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A Tour of the CellLecture 2, Part 1
Fall 2008
Cell Theory
Cells are the basic unit of structure and function
• The lowest level of structure that can perform all activities required for life– Reproduction– Metabolic activity
• Cell Theory:– All organisms are made of cells– All cells arise from other cells
1
How do we study cells?
Fig. 6.2
2
How do we study cells?
Fig. 6.4
Fig. 6.5
Cell Fractionation
3
Size & Function
• Limits to size• Surface area to
volume ratio
Fig. 6.8
4
Prokaryotes & Eukaryotes5
Prokaryotes Eukaryotes
Prokaryotes vs. Eukaryotes
What differences do you see?
6
Eukaryote
Prokaryote
Fig. 6.6
Characteristics of all cells
• Plasma membrane• Cytosol• Chromosomes• Ribosomes
Fig. 6.7
7
Plasma MembranePresent in all cell typesFunction:• Separates the internal from the external
environment• Regulate chemical exchanges within the
environment– Chemical reactions more efficient
• Dynamic selective barrier
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Major differencesProkaryotes• No nucleus
– Nucleoid region
• Simple• No membrane bound
organelles
• Smaller (1-5 nm)• Evolutionarily older
Eukaryotes• Nucleus
– (DNA in a membrane-bound region)
• Complex• Membrane bound
organelles– Organelle – a structure with a
specified function w/i a cell
• Larger (10-100 nm)• Evolutionarily younger
9
Views of Prokaryote Cells10
See Fig. 27.2
The Origin of Eukaryotic Cells
Evolution of the endomembrane system
• All the membrane bound organelles within a cell, except for mitochondria and chloroplasts
• Inward folding of plasma membrane formed nuclear envelope, organelles
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Eukaryotes: Animal & Plant CellsAnimal cell structures:• Plasma membrane• Nucleus• Cytosol • Ribosomes• Endoplasmic reticulum• Golgi apparatus• Mitochondria• Cytoskeleton• Vacuoles• Peroxisome
Not typically found in plants:• Centrosome• Lysosomes• Flagella
See Fig. 6.9 –Animal cell
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Views of Animal Cells13
Cheek cells (400X)
Cardiac muscle cells
Intestinal (smooth) muscle cells
Brain cells (astrocytes)
Eukaryotes: Animal & Plant CellsPlant cell structures:• Plasma membrane• Nucleus• Cytosol • Ribosomes• Endoplasmic reticulum• Golgi apparatus• Mitochondria• Cytoskeleton• Peroxisome
Not found in animals:• Cell Wall w/plasmodesmata• Plastids (Chloroplasts,
Amyloplasts, Chromoplasts)• Central vacuole
Fig. 4.6 –Animal cell
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See Fig. 6.9 – Plant cell
Views of Plant Cells15
Leaf cells
Leaf cells w/chloroplasts
Plant cell
Root cell w/amyloplasts
Leaf epidermal (surface) cells
Cytosol
Cytoplasm• Area between the
nucleus and the plasma membrane
Cytosol• Fluid of the
cytoplasm
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NucleusFunctions• Store genes on chromosomes• Regulate gene expression• Transport regulatory factors and gene
products• Produce messages (mRNA) that code
for proteins• Produce the components of ribosomes• Replication of genetic material
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NucleusNuclear envelope• Double
membrane
Pore complexes• Gatekeepers
Nuclear lamina• Protein filaments• Maintains shape
of nucleus
Fig. 6.10
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Nucleus
Chromosomes• Discrete units of DNA• Chromatin - Association of
DNA molecules and proteins
• One chromatin = one chromosome
Nucleolus• Ball-like mass of fibers &
granules• Produces ribosomal RNA
(rRNA)• Assembles components of
ribosomes
Fig. 6.10
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RibosomesComplex of proteins & rRNAFunction: Protein synthesis• Ribosome parts are made in nucleus by
nucleolus• Parts travel out of nucleus, into cytoplasmTwo types: • Bound ribosome
– Bound to endoplasmic reticulum (ER)– Make proteins for membranes or exportation from cell
• Free ribosomes– make proteins that stay
in cytosol
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Fig. 6.11
DNA Control of the Cell
DNA – Protein production
1. mRNA synthesis
