Cell Junctions, Plasma Membrane and Solutions

• Lecture 2 is about the cell.
• The cell's three main parts, along with their functions, will be explained, including an overview of the cells, the plasma membrane, cytoplasm, and nucleus.
• The stages of the cell life cycle will be examined, and their importance, most notably mitosis.

Overview of Cells

• Cells are diverse and come in many forms, each with specific structures and functions.
• The human body contains approximately 50–100 trillion cells. With over 250 different types.
• Cells can be categorized as either somatic cells or sex cells.

Generalized Cells

• Plasma Membrane separates the inside from the outside
• Cytoplasm includes the cytoskeleton, cytosol, organelles, and inclusions
• Nucleus acts as the control center

Plasma Membrane: Cell Boundary

• Membrane lipids consisting of phospholipids, cholesterol, and glycolipids.
• Phospholipids comprise about 75% of membrane lipids and form a bilayer with hydrophilic heads and hydrophobic tails, making them amphipathic.
• Cholesterol constitutes about 20% of membrane lipids and contributes to membrane fluidity.
• Glycolipids make up about 5% and contribute to the glycocalyx-carbohydrate coating.
• Membrane proteins can be integral or peripheral.
• Integral proteins pass through the membrane.
• Glycoproteins are integral proteins.
• Peripheral proteins adhere to either face of the membrane only.
• The plasma membrane is dynamic, and plays a key role in cellular activity

Fluid Mosaic Model

• Phospholipid bilayer has a hydrophilic head and hydrophobic tail.
• Membrane proteins include peripheral proteins, integral (transmembrane) proteins, and glycoproteins (glycocalyx).
• This membrane acts like a mosaic, allowing movement.

Functions of Membrane Proteins

• Receptor binds to chemical messengers.
• Enzyme breaks down a chemical messenger, terminating its effect.
• Channel is a protein that is constantly open allowing solutes to pass into and out of the cell
• Gated Channel opens and closes to allows solutes through at certain times only
• Identity marker distinguishes the body's own cells.
• Cell-adhesion molecule (CAM) binds one cell to another.

Plasma Membrane Functions

• Serves as a protective barrier
• Has receptors for communication
• Has selective permeability for membrane transport

Cell Junctions

• Located at the cell surface.
• They attach cells together and to the extracellular material.
• Cell junctions enable cells to resist stress, grow and divide normally, communicate, and control movement of substances.

Types of Cell Junctions

• Tight junctions act as a sealant
• Gap junctions facilitate communication.
• Desmosomes resist stress.
• Most cells have more than one type of junction.

Specific Junctions

• Tight Junctions attach neighboring cells tightly; plasma membranes are linked by transmembrane adhesion proteins and have intercellular space.
• Desmosomes are a protein patch that holds cells tightly, keeping cells from pulling apart and enabling tissue resistance to mechanical stress.
• Gap (communication) Junctions form a channel that allows specific ions and molecules to diffuse directly from the cytoplasm of one cell to another.

Membrane Transport

• Simple Diffusion occurs when lipid-soluble solutes diffuse through the membrane phospholipid.
• Water-soluble solutes diffuse through channel proteins.
• Osmosis is a special case of simple diffusion involving the movement of water from a "more watery" side to a "less watery" side.

Tonicity

• Tonicity: ability of a solution to cause a cell to shrink or swell
• Isotonic solution has the same solute concentration as that of the cytosol.
• Hypertonic solution has a greater solute concentration than that of the cytosol.
• Hypotonic solution has a lesser solute concentration than that of the cytosol.

Osmolarity and Tonicity Solutions

• Hypotonic solutions contain a lower concentration of nonpermeating solutes than intracellular fluid (ICF)
• High water concentration occurs
• Cells absorb water, swell, and may burst (lyse)
• Hypertonic solutions contain a higher concentration of nonpermeating solutes
• Low water concentration occurs
• Cells lose water and shrivel (crenate).
• Isotonic solutions have the same concentration in the cell and ICF
• No changes occur in cell volume or shape.
• Normal saline solution.

Carrier-Mediated Transport Types

• Uniport carries only one solute at a time.
• Symport carries two or more solutes simultaneously in the same direction (cotransport).
• Antiport carries two or more solutes in opposite directions (countertransport).
• The sodium-potassium pump brings in K+ and removes Na+ from cells

Carrier Transport

• Facilitated diffusion occurs when transport moves down its concentration gradient
• ATP is not consumed.
• Solute attaches to the binding site on a carrier

Active Transport

• Solute binds to the receptor site on the transport protein.
• Protein breaks down ATP, P, binds to protein, and shape changes.
• Protein releases solute to the other side of the membrane, releasing Pi.

Vesicular Transport

• Carries out processes that move large particles, fluid droplets, or numerous molecules at once through the membrane in vesicles.
• Endocytosis transports into the cell.
• Exocytosis transports out of the cell.
• Transcytosis transports into, across, and then out of the cell.

Endocytosis

• Phagocytes adhere to pathogens or debris.
• Phagocytes form pseudopods that eventually engulf particles, forming a phagosome.
• Lysosomes fuse with the phagocytic vesicle, forming a phagolysosome.
• Lysosomal enzymes digest the particles, leaving a residual body.
• Exocytosis of the vesicle removes indigestible and residual material.

