AP Biology Unit 4: Cell Communication and Cell Cycle Notes Pt. 1

Cell Communication

1. What is quorum sensing and what role does it play for soil-dwelling bacteria when it happens? 

   1. Quorum sensing is a bacteria's ability to detect and respond properly to its surrounding cell population. The extracellular signaling molecules involved are autoinducers. The bacteria is able to share information about cell density in their environment and then alter their cellular response appropriately. It allows the bacterial population to act together to produce a coordinated response that benefits the community of bacteria as a whole, rather than by itself. 

2. What type of local signaling is important for embryonic development and immune response? 

   1. The local signaling that is important for embryonic development and immune response is cell to cell recognition. Stem cells are able to differentiate into various cells necessary for an embryo to properly develop during embryonic development. This heavily relies on the glycoproteins that are on the cell membranes reacting to each other. Cells involved in the immune system use cell to cell communication to be able to distinguish between foreign invading cells from cells of the body. This is necessary for the body because if immune cells can’t tell the difference, they attack all of the cells, which causes an autoimmune disease. 

3. What are the differences between paracrine signaling and endocrine signaling?

   1. Paracrine signaling is a type of local signaling local regulator that is often involved in growth factors. Local regulating molecules are released into the extracellular fluid by the secreting cell The secreted molecules diffuse throughout the fluid and are detected by the receptors in the target cells, causing a reaction. Endocrine signaling is a long distance signaling that uses hormones. The signals are carried in the blood to the target cells. Target cells only react to certain ligands because each cell is specific so not all signals are picked up by all cells. Hormones travel long distances. 

Cell Signaling Worksheet

1. What is the key difference between RTKs and GPCRs?

   1. With a common structure and signaling method, GPCRs are cell surface receptors. They have many different protein segments that pass through  the phospholipid bilayer membrane and the message is transmitted into the cell using a g protein. They are able to bind with many different types of ligands because they are diverse. RTKs are enzyme linked receptors that are found that transfer an inorganic phosphate to the tyrosine amino acid. They work by binding the ligand to the extracellular domain of 2 nearby receptor tyrosine kinases. Then the neighboring receptors dimerize. Next the receptors attach phosphates to the tyrosine in the opposite intracellular domain. The phosphorylated tyrosine is able to transmit signals to other molecules. 

2. What type of receptors are the odorant receptors. Explain about the way they may transfer the sense of smell. (Your explanation should be from this page so it should be very simple, any complicated explanation about physiology of sense of smell will be considered plagiarism)

   1. GPCRs are the odorant receptors. Humans have 800 of these odorant receptors and each bonds its own “scent molecule” like a chemical in cologne or the scent of vegetables rotting. When a ligand binds to the receptor, a signal from the receptor is directly sent to the brain which makes us smell the scent. 

3. Overactivation or over abundance of which type of receptor may cause cancer? Why do you think this happens?

   1. Overactivation or overabundance of RTKs may cause cancer. This is because RTKs are able to bind to growth factors that produce signals that promote cell division. In the case of a cancerous cell being processed by an RTK, a cancer cell rapidly multiplies, causing cancer. 

4. Name some steroid hormones. Where are the receptors for these types of hormones located?

   1. Some steroid hormones are estradiol, testosterone and vitamin d. The receptors for these types of hormones are located in the nucleus or the cytoplasm. This is possible because hormones are small, hydrophobic ligands can through the membrane and bind without any imposing factors to the receptors. One issue that appears is the necessity of binding to a carrier protein to travel through the bloodstream because of their hydrophobic traits.

Cell Signaling Review

- Local Signaling: Macrophage attaches to the germ cell and later engulfs it

- Yeast mating: Alpha mating factor is docked onto type a cell receptor

- Receptor tyrosine kinase signaling pathway: can activate many relay proteins after binding one ligand molecule

- The GPCR signaling pathway has the GTPase activity: G-Protein

- Difference between phosphorylase and kinase: phosphorylase phosphorylates molecules by using phosphate group without using ATP

Osmosis Lab

1. Using the sodium data you collected and what you have learned from the seizure handbook, why are the free water molecules diffusing out of the vessel?

   1. The free water molecules are diffusing out of the vessel since there is a higher concentration of sodium in the matrix when compared to the concentration of sodium in the blood. The matrix is hypertonic when compared to the blood, causing the water to naturally diffuse down the gradient and move to the matrix and balance out the uneven gradient. 

2. Why is the pressure in the matrix high?

   1. The pressure in the matrix is high since the water moves into the matrix of the brain from the blood. This increase in water increases the pressure of the brain since the brain is forced to expand and push up against the skull. 

3. What does Clark have?

   1. Clark most likely has cerebral edema since he has a normal sodium concentration in the matrix, but a low sodium concentration in the blood. The pressure in the matrix of his brain is also high, which is caused by the brain swelling. The data along with the seizures make it most likely that Clark has cerebral edema. 

4. Treatment

   1. Your treatment choices are saline solutions with different amounts of salt (NaCl) that can be added to Clark's blood and affect osmosis in the brain.

   2. In medicine and veterinary medicine, saline solutions are compared with the normal concentration of sodium (~143 mmol/L) in healthy blood. Three saline solutions are available: isotonic, hypotonic, and hypertonic.

5. Into the vessel

   1. Homeostasis is the main goal of this treatment. By giving Clark a hypertonic solution, the goal is to have the movement of water to be moving into the vessel to bring down the concentration of water in the brain matrix.

6. Blood Sodium Concentration

   1. Blood sodium concentration increased because the Hypertonic Saline has a higher sodium concentration than the blood.

7. Brain Matrix Pressure

   1. Hypertonic Saline reduced the concentration of free water in the blood and caused the free water to diffuse from the matrix back into the blood vessel and reduce matrix pressure.

