cellular structure

• Cell


  Structural units that constitute living organisms, with specialized functions and components to perform and perpetuate these functions
• Components of a cell

  • Plasma membrane
  • Membrane-bound nucleus (except mature red blood cells and platelets)
  • Other unique subcellular structures and organelles
• Plasma membrane


  • Provides physical barrier for cell
  • Facilitates and restricts interchange of substances with environment
  • Maintains electrochemical gradient
  • Has receptors for signal transduction
• Plasma membrane


  Lipid bilayer consisting of phospholipids, cholesterol, proteins; glycolipids and glycoproteins form a glycocalyx
• Transmembrane proteins


  Traverse the entirety of the lipid bilayer in one or more passes and penetrate the plasma and cytoplasmic layers of the membrane
• Cytoskeletal proteins


  Found only on the cytoplasmic side of the membrane and form the lattice of the cytoskeleton
• Glycocalyx


  External protective carbohydrate coating on the cell surface, formed by carbohydrate chains of glycoproteins and glycolipids
• Nucleus


  Control center of the cell, composed of chromatin, nuclear envelope, and nucleoli
• Chromatin


  One long molecule of double-stranded DNA in each chromosome, tightly folded with histone and nonhistone proteins
• Nucleosome


  11 nm in length, consisting of approximately 150 base pairs of DNA wrapped around a histone protein core
• Heterochromatin


  Darkly stained, condensed chromatin that is transcriptionally inactive
• Euchromatin


  Diffusely stained chromatin that is transcriptionally active
• Nuclear envelope


  Double membrane surrounding the nucleus, with nuclear pores that allow exchange of materials between the nucleus and cytoplasm
• Nucleolus


  Composed of ribosomal RNA and the genes coding it, and accessory proteins; may have one to several within the nucleus
• Ribosomes


  Macromolecular complexes composed of protein and ribosomal RNA, consisting of large and small subunits
• Endoplasmic reticulum


  Branching, membrane-lined tubules and sacs, studded with ribosomes on outer surface; membrane continuous with the nuclear membrane
• Smooth endoplasmic reticulum


  Membrane-lined tubules lacking ribosomes, continuous with rough endoplasmic reticulum
• Golgi apparatus


  System of stacked, membrane-bound, flattened sacs
• Mitochondria


  Elliptical or oval structures surrounded by inner and outer membranes, with inner membrane having infoldings called cristae
• Lysosomes


  Membrane-bound sacs containing hydrolytic enzymes that degrade unwanted material in the cell
• Microfilaments


  Double-stranded, intertwined solid structures of actin, 5-7 nm in diameter
• Intermediate filaments


  Solid structures 8-10 nm in diameter, self-assemble into larger bundles
• Microtubules


  Hollow cylinders 25 nm in diameter, consisting of 13 protofilaments formed from α- and β-tubulin
• Centrosome


  Composed of two cylinder-shaped centrioles, each with nine sets of triplet microtubules, oriented at right angles to each other
• Hematopoietic microenvironment


  General structure and function, and effect of growth factors
• Cell cycle


  Stages and regulation by cyclins and cyclin-dependent kinases, with checkpoints
• Cell death


  Differentiation between apoptosis and necrosis
• Chromatin


  Highly structured folding that allows the long strands of DNA to be tightly condensed in the nucleus when inactive and enables segments of the DNA to be rapidly unfolded for active transcription when needed
• Types of chromatin


  • Heterochromatin (transcriptionally inactive)
  • Euchromatin (genetically active)
• Nuclear envelope


  • Consists of two phospholipid bilayer membranes
  • Inner membrane surrounds the nucleus
  • Outer membrane is continuous with the membrane of the endoplasmic reticulum
  • 30- to 50-nm perinuclear space between the two membranes is continuous with the lumen of the endoplasmic reticulum
  • Nuclear pore complexes penetrate the nuclear envelope, allowing passage of molecules between the nucleus and the cytoplasm
• Nucleolus


  Site of ribosomal RNA (rRNA) production and assembly into ribosome subunits
• As blood cells mature

  Protein synthesis decreases, and the nucleoli eventually disassemble
• Ribosome biogenesis


  • rDNA is first transcribed to rRNA precursors
  • rRNA precursors are processed into smaller RNA molecules and subsequently complexed with proteins forming the small and large ribosome subunits
  • Ribosomal proteins enter the nucleus through the nuclear pores after being synthesized in the cytoplasm
  • Ribosome subunits are transported out of the nucleus through the nuclear pores
  • Large and small ribosome subunits self-assemble into a functional ribosome during protein synthesis
• Cytoplasmic matrix


  Homogeneous, continuous, aqueous solution called the cytosol
• Ribosomes


  • Macromolecular complexes composed of a small and large subunit of rRNA and many accessory ribosomal proteins
  • Found free in the cytoplasm or on the surface of rough endoplasmic reticulum
  • May exist singly or form chains (polyribosomes)
  • Site of protein synthesis using transfer RNA (tRNA) for amino acid transport and specific mRNA molecules
• Cells that actively produce proteins

  Have many ribosomes in the cytoplasm, which gives it a dark blue color (basophilia) when stained with Wright stain
• Endoplasmic reticulum (ER)


  • Membrane-bound, interconnected network of flattened sacs and tubes located adjacent to the nucleus and extending throughout the cytoplasm
  • Membrane is continuous with the outer membrane of the nucleus and its lumen is continuous with the perinuclear space between the outer and inner nuclear membranes
  • Rough ER (RER) has ribosomes on its outer surface and synthesizes and processes membrane-bound proteins and proteins that will be secreted from the cell
  • Smooth ER (SER) is continuous with the RER but does not have ribosomes and is involved in synthesis of phospholipids and steroids, detoxification or inactivation of harmful compounds or drugs, and calcium storage and release
• Golgi apparatus


  • System of membrane-bound, stacked, flattened sacs called cisternae involved in modifying, sorting, and packaging macromolecules for secretion or delivery to other organelles
  • Contains numerous enzymes for these activities
  • Locates in close proximity to the RER and the nucleus
  • Vesicles containing membrane-bound and soluble proteins from the RER enter the Golgi network on the "cis face" and are directed through the stacks where the proteins are modified
  • Vesicles with processed proteins exit the Golgi on the "trans face" to form lysosomes or secretory vesicles bound for the plasma membrane
• Mitochondria


  • Have an outer and inner membrane separated by an intermembrane space
  • Inner membrane is highly convoluted forming many infoldings called cristae
  • Interior of the mitochondrion, called mitochondrial matrix, is surrounded by the inner membrane and contains mitochondrial DNA, ribosomes, and various enzymes and proteins
  • Generate most of the adenosine triphosphate (ATP) for the cell by aerobic respiration
  • Capable of self-replication and have their own circular DNA for the mitochondrial division cycle and RNA for protein synthesis
• Lysosomes


  • Contain hydrolytic enzymes bound within a membrane and are involved in the intracellular digestive process
  • Membrane prevents enzymes from digesting cellular components and macromolecules
  • Lysosomal enzymes are activated at the acidic pH of the lysosome and inactivated at the higher pH of the cytosol