Final Exam (Material From Last 4 Chapters)

Question 1

What are the three major types of cytoskeletal proteins, their basic subunits, their energy usage, and their stability?

Answer 1

Microtubules
-alpha and beta tubulin
-GTP hydrolysis
-dynamic instability

Intermediate Filaments
-fibrous protein subunits (keratin, vimentin)
-does NOT require energy
-high stability, dynamic

Actin Filaments
-actin protein subunits
-require ATP hydrolysis
-less stable, rapid turnover

Question 2

Rank the three major types of cytoskeletal proteins from smallest to largest

Answer 2

SMALLEST: Actin Filaments
NEXT: Intermediate Filaments
LARGEST: Microtubules

Question 3

What are some functions of Intermediate Filaments and where are they located in a cell?

Answer 3

-stabilize nuclear membrane
-help form cell-cell junctions (desmosomes)

found throughout the cytoplasm

Question 4

What types of cells would you expect to have a great deal of intermediate filaments in the cytoskeleton, and why?

Answer 4

-Epithelial cells
-Muscle cells

these are cells that experience mechanical stress, where structural support and mechanical capabilities are greatly needed

Question 5

Microtubules can be very dynamic structures. When would you expect cytoskeletal proteins
to form stable, relatively permanent structures in a cell vs. transient, temporary structures?

Answer 5

PERMANENT:
-when long-term structural support or tissue integrity is required

TRANSIENT:
-for dynamic cellular processes like cell division, migration, and intracellular transport

Question 6

Name one disease/problem that may occur in Microtubules, Intermediate Filaments, and Actin Filaments

Answer 6

Microtubules - Kartagener Syndrome (fertility problems, lung infections, cilia are disrupted and unable to function)

Intermediate Filaments - Progeria (genetic, impaired cell division and nuclear instability)

Actin Filaments - Phalloidins (inhibit depolymerization of actin)

Question 7

Give some examples of how the cytoskeleton facilitates intracellular transport.

Answer 7

-mitotic spindle formation with cell division (microtubules)
-vesicle transport (actin)
-kinesin and dyesin transport of cargo

Question 8

Describe the structure of the nucleus. Include in your description, nuclear pores, nuclear envelope, nuclear lamina, and nucleolus.

Answer 8

Nuclear Envelope = acts as a barrier, separating the contents of the nucleus from the cytoplasm (double membrane that surrounds the nucleus

Nuclear Pores = large protein complexes embedded in the nuclear envelope, gateways for the transport of molecules between the nucleus and the cytoplasm, regulate the passage of ions, small molecules, and macromolecules

Nuclear Lamina = meshwork of intermediate filaments that lies on the inner surface of the nuclear envelope, structural support to the nucleus and helps maintain its shape

Nucleolus = rRNA synthesized, within the nucleus

Question 9

How does a nuclear pore differ from an ion channel?

Answer 9

-requires energy in the form of GTP
-proteins transported in folded state
-use nuclear transport receptors that are able to bind to a protein (through signals) and pull them through the pore via their amino acid sequences

Question 10

How are proteins targeted to the nucleus rather than some other organelle within the
cell? Give examples of proteins that you might expect to be targeted to the nucleus

Answer 10

nuclear localization signals (NLS) facilitate their import into the nucleus

-transcription factors
-histones

Question 11

Describe how proteins are transported into the nucleus and understand the role that
GTP plays in this process.

Answer 11

1. NLS binds to cargo protein
2. Receptor transports cargo protein to nucleus
3. Cargo protein delivered to nucleus when Ran-GTP bind to transport receptor, releasing the cargo protein
4. Empty receptor returns to cytosol and Ran-GDP dissociates (GTP is hydrolized)

Question 12

Describe the three mechanisms by which proteins are imported into organelles

Answer 12

1. Transport through Nuclear Pores
2. Transport across Membranes (STOP-TRANSFER SEQUENCES!)
3. Transport by Vesicles (inward or outward)

Question 13

What is the difference between a free and bound ribosome? Are they structurally the
same or different? Where do proteins go that are produced by each?

Answer 13

free ribosomes are located in the cytoplasm and synthesize proteins for the cytoplasm itself or organelles within the cytoplasm.

Bound ribosomes are associated with the ER membrane and produce proteins that are targeted to secretory pathways or specific organelles.

Question 14

What are the two types of endoplasmic reticulum (ER)?

Answer 14

Rough and Smooth

Question 15

What is the role of the signal recognition peptide (SRP) in protein synthesis?

Answer 15

binds to SRP on the ribosome to “pull it to the spot” for which the proteins polypeptide chain can be translocated into the ER lumen

Question 16

What type of protein modifications can occur in the RER? Give a specific example
of two types of modification

Answer 16

-form disulfide bonds (insulin)
-glycosylation by glycosyltransferases
-protein folding
-cleaving by peptidases

Question 17

How does a transport vesicle get from the RER to the Golgi apparatus?

