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Transcript of Chapter 6:
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Chapter 6:A Tour of the Cell
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Key Concepts6.1 To study cells, biologists use microscopes and the tools of
biochemistry.6.2 Eukaryotic cells have internal membranes that
compartmentalize their functions, and membrane bound organelles.
6.3 The Eukaryotic cell’s genetic instructions are found in the nucleus and carried out by the ribosomes.
6.4 The endomembrane system (ER) regulates protein traffic and performs metabolic function of the cell.
6.5 Mitochondria and chloroplasts change energy from one form to another.
6.6 The cytoskeleton is a network of fibers that organizes structures and activities inside the cell.
6.7 Extracellular components (outside the cell) and connections between cells (desmosomes, gap junctions, tight junctions, and plasmodesmata) help coordinate cellular activities.
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Microscopy• The study of cells progressed with the invention
of the microscope in 1590, and their improvement in the 17th century.
• Light Microscope- earliest form, uses beam of light passed thru specimen and then thru glass lenses.
• Electron Microscope- (1950’s) focuses a beam of electrons thru a specimen, or onto its surface. Highest magnification and resolution.
• Transmission EM- (TEM) used to study the internal structures of a cell.
• Scanning EM- (SEM) used to study the surface of a specimen.
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Light Microscope
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TEM
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SEM
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Fig. 6-4
(a) Scanning electron microscopy (SEM)
TECHNIQUE RESULTS
(b) Transmission electron microscopy (TEM)
Cilia
Longitudinalsection ofcilium
Cross sectionof cilium
1 µm
1 µm
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Parameters in Microscopy
• Magnification- the ratio of an objects image size to its real size
• Resolution- a measure of the clarity of an object
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Staining Technique• The addition of certain chemical
pigments allows for increased contrast between cell structures.
• Makes structures easier to distinguish and study.
• Examples- bromthymol blue, methylene blue, crystal violet, safranin, malachite green, eosin
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Fig. 6-3ab
(a) Brightfield (unstained specimen)
(b) Brightfield (stained specimen)
TECHNIQUE RESULTS
50 µm
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Cell Fractionation•The goal of cell fractionation is to take cells apart and separate major organelles from one another.
•The instrument used is a Centrifuge.
•The centrifuge spins test tubes holding mixtures of disrupted cells at high speeds.
•Uses centrifugal force.
•Enable scientists to prepare specific components of cells in bulk quantities to study their composition and structure.
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Fig. 6-5
Homogenization
TECHNIQUE
HomogenateTissuecells
1,000 g(1,000 times theforce of gravity)
10 min Differential centrifugation
Supernatant pouredinto next tube
20,000 g20 min
80,000 g60 minPellet rich in
nuclei andcellular debris
Pellet rich inmitochondria(and chloro-plasts if cellsare from a plant)
Pellet rich in“microsomes”(pieces of plasmamembranes andcells’ internalmembranes)
150,000 g3 hr
Pellet rich inribosomes
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Fig. 6-5b
1,000 g(1,000 times the force of gravity)
10 min
Supernatant poured into next tube
20,000 g20 min
80,000 g60 min
150,000 g3 hr
Pellet rich in nuclei and cellular debris
Pellet rich in mitochondria (and chloro-plasts if cellsare from a plant)
Pellet rich in “microsomes” (pieces of plasmamembranes and cells’ internal membranes) Pellet rich in
ribosomes
TECHNIQUE (cont.)
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Cells of Living Things
ProkaryoticUsually single celled.
Can form colonies.No nucleus or
membrane-bound organelles.
Genetic material localized (nucleoid)
Ex. Bacteria
Eukaryotic
Kingdoms: Protista, Fungi, Plants, Animals.
Nuclear membrane encloses DNA.
Organelles that have membrane.
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• Surface to Volume Ratio limits size of cells. Large cells require more raw materials.
• V = cm3 S.A. = cm2 Restrictions on size and shape
• Cells compartmentalize to increase SA/Vol, specialize rxn within, localize reactions where needed.
