mod 1.2

• Meaning of a cell:

  • Cells are the basic units of all living things, including humans
• Differentiation:

  • The process by which cells of an embryo become specialized structurally to augment specific cytoplasmic activities for functions at the level of tissues and organs
• Functions of a cell:

  • Cells metabolize and release energy
  • Cells synthesize molecules
  • Cells provide a means of communication
  • Cells reproduce and provide for inheritance
• Function, structures, substances, inclusions present in the cell:

  • Cytoplasm:
  • Homogenous substance that fills the cell and the various formed elements embedded in it
  • Plasma membrane:
  • Outermost layer of the cell
  • Lipid bilayer composed of phospholipids and cholesterol with proteins extend across or are embedded in either surface of the lipid bilayer
  • Glycolipids:
  • Include oligosaccharide chains that extend outward from the cell surface and contribute to a delicate cell surface coating to the glycocalyx
  • Integral proteins:
  • Incorporated directly within the lipid bilayer
• • Extracted only by using detergents to disrupt the lipids
  • Peripheral proteins:
  • Bound to one of the two membrane surfaces, particularly on the cytoplasmic side
  • Functions as the outer boundary of cells, controls the entry and exit of substances, receptor proteins function in intercellular communication, marker molecules enable cells to recognize one another, catalyzes chemical reactions, and serves as an attachment for the cytoskeleton
• Membrane transport:

  • Passive transport:
  • The cell does not expend metabolic energy during transport
  • Includes diffusion, facilitated diffusion, and osmosis
  • Active transport:
  • A mediated transport mechanism that requires energy provided by ATP
  • Includes primary & secondary active transport, vesicle membrane transport
• Diffusion (Passive membrane transport):

  • Movement of a solute from an area of higher concentration to an area of lower concentration within a solvent
  • Channels:
  • Multi-pass proteins forming transmembrane pores through which ions or small molecules pass selectively
  • Carriers:
  • Transmembrane proteins that bind small molecules and translocate them across the membrane via conformational changes
• Osmosis (Passive membrane transport):

  • Movement of a solvent (water) across a selectively permeable membrane from a higher water concentration to lower water concentration
  • Osmotic pressure, isosmotic, hyperosmotic, and hyposmotic solutions
  • Effects of hypotonic, isotonic, and hypertonic solutions on cells
• Primary active transport:

  • A mediated transport process that requires energy provided by ATPSecondary active transport:
  • Involves the active transport of an ion, such as sodium, and provides the energy necessary to move a different ion or some other molecule into the cell
• Vesicular transport:

  • Refers to the movement of larger volumes of substances across the plasma membrane through the formation or release of vesicles, membrane-bound sacs, in the cytoplasm
  • Endocytosis:
  • The movement of materials into cells by the formation of a vesicle, including phagocytosis, pinocytosis, receptor-mediated endocytosis
  • Exocytosis:
  • The secretion of materials from cells by vesicle formation
• Signal reception & transduction:

  • Endocrine signaling:
  • Signal molecules (hormones) are carried in the blood from their sources to target cells throughout the body
  • Paracrine signaling:
  • The chemical ligand diffuses in extracellular fluid but is rapidly metabolized so that its effect is only local on target cells near its source
• Mitochondria:

  • Enclosed by double membrane
  • Diameter of 0.5 - 1 μm and lengths up to 10 times greater
  • Abundant in cardiac muscle and cells of some kidney tubules
  • In light microscope, appear as numerous eosinophilic structures in H&E
  • Under TEM, double membrane creates two compartments: innermost matrix and narrow intermembrane space
  • Outer membrane is sieve-like, containing transmembrane proteins called porins
  • Inner membrane has cristae, many long folds that greatly increase the membrane's surface area
  • Number of cristae corresponds to the energy needs of the cell
• Peroxisomes:

  • Spherical organelles enclosed by a single membrane
  • Contains enzymes that produce & degrade hydrogen peroxide (H2O2)
  • Oxidase produces H2O2, Catalase breaks down H2O2
  • Inactivate potentially toxic molecules, particularly in liver and kidney cells
  • Form in two ways: budding of precursor vesicles from the ER growth and division of preexisting peroxisomes
  • Site for formation of bile acids and cholesterol
• Cytoskeleton:

  • Complex array of Microtubules, microfilaments (actin filaments), and intermediate filaments
  • Determines cell shapes and movements of organelles, vesicles, and entire cells
  • General functions: structural support, cell motility, organelle movement, cell division
• Microtubules:

  • Fine tubular structures within the cytoplasm of eukaryotic cells
  • Organized into larger, stable arrays called axonemes in cilia and flagella
  • Hollow with an outer diameter of 25 nm and a wall 5 nm thick
  • Motor proteins control transport along microtubules using ATP
  • Kinesins for anterograde transport, cytoplasmic dyneins for retrograde transport
• Centrosome:

  • Microtubule-organizing center for the mitotic spindle
  • Consists of paired centrioles
  • Each centriole about 0.2 μm in diameter and 0.3 - 0.5 μm in length
  • Composed of nine highly organized microtubule triplets
  • Determines cell polarity during cell division
• Microfilaments (Actin filaments):

  • Composed of actin subunits and allow motility and contractile activity in cells
  • Thin, polarized polymers, shorter and more flexible than microtubules
  • Functions include cytoplasmic streaming, transport of organelles, cell surface changes, and forceful contractions in specialized cells like muscle
• Intermediate filaments:

