The Cellular Level of Organization Chapter 3 Levels

The Cellular Level of Organization Chapter # 3

Levels of Organization

The human body has 50 to 100 trillion cells. The trillions of cells in the human body include over 200 different cell types. Somatic Cells Sex Cells or Gametes Sperm Oocyte

Principal Parts of a Model Cell Cytosol (intracellular fluid) Organelles Nucleus Cell membrane, plasma membrane, or plasmalemma (Little organs with specific functions) : . : Inclusions (Glycogen granules, lipid droplets, , pigment granules) Cytoplasm (Material between the plasma membrane and the nuclear envelope)

The Cytosol Extracellular fluid or Interstitial fluid Lower concentration of Potassium. Higher concentration of Sodium. Lower concentration of suspended proteins. It is a transport medium and no reserves are stored there. It contains masses of insoluble materials (melanin in skin and mineral deposits in bone). Plasma membrane Intracellular fluid or Cytosol Higher concentration of Potassium. Lower concentration of Sodium. Higher concentration of suspended proteins. It contains small reserves of carbohydrates, aminoacids and lipids. It contains masses of insoluble materials called inclusions (glycogen and lipid droplets, pigment granules).

The Organelles NONMEMBRANOUS ORGANELLES

The Cytoskeleton It functions as the cell’s skeleton. It provides an internal protein framework that gives the cytoplasm strength and flexibility. 1 -Microfilaments 2 - Intermediate filaments 3 - Microtubule 4 - Thick filaments

Microfilaments: They are composed of the protein actin. 1 - They anchor the cytoskeleton to integral proteins of the plasma membrane. 2 - They interact with other proteins, determine the consistency of the cytoplasm. 3 - Actin can interact with the protein myosin to produce active movement. Thin filaments (actin) Thick filaments (myosin) Intermediate filaments: 1 - They strengthen the cell and help maintain its shape. 2 - They stabilize the position of the organelles. 3 - They stabilize the position of the cell with respect to surrounding cells.

Microtubules: 1 - They are the primary components of the cytoskeleton, giving the cell strength and rigidity and anchoring the position of major organelles. 2 - The disassembly of microtubules provides a mechanism for changing the shape of the cell, perhaps assisting in cell movements. 3 - They serve as a kind of monorail system to move vesicles or other organelles within the cell. 4 - During cell division, microtubules form the mitotic spindle, which distributes the duplicated chromosomes to opposite poles of the cell. 5 - They form structural components of organelles, such as centrioles and cilia.

Thick filaments: They are bundles of subunits composed of the protein myosin. They appear only in muscle cells, where interact with actin filaments to produce the muscle contraction. Thin filaments (actin) Thick filaments (myosin)

Microvilli They are small finger-shaped projections of the plasma membrane on their exposed surfaces. Function: They increase the surface area of cells that are actively absorbing materials from the extracellular fluid, such as cells lining the digestive tract.

Centrioles They are cylindrical structures composed of short microtubules. Function: They form the mitotic apparatus (mitotic spindle) during cell division. 9+0 array

Cilia They are relatively long, slender extensions of the plasma membrane. 9+2 array Function: They beat rhythmically to move fluids or secretions across the membrane surface (ciliated cells of trachea). 9+0 array Ciliated cells of the uterine tubes move oocytes along the tubes, and ciliated cells of the reproductive male tract waft the sperm from the testes.

One of the most important function of most cells is to produce proteins Cells that synthesize proteins for exportation Pancreatic acini Pancreatic islet Digestive enzymes Insulin Plasma cell Antibodies Cells that synthesize proteins to be used by their self

Along the Protein Production Path Nucleus Ribosomes Rough endoplasmic reticulum Golgi complex Proteins are assembled in the ribosomes, which are in the cytoplasm. The instructions for the assembling are in the nucleus.

Ribosomes They are small, dark staining granules composed of 40 % of protein and 60 % of ribosomal RNA. Each ribosome consists of two subunits. Free ribosomes They are scattered through the cytoplasm and produce proteins that enter the cytosol. Fixed ribosomes They are attached to the rough endoplasmic reticulum and produce proteins that are modified and packaged for secretion.

Ribosomal RNA ( r. RNA ) Types of RNA Messenger RNA ( m. RNA ) Transfer RNA ( t. RNA ) 1 - Ribosomal RNA ( r. RNA ): It is structural part of the ribosomes. 2 - Messenger RNA ( m. RNA ): It carries the instructions from the DNA to the cytoplasm for the synthesis of proteins. 3 - Transfer RNA ( t. RNA ): Select and transport the aminoacids to be incorporated in the polypeptide chain. r. RNA m. RNA t. RNA

Cytoplasm Nucleus DNA a. a r. RNA m. RNA t. RNA m. RNA Function of Ribosomes: They are responsible for protein synthesis. t. RNA Aminoacid chain

Proteosomes They are organelles that contain protein-digesting enzymes. Function: They digest proteins destined for recycling, which have been labeled with the protein ubiquitin. Endoplasmic Reticulum It is a network of intracellular membranes connected to the nuclear envelope.

