Cell Biology Chapter 1

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CHAPTER 1
INTRODUCTION TO CELLS
© 2009 Garland Science Publisin!
Uni"# and Di$ersi"# %& Cells
1-1 Living systems are incredibly diverse in size, shape, environment, and behavior. It is
estimated that there are between 10 million and 100 million different species. Despite this
wide variety of organisms, it remains difficult to define what it means to say something is
alive. Which of the following can be described as the smallest living unit
!a" D#$
!b" cell
!c" organelle
!d" protein
1-2 Indicate whether the following statements are true or false. If the statement is false,
e%plain why it is false.
$. $ virus is a living organism.
&. 'ells of different types can have different chemical re(uirements.
'. $ human white blood cell is larger than a Paramecium cell.
1-3 )or each of the following sentences, fill in the blan*s with the best word or phrase
selected from the list below. #ot all words or phrases will be used+ each word or phrase
should be used only once.
'ells can be very diverse, superficially, they come in various sizes,
ranging from bacterial cells such as Lactobacillus, which is a few
------------------ in length, to larger cells such as a frog.s egg, which
has a diameter of about one ------------------. Despite the diversity,
cells resemble each other to an astonishing degree in their chemistry. )or
e%ample, the same /0 ------------------ are used to ma*e proteins.
0imilarly, the genetic information of all cells is stored in their
------------------. $lthough ------------------ contain the same
type of molecules as cells, their inability to reproduce themselves by their
own efforts means that they are not considered living matter.
amino acids micrometer!s" viruses
D#$ millimeter!s" yeast
fatty acids plants
meter plasma membranes
1-4 1he flow of genetic information is controlled by a series of biochemical reactions that
result in the production of proteins, each with its own specific order of amino acids.
'hoose the correct series biochemical reactions from the options presented here.
!a" replication, transcription, translation
!b" replication, translation, transcription
!c" translation, transcription, replication
!d" translation, replication, transcription
1-5 2roteins are important architectural and catalytic components within the cell, helping to
determine its chemistry, its shape, and its ability to respond to changes in the
environment. 3emar*ably, all of the different proteins in a cell are made from the same
/0 ----------. &y lin*ing them in different se(uences, the cell can ma*e protein
molecules with different conformations and surface chemistries, and therefore different
functions.
!a" nucleotides
!b" sugars
!c" amino acids
!d" fatty acids
1-6 'hanges in D#$ se(uence from one generation to the ne%t may result in offspring that
are altered in fitness compared with their parents. 1he process of change and selection
over the course of many generations is the basis of ----------.
!a" mutation
!b" evolution
!c" heredity
!d" reproduction
Cells Under "e 'icr%sc%(e
1-7 What unit of length would you generally use to measure a typical human cell
!a" centimeters
!b" nanometers
!c" millimeters
!d" micrometers
1-8 4atch the type of microscopy on the left with the corresponding description provided
below. 1here is one best match for each.
$. confocal
&. transmission electron
'. fluorescence
D. phase contrast
5. scanning electron
). bright6field
____ uses a light microscope with an optical component to ta*e advantage of the different
refractive inde%es of light passing through different regions of the cell.
____ employs a light microscope and re(uires that samples be fi%ed and stained in order
to reveal cellular details.
____ re(uires the use of two sets of filters. 1he first filter narrows the wavelength range
that reaches the specimen and the second bloc*s out all wavelengths that pass bac*
up to the eyepiece e%cept for those emitted by the dye in the sample.
____ scans the specimen with a focused laser beam to obtain a series of two6dimensional
optical sections, which can be used to reconstruct an image of the specimen in
three6dimensions. 1he laser e%cites a fluorescent dye molecule, and the emitted
light from each illuminated point is captured through a pinhole and recorded by a
detector.
____ has the ability to resolve cellular components a small as / nm.
____ re(uires coating the sample with a thin layer of a heavy metal to produce three6
dimensional images of the surface of a sample.
1-9 'ell biologists employ targeted fluorescent dyes or modified fluorescent proteins in both
standard fluorescence microscopy and confocal microscopy to observe specific details in
the cell. 5ven though fluorescence permits better visualization, the resolving power is
essentially the same as that of a standard light microscope because the resolving power of
a microscope is limited by the ---------- of light.
