Chapter # 1
Cells, Tissues, Organs, And Organ Systems
What are Cells ?
"Cells are functional unit of life , In which all of the chemical reactions takes place which are necessary for the maintenance of life to takes place" . They are smallest functional independent units of life , Cells either prokaryotic or euokaryotic .
Prokaryotic Cells :
All prokaryotic cells ("Before Nucleus") are independent single-celled orgamisms (e.g., Bacteria) . The word "prokaryote" describes cells in which DNA is localized in region but but not bound by membrane.
Eukaryotic Cells :
All eukaryotes ("True Nucleus") have cells with membrane-bound nucleus containing DNA . In addition eukaryotic cells contains many other organelles ("little organs") that perform specific functions. Eukaryotic cells have a cytoskeleton which gives shape to the cell and allow multicellular movements .
All eukaryotic cells have there basic properties....!
1. The plasma membrane is the outer boundary membrane of the cell.
2. Cytoplasm is the outer portion of the cell outside the nucleus. The semifluid portion of the cytoplasm is called cytosole . Suspended whithin the cytosole are the organelles.
3. The nucleus is the cell control center. It contains the chromosomes and is spread from the cytoplasm by own nuclear envelope. The Nucleoplasm is the semifluid ,aterial in the nucleus.
Why Are Most Cells Small ?
Most cells are small and can only seen with the aid of microscope . One reason for the smallness of the cells is that the ratio of the volume of the cell's nucleus to the volume of its cytoplasm must not be so small that the nucleus , the cell's major control center ,can't control the cytoplasm .
Cell Membrane :
The plasma membrane surrounds the cell . other membrane inside the cells enclose some organelles and have properties similar to the plasma membrane .
Structure of the Cell Membrane :
In 1972, S. Jonarhan Singer and Garth Nicolson developed the "Fluid-Mosaic Model" of membrane structure. According to this model a membrane is double layer of protein and phospholipids , and fluid rather than solids. The phospholipids bilayer form a fluid "sea"in which specific proteins float like ice bags. being fluid the membrane is in constant state of flux-shifting and changing , while retaining its uniform structure . the word mosaic refers to the many different kinds of proteins dispersed in phospholipids bilayer.
Followings are the important points of Fluid-Mosaic Model :
1. The phospholipids have one polar end and one non-polar end . The polar ends are oriented on one side towards outside of the cell and into the fluid cytoplasm , on the other side, and non-polar ends face each other in the middle of the bilayer . The "Tails" of both layers of phospholipids molecules attract each and repelled by water ( they are hydrophobic , "Water Dreading" ) . As result , The polar "spherical"heads" ( the spherical portion ) are located over the cell surfaces (outer and inner) and are "water attracting" (They are Hydophilic).
2. Cholesterol is present in plasma membrane of eukaryotic cells . The Cholesterol molecule s are embedded in the interior of the membrane and help to make membrane less permeable to water soluble substance . In addition, the relatively rigid substance of cholesterol molecules help to stabilize the membrane .
3. The membrane proteins are individual molecules attached to inner or outer membrane surface or embedded in it .Some intrinsic proteins are link to sugar-protein makers on the cell surface.Other intrinsic proteins help to move ions or molecules across the membrane to the cells inner scaffolding (The exoskeleton) or to the various molecules outside the cell.
4. When carbohydrates unite with proteins , they form glycoproteins , and when they unite with lipids they form glycolipids on the surface of the plasma membrane . Surface carbohydrates and proteins of the proteinsand lipids make up the glycocalyx ("Cell Coat") The Complexly arranged and distinctively shapedgroups of sugar molecules of glycocalyx act as molecular "fingerprint" for each cell type. Glycocalyx is necessary for cell-to-cell recognitionand the behavior of certain cell.
Functions Of Cell Membrane :
Functions of the CELL MEMBRANE are given as ;
1. Regulate material moving into and out of the cell, and through one part to another part of the cell.
2. Separates inside of the cell from the outside.
3. Separates various organelles within the cell .
4. Provide a large surface area on which specific chemical reactions occur.
5. Separates cells from one another.
6. And have receptors containing specific cell identifications marks that differentiate one cell type from another.
Movement Across Membrane :
Molecule can cross membranes in the number of ways , Both by using their own energy and by replying on an outside energy source.