Cell Size and Shape
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Basic Aspects of Cell Structure and Function
• Plasma membrane• Lipid bilayer
• Proteins
– Channels, transport, pumps, receptors
• DNA-containing region
• Cytoplasm
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Prokaryotic Cells•Highly disorganized
•No membrane bound organelles
•Have a nucleoid (like a nucleus)
•Nucleoid contains genetic material (DNA)
•Have a plasma membrane
•Have cytosol inside the cell in which the organelles are found
•Have ribosomes
•Smaller than Eukaryotic cells
•Examples- Bacteria, Archae
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Typical Prokaryote (Bacterial) Cell
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Fig. 6-6
Fimbriae
Nucleoid
Ribosomes
Plasma membrane
Cell wall
Capsule
Flagella
Bacterialchromosome
(a) A typical rod-shaped bacterium
(b) A thin section through the bacterium Bacillus coagulans (TEM)
0.5 µm
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Eukaryotic Cells• Have membrane bound organelles
• Are very organized
• Have a nucleus (DNA)
• Surrounded by either a cell wall or a plasma membrane
• Examples- plants, animals, fungi, protists (amoeba, paramecium,euglena)
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Defining Structures of Eukaryotic Cells
A Plant Cell An Animal Cell
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Plant vs. Animal Cell
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Fig. 6-9a
ENDOPLASMIC RETICULUM (ER)
Smooth ERRough ERFlagellum
Centrosome
CYTOSKELETON:
Microfilaments
Intermediatefilaments
Microtubules
Microvilli
Peroxisome
MitochondrionLysosome
Golgiapparatus
Ribosomes
Plasma membrane
Nuclearenvelope
Nucleolus
Chromatin
NUCLEUS
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Fig. 6-9b
NUCLEUS
Nuclear envelopeNucleolus
Chromatin
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
Ribosomes
Central vacuole
Microfilaments
Intermediate filaments
Microtubules
CYTO-SKELETON
Chloroplast
PlasmodesmataWall of adjacent cell
Cell wall
Plasma membrane
Peroxisome
Mitochondrion
Golgiapparatus
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Structures in the Cell• The tiny organs found inside the cell are
called organelles.
• Each of these structures performs a specific function that allows the cell to survive.
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Major Cellular Components • Nucleus
• Ribosomes
• Endoplasmic reticulum– Smooth and Rough
• Golgi body
• Various vesicles
• Mitochondria
• Cytoskeleton
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Structures found in both Plant and Animal Cells
1. Plasma membrane2. Nucleus3. Chromatin4. Nucleolus5. Ribosomes6. Endoplasmic Reticulum7. Golgi Apparatus8. Mitochondria9. Peroxisomes10. Cytoskeleton11. Centrosomes
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Structures Associated with Animal Cells
1. Lysosomes
2. Centrioles
3. Flagella
4. Extracellular matrix
5. Tight Junctions
6. Desmosomes
7. Gap Junctions
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Structures Associated with Plant Cells
1. Central Vacuoles
2. Chloroplasts
3. Cell Wall
4. Plasmodesmata
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Components of the Nucleus
• Nuclear envelope - Surrounds nucleus
• Chromosome - One DNA molecule and associated
proteins. Organized DNA.
• Chromatin - DNA molecules and histone proteins.
Condenses to form DNA.
• Nucleolus - RNA and proteins that will be assembled
into ribosomal subunits. Cells may have more than
one.
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The Nuclear Envelope• Double - membrane system
– Two lipid bilayers. 20-40 nm thick.
– Surrounds chromatin/nucleoplasm
• Pores allow exchange. Composed of about 100 proteins.
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Ribosomes• Smallest, most numerous
organelle.• Composed of rRNA and proteins.
Synthesized by nucleolus. • Large and small subunits.• Found free and bound to E.R.
Differ only in what they are making.
• Catalyzes formation of peptide bonds.
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The Endomembrane System
• Organelles in which lipids are assembled and
proteins are produced and modified
• Are in direct contact or send vesicles (membrane-
bound sacs).
• Occupy ½ of cell volume.
• Nuclear envelope, endoplasmic reticulum, golgi
apparatus, lysosomes, vacuole
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The Endoplasmic Reticulum
• Network of tubes and sacs that are continuous with nuclear membrane. Most extensive mem. Sys.
• Rough (ribosome studded) and Smooth.– Rough: production of secretory proteins. Signal sequence
on polypeptide instructs ribosome to attach to ER.
