Cell Bio Exam 4

An inheritance of which of the following could be used to block the release of calcium from the endoplasmic reticulum?

Phospholipase C

Which of these statements regarding sexual reproduction and sex chromosomes is true?

NOT across different species, sexual life cycles differ with respect to the release timing of meiosis and fertilization

Which of the following is characterized by a cell releasing a signal molecule into the environment, followed by a number of cells in the immediate vicinity responding?

Paracrine signaling

In general, signal transduction via cascading phosphorylation of a series of proteins

NOT none of the answers are correct

Which of the following best describes a karyotype?

NOT a pictorial representation of all genes found on a chromosome

Most signal transduction pathways have multiple steps, which of the following explanations why this is advantageous (i.e. why signal transduction pathways evolve this way)

NOT a multi-step pathway requires less energy to transduce a signal

What is the relationship between cyclines and Cdk’s?

Cyclins are regulatory proteins that band and activate Cdk’s, which in turn induces events in the cell cycle

Which of the following is true for flagella in both prokaryotes and eukaryotes?

NOT flagella are extracellular structures

Using the figure shown above, indicate which grouping represents a set of sister chromatids

NOT group B

Which of the following is true for glycosaminoglycans (GAGs) and proteoglycans?

They produce gels in connective tissues

The GTP cap of a molecule can be described as

The buffer zone of GTP-bound tubulin dimers at the growing end of a microtubule

What is the phenomenon that occurs when the rate of new actin subunits attaching to the plus end of an actin filament is the same as the rate of dissociation of actin subunits at the minus end?

Treadmilling

Compared to females, males are more often affected by X-linked disorders because

males are hemizygous for genes on the X-chromosome

Recombination between linked genes comes about for what reason?

Crossover occurs at a point between these genes during synapsis

Compared the asexual reproduction, what advantage does sexual reproduction offer in natural selection?

Sexual reproduction results in many new gene combinations, some of which will lead to a differential reproductive success.

Connective tissues typically have

NOT all of the answers are correct

Which of the following occurs in meiosis but not in mitosis?

Synapsis of chromosomes

When a neurotransmitter binds to a neuron’s receptors and initiates a cascade of relay protein activation that ultimately results in charge to the membrane potential of the neuron (e.g. the opening of GIRK channels), the neurotransmitter is said to be serving as which part of the signal pathway?

First messenger

Which of these statements regarding sexual reproduction and sex chromosomes is true?

All of these are true

The GTP cap of a microtubule can be desceibed as

the buffer zone of GTP-bound tubulin dimer at the growing end of a microtubule

For the alveoli of lungs, having the shortest distance possible for gases to diffuse between air and the blood is critical. Considering this, what type of epithelium (i.e. epithelial cell arrangement) would be present at this interface?

NOT stratified squamous epithelium

The centromere is the region of a chromosome where

NOT new mitotic spindles originate (i.e. the grow outward from this location)

Regarding synapsis, a chromosomal tetrad is composed of which of the following sets of DNA strands?

NOT Four homologous chromosomes composed of signal chromatids

In general, signal transduction via cascading phosphorylation of a series of proteins

NOT requires transport of the signaling molecule inside of the cell to initiate the first phosphorylation event

Whish of the following statements describes proto-oncogenes?

NOT they are pseudogenes that can be activated by mutation to regulatory regions (e.g. promoters and enhancers)

Which process can produce daughter cells that are generally different?

Meiosis I and meiosis II

Which of the following is true for flagella in both prokaryotes and eukaryotes?

NOT flagella are extracellular structures

After telophase I of meiosis, the chromosomal makeup of each daughter cell is

haploid, and the chromosomes are each composed of two chromatids

The cortex of a cell can be described as

the region where actin filaments are numerous between the plasma membrane and the deeper parts of the cell

If a cell has a mutation that prevents is from making a protein kinase needed for the M phase checkpoint, which of the following would likely be the result of this mutation?

NOT the cell would prematurely enter anaphase

What is the earliest checkpoint here the cell become committed to continue the cell cycle all the way through mitosis? (Hint: if a cell passes this checkpoint but fails to eventually go through mitosis, it will usually die)

G₁ checkpoint

Testosterone and other steroid hormones function inside a cell by

binding soluble receptors that enter the nucleus and act as transcription factors

Auto-phosphorylation is a characteristic of both receptor tyrosine kinases (RTK’s) and which of the following?

None of these answers are correct

How might a proto-oncogene become an oncogene?

All of these answers are correct

When GCPR’s bind their ligand (signalling molecule) they activate G-proteins by

facilitating the exchange of GDP for GTP at the G-protein alpha subunit

Which of the following proteins is an example of a tumor suppressor gene

NOT growth factors

Which of the major categories of receptors reacts to the binding of its ligand (signaling molecule) by forming receptor dimers, undergoing auto-phosphorylation, and then activating relay proteins?

Receptor tyrosine kinases

In regards to signal transduction, what are scaffolding proteins?

Large proteins to which several relay proteins attach to increase the efficiency and speed of a phosphorylation cascade

Which of the following is they cytoskeletal component at the core of cilia and eukaryotic flagella?

