MOD 1 UNIT 2: THE CELL (PART 2)

Question 1

These irregular vesicles near the cell periphery form part of the pathway for receptor-mediated endocytosis and contain receptor–ligand complexes.

Answer 1

early endosomes

Question 2

PAPASA BA TAYO DITO?

Answer 2

YES IS THE ONLY OPTION BITCH

Question 3

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

early endosomes are also known as the Compartment for Uncoupling of Receptors and
Ligands (CURL).

Their acidic interiors (pH _ 4) are maintained by ATP-driven proton pumps.

Answer 3

“A”

second statement, “pH 6”

Question 4

TRUE OR FALSE

Lysosomes are formed when sequestered material fuses with a late endosome,
and enzymatic degradation begins.

Answer 4

TRUE

Question 5

TRUE OR FALSE

In early endosomes, the acidity aids in the uncoupling of receptors and ligands; receptors return to the plasma membrane and ligands move to a late endosome.

Answer 5

TRUE

Question 6

These irregular vesicles (pH _ 5.5) deep within the cell receive ligands via microtubular transport of vesicles from early endosomes.

Answer 6

Late endosomes

Question 7

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

Late endosomes play a key role in various lysosomal pathways and therefore are
sometimes known as the intermediate compartment.

Late endosomes contain both lysosomal hydrolases and lysosomal
membrane proteins, these are formed in the RER, transported to the Golgi complex
for processing, and delivered in separate vesicles to late endosomes.

Answer 7

“C”

Question 8

TRUE OR FALSE

Once late endosomes have received a full complement of lysosomal enzymes,
they begin to degrade their ligands and are classified as chromosomes.

Answer 8

FALSE

“classified as lysosomes”

Question 8

are formed by fusion of an early endosome containing endocytic vesicles with a late endosome.

Answer 8

Multivesicular bodies

Question 9

are formed by fusion of a phagocytic vacuole with a late endosome
or a lysosome.

Answer 9

Phagolysosomes

Question 10

are formed by fusion of an autophagic vacuole with a late endosome or lysosome.

Answer 10

Autophagolysosomes

Question 11

are formed when cell components targeted
for destruction become enveloped by smooth areas of membranes derived from the RER.

Answer 11

Autophagic vacuole

Question 12

are lysosomes of any type that have expended their capacity to degrade material. They contain undegraded material (e.g., lipofuscin and hemosiderin) and eventually may be excreted from the cell.

Answer 12

Residual bodies

Question 13

are characterized by a visible cytoplasmic surface coat

Answer 13

Coated vesicles

Question 14

are formed during receptor-mediated uptake (endocytosis) of specific molecules by the cell, this also function in the signal-directed (regulated) transport of proteins from the TGN either to the secretory granule pathway or to the late endosome–lysosome pathway.

Answer 14

Clathrin-coated vesicles

Question 15

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

clathrin-coated vesicles consists of ten large and three small polypeptide chains that form a triskelion (three-legged structure).

Proteins called adaptins are also part of clathrin-coated vesicles.

Answer 15

“B”

first statement, “three large”

Question 16

forms a ring around the neck of a budding vesicle or pit and aids in pinching it off the parent membrane to form a free clathrin-coated vesicle.

Answer 16

Dynamin (guanosine triphosphate (GTP)–
binding protein)

Question 17

mediate the continuous constitutive protein transport (default pathway; bulk flow) within the cell. This also transport proteins from the RER to the VTC to the Golgi
apparatus, from one Golgi cisterna to another, and from the TGN to the plasma
membrane.

Answer 17

Coatomer-coated vesicles

Question 18

ensure that the vesicle docks and fuses only with its correct target membrane.

Answer 18

SNARES protein

Question 19

recognize and bind to complementary target SNARES (t-SNARES) to deliver not only cargo molecules but also membrane to the target compartment.

Answer 19

Coated vesicle SNARES (v-SNARES)

Question 20

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

COP-II transports molecules backward from the RER to the VTC to the cis Golgi and
across the cisternae to the TGN (anterograde transport).

COP-I facilitates retrograde transport (from the VTC or any Golgi cisternal
compartment or from the TGN) to the RER.

Answer 20

“B”

first statement, “transport molecules forward”

Question 21

TRUE OR FALSE

Caveolin-coated vesicles are less common and less well understood

Answer 21

TRUE

Question 22

They have been associated with cell signaling and a variety of transport
processes, such as transcytosis and endocytosis, they also are invaginations of the plasma membrane in endothelial and smooth muscle cells.