– Smooth: Lipids production, CH2O metabolism, storage of
ions, detoxification of drugs/alcohol
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Fig. 6-11
Cytosol
Endoplasmic reticulum (ER)
Free ribosomes
Bound ribosomes
Large subunit
Small subunit
Diagram of a ribosomeTEM showing ER and ribosomes
0.5 µm
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Fig. 6-10
NucleolusNucleus
Rough ER
Nuclear lamina (TEM)
Close-up of nuclear envelope
1 µm
1 µm
0.25 µm
Ribosome
Pore complex
Nuclear pore
Outer membraneInner membraneNuclear envelope:
Chromatin
Surface ofnuclear envelope
Pore complexes (TEM)
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Fig. 6-12Smooth ER
Rough ER Nuclear envelope
Transitional ER
Rough ERSmooth ERTransport vesicle
RibosomesCisternaeER lumen
200 nm
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Fig. 6-16-1
Smooth ER
Nucleus
Rough ER
Plasma membrane
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Fig. 6-16-2
Smooth ER
Nucleus
Rough ER
Plasma membrane
cis Golgi
trans Golgi
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Fig. 6-16-3
Smooth ER
Nucleus
Rough ER
Plasma membrane
cis Golgi
trans Golgi
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Golgi Bodies
• Enzymatic finishes on proteins
and lipids, and packaging in
vesicles.
• Polarity of cisternae.
• Forms glycolipids,
glycoproteins,
• Products of Golgi leave as
vessicles. From one cisternae
to another or out of cell.
Cis (forming) face
Trans (exit) face
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Lysosomes
• Membrane-bound organelle that contains hydrolytic enzymes responsible for the digestion of macromolecules, autolysis, intracellular digestion.
• Dead cells no longer able to maintain H+ gradient (use H+ pump) so organelle breaks down releasing contents.
• Made by ER and Golgi.
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Lysosome Function and Production
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From Production to Export
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Vacuoles
• Storage of water or ions, pigments, hold food, pump out water.
• Are larger than vesicles formed from golgi/E.R.
• In plants is enclosed by Tonoplast (membrane) and provides cell with hydrostatic pressure
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Peroxisomes• Contain enzymes
(catalase) that break down H2O2 formed during metabolism of alcohols, F.A.’s.
• Specialized forms [glyoxysome] found in seeds and function during germination.
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Mitochondria
• Production of ATP
• Double-membrane system– Two distinct compartments
• Have their own DNA. Maternal in
origin.
• Divide on their own, independent
of cell.
• Have ribosomes, produce
enzymes necessary for ATP
production.
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Chloroplast
• Found in photosynthetic eukaryotes
• Two outer membranes
• Semifluid stroma; site of carbon fixation.
• Inner thylakoid membrane system; converts l.e. into c.e.
• Photosynthetic pigments found in other plastids.
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Cytoskeleton
• Protein fibers that support and give shape to a cell, involved in organelle movement throughout cell, chromosome movement during cell division and large cell movements (cell motility and cytokinesis)
• 3 Groups of Fibers classified according to size:– Mircrotubules (thickest)– Intermediated filaments (middle sized)– Microfilaments (thinnest)
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Components of the Cytoskeleton
• Microtubules and Tubulin subunits; form hollow tube.
– Provide framework for cell, organized by
centrosome from which they usu. originate.
– “Rail” system for organelle transport.
• Component of Centriole.
– Replicated prior to mitosis.
• Form Cilia and Flagella.
– 9 + 2 arrangement (eukaryotic characteristic)
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Fig. 6-UN3
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Cilia and Flagella and the Structural Basis of Cell Motility
• Surrounded by plasma membrane.
• Motor proteins (dynein) on microtubules use ATP to change shape and “ratchet” past one another.
• Movement causes bending of cilia/flagella.
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Components of the Cytoskeleton
• Microfilaments (aka actin filaments)
– Solid “rope”of two actin proteins
– Thinner and more flexible than microtubules
– Principle component of muscle fibers.
– Provide mechanism to support cell shape. Found just inside the c. mem.
– Enable cell movement, phagocytosis and cytokinesis.
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Components of the Cytoskeleton
• Intermediate Filaments
– Tough and durable; made of keratin.
– Mechanically strengthen/reinforce cells or cell parts that are under stresses.
• Provide structure to long cells.
• Found in desmosomes.
• Give nucleus shape (nuclear lamina)
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Cell-to Cell Junctions
• Plants
– Plasmodesmata
• Perforations in cell wall that allow passage for water/solutes to adjacent
cells.
