Presentation on theme: "Cells The Living Unit Chapter 3. Cell Theory Cells are the building blocks of all plants and animals. All cells come from the division of pre-existing."— Presentation transcript:
Cells The Living Unit Chapter 3
Cell Theory Cells are the building blocks of all plants and animals. All cells come from the division of pre-existing cells. Cells are the smallest units that perform all vital physiological functions. Each cell maintains homeostasis. Homeostasis at the level of the tissue, organ, organ system and organism reflects the combined and coordinated actions of many cells.
The study of cellular structure and function, or cytology, is part of the broader discipline called cellular biology. The human body contain two general classes of cells: sex cells and somatic cells. Sex cells(germ cells or reproductive cells)are either the sperm of the male or oocytes of the female.
Anatomy of Animal Cell
Anatomy of a Generalized Cell Our model cell is surrounded by a watery medium known as extracellular fluid. Extracellular Fluids: all body fluid other than that within cells; includes plasma and interstitial fluid. The extracellular fluid in most tissue is called interstitial fluid. The cell membrane separates the cell content or cytoplasm.
A cell membrane separates the cells content or Cytoplasm, from the extracellular fluid can be divided into cytosol, a liquid, and intracellular structures collectively known as organelles or ‘little organs’.
Plasma Membrane The plasma membrane is often referred to as the cell membrane. Nearly all organelles are made of membrane. We will specify the outer membrane that surrounds a cell as the plasma membrane
Functions of the cell membrane Physical Isolation: Keeping the inside separated from the outside. Regulation and exchange with the environment: controls the entry of ions and nutrients and the elimination of wastes Sensitivity to the environment: membrane is the first part of the cell affected by changes in the composition, concentration, or pH of extracellular fluid. Structural Support: Specialized connections between cell membranes, or between membranes and extracellular material, gives tissue stability.
Nonmembranous Organelles Cytoskeleton: microtubules & microfilament. Made of proteins organized in fine filaments or slender tubes. Function: strength and support; movement of cellular structures and materials; cell movement Microvilli: membrane extensions containing microfilaments. Function: Increase surface area to facilitate absorption of extracellular materials
Cilia: membrane extensions containing microtubule doublets. Function: movement of materials over cell surface. Centriole/ centrosomes: Cytoplasm containing two centrioles at right angles; each centriole is composed of 9 microtubules triplets. Function: essential for movement of chromosomes during cell division
Ribosomes: RNA + proteins; fixed ribosome bound to rough ER, free ribosome scattered in cytoplasm. Function: protein synthesis. Proteasomes: Hollow cylinder of proteolytic enzymes with regulatory proteins at ends. Function: Breakdown and recycling of intracellular proteins.
Membranous Organelles Mitochondria: double membrane, inner membrane folds (cristae) enclosing important metabolic enzymes. Function: Produces 95% of ATP required by the cell.
Endoplasmic reticulum [ER]: network of membranous channels extending throughout cytoplasm. Function: synthesis of secretory products, intracellular storage and transport. Rough ER: Has ribosome bound to membranes Function: Modification and packaging of newly synthesized proteins. Smooth ER: lacks attached ribosomes Function: Lipid and carbohydrate synthesis.
Golgi Apparatus or body: stacks of flattened membranes (cristernae) containing chambers. Function: storage, alteration, and packaging of secretory products and lysosomal enzymes.
Lysosomes: vesicles containing powerful digestive enzymes. Function: intracellular removal of damaged organelles or pathogens. Peroxisomes: vesicles containing degradative enzymes. Function: neutralization of toxic compounds.
Plasma Membrane The plasma membrane consists of two lipid layers arranged “tail to tail” in which protein molecules float. Most of the lipid portion is phospholipids (some with attached sugars), a substantial amount of cholesterol is also found in the plasma membrane
The polar heads of the phospholipids molecules are hydrophilic or water loving and are attracted to water, the main component of the intercellular and extracellular fluids. Because of this they lie on both sides of the membrane surface.
The nonpolar tails of the phospholipids are hydrophobic or water hating and avoid water. They line up in the center of the membrane. It is this hydrophobic feature that makes the membrane impermeable to most water – soluable molecules. Cholesterol has a stabilizing effect and helps keep the membrane fluid.
Proteins scattered in the lipid bilayer are responsible for most of the specialized functions of the membranes. Some are enzymes, receptors, binders and some have a transport function. Most proteins are for transport.