More Endocytosis

• Pinocytosis "cell drinking" is in folding the plasma membrane

• Receptor-mediated endocytosis molecules bind to receptors on the plasma membrane, then receptors cluster together. The membrane sinks inward, forming clathrin-coated pits. Pits separate from the plasma membrane, and clathrin-coated vesicles result

Exocytosis

• Material is secreted and the plasma membrane is replaced, removing endocytosis

Glycocalyx Functions

• The carbohydrate component that belongs to the membranes's glycolipids and glycoproteins that forms this
• Acts as protection on the cell´s surface
• Cell´s identity
• Binds tissues
• Carries out fertilization functions
• Acts as defence against cancer

Cell Structures and Functions

• The plasma membrane has a structure consisting mainly of phospholipids and proteins which function to protect, communicate and transport selectively.
• Cytoplasm-cytosol, organelles, inclusions, cytoskeleton
• Cytosol is a jelly-like fluid with proteins in it
• Organelles are functional units
• Inclusions are temporary structures mainly for storage
• Cytoskeleton

Organelles: 9 Main Types

• Ribosomes: Proteins bound to Rough ER or free floating in cytoplasm. The function is to synthesize proteins
• Endoplasmic Reticulum (ER): Interconnected membranes that are contiguous with the nuclear and cell membrane,. The functions are to synthesize, store, transport, detox.
• Rough ER synthesizes proteins
• Smooth Er synthesizes lipids and helps break down drugs.
• Golgi apparatus: Flattened membrane sacs (cisternae) that remain continuous with Rough ER. Its function is to modify pack and deliver protein in vesicles. Vesicles have 3 destinations: to leave the cell with exocytosis, to move to the plasma cell membrane or remain in the cell as lysosomes.
• Lysosomes digest waste or "garbage disposal"
• Peroxisomes detoxify harmful substances
• Mitochondria produce in the form of ATP/ Uses Oxygen. Known as the power plant.
• Cytoskeleton
• Centrosomes/ centrioles

Inclusions

• Not essential to the cell survival
• Stored cellular products
  • Pigments
  • Fat Droplets
  • Granules of glycogen
• Foreign bodies -Dust Particles -Viruses -Intracellular Bacteria

Cytoskeleton

• Structure: Series of roads (proteins) throughout the cytosol
• Function: "cell skeleton" and support
• Types: -Microfilaments -Immediate filaments -Microtubules

Centrosomes

• Located in the cytoplasm, centrosomes are the organizing center within the cell from which all microtubules form
• Centrioles have the role of forming the spindle during mitosis for division of this nucleus

Surface Extensions

• Microvilli:
  • Plasma membrane extensions to increase Surface Area and form brush borders.
• Cilia:
  • Primary- cilium
  • Motile- cilia -axoneme-microtubules -Dynein-motor protein
• Flagella: -Long Axoneme -Propels sperm cell

Nucleus

• Function: control center
• Structures: -Nuclear enevelope( Membrane) -Nucleolus( Synthesizes Ribosomes) -Chromatin: DNA + proteins

Cell Summary

• The cytoplasm contains cytosol, inclusions, and many organelles, each with a specific structure and function.
• The Nulceus contains DNA and controls thecell.

Cellular Terminology:

• Apical cell surface
• Basal cell surface
• Lateral cell surface

Cell life cycle

• Interphase. (G1 G, S, G2)
• Mitosis.( Prophase, metaphase, anaphase, telophase)

Cell cycle continued

• Interphase: -First phase (G1) * Growth and metabolic roles -Synthesis phase (S) * DNA replication -Second gap phase (G2) * Growth and preparations for mitosis
• DNA proof reading

Mitotic phase details:

• Prophase -Chromatin Condenses -Nuclear envelope breaks down -Nucleolus disappears -Spindle fibers form to connect to Kinetochore
• Metaphase: -Chromosomes align at the center of cell
  • Aster attached to Plasma Membrane
• Anaphase: -Daughter Chromosomes move to oposite poles. -Telophase: . -Chromatids at each pole decondense -Surrounded by new nuclear membrane -Nucleoli reformed

Cytokinesis:

• Division of cytoplasm Begins in anaphase Phase
• Clevage furrow Developed

Final mitotic phase details:

·Cell pinches into two identical daughter cells

Consequences to the cell life cycle

Cancer is uncontrolled cell division which Can cause tumor growth

Stem Cells

• Immature cells that can develop in one or more types of mature, specialized cells. -Developmental Plasticity
• Adult Stem (As) cells
  • In most body organs -Producted cells for normal turn over -Mutipotent
• Embrionic Stem(ES) cells -Emryo up to 150 cells -Pluripotent -Escesss of in vitro Fertiliztion

###Cell cycle - Summarized The cell life cycle includes interphase and mitosis which is the divition of the nuleus into 2 cells. Altening normal cell divition can lead to cancer and used in stem cells.

Test your knowledge of cell junctions and plasma membranes. This quiz covers cell junctions, plasma membrane structure, and types of solutions. Understand the functions of different cell components.