cells: the living units
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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 - PowerPoint PPT PresentationTRANSCRIPT
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CELLS: The Living Units
BIO 200 Chp 3
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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
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Figure 3.1
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Cell Structure
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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
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Figure 3.3
Plasma Membrane Structure The Fluid Mosaic Model
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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)
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Functions of Membrane Proteins• Transport• Enzymatic activity• Receptors for signal transduction
Cell Plasma Membrane
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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
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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
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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.
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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
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Passive Transport:
Diffusion1. Simple diffusion – nonpolar and lipid-
soluble substances • Diffuse directly through the lipid bilayer• Diffuse through channel proteins• Molecules disperse evenly
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Figure 3.6
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Passive Transport
Diffusion2. Facilitated diffusion • Allows transport of glucose, amino acids,
and ions • Transported substances bind carrier
proteins or pass through water-filled protein channels
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Passive TransportFacilitated 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
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Passive Transport3. 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
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Figure 3.7
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Figure 3.8
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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
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Figure 3.10
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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
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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
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Figure 3.12
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Figure 3.13a
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Figure 3.13b
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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
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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
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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
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Cytroplasmic Organelles
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Cytoplasmic Organelles
• Membranous - mitochondria, peroxisomes, lysosomes, endoplasmic reticulum, and Golgi apparatus
• Nonmembranous - cytoskeleton, centrioles, and ribosomes
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Figure 3.17
Mitochondrion
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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
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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
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Endoplasmic Reticulum (ER)
• Interconnected tubes and parallel membranes enclosing cristernae (cristae)
• Continuous with the nuclear membrane• Two varieties – rough ER and smooth ER
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Figure 3.18
Endoplasmic Reticulum (er)
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Rough (ER)• External surface studded with
ribosomes• Manufactures all secreted proteins• Responsible for the synthesis of
integral membrane proteins and phospholipids for cell membranes
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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
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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
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Figure 3.20
Golgi Apparatus
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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
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Lysosomes
• Breakdown nonuseful tissue• Breakdown bone to release Ca2+• Secretory lysosomes are found in white
blood cells, immune cells, and melanocytes
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Figure 3.22
Lysosomes
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Figure 3.23
The Endomembrane System
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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
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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
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Cytoskeleton• The “skeleton” of the cell• Dynamic, elaborate series of rods running
through the cytosol• Consists of microtubules, microfilaments,
and intermediate filaments
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CytoskeletonMicrotubules• Dynamic, hollow tubes made of the
spherical protein tubulin• Determine the overall shape of the cell
and distribution of organellesMicrofilamentsDynamic strands of protein Actin• Attached to the cytoplasmic side of the
plasma membrane• Braces and strengthens the cell surface
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Cytoskeleton
• Intermediate Filaments• Tough, insoluble protein fibers with high
tensile strength• Resist pulling forces on the cell and help
form desmosomes
Pg 91
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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
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Figure 3.26
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Figure 3.27a
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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
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Figure 3.27c
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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
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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
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Figure 3.28
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Figure 3.31b
DNA Replication
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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
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Cell Growth and Reproduction
Cell Division - M Phase (Mitotic)• 2 phases: Mitosis & Cytokinesis• Phase 1: Mitosis – nuclear division
a) prophaseb) metaphasec) Anaphased) telophase
• Phases merge together
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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
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Figure 3.32
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Figure 3.32