8. Net Free Water Movement

   1. Hypertonic saline reduced free water concentration in the blood and free water molecules diffused from the brain matrix into the blood.

   2. After treatment, equilibrium had been reached and water moved both ways across the blood vessel wall.

Cerebral Edema

• Too much water in body tissues is called edema. Edema in the brain is called cerebral edema and can happen if the concentration of sodium ions in the blood decreases.

• The brain can be damaged by cerebral edema. The skull limits how much the brain can swell. This increases the pressure in the brain and stops normal neuron function.

• Animals and people with cerebral edema develop changes in behavior, have difficulty walking, become blind and develop seizures. If not treated cerebral edema may result in death.

1. Summary

   1. Clark is a Bovine that weighs 110 lbs. He is 5 days old and is suffering from seizures. He is lying down, non responsive, has diarrhea and is seizuring. He received extra water. 

2. Explain the lab data from when Clark arrived at the hospital.

   1. He had a normal sodium concentration in his matrix of the brain. The pressure of the matrix was high. The blood sodium level was low and the blood pressure was normal. The neuron firing rate was high. 

3. Explain the Treatment Goals.

   1. The treatment goal is to obtain homeostasis by initially providing Clark with a hypertonic solution. Eventually, once this treatment is administered, his body will return to its natural state of homeostasis. This will be done since the hypertonic solution will cause the free water to flow from the matrix to the blood, to finally reach a state of equilibrium. 

4. How was osmosis involved in causing Clark's seizures?

   1. Osmosis was involved in causing Clark's seizures since the sodium concentration of his blood decreased from the diarrhea. He was given too much water, which caused the low blood sodium concentration. This disruption to homeostasis causes osmosis to move the water from the low sodium concentration of the blood into the high sodium concentration in the brain matrix. The matrix pressure increased, which caused abnormal neuron firing rate, which finally ended in Clark having seizures. 

5. How was osmosis used to stop Clark's seizures?

   1. Osmosis was used to stop Clark's seizures since a hypertonic solution was used to treat Clark. This increased the blood sodium concentration which caused the net movement of free water to go into the vessel. This decreased the neuron firing rate, which in turn decreased the matrix pressure. Finally, Clark's seizures stopped. 

Cell Cycle

1- What is the longest phase of the cell cycle and what happens during that phase?

The longest phase of the cell cycle is interphase. In this phase, the cell grows and duplicates its genetic material, and grows again. Interphase is made of three stages which are g1, s, and g2. In g1 and g2, the cell grows and in s, the DNA is duplicated. It is preparation for mitosis. 

2- What is G0 subphase?

The g0 subphase is the non dividing state. Some cells can re-enter the cell cycle, but others remain here indefinitely. The cells that are waiting to re-enter are called quiescent and they react based on chemical cues. Cells that remain in g0 indefinitely are fully differentiated so they continue to function but do not divide. 

3-Mitotic spindles form between which structures?

Mitotic spindle fibers form between the centrioles and the chromosomes. It does not attach to the entire chromosome, just the kinetochore which forms on opposite poles of the centromere. 

4- How do cytokinesis differ in plant cells compared to the animal cell?

Cytokinesis differs in plant cells since animal cells use an actin ring to form a cleavage form which eventually splits the cytoplasm into half. In plant cells, the cell wall remains, keeping the cells connected. Then a cell plate is formed in between the two daughter plant cells. 

5- What type of mutations of cell cycle regulators can promote the development of cancer?

Positive regulators which promote cell growth can be hyperactivated and eventually promote cancer growth. Negative regulators may also cause cancer if they are inactivated since they must be active to prevent tumor formation. 

6- In your own words, write down 2 misconceptions regarding cell cycle.

Many people believe that interphase is a stage of mitosis. This is incorrect since interphase is the stage prior to mitosis, where the cell grows in g1, duplicates DNA in s, and grows more in g2. Interphase, mitosis and cytokinesis are the three stages of a cell cycle. DNA is duplicated in interphase, and not prophase. Genetic material is duplicated in the s phase of interphase. This is then used in mitosis to split the cell evenly so the parent cell is identical to the two daughter cells. 

Cyclin Worksheet

1- - Cyclin in the PDGF could be considered as what type of cyclins (G1, G1/S,...)? Cyclin in the PDGF could be considered as a G1/S cyclin. Since they are responsible for stimulating the division of human fibroblast cells in culture, the peak is in between the G1 and S phase.

2- In your own words, explain how the complex of MPF gets inactivated (you must explain all needed steps including APC/C) The MPF complex is inactivated when the cyclin is broken down. APC/C is an enzyme that attaches an ubiquitin which tags the cyclin as something to be destroyed. The tag is attached to securin on the chromatids. The securin normally binds and inactivates separase but when the securin is sent for recycling, the separase is activated. The securin with a ubiquitin is sent to the proteasome or recycle bin and is broken down. The separase breaks down the cohesin that is holding the sister chromatids together, leading to the separation.

3- What is the role of p53 gene and how it performs this role (you must explain in complete sentences) The p53 gene is a protein that is released in response to DNA being damaged. It suppresses tumors and works to prevent damaged DNA from performing mitosis. The cell is stopped at the G1 checkpoint by the production of CKI which blocks the activity. This activity being blocked allows for the DNA to be repaired. The p53 then activates the DNA repairing enzymes. In the case that the DNA is too damaged beyond repair, the p53 will trigger apoptosis to ensure that the damaged DNA is not passed onto daughter cells.