Answer 22

Caveolin-coated vesicles

Question 23

is an irregular network of membrane-bounded channels that lacks
ribosomes on its surface, which makes it appear smooth. It usually appears as branching, anastomosing tubules, or vesicles, whose membranes do not contain ribophorins.

Answer 23

Smooth endoplasmic reticulum (SER)

Question 24

This is a double-membrane organelle (like the nucleus) that generates adenosine
triphosphate (ATP) to fuel energy-requiring activities of the cell. It also functions in some
specialized synthetic pathways such as that for steroid hormones.

Answer 24

Mitochondrion

Question 25

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

Mitochondria possess an inner membrane, which surrounds the organelle, and an inner
membrane, which invaginates to form cristae.

Mitochondria are subdivided into an intermembrane compartment between the two membranes and an inner matrix
compartment.

Answer 25

“B”

first statement, “outer membrane”

Question 26

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

Elementary particles (visible on negatively stained cristae) represent adenosine
triphosphate (ATP) synthase, a special enzyme embedded in the inner mitochondrial
membrane.

It consists of a head portion and a transmembrane H_ carrier and is involved in
coupling oxidation to phosphorylation of adenosine diphosphate (ADP) to form ATP.

Answer 26

“C”

Question 27

are found in rapidly growing cells (e.g., germ cells, embryonic cells, and tumor cells), but their function and significance remain unknown.

Answer 27

Annulate lamellae

Question 27

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

Mitochondria may have originated as symbionts (intracellular parasites).

Mitochondria proliferate by division (fission) of preexisting mitochondria and typically
have a 6-day life span.

Answer 27

“A”

second statement, “10-day life span”

Question 27

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

In condensed mitochondria, the size of the inner compartment is decreased and the matrix density is increased.

Condensed mitochondria are present in brown fat cells, which produce heat, rather
than ATP because they have a special transport protein in their inner membrane that
uncouples respiration from ATP synthesis.

Answer 27

“C”

Question 27

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

Mitochondria does not synthesize ATP via the Krebs cycle, which traps chemical energy and
produces ATP by oxidation of fatty acids, amino acids, and glucose.

ATP is also synthesized via a chemiosmotic coupling mechanism involving enzyme
complexes of the electron transport chain and ATP synthase present in elementary
particles of cristae.

Answer 27

“B”

first statement, “Mitochondria synthesize ATP”

Question 28

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

Annulate lamellae are parallel stacks of membranes (usually 6 to 10) that
resemble the nuclear envelope, including its pore complexes.

They are often arranged
with their annuli (pores) in register and are frequently continuous with the RER.

Answer 28

“C”

Question 29

(also known as microbodies) are membrane-bound, spherical, or ovoid
organelles that may be identified in cells by a cytochemical reaction for catalase.

Answer 29

Peroxisomes

Question 30

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

Peroxisomes may contain a nucleoid, a crystalline core consisting of urate oxidase (uricase)

The human peroxisome is abundant in nucleoid.

Answer 30

“A”

second statement, “lacks a nucleoid”

Question 31

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

They originate from preexisting peroxisomes, which grow by importing specific
cytosolic proteins that are recognized by receptor proteins (called peroxins) in the
peroxisomal membrane.

Then the peroxisome divides by fission; it has a life span of approximately 5 to 6 months.

Answer 31

“A”

second statement, “5 to 6 days”

Question 31

contain various enzymes whose functions vary from the oxidation of long-chain fatty acids to the synthesis of cholesterol to the detoxification of substances such as ethanol.

Answer 31

peroxisomes

Question 32

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

Inclusions are accumulations of material that is not metabolically active.

They usually are present in the cytosol only temporarily.

Answer 32

“C”

Question 33

TRUE OR FALSE

Glycogen appears as small clusters (or in hepatocytes as larger aggregates, known as
rosettes) of electron-dense 20- to 30-nm _-particles, which are similar in appearance to but
smaller than ribosomes.

Answer 33

FALSE

“larger than ribosomes”

Question 34

serves as a stored energy source that can be degraded to glucose, which enters the bloodstream to elevate blood sugar levels.

Answer 34

Glycogen

Question 35

are storage forms of
triglycerides (an energy source) and cholesterol (used in the synthesis of steroids and
membranes).

