CELLS: The Living UnitsBIO 200 Chp 3

Cell Theory:

The cell is the basic structural and functional unit of life

Organismal activity depends on individual and collective activity of cells

Biochemical activities of cells are dictated by subcellular structure

Continuity of life has a cellular basis

Cell Structure

Plasma Membrane

Separates intracellular fluids from extracellular fluids. Plays a dynamic role in cellular activity

Glycocalyx (a glycoprotein) bordering the cell that provides highly specific biological markers by which cells recognize one another

Fluid Mosaic Model – a Double bi-layer of lipids with imbedded proteins. It forms the basic “fabric” of the cell membrane. The Bi-layer consists of phospholipids, cholesterol and glycolipids

Hydrophilic – attracts water (polar head)

Hydrophobic – repel water (nonpolar tails)

Functions of Membrane Proteins

Transports; hasEnzymatic activity; utilizes Receptors for signal transduction

Cell Plasma Structure - The plasma aims to maintain homeostasis with Lipid molecules of the by-layer move freely

Polar-nonpolarity interactions keeps stability

Microvilla – (hairs) increase the plasma membrane surface

Plasma Membrane (Membrane Junctions) – help to knit or adhere cellular tissue (enzymes). It’s a

Tight junction – impermeable junction that encircles the cell, prevents molecules from passing through

Desmosome – anchoring junction scattered along the sides of cells, aid in mechanical stress

Gap junction – a nexus that allows chemical substances (electrical activity) to pass between cells

Functions of Plasma Membrane: Membrane transport

The Cells are surrounded by extacelluar or interstitial fluid. Interstitial fluid is rich and nutritious that Derives from the blood stream. The Ingredients include: amino acids, sugars, fatty acids, vitamins, hormones, salts, waste products.

Substances can move continuously across the plasma membrane. It allows some substances to pass and excludes others. The plasma membrane is a: Selective barrier; Differential barrier; Permeable barrier

Passive Transport: Diffusion

1. Simple diffusion – nonpolar and lipid-soluble substances

Diffuse directly through the lipid bilayer. Diffuse through channel proteins. Molecules disperse evenly

Passive Difussion: Facilitated diffusion -Allows transport of glucose, amino acids, and ions

Transported substances bind carrier proteins or pass through water-filled protein channels

Carrier Proteins - Are integral transmembrane proteins

Show specificity for certain polar molecules like sugars and amino acids

Molecules too large to pass so they are carried through by transport receptor carriers

Passive Transport: Diffussion through Osmosis

Occurs when concentration of a solvent is different on opposite sides of a membrane

Diffusion of water across a semi-permeable membrane

Osmolarity – total concentration of solute particles in a solution. Tonicity – how a solution affects cell volume

Active Transport - Uses ATP to move solutes across a membrane. Requires carrier proteins

Types of Active Transport:

  1. Primary active transport – hydrolysis of ATP phosphorylates the transport protein causing conformational change
  2. Secondary active transport – use of an exchange pump (such as the Na+-K+ pump) indirectly to drive the transport of other solutes
  3. Vesicular Transport - Transport of large particles and macromolecules across plasma membranes
  4. Exocytosis – moves substance from the cell interior to the extracellular space
  5. Endocytosis – enables large particles and macromolecules to enter the cell

Vesicular Transport performs the following:

Transcytosis – moving substances into, across, and then out of a cell

Vesicular trafficking – moving substances from one area in the cell to another

Phagocytosis – pseudopods engulf solids and bring them into the cell’s interior

Membrane Potential of the plasma membrane

Voltage (electrical potential) across a membrane

Resting membrane potential – the point where K+ potential is balanced by the membrane potential

range -50 to -100 millivolts (mV). The Cells become polarized which results from Na+ and K+ concentration gradients across the membrane. This is a steady state – maintained by active transport of ions

Cell Membrane - Cell adhesion molecules - anchor cells to the extracellular matrix, assist in movement,

Membrane Receptors - important in immunity, regulates voltage in nerve and muscle tissue and neurotransmitters

Cytoplasm – material between plasma membrane and the nucleus

Cytosol – viscous semi-fluid, 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

Cytoplasmic Organelles

Membranous - mitochondria, peroxisomes, lysosomes, endoplasmic reticulum, and Golgi apparatus

