week 6

Question 1

what are the cell cycle checkpoints and what do they entail?

Answer 1

• End of G1:
  Restriction point: Check for cell size and favourable environmental conditions; Check for DNA damage.
• During G2: Check for damaged or unduplicated DNA; Check for unduplicated centrosomes.
• End of M: Check for chromosome attachment to mitotic spindle.
• If the cell fails these checks, the cell cycle is arrested

Question 2

What controls cell division?

Answer 2

Cell division is controlled by the Cell Cycle.

Question 3

When does nuclear division occur in the cell cycle?

Answer 3

Nuclear division occurs during mitosis.

Question 4

When does cytokinesis occur in the cell cycle, and what does it result in?

Answer 4

Cell division—cytokinesis—occurs at the end of the M phase, resulting in the physical separation of the cytoplasm and the formation of two daughter cells.

Question 5

What happens during the G1 phase of the cell cycle?

Answer 5

Cells that do not divide are usually arrested in the G1 phase.

Question 6

At what phase is DNA replicated in the cell cycle?

Answer 6

DNA is replicated during the S phase.

Question 7

What can extracellular stimuli lead to in a cell?

Answer 7

Extracellular stimuli can lead to cell division (proliferation), cell death, or a change in function (differentiation).

Question 8

What is an example of a biological response triggered by an extracellular stimulus?

Answer 8

The fertilization of an egg triggers a wave of calcium ions [Ca2+] that stimulates the initiation of development.

Question 9

How does serotonin impact nerve cells?

Answer 9

The neurotransmitter serotonin activates a response in nerve cells via a cAMP signaling pathway, with a rapid increase in intracellular cAMP concentration observed within 20 seconds of exposure.

Question 10

What role do G-protein-coupled receptors and cAMP-gated ion channels play in sensory perception?

Answer 10

They are involved in our sense of smell, where the influx of Na+ and Ca2+ stimulates nerves to send signals to the brain.

Question 11

describe what happens during each stage of mitosis?

Answer 11

During interphase, the nucleus replicates its DNA and centrosomes.

During prophase, the chromatin coils and supercoils, becoming more compact and condensing into visible chromosomes. The centrosomes move to opposite poles.

In prometaphase, the nuclear envelope breaks down, kinetochore microtubules appear, and connect the kinetochores to the poles.

In metaphase, the centromeres of chromosomes become aligned in a plane at the cell’s equator, known as the metaphase plate.

During anaphase, the paired sister chromatids separate, and the new daughter chromosomes begin to move toward the poles.

In telophase, the daughter chromosomes reach the poles. The nuclear envelope and nucleolus re-form, the chromatin condenses, and after cytokinesis, the daughter cells enter interphase once again.

Question 12

what are the different types of cell death?

Answer 12

• Programmed cell death:
• Apoptosis
• Autophagic cell death
• Necroptosis

Not programmed:
* Necrosis

Question 13

What is the role of cyclins in the cell cycle?

Answer 13

Cyclins are synthesized and destroyed at different points of the cell cycle, regulating the activity of cyclin-dependent kinases (CDKs).

Question 14

How do cyclins and CDKs drive the cell cycle?

Answer 14

Specific cyclin-CDK complexes are responsible for advancing the cell through various phases of the cell cycle, such as the G1 to S and G2 to M phase transitions.

Question 15

What happens if the cell cycle signaling machinery becomes defective?

Answer 15

A cell may enter the cell cycle permanently, leading to the proliferation of identically defective daughter cells.

Question 16

How is DNA organized in the nucleus?

Answer 16

DNA is tightly packed into nucleosomes, which consist of DNA wrapped around histone proteins.

Question 17

What happens to nucleosomes prior to mitosis?

Answer 17

Nucleosomes become supercoiled, which makes DNA even more tightly wrapped than usual and inaccessible to proteins involved in replication and transcription.

Question 18

How is the segregation of chromosome pairs mediated during mitosis?

Answer 18

Segregation is mediated by the mitotic spindle, where condensed chromosomes attach to microtubules radiating from the two centrosomes.

Question 19

How is cytokinesis carried out in animal cells?

Answer 19

In animal cells, cytokinesis is driven by the contraction of an acto-myosin ring, which pinches the cell into two daughter cells.

Question 20

What is the process of cytokinesis in plant cells?

Answer 20

In plant cells, cytokinesis occurs through the construction of a new cell wall inside the cell, separating the daughter cells.

Question 21

What causes necrosis in cells?

Answer 21

Necrosis is caused by cell-damaging agents such as extreme temperatures, toxins, or by oxygen or nutrient starvation.

Question 21

What is apoptosis?

Answer 21

Apoptosis is a form of “cell suicide” with characteristic morphological features such as cell condensation, membrane blebbing, nuclear shrinkage, and chromatin condensation and fragmentation.

Question 22

What are apoptotic bodies and what happens to them?

Answer 22

Apoptotic bodies are small vesicles that form from a dying cell during apoptosis. They contain cell contents, DNA, and proteins that are broken down and eventually engulfed by phagocytic cells.

Question 23

Does apoptosis cause an inflammatory response?

Answer 23

No, apoptosis does not cause an inflammatory response because the cell contents are contained and safely disposed of by phagocytes.

Question 24

What are the two distinct classes of caspases?

