and molecules have been sorted, they are secreted from the Golgi via transport vesicles to their intended destinations.
Lysosomes are organelles that are found in most animal cells and act as the digesters of a eukaryotic cell. Lysosome enzymes are made by proteins from the endoplasmic reticulum and enclosed within vesicles by the Golgi apparatus. Lysosomes are formed by budding from the Golgi complex.
Lysosomes contain various hydrolytic enzymes (around 50 different enzymes) that are capable of digesting nucleic acids, polysaccharides, lipids, and proteins. The inside of a lysosome is kept acidic as the enzymes within work best in an acidic environment.
When cell is about to die, lysosome burst up and digest the cell to make room for the new cell, hence they are called as Suicidal Bags.
Mitochondria are considered the "power houses" of eukaryotic cells. These organelles generate power by converting energy into forms that are usable by the cell. Located in the cytoplasm, mitochondria are the sites of cellular respiration. Cellular respiration is a process that ultimately generates fuel for the cell's activities from the foods we eat. Mitochondria produce the energy required to perform processes such as cell division, growth, and cell death.
Mitochondria have a distinctive oblong or oval shape and are bounded by a double membrane. The inner membrane is folded creating structures known as cristae.
·        Mitochondria are found in both animal and plant cells.
·        They are found in all body cell types, except for mature red blood cells.
·        The absence of mitochondria and other organelles in red blood cells leaves room for the millions of haemoglobin molecules needed in order to transport oxygen throughout the body.
·        Muscle cells, on the other hand, may contain thousands of mitochondria needed to provide the energy required for muscle activity.
·         Mitochondria are also abundant in fat cells and liver cells.
Mitochondrial DNA
Mitochondria are semi-autonomous in that they are only partially dependent on the cell to replicate and grow. They have their own DNA, ribosomes, make their own proteins, and have some control over their reproduction. Similar to bacteria, mitochondria have circular DNA and replicate by a reproductive process called binary fission. Prior to replication, mitochondria merge together in a process called fusion. Fusion is needed in order to maintain stability, as without it, mitochondria will get smaller as they divide. These smaller mitochondria are not able to produce sufficient amounts of energy needed for proper cell function.
Ribosomes are cell organelles that consist of RNA and proteins. They are responsible for assembling the proteins of the cell. Depending on the protein production level of a particular cell, ribosomes may number in the millions.
A vacuole is a cell organelle found in a number of different cell types. Vacuoles are fluid-filled, enclosed structures that are separated from the cytoplasm by a single membrane. They are found mostly in plant cells and fungi. However, some Protista, animal cells, and bacteria also contain vacuoles. Vacuoles are responsible for a wide variety of important functions in a cell including nutrient storage, detoxification, and waste exportation.
Photosynthesis occurs in eukaryotic cell structures called chloroplasts. A chloroplast is a type of plant cell organelle known as a plastid. Plastids assist in storing and harvesting needed substances for energy production. A chloroplast contains a green pigment called chlorophyll, which absorbs light energy for photosynthesis. Hence, the name chloroplast indicates that these structures are chlorophyll-containing plastids. Like mitochondria, chloroplasts have their own DNA, are responsible for energy production, and reproduce independently from the rest of the cell through a division process similar to bacterial binary fission. Chloroplasts are also responsible for producing amino acids and lipid components needed for chloroplast membrane production. Chloroplasts can also be found in other photosynthetic organisms such as algae.
Types of Cell Division
1.      Amitosis
Cell division by simple cleavage of the nucleus and division of the cytoplasm without spindle formation or appearance of chromosomes.
2.      Mitosis
Mitosis is a part of the cell cycle when replicated chromosomes are separated into two new nuclei. It occurs in somatic Cell.
3.      Meiosis
Meiosis is a specialized type of cell division that reduces the chromosome number by half, creating four haploid cells, each genetically distinct from the parent cell that gave rise to them. This process occurs in all sexually reproducing single-celled and multicellular eukaryotes, including animals, plants, and fungi
Tissues are groups of cells that have a similar structure and act together to perform a specific function. There are four different types of tissues in animals: connective, muscle, nervous, and epithelial. In plants, tissues are divided into three types: vascular, ground, and epidermal.
a.       Epithelial Tissue
Epithelial tissue, or epithelium, covers the surfaces of organs including the skin, the trachea, the reproductive tract, and the digestive tract’s inner lining. It creates a barrier that helps protect organs.
b.      Connective Tissue
Connective tissue connects or separates groups of other tissues. It is found in between all the other tissues and organs in the body. Connective tissue is made up of cells and ground substance, which is a gel that surrounds cells. Most connective tissue, except for lymph and blood, also contains fibres, which are long, narrow proteins.
c.        Muscle Tissue
Muscle tissue comprises all the muscles in the body, and the specialized nature of the tissue is what allows muscles to contract. There are three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle
d.       Nervous Tissue
Nervous tissue is found in the brain, spinal cord, and peripheral nerves, which are all parts of the nervous system. It is made up of neurons, which are nerve cells, and neuroglia, which are cells that help nerve impulses travel

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