Simple Diffusion :
Molecule randomly (Due to spontaneous motion) from area where they are in high concentration to area of low concentration , until they are eventually distributed in a state of dynamic equilibrium. This process is called simple diffusion.
Facilitated Diffusion :
Polar molecules ("not soluble in lipids") may diffuse through protein channels (pores) in the lipid bilayer . The protein channel offers a continuous pathway for specific molecule to move across plasma membrane so that they never come into contact with hydrophobic layer or the membrane's polar surface.
Large molecules some of those not soluble in lipids require energy assistance in passing across plasma membrane . These molecule use facilitated diffusion , which is like simple diffusion , require no energy input. To pass across the membrane , a molecule temporarily bind with carrier protein in the plasma membrane and is transported through an area of high concentration to area of lower concentration.
Osmosis :
Diffusion of water from selectively permeable membrane , from an area of high concentration to an area of lower concentration is called osmosis.
TONICITY :
The term tonicity refers to the relative concentration of solution inside or outside the cell.
Isotonic Condition : In this condition concentration of solute/Ion inside and outside the cell is same and and net movement of water across the cell will be zero. and there will be no effect of environment on the cell.
Hypertonic Condition :If the concentration of solute/Ion inside the cell is LOW than the external environment than the cell will shrinks and this condition is called hypertonic.
Hypotonic Condition :If the concentration of solute/Ion inside the cell is GREATER than the external environment than the cell will swells and this condition is called hypotonic.
Active Transport :
It is the process during which movement of molecules and other substance across selectively permeable membrane against concentration dient-That is From area of lower concentration to area of higher concentration . For this process energy is required in the form of ATP , because this transportation is against the concentration dient.
ENDOCYTOSIS :
It is an other process during which substance move across PLASMA MEMBRANE is called endocytosis. It is of three types which are
1. Pinocytosis :
It is Greek word means ( Pinien, To drink + Cyto, Cell ). It is nonspecific uptake of extracellular fluid. Any solid dissolved in fluid is also taken into the cell. Picocytosis occurs when an indent is produced on the cell's plasma membrane . The open end of invagination seals itself off, forming a small vesicle . This tiny Vesicle detaches fro the plasma membrane and moves into cytoplasm.
2. Phagocytosis :
It is Greek word means ( Phagein, To eat + Cto, Cell ) so its means Cells that eat solid particles. It is similar to Pinocytosis except cell takes solid particle instead of liquid . Commonly called an organelle called lysosome combine with vesicle to form phagolysosome , and lysosomal digestive enzymes digest and break down the vesicle contents.
3. Receptor-mediate Endocytosis :
Receptor-mediate Endocytosis involves a specific receptor protein on plasma membrane that recognizes an extracellular molecule and binds with it. The reaction some how stimulates the membrane to indent and creating a vesicle containing the selected molecule. A variety of important molecules ( Such as Cholesterol )are brough into cells in this manner .
Exocytosis :
An organelle Colgi apparatus ( Described later ) package protein and other molecule that cells produces into vesicles for secretions . In the process of exocytosis these secretory vesicles fuse with plasma membrane and release their contents into extracellular environment . The process aids new membrane material , which replace the plasma membrane lost during endocytosis.
CYTOPLASM , ORGANELLES, AND CELLULAR COMPONENTS :
Many cells functions that are performed in the cytoplasmic compartment result from activity of specific structures called organelles,
CYTOPLASM :
The Cytoplasm of the cell has two different parts,
1. THE CYTOMEMBRANE SYSTEM Consist of well defined structure such as endoplasmic reticulm , Golgi Apparatus , Vacuoles and Vesicles.
2. THE FLUID CYTOSOL The fluid cytosol suspends structures of cytomembrane system and contains various dissolved molecules .
RIBOSOMES :
Ribosomes are non-membrane bound structure that are sites for protein synthesis.
ENDOPLASMIC RETICULUM :
The Endoplasmic recticulum is a complex, membrane-bound labyrinth of flattened sheets , sacs, and tubes that branches and spreads throughout cytoplasm. The E.R is continuous from the nuclear envelope to the plasma membrane and is series of channels that helps various materials to circulate throughout the cytoplasm .