  • Intermediate in size with a diameter averaging 10 nm
  • Provide increased mechanical stability to cell structure
  • Made up of different protein subunits in different cell types
  • Form antiparallel tetramers and large cable-like bundles
• Nucleus:

  • Large organelle located near the center of the cell
  • Consists of nuclear envelope containing chromatin and nucleoli
  • Houses DNA for directing protein synthesis and serves as the control center of the cell
• Nuclear envelope:

  • Forms a selectively permeable barrier between the nuclear and cytoplasmic compartments
  • Consists of two concentric membranes separated by a perinuclear space
  • Nuclear pore complexes regulate movement of macromolecules between nucleus and cytoplasm
• Chromatin:

  • Consists of DNA and associated proteins involved in the organization and function of DNA
  • Contains 46 chromosomes (23 pairs), chromatids, histones, and nucleosomes
  • Types include euchromatin and heterochromatin
• Nucleolus:

  • Spherical subdomain of nuclei engaged in protein synthesis
  • Contains densely concentrated ribosomal RNA (rRNA)
  • Reveals fibrillar and granular subregions reflecting stages of rRNA maturation
• Cell Cycle:

  • Repeated cycles of macromolecular synthesis and division
  • Four distinct phases: G1, S, G2, and G0
  • Mitosis is the period of cell division, while interphase is between cell divisions
  • Stem cells divide asymmetrically for tissue renewal
• Meiosis:

  • Involves two unique cell divisions and produces four haploid cells
  • Crossing over produces new gene combinations
  • Occurs in cells forming sperm and egg cells
• Apoptosis:

  • Process of cell suicide
  • Highly regulated cellular activity resulting in elimination of defective and unneeded cells
  • Morphologic features include loss of mitochondrial function, DNA fragmentation, cell volume shrinkage, membrane changes, and apoptotic body formation
• Meaning of a cell:

  • Cells are the basic units of all living things, including humans
• Differentiation:

  • The process by which cells of an embryo become specialized structurally to augment specific cytoplasmic activities for functions at the level of tissues and organs
• Functions of a cell:

  • Cells metabolize and release energy
  • Cells synthesize molecules
  • Cells provide a means of communication
  • Cells reproduce and provide for inheritance
• • Extracted only by using detergents to disrupt the lipids
  • Peripheral proteins:
  • Bound to one of the two membrane surfaces, particularly on the cytoplasmic side
  • Functions:
  • Outer boundary of cells
  • Controls the entry and exit of substances
  • Receptor proteins function in intercellular communication
  • Marker molecules enable cells to recognize one another
  • Catalyzes chemical reactions
  • Attachment for the cytoskeleton
• Function, structures, substances, inclusions present in the cell:

  • Cytoplasm:
  • Homogenous substance that fills the cell and the various formed elements embedded in it
  • Plasma membrane:
  • Outermost layer of the cell
  • Lipid bilayer composed of phospholipids and cholesterol with proteins extend across or are embedded in either surface of the lipid bilayer
  • Glycolipids:
  • Include oligosaccharide chains that extend outward from the cell surface and contribute to a delicate cell surface coating to the glycocalyx
  • Integral proteins:
  • Incorporated directly within the lipid bilayer
• Membrane transport:

  • Passive transport:
  • The cell does not expend metabolic energy during transport
  • Diffusion, Facilitated diffusion, Osmosis
  • Active transport:
  • A mediated transport mechanism that requires energy provided by ATP
  • Primary & Secondary Active Transport, Vesicle Membrane Transport
• Diffusion (Passive membrane transport):

  • Movement of a solute from an area of higher concentration to an area of lower concentration within a solvent
  • Channels:
  • Multi-pass proteins forming transmembrane pores through which ions or small molecules pass selectively
  • Carriers:
  • Transmembrane proteins that bind small molecules and translocate them across the membrane via conformational changes
• Osmosis (Passive membrane transport):

  • Movement of a solvent (water) across a selectively permeable membrane from a higher water concentration to lower water concentration
  • Osmotic pressure
  • Isosmotic, Hyperosmotic, Hyposmotic solutions
  • Effects of different solutions on cells
• Primary Active Transport:

  • Active transport process that requires energy provided by ATP
• Secondary Active Transport:

  • Involves the active transport of an ion, such as sodium, to move a different ion or molecule into the cell
  • Example: Glucose transport
• Vesicular transport:

  • Refers to the movement of larger volumes of substances across the plasma membrane through the formation or release of vesicles, membrane-bound sacs, in the cytoplasm
• Endocytosis:

  • The movement of materials into cells by the formation of a vesicle
  • Phagocytosis, Pinocytosis, Receptor-mediated endocytosis
• Exocytosis:

  • The secretion of materials from cells by vesicle formation
• Cell signaling:

  • Endocrine signaling
  • Paracrine signaling
  • Synaptic signaling
  • Autocrine signaling
  • Juxtacrine signaling
• Cytoplasmic organelles:

  • Ribosomes
  • Endoplasmic reticulum (Rough, Smooth ER)
  • Golgi apparatus
  • Secretory granules
  • Lysosomes
  • Proteasomes
  • Mitochondria
  • Peroxisomes