NEXT LIVE PERFORMANCE: 5/14/20

Join us for the last live review session before the AP Bio exam on 5/18/20.

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May 12, 2020

May 7, 2020

April 30, 2020

April 28, 2020

The image below is a schematic diagram of a signal transduction pathway within a single cell. Arrows represent activation, while a “T” (which may be upside down: see the one between JNI and Bcl2 below) represents inhibition. The overall result of this pathway is apoptosis (programmed cell death).

Some of the key events that occur within this pathway are as follows: 1) Tumor necrosis factor (TNF) binds to and activates its specific receptor (tumor cell necrosis factor receptor, or TNFR). 2) The activated TNFR activates JNI. 3) The activated JNI activates caspases by inducing mitochondria to release cytochrome C,  and also by inhibiting Bcl2. Bcl2, when active, promotes cell survival by inhibiting caspases. 4) The active caspases result in DNA damage and cell death.

PART 1: Several elements of the system above have been implicated in the development of cancer. Some of these are loss of function mutations, where a previously functioning component of a cell stops working. Based on the signaling pathway shown, describe the effect of a loss of function mutation of each of the following upon apoptosis (compared with wild type cells lacking this mutation).

* TNFR * BCl2 * Caspases

PART 2: Gain of function mutations are mutations where a cell component gains a capability that it previously lacked. Based on the schematic above, identify the component(s) of this signaling pathway that might promote cancer cell growth if they had a gain-of-function mutation that increased that component’s activity.

PART 3: Tumor suppressor genes inhibit cell division. List the component(s) of the system above that may be the product of tumor suppressor genes and that would promote cancer cell growth if they had a loss-of-function mutation.

April 23, 2020

April 20, 2020

April 16, 2020

The bos/seven receptor, shown below, is a receptor tyrosine kinase. This receptor is required for the differentiation of a particular cell, called R7. Like all receptor tyrosine kinases, the protein is inactive as a monomer. Binding of ligand causes the monomeric form of the receptor to form a dimer (shown on the right). Dimerization causes phosphorylation of the receptor’s intracellular domain, activating the protein.
During protein synthesis and processing of the receptor, the extracellular domain is cleaved and a disulfide bridge forms between two cysteine amino acid residues. The disulfide bridge tethers the ligand-binding domain to the rest of the protein.

PART 1: Predict the effect of a mutation in the DNA for the receptor that resulted in changing one of the cysteine amino acid residues into an alanine. Justify your prediction.

PART 2: How would this mutation affect differentiation in cell type R7?

April 14, 2020

FRQ # 1

The diagram at right represents a portion of the electron transport system in the inner mitochondrial membrane. As is shown, this pathway transfers electrons from NADH (and FADH2) to O2. Energy from this reaction is coupled to pumping of H+

Normally, cells carrying out respiration consume O2, produce CO2, and produce ~ 36 ATP for each glucose consumed.

As is shown in the diagram, two drugs, drug X and drug Y, can pick up electrons from particular intermediates in this pathway.

PART 1: Cells carrying out respiration are treated with a saturating dose of drug X, so that all the electrons which would normally continue along the pathway are captured by drug X. Under these conditions, PREDICT whether:

* The cells will continue to consume O2.

* The cells will continue to produce CO2.

* The rate of ATP synthesis will increase, decrease or stay the same.

For each prediction, EXPLAIN your reasoning.

PART 2: Cells carrying out respiration are treated with a saturating dose of drug Y, so that all the electrons which would normally continue along the pathway are captured by drug Y. Under these conditions, PREDICT whether:

* The cells will continue to consume O2.

* The cells will continue to produce CO2.

* The rate of ATP synthesis will increase, decrease or stay the same.

For each prediction, EXPLAIN your reasoning.

April 9, 2020

 

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6. Disrupted Systems

5. Experimental Design

4. Cancer drugs and their Effect on Cellular Proliferation

Proto-oncogenes, when they mutate to become oncogenes, can cause cells to become cancerous.A lysogenic virus infects a particular cell type and integrates its genome into a site that contains a proto-oncogene. This transforms the cell and increases the level of a protein X. Protein X, in turn, increases cellular proliferation (division and spread).

 

Tumor suppressor genes code for proteins that prevent cells from becoming cancerous. A compound P is known to increase the level of tumor suppressor proteins in that cell type. A second compound, Q helps in stimulating protein Z. Protein Z has been shown to be capable of binding to X rendering it inactive.

In the graphs at right, a minus sign indicates that substance P or Q was not applied to experimental cell cultures, while a plus sign indicates that substance P or Q was applied.

 

Identify which of the following graphs correctly represents the mode of action of P and Q. Justify your response.

 

3. Plasmids, Restriction Enzymes, Gel Electrophoresis, and DNA Fingerprinting

 

QoD # 3: With reference to this plasmid map, do the following:

PART 1: Explain how restriction enzymes work.

PART 2: Explain what a DNA fingerprint is, and how a DNA fingerprint can be created through Gel Electrophoresis.

PART 3. Predict the DNA fingerprints that would results from electrophoresis following

  1. Digestion with each restriction enzyme separately.
  2. Digestion with both restriction enzymes together.

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2. CO2 Uptake and Light Intensity

 

QOD # 2: The graph below shows the relationship between carbon dioxide uptake and light intensity in two plant species, A and B. One of these species is adapted to living in full sun, while the other is adapted to shade.

PART 1: Explain what processes can be measured by measuring carbon dioxide uptake.

PART 2: Using TWO pieces of information from this graph, determine which species is adapted to living in the shade. Explain your answer.

PART 3: Identify the species with the lower rate of respiration. Explain how this can be determined from the graph.

PART 4: Describe the significance that a low rate of respiration could have for this plant in its natural habitat.

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1. Signal Transduction

QOD # 1: The diagram below represents signal transduction.

PART 1: Explain how the initiation of signal transduction ensures that a cell’s response to a signal will be controlled and specific.

PART 2: List the type of molecules that generally act as intermediate or relay molecules.

PART 3: In a multicellular organism, signals can come in various forms. Explain how you know that in the system shown above, the ligand is NOT a steroid hormone.

PART 4: Describe a specific example of a cellular response that could occur in the kind of system depicted above.

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