USES :
Its is used in storing of enzymes, and other proteins and provide points fro attachment for ribosomes .
ROUGH E.R & SMOOTH E.R :
E.R with attached ribosomes is called rough E.R, and E.R without ribosomes being attached is called SMOOTH E.R.
USES :
The Smooth E.R is the site for Lipid Production , Detoxification of wide variety of organic molecules , And Storage for CALCIUM ions in muscle cells. In most cells contains both type of ER , Although ROUGH As well as SMOOTH ER.
GOLGI APPARATUS :
Golgi apparatus is complex of membranes associated physically and functionally with ER in the cytoplasm .it is composed of flattened stacks of membrane bound cisternea (single cisterna) . The Golgi apparatus sorts, pakages, and secretes proteins and lipids.
Protein that ribosomes synthesize are sealed off in the little packets called transfer vesicles . Transfer vesicles pass from ER to Golgi apparatus and fuse with it. In Golgi apparatus , protein is concentrated and chemically modified. On Function of chemical modification seems to be to mark and sort of protein into different batches for different destinations .
LYSOSOMES : DIGESTION & DEGRADATION
LYSOSOMES are membrane bound spherical organelles that contains acid hydrolase which is capable for digestion of organic matter like lipids,proteins,nucleic acid , and polysaccharides . the enzyme is being ready into the ER and Transported to Golgi apparatus for further process.. Lysomes fuse with phagocytic vesicles, hence exposing the vesicle's contents to lysosomal enzymes.
MITOCHONDRIA :(the cell power house)
Mitochondria is double membrane bound organelles that are spherical to elongate shape . A small space separates inner layer from outer layer. The Inner layer folds and double in on itself to form incomplete partition called cristae (single Crista). Cristae increase surface area for chemical reaction to be occurred and traps usable energy. The space between cristae is called matrix. Matrix contains ribosomes circular DNA and other materials.
CYTOSKELETON : MICROTUBULES , INTERMEDIATE FILAMENTS, MICROFILAMENTS
In most micro-tubules , Intermediate filaments and microfilaments from the flexible circular framework called cytoskeleton. This latticed framework extends throughout the cytoplasm , Connecting the various circular components .
MICROTUBULES : are hollow , slender cylindrical structure in animal cells . Each microtubule is of spiraling subunits of globular proteins called tubulin subunits . Microtubules function is movement of organelle such as secretory vesicles.
INTERMEDIATE FILAMENTS : are chemically hetrogeneous of protein fibers, the specific proteins of which can vary with cell type.These filaments helps to maintain shape and spatial organization of organelles as well as promote mechanical activities in the cytoplasm.
MICROFILAMENTS : are solid string protein (actin) molecule. Actin microfilaments are most highly developed in muscle cells as myofibirls . Which help muscle cells to shorten or contract . Actin microfilaments in muscle cell provides mechanical support for several cellular structures and help form contractile system responsible for some cellular movements in same protozoa.
CILIA AND FLAGELLA : MOVEMENT
Cilia and flagella are cell organelles that are
structurally similar but are differentiated based on their function
and/or length. Cilia are short and there are usually many (hundreds)
cilia per cell. On the other hand, flagella are longer and there are
fewer flagella per cell (usually one to eight). Though eukaryotic flagella and motile cilia are structurally identical, the beating
pattern of the two organelles can be different. The motion of flagella
is often undulating and wave-like, whereas the motile cilia often
perform a more complicated 3D motion with a power and recovery stroke.
CELL VACUOLE :
A cell is a tiny world of elements, one of which is the vacuole. Found in animal cells, a vacuole is a fluid-filled pocket in the cell's cytoplasm that serves varying functions depending on the cell's requirements.
Look at the word vacuole. Reminds you of "vacuum," doesn't it? That's because both words comes from the Latin word vacuus, which means "empty." In fact, vacuole comes from the French word that means "little vacuum." However, whereas a "vacuum" refers to an empty space, the vacuole usually contains a watery fluid. It is a space in the cell that has no specific purpose, but usually functions as a storage bin for everything from water and food to waste products.
The cell vacule of eukaryotic cell is shown in the above figure , and mentioned as that you can find it easily .
