1. 4
A Tour of the Cell

2. Overview: The Fundamental Units of Life
All living cells have 4 basic features:
Cytoplasm (cytosol): gel-like substance inside cells
Plasma membrane (PM): also called cell membrane
Outermost surface of cell
Surrounds cell from external environment
Chromosome(s): contains genes/DNA; blueprint of life
Ribosomes: site of protein synthesis
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3. 2 Major Kinds of Cells Prokaryotic Cells Eukaryotic Cells
Only in Domains Archae and Bacteria (all bacteria)
No nucleus: DNA in nucleoid region
No membrane-bound organelles
All have cell walls
Eukaryotic Cells
Domain Eukarya; Protista, Plantae, Fungi, Animalia
Has a nucleus with nuclear membrane
DNA in nucleus
Contains membrane-bound organelles
Plant and fungal eukaryotes: have a cell wall
Animal eukaryotes: no cell walls
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4. Concept 4.1: Biologists use microscopes and the tools of biochemistry to study cells
In a light microscope (LM), visible light is passed through a specimen and then through glass lenses
Lenses refract (bend) the light, so that the image is magnified
LMs can magnify effectively to about 1,000 times the size of the actual specimen
Most subcellular structures, including organelles (membrane-enclosed compartments), are too small to be resolved by light microscopy
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5. 10 m 1 m 0.1 m 1 cm 1 mm 100 mm 10 mm 1 mm 100 nm 10 nm 1 nm 0.1 nm
Figure 4.2
10 m
Human height
1 m
Length of some
nerve and
muscle cells
0.1 m
Chicken egg
Unaided eye
1 cm
Frog egg
1 mm
Human egg
100 mm
Most plant and
animal cells LM
10 mm
Nucleus
Most bacteria
1 mm
Mitochondrion EM
Figure 4.2 The size range of cells
100 nm
Smallest bacteria
Super-
resolution
microscopy
Viruses
Ribosomes
10 nm
Proteins
Lipids
1 nm
Small molecules
0.1 nm
Atoms
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6. Electron Microscopes: Used to study Subcellular Organelles
2 basic types of electron microscopes (EMs):
Scanning electron microscopes (SEMs) :focus a beam of electrons onto the surface of a specimen, producing images that look three-dimensional
Transmission electron microscopes (TEMs) focus a beam of electrons through a specimen
TEM is used mainly to study the internal structure of cells
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7. Electron Microscopy (EM)
Figure 4.3
Light Microscopy (LM)
50 mm
Brightfield
(unstained specimen)
Brightfield
(stained specimen)
Phase-contrast
Differential-interference
contrast (Nomarski)
50 mm
10 mm
Fluorescence
Confocal (without
technique)
Confocal (with technique)
Electron Microscopy (EM)
Longitudinal section
of cilium
Cross section
of cilium
Figure 4.3 Exploring microscopy
Cilia
2 mm
Scanning electron
microscopy (SEM)
Transmission electron
microscopy (TEM)
2 mm
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8. Plasma Membrane Found in all cells Bilayer of phospholipids
Hydrophilic “heads” turn outward
Hydrophobic “tails” face inward
Proteins embedded in PL bilayer
Surrounds cell; controls chemical traffic; selectively permeable
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9. (a) TEM of a plasma membrane
Figure 4.5
Outside of cell
(a) TEM of a plasma membrane
Inside of cell
0.1 mm
Carbohydrate side chains
Hydrophilic
region
Figure 4.5 The plasma membrane
Hydrophobic
region
Hydrophilic
region
Phospholipid
Proteins
(b) Structure of the plasma membrane
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10. A thin section through the bacterium Corynebacterium
Figure 4.4
Fimbriae
Nucleoid
Ribosomes
Plasma membrane
Bacterial
chromosome
Cell wall
Capsule
0.5 mm
Flagella
Figure 4.4 A prokaryotic cell
(a)
A typical rod-shaped
bacterium
(b)
A thin section through the
bacterium Corynebacterium
diphtheriae (colorized TEM)
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11. Animation: Tour of an Animal Cell
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12. Animation: Tour of a Plant Cell
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13. ENDOPLASMIC RETICULUM (ER) Nuclear envelope Smooth ER NUCLEUS
Figure 4.7-1
ENDOPLASMIC RETICULUM (ER)
Nuclear
envelope
Smooth ER
NUCLEUS
Nucleolus
Flagellum
Rough ER
Chromatin
Centrosome
Plasma
membrane
CYTOSKELETON:
Microfilaments
Intermediate
filaments
Microtubules
Ribosomes
(small brown
dots)
Microvilli
Figure Exploring eukaryotic cells (part 1: animal cell cutaway)
Golgi apparatus
Peroxisome
Lysosome
Mitochondrion
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14. Ribosomes (small brown dots)
Figure 4.7-2
Nuclear envelope
Rough endoplasmic
reticulum
Nucleolus
Smooth endoplasmic
reticulum
Chromatin
NUCLEUS
Ribosomes (small brown
dots)
Golgi
apparatus
Central vacuole
Microfilaments
CYTO-
SKELETON
Microtubules
