Cell Physiology: Organization and Protoplasm

Cell Physiology

• Cell physiology focuses on understanding the functions of organs by studying the basic organization of cells.

Organization of Cells

• The two major parts of a cell are the nucleus and cytoplasm.
• A nuclear membrane separates the nucleus from the cytoplasm.
• The cytoplasm is separated from the surrounding fluids by a cell or plasma membrane.

Protoplasm

• Protoplasm comprises the cytoplasm and nucleus.
• The cytoplasm is made up of substances.
• Five basic substances make up protoplasm: water, protein, lipids, electrolytes, and carbohydrates.

Water in Protoplasm

• Water serves as the principal fluid medium of the cell.
• Water is present in most cells at a concentration of 70-85%, except for fat cells.
• Chemical reactions occur among dissolved chemicals or on the surface of suspended particles or membranes due to water.

Ions in Cells

• Ions found in cells include potassium, magnesium, phosphate, sulfate, and bicarbonate.
• Small quantities of sodium, calcium, and chloride are also present.
• Ions provide inorganic chemicals for cellular reactions.
• Ions at the cell membrane transmit electrochemical impulses in nerve and muscle fibers.

Lipids in Cells

• Lipids are grouped together because of their solubility in fat solvents.
• Lipids include phospholipids and cholesterol.
• Lipids make up approximately 2% of total cell mass.
• Lipids are mainly insoluble in water.
• Lipids form the plasma membrane and intracellular membranes.
• Lipids create separation of cell compartments.

Triglycerides

• Triglycerides are a type of lipid considered "neutral fat."
• In fat cells, triglycerides can make up 95% of the cell mass.
• Fat stored in these cells are energy-giving nutrients that can be dissolved to provide energy where needed in the body.

Carbohydrates in Cells

• Carbohydrates have little structural function in the cell.
• Carbohydrates average 1% of total cell mass.
• Carbohydrates may increase to 3% in muscle cells and up to 6% in the liver.
• A small amount of carbohydrate is stored as glycogen, which can be rapidly depolymerized to meet energy needs.

Physical Structure of Cells

• The physical structure of cells includes membranous structures, cytoplasm, cell membrane, and intracellular organelles.

Membranous Structures

• Most cell organelles are covered by membranes of lipids and proteins.
• Key membranous structures include the cell membrane, nuclear membrane, Golgi apparatus membrane, endoplasmic reticulum membrane, and mitochondria and lysosome membranes.
• Lipids in membranes impede water entry into compartments because water is not soluble in lipids.

Cell Membrane

• The cell membrane is a thin, pliable, elastic structure of 7.5 to 10 nm in thickness.
• The approximate components of the cell membrane include:
  • Proteins - 55%
  • Phospholipids - 25%
  • Cholesterol - 13%
  • Other lipids - 4%
  • Carbohydrates - 3%

Lipid Bilayer

• The lipid bilayer is a thin, double layer of lipids, with each layer being one molecule thick, and continuous over the entire cell surface.
• It is composed of phospholipid molecules.
• One end of a phospholipid is water-soluble (hydrophilic), and the other is soluble only in fats (hydrophobic).

Phospholipid Bilayer Function

• The middle lipid layer is impermeable to water-soluble substances, such as ions, glucose, and urea.
• Fat-soluble substances, including oxygen, carbon dioxide, and alcohol, can pass with ease.
• Cholesterol molecules, highly fat-soluble, are responsible for determining the membrane’s permeability.

Membrane Proteins

• Membrane proteins appear as globular masses floating in the lipid layer.
• Glycoproteins are the most common membrane proteins.
• Two types of proteins in membranes: integral and peripheral.

Integral Proteins

• Integral proteins protrude entirely through the membrane.
• Integral proteins provide structural channels, or pores, for water and ions to diffuse between extracellular and intracellular fluids.
• Some integral membrane proteins function as carrier proteins.
• Carrier proteins assist in the movement of substances that cannot penetrate the lipid layer or transport substances against their electrochemical gradient.
• Some integral proteins act as enzymes or receptors for water-soluble substances (e.g., peptide hormones).
• Interaction of membrane receptors with ligands causes changes in the receptors.
• They induce interactions between receptors and cytoplasmic proteins, and relay information from the cell exterior to its interior.

Peripheral Proteins

• Peripheral proteins attach only to one surface of the membrane.
• Peripheral proteins are often attached to integral proteins.
• Peripheral proteins function as enzymes or transport controllers through cell membrane pores.

Membrane Carbohydrates

• Membrane carbohydrates exist in combination with glycoproteins or glycolipids.
• Most integral proteins are glycoproteins.
• About 1/10 of lipid molecule proteins are glycolipids.
• The "Glyco" component of these molecules protrudes outside the cell, dangling outward at the cell surface.
• Many carbohydrate compounds including proteoglycans, which are carbohydrate substances attached to a small core protein.
• The glycocalyx is a loose carbohydrate coat on the cell, found on the outside surface of the cell.

