CM

Cell and Tissue Characteristics Notes

The Nucleus

  • Nuclear Envelope:

    • Contains nuclear pores that regulate the transport of molecules between the nucleus and cytoplasm.

    • Composed of two membranes, an inner and an outer membrane.

  • DNA:

    • Contains chromatin, which is a complex of DNA and proteins (histones).

    • DNA contains the genetic information necessary for cell function and replication.

  • RNA Synthesis:

    • Messenger RNA (mRNA): carries genetic information from DNA to ribosomes for protein synthesis.

    • Ribosomal RNA (rRNA): a structural component of ribosomes; essential for protein synthesis.

    • Transfer RNA (tRNA): transfers amino acids to ribosomes during protein synthesis.

  • Nucleolus:

    • Site of ribosome subunit synthesis.

    • Contains genes that code for rRNA.

Functional Components of the Cell

  • Nucleus:

    • Control center of the cell, containing genetic material.

  • Cytoplasm:

    • Contains organelles and cytosol, facilitating cellular processes.

  • Cell Membrane:

    • Outer boundary of the cell, regulating the movement of substances in and out of the cell.

Protoplasm

  • Composition:

    • Water: primary component of protoplasm, serving as a solvent for various biochemical reactions.

    • Proteins: perform various functions; structural support, enzymes, and signaling molecules.

    • Electrolytes: ions such as sodium, potassium, and chloride, essential for maintaining osmotic balance and membrane potential.

  • Regions:

    • Cytoplasm: the region outside the nucleus, containing organelles and cytosol.

    • Nucleoplasm: the region within the nucleus.

The Cytoplasm and Organelles

  • Cytoplasm:

    • Workspace for the cell, where various metabolic activities occur.

    • Contains water, electrolytes, proteins, fats, glycogen, and pigments.

  • Organelles:

    • Ribosomes: synthesize proteins.

    • Endoplasmic Reticulum:

    • Rough Endoplasmic Reticulum: contains ribosomes, involved in protein synthesis and modification.

    • Smooth Endoplasmic Reticulum: involved in lipid and steroid synthesis, as well as detoxification.

    • Golgi Complex: processes and packages proteins and lipids.

    • Mitochondria: generate energy (ATP) through cellular respiration.

    • Lysosomes: contain enzymes for intracellular digestion.

    • Proteasomes: degrade damaged or misfolded proteins.

Membranes

  • Cell Membrane:

    • Lipids:

    • Phospholipids (amphipathic): form the basic structure of the cell membrane with hydrophilic heads and hydrophobic tails.

    • Cholesterol (hydrophobic): stabilizes the membrane structure.

    • Proteins:

    • Integral: embedded within the lipid bilayer; function as channels, transporters, or receptors.

    • Surface: located on the inner or outer surface of the membrane; support cell structure & signaling.

  • Membranous Barriers in Organelles:

    • Membranes enclose organelles, creating distinct compartments for specialized functions.

Cell Membrane Components

  • Lipid Bilayer:

    • Basic fluid structure of the membrane.

    • Serves as a semipermeable barrier, controlling the movement of substances in and out of the cell.

    • Composed of phospholipids with a hydrophilic head and a hydrophobic tail.

  • Integral Proteins:

    • Span the entire lipid bilayer.

    • Include ion channels, which facilitate the transport of ions across the membrane.

  • Peripheral Proteins:

    • Bound to one or the other side of the membrane.

    • Participate in cell signaling and structural support.

  • Glycocalyx:

    • Participates in cell-to-cell recognition and adhesion.

    • Protects the cell surface and involved in cell interactions.

Cell Membrane Function

  • Provides receptors for hormones and other biologically active substances.

  • Participates in the electrical events that occur in nerve and muscle cells, such as action potentials.

  • Aids in the regulation of cell growth and proliferation.

Question #1

  • False. The cell membrane is made up of lipids, cholesterol, and proteins.

The Cytoskeleton

  • Microtubules:

    • Develop and maintain cell form.

