AP Biology Unit 4 Cell Communication and Cell Cycle Exam Review
How do cyclins and cdk's interact to allow passage of the G2 checkpoint?
Levels of CdK's are constant throughout the cell cycle. Levels of cyclins change. As cyclins increase they bind and activate CdK's which allow the cell to proceed from G2 into mitosis.
What is apoptosis?
Programmed cell death
Identify the phase of mitosis that ensures equal transfer of chromosomes.
metaphase
What causes apoptosis?
p53 proteins block mitosis if there is DNA damage in a cell. P53 acts at the G1 -S checkpoint and initiates DNA repair or signals damaged cells to self destruct (undergo apoptosis)
How do cells communicate over a short distance? Identify two examples.
paracrine signaling; neurotransmitters, quorum sensing
Where is the receptor for a protein hormone?
plasma membrane (ligand can't move through membrane because of hydrophobic interior of the membrane)
What is a transcription factor?
proteins that help turn specific genes "on" or "off" by binding to DNA
What would happen if there was a mutation in a transduction protein? How would this affect the response of the cell?
proteins would be misfolded and would not be active; therefore, they couldn't activate downstream signaling pathways or amplify signals and the response would most likely not happen
What are the components of a signal transduction pathway?
reception, transduction, response
Identify one example of a chemical that activates a signaling pathway.
steroids such as testosterone or thyroid hormones
Where are the chemical signals processed?
target cell
How are proteins modified during the process of transduction?
A phosphate is added to activate the protein, and that phosphate is removed to deactivate the protein
Where does the ligand bind on the receptor?
Fits a specific place on receptor (like lock with key)
What occurs with a G-protein coupled receptor after binding to a ligand?
G protein binds GTP (similar to ATP)
What are the phases of interphase? What occurs in each of these phases?
G1 - Growth. S - DNA is copied. G2 - Growth; cell makes the molecules and organelles needed for cell division
What occurs at the G2 checkpoint?
G2 checkpoint checks for damage after DNA is replicatedIf there is damage, it prevents the cell from going into mitosis.
How are signals amplified after reception?
Phosphorylation cascade
What occurs in each of these phases?
Prophase I - Chromatin condenses into chromosomes, nuclear envelope disappears, spindle/centrosomes appear; synapsis/crossing over of homologous chromosomes. Metaphase I - Homologous chromosomes line up together in middle of cell. Anaphase I - homologous chromosomes separate and move to opposite poles; segregation and independent assortment. Telophase I - chromosomes unwind into chromatin, nuclear membrane returns; spindle/centrosomes disappear. Prophase II - same as mitosis prophase. Metaphase II- same as mitosis metaphase Anaphase II - same as mitosis anaphase. Telophase II - same as mitosis telophase
What are the phases of mitosis? What occurs in each of these phases?
Prophase- Chromatin condenses into chromosomes, nuclear envelope disappears, spindle/centrosomes appear. Metaphase- chromosomes line up independently in middle of cell. Anaphase - chromatids separate; chromosomes move to opposite poles in cell. Telophase - chromosomes unwind into chromatin, nuclear membrane returns; spindle/centrosomes disappear
What is a proto-oncogene? How do the proto-oncogenes cause cancer?
Proto-oncogenes are normal genes involved in cell growth and proliferation. When mutated proto-oncogenes are upregulated the cell keeps dividing like "car with gas pedal stuck"
What occurs with a tyrosine kinase receptor after binding to a ligand?
RTK's bind to each other to form a dimer. Once dimerization occurs, they work to phosphorylate downstream members of the signaling cascade
What occurs at the G1 checkpoint?
Restriction checkpoint; cell becomes "committed" to the cell cycle or stays in G1
What would happen if there was a mutation in the receptor protein? How would this affect the response of the cell?
there could potentially be misfolding or altered expression that could lead to disease, but sometimes it can lead to increased binding of the ligand which causes higher response
How does a transcription factor change gene expression?
they bind to the DNA near the promoter region and can recruit RNA polymerase to transcribe the gene
How can a chemical interfere with the signaling pathway?
they can bind to the receptor protein and inhibit the ligand from binding
How does this process ensure that identical genetic information is transferred?
this phase ensures that the DNA is copied so that each cell will have identical genetic information
How can a signal change the phenotype of an organism?
whether or not a specific gene is turned on or off would affect whether that phenotype would be present or not in an organism
Identify three roles of mitosis.
Asexual reproduction, growth of multicellular organisms, repair/replace worn out/damaged cells
What occurs at the G1 checkpoint?
Checkpoint controls the commitment of eukaryotic cells to transition through the G1 phase to enter into the DNA synthesis S phase Cell size, environment, growth factors, play a role in a cell passing through the G1 checkpoint.
What occurs at the M checkpoint?
Checks that the mitotic spindles/microtubules are properly attached to the kinetochores (anchor sites on the chromosomes). If the spindles are not anchored properly, the cell does not continue on through mitosis.
How do cells communicate over a long distance? Identify one example.
Hormones; Blood glucose levels via insulin
Identify a message communicated by direct cell-to-cell contact. What occurs during this process?
Immune cell (b-cell activation: b-cells bind to an infected cell). Immune cell (b-cell activation: b-cells bind to an infected cell)
What are the three phases of the cell cycle? What occurs in each of these three phases?
Interphase- cell growth, replication of DNA. Mitosis - cell/nucleus division. Cytokinesis - cytoplasmic division
What process allows for the passage of the M checkpoint?
Mitotic spindle microtubules are properly attached to the kinetochores of all chromosomes
Identify a message communicated by chemical signaling. What occurs during this process?
Neurotransmitters; exocytosis releases the chemicals; chemicals travel across the synapse and bind to receptors on the surface.
What is an oncogene?