In the diagram you can see the ways in which each of these proteins are used by the plasma membrane.
Specialization of the Plasma Membrane Microvilli are fingerlike projections that increase the surface area of a cell for absorption. Membrane junctions: tight, desmosomes, and gap junctions. The gap junctions are filled with connexons.
Cytoplasm The cytoplasm is identified as the cellular material outside of the nucleus and inside the plasma membrane. The cytoplasm has three major elements: Cytosol Organelles Inclusions
Cytosol The cytosol is a semitransparent fluid that suspends the other elements. Dissolved in cytosol, which is mainly water are nutrients and a variety of solutes.
Organelles Organelles are the metabolic machinery of the cell. Each type of organelle is specialized to carry out a specific function for the cell.
Inclusions Inclusions are not functioning units, but are chemical substances that may or may not be present, depending on the specific cell. Most inclusions store nutrients or cell products. Which include lipid droplets, glycogen granules, pigment, mucous and other secretions and various crystals
Nucleus In a cell the nucleus is the control center or headquarters. The nucleus contains many parts. Nuclear Envelope which is a double membrane barrier. It controls what enters and exits the nucleus.
Nucleoli found in the center of the nucleus is where the ribosome are assembled. Nucleoli are composed of RNA, enzymes and a protein called histones. Ribosome serve as the site for protein synthesis. Chromatin: in a non – dividing cell looks like bumpy threads. During cell division they condense to form chromosomes. All of these are found within or around the nucleus.
The chemical language the cell uses is known as the genetic code. The genetic code is called a triplet code, because a sequence of three nitrogenous bases (codon) specify the identity of a single amino acid. Gene is a functional unit of heredity.
Before a gene can affect a cell, the portion of the DNA molecule containing the gene must be uncoiled and the histone temporarily removed. The factor that controls this process is called gene activation. Gene activation is the start of the transcription process in which the DNA strand must separate from its complement.
Steps of Transcription mRNA Step 1: DNA strands have separated and the promoter has been exposed, transcription can begin. Key event attachment of RNA polymerase to the template strand. Step 2: DNA strand gets its RNA complement. A=U, G=C Step 3: At the stop signal, the mRNA and enzyme detach from the DNA strand and transcription ends.
Translation Protein synthesis is the assembling of functional polypeptides in the cytoplasm. Protein synthesis occurs through translation, the formation of a linear chain of amino acids, using the information provided by an mRNA strand.
Movement of Substances In and Out of the Cell Key Terms: permeability, impermeable, freely permeable and selective permeability. These are the term that describes the cell membrane. Only very select substances can go in and out of the cell. This passage across the membrane can be passive or active.
Passive process moves ions or molecules across the cell membrane with no expenditure of energy by the cell. Active process requires the cell to expend energy, usually in the form of ATP
Types of Transport Diffusion: passive Carrier mediated transport: both passive and active transport Vesicular transport: active transport
Diffusion Diffusion: passive molecular movement from an area of higher concentration to an area of lower concentration
Important Factors the Influence Diffusion Distance: the shorter the distance the more quickly the concentration gradients are eliminated. Molecule size: Ions and small organic molecules diffuse more rapidly than larger ones do. Temperature: The higher the temperature the faster the diffusion rate. Gradient Size: The larger the concentration gradient the faster diffusion proceeds. Electrical Forces: Opposite charges attract each other and like charges repel
Diffusion Over time the molecules in any given space tend to become evenly distributed. This distribution process is called diffusion. As molecules move around there will be a net movement of materials from an area of higher concentration to an area of lower concentration. The difference between the high and low concentration is a concentration gradient(and thus a potential energy gradient.)
Channel – Mediated Diffusion Membrane channels are very small passageways created by transmembrane proteins. Water molecules can enter and exit freely, glucose is too big to fit through the channel. Whether or not a substances can transit a particular membrane depends on many factors: Size and charge of the ion Size of the hydration sphere Interaction between ion and the channel wall.
Osmosis Osmosis the net diffusion of water across a membrane. Water tends to flow across a membrane toward the solution containing the higher solute concentration, because this movement is down the concentration gradient for water. This movement will continue until water concentrations and thus solute concentrations are the same on both sides of the membrane
Characteristics of Osmosis Osmosis is the movement of water molecules across a membrane. Osmosis occurs across a selectively permeable membrane that is freely permeable to water, but not freely permeable to solutes. In osmosis, water flows across a membrane toward the solution that has a higher concentration of solutes, because that is where the concentration of water is the lowest.
