1. 4
A Tour of the Cell

2. Overview: The Fundamental Units of Life
All organisms are made of cells
The cell is the simplest collection of matter that can be alive
All cells are related by their descent from earlier cells
Though cells can differ substantially from one another, they share common features
© 2014 Pearson Education, Inc. 2

3. Figure 4.1
Figure 4.1 How do your brain cells help you learn about biology? 3

4. Concept 4.1: Biologists use microscopes and the tools of biochemistry to study cells
Most cells are between 1 and 100 m in diameter, too small to be seen by the unaided eye
© 2014 Pearson Education, Inc. 4

5. Microscopy
Scientists use microscopes to visualize cells too small to see with the naked eye
In a light microscope (LM), visible light is passed through a specimen and then through glass lenses
© 2014 Pearson Education, Inc. 5

6. Three important parameters of microscopy
Magnification
Resolution
Contrast
© 2014 Pearson Education, Inc. 6

7. Super- resolution microscopy
Figure 4.2
10 m
Human height
1 m
Length of some
nerve and
muscle cells
0.1 m
Unaided eye
Chicken egg
1 cm
Frog egg
1 mm
Human egg
100 m
Most plant and
animal cells LM
10 m
Nucleus
Most bacteria
Mitochondrion
1 m EM
Figure 4.2 The size range of cells and how we view them
Smallest bacteria
100 nm
Super-
resolution
microscopy
Viruses
Ribosomes
10 nm
Proteins
Lipids
1 nm
Small molecules
0.1 nm
Atoms 7

8. Super- resolution microscopy
Figure 4.2b
100 m
Most plant and
animal cells
10 m
Nucleus
Most bacteria
Mitochondrion LM
1 m EM
Smallest bacteria
Super-
resolution
microscopy
100 nm
Viruses
Ribosomes
10 nm
Figure 4.2b The size range of cells and how we view them (part 2: EM to LM)
Proteins
Lipids
1 nm
Small molecules
Atoms
0.1 nm 8

9. LMs can magnify effectively to about 1,000 times the size of the actual specimen
Various techniques enhance contrast and enable cell components to be stained or labeled
Most subcellular structures, including organelles (membrane-enclosed compartments), are too small to be resolved by light microscopy
© 2014 Pearson Education, Inc. 9

10. TEM is used mainly to study the internal structure of cells
Two basic types of electron microscopes (EMs) are used to study subcellular structures
Scanning electron microscopes (SEMs) focus a beam of electrons onto the surface of a specimen, providing 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
© 2014 Pearson Education, Inc. 10

11. Light Microscopy (LM) 50 m Brightfield (unstained specimen)
Figure 4.3a
Light Microscopy (LM)
50 m
Brightfield
(unstained specimen)
Brightfield
(stained specimen)
Figure 4.3a Exploring microscopy (part 1: light microscopy)
Phase-contrast
Differential-interference
contrast (Nomarski) 11

12. Light Microscopy (LM) 50 m 10 m Fluorescence Confocal Figure 4.3b
Figure 4.3b Exploring microscopy (part 2: light microscopy)
Fluorescence
Confocal 12

13. Electron Microscopy (EM)
Figure 4.3c
Electron Microscopy (EM)
Longitudinal section
of cilium
Cross section
of cilium
Cilia
Figure 4.3c Exploring microscopy (part 3: electron microscopy)
Transmission electron
microscopy (TEM)
2 m
Scanning electron
microscopy (SEM) 13

14. Cell components separate based on their relative size
Cell Fractionation
Cell fractionation breaks up cells and separates the components, using centrifugation
Cell components separate based on their relative size
Cell fractionation enables scientists to determine the functions of organelles
Biochemistry and cytology help correlate cell function with structure
© 2014 Pearson Education, Inc. 14

15. Protists, fungi, animals, and plants all consist of eukaryotic cells
Concept 4.2: Eukaryotic cells have internal membranes that compartmentalize their functions
The basic structural and functional unit of every organism is one of two types of cells: prokaryotic or eukaryotic
Organisms of the domains Bacteria and Archaea consist of prokaryotic cells
Protists, fungi, animals, and plants all consist of eukaryotic cells
© 2014 Pearson Education, Inc. 15

