Down Syndrome

Down Syndrome

Down Syndrome is a chromosomal condition characterized by the addition of either half or whole of an extra chromosome. Chromosomes are strands of DNA (deoxyribonucleic acid) and proteins which are present in every cell of the body and make up our individual genetic material. Down Syndrome affects 1 in every 800 babies born. The extra genetic material can impair the mental and physical development in a child although the extent of this impairment varies from patient to patient (Gavin, 2012). With current research continuing, the possibilities of minimizing the risk of Down Syndrome will increase.
Down Syndrome is the most common chromosomal disorder in the world. Our cells divide in two ways, firstly is ordinary cell division which is called mitosis in which our body needs to grow. Secondly is in the ovaries and testicles where meiosis occurs. This cell division consists of one cell splitting into two creating sperm and egg cells (refer to figure 1).

Normally during conception 23 chromosomes from the mother and 23 chromosomes from the father are inherited, totaling to 46 chromosomes, and these chromosome contain genetic information. Recent research suggests that in the majority of Down Syndrome cases there is an ovarian nondisjunction during meiosis and he child will obtain an extra chromosome 21 for a total of 47 chromosomes rather than 46 as mentioned earlier (refer to figure 2). A possible cause for this is maternal age although the exact cause is not yet known (Gavin, 2012).

                                                Figure 2: Down Syndrome Chromosomes

The life expectancy of an individual with Down Syndrome is usually around 50 years of age. This is quite low due to almost every system in their bodies being at risk from the effects of Down Syndrome (Schoenstadt, 2012). The exact effects of Down Syndrome are still not known as chromosome 21 codes for approximately 360 proteins although there are some common health problems, such as decreased brain size, congenital heart disease and lens defects. Individuals with Down Syndrome also suffer from increased purine levels which can lead to mental retardation and immune deficiencies. Purine is an organic compound that contributes to the contents of RNA and DNA. As well as health problems there are some physical attributes that are common in Down Syndrome patients for example slanted eyes, shorter neck and shorter limbs (Cunningham, 2008).
There are treatment and therapies available for Down Syndrome patients including physiotherapy to help strengthen muscles, surgery for heart disease  and regular check ups and screening to prolong the life of the individual (Cifra-Bean, 2012). Research in the field of genetics is very promising although it must only be considered in the future as the genes need to be identified and their function be determined before any radical medical procedures are recommended. Interactions between genes can also be a key factor to help minimizing Down Syndrome (Cifra-Bean, 2012).
It is a very promising time in research in Down Syndrome as the advent of the completion of the human genome project is more understood and practiced than ever before. Future research could help improve life expectancy, symptoms and possibly even help repair the chromosome 21 in this devastating chromosomal disorder.

Changing the Gentic Code

Changing the Gentic Code

All life possesses a genome and the nature of that life is determined by it's genome. The genome consists of DNA which is made up of four nucleotides (Adenine, Cytosine, Guanine, Thymine), a series of three of these nucleotides is called a codon (64 codons in total) with each of these codons corresponding to one of the 20 amino acids or one stop codons. These codons are then translated into their respective amino acids until a stop codon is reached. Now what would happen if an organism had a codon that it did not normally have?

                                                            FIG   :  E coli just chiling

In theory an organism with non-naturally occurring amino acids could be made immune to viruses at the very least. Viruses replicate basically by commandeering a cell's ribosome and the other components used for replication.“Viruses depend on the fact that their proteins are encoded by the same codons as those of their hosts”(Young, Discover magazine 2011) If the organism has unnatural codons the viruses are almost certainly not going to have those codons and as such be unable to take over.

A team led by Farren Issacs at Yale University is attempting to answer that question. To do this they have edited the genome of Escherichia coli replacing the E coli's TAG stop codon with TAA another stop codon. First the team identified all 314 TAG codons in E coli, they then created small segments of DNA that had TAA instead of TAG which they mixed into a nutrient rich solution that was swimming with viral enzymes then submerged around a billion E coli in this solution.

The first of two processes MAGE was then used. MAGE or multiplex automated genome engineering, was first used a few years ago and allows bioengineers to do in days what would have previously taken them years. Essentially a specially prepared segment of DNA is placed in a solution with the cell and then electricity is run through the solution. This causes the cell to open pores in it's membrane allowing the DNA inside. Then when the cell next undergoes mitosis it will use this new DNA in the process. The DNA can then be found in the genome of the daughter cells.

MAGE gave the researchers E coli that had some TAA codons, however to create E coli that only had TAA they would have to use another process call CAGE. CAGE or conjugative assembly genome engineering relies on the bacterial form of sex, Bacterial conjugation, where one bacteria transfers genetic material (in this case the TAA codons) to another. The researches separated the E coli into 32 groups then used CAGE until they had a strain with almost entirely TAA codons.

