CELL 2024.pptx

The cell and its function Cell is the basic unit of the body  Human Cell Each of the 100 trillion cells in a human being is a living structure that can survive for months or many years if its surrounding fluids contains appropriate nutrients.  Organization of Cell A typical cell as seen by the...

The cell and its function Cell is the basic unit of the body  Human Cell Each of the 100 trillion cells in a human being is a living structure that can survive for months or many years if its surrounding fluids contains appropriate nutrients.  Organization of Cell A typical cell as seen by the light microscope shows two major parts: 1. Nucleus 2. Cytoplasm Nucleus is separated from the cytoplasm by a nuclear membrane and the cytoplasm is separated from the surrounding fluids by a cell membrane or plasma membrane. The different substances that make up the cell are collectively called as protoplasm. Protoplasm is composed mainly of five substances:  Cell composition Water :70-85% Ions Proteins: 10-20% Lipids : 2-95% Carbohydrates : 1-6 % 1-Water: The principal fluid medium of the cell  is present in most cells except fat cells, in a concentration of 75 to 80%.  Many cellular chemicals are dissolved in the water.  Chemical reactions take place among the dissolved chemicals or at the surfaces of the  2.Ions  The most important ions in the cell are 1. Potassium 2. Magnesium 3. Phosphate 4. Sulfate 5. Bicarbonate  Less in quantity are: 1. Sodium 2. Chloride 3. Calcium These ions provide inorganic chemicals for chemical reactions.  they are also essential for some of the operation of cells like transmission of nerve impulses in nerve and muscle fibers.  3.Proteins After water, proteins are the most abundant substance present in most cell nearly about 10 to 20%.These proteins are divided into two types: Structural proteins Functional proteins Structural proteins They are present in Extracellularly the form of long fibrillar proteins are filaments and their found specially in main function is to  Collagen and elastic form microtubules fibers of connective that provides tissue cytoskeletons of such  Blood vessel walls cellular organelles as Tendons Ligaments Cilia Nerve axons  Mitotic spindles of mitosing cells Cilia and Axons Fibrillar Proteins Functional Proteins They are mainly in the tubular-globular form.  These proteins are mainly the enzymes of the cell and in contrast to structural proteins they are often mobile in the cell fluid. Also, many of them are adherent to membranous Cell Enzymes  4.Lipids:2% Important lipids are : phospholipids and cholesterol insoluble in water and therefore are used to form the cell membrane and intracellular membrane barriers that separate the different cell compartments. Neutral fat (triglycerides): in fat cell triglycerides account for 95% of the cell mass. The fat stored in these cells represent the body’s main storehouse of energy-giving nutrients.  5.Carbohydrates : Little structural function in the cell and play a major role in nutrition of the cell. Most human cells do not maintain large stores of carbohydrates , the amount usually averages about 1% of their total mass but increase to 3% in muscle cell and 6% in liver.  Carbohydrates in the form of dissolved glucose is always present in the Membranous structure of the cell Cell membrane Nuclear membrane Membrane of the endoplasmic reticulum Membrane of mitochondria, lysosomes and Golgi apparatus.  Most organelles of the cell are covered by membranes composed primarily of lipids and proteins. The lipids of the membranes provide a barrier that impedes the movement of water and water-soluble substances from one cell compartment to another because water is not soluble in lipids. Protein molecules in the membrane often do penetrate all the way through the membrane, thus providing specialized pathways. Also, many other membrane proteins are  Cell membrane Thin ,elastic structure 7.5 – 10 nanometers thick Mainly composed of proteins and lipids. Composition Cell Membrane is made-up of: Proteins: 55% Phospholipids: 25% Cholesterol: 13% Other lipids: 4% Carbohydrates: 3% Composition of Cell Membrane Lipid Barrier of Cell Membrane Basic structure of cell membrane is Lipid Bilayer Which is a thin, double-layered film of lipids, each one molecule thick and it covers the entire cell surface. Interspersed in this lipid layers are large globular protein molecules. One end of each phospholipid molecule is soluble in water (Phosphate end) Hydrophilic while the other end is soluble only in fats (fatty acid portion) Hydrophobic.  Hydrophobic portion of the phospholipid molecule are repelled by water but they are attracted by each other therefore they naturally attach to each other in the middle of the membrane. Hydrophilic phosphate portion then constitute the two surfaces of cell membrane, in direct contact with intracellular water on the inside of the cell membrane. and extracellular water on the outside of the cell membrane. Phosphate Portion of Cell Membrane Lipid layer in the middle of the membrane is impermeable to the usual water-soluble substance like: Ions Glucose Urea Thus these cannot pass the membrane as such. Lipid layer in the middle of the membrane is permeable to fat soluble substances like: Oxygen Carbon dioxide Alcohol Thus these can pass the membrane as such.  