The Cellular Level of Organization Anatomy & Physiology – Honors

Essential Question What are the essential functions of cells and cell organelles? What is the basic function of the cell nucleus?

Contemporary Cell Theory Cells are the building blocks of all plants and animals Cells are produced by the division of pre-existing cells Cells are the smallest units that perform all vital physiological functions Each cell maintains homeostasis at the cellular level Homeostasis at the tissue, organ, organ system, and organism levels reflect the combined and coordinated actions of many cells.

Studying Cells Cytology is the study of the structure and function of cells It is part of cell biology The human body contains two types of cells Sex cells Sperm oocytes Somatic cells All other cells

Cytoplasm – material between plasma membrane and the nucleus Cytosol – largely water with dissolved protein, salts, sugars, and other solutes Cytoplasmic organelles – metabolic machinery of the cell Inclusions – chemical substances such as glycosomes, glycogen granules, and pigment

The Cytoplasm The Cytosol The cytoplasm contains the fluid cytosol and the organelles the cytosol surrounds

Organelles Non-membrane organelles Not enclosed by membranes Always in contact with the cytosol Include the following: Cytoskeleton Microvilli Centrioles Cilia Flagella Ribosomes

Membranous organelles surrounded by lipid membranes Isolates them from the cytosol Include the following: Endoplasmic reticulum Golgi apparatus Lysosomes Peroxisomes Mitochondria

Cytoskeleton The “skeleton” of the cell Gives cytoplasm strength & flexibility Dynamic, elaborate series of rods running through the cytosol Consists of microtubules, microfilaments, and intermediate filaments

Microfilaments Dynamic strands of the protein actin Attached to the cytoplasmic side of the plasma membrane Braces and strengthens the cell surface Attach to CAMs and function in endocytosis and exocytosis Functions of microfilaments Anchor the cytoskeleton to integral membrane proteins Interact with other filaments to produce cellular movement

Intermediate Filaments Tough, insoluble protein fibers with high tensile strength Resist pulling forces on the cell and help form desmosomes Functions of intermediate filaments: Provide strength Stabilize position of other organelles Transport materials within the cytoplasm

Microtubules Dynamic, hollow tubes made of the spherical protein tubulin Determine the overall shape of the cell and distribution of organelles Functions of microtubules: Provide cell strength, rigidity and anchoring organelles Alter shape of cell, perhaps assisting with cell movement Can relocate organelles within the cell Form the spindle apparatus for cell division Form centrioles, cilia and flagella

Thick filaments – made of myosin

Motor Molecules Protein complexes that function in motility Powered by ATP Attach to receptors on organelles

Microvilli Small projections of the cell membrane Increase the surface area exposed to the extracellular environment Usually located on cells that are involved in transporting substances across the cellular membrane from extracellular fluid Microvilli contain microfilaments

Centrioles Small barrel-shaped organelles located in the centrosome near the nucleus Pinwheel array of nine triplets of microtubules Organize mitotic spindle during mitosis Direct movement of chromosomes during cell division Organize the cytoskeleton Centrosome is the cytoplasm surrounding the centrioles Form the bases of cilia and flagella

Cilia Anchored by a Basal Body Beat rhythmically to move fluids or secretions across the cell surface Whiplike, motile cellular extensions on exposed surfaces of certain cells Move substances in one direction across cell surfaces

Flagella Move a cell through surrounding fluid rather than moving fluid past a stationary cell

Ribosome Intracellular factory Manufactures proteins Composed of small and large ribosomal units ribosomal RNA (rRNA) Free Ribosomes are in the cytoplasm Free ribosomes synthesize soluble proteins

Fixed Ribosomes are attached to the rough Endoplasmic Reticlum Granules containing protein and rRNA Site of protein synthesis Membrane-bound ribosomes synthesize proteins to be incorporated into membranes

Endoplasmic Reticlum (ER) Network of intracellular membranes that function in Synthesis of proteins, carbohydrates and lipids Storage of materials Transport of materials within the cell Detoxification of drugs or toxins Forms Hollow tubes Flattened sheets Round chambers called cisternae Continuous with the nuclear membrane Two varieties – rough ER and smooth ER

Rough Endoplasmic Reticulum (RER) External surface studded with ribosomes Manufactures all secreted proteins Responsible for the synthesis of integral membrane proteins and phospholipids for cell membranes Contains ribosomes on its outer surface forms transport vesicles Functions specific to the RER Synthesis and modification of proteins Packaging proteins for transport to the Golgi

Tubules arranged in a looping network Catalyzes the following reactions in various organs of the body In the liver – lipid and cholesterol metabolism, breakdown of glycogen and, along with the kidneys, detoxification of drugs In the testes – synthesis of steroid-based hormones In the intestinal cells – absorption, synthesis, and transport of fats In skeletal and cardiac muscle – storage and release of calcium

Smooth Endoplasmic Reticulum (SER) Functions specific to the SER - Synthesis of phospholipids and cholesterol - Synthesis of steroid hormones, in gonads and adrenals - Synthesis of storage of glycerides, in liver and fat cells - Detoxification of drugs, in liver and kidney cells - Synthesis and storage of glycogen, in muscle and liver cells

Golgi Apparatus Stacked and flattened membranous sacs Functions in modification, concentration, and packaging of proteins Transport vessels from the ER fuse with the cis face of the Golgi apparatus Proteins then pass through the Golgi apparatus to the trans face Secretory vesicles leave the trans face of the Golgi stack and move to designated parts of the cell

Secretions are discharged from the cell by exocytosis Forms secretory vesicels new membrane components packages lysosomes Secretions are discharged from the cell by exocytosis Functions of the Golgi include Synthesis and packaging of secretions for exocytosis Renewal or modification of the cell membrane Packaging of enzymes for use in the cytosol

Lysosomes Spherical membranous bags containing digestive enzymes Digest ingested bacteria, viruses, and toxins Degrade nonfunctional organelles Breakdown glycogen and release thyroid hormone Breakdown nonuseful tissue Breakdown bone to release Ca2+ Secretory lysosomes are found in white blood cells, immune cells, and melanocytes

Peroxisomes Membranous sacs containing oxidases and catalases Carry enzymes that neutralize toxins Neutralize dangerous free radicals Free radicals – highly reactive chemicals with unpaired electrons (i.e., O2–)

Mitochondria Double membrane structure with shelflike cristae Responsible for 95% of the ATP production in a typical cell The matrix, or fluid contents of a mitrochondrion, lie inside the cristae, or folds of an inner membrane Contain their own DNA and RNA

Nucleus Contains nuclear envelope, nucleoli, chromatin, and distinct compartments rich in specific protein sets Gene-containing control center of the cell Contains the genetic library with blueprints for nearly all cellular proteins Dictates the kinds and amounts of proteins to be synthesized

Nucleoli Dark-staining spherical bodies within the nucleus Site of ribosome production

Nuclear Envelope Selectively permeable double membrane barrier containing pores Encloses jellylike nucleoplasm, which contains essential solutes Outer membrane is continuous with the rough ER and is studded with ribosomes Inner membrane is lined with the nuclear lamina, which maintains the shape of the nucleus Pore complex regulates transport of large molecules into and out of the nucleus

Chromatin Threadlike strands of DNA and histones Arranged in fundamental units called nucleosomes Form condensed, barlike bodies of chromosomes when the nucleus starts to divide

Endomembrane System System of organelles that function to: Produce, store, and export biological molecules Degrade potentially harmful substances System includes: Nuclear envelope, smooth and rough ER, lysosomes, vacuoles, transport vesicles, Golgi apparatus, and the plasma membrane