!a" absorption
!b" intensity
!c" filtering
!d" wavelength
Te Pr%car#%"ic Cell
1-10 &y definition, procaryotic cells do not possess ----------.
!a" a nucleus
!b" replication machinery
!c" ribosomes
!d" membrane bilayers
1-11 $lthough there are many distinct procaryotic species, most have a small range of shapes,
sizes, and growth rates. Which of the following characteristics are not observed in
procaryotes
!a" a highly structured cytoplasm
!b" endoplasmic reticulum
!c" the ability to divide rapidly
!d" a cell wall
1-12 Indicate whether the following statements are true or false. If the statement is false,
e%plain why it is false.
$. 7%ygen is to%ic to certain procaryotic organisms.
&. 4itochondria are thought to have evolved from anaerobic bacteria.
'. $lthough bacteria use a variety of organic substances as food, bacteria are not
able live on inorganic substances.
Te Eucar#%"ic Cell
1-13 8se the list of structures below to label the schematic drawing of an animal cell in )igure
9161:.
$. plasma membrane
&. nuclear envelope
'. cytosol
D. ;olgi apparatus
5. endoplasmic reticulum
). mitochondrion
;. transport vesicles
)igure 9161:
1-14 )or each of the following sentences, fill in the blan*s with the best word or phrase
selected from the list below. #ot all words or phrases will be used+ each word or phrase
should be used only once.
5ucaryotic cells are bigger and more elaborate than procaryotic cells. &y
definition, all eucaryotic cells have a ------------------, usually the
most prominent organelle. $nother organelle found in essentially all
eucaryotic cells is the ------------------, which generates the
chemical energy for the cell. In contrast, the ------------------ is a
type of organelle found only in the cells of plants and algae, and performs
photosynthesis. If we were to strip away the plasma membrane from a
eucaryotic cell and remove all of its membrane6enclosed organelles, we
would be left with the ------------------, which contains many long,
fine filaments of protein that are responsible for cell shape and structure
and thereby form the cell.s ------------------.
chloroplast cytosol nucleus
chromosome endoplasmic reticulum ribosomes
cytos*eleton mitochondrion
1-15 1he ---------- ---------- is made up of two concentric membranes and is continuous
with the membrane of the endoplasmic reticulum.
!a" plasma membrane
!b" ;olgi networ*
!c" mitochondrial membrane
!d" nuclear envelope
1-16 1he nucleus, an organelle found in eucaryotic cells, confines the ----------, *eeping
them separated from other components of the cell.
!a" lysosomes
!b" chromosomes
!c" pero%isomes
!d" ribosomes
1-17 Which of the following organelles has both an outer and an inner membrane
!a" endoplasmic reticulum
!b" mitochondrion
!c" lysosome
!d" pero%isome
1-18 <ou fertilize egg cells from a healthy plant with pollen !which contains the male germ
cells" that has been treated with D#$6damaging agents. <ou find that some of the
offspring have defective chloroplasts, and that this characteristic can be passed on to
future generations. 1his surprises you at first because you happen to *now that the male
germ cell in the pollen grain contributes no chloroplasts to the fertilized egg cell and thus
to the offspring. What can you deduce from these results
1-19 4itochondria contain their own genome, are able to duplicate, and actually divide on a
different timeline from the rest of the cell. #evertheless, mitochondria cannot function for
long when isolated from the cell because they are
!a" viruses.
!b" parasites.
!c" endosymbionts.
!d" anaerobes.
1-20 1he mitochondrial proteins found in the inner membrane are involved in the conversion
of $D2 to $12, a source of energy for the cell. 1his process consumes which of the
following substances
!a" o%ygen
!b" nitrogen
!c" sulfur
!d" carbon dio%ide
1-21 'hloroplasts are found only in eucaryotic cells that carry out photosynthesis, plants and
algae. 2lants and algae appear green as a result of the presence of chlorophyll. Where is
chlorophyll located in the chloroplast
!a" in the first, outer membrane
!b" in the space between the first and second membranes
!c" in the second, inner membrane
!d" in the third, innermost membrane
1-22 2hotosynthesis enables plants to capture the energy from sunlight. In this essential
process, plants incorporate the carbon from '7
/
into high6energy ---------- molecules,
which the plant cell mitochondria use to produce $12.