Oncogenes are mutated forms of proto-oncogenes that have been upregulated to be permanently activated.
Why would a different cell respond differently to the same chemical signal?
They could have different internal transduction processes
True or False: Only specific cells will respond to specific chemical signals because they have a receptor for the chemical signal.
True
What is a tumor suppressor gene? How do the tumor-suppressor genes cause cancer?
Tumor suppressor genes code for proteins that function to repair damaged DNA or eliminate damaged cells. Tumor suppressor genes can cause cancer when they have mutations that cause them to be non-functional so damaged cells are not destroyed like "car with no brakes"
What is positive feedback? Identify two examples of positive feedback.
a process in which the end products amplify the original action; brings the system further from homeostasis. . Oxytocin, Ethylene production and fruit ripening, Polar ice melt
What is negative feedback? Identify two examples of negative feedback loops.
a process in which the production of a reaction leads to a decrease in that reaction; brings the system closer to homeostasis. blood sugar regulation and thermoregulation
What is the process that results in the release of a chemical signal from a cell?
exocytosis, cell signaling
How does a cell use negative feedback to return to a target set point after a disturbance?
has two different loops that control both directions of the set point
What occurs with an ion channel receptor after binding to a ligand?
acts as a gate, opening to let ions in or out (namely, Na+ and Ca2+)
What is the function of a kinase?
adds a phosphate to activate an enzyme in the transduction cascade, turning the molecular switch on
Using an example, explain how positive feedback can be used to maintain homeostasis?
baby moves towards cervix causing stretch receptors to be stimulated and the hypothalamus then releases oxytocin to cause the uterine wall to contract, which continues as the baby continues to push towards the cervix
How do chromosomes move through the process of mitosis?
chromosomes condense, move to the center of the cell, separate, and uncondense
What happens if the cell prematurely bypasses this checkpoint?
chromosomes won't be attached to spindle fibers and it could potentially divide with an uneven number of chromosomes present in each cell
What is the function of a phosphatase?
To dephosphorylate activated enzymes in the transduction cascade, functionally acting as a molecular off switch
What occurs to re-enter the cell cycle from G0?
A cell can reenter the cell cycle in response to appropriate cues.
How is cytokinesis different in a plant versus an animal?
Animal cells "pinch" using a cleavage furrow; plants build a cell plate to divide cell
What is the role of the receptor in the signal transduction pathway?
Binds with receptor to start signal transduction pathway
What is G0?
Cell has left cycle and stopped dividing
What occurs when the ligand binds to the receptor that initiated transduction?
the intracellular part of the receptor changes shape that can lead to the activation of many molecules
What are CdKs?
Cyclin-dependent Kinases are a family of proteins that regulate passage through the cell cycle by phosphorylating other molecules.
What occurs during cytokinesis?
Division of cytoplasm
What is the role of the ligand in the signal transduction pathway?
Signaling molecule
What are cyclins?
Small regulatory proteins that work by activating CdK's
What occurs during the process of transduction?
converts the signal to a form that can bring about a cellular response
Why would a receptor be in different locations?
differences in polarity of the molecules require receptors on the surface (if the molecule is hydrophilic) or molecules in the nucleus (if the molecule can cross the membrane)
How does this process ensure there is an equal transfer of chromosomes?
during metaphase chromosomes are attached to the spindle fibers to ensure that they will be pulled apart during anaphase
Using an example, explain how negative feedback can be used to maintain homeostasis?
if blood glucose gets too low, the body releases glucagon, which will release glucose from the cell and if blood glucose gets too high the pancreas releases insulin, which triggers certain tissues to absorb glucose where it is stored
Using an internal change, describe how an organism responds using feedback loops.
if blood glucose gets too low, the body releases glucagon, which will release glucose from the cell and if blood glucose gets too high the pancreas releases insulin, which triggers certain tissues to absorb glucose where it is stored
Identify the phase of mitosis that ensures identical genetic information is transferred?
interphase, S phase
How does positive feedback amplify the response? Identify one example.
it moves away from the set point. childbirth, fruit ripening
Identify one example of a chemical that inhibits a signaling pathway.
many cancer therapeutic drugs that target cell growth and differentiation by inhibiting the signaling pathway
Identify two examples of a cell responding to its environment. What occurs in each of these examples?
metabolic response, cell division; turning on transcription of an operon (lactose) because of lactose being present in its environment or dividing in response to cell signals telling the cell to move through the cell cycle
How does the cell undergo cytokinesis?
microtubules reorganize into an actin-myosin ring and pinch off animal cells
Why would a cell undergo apoptosis?
normal development, unneeded cells
Where is the receptor for a steroid hormone?
nucleus (steroid is hydrophobic so it can pass through cell membrane and enter cell
Identify three possible cellular responses.
opening of an ion channel, contraction of muscles, cell movement, synthesis of new proteins
What is a phosphorylation cascade?
sequence of signaling events where one enzyme phosphorylates another, causing a chain reaction leading to the phosphorylation of many other proteins
What occurs during reception?
signal molecule binds to receptor
What is a second messenger? Identify two examples.
small molecule or ion that relays signals received by receptors to proteins. cAMP and Ca++
Identify three causes of cancer. How does each affect the cell cycle?
smoking, radiation, viruses; they can damage or mutate DNA that can then cause the cell cycle to not make correct proteins that regulate the cell cycle
What occurs during the process of reception?
target cell's detection of the signaling molecule coming from outside the cell
Using an external change, describe how an organism responds using feedback loops.
temperature outside decreases, which can cause body temperature to decrease, thermoreceptors sense change, hypothalamus compares against set point and makes your muscles shiver and your blood vessels constrict
How does a ligand binding to a channel cause a cellular response?
the channel will let ions cross the membrane. changes in ion levels can change the activity of other molecules to produce a response