16. Comparing Prokaryotic and Eukaryotic Cells
Basic features of all cells
Plasma membrane
Semifluid substance called cytosol
Chromosomes (carry genes)
Ribosomes (make proteins)
© 2014 Pearson Education, Inc. 16

17. Prokaryotic cells are characterized by having
No nucleus
DNA in an unbound region called the nucleoid
No membrane-bound organelles
Cytoplasm bound by the plasma membrane
Typically much smaller than eukaryotic cells (1-5um)
© 2014 Pearson Education, Inc. 17

18. (a) A typical rod-shaped bacterium (b) A thin section through
Figure 4.4
Fimbriae
Nucleoid
Ribosomes
Plasma membrane
Bacterial
chromosome
Cell wall
Capsule
0.5 m
Flagella
(a) A typical rod-shaped
bacterium
(b) A thin section through
the bacterium Bacillus
coagulans (TEM)
Figure 4.4 A prokaryotic cell 18

19. Eukaryotic cells are characterized by having
DNA in a nucleus that is bounded by a membranous nuclear envelope
Membrane-bound organelles
Cytoplasm in the region between the plasma membrane and nucleus
Eukaryotic cells are generally much larger than prokaryotic cells (10-100um)
© 2014 Pearson Education, Inc. 19

20. The plasma membrane is a selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell
The general structure of a biological membrane is a double layer of phospholipids
© 2014 Pearson Education, Inc. 20

21. Carbohydrate side chains
Figure 4.5
(a) TEM of a plasma
membrane
Outside of cell
Inside
of cell
0.1 m
Carbohydrate side chains
Hydrophilic
region
Figure 4.5 The plasma membrane
Hydrophobic
region
Hydrophilic
region
Phospholipid
Proteins
(b) Structure of the plasma membrane 21

22. (a) TEM of a plasma membrane Outside of cell Inside of cell 0.1 m
Figure 4.5a
(a) TEM of a plasma
membrane
Outside of cell
Figure 4.5a The plasma membrane (TEM)
Inside
of cell
0.1 m 22

23. Metabolic requirements set upper limits on the size of cells
The ratio of surface area to volume of a cell is critical
As the surface area increases by a factor of n2, the volume increases by a factor of n3
Small cells have a greater surface area relative to volume
© 2014 Pearson Education, Inc. 23

24. Surface area increases while total volume remains constant
Figure 4.6
Surface area increases while
total volume remains constant 5 1 1
Total surface area
[sum of the surface areas
(height  width) of all box
sides  number of boxes] 6
150
750
Total volume
[height  width  length
 number of boxes]
Figure 4.6 Geometric relationships between surface area and volume 1
125
125
Surface-to-volume
ratio
[surface area  volume] 6
1.2 6 24

25. A Panoramic View of the Eukaryotic Cell
A eukaryotic cell has internal membranes that divide the cell into compartments—organelles
The plasma membrane and organelle membranes participate directly in the cell’s metabolism
Animation: Tour of an Animal Cell
Animation: Tour of a Plant Cell
© 2014 Pearson Education, Inc. 25

26. ENDOPLASMIC RETICULUM (ER) Nuclear envelope Smooth ER NUCLEUS
Figure 4.7a
ENDOPLASMIC RETICULUM (ER)
Nuclear
envelope
Smooth ER
NUCLEUS
Nucleolus
Flagellum
Rough ER
Chromatin
Centrosome
Plasma
membrane
CYTOSKELETON:
Microfilaments
Intermediate
filaments
Ribosomes
Microtubules
Figure 4.7a Exploring eukaryotic cells (part 1: animal cell cutaway)
Microvilli
Golgi apparatus
Peroxisome
Mitochondrion
Lysosome 26

27. Rough endoplasmic Nuclear envelope reticulum Nucleolus
Figure 4.7b
Rough endoplasmic
reticulum
Nuclear envelope
Nucleolus
Smooth endoplasmic
reticulum
Chromatin
NUCLEUS
Ribosomes
Central vacuole
Golgi
apparatus
Microfilaments
Intermediate
filaments
CYTO-
SKELETON
Microtubules
Figure 4.7b Exploring eukaryotic cells (part 2: plant cell cutaway)
Mitochondrion
Peroxisome
Plasma membrane
Chloroplast
Cell wall
Plasmodesmata
Wall of adjacent cell 27