!a" fat
!b" sugar
!c" protein
!d" fiber
1-23 Indicate whether the following statements are true or false. If the statement is false,
e%plain why it is false.
$. 4embrane components in the cell are made in the endoplasmic reticulum.
&. 1he ;olgi apparatus is made up of a series of membrane6enclosed compartments
through which materials destined for secretion must pass.
'. Lysosomes are small organelles where fatty acid synthesis occurs.
1-24 'ircle the appropriate cell type in which the listed structure or molecule can be found.
#ote that the structure or molecule can be found in more than one type of cell.
1-25 1he protozoan Didinium feeds on other organisms by engulfing them. Why are bacteria,
in general, unable to feed on other cells in this way
1-26 1he cell constantly e%changes materials by bringing nutrients in from the e%ternal
environment and shuttling unwanted by6products bac* out. Which term describes the
process of by which e%ternal materials are captured inside vesicles and brought into the
cell
!a" degradation
!b" e%ocytosis
!c" phagocytosis
!d" endocytosis
1-27 ---------- are fairly small organelles that provide a safe place within the cell to carry
out certain biochemical reactions that generate harmful, highly reactive o%ygen species.
1hese chemicals are both generated and bro*en down in the same location.
!a" nucleosomes
!b" lysosomes
!c" pero%isomes
!d" endosomes
1-28 1he cytos*eleton provides support, structure, motility, and organization, and it forms
trac*s to direct organelle and vesicle transport. Which of the cytos*eletal elements listed
below is the thic*est
!a" actin filaments
!b" microtubules
!c" intermediate filaments
!d" none of the above !all the same thic*ness"
1-29 Despite the differences between eucaryotic and procaryotic cells, procaryotes have
proteins that are distantly related to eucaryotic actin filaments and microtubules. What is
li*ely to be the most ancient function of the cytos*eleton
!a" cell motility
!b" vesicle transport
!c" membrane support
!d" cell division
1-30 Which of the following characteristics would not support the idea that the ancestral
eucaryote was a predator cell that captured and consumed other cells
!a" dynamic cytos*eleton
!b" large cell size
!c" ability to move
!d" rigid membrane
1-31 Indicate whether the following statements are true or false. If the statement is false,
e%plain why it is false.
$. 2rimitive plant, animal, and fungal cells probably ac(uired mitochondria after
they diverged from a common ancestor.
&. 2rotozoans are single6celled eucaryotes with cell morphologies and behaviors that
can be as comple% as those of some multicellular organisms.
'. $nimal, plant, fungal, and bacterial cells all possess cell walls.
'%del Or!anis)s
1-32 ;iven what you *now about the differences between procaryotic cells and eucaryotic
cells, rate the following things as =good> or =bad> processes to study in the model
organism, E. coli.
$. formation of the endoplasmic reticulum
&. D#$ replication
'. how the actin cytos*eleton contributes to cell shape
D. how cells decode their genetic instructions to ma*e proteins
5. how mitochondria get distributed to cells during cell division
1-33 $. In what way does a fungal cell structurally resemble a plant cell, rather than an
animal cell
&. Which principal organelle does a plant cell contain that a fungal cell does not
1-34 &iologists cannot possibly study all living species. Instead, they try to understand cell
behavior by studying a select subset of them. Which of the following characteristics are
useful in an organism chosen for use as a model in laboratory studies
!a" amenability to genetic manipulation
!b" ability to grow under controlled conditions
!c" rapid rate of reproduction
!d" all of the above
1-35 4any of the mechanisms that cells use for maintenance and reproduction were first
studied at the molecular detail in bacteria. Which bacterial species had a central role in
advancing the field of molecular biology
!a" E. coli
!b" D. melanogaster
!c" S. pombe
!d" C. elegans
1-36 &rewer.s yeast, apart from being an irreplaceable asset in the brewery and in the ba*ery,
is an e%perimental organism used to study eucaryotic cells. ?owever, it does face some
limitations. Which of the processes below cannot be studied with yeast
!a" D#$ replication
!b" cell motility
!c" e%ocytosis
!d" cell division
1-37 'ircle the simplest model organism best used to study the following processes,
1-38 A. thaliana, or Arabidopsis, is a common weed. &iologists have selected it over hundreds
of thousands of other flowering plant species to serve as an e%perimental model organism
because ------------------.