Osmosis and Osmotic Pressure The osmotic pressure of a solution is an indication of the force with which pure water moves into that solution as a result of its solute concentration.
Hydrostatic Pressure Hydrostatic Pressure: fluid pressure Opposing pressure can prevent the flow of water into solution. Hydrostatic pressure opposes the osmotic pressure of solution so that no net osmotic flow occurs.
Osmolarity and Tonicity The total solute concentration in an aqueous solution is the solution’s osmolarity, or osmotic concentration. The nature of the solutes, however, is often as important as the total osmolarity. Therefore, when we describe the effects of various osmotic solutions on cells, we usually use the term tonicity instead of osmolarity.
Tonicity Isotonic Isotonic: A solution that does not cause the flow on water into or out of the cell. Cell remain unaffected by the solution
Hypotonic If a red blood cell is in a hypotonic solution, water will flow into the cell, causing it to swell up like a balloon. Therefore, the solute concentration is higher inside the cell than outside the cell. The cell may eventually burst, releasing its contents. This is known as hemolysis.
Hypertonic If a red blood cell is placed in a hypertonic solution, water will leave the cell causing it to shrivel or dehydrate. Therefore the solution concentration is higher outside the cell than inside the cell. The shrinking of the cell is called crenation.
Carrier – Mediated Transport In carrier- mediated transport proteins bind to substrates and carry them across the cell membrane. All forms of carrier – mediated transport have the following characteristics that they all share: Specificity Saturation Limits regulation
Carrier – mediated transport can involve the movement of a single molecule to multiple molecules. Cotransport or symport the carrier transports two substrates in the same direction, either into or out of the cell. In countertransport or antiport, one substance moves in as another substance moves out.
Facilitated Diffusion Many essential nutrients are insoluble in lipids and too large to fit through the membrane channels. Substances can be passively transported across the membrane by carrier proteins in a process call facilitated diffusion. The molecule to be transported must first bind to a receptor site on the protein. The shape of the protein then changes, moving the molecule across the membrane into the cytoplasm.
Active Transport Active transport is the cell uses energy to move substances (ions or molecules) across the cell membrane. Despite the energy cost to the cell there is an advantage as no concentration gradient is needed. All cells contain carrier proteins called ion pumps
Many of these carrier proteins move specific cations or anions in one direction only, either into or out of the cell. In a few instances, one carrier protein will move more than one kind of ion at the same time. If countertransport occurs, the carrier protein is called an exchange pump.
Sodium – Potassium Exchange Pump Sodium and potassium are the principle ions in body fluids. Sodium concentration is high in the extracellular fluid, but low in the cytoplasm. Potassium is low in the extracellular fluid and high in the cytoplasm. Due to the concentration gradient, sodium slowly diffuses into the cell and potassium diffuses out through leak channels.
Homeostasis within the cell depends on the ejection of sodium ions and the recapture of potassium ion. Carrier protein is called sodium – potassium ATPase. Sodium – potassium exchange intracellular sodium for extracellular potassium. For 1 ATP molecule consumed 3 sodium ions are ejected and 2 potassium ions are reclaimed.
Secondary Active Transport In this type of transport no energy is expended. However, later on the cell may need to expend ATP to maintain homeostasis.
Vesicular Transport Vesicular transport, materials move into or out of the cells in vesicles, small membranous sac that form at, or fuse with, the cell membrane. Because large volumes of fluids and solutes are transport in this way, this process is also known as bulk transport. The two major categories of vesicular transport are endocytosis and exocytosis
Endocytosis The process by which extracellular materials can be packaged in vesicles at the cells surface and imported into the cell is called endocytosis. This process involves relatively large volumes of extracellular material and requires energy in the form of ATP. The three major types of endocytosis are : receptor – mediated endocytosis, pinocytosis, and phagocytosis. All three require energy in the form of ATP.
Exocytosis In exocytosis, a vesicle created inside the cell fuses with the cell membrane and discharges its contents into the extracellular environment.
Transmembrane Potential The potential difference between the two sides of a cell membrane is a transmembrane potential. The unit of measurement of potential difference is the (V) volt The transmembrane potential in an undisturbed cell is the cell’s resting potential.
Cell’s Life Cycle Between fertilization and physical maturation there is a tremendous amount of change in organization and complexity. At fertilization, a single cell is all there is; at maturity, your body has roughly 75 trillion cells. This amazing transformation involves a form of cellular reproduction called cell division.
