--

Question 1

cell size

Answer 1

- Most cells are between 1 and
100 μm in diameter
- most cells are
invisible to the naked eye; Light microscopy (LM) can be
used to visualize most cells.
Electron microscopy (EM) is
needed to see sub-cellular
structures

Question 2

light microscopy (LM)

Answer 2

• In light microscopy (LM), visible light is passed
  through a specimen and then through glass lenses.
• The lenses refract (bend) the light in such a way that
  the image of the specimen is magnified as it is projected into the eye or into a camera.

Question 3

brightfield

Answer 3

• Brightfield (unstained specimen).: Light passes directly through the specimen. Unless the cell is naturally
  pigmented or artificially stained, the
  image has little contrast.
• Brightfield (stained specimen).
  Staining with various dyes enhances
  contrast. Most staining procedures require
  that cells be fixed (preserved).

Question 4

phase-contrast

Answer 4

Variations in density
within the specimen are amplified to
enhance contrast in unstained cells, which
is especially useful for examining living,
unpigmented cells.
- (for examining cells in a single layer)

Question 5

Differential
Interference
Contrast
(DIC or Nomarski)

Answer 5

As in phase-contrast microscopy, optical modifications are used to
exaggerate differences in density, making
the image appear almost 3-D.
- (for examining cells in a single layer)

Question 6

confocal w/ fluorescence

Answer 6

- Specimen is stained with
a dye that fluoresces
- image is “optically sectioned”
with a laser, one plane of focus
at a time. By capturing
sharp images at many different planes,
a 3-D reconstruction can be created.
- Out of focus layers are excluded
with each pass of the laser and
then digitally added back later
to give a 3D look. 
- (for examining cells in a big blob of cells)

Question 7

e- microscope (EM)

Answer 7

Until recently, the resolution barrier prevented cell biologists from using standard light microscopy to study
organelles.
- Rather than light, the
electron microscope (EM) focuses a beam of electrons
through the specimen or onto its surface.
- Two basic types of electron microscopes (EMs) are used to
study subcellular structures – scanning and transmission

Question 8

Scanning electron microscopes (SEMs)

Answer 8

• S for Surface: especially
  useful for detailed study of the topography of a specimen
• focus a beam of
  electrons onto the surface of a specimen. this beam scans the surface. pattern of electrons – The result is an image of
  the specimen’s surface that appears three-dimensional.

Question 9

Transmission electron microscopes (TEMs)

Answer 9

• T for Through: focus a beam
  of electrons through a specimen.
• TEMs are used mainly to study the internal structure of cells.

Question 10

cell fractionation

Answer 10

A useful technique for studying cell structure and function is
cell fractionation, which takes cells apart and separates
major organelles and other subcellular structures from one another. (used to isolate (fractionate) cell
components based on size and density)
- Cells are ground up in a blender and the homogenate is then subjected to centrifugation. At lower speeds, the pellet consists of larger components, and higher speeds yield a pellet with smaller components. Larger particles will “pellet” to the bottom, smaller pieces remain suspended in the “supernatant”. (each subsequent centrifugation - higher speed, longer time)

Question 11

Cell fractionation enables researchers

Answer 11

to prepare specific
cell components in bulk and identify their FUNCTIONS, a task
not usually possible with intact cells. For example, on one of
the cell fractions, biochemical tests showed the presence of
enzymes involved in cellular respiration, while electron
microscopy revealed large numbers of the organelles called
mitochondria. Together, these data helped biologists determine that mitochondria are the sites of cellular respiration.

Question 12

Differential

centrifugation: order of pellets

Answer 12

(slowest to fastest)
1. Pellet rich in nuclei and cellular debris
2. “ “ “ mitochondria (and chloroplasts if plant)
3. “ “ “ microsomes (pieces of plasma
membranes and cells’ internal membranes)
4. ribosomes

Question 13

prokaryotic cells

Answer 13

Only organisms of the domains Bacteria and Archaea consist of prokaryotic cells
(“pro”, before; “karyon”, kernel or core) These cells lack nucleus and internal
membrane-bound structures.

