Like ourselves, the individual cells that form our bodies
can grow, reproduce, process information, respond to
stimuli, and carry out an amazing array of chemical re-
actions. These abilities define life. We and other multicellular
organisms contain billions or trillions of cells organized into...
A single ~200 micrometer (m) cell, the huma
sperm, which are also single cells. From the u
and sperm will arise the 10 trillion cells of a h
[Photo Researchers, Inc.]
L
ike ourselves, the individual cells that form our bodies 1.1 The Diversity and Comm
can grow, reproduce, process information, respond to
stimuli, and carry out an amazing array of chemical re- of Cells
actions. These abilities define life. We and other multicellular Cells come in an amazing variety of sizes an
organisms contain billions or trillions of cells organized into 1-1). Some move rapidly and have fast-chang
complex structures, but many organisms consist of a single we can see in movies of amoebae and rot
cell. Even simple unicellular organisms exhibit all the hall- largely stationary and structurally stable. O
mark properties of life, indicating that the cell is the funda- cells but is an absolute requirement for othe
mental unit of life. As the twenty-first century opens, we face multicellular organisms are intimately invo
an explosion of new data about the components of cells, cells. Although some unicellular organisms
what structures they contain, how they touch and influence others form colonies or live in close associ
each other. Still, an immense amount remains to be learned, types of organisms, such as the bacteria that
particularly about how information flows through cells and tract nitrogen from the air or the bacteria th
how they decide on the most appropriate ways to respond. testines and help us digest food. Despite the
Molecular cell biology is a rich, integrative science that
brings together biochemistry, biophysics, molecular biology,
,2 CHAPTER 1 • Life Begins with Cells
(a) (b) (c) (d)
(e) (f) (g) (h)
▲ FIGURE 1-1 Cells come in an astounding assortment of Purkinje neuron of the cerebellum, which can form m
shapes and sizes. Some of the morphological variety of cells is hundred thousand connections with other cells throu
illustrated in these photographs. In addition to morphology, cells branched network of dendrites. The cell was made v
differ in their ability to move, internal organization (prokaryotic introduction of a fluorescent protein; the cell body is
versus eukaryotic cells), and metabolic activities. (a) Eubacteria; the bottom. (g) Cells can form an epithelial sheet, as
note dividing cells. These are Lactococcus lactis, which are used through intestine shown here. Each finger-like tower
to produce cheese such as Roquefort, Brie, and Camembert. villus, contains many cells in a continuous sheet. Nu
(b) A mass of archaebacteria (Methanosarcina) that produce their transferred from digested food through the epithelia
energy by converting carbon dioxide and hydrogen gas to blood for transport to other parts of the body. New c
methane. Some species that live in the rumen of cattle give rise continuously near the bases of the villi, and old cells
to >150 liters of methane gas/day. (c) Blood cells, shown in false from the top. (h) Plant cells are fixed firmly in place
color. The red blood cells are oxygen-bearing erythrocytes, the plants, supported by a rigid cellulose skeleton. Space
white blood cells (leukocytes) are part of the immune system the cells are joined into tubes for transport of water
and fight infection, and the green cells are platelets that provide [Part (a) Gary Gaugler/ Photo Researchers, Inc. Part (b) Ralp
substances to make blood clot at a wound. (d) Large single cells: Visuals Inlimited, Inc. Part (c) NIH/Photo Researchers, Inc. P
fossilized dinosaur eggs. (e) A colonial single-celled green alga, John D. Cunningham/Visuals Unlimited, Inc. Part (e) Carolin
Volvox aureus. The large spheres are made up of many individual Biological/Visuals Unlimited, Inc. Part (f) Helen M. Blau, Sta
cells, visible as blue or green dots. The yellow masses inside are University. Part (g) Jeff Gordon, Washington University Scho
daughter colonies, each made up of many cells. (f) A single Medicine. Part (h) Richard Kessel and C. Shih/Visuals Unlim
, 1.1 • The Diversity and Commo
(a) Prokaryotic cell (b) Eukaryotic cell
Periplasmic space Nucleus
and cell wall
Golgi v
Mito
Outer membrane Inner (plasma) Nucleoid
membrane 0.5 m
Endoplasmic reticulum 1
Nucleoid
Nuclear membran
Plas
Nucleus
Inner (plasma) membrane
Cell wall
Periplasmic space
Outer membrane
Rough endoplasmic
reticulum
▲ FIGURE 1-2 Prokaryotic cells have a simpler internal characteristic of eukaryotic cells is segregation o
organization than eukaryotic cells. (a) Electron micrograph of a within a defined nucleus, which is bounded by a
