B2

• Cell structures


  • No Membrane
  • Single Membrane Bound
  • Double Membrane Bound
• Not enclosed by a phospholipid bilayer


  Solid structures located within the cytoplasm or nucleoplasm
• Organelles


  • Ribosomes
  • Centrioles
  • Nucleolus
  • Vesicles and Vacuoles
  • Rough Endoplasmic Reticulum
  • Smooth Endoplasmic Reticulum
  • Golgi Apparatus
  • Lysosomes
  • Nucleus
  • Mitochondria
  • Chloroplasts
• The plasma membrane itself is considered an organelle
• Organelles


  Discrete structures in cells that are adapted to perform a specific function
• Structures that do not meet the requirements of being classified as an organelle


  • Cell Wall
  • Cytoplasm
  • Cytoskeleton
• The cell wall is outside of the cell membrane, it is "extracellular." It is not in the cell so the cell wall is not an organelle
• Cytosol is the liquid part of the cytoplasm, a structure common to all cells. It is composed of about 80 percent water and many dissolved solutes. While many metabolic reactions occur in the cytoplasm it is not specialized to perform a specific function. Therefore, the cytoplasm is not an organelle
• The cytoskeleton is composed of many different types of filaments and tubules. It is not a discrete structure, so the cytoskeleton is not an organelle
• A distinguishing feature of eukaryotic cells is that they contain many membrane-bound organelles
• Biological membranes act as barriers between aqueous solutions and are only permeable to a small number of substances, the membrane around an organelle creates a compartment with controlled conditions inside
• These subcellular compartments are distinct from the environment of the surrounding cytosol and are tailored to the specific functions of the organelle
• Advantages of compartmentalization


  • Enzymes and metabolites can be concentrated in a small space, increasing the chance for collision between active site and substrate
  • Substances that can damage cells can be isolated within a membrane, protecting remaining structures from degradation
  • Conditions, such as pH, can be maintained at an optimal value for a particular reaction
  • Large areas of membrane can become dense with proteins for a specific process
• Lysosomes


  Membrane-enclosed organelles that contain a high concentration of enzymes capable of hydrolyzing all types of biological polymers
• All of the lysosomal enzymes are acid hydrolases, which are active at an acidic pH (about 5) that is maintained within lysosomes but not at the neutral pH (about 7.2)
• The requirement of these lysosomal hydrolases for acidic pH provides double protection against uncontrolled digestion of the contents of the cytoplasm
• Phagocytosis


  1. Cell uses its plasma membrane to engulf a large particle, giving rise to an internal compartment called a phagocytic vacuole (AKA the phagosome)

  2. Phagocytosis is one type of endocytosis
• A cell that performs phagocytosis is called a phagocyte
• Mitochondria


  Uses glucose to produce adenosine triphosphate, providing energy for cellular reactions
• Mitochondria


  • Outer membrane separates the content of mitochondria from the rest of cell
  • Matrix is a cytoplasm like cell that contains the necessary enzymes for stages in respiration
  • Cristae are tubular regions that increase the surface area for reactions to take place
  • Inner membrane contains the carriers and enzymes for the final stages of respiration
  • Intermembrane space is a reservoir for hydrogen ions allowing a high concentration of protons
• Chloroplasts


  Do photosynthesis, an anabolic process for autotrophs, organisms that make their own food
• Chloroplasts


  • Membrane surface of thylakoids allow greater absorption of light by photosystems
  • Small space (lumen) and low volumes of fluid within thylakoid allow for faster accumulation of protons to create a concentration gradient
  • Stroma region provides a region where enzymes for Calvin cycle can work
  • Double membrane isolates the working parts and the enzymes from the rest of the cytoplasm
• Nucleoplasm


  The semifluid matrix found inside the nucleus

  
• DNA within the nucleus is found as chromatin, the less condensed form of the cell's DNA that organizes to form chromosomes during prophase of mitosis or meiosis
• The nucleus also contains one or more nucleoli, organelles that synthesize ribosomes
• Nucleus


  • Surrounded by a system of two concentric membranes, called the inner nuclear membrane and the outer nuclear membrane
  • The outer nuclear membrane is continuous with the endoplasmic reticulum
  • Like other cell membranes, the nuclear membranes are phospholipid bilayers, which are permeable only to small nonpolar molecules. Other molecules are unable to diffuse through the phospholipid bilayer
  • Nuclear pore complexes create a selective passageway through which molecules are able to travel between the nucleus and the cytoplasm
  • The double membrane structure allows for the formation of the large nuclear pores. A hole as large as a nuclear pore would only occur to the cell membrane if it had been damaged
• Ribosomes


  Made from dozens of proteins arranged on a scaffold of ribosomal RNA (rRNA)
• Endoplasmic Reticulum


  Part of the ENDOMEMBRANE SYSTEM
• Rough Endoplasmic Reticulum


  • A series of connected flattened membranous sacs with bound ribosomes
  • The ribosomes synthesize polypeptides and release them in to the inside of the rER
  • From the rER, the polypeptide can be transported elsewhere in the cell by a vesicle that buds off from the rER
  • The typical destination of a vesicle from the rER is the Golgi apparatus
• Golgi Apparatus


  • Composed of flattened membrane-enclosed sacs called cisternae
  • Within the Golgi cisternae, polypeptides are modified into their functional state
• By adding a carbohydrate to make a glycoprotein, or by combining with other polypeptides to form the quaternary structure of a protein, the polypeptide is a functional protein
• The trans face of the Golgi sorts, concentrates and packs proteins into vesicles that transport the protein to lysosomes or vacuoles for digestive enzymes used within the cell
• Vesicle formation


  1. A vesicle forms when the membrane bulges and pinches off

  2. Clathrin is a protein that plays a major role in the formation of vesicles

  3. Clathrin creates a "coat" that helps the phospholipids create a rounded shape as the vesicle is forming

  4. Once the vesicle is formed, the clathrin coat is removed from the vesicle
• Once formed, vesicles are moved through the cell by motor proteins along the cytoskeleton "track"
• Types of vesicles


  • Transport Vesicles: transport proteins and lipids from one location to another within the cell (to the Golgi from the ER, from the Golgi to lysosomes or vacuoles)
  • Secretory Vesicles: transport proteins and lipids from inside the cell to the the plasma membrane (for integral proteins within the plasma membrane such as pumps, channels, adhesion proteins or receptor proteins)
• Vesicle fusion


  The merging of a vesicle with another organelle or with part of a cell membrane
• Fertilization is a multi-step process in which a sperm and egg fuse to form a single cell called a zygote
• Cell specialization


  Allows cells to perform a function with increased efficiency
• Aspects of cell specialization


  • Cells can develop into specific shapes and sizes
  • Cells can create proteins needed to carry out specific metabolic reactions
• Differentiation


  Occurs when different cell types express different genes