Answer 17

COP II

Question 18

How can proteins be further modified in the Golgi apparatus? Give an example.

Answer 18

glycosylation

Question 19

Define the difference between pinocytosis, phagocytosis, and receptor-mediated endocytosis

Answer 19

Pinocytosis = “drinking,” extracellular fluid
Phagocytosis = “eating,” solid particles
Receptor-mediated endocytosis = molecules bind to receptors and coated pit engulfs and forms vesicle to bring into the cell

Question 20

What is a KDEL receptor?

Answer 20

grabs signal sequence

Question 21

What are the three types of receptors present on the cell surface, and an example for each?

Answer 21

1. Ion Channels (Na+)
2. GPCRs (epinephrine)
3. Enzyme-coupled receptors (insulin)

Question 22

Which of the following is true of G-protein coupled receptors (GPCRs)?

a. A ligand binds to the alpha subunit of the GPCR, which then hydrolyzes GTP to GDP
b. When a ligand binds to the receptor portion of the GPCR, the alpha subunit dissociates
and is involved in down-stream signaling events.
c. A ligand hydrolyzes GTP to GDP, which activates the receptor portion of the GPCR.
d. The beta-gamma subunit does not participate in any down-stream signaling events.
e. All of the above are true

Answer 22

b. When a ligand binds to the receptor portion of the GPCR, the alpha subunit dissociates
and is involved in down-stream signaling events.

Question 23

What are three reasons that a cell might divide?

Answer 23

1. growth and development
2. tissue repair
3. reproduction

Question 24

What is P53?

Answer 24

induces apoptosis if DNA cannot be repaired (in S phase)

“Guardian of the Genome

Question 25

Why are cyclins named “cyclins”?

Answer 25

they are proteins whose concentration “cycles” in the cell cycle (higher in mitosis, lower in interphase

Question 26

What is the role of the cytoskeleton in the cell cycle?

Answer 26

-formation of nuclear lamina
-cytokinesis
-movement of chromosomes

Question 27

Describe specific examples of the cell cycle events regulated by S-Cdk

Answer 27

-initiates DNA replication in late G1 Phase
-phosphorylates proteins involved in DNA replication

Question 28

Describe the role of motor proteins in mitosis.

Answer 28

-chromosome movement
-aid in spindle organization

Question 29

Discuss how M-Cdks are involved in the molecular regulation of the cell cycle

Answer 29

-Phosphorylates proteins involved in mitosis and cell division

Question 30

Define “cell cycle.” How might the cell cycle of a developing embryonic cell differ from a
neuron? How about from a skin cell?

Answer 30

series of events that occur in a cell’s life from its formation to its division into two daughter cells

Embryonic cell = rapid division
Neuron = liimited division
Skin cell = moderate division

Question 31

What is the role of cAMP in cell-cell communication? How is its concentration
regulated?

Answer 31

significant role in cell-cell communication as a second messenger. It relays signals from various extracellular molecules, such as hormones or neurotransmitters, to the inside of the cell, thereby initiating a cellular response. Its role is particularly prominent in the signaling pathway mediated by G protein-coupled receptors (GPCRs)

Here’s an overview of the role of cAMP in cell-cell communication:

Activation of GPCR: When a specific molecule binds to a GPCR on the cell surface, it activates the associated G protein.
Activation of Adenylyl Cyclase: The activated G protein stimulates an enzyme called adenylyl cyclase, which converts ATP (adenosine triphosphate) into cAMP.
cAMP Production: Adenylyl cyclase generates cAMP molecules from ATP in the cytoplasm.
Activation of Protein Kinase A (PKA): cAMP serves as a second messenger by binding to and activating an enzyme called protein kinase A (PKA). This leads to the activation of PKA and the release of its catalytic subunits.
Phosphorylation of Target Proteins: The activated PKA catalytic subunits phosphorylate specific target proteins within the cell, modifying their activity and initiating downstream cellular responses.
Cellular Response: The phosphorylation of target proteins can have various effects, depending on the specific signaling pathway and cell type involved. Examples include changes in gene expression, ion channel activity, enzyme function, or cellular metabolism.

Question 32

Name two second messengers and describe their functions

Answer 32

Calcium: triggers a cascade of events that can lead to an increase in intracellular calcium levels (e.g. muscle contraction)

cAMP: produced by the enzyme adenylyl cyclase in response to the activation of certain receptors, particularly G protein-coupled receptors (GPCRs). It activates protein kinase A (PKA), which phosphorylates target proteins, leading to changes in their activity and cellular responses

Question 33

Cells receive many types of extracellular signals. What is the main difference
between “short-acting” cellular responses and “long-acting” cellular responses?

Answer 33

short-acting cellular responses are rapid, transient, and reversible, while long-acting cellular responses are sustained over a more extended period