Answer 35

Lipid droplets

Question 36

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

Lipid droplets vary markedly in size and appearance depending on the method of
fixation, and they are not bound by a membrane.

Lipofuscin appears as membrane-bound, electron-dense granular material varying
greatly in size and often containing lipid droplets.

Answer 36

“C”

Question 37

represents a residue of
undigested material present in residual bodies. Because the amount of this material
increases with age, it is called age pigment.

Answer 37

Lipofuscin

Question 38

TRUE OR FALSE

Lipofuscin is most common in nondividing cells (e.g., cardiac muscle cells, neurons) but also is found in hepatocytes.

Answer 38

TRUE

Question 39

it is the major microtubule-organizing center in the cell, this is composed of a pair of centrioles embedded in amorphous material.

Answer 39

centrosome

Question 40

TRUE OR FALSE

The centrosome functions in organizing the array of microtubules in the cell’s cytoplasm and in developing the spindle apparatus during cell division.

Answer 40

TRUE

Question 41

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

centrosome contains two centrioles and a
cloud of pericentriolar material.

Each member of the pair is
composed of five triplets of microtubules (5 _ 0 axoneme pattern) arranged radially in the
shape of a pinwheel.

Answer 41

second statement, “nine triplets”

Question 42

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

The centrioles self-duplicate in the S phase of the cell cycle, as each parent centriole a
procentriole at right angles to itself.

Centrioles also form basal bodies, which appear identical to unpaired centrioles and
which give rise to the axonemes of cilia and flagella.

Answer 42

“C”

Question 43

TRUE OR FALSE

Centrioles play big role in nucleating microtubules, and they help to maintain the
organization of the centrosome.

Answer 43

FALSE

“centrioles play no role in nucleating microtubules”

Question 44

is the structural framework within the cytosol. It functions in maintaining cell shape, stabilizing cell attachments, facilitating endocytosis and
exocytosis, and promoting cell movement.

Answer 44

cytoskeleton

Question 45

maintain cell shape; aid in the transport of macromolecules within the cytosol; assemble into the mitotic spindle during mitosis and ensure the correct distribution of chromosomes to daughter cells; and assist in the formation of cell appendages called cilia and flagella, which beat rhythmically and precisely.

Answer 45

MICROTUBULES

Question 46

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

microtubules have a rigid wall composed of 20 protofilaments, each of which consists of a
linear arrangement of tubulin dimers; each dimer consists of nonidentical and tubulin
subunits.

Microtubules are polar, with polymerization (assembly) and depolymerization
(disassembly) occurring preferentially at the plus end when GTP is bound to tubulin dimers.

Answer 46

“B”

first statement, “13 protofilaments”

Question 47

TRUE OR FALSE

Kinesin moves cargo toward the plus end of the
microtubule (outward), whereas cytoplasmic dynein moves it toward the minus end
(inward).

Answer 47

TRUE

Question 48

play a role in many cellular processes, such as establishing focal contacts between the cell and the extracellular matrix, locomotion of nonmuscle cells, formation of the contractile ring (in dividing cells), and the folding of epithelia into tubes during development.

Answer 48

ACTIN FILAMENTS

Question 48

TRUE OR FALSE

Actin filaments measure 7 nm in diameter and are composed of globular
actin monomers (G actin) linked into a double helix (F actin). They are thin, flexible, and
abundant in cells.

Answer 48

TRUE

Question 49

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

Actin filaments display non-polarity similar to that of microtubules; that is, their polymerization and depolymerization occur preferentially at the plus end when ATP is bound by G actin.

Actin filaments are abundant at the periphery of the cell, where they are anchored to
the plasma membrane via one or more intermediary proteins (e.g., actinin, vinculin, and
talin).

Answer 49

“B”

first statement, “display polarity”

Question 50

They constitute a population of
heterogeneous filaments that includes keratin, vimentin, desmin, glial fibrillary acidic
protein (GFAP), lamins, and neurofilaments.

Answer 50

intermediate filaments

Question 51

TRUE OR FALSE

intermediate filaments provide mechanical strength to cells. They lack polarity and do not require GTP or ATP for assembly, which occurs along the entire length of the filament.

Answer 51

TRUE

Question 52

TRUE OR FALSE

Cell membranes are composed primarily of phospholipids and proteins

Answer 52

TRUE

Question 53

have a glycerol backbone, which is the hydrophilic (water soluble) head,
and two fatty acid tails, which are hydrophobic (water insoluble).