Question 14

eukaryotic cells

Answer 14

Protists, fungi, animals, and plants all consist of eukaryotic cells (“eu”, true). This
means that the genetic material is physically separated from the rest of the cell by a
membrane

Question 15

All cells share certain basic features:

Answer 15

• They are all bounded by
  a selective barrier, called the plasma membrane.
• Inside all cells
  is a semifluid, jellylike substance called cytosol, in which
  subcellular components are suspended.
• All cells contain
  chromosomes, which carry genes in the form of DNA.
• And all
  cells have ribosomes, tiny complexes that make proteins according to instructions from the genes.

Question 16

Prokaryotic cells are characterized by having…

Answer 16

No nucleus (the nucleoid is the region where the
DNA is located but is not membrane bound).
In fact, no membrane-bound organelles.

Question 17

cytoplasm

Answer 17

The interior of either type of cell is called the cytoplasm; in
eukaryotic cells, this term refers only to the region between the
nucleus and the plasma membrane.

Question 18

Eukaryotic cells are characterized by having…

Answer 18

only about 5% of the
membrane of a eukaryotic cell is the plasma membrane.
- DNA in a nucleus that is bounded by (double membrane) a membranous
nuclear envelope.
- Membrane-bound organelles (internal membranes that
compartmentalize different functions).
- Cytoplasm in the region between the plasma
membrane and nucleus (note: cytosol is the fluid
portion of the cytoplasm).

Question 19

euk prok size numbers

Answer 19

• At the lower limit,
  the smallest cells known are bacteria called mycoplasmas,
  which have diameters between 0.1 and 1.0 μm. These are
  perhaps the smallest packages with enough DNA to program
  metabolism and enough enzymes and other cellular equipment to carry out the activities necessary for a cell to sustain
  itself and reproduce.
• Typical bacteria are 1–5 μm in diameter.
• Eukaryotic cells are typically 10–100 μm in diameter.

Question 20

SA/V ratio rationale

Answer 20

• At the boundary of
  every cell, the plasma membrane functions as a selective
  barrier that allows passage of enough oxygen, nutrients, and
  wastes to service the entire cell.
• For each square micrometer of membrane, only a limited amount of a particular substance can cross per second, so the ratio of surface area to
  volume is critical.
• As a cell (or any other object) increases in
  size, its volume grows proportionately more than its surface area. The center gets farther and farther
  away from the surface.

Question 21

Eukaryotes have exploited the SA:V principle in two ways:

increased the surface area of these large cells

Answer 21

1. Larger organisms do not have larger cells, they just have more cells.
2. The internalization of membrane bound structures has effectively increased the surface area of these large cells (imagine each small box as being an internal, membrane-bound organelle).

Question 22

nucleus

Answer 22

The nucleus contains most of the genes in the eukaryotic

cell. (Some genes are located in mitochondria and chloroplasts.)

Question 23

nuclear envelope

Answer 23

The nuclear envelope is a double membrane. Two membranes, each a lipid bilayer with associated proteins.

• pore complex
• nuclear lamina
• nuclaer matrix

Question 24

pore complex

Answer 24

• The envelope is perforated by
  pore structures. At the lip of
  each pore, the inner and outer membranes of the nuclear envelope are continuous.
• Inside each pore is a pore complex that consists of eight very large protein granules
  arranged in an octagon.
• It plays an important role in the
  cell by regulating the entry and exit of proteins and RNAs, as
  well as large complexes of macromolecules.

Question 25

nuclaer lamina

Answer 25

Except at the
pores, the nuclear side of the envelope is lined by the nuclear
lamina, a netlike array of protein filaments that maintains
the shape of the nucleus by mechanically supporting the nuclear envelope.

Question 26

nuclaer matrix

Answer 26

There is also much evidence for a nuclear
matrix, a framework of protein fibers extending throughout
the nuclear interior. The nuclear lamina and matrix may help
organize the genetic material so it functions efficiently

Question 27

nucleolus

Answer 27

• A prominent structure within the nondividing nucleus
• Consists of ribosomes and ribosomal RNA (rRNA); site of ribosome synthesis
• rRNA is synthesized from instructions
  in the DNA. Also in the nucleolus, proteins imported from
  the cytoplasm are assembled with rRNA into large and small
  subunits of ribosomes. These subunits then exit the nucleus
  through the nuclear pores to the cytoplasm, where a large and
  a small subunit can assemble into a ribosome.

Question 28

chromosomes

Answer 28

• condensed chromatin
  Within the nucleus, the DNA is organized into discrete units
  called chromosomes, structures that carry the genetic information.
• Each chromosome contains one long DNA molecule
  associated with many proteins.
• Some of the proteins help coil the DNA molecule of each chromosome, reducing its length
  and allowing it to fit into the nucleus.