Even when development is complete, cell division continues to be essential for survival. Cells are highly adaptable but are sensitive to damage, wear and tear, toxins, and the environment and just like us they age. Life span of a cell can be hours to decades, depending on the type of cell and its stressors.
Many cells self – destruct after a certain period of time as a result of the activation of a specific “suicide gene” in the nucleus. The genetically controlled death of cells is called apoptosis.
For cell division to be successful, the genetic material in the nucleus must be duplicated accurately, one copy must be distributed to each daughter cell. The duplication of the genetic material is called DNA replication and nuclear division is called mitosis. The production of sex cells is called meiosis.
Interphase Somatic cells spend the majority of their functional lives in a state known as interphase. During this phase the cell grows and develops and prepares for cell division. In a cell preparing to divide interphase can be divide into G 1, S, and G 2 phases. An interphase cell in the G 0 phase is not preparing for division.
G 1 Phase In this phase, the cell makes enough mitochondria, cytoskeleton element, endoplasmic recticula, ribosome, cytoskeleton elements, Golgi membranes, and cytosol for two functional cells. Such cells pour all their energy into mitosis, and all other activities cease.
S Phase This phase takes about 6 – 8 hours. In this phase the duplicates its chromosomes. This involves DNA replication and the synthesis of histones and other proteins of the nucleus.
G 2 Phase Once DNA replication has ended, there is a brief (2 - 50) hour G 2 phase. This phase is considered the check list phase. Protein synthesis, and to completion of centrioles replication. The cell enters the M phase and mitosis begins.
Mitosis Mitosis separates the duplicated chromosomes of a cell into two identical nuclei. The term mitosis specifically refers to the division and duplication of the cell’s nucleus. The division of the cytoplasm to form two distinct new cells involves a separate, but related process called cytokinesis.
Prophase Prophase begins with the chromosome coil so tight that they become visible as individual structures. Each copy, called chromatid, is physically connected to its duplicate copy at a single point known as centromere. The centromere is surrounded by a protein complex known as the kinetochore. Chromosomes appear and the centrioles move to opposite poles of the cell. An array of microtubules called spindle fibers extend between the centrioles pairs.
Metaphase Metaphase begins as the chormtids move to a narrow central zone call the metaphase plate. Metaphase ends when all the chromatids are aligned in the center of the metaphase plate.
Anaphase Begins when the centromere of each chromatid pair splits and the chromatids separate. The two daughter chromosomes are now pulled toward opposite ends of the cell along chromosomal microtubules. Anaphase ends when the daughter chromosomes arrive near the centrioles at the opposite ends of the cell.
Telophase Each new cell prepares to return to the interphase state. Nuclear membrane re – forms, nuclei enlarge, and chromosomes gradually uncoil. Once the chromosomes have relaxed and the fine filaments of chromatin become visible again. This marks the end of mitosis.
Cytokinesis Cytokinesis is the cytoplasmic division of the daughter cells.
Mitotic Rate: the frequency of cell division is determined my the number of cells in mitosis at any time. Stem Cell: maintain the population of cells through repeated cycles of cell division. MPF (M – Phase promoting Factor) : also known as maturation – promoting factor. MPF is assembled into two parts: cell division cycle protein called Cdc 2 and a second protein called cyclin. Cyclin get mitosis started.
Growth Factor: Hormones and other compounds that stimulate cell growth. Repressor Gene: genes that inhibit cell division. P53: controls a protein that is found in the nucleus and activates genes that direct the production of growth – inhibiting factors inside the cell. Roughly half of all cancers are associated with abnormal form of the p53 gene. Telomeres: are terminal segments of DNA associated protein.
Tumor: neoplasm, is a mass of swelling produced by abnormal cell growth and division. Benign tumor: the cell’s usually remain within the epithelium or a connective – tissue capsule. Non – cancerous. Malignant Tumor: no longer respond to normal control mechanism. These tumors move beyond epithelium or connective tissue capsule. primary tumor or primary neoplasm. Invasion: spreading to other tissue. Metastasis: malignant cells that spread to other tissue and establish a secondary tumor.
Cancer is an illness characterized by mutations that disrupt normal control mechanisms and produce potentially malignant cells. Normal cells often become malignant when a mutation occurs in the genes involved in cell growth. Oncogenes: modified genes that can cause cancer.