!a" it can withstand e%tremely cold climates
!b" it can reproduce in @A10 wee*s
!c" it produces thousands of offspring per plant
!d" &oth !b" and !c" are true.
1-39 Drosophila melanogaster is aBan ----------. 1his type of animal is the most abundant
of all animal species, ma*ing it an appropriate choice as an e%perimental model.
!a" insect
!b" bird
!c" amphibian
!d" mammal
1-40 C. elegans is a nematode. During its development, it produces more than 1000 cells
?owever, the adult worm only has CDC somatic cells. 1he process by which 1:1 cells are
specifically targeted for destruction is called
!a" directed cell pruning.
!b" programmed cell death.
!c" autophagy.
!d" necrosis.
1-41 Eebrafish !Danio rerio" are especially useful in the study of early development because
their embryos --------------.
!a" are e%ceptionally large
!b" develop slowly
!c" are transparent
!d" are naturally fluorescent
1-42 <ou wish to e%plore how mutations in specific genes affecting sugar metabolism might
alter tooth development. Which organism is li*ely to provide the best model system for
your studies and why
!a" horses
!b" mice
!c" E. coli
!d" Arabidopsis
1-43 ;enes that have homologues in a variety of species have been discovered through the
analysis of genome se(uences. In fact, it is not uncommon to find a family of
homologous genes encoding proteins that are unmista*ably similar in amino acid
se(uence in organisms as diverse as budding yeast, archaea, plants, and humans. 5ven
more remar*ably, many of these proteins can substitute functionally for their homologues
in other organisms. 5%plain what it is about the origins of cells that ma*es it possible for
proteins e%pressed by homologous genes to be functionally interchangeable in different
organisms.
1-44 4atch each biological process with the model organism that is best suited or most
specifically useful for its study, based on information provided in your te%tboo*. <ou
may list individual processes more than once.
$. cell division
&. development !multicellular"
'. programmed cell death
D. photosynthesis
5. immunology
----- A. thaliana !Arabidopsis"
----- M. musculus !mouse"
----- S. pombe
----- C. elegans
----- S. cerevisiae
----- D. rerio !zebrafish"
----- D. melanogaster
Tes"in! "e C%nce("s
1-45 5volutionary biologists have always used a broad range of modern organisms to infer the
characteristics that ancestral organisms may have possessed. ;enomic se(uences are now
available for an increasing number of species, and scientists studying evolutionary
processes can ta*e advantage of this enormous amount of data to bring evolution into the
arena of molecular studies. &y aligning the se(uences of homologous genes and loo*ing
for regions of similarity and where changes have occurred, it is possible to infer the
se(uence of the ancestral gene.
$. What term is used to describe the changes in gene se(uence that have occurred
?ow can we use what we *now about this process to construct a timeline showing
when various se(uence changes occurred and when they lead to the modern
se(uences that we *now today
&. It is possible to e%press an ancestral gene se(uence in modern organisms and
subse(uently compare its function with that of the modern protein. Why might
this approach give misleading conclusions
1-46 1he antibiotic streptomycin inhibits protein synthesis in bacteria. If this antibiotic is
added to a culture of animal cells, protein synthesis in the cytosol continues normally.
?owever, over time the population of mitochondria in the cell becomes depleted.
0pecifically, it is observed that the protein synthesis machinery inside the mitochondria is
inhibited.
$. 5%plain this observation based on what you *now about the origins of the modern
eucaryote.
&. What do you e%pect to observe if, in a new e%periment, animal cells are treated
with diphtheria to%in, a compound that is *nown to bloc* cytosolic protein
synthesis but does not have any impact on bacterial growth
1-47 <our friend has Fust returned from a deep sea mission and claims to have found a new
single6celled life form. ?e believes this new life form may not have descended from the
common ancestor that all types of life on 5arth share. <ou are convinced that he must be
wrong, and you manage to e%tract D#$ from the cells he has discovered. ?e says that the
mere presence of D#$ is not enough to prove the point, his cells might have adopted
D#$ as a useful molecule (uite independently of all other *nown life forms. What would
you do to persuade him that he was wrong
Ans*ers
1-1 !b"
1-2 $. )alse. $ virus lac*s the full machinery re(uired to copy itself and is therefore not
considered a living organism.