CO2 O2 N2 ions glucose H2O urea halothane hydrophilic “head” hydrophobic FA “tail”  The cholesterol in the membrane help to determine the degree of permeability(or impermeability) of the bilayer to water soluble constitutes of body fluids. Cholesterol controls much of the fluidity of the membrane. 2- Proteins : Integral Peripheral K+ Integral Proteins They protrude all the way through the membrane. They provide channels or pores through which water molecules and water-soluble substances specially ions can diffuse between intracellular and extracellular fluids. Some of the integral proteins act as carrier proteins for transporting substances that otherwise could not penetrate the lipid bilayer. Some of them act as enzymes. Others serves as receptors. Peripheral Proteins They are often attached to the integral proteins. They almost entirely act as enzymes or as controllers of transport of substances through the cell membrane pores.  3 - Carbohydrates: glycolipids (approximately 10%) glycoproteins (majority of integral proteins) proteoglycans (carbs bound to protein cores) Glycocalyx loose carbohydrate coat outside surface of the cell GLYCOCALYX  negative charge of the carbo chains repels other negative charges. o involved in cell-cell attachments/interactions o play a role in immune reactions o Act as receptor substance for binding hormones. Major Functions of the Cell Membrane The cell membrane functions as a barrier that makes it possible for the cytoplasm to maintain a different composition from the material surrounding the cell. It contains various pumps and channels made of specific transverse membrane proteins that allow concentration gradients to be maintained between the inside and outside of the cell.  Cytoplasm Cytoplasm is the substance which fills the cells of an organism. Cytoplasm is a jelly-like substance which is comprised of 80% water and is colorless. It is like a thick gel, but liquefies when stirred or shaken. The clear fluid portion of the cytoplasm in which the particles are dispersed is called as Cytosol.  Cytoplasm is filled with both minute and large dispersed particles and organelles. Eachparticle and organelle is concerned with specific function. From the formation of energy till the removal of waste these organelles are involved in some ways. Cytoplasm Cell Organelles Five important organelles present in cytoplasm are: Endoplasmic Reticulum Golgi Apparatus Mitochondria Lysosomes Peroxisomes Cell Organelles  1 - The Endoplasmic Reticulum: Network of tubular and flat vesicular structures. The tubules and vesicles interconnect with one another. Membrane is similar to the plasma membrane. Space inside the tubules is called the endoplasmic matrix. the space inside the endoplasmic reticulum is connected with the space between the two membrane surfaces of the nuclear membrane. Substances formed in some parts of the cell enter the space of the endoplasmic reticulum and are then conducted to other parts of the cell. Also, the vast surface area of this reticulum and the multiple enzyme systems attached to its membranes provide machinery for a major share of the metabolic functions of the cell.  Rough or Granular ER Attached to the outer surfaces of many parts of the endoplasmic reticulum are large numbers of minute granular particles called ribosomes. The ribosomes are composed of a mixture of RNA and proteins, and Smooth ER (a Granular ER) Part of ER has no attached ribosomes. site of lipid synthesis -phospholipids - cholesterol growing ER membrane buds continuously forming transport vesicles, most of which migrate to the Golgi apparatus  The Golgi Membrane composition similar Apparatus: to that of the smooth ER and plasma membrane. Composed of 4 or more stacked layers of flat vesicular Structures. This apparatus is prominent in secretory cell, where it is located on the side of the cell from which the secretory substance are extruded.  Receives transport vesicles from smooth ER. Transported substance are then processed in Golgi apparatus to form : - Lysosomes - Secretory vesicle - Cytoplasmic component  Lysosomes : esicular organelle formed from budding Golgi v apparatus. Lysosome provide an intracellular digestive system that allows the cell to digest: -damaged cellular structure -food particles that have been ingested by cell -unwanted matter such as bacteria contain hydrolytic enzymes (acid hydrolases) , protein is hydrolyzed to form amino acids, glycogen is hydrolyzed to form glucose, and lipids are hydrolyzed to form fatty acids and glycerol. fuse with pinocytotic or Peroxisomes: similar physically to lysosomes two major differences: formed by self-replication Or perhaps by budding off from smooth endoplasmic reticulum. they contain oxidases (hydrogen peroxide and catalase) Function: oxidize substances (e.g. alcohol) that may be otherwise poisonous  Mitochondria (powerhouse) : Primary function: extraction of energy from nutrients Mitochondria are self-replicative Mitochondria contain DNA similar to that found in the cell nucleus. Matrix: contain large amount of dissolve enzymes Mitochondria Mitochondria are membrane-bound organelles, and like the nucleus have a double membrane. The outer membrane is fairly smooth. But the inner membrane is highly convoluted, forming folds called cristae. Cristae of Mitochondrial Membrane Many folding of the inner membranes form shelves on to which oxidative enzymes are attached. The inner cavity of the mitochondrion is filled with a matrix that contain large amount of dissolved enzymes that are necessary for extracting energy from nutrients.  