Module 13: Cell Cycle

Question 1

What are the 4 main phases of the eukaryotic cell cycle?

Answer 1

M phase, G1 phase, S phase, G2 phase.

Question 2

What is interphase and which phases does it include?

Answer 2

Interphase is the “superphase” consisting of G1, S and G2 phases, during which the cell grows and replicates its DNA.

All 3 consistent in timing (take hours).

Question 3

Name the 5 sub-phases of M phase in order.

Answer 3

Prophase, prometaphase, metaphase, anaphase, telophase.

Question 4

What occurs during cytokinesis?

Answer 4

The cytoplasm divides, forming two daughter cells.

Question 5

What is G0 phase?

Answer 5

A resting or senescent state where cells exit the cell cycle and stop dividing. Can be permanent (brain and muscle) or transient (liver, fibroblasts, lymphocytes).

Question 6

What are the three main cell cycle checkpoints?

Answer 6

Start (restriction point) in late G1, G2/M transition, metaphase-to-anaphase transition.

Question 7

What is the role of cyclin-dependent kinases (Cdks)?

Answer 7

Cdks regulate the cell cycle by activating or inhibiting key processes when bound to cyclins. Cdk levels are constant (therefore, constitutively expressed).

Question 8

What is the function of cyclins?

Answer 8

Cyclins bind and activate Cdks, regulating the cell cycle’s progression. Cyclin expression rises and falls in a cycle.

Question 9

What enzyme activates Cdks?

Answer 9

Cdk-activating kinase (CAK).

Question 10

What is the role of Wee1 kinase?

Answer 10

It inhibits cyclin-Cdk complexes by adding an inhibitory phosphate group.

Question 11

How does Cdc25 phosphatase regulate Cdks?

Answer 11

It removes the inhibitory phosphate group, activating cyclin-Cdk complex.

Question 12

Name 3 Cdk inhibitors (CKIs).

Answer 12

p27 - binds cyclin A-Cdk2 complex, disrupting the active site and ATP-binding.
p21 - suppresses G1/S- and S-Cdk following DNA damage.
p16 - suppresses G1-Cdk activity; frequently inactivated in cancer.

Question 13

What is the anaphase promoting complex/cyclosome (APC/C)?

Answer 13

A ubiquitin ligase that targets proteins like securin and cyclins for degradation, promoting anaphase. Remains active through G1.

Question 14

What is the function of DNA helicase?

Answer 14

Unwinds the DNA double helix during replication.

Question 15

What enzyme synthesizes new DNA strands?

Answer 15

DNA polymerase.

Question 16

What is the origin recognition complex (ORC)?

Answer 16

A protein complex that marks the origin of replication and helps initiate DNA synthesis.

Question 17

What is the role of the pre-replication complex (Pre-RC)?

Answer 17

It assembles at the replication origin during G1 and helps initiate DNA replication in S phase.

Question 18

What is the mitotic spindle?

Answer 18

A structure made of microtubules that segregates chromosomes during anaphase.

Question 19

What are the three types of microtubules involved in the mitotic spindle?

Answer 19

Astral MTs, Kinetochore MTs, Interpolar MTs.

Question 20

What protein complex anchors chromosomes to spindle microtubules?

Answer 20

Kinetochore.

Question 21

What protein helps condense chromosomes during mitosis?

Answer 21

Condensin.

Question 22

What is the role of the Ndc80 complex?

Answer 22

Helps attach kinetochore to microtubules.

Question 23

What does Aurora B kinase do?

Answer 23

Ensures proper chromosome attachment and tension sensing at the kinetochore.

Question 24

What triggers the separation of sister chromatids during anaphase?

Answer 24

Cohesins are released through phosphorylation of securin, activating separase.

Question 25

What structure is responsible for cytokinesis?

Answer 25

The contractile ring made of actin and myosin filaments.

Question 26

What are the stages of early embryonic development in order?

Answer 26

Zygote -> Morula -> Blastula -> Gastrula.

Question 27

What are germline cells?

Answer 27

Cells that give rise to gametes (sperm and egg).

Question 28

What are somatic cells?

Answer 28

All body cells except germline cells.

Question 29

Define totipotent stem cells.

Answer 29

Stem cells that can differentiate into all cell types, including extraembryonic tissues.

Question 30

Define pluripotent stem cells.

Answer 30

Stem cells that can differentiate into any cell type within the body but not extraembryonic tissues.

Question 31

What are multipotent stem cells?

Answer 31

Stem cells that can develop into a limited range of cell types (ex. hematopoietic stem cells).

Question 32

What are induced pluripotent stem cells (iPSCs)?

Answer 32

Adult somatic cells that have been reprogrammed to behave like pluripotent stem cells.

Question 33

What is the role of telomerase in stem cells?

Answer 33

It maintains chromosome ends (telomeres), allowing indefinite cell division.

Question 34

What is cell differentiation?

Answer 34

The process by which a cell becomes specialized for a specific function.

Question 35

What is cellular senescence?

Answer 35

A permanent state of cell cycle arrest that prevents further division, often in response to DNA damage or cellular stress.

Question 36

Describe how stem cells are important in the epithelium lining of small intestine.

Answer 36

Paneth cells, which are part of the innate immune system and secrete proteins that kill bacteria; stay in the crypt of epithelium in intestine lining. Stem cells are on either side of the crypt, can replace the cells traveling up the villi. ##Footnote: Derived from stem cells but committed to differentiation.

Question 37

What is the Wnt signaling pathway?

Answer 37

Keeps cells in a proliferative state (ex. microvilli in the gut).

Question 38

What is notch signaling?

Answer 38

Induces differentiation of cells as they move up the crypt.