&. 1rue.
'. )alse. $ human white blood cell is about 10 Gm in diameter. 1he single6celled
paramecium is roughly 10 times that size.
1-3 'ells can be very diverse, superficially, they come in various sizes, ranging from
bacterial cells such as Lactobacillus, which is a few micrometers in length, to larger
cells such as a frog.s egg, which has a diameter of about one millimeter. Despite the
diversity, cells resemble each other to an astonishing degree in their chemistry. )or
e%ample, the same /0 amino acids are used to ma*e proteins. 0imilarly, the genetic
information of all cells is stored in their DNA. $lthough viruses contain the same type of
molecules as cells, their inability to reproduce themselves by their own efforts means that
they are not considered living matter.
1-4 !a"
1-5 !c"
1-6 !b"
1-7 !d"
1-8 D
)
'
$
&
5
1-9 !d"
1-10 !a"
1-11 !a", !b"
1-12 !a" 1rue.
!b" )alse. 4itochondria use o%ygen to generate energy and are thought to have
evolved from aerobic bacteria.
!c" )alse. 0ome bacteria can live by consuming e%clusively inorganic substances
such as '7
/
, #
/
, water, and minerals.
1-13 $. 2lasma membraneH:
&. #uclear envelopeHD
'. 'ytosolH1
D. ;olgi apparatusH/
5. 5ndoplasmic reticulumHI
). 4itochondrionHJ
;. 1ransport vesiclesHK
1-14 5ucaryotic cells are bigger and more elaborate than procaryotic cells. &y definition, all
eucaryotic cells have a nucleus, usually the most prominent organelle. $nother organelle
found in essentially all eucaryotic cells is the mitochondrion, which generates the
chemical energy for the cell. In contrast, the chlorolast is a type of organelle found only
in the cells of plants and algae, and performs photosynthesis. If we were to strip away the
plasma membrane from a eucaryotic cell and remove all of its membrane6enclosed
organelles, we would be left with the c!tosol, which contains many long, fine filaments
of protein that are responsible for cell shape and structure and thereby form the cell.s
c!tos"eleton.
1-15 !d"
1-16 !b"
1-17 !b"
1-18 <our results show that not all of the information re(uired for ma*ing a chloroplast is
encoded in the chloroplast.s own D#$+ some, at least, must be encoded in the D#$
carried in the nucleus. 1he reasoning is as follows. ;enetic information is carried only in
D#$, so the defect in the chloroplasts must be due to a mutation in D#$. &ut all of the
chloroplasts in the offspring !and thus all of the chloroplast D#$" must derive from those
in the female egg cell, since chloroplasts only arise from other chloroplasts. ?ence, all of
the chloroplasts contain undamaged D#$ from the female parent.s chloroplasts. In all
the cells of the offspring, however, half of the nuclear D#$ will have come from the
male germ cell nucleus, which combined with the female egg nucleus at fertilization.
0ince this D#$ has been treated with D#$6damaging agents, it must be the source of the
heritable chloroplast defect. 1hus, some of the information re(uired for ma*ing a
chloroplast is encoded by the nuclear D#$.
1-19 !c"
1-20 !a"
1-21 !d"
1-22 !b"
1-23 $. 1rue.
&. 1rue.
'. )alse. Lysosomes house enzymes that brea*down nutrients for use by the cell and
help recycle materials that cannot be used, which will later be e%creted from the
cell.
1-24
1-25 Didinium engulfs prey by changing its shape, and for this it uses its cytos*eleton.
&acteria have no cytos*eleton and cannot easily change their shape because they are
generally surrounded by a tough cell wall.
1-26 !d"
1-27 !c"
1-28 !b"
1-29 !d"
1-30 !d"
1-31 $. )alse. 1he mitochondria in modern plant, animal, and fungal cells are very
similar, implying that these lines diverged after the mitochondrion was ac(uired
by the ancestral eucaryote.
&. 1rue.
'. )alse. 1he outermost layer in animal cells is the plasma membrane.
1-32 $. bad
&. good
'. bad
D. good
5. bad
1-33 $. Li*e plant cells, fungal cells have cell walls.