These enzymes operate in association with oxidative enzymes on the shelve to cause oxidation of the nutrients, thereby forming carbon dioxide and water and at the same time releasing energy. The liberated energy is used to synthesize a high energy substance called adenosine triphosphate (ATP). ATP is then transported out of the mitochondrion and it diffuses out the cell to release its own energy where ever it is needed for performing cellular functions. Replication of Mitochondria The Nucleus: “Control Center” of the Cell Nucleus contains large quantities of DNA ,which are the genes.  The Nucleus: “Control Center” of the Cell Nucleus: control center; houses DNA; directs activities of the cell Nuclear membrane is two separated bilayer membrane, the outer membrane is continuous with the endoplasmic reticulum. Nuclear membrane penetrated by several thousand nuclear pores. Chromatin (condensed DNA) is found in the nucleoplasm o Nucleolus one or more per nucleus contains RNA and proteins not membrane delimited functions to form the granular “subunits” of ribosomes  it is simply an accumulation of large amounts of RNA and proteins of the types found in ribosomes. The nucleolus becomes considerably enlarged when the cell is actively synthesizing proteins. Formation of the nucleoli (and of the ribosomes in the cytoplasm outside the nucleus) begins in the nucleus. First, specific DNA genes in the chromosomes cause RNA to be synthesized.  Some of this is stored in the nucleoli, but most of it is transported outward through the nuclear pores into cytoplasm. Here, it is used in conjunction with specific proteins to assemble “mature” ribosomes that play an essential role in forming cytoplasmic proteins.  TRANSPORT ACROSS CELL MEMBRANES simple diffusion CARRIER MEDIATED TRANSPORT Facilated diffusion Primary active transport Secondary active transport co transport Simple diffusion It is the only form of diffusion which is not carrier dependent. It occurs down an electrochemical gradient [downhill]. It does not require metabolic energy and therefore is passive. It is kinetic movement of molecules or ions occurs through a membrane opening. Rate of diffusion is determined by the amount of substance available , the velocity of kinetic motion , and the number and size of openings in the membrane.  Facilitated diffusion Characteristics of facilitated diffusion : occurs down an electrochemical gradient (“downhill”), similar to simple diffusion. does not require metabolic energy and therefore is passive is more rapid than simple diffusion. Example of facilitated diffusion Glucose transport in muscle and adipose cells is “downhill,” is carrier-mediated, and is exhibited by sugars such as galactose; therefore, it is categorized as facilitated diffusion. In diabetes mellitus, glucose uptake by muscle and adipose cells is impaired because the carriers for facilitated diffusion of glucose require insulin.  Primary active transport Characteristics of primary active transport: occurs against an electrochemical gradient (“uphill”). requires direct input of metabolic energy in the form of adenosine triphosphate (ATP) and therefore is active. is carrier-mediated. Examples of primary active transport a. Na+,K+-ATPase (or Na+–K+ pump) in cell membranes transports Na+ from intracellular to extracellular fluid and K+ from extracellular to intracellular fluid; it maintains low intracellular [Na+] and high intracellular [K+]. Both Na+ and K+ are transported against their electrochemical gradients. 3 Na+/2 K+. Energy is provided from the terminal phosphate bond of ATP. b. Ca2+-ATPase (or Ca2+ pump) in the sarcoplasmic reticulum (SR) or cell membranes transports Ca2+ against an electrochemical gradient. c. H+,K+-ATPase (or proton pump) in gastric parietal cells transports H+ into the lumen of the stomach against its electrochemical gradient. SECONDARY ACTIVE TRANSPORT Characteristics of secondary active transport : a.The transport of two or more solutes is coupled. b.One of the solutes (usually Na+) is transported “downhill” and provides energy for the “uphill” transport of the other solute(s). c. Metabolic energy is not provided directly, but indirectly from the Na+ gradient that is maintained across cell membranes.(Thus, inhibition of Na+,K+-ATPase will decrease transport of Na+ out of the cell, decrease the transmembrane Na+ gradient, and eventually inhibit secondary active transport). d.If the solutes move in the same direction across the cell membrane, it is called co-transport, or symport. (Examples are Na+–glucose cotransport in the small intestine and Na+–K+2Cl– cotransport in the renal thick ascending limb) Thank you