Answer 53

Phospholipids

Question 54

TRUE OR FALSE

The hydrophobic tails face each other and form a bilayer.

Answer 54

TRUE

Question 55

cross cell membranes because they can dissolve in the hydrophobic lipid bilayer. (e.g., O2, CO2, steroid hormones)

Answer 55

Lipid-soluble substances

Question 56

cannot dissolve in the lipid of
the membrane, but may cross through water-filled channels, or pores, or may be
transported by carriers. (e.g., Na , Cl−, glucose, H2O)

Answer 56

Water-soluble substances

Question 57

are anchored to, and imbedded in, the cell membrane through hydrophobic
interactions.

Answer 57

integral proteins

Question 58

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

Integral proteins may span the cell membrane.

This include ion channels, transport proteins, receptors, and guanosine 5′-triphosphate
(GTP)–binding proteins (G proteins).

Answer 58

“C”

Question 59

are not imbedded in the cell membrane.

Answer 59

Peripheral proteins

Question 60

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

Peripheral proteins are covalently bound to membrane components.

They are loosely attached to the cell membrane by electrostatic interactions.

Answer 60

“B”

first statement, “are not covalently bound”

Question 61

They are usually motile, with a whipping motion that consists of a power stroke and a recovery
stroke.

Answer 61

Cilia

Question 62

These are cylindrical, nonmotile extensions, typically about 80 nm in diameter and 1
μm long.

Answer 62

Microvilli

Question 63

TRUE OR FALSE

In some cells, microvillis are several micrometers long, in which case, they are called
stereocilia.

Answer 63

TRUE

Question 64

Also called tight junctions, these are sites of fusion between plasmalemmas of adjacent epithelial cells that separate the lumen from the underlying connective tissue.

Answer 64

ZONULA OCCLUDENS

Question 65

prevent materials from passing from one compartment to another by
diffusing through the space between adjacent epithelial cells.

Answer 65

Tight junctions

Question 66

TRUE OR FALSE

tight junction may be “tight” (impermeable), as in the renal distal tubule, or “leaky” (permeable),
as in the renal proximal tubule and gallbladder.

Answer 66

TRUE

Question 67

These are sites of mechanical adhesion between adjacent epithelial cells. They are
generally associated with and parallel to tight junctions.

Answer 67

ZONULA ADHERENS

Question 68

Also called desmosomes, these, like zonula adherens, are sites of mechanical
adhesion between cells, but they are configured as spots rather than bands.

Answer 68

Macula adherens

Question 69

Also called nexus junctions, the small space between the membranes is bridged by
connexons, each of which is a cylindrical complex of proteins forming a pore.

Answer 69

gap junctions

Question 70

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

gap junctions do not allow free flow of small ions between cells, so that the cells are electrically
coupled.

are the attachments between cells that permit intercellular communication.

Answer 70

“B”

first statement, “allow free flow”

Question 71

Infoldings of the plasmalemma at the basal surface of an epithelial cell provide
greatly increased surface area in support of extensive traffic of substances between the
cytosol and the underlying interstitial compartment.

Answer 71

Basolateral folds

Question 72

This is an extracellular layer at the interface of a cell and the adjacent connective
tissue. These are characteristic of the basal surfaces of epithelia, but they are not
restricted to epithelia.

Answer 72

Basal lamina

Question 72

TRUE OR FALSE

Lateral folds can
have an additional function of contributing mechanical strength to a layer of cells by
interlacing with complementary folds of an adjacent cell.

Answer 72

TRUE

Question 73

is the uptake (internalization) of material by cells, this includes pinocytosis, receptor-mediated endocytosis, and phagocytosis.

Answer 73

Endocytosis

Question 74

is the nonspecific (random) uptake of extracellular fluid and material in solution into pinocytic vesicles.

Answer 74

Pinocytosis (“cell drinking”)

Question 75

is the specific uptake of a substance (e.g., low-density lipoproteins [LDLs] and protein hormones) by a cell that has a plasma membrane receptor
for that substance (which is termed a ligand).

Answer 75

Receptor-mediated endocytosis

Question 76

[SEQUENCING]

Receptor-mediated endocytosis sequence of events:

A ligand binds specifically to its receptors on the cell surface.

The cytoplasmic clathrin coat is rapidly lost, leaving an uncoated endocytic vesicle
containing the ligand.

Ligand–receptor complexes cluster into a clathrin-coated pit, which invaginates and
gives rise to a clathrin-coated vesicle containing the ligand.

