Chapter1 Diversity and Universality of Organisms

Chapter2 Replication of Genetic Information

Chapter3 Expression of Genes

Chapter 4 Regulation of Gene Expression

Chapter 5 Cell Membrane Structure and Organelles

Chapter 6 Cytoskeleton

Chapter 7 Metabolism

Chapter8 Energy

Chapte9 Signal Transduction and Cell Growth

Chapte10 Development and Differentiation

Chapte11 Intercellular Communication and Tissue Architecture

Chapte12 Reproduction and Meiosis

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9Problems

 

 

Depending on intercellular soluble molecules, signal transduction can be roughly classified into endocrine, paracrine, autocrine, cell contact and nerve modes. Explain the difference between these types. Insulin produced in the pancreas is secreted, and acts on receptors located across the body. Indicate which of the above signal transduction types is applied to this mechanisms, and explain the reasons for your choice.

 

 

Compare signal transduction by neurons (nerve type), which secrete neurotransmitters from the synapse, with signal transduction by endocrine cells, which secrete hormones into the blood (endocrine type). Outline the advantages of both types.

 

 

Cells may be programmed to actively die even with a sufficient supply of nutrients. Provide the name of this mechanism and outline the circumstances in which it is used.

 

 

Using specific names, outline a typical mechanism in which a ligand binds to a G protein-coupled receptor, which then activates a G protein trimer, which in turn increases the intracellular Ca2+ level to transduce signals.

 

1)

List the names of the cell cycle stages.

2)

Explain the molecular mechanisms necessary for the cell cycle to progress irreversibly in one direction.

 

 

In a normal cell culture, the cell cycle varies among cells, and those in the M and S phases are mixed together. Explain the method by which the cell cycle of all cultured cells is synchronized (known as synchronized culture).

 

 

Depending on intercellular soluble molecules, signal transduction can be roughly classified into endocrine, paracrine, autocrine, cell contact and nerve modes. Explain the difference between these types. Insulin produced in the pancreas is secreted, and acts on receptors located across the body. Indicate which of the above signal transduction types is applied to this mechanisms, and explain the reasons for your choice.

In the autocrine type, cells are acted on by the signal transducers they secrete into the area outside. In the paracrine type, signal transducers released by cells diffuse into the extracellular fluid and act locally on the surrounding cells. In the endocrine type, signal transducers (such as hormones) produced in endocrine cells are secreted into the blood flow, and act on distant target organs. In the cell contact type, membrane proteins on the surface of adjacent cells come into contact with and act on each other. In the nerve type, parts of cells extend to form synapses, through which signals are transmitted. Insulin’s signal transduction type is the endocrine type. Insulin secreted from the pancreas (from β-cells in the islets of Langerhans) is circulated by the blood and binds to insulin receptors in cells located around the body, thus transmitting signals.

 

 

Compare signal transduction by neurons (nerve type), which secrete neurotransmitters from the synapse, with signal transduction by endocrine cells, which secrete hormones into the blood (endocrine type). Outline the advantages of both types.

Neurons mainly use a type of intracellular signal transduction (electric signals) to send signals to distant parts of an organism, whereas hormones transmit signals endocrinologically (see [1]). As a result, the signal transduction rate and level of coverage differ between the two mechanisms. This serves as an advantage for each mechanism; in signal transduction by neurons, rapid transduction on a millisecond time scale is possible, whereas transduction in hormones means that a wide area of the body can be covered, e.g., signals can be sent to the muscles of the whole body by hormone release from one organ.

 

 

Cells may be programmed to actively die even with a sufficient supply of nutrients. Provide the name of this mechanism and outline the circumstances in which it is used.

Apoptosis. In multicellular organisms, it is important that cells survive only when necessary and in places where they are needed. Apoptosis is observed in the formation of fingers (cells between fingers die), the removal of cells infected with viruses, the removal of cancerous cells and the disappearance of the tail of tadpoles during their development into frogs.

 

 

Using specific names, outline a typical mechanism in which a ligand binds to a G protein-coupled receptor, which then activates a G protein trimer, which in turn increases the intracellular Ca2+ level to transduce signals.

A G protein-coupled receptor is a membrane protein that penetrates the membrane seven times, and consists of three G proteins (Gα, Gβ and Gγ) forming a trimer. The GDP bound to unstimulated Gα is converted to GTP after a ligand binds to a receptor, thus activating the GDP. The Gα that has bound to GTP and become activated leaves Gβ-Gγ and activates phospholipase C. This activated phospholipase C degrades phospholipids to form inositol trisphosphate and diacylglycerol, and the inositol trisphosphate activates the inositol trisphosphate receptors in endoplasmic reticula. This activation causes the release of Ca2+ in the endoplasmic reticula into the cell, thus raising the intracellular Ca2+ concentration. The active Gα also activates adenylyl cyclase. As a result, the intracellular cAMP concentration increases, which activates cAMP-dependent kinase (A kinase), thus facilitating the opening of the Ca2+ channel and in turn increasing the intracellular Ca2+ concentration. This increased intracellular Ca2+ level activates kinases (which are activated in the presence of Ca2+-binding proteins) and serine/threonine phosphatases. These kinases and phosphatases in turn activate various intracellular signals.

 

1)

List the names of the cell cycle stages.

G1, S, G2 and M phases. Some cells may enter the G0 (i.e., resting) phase at the G1 phase.

2)

Explain the molecular mechanisms necessary for the cell cycle to progress irreversibly in one direction.

Proteins that regulate the cell cycle include cyclines and CDKs. These proteins form a complex and are modified, thereby regulating the cell cycle. Cyclines are ubiquitinated at a particular stage of the cell cycle and are then immediately degraded. Thus, degradation of the proteins that regulate the cell cycle is the driving force behind the cycle’s irreversible progress.

 

 

In a normal cell culture, the cell cycle varies among cells, and those in the M and S phases are mixed together. Explain the method by which the cell cycle of all cultured cells is synchronized (known as synchronized culture).

There are several methods for synchronized culture. Cells in the mitotic phase have relatively weak adhesion, and do not stick firmly to glass. They can therefore be collected easily by gently rinsing a culture dish with a culture medium. When alga cells are cultured through a cycle with light and dark periods, the cell cycle synchronizes with the experimental cycle.
A more direct method is the addition of a DNA synthesis inhibitor (aphidicolin) to a cell culture. When cells are cultured for one cell cycle or more in the presence of aphidicolin, the growth stage of all cells stops at the S phase. The cycle of all cells can therefore be synchronized by replacing the culture medium with a new one to remove aphidicolin. The growth stage of all cells can also be synchronized to the G1 phase by removing serum from the culture medium to arrest the growth stage of all cells at the G0 phase and by restarting the growth process through the addition of serum to the culture.

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