Friday, April 29, 2011

Cortical Reaction

Fertilisation, no it is not a typo for fertilization, which is more so directed towards humans. Fertilisation identifies the fusion of gametes to produce a new organism. Fertilisation can be used in reference to anything from flowering plants to humans. In humans the process involves the fusion of a sperm to an ovum, which is the first step in initiating the cortical reaction.

The cortical reaction begins when the sperm unites with the eggs plasma membrane, leading to an influx of intracellular calcium, resulting to the exocytosis of cortical granules. The cortical granules are secretory vesicles, composed of contents that vary with species and are released into the extracellular space. The exact roll in the excretion of these vesicles containing varying contents is not quite fully understood. Upon the release of the cortical granules the vitelline layer is then altered. In mammals that layer is identified as the zona pellucida. The zona pellucida, or vitelline layer, is an external membrane to the plasma membrane of an egg cell. The alteration of the vitelline layer is an effect of an increase of osmotic pressure causing water to fill the space between the layer and the plasma membrane. This single event is responsible for the successful fertilization of an egg, because it raises all of the other non-fertilizing sperm from the plasma membrane. This is so important because it prevents polyspermic fertilisation, a lethal fate to an oocyte.

The reaction is represented in the shown diagram. A sort of signal transduction cascade is initiated upon uniting the sperm to the egg. Evidence supports the theory that the PIP2 cascade mediates the cortical reaction. The PIP2 cascade generates two second messengers, IP3 and DAG. DAG is responsible for inducing the release of intracellular Ca2+ from the sarcolemma and various storage organelles. This sudden influx in calcium leads to the exocytosis of the cortical granules. The granules then induce the alteration of the zona pellucida, which prevents polyspermic fertilisation and allowing only one sperm to fertilize the egg leading to the completion of the cortical reaction.

Skeletal Muscle Contraction

A muscle fiber contraction is a complex interaction of organelles and molecules in which myosin binds to actin and exerts a pulling action. This results in a movement within the myofibrils in which the filaments of actin and myosin slide past one another. This action shortens the muscle fiber so that it pulls on its attachments.
A skeletal muscle fiber normally does not contract until a neurotransmitter stimulates it. Acetylcholine is the neutrotransmitter that causes muscle contraction. This neurotransmitter is synthesized in the cytoplasm of the motor neuron and stored in vesicles at the distal end of the motor neuron axons.

When a nerve impulse reaches the end of a motor neuron axon, some of the vesicles release their acetylcholine into the space between the motor neuron axon and the motor end plate. Acetylcholine diffuses rapidly across the synaptic cleft and binds to specific protein receptors in the muscle fiber membrane. The binding allows for increased membrane permeability to sodium ions. These charged particles stimulate a muscle impulse.

The sarcoplasmic reticulum contains a high concentration of calcium ions. In response to a muscle impulse, the membranes of the cisterne become more permeable to these ions, and the calcium ions diffuse into the sarcoplasm of the muscle fiber. When there is a high concentration of calcium ions in the sarcoplasm, troponin and tropomycin interact. This interaction causes the binding site on actin to become exposed. As a result, linkages form between the actin and myosin filaments, and the muscle fiber contracts. ATP is also required for the muscle contraction as long as nerve impulses release acetylcholine.

Thursday, April 28, 2011

Review by Powerpoint

Through the endless pursuit of research, some of the best stories are the result of approaching a topic through multiple expertise. For instance, there was a study our of Pittsburgh that attempted to tackle the understanding of why teenagers seem to be "impulsive." This has an impact on society since EVERYONE has experienced this impulsiveness, and it would be beneficial to understand this moment in life.

I will let you first take a gander at the power point real quick, since I intended you to do so. Don't feel guilty and just do it.

O.K., now that you have looked over these few slides, I just want to expound upon a little bit. The value of this study was that it took an apparent observation -teenagers seem to act more recklessly than adults- and then explored whether there was a biological explanation for this observation. An experiment using mice resulted in significant results showing that indeed there must be some biological explanation, and that under stressful conditions further exacerbates this impulsiveness.

The ironic thing is that in the end the most likely explanation of this impulsiveness is that it is a maturity thing...but of the brain. It is likely that there are some changes that the brain undergoes in its development that makes people and animals to be more cautious and less impulsive. Now the next step is to verify this hypothesis with some continual studies, and then we will truly know why teenagers are impulsive.

Monday, April 25, 2011

Ecology: Just in case you forgot...

 Since it has literally been eight years since I have taken basic biology, my ecological knowledge has gone from so-so to oh-no! Judging by the questions regarding ecology, I could use a basic refresher, and I would imagine that others could benefit as well. I really wanted to stick with the suggestions for my powerpoint layout and truly attempt to "keep it simple" and resist the urge to fill in all of the negative space. I tried to allow the slides to enhance my presentation material with a simple visual aid, and very minimal text. I also tried to use complimentary color contrasts of warm and cool colors for my background and font, as suggested.

My first slide is intended as an intro, or title slide to aid in the delivery of some basic general information about ecology as a science, as well as some general terminology. I would have discussed and defined terms such as "ecosystem", "deme", "population", "subpopulation", "aggregation", and "metapopulation".

Moving on to the second slide, my intention was to discuss some aspects of energy exchange and trophic levels using a food web as an example. Discussion of the different trophic levels such as primary producers, primary, secondary, tertiary, and quaternary consumers. Discussion of the concepts of niche and biomass would have worked well here. Also, the discussion and description of keystone species would have been necessary.  

Next, on the third slide, I felt discussion of biomes, and the variety of populations existing within would have been an interesting supplement. Specific examples of biomes, and potential organisms within would have served well here. This also would have transitioned well into my fourth slide.

For the final slide, I chose to discuss certain aspects of adaptation and natural selection with regard to the different biomes. Discussion of evolutionary adaptations such as those seen in different species of birds, which hail from a common ancestor, would have worked well to discuss the relationship between form and function due to certain environmental influences.

With so much to know about such a diverse science, this seems to be a good foundational start. My intention, as stated, was to recall some of the basic concepts of ecology, so if nothing else, at least the jargon would make sense whenever it arises again.

Friday, April 1, 2011


So you might ask yourself what is the difference between a virus and a retrovirus? The answer is the function of how each replicates its genetic material. A virus has a single strand of genetic material-either DNA or RNA. A retrovirus consists of a single strand of RNA. Once a retrovirus enters a cell, it collects nucleotides and assembles itself as a double strand of DNA that splices itself into the host's genetic material.Retroviruses contain RNA as the hereditary material in place of the more common DNA. In addition to RNA, retrovirus particles also contain the enzyme reverse transcriptase (or RTase), which causes synthesis of a complementary DNA molecule (cDNA) using virus RNA as a template.

When a retrovirus infects a cell, it injects its RNA into the cytoplasm of that cell along with the reverse transcriptase enzyme. This enzyme copies the viral RNA genome into a single minus strand of DNA. The resulting double stranded DNA is integrated into the chromosomal DNA of the infected cell. The proviral DNA is then transcribed by the cell’s own machinery into RNA, which will be either translated into viral proteins or is packaged into other proteins. Because most retroviruses do not kill their host cells, infected cells can replicate, producing daughter cells with integrated proviral DNA. These daughter cells continue to transcribe the proviral DNA and bud progeny virions.