Once the process is complete, the researchers could assign the now unnecessary TAG codon to an amino acid (natural or otherwise) instead of a stop codon. As mentioned before this could make bacteria immune to viruses, (a great thing if that bacteria is used in the production of medicine), what else this could potentially do we can at the moment only speculate. . It should be noted that the E coli seem to suffer no effects from their lack of TAG codons, raising the question what effects the stop different codons have.

DNA methylation

DNA methylation:

 A new approach to modifying cancerous & other diseased cells.


Epigenetics is a fairly new area of genetics, epi- is a Greek prefix meaning above, on or over and epigenetics refers to the study of gene expression other than that of a specific change in the nucleotide sequencing. DNA methylation is a form of epigenetic signature, it is fairly common throughout DNA and is more closely related to cell identity, which is what it sounds like; how’s cells identify themselves. Or for example; how a skin cell, knows not need to produce insulin, while a pancreatic cell knows that it shouldn’t produce pigment. (Health Canal 2012) I won’t dive too deep into the specifics but basically; a methyl group is attached to specific CG sites in the DNA sequence. This is where Cytosine and Guanine are sitting side by side, within DNA. A research paper was published earlier this month in the scientific journal Cell Metabolism titled “Acute Exercise Remodels Promoter Methylation in Human Skeletal Muscle”, the subject of the study being how exercise induces instantaneous methylation changes, subsequently altering gene activity to better burn lipids and carbohydrates within mitochondrial function. The research recruited fourteen young and healthy recruits who were punished on an ergometer for incremental short bursts of exercise – fun. Immediately after the pain, more pain was administered in the form of a muscle biopsy which was taken and the methylation then tested. Another biopsy was taken twenty minutes later to examine the difference in methylation levels, and what do you know, they discovered “that acute exercise induces gene-specific DNA hypomethylation in human skeletal muscle.”
Figure A shows the change in methylation, whereas figure B shows the ratio between the levels of methylation on specific genes.

Barrès and co. believed they made a pretty significant discovery, seeing as epigenetics when it first came about wasn’t seen as an important player in the game of genetics. But what they discovered is that hypomethylation is occurring all the time within our DNA, so it’s not as stable a process as once was believed. Their hopes with this is that this can remove some of the fear around tampering with methylation levels within DNA. In other scientist’s defence, this is a fair call as a methylation imbalance has been linked tumour progression (Baylin et al. 1998).

So how does this mean that we can modify cancerous and other diseased cells? Well Barrès believes that they “have shown, that just by exercising, you, yourself manipulate the DNA of your cells. Our DNA is not as stable and unchangeable as previously thought.” (Health Canal 2012). As I said earlier, cell identity and gene expression has much to do with methylation, so how about telling different cells to heal themselves? Or seeing as the original discovery was in fact to do with methylation caused by exercise, what I we could tell cells that they were exercising when they were performing little or no exercise? I can imagine international pharmaceutical giants salivating at this thought – but it could be put to much better use to by simulating exercise for diabetics who have lost both legs to their diabetes. Or perhaps people with severe depression – exercise and fitness is known to improve the symptoms within these people.
Barrès and co. have hungry eyes at this stage and feel that they have opened the door to a whole avenue of new research, but it is very early days so you shouldn’t be getting too excited about that ‘diet pill’ just yet.

S is for Sister Chromatids

S is for Sister Chromatids

Sister chromatids are two identical chromosomes attached to each other at the centromere. Since they are identical, they carry exactly the same genes. So what's the point of having two identical chromosomes attached to each other? This is the body's way of making more cells. When it undergoes mitosis the DNA needs to replicate itself so the new daughter cell will have the same amount of genetic material.

V is for Vesicle

V is for Vesicle 

A vesicle is something that is used to carry molecules through the body. Since the body consists of mostly water, these vesicles need to be hydrophilic on the outside, but most molecules in need of transport are hydrophobic, so the inside of the vesicle must be hydrophobic. This means that they can be made from phospholipids. Phospholipids have a hydrophobic tail and a hydrophilic body (and they look like sperm).



This is a picture of a liposome. It has a phospholipid bilayer to accommodate hydrophilic molecules.

Since there are so many molecules that need to be transported in the body there are many, many vesicles. The ones that I am most familiar with are those that carry neurotransmitters because that is what I am currently learning about in my psychopharmacology class. In our neurons we have vesicles that take our neurotransmitters to the presynaptic part of the nerve. Once the vesicles reach the destination they push the molecules through their membrane and out into the cytoplasm or cell body (wherever they are, really).