&. 'hloroplasts
1-34 !d"
1-35 !a"
1-36 !b"
1-37
1-38 !b"
1-39 !a"
1-40 !b"
1-41 !c"
1-42 !b". 4ice are li*ely to provide the best model system. 4ice have teeth and have long
been used as a model organism. 4ice reproduce relatively rapidly and the e%tensive
scientific community that wor*s with mice has developed techni(ues to facilitate genetic
manipulations. E. coli !a bacterium" and Arabidopsis !a plant" do not have teeth. ?orses
li*e sugar and have big teeth, but they would not be a good model organism. 1here is not
an e%tensive scientific community wor*ing on the molecular and biochemical
mechanisms of cell behaviors in horses+ they are e%pensive and have a long reproduction
time, which ma*es genetic studies costly and slow+ and tools for genetic manipulation
!other than traditional breeding" have not been developed.
1-43 $ll living beings on 5arth !and thus, all cells" are thought to be derived from a common
ancestor. 0olutions to many of the essential challenges that face a cell !such as the
synthesis of proteins, lipids, and D#$" seem to have been achieved in this ancient
common ancestor. 1he ancestral cell therefore possessed sets of proteins to carry out
these essential functions. 4any of the essential challenges facing modern6day cells are
the same as those facing the ancestral cell, and the ancient solutions are often still
effective. 1hus, it is not uncommon for organisms to use proteins and biochemical
pathways inherited from their ancestors. $lthough these proteins usually show some
species6specific diversification, they still retain the basic biochemical characteristics of
the ancestral protein. )or e%ample, homologous proteins often retain their ability to
interact with a specific protein target, even in cells of diverse species. &ecause the basic
biochemical characteristics are retained, homologous proteins are often capable of
functionally substituting for one another.
1-44 &, D A. thaliana !Arabidopsis"
&, 5 M. musculus !mouse"
$ S. pombe
' C. elegans
$ S. cerevisiae
& D. rerio !zebrafish"
& D. melanogaster
1-45 $. 'hanges in gene se(uence occur through mutation. 4utations accumulate over
time, occurring independently and at different sites in each gene lineage.
?omologous genes that diverged recently will differ only slightly+ genes that
diverged long ago will differ more. Lnowing the average mutation rate, you can
estimate the time that has elapsed since the different versions of the gene
diverged. &y seeing how closely the various members of the family of
homologous genes resemble one another, you can draw up a family tree, showing
the se(uence of lineage splittings that led from the ancestral gene to its many
modern descendants. 0uppose this family tree shows that family members $ and
& diverged from one another long ago, but that ' diverged from & more recently+
and suppose that at a certain site in the gene $ and & have the same se(uence but
' is different. 1hen it is li*ely that the se(uence of $ and & is ancestral, while
that of ' reflects a recent mutation that has occurred in the lineage of ' alone.
&. $lthough an inferred ancestral se(uence can be reconstructed and the protein
e%pressed, you would be placing an inferred, ancient protein in the conte%t of a
modern cell. If there are important interacting partners for the modern protein,
there is a chance they may not recognize the ancestral protein, and therefore any
information about its function may be inaccurate.
1-46 $. If the mitochondria originated from an ancient aerobic bacterium that was
engulfed by an ancient eucaryote, as postulated, it is possible that an antibiotic
that inhibits protein synthesis in bacteria could also bloc* that process in
mitochondria.
B. We would expect that although cytosolic protein synthesis would stop,
mitochondrial protein synthesis should still occur normally (at least for a little
while). This result would lend further support to the idea that mitochondria are
derived from a non-eucaryotic organism. If this were not the case, these
compounds would be expected to affect protein synthesis at both locations.
1-47 <ou could use modern technology to discover the se(uence of the D#$. If you are right,
and he is wrong, you would e%pect to find parts of this se(uence that are unmista*ably
similar to corresponding se(uences in other, familiar, living organisms+ it would be
highly improbable that such similar se(uences would have evolved independently. <ou
could, of course, also analyze other features of the chemistry of his cells H for e%ample,
do they contain proteins made of the same set of /0 amino acids &ut he would probably
not find such general chemical similarities as persuasive as detailed similarities of D#$
se(uence.

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