Answer 24

The two distinct classes of caspases are initiator caspases (Caspases 8, 9, and 10) and executor caspases (Caspases 3, 6, and 7).

Question 25

How are initiator caspases activated and what is their role?

Answer 25

Initiator caspases are activated by pro-apoptotic stimuli and are responsible for cleaving and activating executor caspases.

Question 26

What do executor caspases do upon activation?

Answer 26

Executor caspases cleave a variety of target proteins, resulting in the execution of apoptosis. This includes dismantling cytoskeletal and nuclear proteins.

Question 27

What triggers the release of cytochrome c and caspase activation in apoptosis?

Answer 27

he opening of pores in the mitochondrial outer membrane triggers the release of cytochrome c and subsequent caspase activation.

Question 28

What is the role of Bcl-2 in apoptosis?

Answer 28

Bcl-2 prevents the formation of pores in the mitochondrial outer membrane and is therefore anti-apoptotic.

Question 29

What must a cell do to activate the programmed cell death pathway?

Answer 29

The cell must overcome the anti-apoptotic effects of Bcl-2 to activate the programmed cell death pathway.

Question 30

What is differentiation?

Answer 30

Differentiation is the process by which unspecialized cells, like stem cells, become specialized into distinct types of cells with specific functions, such as nerve cells, skin cells, or leaf cells.

Question 31

What are stem cells?

Answer 31

Stem cells are undifferentiated cells that have the ability to enter a dormant state, undergo cell division when activated, and can self-renew through asymmetric division to replenish the stem cell pool throughout life.

Question 32

What is the role of stem cells in differentiation?

Answer 32

Stem cells are the undifferentiated precursor cells that have the capacity to differentiate into mature, specialized cells.

Question 33

What is totipotency?

Answer 33

Totipotency is the ability of a single cell to give rise to all embryonic and extra-embryonic cell types.

Question 34

What does pluripotency refer to in stem cells?

Answer 34

Pluripotency refers to the ability of a single cell to give rise to all cell types found in the complete adult organism, i.e., cells of all germ layers.

Question 35

How does multipotency differ from totipotency and pluripotency?

Answer 35

Multipotency is the ability of a single cell to give rise to multiple, but not all, cell types found in the complete adult organism. The differentiation ability of multipotent cells is restricted to certain cell types.

Question 36

How does differentiation occur at the genetic level?

Answer 36

Differentiation occurs when cells switch on certain genes and switch off others, so the type of cell that is formed is determined by the pattern of gene expression in the cell.

Question 37

Is any DNA lost during the differentiation process?

Answer 37

No DNA is lost during differentiation, with some rare exceptions such as lymphocyte development, where rearrangements and deletions of DNA segments occur.

Question 38

What is the role of specific transcription factors in differentiation?

Answer 38

Specific transcription factors, often referred to as master regulators, are expressed early in the differentiation process and induce or suppress the transcription of various target genes, leading to cell differentiation.

Question 39

What is the power of master regulators in cell differentiation?

Answer 39

Master regulators can be so powerful that when misexpressed, they can respecify the fate of cells or even induce transdifferentiation of mature cell types into other types, like converting fibroblasts into myoblasts with the artificial overexpression of MyoD.

Question 40

How is cell division related to cell differentiation?

Answer 40

Cell division and cell differentiation are mostly mutually exclusive processes. Cell division needs to be shut down for differentiation to occur, which is mediated by factors like MyoD through the upregulation of cell cycle inhibitors such as p21.

Question 41

What is determination in the context of cell development?

Answer 41

Determination is the stage in cell development where the fate of a cell becomes specified, even though it may not yet be apparent in its outward phenotype. This occurs before differentiation.

Question 42

How is determination related to differentiation?

Answer 42

Determination is the process by which a cell’s developmental fate is set, whereas differentiation is the process by which a cell realizes this fate and acquires a specific structure and function.

Question 43

When does the first determination occur during embryonic development?

Answer 43

The first determination occurs when cells in an embryo become increasingly restricted in their potential fates.

Question 44

What was Hans Driesch’s conclusion about the developmental potential of the cells of a two-cell embryo?

Answer 44

Hans Driesch concluded that both cells of a two-cell sea urchin embryo carry the potential to develop into a normal embryo, providing the basis for the existence of identical twins.

Question 45

What developmental differences are evident at the 8-cell stage of a sea urchin embryo according to Hans Driesch?

Answer 45

At the 8-cell stage, the upper and lower halves of a sea urchin embryo differ in their developmental potential, indicating the beginning of cell fate determination.

Question 46

Is cellular differentiation reversible?

Answer 46

In plants, cellular differentiation is reversible. Mature plant cells can be experimentally induced to dedifferentiate to a totipotent state, allowing them to form an entire new plant, which is a form of cloning

Question 47

What was significant about Dolly the sheep in the context of cellular differentiation?

Answer 47

Dolly the sheep was significant because she was the first mammal cloned from a differentiated cell, demonstrating that, under certain conditions, mammalian cellular differentiation can also be reversed.

Question 48

How were Hua Hua and Zhong Zhong, the macaques, cloned?

Answer 48

Hua Hua and Zhong Zhong were cloned using a technique similar to that used for Dolly, involving the fusion of a differentiated cell with an enucleated totipotent egg cell.