Question 29

chromatin

Answer 29

Consists of DNA and its associated proteins,
in particular a group of proteins called histones around which
the DNA is wound. In addition, there are many regulatory proteins
that function in controlling gene expression.

Question 30

endomembrane system

Answer 30

• regulates protein traffic and
  performs metabolic functions in the cell.
• NEGLVP: nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, various kinds of vesicles and vacuoles, and the plasma membrane
• The membranes of this system are related either
  through direct physical continuity or by the transfer of membrane segments as tiny vesicles (sacs made of membrane).
• Despite these relationships, the various membranes are not
  identical in structure and function. Moreover, the thickness,
  molecular composition, and types of chemical reactions carried out in a given membrane are not fixed, but may be modified several times during the membrane’s life.

Question 31

ER stats

Answer 31

• About half of the cell’s membrane is ER membrane.
• Approximately 15% of the entire fluid volume of the
cell is inside the ER.

Question 32

ER

Answer 32

• The ER is a network of interconnecting membrane
enclosed sacs distributed throughout the cytoplasm.
• The ER is folded into a series of tubules (cisternae).
• The internal compartment (the lumen) is called the
cisternal space and is a separate from the cytosol. It
has a distinct protein and ion composition.
• At certain sites, the ER membrane is continuous with
the outer nuclear envelope membrane; the
space between the two membranes of the nuclear envelope is continuous with the lumen of the ER.

Question 33

smooth vs rough ER

Answer 33

Smooth ER is so named because its outer surface lacks ribosomes. Rough ER is studded with ribosomes on the outer
surface of the membrane and thus appears rough.
- Ribosomes are
also attached to the cytoplasmic side of the nuclear envelope’s
outer membrane, which is continuous with rough ER

Question 34

smooth ER

Answer 34

• The smooth ER functions in diverse metabolic processes,
  which vary with cell type
• (4): Synthesize lipids, Metabolize carbohydrates, Detoxify drugs and poisons, Store calcium ions

Question 35

smooth ER: lipid synthesis

Answer 35

Enzymes of the smooth ER are important in the synthesis
of lipids, including oils, phospholipids, and steroids. Among
the steroids produced by the smooth ER in animal cells are
the sex hormones of vertebrates and the various steroid hormones secreted by the adrenal glands. The cells that synthesize and secrete these hormones—in the testes and ovaries,
for example—are rich in smooth ER, a structural feature that
fits the function of these cells

Question 36

smooth ER: detox

Answer 36

• Other enzymes of the smooth ER help detoxify drugs and
  poisons, especially in liver cells. Detoxification usually involves adding hydroxyl groups to drug molecules, making
  them more soluble and easier to flush from the body
• Many drugs induce
  the proliferation of smooth ER and its associated detoxification enzymes, thus increasing the rate of detoxification. This,
  in turn, increases tolerance to the drugs.

Question 37

smooth ER: Ca2+

Answer 37

In muscle cells,
for example, the smooth ER membrane pumps calcium ions
from the cytosol into the ER lumen. When a muscle cell is
stimulated by a nerve impulse, calcium ions rush back
across the ER membrane into the cytosol and trigger contraction of the muscle cell. In other cell types, calcium ion release
from the smooth ER triggers different responses, such as secretion of vesicles carrying newly synthesized proteins

Question 38

rough ER function

Answer 38

• functions in protein synthesis.
• Many types of cells secrete proteins produced by ribosomes
  attached to rough ER.
• rough ER is a
  membrane factory for the cell; it grows in place by adding
  membrane proteins and phospholipids to its own membrane.
• As polypeptides destined to be membrane proteins
  grow from the ribosomes, they are inserted into the ER
  membrane itself and anchored there by their hydrophobic
  portions.
• Like the smooth ER, the rough ER also makes
  membrane phospholipids; enzymes built into the ER membrane assemble phospholipids from precursors in the cytosol.
• The ER membrane expands and portions of it are
  transferred in the form of transport vesicles to other components of the endomembrane system.

