cell theory and structure ppt
TRANSCRIPT
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Cell Structure and Function
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Agre and cells
in the news
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Cells
• Smallest living unit
• Most are microscopic
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Discovery of Cells
• Robert Hooke (mid-
1600s)
– Observed sliver of cork
– Saw “row of empty boxes”
– Coined the term cell
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Cell theory
• (1839)Theodor Schwann & Matthias Schleiden
“ all living things are made of cells”
• (50 yrs. later) Rudolf Virchow
“all cells come from cells”
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Principles of Cell Theory
• All living things are made of cells
• Smallest living unit of structure and
function of all organisms is the cell
• All cells arise from preexisting cells
(this principle discarded the idea of
spontaneous generation)
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Cell Size
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Cells Have Large Surface
Area-to-Volume Ratio
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Characteristics of All Cells
• A surrounding membrane
• Protoplasm – cell contents in thick fluid
• Organelles – structures for cell
function
• Control center with DNA
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Cell Types
• Prokaryotic
• Eukaryotic
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Prokaryotic Cells
• First cell type on earth
• Cell type of Bacteria and Archaea
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Prokaryotic Cells
• No membrane bound nucleus
• Nucleoid = region of DNA
concentration
• Organelles not bound by membranes
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Eukaryotic Cells• Nucleus bound by
membrane
• Include fungi, protists, plant,
and animal cells
• Possess many organelles
Protozoan
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Representative Animal Cell
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Representative Plant Cell
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Organelles
• Cellular machinery
• Two general kinds
– Derived from membranes
– Bacteria-like organelles
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Bacteria-Like Organelles
• Derived from symbiotic bacteria
• Ancient association
• Endosymbiotic theory
– Evolution of modern cells from
cells & symbiotic bacteria
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Plasma Membrane
• Contains cell contents
• Double layer of phospholipids & proteins
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Phospholipids
• Polar
– Hydrophylic head
– Hydrophobic tail
• Interacts with water
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Movement Across the Plasma Membrane
• A few molecules move freely
– Water, Carbon dioxide, Ammonia, Oxygen
• Carrier proteins transport some molecules
– Proteins embedded in lipid bilayer
– Fluid mosaic model – describes fluid nature of
a lipid bilayer with proteins
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Membrane Proteins
1. Channels or transporters
– Move molecules in one direction
2. Receptors
– Recognize certain chemicals
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Membrane Proteins
3. Glycoproteins
– Identify cell type
4. Enzymes
– Catalyze production of substances
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Cell Walls
• Found in plants, fungi, & many protists
• Surrounds plasma membrane
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Cell Wall Differences
• Plants – mostly cellulose
• Fungi – contain chitin
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Cytoplasm• Viscous fluid containing organelles
• components of cytoplasm– Interconnected filaments & fibers – Fluid = cytosol– Organelles (not nucleus)– storage substances
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Cytoskeleton• Filaments & fibers
• Made of 3 fiber types– Microfilaments
– Microtubules
– Intermediate filaments
• 3 functions:– mechanical support
– anchor organelles
– help move substances
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A = actin, IF = intermediate filament, MT = microtubule
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Cilia & Flagella
• Provide motility
• Cilia – Short
– Used to move substances outside human cells
• Flagella – Whip-like extensions
– Found on sperm cells
• Basal bodies like centrioles
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Cilia & Flagella Structure
• Bundles of microtubules
• With plasma membrane
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Centrioles
• Pairs of microtubular structures
• Play a role in cell division
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Membranous Organelles
• Functional components within cytoplasm
• Bound by membranes
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Nucleus
• Control center of cell
• Double membrane
• Contains
– Chromosomes
– Nucleolus
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Nuclear Envelope
• Separates nucleus from rest of cell
• Double membrane
• Has pores
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DNA
• Hereditary material