Answer 76

1,3,2

Question 77

also known as “cell eating”, is the uptake of microorganisms, other cells, and particulate matter (frequently of foreign origin) by a cell.

Answer 77

Phagocytosis

Question 78

[SEQUENCING]

Phagocytosis degrade proteins
and cellular debris and involves the following sequence of events:

A macrophage binds via its Fc receptors to a bacterium coated with the antibody
immunoglobulin G (IgG) or via its C3b receptors to a complement-coated bacterium.

Binding progresses until the plasma membrane completely envelops the bacterium,
forming a phagocytic vacuole.

Answer 78

1,2

Question 79

is the release of material from the cell via fusion of a secretory granule
membrane and the plasma membrane. It requires interaction of receptors in both the
secretory granule membrane and the plasma membrane as well as the coalescence
(adherence and joining) of the two phospholipid membrane bilayers.

Answer 79

Exocytosis

Question 80

TRUE OR FALSE

Exocytosis takes place in both regulated and constitutive secretion.

Answer 80

TRUE

Question 81

is the release, in response to an extracellular
signal, of proteins and other materials stored in the cell.

Answer 81

Regulated secretion (signal directed)

Question 82

is the more or less continuous release of
material (e.g., collagen and plasma proteins) without any intermediate storage step.

Answer 82

Constitutive secretion (default pathway)

Question 83

TRUE OR FALSE

An extracellular signal is required for constitutive secretion.

Answer 83

FALSE

“it is not required”

Question 84

maintains a relatively constant plasma membrane surface area following exocytosis. In this process, the secretory granule membrane added to the plasma membrane surface during exocytosis is retrieved through endocytosis via clathrin coated vesicles

Answer 84

Membrane recycling

Question 85

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

Synthesis of membrane-packaged proteins involves translation of mRNAs encoding the
protein on polyribosomes at the surface of the RER, transport of the growing polypeptide
chain across the RER membrane and into the cisterna (lumen)

These water-soluble proteins will bud from the RER and be transported in vesicles
either for transfer into the lumen (or interior) of another organelle or for secretion from the
cell.

Answer 85

“C”

Question 86

[SEQUENCING]

A three-step process translates mRNA as follows:

The mRNA moves a distance of one codon (three nucleotides) through the small subunit, and the “spent” initiator tRNA moves to the E site and is ejected, leaving the A site empty so that a new aminoacyl tRNA can bind

Methionine at the P site forms the first peptide bond with the incoming amino acid forming
a dipeptide

mRNA binds to the small subunit
of a ribosome that has three binding sites (A, P, and E) for tRNA molecules. The next codon is recognized by an aminoacyl tRNA bearing the proper amino acid, which then binds to the A site

Answer 86

3,2,1

Question 87

[SEQUENCING]

Transport of the newly formed peptide into the RER cisterna is thought to occur by
a mechanism described by the signal hypothesis as follows:

mRNAs for secretory, membrane, and lysosomal proteins contain codons that encode a
signal sequence.

Synthesis of the growing chain stops until the SRP facilitates the relocation of the
polysome to SRP receptors in the RER membrane.

The large subunits of the ribosomes interact with ribosome receptor proteins, which bind
them to the RER membrane. The SRP detaches, and multisubunit protein translocators form a pore across the RER membrane. Synthesis resumes, and the newly formed polypeptide is threaded through the pore and into the RER cistern (lumen).

When the signal sequence is formed on the ribosome, a signal recognition particle (SRP)
in the cytosol binds to it.

Answer 87

1342

Question 87

TRUE OR FALSE

not only one particular type of the many tRNAs in a cell can base-pair with each codon

Answer 87

FALSE

“only one type”

Question 87

[SEQUENCING]

Posttranslational modification in the RER

The polypeptide is glycosylated.

After the newly formed polypeptide enters the cisterna, a signal peptidase cleaves the
signal sequence from it.

Disulfide bonds form, converting the linear polypeptide into a globular form.

Answer 87

2,1,3

Question 87

TRUE OR FALSE

The ribosome moves along the mRNA in the 5_ to 3_ direction using acylated tRNAs as adapters to add each amino acid to the end of the
growing peptide chain, which is always located at the P site of the large subunit of the ribosome.

Answer 87

TRUE

Question 88

[SEQUENCING]

Protein transport from the RER to the cis Golgi

Transitional elements of the RER give rise to COP-II coatomer–coated vesicles
containing newly synthesized protein.