Microtubules

Ion can travel directly from the cytoplasm of one animal cell to the cytoplasm of an adjacent cell through

Gap junctions

SHORT ANSWER What are ES cells and iPS cells? Be sure to explain the differences in their “potential” and source

ES cells are embryonic stem cells. ES cells are usually gathered from the source of internal embryo masses. Since these cells are totipotent, ES cells have the ability to differentiate into any type of specialized cell needed. iPS cells are induced pluripotent cells. iPS cells are usually gathered and cultured from mature organisms. iPS cell potential comes from having multiple chemical and biological processes occur, leading the cultured cells to be reverted back to a state before differentiation, allowing them to be stem cells that could be turned into other cell types like ES cells.

In terms of research or clinical applications, what are the advantages of iPS cells when compared to ES cells?

iPS cells have an advantage for both clinical and research wise of being considerably more ethical, as many times ES cells are gathered through the breaking open of embryos. iPS cells are considerably cheaper to propagate as ES cells are extremely difficult to culture and require multiple procedures, time, and effort. For stem cell therapy, iPS cells taken from a person, reverted, and transformed into the cell types needed and put back into the same person, there is a much higher chance that the cell will not be rejected compared to ES cells that have the chance of being rejected during stem cell therapy. iPS cells can be differentiated more specifically than ES cells can for a specific type of stem cell therapy as using iPS cell that are similar to the one trying to be stimulated, recovered, or targeted will be easier to do with the already specific stem cell used within the clinical application

In terms of research or clinical applications, what are the disadvantages of iPS cells when compared to ES cells?

iPS cells are not tolerant like ES cells are. iPS cells are limited to what cells they can be differentiated into while ES cells can be differentiated into any type. iPS cells may cause unwanted diseases or infections due to one of the most common ways to revert the cells into a stem cell state being by using retroviruses. Gathering enough specific iPS cells may be difficult as reverted multiple iPS cells from different people may lead to different responses due to the varying amount of alterations that need to be done on these cells to revert them, compared to ES cells that do not need to be reverted. iPS cells cannot be used to stimulate natural life reactions to different diseases trying to be researched as they are genetically modified and would not be a solid representation of how the body would actually react.

Rigor mortis occurs a few hours after death and presents as a stiffening of the muscles of the body. This eventually subsides after hours or days have past. Given what you know about the molecular workings of muscle cells and the cytoskeletal components and motors that allow them to contract, answer the following: 

(A) Why does the onset of rigor mortis NOT occur immediately after death? 

Rigor mortis does NOT occur immediately after death due to both ATP and calcium still being present within the body. ATP specifically enacts different muscle movements by inducing power stroke. ATP will bind to the myosin-Il head, allowing the release of actin. The release of actin allows a bit of movement as the myosin-ll head will be induced to a conformational change sending the head to a higher energy state to prepare for power stroke. As ATP hydrolysis occurs, an inorganic phosphate will be released, allowing a loose attachment of the myosin-ll to the actin again. Once ADP is then released from the myosin-Il head, the myosin re-attaches to the actin and causes a power stroke movement. Since ATP is still present in the body, the power stroke allows for the movement of muscles. This works hand in hand with calcium. Since calcium is still present from the body the troponin complex can still function. Calcium binds to the troponin, causing the molecule to release tropomyosin, encouraging the tropomyosin to move away from the troponin with ADP-bound myosin heads being involved by loosely attaching to one of the seven now open spots on the tropomyosin. This allows for muscle contractions as after calcium is dispensed from the troponin there will be reattachment to the tropomyosin creating the complex again.

Why do muscles become locked in place during rigor mortis, and why don’t they contract further?

As mentioned before, right after death ATP and calcium will still be present in the body, but after some time, both molecules will be expended causing the rigid state of rigor mortis. ATP is specifically used to cause power stroke with myosin-ll heads. With the body no longer making ATP, there will no longer be any ATP molecules to induce the mysoin-Il head to release the actin. With no releasing of the actin, there will be no space for the myosin-II head to induce conformational change, with no power stroke movement resulting. Calcium will also, no longer be propogated within the body after death. The body will no longer be able to signal the sarcoplasmic reticulum to release calcium and in turn, will not trigger the movement and contractions of the troponin complex. Without calcium to bind to the troponin, the tropomyosin will not be released and will not be encouraged to move away from the troponin. Without this movement, muscle contractions will not occur. In both situations, without ATP and calcium, both muscle movement systems will be stuck. No unattachments and overall, no movements. These systems being stuck leads to the muscles locking in the rigid position seen during rigor mortis with there being no chance that they will contract any further. 

Explain why rigor mortis eventually ends

Rigor mortis will eventually end due to other natural processes. After some time, the body will start to decompose. This decomposition comes from enzymes released through autolysis, and bacteria. Both the enzymes and bacteria will break down and decompose different parts of the body, especially the muscle tissue and in turn the cytoskeleton. The decomposition of both will eventually release the body from rigor mortis and the overall rigid state as myosin-Il heads and troponin will have nothing to stay rigidly attached to if everything is decomposed. Once this decomposition release occurs, rigor mortis ends, and the body reaches back to an overall relaxed state. This process usually occurs over 36 hours later.