2. mRNA travels to ribosomes
3. Ribosomes use mRNA to synthesize proteins
21
Endomembrane System
Functions: • Manufacturing and distributing cellular products• Detoxification of poisons
Contains:• Nuclear envelope• The endoplasmic reticulum (ER)• The Golgi apparatus• Lysosomes & Vacuoles• Plasma membrane not Endo, but related
Membranes unique in structure & function
Membranes dynamic
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Endoplasmic Reticulum
Function: manufacturing of many cellular products• Large – more than ½ of all membrane in cell• Continuous with nuclear envelope• Cisternae
– Membranous tubules & sacs– Cisternal space
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Fig. 6.12
Endoplasmic Reticulum
Smooth ER• No ribosomes
Functions:• Lipid production
– E.g., steroids, phospholipds
• Metabolism of carbohydrates
• Detoxification of drugs• Calcium ion storage
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Fig. 6.12
Endoplasmic Reticulum
Rough ER• Ribosomes bound to ERFunction:• Produces secretory
proteins– Glycoproteins– Transport vesicles
• Produces membrane proteins
• Makes phospholipids for membrane
25
Fig. 6.12
The Golgi ApparatusFunction:• Receives products from ER• Modifies products• Stores products• Delivers products
– Other parts of cell– Other cells (secretion/exportation)
• Manufactures some macromolecules
26
Fig. 6.13
The Golgi Apparatus
Cis face – receivingTrans face – shipping• Products identified and “tagged”
e.g., phosphate groups added to products
e.g., recognition proteins on transport vesicles
Cisternal maturation model• Dynamic process• Cisturnae move from cis to trans• Products modified as cisturnae
move
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Fig. 6.13
LysosomesLysosome• Membrane bound sac of hydrolytic
enzymes• Keeps enzymes from rest of cell• Higher pH in lysosome optimal for
lysosomal enzymesProduction:• ER makes hydrolytic enzymes &
lysosomal membranes• Transported to GA for processing• Some bud directly from GA
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Fig. 6.14
LysosomesFunction:• Nutrient digestion
– Part of phagocytosis• Destroy harmful bacteria• Recycle damaged organelles
– Autophagy• Embryonic development
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Fig. 6.14
Vacuoles: Animal Cells
Membrane bound sacs that form (“bud”) from the ER, Golgi apparatus or plasma membrane.
Function:• Contain material• Food vacuole• Water pumps• Contractile vacuoles
30
Central Vacuole: Plant CellsCentral Vacuole• Large – can occupy 90% volume
of cell• Coalescence of many smaller
vacuoles from ER, GA• Single membrane• Water, salts, other molecules
inside• Few enzymesFunction• Storage• Growth of cell• Protection• Helps concentrate enzymes in
rest of cell
Fig 6.15
31
Endomembrane System32
Fig. 6.16
MitochondriaFunction: • Cellular respiration
– Converts carbon compounds into ATP– ATP (adenosine triphosphate) –energy for cellular work
• Found in most eukaryotic cells• Not part of endomembrane systems
• Contains its own DNA
• Has a double membrane– Membrane proteins
made by free ribosomes
• Cristae – infoldings of inner membrane
33
Fig. 6.17
ChloroplastsFunction: Photosynthesis• Creates carbon compounds using energy from the sun• Contain chlorophyll a & other pigments• Not part of endomembrane systems• Contains its own DNA• Has a double membrane• Thylakoids – flattened interconnected stacks• Granum – stacks of thylakoids• Stroma – fluid outside thylakoids
• Intermembrane space
• Stroma
• Thylakoid space
34
Fig. 6.18
Other PlastidsPlastid• Organelle with 2 membranes• Has its own DNA & RNA• Found in plants, some protists
Three main types• Chloroplasts• Chromoplasts
– Function: Stores lipid soluble pigments – Usually colored
• Amyloplasts– Function: Stores starch
35
Peroxisomes• Specialized membrane compartment• Single membraneFunction:• Contains enzymes that transfer hydrogen to
oxygen, producing hydrogen peroxide• Breaks down fatty acids• Detoxify
Composed of:• Proteins from cytosol• Lipids from ER• Lipids synthesized in
Peroxisome
Fig. 6.19
36