Cell Membrane Proteins Function

• Cell membrane carbohydrate moieties function to:
  • Impart a negative charge to the cell, repelling other negative objects.
  • Attach some cells to the glycocalyx of other cells.
  • Serve as receptor substances for binding hormones.
  • Mediate immune reactions.

Cytoplasm

• The cytoplasm contains both minute and large dispersed particles and organelles.
• Cytosol is the clear fluid portion of the cytoplasm, containing dissolved proteins, glucose, and electrolytes.
• Five important organelles exist in the cytoplasm.

List of Organelles

• The five major organelles are:
  • Endoplasmic reticulum
  • Golgi apparatus
  • Mitochondria
  • Lysosomes
  • Peroxisomes

Endoplasmic Reticulum

• The endoplasmic reticulum is a network of tubular and flat vesicular structures interconnected with each other.
• The walls of the endoplasmic reticulum are constructed of a lipid bilayer membrane.
• The endoplasmic reticulum contains a substantial number of proteins.
• The total surface area can be 20-30 times that of the cell membrane area.
• The space inside the tubules and vesicles is filled with endoplasmic reticulum matrix.
• A watery medium different from the fluid in the cytosol lies outside the ER.
• A vast surface area and many attached enzyme systems provide machinery for metabolic processes of the cell.

Granular Endoplasmic Reticulum

• Ribosomes are attached to the surface of the granular endoplasmic reticulum.
• Ribosomes are composed of a mixture of RNA and proteins.
• Its function synthesizes new proteins in the cell.
• Some proteins extrude directly into the cytosol.

Agranular Endoplasmic Reticulum

• Agranular endoplasmic reticulum contains no attached ribosomes.
• The agranular reticulum deals with lipid molecule synthesis.
• Lipids and cholesterol are synthesized in the agranular reticulum.
• Lipids are rapidly incorporated onto the layer of the agranular reticulum.
• Agranular endoplasmic reticulum SER is expanding.
• To prevent the SER from expanding beyond the needs of the cell, secretory vesicles pinch off from the SER.
• Secretory vesicles then migrate to the Golgi apparatus.

Golgi Apparatus

• Golgi apparatus membranes are similar to agranular endoplasmic reticulum membranes.
• The Golgi apparatus comprises four or more stacked layers of thin, flat enclosed vesicles near one side of the nucleus.
• The Golgi apparatus is prominent in secretory cells and is located on the side of the cell from which secretory substances are extruded.
• Golgi Apparatus functions in association with ER.
• Small ER vesicles pinch off and fuse with the Golgi apparatus.
• Substances are then processed in the Golgi apparatus to form lysosomes, secretory vesicles, and other cytoplasmic components.

Lysosomes

• Lysosomes are vesicular organelles formed by breaking off from the Golgi apparatus.
• They function as an intracellular digestive system.
• Lysosomes allow cells to digest damaged cell structures, food particles & unwanted matter, like bacteria.

Lysosomes Characteristics

• Lysosomes differ in many cells.
• Their diameter is different than many cells.
• They are around 250 to 750nm in diameter.
• They have a typical lipid bilayer membrane.
• They are filled with granules 5-8 nm in diameter.
• These granules are aggregates of as many as 40 hydrolazes.

Hydrolytic Enzymes

• Hydrolytic enzymes are capable of splitting organic compounds into one or more parts.
• The protein is hydrolyzed into amino acids.
• Glycogen is hydrolyzed to form glucose.
• Lipids are hydrolyzed into fatty acids and glycerol.

Lysosomes Membranes

• The membrane of this organelle prevents the exit of hydrolytic enzymes and contact other substances in the cell.
• The membrane prevents digestive actions.
• There are conditions in the cell that break the membrane and release hydrolytic enzymes.

Peroxisomes

• Peroxisomes are similar to lysosomes.
• Peroxisomes differ in two ways:
  • They are believed to be a product of self-replication rather than originating from the Golgi apparatus.
  • They contain oxidases rather than hydrolases.

Peroxisomes and Oxidases

• Several oxidases are capable of combining oxygen with hydrogen ions to form hydrogen peroxide.
• Hydrogen peroxide is a highly oxidizing substance working with catalases.
• Oxidizing substances that can be poisonous to the cell
• Alcohol oxidized by peroxisomes in liver cells.

Mitochondria

• Mitochondria are the powerhouses of the cell.
• Mitochondria are present in all areas of the cell’s cytoplasm.
• The number of mitochondria varies from several hundred to thousands.
• The number of mitochondria depends on the energy requirements of the cell.

Mitochondria Membrane

• The cell membrane has 2 parts.
• The cell membrane consists of the inner and outer membrane.
• Infoldings of the inner membrane form compartments.
• Compartments contain matrix that houses enzymes necessary for extracting energy from nutrients.

Creation of Energy

• The liberation of energy is employed to synthesize substances called ATP.
• Mitochondria are self-replicative.
• Depending on energy requirements, one can replicate one, two, or three more.

Cytoskeleton Elements

• The cytoskeleton consists of proteins that support the cell.
• The cytoskeleton holds organelles in place.
• The cytoskeleton changes the shape of the cell.
• Proteins are known as microtubules, microfilaments, and intermediate filaments.

