cells: the living units bio 200 chp 3. the living units cell theory: the cell is the basic...
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CELLS: The Living Units
BIO 200
Chp 3
The Living Units
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
Figure 3.1
Cell Structure
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
Figure 3.3
Plasma Membrane Structure The Fluid Mosaic Model
Fluid Mosaic Model
• Double bi-layer of lipids with imbedded proteins
• Forms the basic “fabric” of the cell membrane
• Bi-layer consists of phospholipids, cholesterol and glycolipids– Hydrophilic – attracts water (polar head)– Hydrophobic – repel water (nonpolar tails)
Functions of Membrane Proteins
• Transport
• Enzymatic activity
• Receptors for signal transduction
Cell Plasma Membrane
Cell Plasma Structure
• The plasma aims to maintain homeostasis
• Lipid molecules of the by-layer move freely
• Polar-nonpolarity interactions keeps stability
• Microvilla – (hairs) increase the plasma membrane surface
Plasma MembraneMembrane Junctions – help to knit or
adhere cellular tissue (enzymes)
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 MembraneMembrane transport
• Cells are surrounded by extacelluar or interstitial fluid
• Interstitial fluid is rich and nutritious
• Derives from the blood stream
• Ingredients: amino acids, sugars, fatty acids, vitamins, hormones, salts, waste products.
Functions of Plasma MembraneMembrane transport
• Substances move continuously across the plasma membrane
• It allows some substances to pass and excludes others
• Selective barrier
• Differential barrier
• Permeable barrier
Characteristics ofa healthy cell
*Damage barriers will imbalance homeostasis
Passive Transport:
Diffusion
1. Simple diffusion – nonpolar and lipid-soluble substances
• Diffuse directly through the lipid bilayer
• Diffuse through channel proteins
• Molecules disperse evenly
Figure 3.6
Passive Transport
Diffusion
2. Facilitated diffusion
• Allows transport of glucose, amino acids, and ions
• Transported substances bind carrier proteins or pass through water-filled protein channels
Passive Transport
Facilitated diffusion
2. 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
3. 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
Figure 3.7
Figure 3.8
Active Transport
• Uses ATP to move solutes across a membrane
• Requires carrier proteins
• Types of Active Transport– Primary active transport – hydrolysis of ATP
phosphorylates the transport protein causing conformational change
– Secondary active transport – use of an exchange pump (such as the Na+-K+ pump) indirectly to drive the transport of other solutes
Figure 3.10
Vesicular Transport
• Transport of large particles and macromolecules across plasma membranes
• Exocytosis – moves substance from the cell interior to the extracellular space
• Endocytosis – enables large particles and macromolecules to enter the cell
Vesicular Transport
• 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
Figure 3.12
Figure 3.13a
Figure 3.13b
Membrane Potential• 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)• Cells become polarized• Results from Na+ and K+ concentration
gradients across the membrane• 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
• 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
Cytroplasmic Organelles
Cytoplasmic Organelles
• Membranous - mitochondria, peroxisomes, lysosomes, endoplasmic reticulum, and Golgi apparatus
• Nonmembranous - cytoskeleton, centrioles, and ribosomes
Figure 3.17
Mitochondrion
Mitochondria
• Double membrane structure with shelf-like cristae
• Provide 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)
• Continuous with the nuclear membrane
• Two varieties – rough ER and smooth ER
Figure 3.18
Endoplasmic Reticulum (er)
Rough (ER)
• External surface studded with ribosomes
• Manufactures all secreted proteins
• Responsible for the synthesis of integral membrane proteins and phospholipids for cell membranes
Smooth (ER)• Looping tubule network• Catalyzes the following reactions in various
organs of the body:• Liver – lipid & cholesterol metabolism,
breakdown of glycogen, detoxification of drugs • In the testes – synthesis steroid-based
hormones• In the intestinal cells – absorption, synthesis, and
transport of fats• 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
Figure 3.20
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
Lysosomes
• Breakdown nonuseful tissue
• Breakdown bone to release Ca2+
• Secretory lysosomes are found in white blood cells, immune cells, and melanocytes
Figure 3.22
Lysosomes
Figure 3.23
The Endomembrane System
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
• Detoxify harmful or toxic substances
• Neutralize dangerous free radicals
• Free radicals – highly reactive chemicals with unpaired electrons
Cytoskeleton
• The “skeleton” of the cell
• Dynamic, elaborate series of rods running through the cytosol
• Consists of microtubules, microfilaments, and intermediate filaments
CytoskeletonMicrotubules• Dynamic, hollow tubes made of the
spherical protein tubulin• Determine the overall shape of the cell
and distribution of organelles
MicrofilamentsDynamic strands of protein Actin• Attached to the cytoplasmic side of the
plasma membrane• Braces and strengthens the cell surface
Cytoskeleton
• 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
Cilia
Figure 3.26
Figure 3.27a
Cellular MotionCELIA
• 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
Figure 3.27c
Cellular MotionFlagella
• Projections are longer
• A single propulsive flagellum
• Movement is achieved by propelling itself across the surface or environment
• Basal bodies in the centrioles form the bases for ceia and flagella
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
Figure 3.28
Figure 3.31b
DNA Replication
Cell Growth and ReproductionCell 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 divisiona) prophase
b) metaphase
c) Anaphase
d) telophase
• Phases merge together
Cell Division - Mitosis
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
Figure 3.32
Figure 3.32