Nonmembranous - cytoskeleton, centrioles, and ribosomes

Mitochondria

Double membrane structure with shelf-like cristae; provides most of the cell’s ATP via aerobic cellular respiration. Contain their own DNA and RNA

Ribosomes

Granules containing protein and rRNA. Site of protein synthesis. Free ribosomes synthesize soluble proteins. Membrane-bound ribosomes synthesize proteins to be incorporated into membranes

Endoplasmic Reticulum (ER)

Interconnected tubes and parallel membranes enclosing cristernae (cristae). It’s a Continuous with the nuclear membrane. There are 2 varieties – rough ER and smooth ER

  1. Rough (ER) - External surface studded with ribosomes. Manufactures all secreted proteins

Responsible for the synthesis of integral membrane proteins and phospholipids for cell membranes

  1. Smooth (ER) - Looping tubule network. Catalyzes the following reactions in various organs of the body:
  1. Liver – lipid & cholesterol metabolism, breakdown of glycogen, detoxification of drugs
  2. In the testes – synthesis steroid-based hormones
  3. In the intestinal cells – absorption, synthesis, and transport of fats
  4. In skeletal and cardiac muscle – storage and release of calcium

Golgi Apparatus

Stacked and flattened membranous sacs. Functions in modification, concentration, and packaging of proteins. “Traffic director” for cellular protein . Transport vesicles from the ER and are received by Golgi apparatus

Lysosomes

Spherical membranous bags containing digestive enzymes. Digest ingested bacteria, viruses, and toxins

Degrade nonfunctional organelles. Breakdown glycogen and release thyroid hormone

Autolysis – self-digestion of the cell. Breakdown nonuseful tissue and breakdown bone to release Ca2+

Secretorylysosomes are found in white blood cells, immune cells, and melanocytes

Endomembrane System

System of organelles that function to: Produce, store, and export biological molecules; Degrade potentially harmful substances

Contains the following system: Nuclear envelope, smooth and rough ER, lysosomes, vacuoles, transport vesicles, Golgi apparatus, and the plasma membrane

Peroxisomes - “Peroxide bodies”

Membranous sacs containing oxidases and catalases. They Detoxify harmful or toxic substances and Neutralize dangerous free radicals. Free radicals – highly reactive chemicals with unpaired electrons

Cytoskeleton - The “skeleton” of the cell

A Dynamic, elaborate series of rods running through the cytosol that Consists of microtubules, microfilaments, and intermediate filaments

  1. Microtubules - Dynamic, hollow tubes made of the spherical protein tubulin. Determine the overall shape of the cell and distribution of organelles
  2. Microfilaments - Dynamic strands of protein Actin. Attached to the cytoplasmic side of the plasma membrane. Braces and strengthens the cell surface
  3. Intermediate Filaments - Tough, insoluble protein fibers with high tensile strength. Resist pulling forces on the cell and help form desmosomes Pg 91

Centrioles

Small barrel-shaped organelles located in the centrosome near the nucleus

Pinwheel array of nine triplets of microtubules

Organize mitotic spindle during mitosis

Form the bases of cilia and flagella

Whip-like, motile cellular extensions on exposed surfaces of certain cells

Move substances in one direction across cell surfaces

Cellular Motion

CELIA - Cellular extensions that provide motility in a whiplike motion. Typically found in large numbers

Located in the exposed surface of the cell. Move substances in one direction across cell surface

Flagella – for locomotion of a cells

Nucleus

The control center containing genetic .Largest cytoplasmic organelle - 5µm. Nuclear envelop –dbl membrane barrier. Nucleoli – DNA & RNA for genetic synthesis.

Chromatin – threadlike coils that form chromosomes in cell division. Genes

Cell Growth and Reproduction: Cell Life Cycle

Cell division – essential for growth and tissue repair. Cells die and continuously reproduce

Some reproduce faster than others (skin, intestinal vs. liver). Some loose ability to divide @ maturation

(nervous tissue, skeletal muscle, heart, RBCs). The DNA replicates before cell division

Cell Growth and Reproduction - Cell Division - M Phase (Mitotic)

2 phases: Mitosis & Cytokinesis

Phase 1: Mitosis – nuclear division

a)prophase

b)metaphase

c)Anaphase

d)telophase

Phases merge together

Phase 2 – Cytokinesis

Cytokinesis - cytoplasmic division. Cleavage furrow formed in late anaphase by contractile ring. Cytoplasm is pinched into two parts after mitosis ends. The forming of 2 daughter cells