Cell structure

• Cell Theory


  • All organism consist of one or more cells
  • Cell is the basic unit of structure for all organism
  • All cells arise only from preexisting cell
• Basic parts of a cell

  • Cell Membrane
  • Nucleus
  • Protoplasm
• Cell Membrane


  This is the structure that separates the cell from it external environment which defines its boundary and serves as a limiting membrane that regulates the entrance and exit of substances from cell and its environment
• Nucleus


  This is the rounded structure usually at the center of the cell enclosed by another membrane called nuclear envelope. This structure is considered as the control center of the cell for most of it metabolic activities
• Protoplasm


  This is known as the living substance within the cell because it contains the functional structure making the cell an independent structure
• Fluid-Mosaic Model


  This model of cell membrane arrangement were proposed by S. Jonathan Singer and Garth Nicholson (1972) which states that the cell membrane is like an ocean or sea in which there are many substances that floats like an icebergs
• Tripartite Arrangement


  This is proposed by Danielle and Dawson (1935) which states that the cell membrane is like a railroad truck with two outer dark bands and a lighter middle core or layer
• Cell Membrane Functions


  • Maintain structural integrity of the cell
  • Control movement of substances in and out of the cell
  • Regulating cell-cell reactions
  • Recognition, via receptors, antigens and foreign cells as well as altered cells
  • Acting as an interface between the cytoplasm and the external milieu
  • Establishing transport systems for specific molecules
  • Transducing extracellular physical or chemical signals into intracellular events
• Cell Membrane Components


  • Phospholipids
  • Cholesterol
  • Proteins
  • Carbohydrates
• Glycocalyx Functions


  • Protection of cell from interaction with inappropriate proteins
  • Protection from chemical physical injury
  • Cell-cell recognition and adhesion
  • In blood clotting and inflammatory reaction
• Membrane Transport Proteins


  • Channel Proteins
  • Carrier Proteins
• Channel Proteins


  Gated or ungated and incapable of transporting substances against concentration gradient
• Carrier Proteins


  Utilize ATP-driven transport mechanism to ferry specific substances across the plasmalemma against the concentration gradient
• Ribosome Components


  • Small Subunit
  • Large Subunit
• Small Subunit


  • Sedimentation Value (40S & 33 Proteins)
  • P-site - for binding peptidyl transfer ribonucleic acid (tRNA)
  • A-site - for binding aminoacyl tRNA
• Large Subunit


  Sedimentation Value (60S & 49 Proteins)
• Endoplasmic Reticulum


  • System of interconnected tubules & vesicles
  • Cistern - the vesicles lumen
  • Metabolic process: Protein synthesis & modification, Lipid & Steroid synthesis, Detoxification of toxic compounds, Membrane manufacture
• Golgi Apparatus


  • Synthesis of carbohydrates
  • Modification and sorting of proteins from RER
  • Made up of series of flattened, slightly curved membrane bound cisternae
  • Each cisterna is dilated peripherally and rimmed with vesicle that either fuse or bud-off from that particular compartment
• Lysosomes


  • Have an acid pH & hydrolytic enzymes
  • A specialized organelle for digestion of substance from the late endosomes
  • Diameter is 0.3 - 0.8 µm
  • Acid hydrolyses present: Sulfatases, Proteases, Nucleases, Lipases, Glycosideses
• Endosomes


  • Also involved in ingestion, sequestering & degradation of substance internalized from extracellular space
  • Has two compartments: Early endosomes - at the cell periphery, Late endosomes - deeper into cytoplasm
• Peroxisomes


  • Self replicative with oxidative enzymes
  • Maintainance of protein population
  • Responsible for proteolysis
  • Aided by the following enzymes: Ubiquitine-activating enzymes, Ubiquitine-conjugation enzymes, Ubiquitine ligases
• Mitochondria


  • Perform oxidative phosphorylation
  • Involved in lipid synthesis
  • Outer Membrane, Inner Membrane - Folds within is called cristae, Intermembrane Space - Between the inner & outer membrane, Matrix Space - Large space within the inner membrane
• Types of Cytoskeleton


  • Thin Filaments (Actin)
  • Intermediate Filaments
  • Microtubules
• Actin Filaments


  • Responsible for intracellular movement
  • 15 % in non-muscle cells
  • It has G-actin - 2 chains of globular subunits coiled around each other forming filaments
  • It has a + end - fast growing end & - end; a slower growing end
• Intermediate Filaments


  • Maintain the 3-D framework of the cell
  • Anchor the nucleus in place
  • Provide connection between cell membrane and cytoskeleton
  • Help nuclear envelope reorganization subsequent to mitosis
• Microtubules


  • Long, straight, hollow cylindrical structure
  • Provide cell rigidity
  • Establish intracellular compartments
  • Provide ciliary and flagellated movement
• Major Components of Nucleus

  • Chromatin
  • Nucleolus
  • Nucleoplasm
• Nuclear Membrane


  • Two-layered membrane fused to form the nuclear pores
  • The inner nuclear membrane (6 nm) nearest to nuclear lamina
  • The outer membrane (6nm) continous with the RER
  • Its cytoplasmic surface synthesizes transmembrane protiens for outer/inner nuclear membranes
• Chromatin


  • Composed of DNA & Protein that are uncoiled chromosomes
  • Heterochromatin - Condense inactive form
  • Euchromatin - The active form of chromatin which is transcribe into RNA
• DNA


  • Repository of genetic materials
  • Double Stranded, double helix molecules
• Nucleolus


  • Site for rRNA synthesis
  • Fibrillar Center, Pars Fibrosa, Pars Granulosa, Nucleolar Matrix