Figure Exploring eukaryotic cells (part 2: plant cell cutaway)
Mitochondrion
Peroxisome
Plasma membrane
Chloroplast
Cell wall
Plasmodesmata
Wall of adjacent cell
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15. The Nucleus: Information Central
Found in all eukaryotes; largest organelles in animal eukaryotes
Contains cell’s hereditary DNA
DNA organized into linear “sticks” called chromosomes;
Each chromosome is one long DNA molecule associated with histone proteins
Segments are called genes
Enclosed by nuclear envelope
Also a PL bilayer that surrounds nucleus, separating it from cytoplasm
Has pores to let molecules out of nucleus, especially mRNA
Nucleolus: located within the nucleus
the site of ribosomal RNA (rRNA) synthesis (which makes up ribosomes)
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16. Nucleus 1 mm Nucleus Nucleolus Chromatin Nuclear envelope:
Figure 4.8
Nucleus
1 mm
Nucleus
Nucleolus
Chromatin
Nuclear envelope:
Inner membrane
Outer membrane
Nuclear pore
Rough ER
Pore
complex
Surface of nuclear
envelope (TEM)
Ribosome
Close-up
of nuclear
envelope
Chromatin
Figure 4.8 The nucleus and its envelope
0.25 mm
0.5 mm
Pore complexes (TEM)
Nuclear lamina (TEM)
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17. Ribosomes: Protein Factories
Found in all cells
Complexes of rRNA and protein
Made in nucleolus
Ribosomes carry out protein synthesis in 2 locations:
In the cytoplasm: called free ribosomes
Make proteins for use in cytoplasm
Attached to endoplasmic reticulum (RER); called bound ribosomes
Make proteins for use in membrane or export
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18. Computer model of a ribosome
Figure 4.9
Free ribosomes
in cytosol
0.25 mm
Ribosomes ER
Endoplasmic
reticulum (ER)
Ribosomes bound
to ER
Large
subunit
Small
subunit
TEM showing ER and
ribosomes
Diagram of a ribosome
Computer model
of a ribosome
Figure 4.9 Ribosomes
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19. Concept 4.4: The endomembrane system regulates protein traffic and performs metabolic functions in the cell
Components of the endomembrane system:
Nuclear envelope
Endoplasmic reticulum
Golgi apparatus
Lysosomes
Vacuoles
Plasma membrane
These components are either continuous or connected through transfer by vesicles
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20. Nucleus Rough ER Smooth ER cis Golgi Plasma membrane trans Golgi
Figure 4.15
Nucleus
Rough ER
Smooth ER
cis Golgi
Figure 4.15 Review: relationships among organelles of the endomembrane system
Plasma
membrane
trans Golgi
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21. The Endoplasmic Reticulum: Biosynthetic Factory
Found in all eukaryotes
ER membrane is continuous with the nuclear envelope
There are 2 regions of ER
Smooth ER (SER): lacks ribosomes
Makes lipids, PL, steroids
Carbohydrate metabolism
Detoxifies drugs and poisons
Stores calcium for muscle contraction
Rough ER (RER): surface is covered in ribosomes
Makes proteins for membranes and export, same as bound ribosomes
Distributes transport vesicles
Membrane factory
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22. Smooth ER Nuclear envelope Smooth ER Rough ER Rough ER ER lumen
Figure 4.10
Smooth ER
Nuclear
envelope
Smooth ER
Rough ER
Rough ER
Figure 4.10 Endoplasmic reticulum (ER)
ER lumen
Cisternae
Transitional ER
Ribosomes
Transport vesicle
0.2 mm
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23. The Golgi Apparatus: Shipping and Receiving Center
Found in all eukaryotes
Consists of flattened membranous sacs called cisternae
Functions of the Golgi apparatus
Modifies products of the ER (takes proteins from RER and makes glycoproteins or lipids from SER and makes glycolipids)
Sorts and packages materials into transport vesicles
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24. Golgi apparatus cis face (“receiving” side of 0.1 mm Golgi apparatus)
Figure 4.11
Golgi
apparatus
cis face
(“receiving” side of
Golgi apparatus)
0.1 mm
Cisternae
Figure 4.11 The Golgi apparatus
trans face
(“shipping” side of
Golgi apparatus)
TEM of Golgi apparatus
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25. Lysosomes: Digestive Compartments
Found in animal eukaryotes only
Membranous sac of hydrolytic (digestive) enzymes that can digest macromolecules
Includes lipases, carbohydrases, proteases, nucleases
Has acidic pH of 5
3 functions:
Intracellular digestion; also called phagocytosis
Human macrophage cells kill bacteria this way
Recycle cell’s own organic material
Programmed cell destruction
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26. Digestion Food vacuole
Figure 4.12
Nucleus
1 mm
Lysosome
Digestive
enzymes
Lysosome
Figure 4.12 Lysosomes: phagocytosis
Plasma
membrane
Digestion
Food
vacuole
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