Question 39

rough ER: producing the protein

Answer 39

• As a polypeptide chain grows
  from a bound ribosome, the chain is threaded into the ER lumen through a pore formed by a protein complex in the ER
  membrane.
• As the new polypeptide enters the ER lumen, it
  folds into its native shape.
• Most secretory proteins are
  glycoproteins, proteins that have carbohydrates covalently
  bonded to them. The carbohydrates are attached to the proteins in the ER by enzymes built into the ER membrane.

Question 40

rough ER: Polypeptides can be directed one of two

ways:

Answer 40

1. to the ER’s cisternal space,
2. incorporated into the ER membrane.
   • Polypeptides can be further modified to change their folding, and/or have carbohydrate
   groups added to begin the process of protein maturation.

Question 41

rough ER: fate of the protein

Answer 41

After secretory proteins are formed, the ER membrane
keeps them separate from proteins that are produced by free
ribosomes and that will remain in the cytosol. Secretory proteins depart from the ER wrapped in the membranes of vesicles that bud like bubbles from a specialized region called
transitional ER.
• Some polypeptides entering the ER have address information that instructs their final
destination (secretion is the default destination).
• Some membrane and lumen proteins remain in the ER to maintain its function; others are
transported to the Golgi apparatus.

Question 42

Where Do Newly Synthesized Proteins Go?

Answer 42

made in rough ER:

1) are released outside the cell.
2) are inserted into the plasma membrane.
3) become part of an organelle.

made in cytoplasm:
4) remain in the cytoplasm as soluble proteins.

To make this happen, all proteins need to be directed to the appropriate
place in the cell.

Question 43

ribosomes

Answer 43

• complexes made of ribosomal RNA
  and protein (>50 proteins)
• large + small subunit
• the cellular components that carry out protein synthesis. Cells that have high rates of protein synthesis have particularly large numbers of ribosomes.
  For example, a human pancreas cell has a few million ribosomes. Not surprisingly, cells active in protein synthesis also
  have prominent nucleoli.

Question 44

ribosomes: 2 locales

Answer 44

Bound and free ribosomes are structurally identical, and ribosomes can alternate between the two roles
- free: suspended in cytosol. synthesize cytoplasmic, soluble proteins - ex: enzymes that catalyze the first steps of sugar breakdown
- bound: attached to the outside of the endoplasmic reticulum or nuclear envelope. Those attached to RER synthesize proteins that
are sometimes insoluble and are destined for insertion into membranes, packaging within certain organelles such as lysosomes, or secretion. Cells that specialize in
protein secretion—for instance, the cells of the pancreas that
secrete digestive enzymes—frequently have a high proportion of bound ribosomes.
- also found on Mitochondria and Chloroplasts

Question 45

mitochondria and chloroplasts

Answer 45

– ENERGY METABOLISM –
• Both of these organelles can move around the cell and divide.
• They have their own ribosomes and DNA that are used to synthesize
some of their proteins.
• These features suggest that at one time they were independent
prokaryotic organisms that developed a symbiotic relationship with
other cells.

Question 46

endosymbiont theory

Answer 46

1. anaerobic pre-eukaryotic cell (w/ ER, nucleus, nuclear envelope) engulfs an oxygen-using nonphotosynthetic prokaryote, which becomes a mitochondrion w/ outer membrane derived from eukaryotic cell
2. now host cell is a nonphotosynthetic eukaryote w/ mitochondrion. it engulfs a photosynthetic prokaryote, which becomes a chloroplast
3. now host cell is a photosynthetic euk

Question 47

mitochondria

Answer 47

• found in virtually all eukaryotic cells.
• vary in size from 1 -10µm (about the same
  size as a bacterium…supporting the
  endosymbiont theory).

Question 48

mitochondria membranes

Answer 48

• Made up of a an outer smooth
membrane, and an inner membrane that is
folded into a series of convolutions called
cristae.
- As highly folded
surfaces, the cristae give the inner mitochondrial membrane
a large surface area, thus enhancing the productivity of cellular respiration. This is another example of structure fitting
function.
•Between these is the intermembrane
space.

Question 49

matrix

Answer 49

Inside the inner membrane is a region
called the matrix (in which there are free ribosomes) that contains many of the
enzymes important for cellular respiration
where the energy derived from
carbohydrates and lipids is transferred to
the molecules, particularly ATP, that are
used as energy sources for many cellular
process

Question 50

chloroplasts

Answer 50

• The organelle that is responsible for photosynthesis: transforming
sunlight into forms of energy that plant cells can use.
• Structure is similar to a mitochondrion in that chloroplasts have a
double membrane. Inside the inner membrane is a compartment
called the stroma (analogous to the matrix of mitochondria). stroma is the fluid outside the thylakoids
• Chloroplasts have another compartment: a series of discs called
thylakoids, which in some cases are stacked into structures called
grana. The thylakoids are where chlorophyll is located and is the site
of photosynthesis.