• Animals
– Tight Junctions. Prevent leakage between cells (ie. Stomach)
– Desmosomes. Mechanically attach cells to each other. Serve as
anchoring sites for inter. filaments in cell.
– Gap Junctions. Analogous to plasmodesma. Fxn as comm.
Pathway between cells. Cardiac muscle, nerves.
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Intracellular Junctions
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Fig. 6-32
Tight junction
0.5 µm
1 µmDesmosome
Gap junction
Extracellularmatrix
0.1 µm
Plasma membranesof adjacent cells
Spacebetweencells
Gapjunctions
Desmosome
Intermediatefilaments
Tight junction
Tight junctions preventfluid from movingacross a layer of cells
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Fig. 6-32a Tight junctions prevent fluid from moving across a layer of cells
Tight junction
Intermediate filaments
Desmosome
Gap junctions
Extracellular matrixSpace
between cells
Plasma membranes of adjacent cells
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Fig. 6-32b
Tight junction
0.5 µm
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Fig. 6-32c
Desmosome1 µm
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Fig. 6-32d
Gap junction
0.1 µm
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Plant Cell Walls
• Protect plants, allow for
shape and prevent excess
H2O uptake.
• Composed of cellulose
• Plasmodesmata connect
neighboring cells.
• Secondary cell wall inside of
primary wall. Forms wood
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Plant Cell Wall
• Cell secretions form pectin (polysaccharide glue) which acts as adhesive. Laid down in middle lamella to hold cells together.
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Fig. 6-31
Interior of cell
Interior of cell
0.5 µm Plasmodesmata Plasma membranes
Cell walls
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Plasma Membrane• Forms the boundary for a cell• Selectively permeable• Made up of phospholipids• Fluid mosaic of lipids and proteins• Integral proteins are embedded in
the membrane• Peripheral proteins are loosely bound to the
membrane’s surface• Carbohydrates on the membrane’s surface
are crucial in cell to cell recognition• Found in both plant and animal cells
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Fig. 6-7TEM of a plasmamembrane
(a)
(b) Structure of the plasma membrane
Outside of cell
Inside ofcell 0.1 µm
Hydrophilicregion
Hydrophobicregion
Hydrophilicregion Phospholipid Proteins
Carbohydrate side chain
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Fig. 6-30
EXTRACELLULAR FLUIDCollagen
Fibronectin
Plasmamembrane
Micro-filaments
CYTOPLASM
Integrins
Proteoglycancomplex
Polysaccharidemolecule
Carbo-hydrates
Coreprotein
Proteoglycanmolecule
Proteoglycan complex
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Fig. 6-30a
Collagen
Fibronectin
Plasma membrane
Proteoglycan complex
Integrins
CYTOPLASMMicro-filaments
EXTRACELLULAR FLUID
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Extracellular matrix (ECM)
• Intricate network of proteins and polysaccharides that are organized into a meshwork on the outside of cells.
• Large polysaccharides and proteoglygans form a “gel-like” material that resist compression.
• Proteins like collagen (most abundant protein in animals as part of
bone and skin) and elastin (stretch and recoil) provide structure and strength.
• Adhesive-like proteins (fibronectins and laminin) help cells attach to the appropriate part of the ECM.
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Extracellular matrix (ECM)
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Table 6-1
10 µm 10 µm 10 µm
Column of tubulin dimers
Tubulin dimer
Actin subunit
25 nm
7 nm
Keratin proteins
Fibrous subunit (keratins coiled together)
8–12 nm
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Table 6-1a10 µm
Column of tubulin dimers
Tubulin dimer
25 nm
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Table 6-1b
Actin subunit
10 µm
7 nm
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Table 6-1c
5 µm
Keratin proteins
Fibrous subunit (keratinscoiled together)
8–12 nm
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Fig. 6-UN1Cell Component Structure Function
Houses chromosomes, made ofchromatin (DNA, the geneticmaterial, and proteins); containsnucleoli, where ribosomalsubunits are made. Poresregulate entry and exit ofmaterials.