Microtubules

• Protein subunits form Microtubules.
• Microtubules assist the cell in cell division.
• Microtubules support the cytoplasm.
• Microtubules form components of organelles such as cilia and flagella.

Microfilaments

• Microfilaments are small fibrils that structurally support the cytoplasm.
• Microfilaments are involved in cell movement.
• The microfilaments allow muscle cells to shorten or contract.

Intermediate Filaments

• Intermediate filaments are smaller in diameter than microtubules but larger than microfilaments.
• Intermediate filaments provide mechanical support to the cell.

Centrosome

• The centrosome is a specialized zone of cytoplasm close to the nucleus where microtubule formation occurs.
• The centrosome contains two centrioles oriented perpendicular to one another.
• Each centriole is a small, cylindrical organelle composed of nine triplets.
• Each triplet contains three parallel microtubules joined together.

Cilia and Flagella

• Cilia are cylindrical structures that extend from the cell.
• Flagella are longer than cilia and occur only one per cell.
• Microvilli are extensions of the cell membrane supported by microfilaments.
• Microvilli does not move the cell.
• Microfilaments are involved in increasing the surface area of cells for absorption.

Cell Locomotion

• 1. Ameboid movement
• 2. Cilia and Ciliary movements

Ameboid Movement

• Ameboid Movement involves the movement of the entire cell in relation to its surroundings.
• It is derived from the fact that amebae move in this manner.
• Locomotion begins with the protrusion of a pseudopodium from one end of the cell.
• The pseudopodium projects outward and secures itself, pulling the rest of the cell.
• Types of cells to exhibit this type of movement are white blood cells, tissue macrophages, fibroblasts, and embryonic cells.

Ciliary Movement

• Ciliary movement involves the whip-like movement of the cilia on the surfaces of cells.
• This occurs in only two places of the human body:
  • Surface of respiratory airways
  • Inside surfaces of the uterine tubes (fallopian tubes)

Ciliary Movement Cont.

• In the nasal cavity, cilia causes a layer of mucus to move at a rate of 1 cm/min toward the pharynx.
• This happens to clear passageways of mucus and particles.
• In the uterine tubes, cilia causes slow movement of fluid from the ostium of the uterine tube toward the uterus.
• This movement of fluid causes the transport of the ovum to the uterus.

Key Aspects of Cilia

• Cilia contain sharp pointed or curved hair.
• They project between 2-4mm from the surface of the cell.
• They exist covered by an outcropping of cell membrane.
• Each Cilium is an outgrowth of a structure beneath the cell membrane basal body.
• Support by 11 Microtubules
  • 9 Double
  • 2 Single Tubules At The Center

Cell Membrane Transport

• Selectively permeable
• Passive transport -Does not require the cell to expend energy - Diffusion - Osmosis - Facilitated Diffusion
• Active membrane transport - Requires the use of energy usually in the form of ATP -Active Transport #-Secondary Active Transport -Endocytosis -Exocystosis

Diffusion

• Movement of solute from an area of higher concentration of solute to an area of lower concentration of the same solute.

Osmosis

 - The di usion of water(solvent) across a selectively permeable membrane.
 - From a region of higher water concentration to a lower water concentration.
 - Predicts the direction of water movement depends on which solution o either side of the membrane has the higher water concentration.

• Terms to Note -Osmotic Pressure-the force required to prevent the movement of water across a selectively permeable membrane.
• Different concentrations -Hypotonic-water concentration is higher and solute concentration is lower than the cell -Isotonic-Concentration of water and solutes is the same -Hypertonic-Water concentration is lower and solute concentration is higher than the cell.

Carrier Mediated Transport

  -The movement of large water soluble of electrically charged molecules across the cell membrane.
  -Amino acids, glucose and proteins cant not enter the cells through diffusion.
  -A molecule binds with a carrier molecule on one side of the membrane.
  -The Transported molecule moves to the opposite side of the membrane.

Active Transport

 - A type of CMT that moves substances from an area of lower concentration to an area of higher concentration against a gradient.
 - Requires ATP, without it - active transport stops

Secondary Active Transport

 - The diffusion of that transported substance or provides energy to transport a secondary substance. Types:
    -Cotransport-Diffusing Subtance moves in the same direction
    -Counter Transport-Diffusing substance moves in the opposite direction.

Endcytosis and Exocytosis

-Large water soluble molecules, matter and even cells can be transported accross cell membranes in membrane bound sacs called Vesicles - Endocytosis - Is the uptake of material through a cell membrane by the formation of a vesicle - Receptor Mediated - Occurs through the cell membrane and has specific Receptors to which specific molecules bind. - Phagocytosis - Uptake of solid particle - Pinocytosis - Formed vesicles contain liquid and are much smaller. -Exocytosis -Mebrane bound sacs accumulate materials for release from the cell , Requires energy in the form of ATP.

Explore cell physiology, focusing on cellular organization and protoplasm. Understand the roles of the nucleus, cytoplasm, and cell membrane. Learn about the five basic protoplasmic substances: water, protein, lipids, electrolytes, and carbohydrates.