thin section of Escherichia coli, a common intestinal bacterium. membrane. The outer nuclear membrane is cont
The nucleoid, consisting of the bacterial DNA, is not enclosed rough endoplasmic reticulum, a factory for asse
within a membrane. E. coli and some other bacteria are Golgi vesicles process and modify proteins, mito
surrounded by two membranes separated by the periplasmic energy, lysosomes digest cell materials to recyc
space. The thin cell wall is adjacent to the inner membrane. peroxisomes process molecules using oxygen, a
(b) Electron micrograph of a plasma cell, a type of white blood vesicles carry cell materials to the surface to rel
cell that secretes antibodies. Only a single membrane (the plasma [Part (a) courtesy of I. D. J. Burdett and R. G. E. Murra
membrane) surrounds the cell, but the interior contains many P. C. Cross and K. L. Mercer, 1993, Cell and Tissue Ult
membrane-limited compartments, or organelles. The defining A Functional Perspective, W. H. Freeman and Compan
, 4 CHAPTER 1 • Life Begins with Cells
Animals Plants so many similarities. In recent years, detailed an
Fungi DNA sequences from a variety of prokaryotic or
Ciliates revealed two distinct types: the so-called “true” ba
Euglena
Microsporidia EUKARYOTA bacteria, and archaea (also called archaebacteria o
Slime molds Working on the assumption that organisms with
Diplomonads
(Giardia lamblia)
genes evolved from a common progenitor more r
those with more dissimilar genes, researchers hav
EUBACTERIA
the evolutionary lineage tree shown in Figure 1-3.
E. coli Sulfolobus this tree, the archaea and the eukaryotes diverged f
ARCHAEA bacteria before they diverged from each other.
B. subtilus Thermococcus Many archaeans grow in unusual, often ex
Thermotoga
ronments that may resemble ancient condition
Methanobacterium
first appeared on earth. For instance, halophile
Halococcus ing”) require high concentrations of salt to s
Flavobacteria thermoacidophiles (“heat and acid loving”) grow i
Green sulfur Halobacterium sulfur springs, where a pH of less than 2 is co
bacteria other archaeans live in oxygen-free milieus a
Borrelia
Methanococcus methane (CH4) by combining water with carbon
jannaschii
burgdorferi
Unicellular Organisms Help and Hurt U
Presumed common progenitor
Bacteria and archaebacteria, the most abundant
of all extant organisms organisms, are commonly 1–2 m in size. Despit
size and simple architecture, they are remarkab
Presumed common progenitor
of archaebacteria and eukaryotes
cal factories, converting simple chemicals into c
logical molecules. Bacteria are critical to the ear
▲ FIGURE 1-3 All organisms from simple bacteria to but some cause major diseases: bubonic plague (B
complex mammals probably evolved from a common, single- from Yersinia pestis, strep throat from Streptom
celled progenitor. This family tree depicts the evolutionary culosis from Mycobacterium tuberculosis, an
relations among the three major lineages of organisms. The Bacillus anthracis, cholera from Vibrio cholera
structure of the tree was initially ascertained from morphological soning from certain types of E. coli and Salmon
criteria: Creatures that look alike were put close together. More Humans are walking repositories of bacter
recently the sequences of DNA and proteins have been plants and animals. We provide food and shelte
examined as a more information-rich criterion for assigning gering number of “bugs,” with the greatest conc
relationships. The greater the similarities in these macromolecular
our intestines. Bacteria help us digest our food
sequences, the more closely related organisms are thought to
are able to reproduce. A common gut bacteriu
be. The trees based on morphological comparisons and the fossil
also a favorite experimental organism. In respon
record generally agree well with those those based on molecular
data. Although all organisms in the eubacterial and archaean
from bacteria such as E. coli, the intestinal cells
lineages are prokaryotes, archaea are more similar to eukaryotes priate shapes to provide a niche where bacteria c
than to eubacteria (“true” bacteria) in some respects. For facilitating proper digestion by the combined e
instance, archaean and eukaryotic genomes encode homologous bacterial and the intestinal cells. Conversely, exp
histone proteins, which associate with DNA; in contrast, bacteria testinal cells changes the properties of the bac
lack histones. Likewise, the RNA and protein components of they participate more effectively in digestion. Su
archaean ribosomes are more like those in eukaryotes than nication and response is a common feature of ce
those in bacteria. The normal, peaceful mutualism of humans
is sometimes violated by one or both parties. W
begin to grow where they are dangerous to us (e.g.,
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