These vesicles move to the VTC where they deliver the protein.

The VTC appears to be the first way station for the segregation of anterograde versus
retrograde transport in the secretory pathway. Either proteins move forward toward the cis
Golgi, or if they are RER-resident proteins that escaped from the RER, they are captured by
a specific membrane receptor protein and returned in COP-I coatomer-coated vesicles to
the RER along a microtubule guided pathway.

Answer 88

1,2,3

Question 88

[SEQUENCING]

Synthesis of membrane-packaged proteins:

Transport of the newly formed peptide into the RER cisterna

Posttranslational modification in the RER

Protein transport from the RER to the cis Golgi

Anterograde transport from the VTC to the cis Golgi

Movement of material anterograde among the Golgi subcompartments

Protein processing in the Golgi complex

Sorting of proteins in TGN

Answer 88

1,2,3,4,5,6,7

Question 89

[SEQUENCING]

Protein synthesis:

Synthesis of cytosolic proteins

Synthesis of membrane-packaged proteins

Synthesis of transmembrane proteins

Answer 89

3,1,2

Question 89

[SEQUENCING]

Movement of material anterograde among the Golgi subcompartments may occur by
cisternal maturation and/or by vesicular transport, as follows:

Cisternae containing proteins may change in biochemical composition as they move
intact across the stack.

COP-II–coated vesicles may bud off one cisterna and fuse with the dilated rim of
another cisterna.

Retrograde vesicular transport occurs between Golgi cisternae and between the Golgi
and the VTC or RER via COP-I–coated vesicles.

Although both mechanisms have been observed, the precise way that anterograde
transport occurs across the Golgi stack of cisternae is unresolved.

Answer 89

1,2,4,3

Question 89

TRUE OR FALSE

Anterograde transport from the VTC to the cis Golgi is via COP-I coatomer–coated
vesicles.

Answer 89

FALSE

“COP-II”

Question 90

TRUE OR FALSE

Protein processing in the Golgi complex occurs as proteins move from the cis to the trans
face of the Golgi complex through distinct cisternal subcompartments.

Answer 90

TRUE

Question 90

are sorted into clathrin-coated regions of the TGN that have receptors for mannose 6-phosphate and are delivered to late endosomes via clathrin-
coated vesicles.

Answer 90

Lysosomal proteins

Question 90

are sorted from membrane and lysosomal proteins and delivered via clathrin-coated vesicles to condensing vacuoles, in which removal of water via ionic exchanges yields secretory granules.

Answer 90

Regulated secretory proteins

Question 91

are sorted into coatomer-coated regions of the TGN and delivered to the plasma membrane in COP-II coatomer–coated vesicles.

Answer 91

Plasma membrane proteins

Question 91

[SEQUENCING]

Protein processing may include the following events, each of which occurs in a different
cisternal subcompartment:

Proteins targeted for lysosomes are tagged with mannose 6-phosphate in the cis
cisterna.

A membrane similar in composition and thickness to the plasma membrane is acquired.

Mannose residues are removed in cis and medial cisternae.

Some proteins undergo terminal glycosylation with sialic acid residues and galactose.

Sulfation and phosphorylation of amino acid residues take place.

Answer 91

1,5,2,3,4

Question 92

also takes place on polyribosomes at the surface of the RER, but rather than entering the lumen, the transfer process is halted (by a stoptransfer
sequence), and the transmembrane protein becomes anchored in the RER membrane.

Answer 92

Synthesis of transmembrane proteins

Question 93

takes place on polyribosomes lying free in the cytosol and is directed by mRNAs that lack signal codons.

Answer 93

Synthesis of cytosolic proteins

Question 94

Give the 2 types of Intracellular digestion

Answer 94

Nonlysosomal digestion and Lysosomal digestion

Question 95

is the degradation of cytosolic constituents by mechanisms outside of the vacuolar lysosomal pathway.

Answer 95

Nonlysosomal digestion

Question 96

is the degradation of material within various types of lysosomes by lysosomal enzymes.

Answer 96

Lysosomal digestion

Question 97

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

The major site for the degradation of
unwanted proteins is the proteosome, a cylindrical complex of nonlysosomal proteases.

Proteins marked for destruction are enzymatically tagged with ubiquitin, which delivers them to the proteosome, where they are broken down to small peptides.

