cell structure and function
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Cell Structure and Function. Cells. Smallest living unit Most are microscopic. Discovery of Cells. Robert Hooke (mid-1600s) Observed sliver of cork Saw “row of empty boxes” Coined the term cell. Cell theory. (1839)Theodor Schwann & Matthias Schleiden - PowerPoint PPT PresentationTRANSCRIPT
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Cell Structure and Function
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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 Proteins3. Glycoproteins
– Identify cell type4. 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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