    • Participate in intracellular transport mechanisms, moving organelles and vesicles.

    • Form basic structure for complex cytoplasmic organelles.

    • Contain cilia and flagella, which facilitate cell movement.

    • Contain centrioles and basal bodies, involved in cell division and the organization of microtubules.

  • Microfilaments:

    • Produce muscle contraction (actin).

    • Support and maintain the asymmetric shape of cells.

    • Thin threadlike cytoplasmic structures.

    • Categorized as thin (actin), intermediate, and thick myosin.

Cell Communication

  • Autocrine Signaling:

    • A cell releases a chemical into the extracellular fluid that affects its own activity.

    • Important in immune responses and cancer development.

  • Paracrine Signaling:

    • Acts on nearby cells.

    • Involved in tissue repair and inflammation.

  • Endocrine Signaling:

    • Relies on hormones carried in the bloodstream to cells throughout the body.

    • Regulates overall body functions such as metabolism and reproduction.

  • Synaptic Signaling:

    • Occurs in the nervous system, where neurotransmitters act only on adjacent nerve cells.

    • Enables rapid and specific communication between nerve cells.

Cell Receptors and Ligands

  • Ion Channel-Linked Receptors:

    • Rapid synaptic signaling between electrically excitable cells.

    • Transmission of impulses in nerve and muscle cells.

  • G-Protein-Linked Receptors:

    • The on-off switch for signal transduction.

    • Activate intracellular signaling pathways via G proteins.

  • Enzyme-Linked Receptors:

    • Receptors for certain protein hormones.

    • Activate an intracellular domain with enzyme activity, such as tyrosine kinases.

  • Intracellular Receptors:

    • Ligands move directly across the membrane to bind to the intracellular receptor.

    • Often affect gene transcription.

  • First Messengers:

    • Neurotransmitters, protein hormones and growth factors, steroids, and other chemical messengers.

  • Second Messengers:

    • Intracellular mechanisms, such as protein kinases, cyclic AMP (cAMP), calcium ions (Ca^{2+}).

The Cell Cycle and Cell Division

  • Main stages of cell cycle (life cycle of a cell):

    • Mitosis: cell division stage, resulting in two identical daughter cells.

    • Interphase: nondividing phase, including G1, S, and G2 phases.

  • Types of cell division:

    • Mitotic cell division: occurs in somatic cells, for growth and repair.

    • Meiosis: occurs in gamete-producing organs, resulting in four genetically distinct daughter cells.

Cell Metabolism and Energy Sources

  • Processes by which fats, proteins, and carbohydrates from the foods we eat are converted into energy in the form of ATP.

  • Metabolism

    • Catabolism: Breaking down stored nutrients and body tissues to produce energy.

    • Aerobic and anaerobic production of ATP.

    • Anabolism: A constructive process in which more complex molecules are formed from simpler ones.

Movement of Substances Across the Cell Membrane

  • Passive Transport:

    • Diffusion: movement of molecules from an area of higher concentration to an area of lower concentration.

    • Osmosis: movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration.

    • Facilitated diffusion: movement of molecules across the membrane with the help of transport proteins.

  • Active Transport:

    • Primary active transport: uses ATP to move molecules against their concentration gradient.

    • Secondary active transport:

    • Symport: two molecules are transported in the same direction.

    • Antiport: two molecules are transported in opposite directions.

  • Endocytosis:

    • Phagocytosis: Cell eating.

  • Exocytosis:

    • Cell secretion.

Membrane Potential

  • Ion Channels:

    • Integral proteins that span the width of the cell membrane.

    • Protein subunits undergo conformational changes to form an open channel or gate through which the ions can move.

    • Selective for specific ions: Sodium ions (Na^+$), potassium (K^+$), calcium (Ca^{2+}), or chloride ions (Cl^−).

  • Electrical potentials exist across the membranes as a result of ion distribution.

    • Describe the ability of separated electrical charges of opposite polarity (+ and −) to do work.