Rough Endoplasmic Reticulum It is where the newly synthesized proteins are chemical modified and packaged for export to the Golgi apparatus. Smooth Endoplasmic Reticulum 1 - Synthesis of phospholipids and cholesterol for maintenance and growth of the plasma membrane. 2 - Synthesis of steroid hormones. 3 - Synthesis and storage of triglycerides in liver cells and adipocytes. 4 - Synthesis and storage of glycogen in skeletal muscle and liver cells.

Golgi Apparatus It is a network of membranes typically consisting of five or six flattened discs called cisternae. Cisternae Functions: 1 - It modifies and packages secretions, such as hormones and enzymes, for release through exocytosis 2 - It renews or modifies the plasma membrane. 3 - It packages special enzymes within vesicles (lysosomes) for use in the cytosol.

3 - Lysosomes 1 - Secretory vesicles 2 - Membrane renewal vesicles

Lysosomes They are small, often spherical bodies, which contain powerful digestive enzymes that breakdown large organic molecules and even complex structures like organelles. Primary lysosome Secondary lysosome

Peroxisomes They are smaller than the lysosomes and carry a different group of enzymes. Functions: 1 - Detoxify the cell of free radicals and hydrogen peroxide. 2 - Absorb and breakdown fatty acids and other organic compounds.

Mitochondria They are threadlike or sausage-shape membranous organelles, enclosed by two membranes. Functions: They are the organelles responsible for the production of the energy that cells require.

Nucleus It is the control center of the cell, which contains the genetic material (genes). The nucleus is composed of: 1 - The nuclear envelope 2 - The nucleoplasm 3 - The nucleoli 4 - The chromatin

Perinuclear space Nuclear envelope

The Nucleolus They are dark staining spherical bodies, which are not membrane bounded, found in the nucleus. Nucleolus Functions: They produce the ribosomal RNA and they are the site where the ribosomes are assembled.

The Plasma Membrane

General Functions of the Plasma Membrane 1 - Physical Isolation The plasma membrane separates the inside of the cell from the surrounding extracellular fluid. 2 - Regulation of Exchange with the Environment It controls: - the entry of ions and nutrients, such as glucose. - the elimination of waste. - the release of secretions. 3 - Sensitivity to the Environment - It is affected by changes in the composition, concentration, or p. H of the extracellular fluid. - It contains receptors that allow the cell to recognize and respond to specific molecules in the environment. 4 - Structural Support Specialized connection between plasma membranes, or between membrane and extracellular materials, gives tissues stability. Cell membrane, plasma membrane, or plasmalemma

Components of the Plasma Membrane Lipids, Proteins, and Carbohydrates EXTRACELLULAR FLUID Carbohydrates (Glycoproteins) Carbohydrates (Glycolipids) Integral protein Peripheral protein Phospholipids Cholesterol CYTOPLASM Lipids

Membrane Lipids They are the most abundant components of the plasma membrane, but they account only about 42 % of its weight. Functions: They isolates the cytoplasm from the surrounding fluid environment. Ions and water-soluble compounds can not cross the lipid portion of the plasma membrane, while only hydrophobic molecules and a few very small molecules can enter the cells easily.

Membrane Proteins 1 - Anchoring Proteins 2 - Recognition Proteins 3 - Enzymes Cytoskeleton 4 - Receptors Proteins 5 - Carrier Proteins 6 - Channel Proteins

Membrane Carbohydrates (Glycocalix) Glycoproteins: They are proteins that contain oligosaccharide chains covalently attached to the polypeptide chain. Proteoglycans: They are glycoproteins that are heavily glycosilated. Glycolipids: They occur where a carbohydrate chain is associated with phospholipids on the plasma membrane. EXTRACELLULAR FLUID alix Glycoc CYTOPLASM Gly coc alix

Functions of the Glycocalix 1 - Lubrication and protection of the plasma membrane 2 - Anchoring and Locomotion: The glycocalix is a sticky layer that help anchor the cell in place. It also participates in the locomotion of specialized cells. 3 - Specificity in Binding: Glycoproteins and glycolipids can function as specific receptors for extracellular components that affect the cell’s behavior (ex: hormone receptors). 4 - Recognition: Glycoproteins and glycolipids are recognized as self or foreign by cells involves in the immune response. A B AB O Blood types are determined by the presence or absence of specific surface antigens in RBC membranes. The surface antigens are glycoproteins and glycolipids whose characteristics are genetically determined.