Nucleus
(ER)
Concept 6.3 The eukaryotic cell’s geneticinstructions are housed inthe nucleus and carried outby the ribosomes
Ribosome
Concept 6.4 Endoplasmic reticulum The endomembrane systemregulates protein traffic andperforms metabolic functionsin the cell
(Nuclearenvelope)
Concept 6.5 Mitochondria and chloro-plasts change energy fromone form to another
Golgi apparatus
Lysosome
Vacuole
Mitochondrion
Chloroplast
Peroxisome
Two subunits made of ribo-somal RNA and proteins; can befree in cytosol or bound to ER
Extensive network ofmembrane-bound tubules andsacs; membrane separateslumen from cytosol;continuous withthe nuclear envelope.
Membranous sac of hydrolyticenzymes (in animal cells)
Large membrane-boundedvesicle in plants
Bounded by doublemembrane;inner membrane hasinfoldings (cristae)
Typically two membranesaround fluid stroma, whichcontains membranous thylakoidsstacked into grana (in plants)
Specialized metaboliccompartment bounded by asingle membrane
Protein synthesis
Smooth ER: synthesis oflipids, metabolism of carbohy-drates, Ca2+ storage, detoxifica-tion of drugs and poisons
Rough ER: Aids in synthesis ofsecretory and other proteins frombound ribosomes; addscarbohydrates to glycoproteins;produces new membrane
Modification of proteins, carbo-hydrates on proteins, and phos-pholipids; synthesis of manypolysaccharides; sorting of Golgiproducts, which are then released in vesicles.
Breakdown of ingested substances,cell macromolecules, and damagedorganelles for recycling
Digestion, storage, wastedisposal, water balance, cellgrowth, and protection
Cellular respiration
Photosynthesis
Contains enzymes that transferhydrogen to water, producinghydrogen peroxide (H2O2) as aby-product, which is convertedto water by other enzymesin the peroxisome
Stacks of flattenedmembranoussacs; has polarity(cis and transfaces)
Surrounded by nuclearenvelope (double membrane)perforated by nuclear pores.The nuclear envelope iscontinuous with theendoplasmic reticulum (ER).
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Fig. 6-UN1a
Cell Component Structure Function
Concept 6.3 The eukaryotic cell’s geneticinstructions are housed inthe nucleus and carried outby the ribosomes
Nucleus Surrounded by nuclearenvelope (double membrane)perforated by nuclear pores.The nuclear envelope iscontinuous with theendoplasmic reticulum (ER).
(ER)
Houses chromosomes, made ofchromatin (DNA, the geneticmaterial, and proteins); containsnucleoli, where ribosomalsubunits are made. Poresregulate entry and exit osmaterials.
Ribosome Two subunits made of ribo-somal RNA and proteins; can befree in cytosol or bound to ER
Protein synthesis
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Fig. 6-UN1b
Cell Component Structure Function
Concept 6.4 The endomembrane systemregulates protein traffic andperforms metabolic functionsin the cell
Endoplasmic reticulum
(Nuclearenvelope)
Golgi apparatus
Lysosome
Vacuole Large membrane-boundedvesicle in plants
Membranous sac of hydrolyticenzymes (in animal cells)
Stacks of flattenedmembranoussacs; has polarity(cis and transfaces)
Extensive network ofmembrane-bound tubules andsacs; membrane separateslumen from cytosol;continuous withthe nuclear envelope.
Smooth ER: synthesis oflipids, metabolism of carbohy-drates, Ca2+ storage, detoxifica-tion of drugs and poisons
Rough ER: Aids in sythesis ofsecretory and other proteinsfrom bound ribosomes; addscarbohydrates to glycoproteins;produces new membrane
Modification of proteins, carbo-hydrates on proteins, and phos-pholipids; synthesis of manypolysaccharides; sorting ofGolgi products, which are thenreleased in vesicles.
Breakdown of ingested sub-stances cell macromolecules, and damaged organelles for recycling
Digestion, storage, wastedisposal, water balance, cellgrowth, and protection
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Fig. 6-UN1c
Cell Component
Concept 6.5Mitochondria and chloro-plasts change energy fromone form to another
Mitochondrion
Chloroplast
Peroxisome
Structure Function
Bounded by doublemembrane;inner membrane hasinfoldings (cristae)
Typically two membranesaround fluid stroma, whichcontains membranous thylakoidsstacked into grana (in plants)
Specialized metaboliccompartment bounded by asingle membrane
Cellular respiration
Photosynthesis
Contains enzymes that transferhydrogen to water, producinghydrogen peroxide (H2O2) as aby-product, which is convertedto water by other enzymesin the peroxisome