Question 51

cytoskeleton

Answer 51

– Structural and transport functions –
• Maintains cell shape, and provides support and anchor points for
organelles.
• Provides the mechanisms for cell movement (flagellae and
pseudopodia) and force generation (e.g. muscle contraction).
• Serves as tracks for motor proteins that move materials and
organelles within cells.
There are three major types of
cytoskeletal components:
• Microfilaments
• Intermediate filaments
• Microtubules

Question 52

motor proteins

Answer 52

Motor proteins that attach to receptors on vesicles (or organelles) can “walk”
the vesicles along microtubules or, in some cases, microfilaments

Question 53

microtubules

Answer 53

• tubulin polymers
• hollow tubes
• 25 nm diameter w/ 15 nm lumen
• protein subunits: tubulin, a dimer of alpha- and beta-tubulin
  functions:
• maintenance of cell shape (compression-resisting “girders”)
• cell motility (cilia/flagella)
• chromosome movements in cell div
• organelle mvmnts

Question 54

microfilaments

Answer 54

• actin filaments
• Two intertwined strands of actin, each
  a polymer of actin subunits
• 7 nm diameter
  functions:
• maintenance of cell shape (tension (pulling forces)-bearing elements)
• changes in cell shape
• muscle contraction
• cytoplasmic streaming in plant cells
• cell motility (amoeboid mvmnt (pseudopodia))
• division of animal cells (cleavage furrow formation)

Question 55

intermediate filaments

Answer 55

• Fibrous proteins supercoiled into thicker cables
• 8-12 nm diameter
• subunits: One of several different proteins (such as
  keratins) , depending on cell type
  functions:
• maintenance of cell shape (tension-bearing elements)
• anchorage of nucleus and certain other organelles
• formation of nuclear lamina

Question 56

centrosome

Answer 56

-  Most animal cells have a centrosome, a region near the nucleus where
the cell’s microtubules grow out from. Within the centrosome is a pair of
centrioles, each about 250 nm (0.25 μm) in diameter. Each is made up of nine
sets of three microtubules. 
•Centrosomes are important for cell
division (mitosis) in animal cells.
• They are made from microtubules
and other proteins 
• The 2 centrioles are oriented at right
angles to each other and are
microtubule organizing centers
(MTOCs)

Question 57

cilia vs flagella

Answer 57

• Microtubules are the structural components of cilia and flagella.
• Cilia and flagella are covered by the cell’s plasma membrane.
• Similar to microvilli but moveable.
• Flagella are usually longer than cilia, and cells that have them usually
only have one or two; not on all cells…only on sperm in mammals
• Cilia are usually present in great numbers.

Question 58

cell junctions

Answer 58

• Neighboring cells often adhere, interact,
  and communicate via sites of direct physical contact.
• In animals, there are three main types of cell junctions: tight
  junctions, desmosomes, and gap junctions.

Question 59

tight junctions

Answer 59

- At tight junctions, the plasma
membranes of neighboring cells are
very tightly pressed against each
other. Forming continuous seals around the cells, tight
junctions prevent leakage of extracellular fluid across a layer of
epithelial cells. 
- As if the
cells were sewn together.

Question 60

desmosomes

Answer 60

• At desmosomes, membranes of neighboring cells are pressed together – function like rivets, fastening cells together into strong sheets.
• Akin to a shirt button.
• Desmosomes are linked to intermediate filaments (these filaments anchor desmosomes in the cytoplasm), providing shear and tensile strength between cells.
• attach muscle cells to each other in a muscle

Question 61

gap junctions

Answer 61

- (communicating junctions)
provide cytoplasmic
channels between adjacent
cells.
- necessary for communication between cells in many
types of tissues, such as heart muscle, and in animal embryos.
- (Analogous to
plasmodesmata of plant
cells.)

Question 62

ECM

Answer 62

• Animal cells lack cell walls but are covered by an elaborate
  extracellular matrix (ECM).
• The ECM is made up of glycoproteins such as collagen,
  fibronectin and proteoglycans.