• Chromosomes
– DNA
– Protiens
– Form for cell division
• Chromatin
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Nucleolus
• Most cells have 2 or more
• Directs synthesis of RNA
• Forms ribosomes
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Endoplasmic Reticulum
• Helps move substances within cells
• Network of interconnected membranes
• Two types
– Rough endoplasmic reticulum
– Smooth endoplasmic reticulum
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Rough Endoplasmic Reticulum
• Ribosomes attached to surface
– Manufacture protiens
– Not all ribosomes attached to rough ER
• May modify proteins from ribosomes
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Smooth Endoplasmic Reticulum
• No attached ribosomes
• Has enzymes that help build molecules
– Carbohydrates
– Lipids
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Golgi Apparatus
• Involved in synthesis of plant cell wall
• Packaging & shipping station of cell
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Golgi Apparatus Function
1. Molecules come in vesicles
2. Vesicles fuse with Golgi membrane
3. Molecules may be modified by Golgi
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Golgi Apparatus Function
(Continued)
4. Molecules pinched-off in separate vesicle
5. Vesicle leaves Golgi apparatus
6. Vesicles may combine with plasma
membrane to secrete contents
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Lysosomes
• Contain digestive enzymes
• Functions – Aid in cell renewal
– Break down old cell parts
– Digests invaders
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Vacuoles
• Membrane bound storage sacs
• More common in plants than animals
• Contents
– Water
– Food
– wastes
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Bacteria-Like Organelles
• Release & store energy
• Types
– Mitochondria
(release energy)
– Chloroplasts
(store energy)
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Mitochondria
• Have their own DNA
• Bound by double membrane
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Mitochondria
• Break down fuel molecules (cellular
respiration)
– Glucose
– Fatty acids
• Release energy
– ATP
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Chloroplasts
• Derived form photosynthetic bacteria
• Solar energy capturing organelle
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Photosynthesis
• Takes place in the chloroplast
• Makes cellular food – glucose
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Review of Eukaryotic Cells
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Review of Eukaryotic Cells
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Molecule Movement & Cells
• Passive Transport
• Active Transport
• Endocytosis
(phagocytosis & pinocytosis)
• Exocytosis
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Passive Transport
• No energy required
• Move due to gradient
– differences in concentration, pressure, charge
• Move to equalize gradient
– High moves toward low
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Types of Passive Transport
1. Diffusion
2. Osmosis
3. Facilitated diffusion
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Diffusion
• Molecules move to equalize concentration
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Osmosis
• Special form of diffusion
• Fluid flows from lower solute
concentration
• Often involves movement of water
– Into cell
– Out of cell
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Solution Differences & Cells• solvent + solute = solution
• Hypotonic
– Solutes in cell more than outside
– Outside solvent will flow into cell
• Isotonic
– Solutes equal inside & out of cell
• Hypertonic
– Solutes greater outside cell
– Fluid will flow out of cell
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Facilitated Diffusion
• Differentially permeable membrane
• Channels (are specific) help molecule or ions enter or leave the cell
• Channels usually are transport proteins
(aquaporins facilitate the movement of water)
• No energy is used
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Process of Facilitated Transport
• Protein binds with molecule
• Shape of protein changes
• Molecule moves across membrane
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Active Transport
• Molecular movement
• Requires energy (against gradient)
• Example is sodium-potassium pump
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Endocytosis
• Movement of large material
– Particles
– Organisms
– Large molecules
• Movement is into cells
• Types of endocytosis
– bulk-phase (nonspecific)
– receptor-mediated (specific)
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Process of Endocytosis
• Plasma membrane surrounds
material
• Edges of membrane meet
• Membranes fuse to form vesicle
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Forms of Endocytosis
• Phagocytosis – cell eating
• Pinocytosis – cell drinking
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Exocytosis
• Reverse of endocytosis
• Cell discharges material
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Exocytosis
• Vesicle moves to cell
surface
• Membrane of vesicle fuses
• Materials expelled
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End Chapter 5