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AP Biology Unit 7: Cell Communication and Cell Cycle Notes Pt. 1

AP Biology Unit 7: Cell Communication and Cell Cycle Notes Pt. 1

  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.

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

    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. 

  1. 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. 

    2. 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. 


Apoptosis is a programmed cell death that is caused by the surrounding cells telling it to do so. It plays a role in growth, immune surveillance and neoplastic surveillance. It is a way for the cell to kill itself neatly because if the inside just spilled out it would cause an inflammatory response. Looking at the video that accompanies this audio, the cell shrinks into itself and looks as though it dissolves. The lipids in the plasma membrane scramble telling other cells to consume the cell. The nucleus condenses, and the DNA breaks down into fragments. This all happens in a matter of minutes. The Fascinating World of Cell Apoptosis includes a video clip of a building being demolished by breaking the entire building but this makes a mess. Apoptosis is a lot like the building being taken down one level at a time to not disturb the surrounding environment. The cell surface coils, then shrinks, then condenses to finally stop moving all together. One example of this is the role in growth and development in the womb to create fingers from the fetal webbed hands. It also removes faulty cells by pathological apoptosis if the DNA is damaged beyond repair. This is done from the inside of the cell using caspades which are a type of protein. In the video, they are shown as a saw-like protein. The caspades must be activated, either with extrinsic or intrinsic pathways. Extrinsic pathway has the initial signal come from outside of the cell, so it is initiated by other cells [t-lymphocytes with fas-l]. Fas-l binds to fas receptors which causes an intracellular reaction which is mediated by a FADD and finally a caspase cascade occurs. Intrinsic pathway is initiated by signals within the cell. It is regulated by anti-apoptotic proteins and pro-apoptotic proteins in the mitochondrial membrane. Normally the anti-apoptotic proteins bind to the pro-apoptotic proteins which block the reaction. In a faulty cell, the pro-apoptotic proteins are free to take apart the cell and cause a caspase cascade.

  1. The Neuromuscular Junction Initiation Of Muscle Contraction

Muscle contractions are caused by a signal that is released from the brain. The signal travels down the spinal cord, to the motor neuron in the neuromuscular junction. The motor neuron fires an action potential which are Na+ down to the motor neuron axon. The Na+ reaches reaches the axon terminal which causes the voltage gated Ca+2 channels to open and flood the axon terminal with Ca+2. Synaptic vesicles are released from the presence of  Ca+2 from their docking sites, and then fuse with the presynaptic membrane to release neurotransmitters(acetylcholine). Acetylcholine then diffuses across the synaptic cleft to bind to nicotinic acetylcholine receptors. They are ligand gated sodium-ion channels which only open in the presence of acetylcholine to flood into the muscle fiber. Na+ is positively charged so it causes a wave of depolarization, which is the action potential. The voltage gated calcium channels open to release Ca+2 from the sarcoplasmic reticulum. The Ca+2 binds to the troponin to pull the tropomyosin off of the myosin binding site to allow for the cross bridge binding site to begin.

  1. Insulin and glucagon

The flow of energy throughout the body is called metabolism. Food is absorbed as amino acids, fats, or carbs, which provides energy into the GI tract. This energy is absorbed and sent elsewhere for use to maintain homeostasis. Carbs contain the most energy, with glucose being the simple sugar. The two hormones that control the availability of glucose are insulin and glucagon. Insulin regulates the storage of glucose, while glucagon regulates the release of glucose from storage. Glucose levels being maintained are necessary for homeostasis. The brain uses 120g of glucose a day which is around 60 to 70% of the glucose we consume. Glucose levels are mostly represented by mg/dL and the range is from 70mg/dL to 120mg/dL. Too much glucose causes hyperglycemia which may lead to diabetes (eye, nerve and kidney disease). Too little glucose causes hypoglycemia which may cause fatigue, a coma, or even death. Once you eat and glucose levels get too high, the body releases insulin to drive the glucose amount down. If you have a decreasing amount of glucose in your blood, the body releases glucagon to increase this amount. Insulin decreases the blood glucose concentration by storing the glucose, and glucagon increases the blood glucose concentration by releasing the glucose from storage. Insulin causes glucose to undergo glycolysis which is irreversible to produce ATP. Another path that may be taken is to undergo glycogenesis which is reversible and means the formation of glycogen to be stored in the short term in the liver or muscle tissue. The final path that may be taken is to undergo lipogenesis which is irreversible, to produce lipids or fatty acids and store it long term in adipose tissue. Glucagon increases the blood sugar level by releasing the glucose from the breaking down of glycogen which is reversible, and is called glycogenolysis.  It can also release glucose from amino acids which undergo gluconeogenesis which is reversible. It can also take fatty acids and convert it into ketone bodies using ketogenesis which is irreversible. Ketone bodies are forms of energy to be used only by the heart and brain, so it is a last resort. Insulin inhibits the release of glucagon.

  1. Action of Epinephrine on a Liver Cell 

Epinephrine is a hydrophilic molecule, so it must bind to a ligand or a receptor protein in order to cause a reaction. This causes a g protein with three subunits to be activated and one subunit which is the g protein subunit to dissociate and replace GDP with GTP. This subunit travels until it finds an adenylyl cyclase which is then activated by the g protein subunit. The adenylyl cyclase catalyzes the formation of cAMP from ATP. The cAMP binds and activates a protein kinase A which adds phosphate groups to proteins. In the liver, protein kinase A activates phosphorylase which then changes the glycogen into glucose 6 phosphate which is then finally converted into glucose. Epinephrine triggers the fight or flight response using glucose that is released into the bloodstream.

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- Explain how the complex of MPF gets inactivated 

- 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?