Question 63

proteoglycan

Answer 63

• A proteoglycan molecule consists of a small core protein w/ attached carbohydrates
• A proteoglycan
  complex consists
  of hundreds of
  proteoglycan
  molecules attached
  noncovalently to a
  single long polysaccharide molecule.

Question 64

collagen

Answer 64

Collagen fibers
are embedded
in a web of
proteoglycan
complexes

Question 65

fibronectin

Answer 65

attaches the
ECM to
integrins
embedded in
the plasma
membrane.

Question 66

integrins

Answer 66

-  ECM proteins bind to receptor proteins in the plasma membrane
called integrins. On the side of the integrin that faces the interior of the cell, it is bound to associated proteins
attached to
microfilaments. 
- This linkage can
transmit signals
between the cell’s
external environment
and its interior and can
result in changes in cell
behavior.

Question 67

where’d all the cell’s internal membranes come from?

Answer 67

- Imagine a prehistoric procaryotic cell with
DNA and ribosomes attached to the plasma
membrane.
- Invaginations of surface membrane
of ancient procaryotic cell led to
 internalization of membranes creating
rough and smooth ER.
- In addition, the DNA became bound
with a double membrane.

Question 68

microvilli

Answer 68

• Increase surface area of the cell.

- Helps to increase rate of uptake of molecules from extracellular space.

Question 69

4 structures in plant cells not in animal cells

Answer 69

• central vacuole (Storage, hydrolysis of macromolecules)
• chloroplast
• cell wall (maintains cell’s shape)
• plasmodesmata (Cytoplasmic channels between adjoining cells)

Question 70

3 structures in animal cells not in plant cells

Answer 70

• flagellum
• centrosome
• lysosome

Question 71

cell organelles

Answer 71

• Important for compartmentalization within the cell - the physical
  separation of cell functions.
• Allows different chemical environments to exist within the cell.
  1. pH; allows enzymes to function in an isolated environment.
  Some hydrolytic enzymes require a low pH to function. These enzymes are
  sequestered in organelles. If they “escape” to the cytosol, they are largely
  ineffective.
  2. Ionic gradients; generation of ATP in mitochondria requires an ionic
  gradient that is established across the mitochondrial inner membrane.

Question 72

Golgi apparatus

Answer 72

• responsible for the functional
  maturation of proteins.
• After leaving the ER, many transport vesicles travel to the Golgi
  apparatus. We can think of the Golgi as a warehouse for receiving, sorting, shipping, and even some manufacturing. Here,
  products of the ER, such as proteins, are modified and stored
  and then sent to other destinations.
• especially extensive in cells specialized for secretion.

Question 73

Golgi structure

Answer 73

• Similar in structure to the smooth ER, and is
usually seen as a series of stacked discs or flattened membranous
sacs (cisternae) within the cell.
• There is a definite direction or polarity to the
structure, with
the membranes of cisternae on opposite sides of the stack differing in thickness and molecular composition.
• Transport vesicles are budded off the
RER and fuse with the Golgi apparatus at
its cis (receiving) face. Processed material leaves at
the trans (shipping) face, where vesicles pinch off and travel to other sites.

Question 74

within the golgi

Answer 74

• Material is transferred from one disc to
another by transport vesicles that are guided by
special signaling proteins or tags attached to
the outside of the vesicles.
•As proteins travel through the Golgi apparatus they are modified until they become the final product that
can either be used by the cell or released from it by secretion.
•This modification process often occurs using specialized enzymes that are located at different points
between the cis and the trans part of the Golgi. Modifications include glycosylation, phosphorylation and
sulfation.

Question 75

products of the golgi

Answer 75

•The main products of the Golgi are sets of small vesicles that bud off from the trans side of the Golgi.
Three main groups:
1. Lysosomes
2. Secretory vesicles—membrane bound organelles that release their contents to the outside of the cell.
3. Vesicles containing proteins destined to be part of the plasma membrane.
- In addition to its finishing work, the Golgi apparatus also
manufactures some macromolecules. Many polysaccharides
secreted by cells are Golgi products.

Question 76

lysosome

Answer 76

• Contain enzymes
  important for the digestion
  of all the major types of
  macromolecules.
• Lysosomal enzymes work best in the acidic environment (pH 5)
  found in lysosomes. If a lysosome breaks open or leaks its contents, the released enzymes are not very active because the cytosol has a neutral pH. However, excessive leakage from a large
  number of lysosomes can destroy a cell by self-digestion.