Answer 97

“C”

Question 98

is the ingestion and degradation of foreign material taken into the cell by
receptor-mediated endocytosis or phagocytosis.

Answer 98

Heterophagy

Question 99

is the segregation of an organelle or other cell constituents within
membranes from the RER to form an autophagic vacuole, which is subsequently digested
in an autophagolysosome.

Answer 99

Autophagy

Question 100

is the fusion of hormone secretory granules and lysosomes and their subsequent digestion.

Answer 100

Crinophagy

Question 101

TRUE OR FALSE

Crinophagy is used to remove excess numbers of secretory granules from the cell.

Answer 101

TRUE

Question 102

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

Digestion of phagocytosed microorganisms occurs in multivesicular bodies

Digestion of endocytosed ligands and foreign particles begins and may be
completed in phagolysosomes.

Answer 102

“D”

first statement, “endocytosed ligands”

second statement, “phagocytosed microorganisms”

Question 103

This constitutes the extracellular environment. It is an organized meshwork of macromolecules
surrounding and underlying cells.

Answer 103

Extracellular matrix

Question 104

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

By affecting the metabolic
activities of cells in contact with it, the extracellular matrix may not alter the cells and influence their shape, migration, division, and differentiation.

Although it varies in composition, in general it consists of an amorphous ground substance (containing primarily glycosaminoglycans [GAGs],
proteoglycans, and glycoproteins) and fibers.

Answer 104

“B”

first statement, “may alter the cells”

Question 105

are long, unbranched polysaccharides composed of repeating identical
disaccharide units.

Answer 105

GAGs (Glycosaminoglycan)

Question 106

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

An amino sugar, either N-acetylglucosamine or N-acetylgalactosamine, is always one of
the repeating disaccharides.

Because GAGs are commonly sulfated and usually possess a uronic acid sugar, which
has a carboxyl group in the repeating disaccharide unit, they have a strong positive
charge.

Answer 106

“A”

second statement, “strong negative charge”

Question 107

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

The attraction of osmotically active cations (e.g., Na_) to GAGs results in a heavily
hydrated matrix that strongly resists compression.

Their extended random coils occupy large volumes of space because they do not fold
compactly.

Answer 107

“C”

Question 108

GAGs may be classified into four main groups

Answer 108

Hyaluronic acid, chondroitin sulfate, dermatan sulfate, heparin and heparan sulfate, and keratan sulfate.

Question 109

is a very large unsulfated molecule up to 20 _m in length that is not attached to a core protein.

Answer 109

Hyaluronic acid

Question 110

consist of a core protein from which many GAGs extend. These large molecules are shaped like a bottlebrush.

Answer 110

Proteoglycans

Question 111

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

Proteoglycans act as binding sites for growth factors and other signaling molecules.

They confer unique attributes to the extracellular matrix in certain locations

Answer 111

“C”

Question 112

are multifunctional molecules whose domains bind to components of the extracellular matrix and to receptors on the cell surface, thereby promoting adhesion between the cell and the matrix.

Answer 112

Glycoproteins

Question 113

an adhesive glycoprotein, forms fibrils in the extracellular matrix.

Answer 113

matrix fibronectin

Question 114

circulating plasma protein that functions in blood clotting, wound healing, and phagocytosis.

Answer 114

plasma fibronectin

Question 115

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

Fibronectin has domains for binding collagen, heparin, various cell-surface receptors,
and cell adhesion molecules (CAMs).

It mediates cell adhesion to the extracellular matrix by binding to fibronectin receptors
on the cell surface.

Answer 115

“C”

Question 116

is located in basal laminae, where it is synthesized by adjacent epithelial cells,
and in external laminae surrounding muscle cells and Schwann cells.

Answer 116

Laminin

Question 117

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

The arms of this large cross-shaped glycoprotein have binding sites for cell surface
receptors (integrins), heparan sulfate, type IV collagen, and entactin.

Laminin mediates interaction between epithelial cells and the extracellular
matrix by anchoring the cell surface to the basal lamina.

Answer 117

“C”

Question 118

is a component of all basal (and external) laminae. This sulfated adhesive glycoprotein binds laminin.

Answer 118

Entactin

Question 119

TRUE OR FALSE

Entactin links laminin with type IV collagen in the lamina densa.

Answer 119

TRUE

Question 120

is an adhesive glycoprotein most abundant in embryonic tissues.

Answer 120

Tenascin

Question 121

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

Tenascin is secreted by glial cells in the developing nervous system.

