Unit 2

• Eukaryotic


  Relating to the biological cells of organisms such as plants, animals, and fungi, which have a clearly defined nucleus
• Eukaryotic Membranous cellular organelles found in Plants and animal cells

  • Cell Nucleus
  • Nuclear envelope
  • Nuclear pores
  • Nucleolus
  • Chromatin
  • Ribosomes
  • Endoplasmic reticulum
  • Golgi apparatus
• Cell Nucleus


  • Contains genetic material (DNA)
  • Stores and process genetic information
  • DNA and RNA synthesis
  • Control protein synthesis
• Nuclear envelope


  • Consist of a double membrane surrounding the nucleus
  • Its fluid content is called the nucleoplasm
  • Nucleoplasm consist of ions, RNA and DNA nucleotides, proteins, and small amounts of RNA & DNA
• Nuclear pores


  • Cover about 10% of the surface of the nucleus
  • Pores permits the movement of ions and small molecules
  • Pores are too small for the passage of proteins and DNA
  • Nuclear pores allows communication between the nucleus and the cytosol
• Nucleolus


  • rRNA transcription and processing
  • Ribosome assembly
• Chromatin


  • Composed of DNA, RNA and proteins
  • Scattered throughout the nucleus
  • Chromatin condenses to form chromosomes when the cell divides
  • Copies (sister chromatids) are formed during S-phase of cell cycle
  • To package DNA into a smaller volume to fit in the cell
  • To reinforce the DNA macromolecule to allow mitosis
  • To prevent DNA damage
  • To control gene expression and DNA replication
• Histones


  Proteins that compact the DNA
• Base pair


  When one purine base is paired with one pyrimidine base
• Only 3 pyrimidine bases (thymine, cytosine, and uracil) and 2 purine bases (adenine and guanine) are needed to produce the incredible diversity of species that inhabit the earth
• DNA and RNA are nearly identical structurally, but there are 2 fundamental differences that account for the very different functions of the two molecules
• RNA


  Has a ribose sugar instead of a deoxyribose sugar like DNA, and RNA nucleotides have a uracil base instead of thymine
• Ribosomes


  • Each ribosome consist of rRNA and protein
  • It is a non-membranous organelle
  • Two types: Free ribosomes (scattered) and Fixed ribosomes (attached to the Endoplasmic reticulum (ER))
  • Ribosomes carry out protein synthesis
• Endoplasmic reticulum


  • Network of membranous channels extending through the cytoplasm
  • Attached to the nucleus by its membranes
  • Rough ER has ribosomes attached to it and aids in packaging of newly synthesising proteins
  • Smooth ER lacks attached ribosomes and synthesizes lipids and carbohydrates
  • Certain cells in the ovaries and testis have large amount of SER for the production of steroid hormones
• Golgi apparatus


  • Consist of five or six Stacks of membrane discs
  • Separates proteins according to their destinations
  • Post-translational modification by adding sugar to makes glycoproteins
  • Packages materials into vesicles which are exported outside the cell - secretion
• Protein synthesis


  1. DNA transcription occurs in the nucleus

  2. RNA polymerase transcribe DNA strand into mRNA

  3. DNA translation occurs in the cytoplasm

  4. mRNA binds with the ribosome

  5. Molecules of tRNA delivers amino acids
• Organelles involved in protein synthesis and processing

  • Nucleus
  • Ribosomes
  • Rough endoplasmic reticulum
  • Golgi apparatus
• Cytoplasm


  Jelly-like fluid that fills a cell, made up of mostly water and salt, responsible for giving a cell its shape
• Cytosol


  The part of the cytoplasm that does not contain organelles (clear jell)
• Mitochondria


  • Double membrane: outer and inner membrane
  • Inner folds called cristae
  • Powerhouses of the cell
  • Make some of their own proteins
  • Number of cellular mitochondria varies from cell to cell depending on the energy demand
  • Absent in RBC
  • Very high in liver cells
• Peroxisome


  • Special vesicles
  • Produced by subdivision of existing peroxisome
  • Contain oxidative enzymes
  • Catabolism of fatty acids and other organic components
  • Bile acid synthesis
  • Lipid biosynthesis
  • Phospholipid exchange
  • Neutralizes toxic compounds produced during catabolic reactions
  • Bigger than lysosomes
• Lysosome


  • Contain 60 hydrolytic enzymes
  • Remove damaged organelles or pathogens within the cell
  • Also function in defence against diseases by fusing with vesicles and engulfing pathogens
  • Primary lysosomes have not yet acquired materials to be digested, formed by budding from trans Golgi apparatus
  • Secondary lysosomes formed by fusion of primary lysosome with substrate to be degraded
• Non-membranous organelles