NUCLEUS THE INFORMATION CENTER :
The nucleus
is a membrane bound structure that contains the cell's hereditary
information and controls the cell's growth and reproduction. It is
commonly the most prominent organelle in the cell.
NUCLEAR ENVELOPE GATE WAY TO NUCLEUS :
It is made up of two layers, each composed of a lipid bilayer. It is perforated with holes, called nuclear pores, to facilitate and regulate the exchange of materials (for example, proteins and RNA) between the nucleus and the cytoplasm. In between these two membranes is a space called perinuclear space. The outer membrane is continuous with the endoplasmic reticulum. The inner membrane is associated with a network of intermediate filaments called nuclear lamina, which is made of lamin. The lamina acts as a site of attachment for chromosomes. It also acts like a shield for the nucleus.
ANIMAL TISSUES :
PAS diastase showing the fungus Histoplasma.
Animal tissues can be grouped into four basic types: connective, muscle, nervous, and epithelial. Multiple tissue types compose organs and body structures. While all animals can generally be considered to contain the four tissue types, the manifestation of these tissues can differ depending on the type of organism. For example, the origin of the cells comprising a particular tissue type may differ developmentally for different classifications of animals.
The epithelium in all animals is derived from the ectoderm and endoderm with a small contribution from the mesoderm, forming the endothelium, a specialized type of epithelium that composes the vasculature. By contrast, a true epithelial tissue is present only in a single layer of cells held together via occluding junctions called tight junctions, to create a selectively permeable barrier. This tissue covers all organismal surfaces that come in contact with the external environment such as the skin, the airways, and the digestive tract. It serves functions of protection, secretion, and absorption, and is separated from other tissues below by a basal lamina.
Connective tissue :
Connective tissues are fibrous tissues. They are made up of cells separated by non-living material, which is called extracellular matrix. Connective tissue gives shape to organs and holds them in place. Both blood and bone are examples of connective tissue. As the name implies, these support and bind other tissues. Unlike epithelial tissue, connective tissue typically has cells scattered throughout an extracellular matrix.
Muscle tissue :
Muscle cells form the active contractile tissue of the body known as muscle tissue or muscular tissue. Muscle tissue functions to produce force and cause motion, either locomotion or movement within internal organs. Muscle tissue is separated into three distinct categories: visceral or smooth muscle, which is found in the inner linings of organs; skeletal muscle, in which is found attached to bone providing for gross movement; and cardiac muscle which is found in the heart, allowing it to contract and pump blood throughout an organism.
Nervous tissue :
Cells comprising the central nervous system and peripheral nervous system are classified as neural tissue. In the central nervous system, neural tissue forms the brain and spinal cord and, in the peripheral nervous system forms the cranial nerves and spinal nerves, inclusive of the motor neurons. Nervous tissue functions to transmit messages in form of impulse.
Epithelial tissue :
The epithelial tissues are formed by cells that cover the organ surfaces such as the surface of the skin, the airways, the reproductive tract, and the inner lining of the digestive tract. The cells comprising an epithelial layer are linked via semi-permeable, tight junctions; hence, this tissue provides a barrier between the external environment and the organ it covers. In addition to this protective function, epithelial tissue may also be specialized to function in secretion and absorption. Epithelial tissue helps to protect organisms from microorganisms, injury, and fluid loss. Functions:
the cell of the body surface form the outer layer of skin.
inside the body,epithelial cells forms lining of mouth & alimentary canal & protect these organ.
epithelial tissues help in absorption of water & nutrient.
epithelial tissues help in elimination of waste product.
The different types of epithelial tissues are as follows:
Squamous epithelium,
Cuboidal epithelium,
Columnar epithelium,
Glandular epithelium,
Ciliated epithelium.
CONNECTIVE TISSUES : CONNECTION AND SUPPORT
As the name implies, connective tissue serves a "connecting" function. It supports and binds other tissues. Unlike epithelial tissue, connective tissue typically has cells scattered throughout an extracellular matrix.
THERE ARE SEVEN TYPES OF CONNECTIVE TISSUES which are given as ;
AEROLAR CONNECTIVE TISSUE :
  Fibrous connective tissue, loosely packed, to hold tissue layers together. |
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