- 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.

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.


AP Biology Unit 7: Cell Communication and Cell Cycle Notes Pt. 1

  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.

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

    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. 

  1. 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. 

    2. 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. 


Apoptosis is a programmed cell death that is caused by the surrounding cells telling it to do so. It plays a role in growth, immune surveillance and neoplastic surveillance. It is a way for the cell to kill itself neatly because if the inside just spilled out it would cause an inflammatory response. Looking at the video that accompanies this audio, the cell shrinks into itself and looks as though it dissolves. The lipids in the plasma membrane scramble telling other cells to consume the cell. The nucleus condenses, and the DNA breaks down into fragments. This all happens in a matter of minutes. The Fascinating World of Cell Apoptosis includes a video clip of a building being demolished by breaking the entire building but this makes a mess. Apoptosis is a lot like the building being taken down one level at a time to not disturb the surrounding environment. The cell surface coils, then shrinks, then condenses to finally stop moving all together. One example of this is the role in growth and development in the womb to create fingers from the fetal webbed hands. It also removes faulty cells by pathological apoptosis if the DNA is damaged beyond repair. This is done from the inside of the cell using caspades which are a type of protein. In the video, they are shown as a saw-like protein. The caspades must be activated, either with extrinsic or intrinsic pathways. Extrinsic pathway has the initial signal come from outside of the cell, so it is initiated by other cells [t-lymphocytes with fas-l]. Fas-l binds to fas receptors which causes an intracellular reaction which is mediated by a FADD and finally a caspase cascade occurs. Intrinsic pathway is initiated by signals within the cell. It is regulated by anti-apoptotic proteins and pro-apoptotic proteins in the mitochondrial membrane. Normally the anti-apoptotic proteins bind to the pro-apoptotic proteins which block the reaction. In a faulty cell, the pro-apoptotic proteins are free to take apart the cell and cause a caspase cascade.

  1. The Neuromuscular Junction Initiation Of Muscle Contraction

Muscle contractions are caused by a signal that is released from the brain. The signal travels down the spinal cord, to the motor neuron in the neuromuscular junction. The motor neuron fires an action potential which are Na+ down to the motor neuron axon. The Na+ reaches reaches the axon terminal which causes the voltage gated Ca+2 channels to open and flood the axon terminal with Ca+2. Synaptic vesicles are released from the presence of  Ca+2 from their docking sites, and then fuse with the presynaptic membrane to release neurotransmitters(acetylcholine). Acetylcholine then diffuses across the synaptic cleft to bind to nicotinic acetylcholine receptors. They are ligand gated sodium-ion channels which only open in the presence of acetylcholine to flood into the muscle fiber. Na+ is positively charged so it causes a wave of depolarization, which is the action potential. The voltage gated calcium channels open to release Ca+2 from the sarcoplasmic reticulum. The Ca+2 binds to the troponin to pull the tropomyosin off of the myosin binding site to allow for the cross bridge binding site to begin.

  1. Insulin and glucagon

The flow of energy throughout the body is called metabolism. Food is absorbed as amino acids, fats, or carbs, which provides energy into the GI tract. This energy is absorbed and sent elsewhere for use to maintain homeostasis. Carbs contain the most energy, with glucose being the simple sugar. The two hormones that control the availability of glucose are insulin and glucagon. Insulin regulates the storage of glucose, while glucagon regulates the release of glucose from storage. Glucose levels being maintained are necessary for homeostasis. The brain uses 120g of glucose a day which is around 60 to 70% of the glucose we consume. Glucose levels are mostly represented by mg/dL and the range is from 70mg/dL to 120mg/dL. Too much glucose causes hyperglycemia which may lead to diabetes (eye, nerve and kidney disease). Too little glucose causes hypoglycemia which may cause fatigue, a coma, or even death. Once you eat and glucose levels get too high, the body releases insulin to drive the glucose amount down. If you have a decreasing amount of glucose in your blood, the body releases glucagon to increase this amount. Insulin decreases the blood glucose concentration by storing the glucose, and glucagon increases the blood glucose concentration by releasing the glucose from storage. Insulin causes glucose to undergo glycolysis which is irreversible to produce ATP. Another path that may be taken is to undergo glycogenesis which is reversible and means the formation of glycogen to be stored in the short term in the liver or muscle tissue. The final path that may be taken is to undergo lipogenesis which is irreversible, to produce lipids or fatty acids and store it long term in adipose tissue. Glucagon increases the blood sugar level by releasing the glucose from the breaking down of glycogen which is reversible, and is called glycogenolysis.  It can also release glucose from amino acids which undergo gluconeogenesis which is reversible. It can also take fatty acids and convert it into ketone bodies using ketogenesis which is irreversible. Ketone bodies are forms of energy to be used only by the heart and brain, so it is a last resort. Insulin inhibits the release of glucagon.

  1. Action of Epinephrine on a Liver Cell 

Epinephrine is a hydrophilic molecule, so it must bind to a ligand or a receptor protein in order to cause a reaction. This causes a g protein with three subunits to be activated and one subunit which is the g protein subunit to dissociate and replace GDP with GTP. This subunit travels until it finds an adenylyl cyclase which is then activated by the g protein subunit. The adenylyl cyclase catalyzes the formation of cAMP from ATP. The cAMP binds and activates a protein kinase A which adds phosphate groups to proteins. In the liver, protein kinase A activates phosphorylase which then changes the glycogen into glucose 6 phosphate which is then finally converted into glucose. Epinephrine triggers the fight or flight response using glucose that is released into the bloodstream.

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- Explain how the complex of MPF gets inactivated 

- 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?

- 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.

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.