  • Resting Membrane Potential

    • Diffusion potential describes the voltage generated by ions that diffuse across the cell membrane.

    • Equilibrium potential is the one in which no net movement of ions occurs because the diffusion and electrical forces are exactly balanced.

Question #2

  • Electrical potentials existing across the membranes as a result of ion distribution.

Answer to Question #2

  • Rationale: The distribution of K^+ is the driving force, and Na^+, Cl^−, Ca^{2+}, organic anions, etc., bring the resting potential to −70 mV.

Organization of Cells into Tissues

  • Cells with similar embryonic origin or function are often organized into larger functional units called tissues.

    • These tissues associate with other, dissimilar tissues to form organs of the body.

  • Four types of tissue:

    • Epithelial

    • Connective

    • Neural

    • Muscle

Epithelial Tissue

  • Forms sheets that function to:

    • Cover the body’s outer surface

    • Line internal surfaces

    • Form glandular tissue

  • Attaches to a basement membrane, providing support and structure.

  • Is avascular, relying on diffusion from underlying connective tissue.

  • Classification according to the number of layers present:

    • Simple: single layer of cells.

    • Stratified: multiple layers of cells.

    • Pseudostratified: appears stratified but is a single layer.

  • Classification according to shape:

    • Squamous: flat cells.

    • Cuboidal: cube-shaped cells.

    • Columnar: column-shaped cells.

Connective or Supportive Tissue

  • Definition

    • The most abundant tissue of the body

    • Connects and binds or supports the various tissues

  • Types

    • Loose or areolar: fills spaces between organs and tissues, providing flexibility and cushioning.

    • Adipose: stores fat for energy and insulation.

    • Reticular: forms a supportive framework in lymphatic organs and bone marrow.

    • Dense connective: provides strong support in tendons and ligaments.

Muscle Tissue

  • Contains actin and myosin filaments, responsible for muscle contraction.

  • Contracts and provides:

    • Locomotion and movement of skeletal structures

    • Pumping blood through the heart

    • Contraction of blood vessels and visceral organs

  • Types

    • Cardiac: found in the heart, responsible for pumping blood.

    • Smooth: found in the walls of internal organs and blood vessels, responsible for involuntary movements.

    • Skeletal: attached to bones, responsible for voluntary movements.

Question #3

  • Which of the following tissues contains actin and myosin?

Answer to Question #3

  • Muscle

  • Rationale: Actin and myosin are the contractile elements (proteins) found in all muscle tissues.

Nervous Tissue

  • Definition

    • Tissues that provide the means for controlling body function and for sensing and moving about the environment

  • Types of cells

    • Neurons: function in communication via electrical and chemical signals.

    • Neuroglial cells: support the neurons, providing nutrients and insulation.

Cell Junctions and Cell-to-Cell Adhesion

  • Tight Junctions

    • Seal the surface membranes of adjacent cells together, preventing leakage of molecules between cells.

  • Adhering Junctions

    • Represent a site of strong adhesion between cells, providing mechanical stability to tissues.

  • Gap Junctions

    • Involve the close adherence of adjoining cell membranes within the formation of channels linking the cytoplasm of the two cells, allowing for direct communication between cells.

Extracellular Matrix

  • Composition

    • Glycosaminoglycans (GAGs), which are usually found linked to protein as proteoglycans

    • Fibrous proteins—the fibrous adhesive proteins that are found in the basement membrane

    • Collagen, elastin, fibronectin, and laminin

  • Function

    • These are secreted locally and organized into a supporting meshwork in close association with cells that produced them.

    • The amount and variety of the matrix vary with different tissues and their function.

  • Adhesion molecules

    • Cellular adhesion molecules (CAM)

    • Cadherins: mediate cell-to-cell adhesion in tissues.

    • Selectins: mediate cell adhesion to carbohydrates on other cells.

    • Integrins: mediate cell adhesion to the extracellular matrix.

    • Immunoglobulin superfamily: mediate cell-to-cell adhesion and immune functions.