  • Centrioles
  • Microvilli
  • Cilia
  • Cytoskeleton
• Centrioles


  • Short cylindrical structures
  • 2 centrioles at angles of the cell
  • Made up of microtubules
  • Essential for movement of chromosomes during cell division
  • Found in all animal cells that can divide
  • Centrioles create the spindle fibers that move DNA during cell division
  • Mature RBC, Skeletal cells, Cardiovascular cells, Neuron cells all lack Centrioles
• Microvilli


  • Finger-like membrane extensions containing microfilaments
  • Increase surface area to facilitate absorption
• Cilia


  • Membrane extension containing microtubules
  • Movement of materials over the surface
• Cytoskeleton


  • An internal protein framework of various threadlike filaments and hollow tubules
  • Provide strength and support to the cell
  • Enable movement of cellular structures and materials
  • Three cytoskeletal elements: Actin filaments (microfilaments), Intermediate filaments, Microtubules
• Microfilaments


  • Are smallest & thinnest filaments of the cytoskeleton, composed of the actin protein
  • Form a dense layer inside the cell membrane
  • Microfilaments attach the cell membrane to the underlying cytoplasm by forming connections with cell membrane proteins
  • By interacting with myosin, actin microfilaments can move and change the shape of the cell, allowing contraction & expansion of cells
• Intermediate filaments


  • Hold the organelles in place within the cytoplasm
  • Anchor the nucleus in place
  • Thicker than microfilaments & thinner than microtubules
• Microtubules


  • Hollow tubes built from the global protein tubulin
  • Form the primary component of the cytoskeleton
  • Provides strength and rigidity
  • Anchor the position of major organelles
  • Form spindle apparatus during cell division
• Cell membrane (Plasma membrane)


  • Outer boundary of the cell
  • Physical isolation
  • Regulation
  • Sensitivity
  • Structural support
  • Barrier for cell contents
• Phospholipid bilayer


  • Made up of a phospholipid bilayer
  • Amphipathic: have both hydrophobic and hydrophilic parts
  • In a phospholipid PO4^3- serves as a link between a diglyceride and a non lipid head
  • Hydrophilic heads (polar head)
  • Hydrophobic tails (non-polar tail)
• Plasma membrane Carbohydrates


  • External surface of the cell
  • Carbohydrate + lipids = Glycolipids
  • Carbohydrate + protein = Glycoproteins
  • Functions: Differentiating host cells from self cells
• Plasma membrane Cholesterol


  Abundant in the membranes of cells, it helps maintain the integrity of these membranes, facilitating cell signalling
• Membrane transport


  • The permeability of the cell determines what substance enters and leave the cell
  • Cell membranes are selectively permeable
  • The size, shape, electrical charge and permeability determine whether or not the substance can cross the membrane
  • Movement across the membrane may be: Passive, Active, Vesicular transport
• Passive transport methods


  • Diffusion: Net movement of molecules from an area of relatively higher concentration to an area of low concentration down the concentration gradient
  • Osmosis: Diffusion of water across the membrane
  • Isotonic solution: Equal concentration in and out of the cell (Equilibrium)
  • Hypertonic: Cell lose water by osmosis, shrinking RDC is called crenation
  • Hypotonic: Water flows into a cell, in case of RBC this event is called hemolysis
  • Filtration: In filtration, hydrostatic pressure forces water & solutes across the membrane
  • Facilitated diffusion: Transport method that uses carrier proteins to transport essential nutrients such as glucose and amino acids that are too large to fit through membrane channels
• In passive transport No ATP is required
• Active transport


  • Requires higher energy bond in ATP
  • Requires a carrier molecule & specific enzyme
  • E.g. Ion pumps: actively transport cations such as Na+, K+, Ca2+ and Mg2+
  • Specialized cells that carry I-, Cl- etc.
• Vesicular transport methods


  • Materials move in and out of the cell by means of vesicles
  • Membrane sacs that form at or fuse with the cell membrane
  • Endocytosis: Packaging extracellular materials in a vesicle for import into the cell, including receptor-mediated endocytosis, pinocytosis, and phagocytosis
  • Exocytosis: Vesicle is created inside the cell and fuse with the cell membrane & discharge its content out of the cell, transporting hormones, mucus, & waste products
• Endosymbiosis


  The co-existence of living matter in which symbiotic organisms lives inside the other