Tenascin promotes cell–matrix adhesion and thus plays a role in cell migration.

Answer 121

“C”

Question 122

a glycoprotein in cartilage, attaches chondrocytes to type II collagen.

Answer 122

Chondronectin

Question 123

TRUE OR FALSE

By influencing the composition of its extracellular matrix, chondronectin plays a
role in the development and maintenance of cartilage.

Answer 123

TRUE

Question 124

This extracellular-matrix calcium-binding glycoprotein found in bone is synthesized by
osteoblasts.

Answer 124

Osteonectin

Question 125

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

Osteonectin has binding sites for type IV collagen and for integrins of osteoblasts and osteocytes.

Osteonectin plays a role in bone formation and remodeling and in maintaining bone mass by influencing calcification.

Answer 125

“Type I collagen”

Question 126

They link fibronectin outside the cell to cytoskeletal components
inside the cell and may activate cell-signaling pathways which determine the
cell’s behavior

Answer 126

Fibronectin receptors

Question 127

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

Fibronectin receptors, which belong to the integrin family of receptors, are
transmembrane proteins consisting of one polypeptide chains.

Because they enable cells to adhere to the extracellular matrix, they are known as
CAMs.

Answer 127

“B”

first statement, “two polypeptide chains”

Question 128

is the most abundant structural protein of the extracellular matrix.

Answer 128

Collagen

Question 129

[SEQUENCING]

Intracellular events in collagen synthesis occur in the following sequence:

Preprocollagen synthesis occurs at the rough endoplasmic reticulum (RER) and is directed by messenger ribonucleic acid (mRNAs) that encode the different types of chains to be synthesized.

Hydroxylation of specific proline and lysine residues of the forming polypeptide chain
occurs within the RER. The reaction is catalyzed by specific hydroxylases that require
vitamin C as a cofactor.

Attachment of sugars (glycosylation) to specific hydroxylysine residues also occurs
within the RER.

Procollagen triple-helix formation takes place in the RER and is precisely regulated by
propeptides (extra nonhelical amino acid sequences) at both ends of each chain. The
three chains align and coil into a triple helix.

Addition of carbohydrates occurs in the Golgi complex, to which procollagen is
transported via transfer vesicles. With the addition of carbohydrates, the oligosaccharide
side chains are completed.

Secretion of procollagen occurs by exocytosis after secretory vesicles from the trans-
Golgi network are guided to the cell surface along microtubules.

Answer 129

1,2,3,4,5,6

Question 130

[SEQUENCING]

Extracellular events in collagen synthesis occur in the following sequence:

Cleavage of procollagen is catalyzed by procollagen peptidases, which remove most
of the propeptide sequences at the ends of each chain, yielding tropocollagen or simply
collagen.

Self-assembly of tropocollagen occurs as insoluble tropocollagen molecules aggregate
near the cell surface.

Answer 130

1,2

Question 131

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

Synthesis of type IV collagen is unique in that it assembles into a meshwork rather than
fibrils.

Type IV collagen constitutes most of the lamina densa of basal laminae and external
laminae.

Answer 131

“C”

Question 132

[ODD ONE OUT]

(1)The propeptide sequences are not removed from the ends of its procollagen
molecules.

(2) Its triple-stranded helical structure is interrupted in many regions.

(3) It forms head-to-toe dimers that interact to form lateral associations, creating
a sheetlike meshwork.

Answer 132

(3)

“head-to-head dimers”

Question 133

an amorphous structural protein, imparts remarkable elasticity to the extracellular
matrix; 90% of elastic fibers or elastic sheets are composed of elastin.

Answer 133

elastin

Question 134

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

Like a rubber band, after being stretched, the elastin returns to its original
shape once the tensile force is released.

Lysine residues of four different chains form covalent bonds called desmosine
cross-links to create an extensive elastic network.

Answer 134

“C”

Question 135

a glycoprotein, organizes elastin into fibers and is the main component of the
peripheral microfibrils of elastic fibers.

Answer 135

fibrillin

Question 136

A- FIRST TRUE
B- SECOND TRUE
C- BOTH TRUE
D- BOTH FALSE

Synthesis of elastic fibers is carried out by fibroblasts in elastic ligaments, smooth muscle
cells in large arteries, and chondrocytes and chondroblasts in elastic cartilage.

Synthesis begins with the elaboration of fibrillin microfibrils that appear near the surface
of the cell.

Answer 136

“C”