Question 77

creation of lysosomes

Answer 77

Hydrolytic enzymes and lysosomal membrane are made
by rough ER and then transferred to the Golgi apparatus for
further processing. At least some lysosomes probably arise by
budding from the trans face of the Golgi apparatus

Question 78

How are the proteins of the inner surface of the
lysosomal membrane and the digestive enzymes themselves
spared from destruction?

Answer 78

the three-dimensional

shapes of these proteins protect vulnerable bonds from enzymatic attack.

Question 79

phagocytosis

Answer 79

• Some types of cells can ingest food in vacuoles in a process called phagocytosis. Amoebas and many other protists eat by engulfing smaller organisms or food particles, a process called phagocytosis.
• The food vacuole formed in this way then fuses with a lysosome, whose enzymes digest the food.
• Digestion products, including simple sugars, amino acids, and other monomers, pass into the cytosol and become nutrients for the cell.

Question 80

autophagy

Answer 80

• Lysosomes also use their hydrolytic enzymes to recycle the cell’s own organelles and macromolecules, a process called autophagy.
• During autophagy, a damaged organelle or small amount of cytosol becomes surrounded by a double membrane (creating a vesicle), and a lysosome fuses with the outer membrane of this vesicle. The lysosomal enzymes dismantle the enclosed material, and the organic monomers are returned to the cytosol for reuse.
• With the help of lysosomes, the cell continually renews itself.

Question 81

Ultrastructure of a MOTILE eukaryotic flagellum or cilium

Answer 81

• 9(2) + 2(1): Nine doublets of microtubules are arranged in a ring; in the center of the ring are two single microtubules; sheathed in an extension of the plasma membrane
• The microtubule assembly of a cilium or
  flagellum is anchored in the cell by a basal body, which is
  structurally very similar to a centriole, with microtubule
  triplets in a “9 + 0” pattern.
• flexible cross-linking proteins,
  evenly spaced along the length of the cilium or flagellum,
  connect the outer doublets to each other and to the two central microtubules
• radial spokes

Question 82

dyneins

Answer 82

Each outer doublet also has pairs of protruding proteins spaced along its length and reaching toward
the neighboring doublet; these are large motor proteins called
dyneins, each composed of several polypeptides. Dyneins
are responsible for the bending movements of the organelle.
- A typical dynein protein has two “feet”
that “walk” along the microtubule of the adjacent doublet
- this walking bends cilia and flagella

Question 83

beating of flagella

Answer 83

- Flagella move in
an undulating pattern
like a snake.
-  generates force in the
SAME direction as the flagellum’s axis

Question 84

beating of cilia

Answer 84

Cilia beat in a wave
pattern with a
power and recovery
stroke.
-  generating force in a direction PERPENDICULAR to
the cilium’s axis

Question 85

cortex

Answer 85

A three-dimensional
network formed by microfilaments just inside the plasma membrane (cortical microfilaments) helps support the cell’s
shape. This network gives the outer cytoplasmic layer of a cell, called the cortex, the semisolid consistency of a gel, in contrast with the more fluid (sol) state of the
interior cytoplasm.
[ cortex: gel w/ actin network; sol: w/ actin subunits ]

Question 86

Microfilaments are well known for their role in cell motility

Answer 86

• particularly as part of the contractile apparatus of muscle cells.
• Thousands of actin filaments are arranged parallel to one
  another along the length of a muscle cell, interdigitated
  with thicker filaments made of a protein called myosin. Myosin acts as a motor protein using “walking mechanism” simialr to dynein. Contraction of the
  muscle cell results from the actin and myosin filaments sliding
  past one another in this way, shortening the cell.
• Localized contraction brought about by actin and myosin
  also plays a role in amoeboid movement. A
  cell such as an amoeba crawls along a surface by extending cellular extensions called pseudopodia. Actin moves forward and extends amoeba.

Question 87

cytoplasmic streaming

Answer 87

In plant cells, both actin-myosin interactions and sol-gel
transformations brought about by actin may be involved in
cytoplasmic streaming, a circular flow of cytoplasm
within cells (Figure 6.27c). This movement, which is especially common in large plant cells, speeds the distribution of
materials within the cell.