Evolution, transposons, retrotransposons.

We all like to think mutation as a random occurrence, an occurrence only due to chance which is mostly harmful and may be evolutionary significant once in a blue moon.
There are actually, contrary evidences to all that. Evidences which will force us to rethink all our notions and accept Jean Baptiste Lamarck as our hero(yeah the Giraffe-neck guy).

How,do you ask? Well, we'll have to begin by learning what 'junk' DNA is. Junk DNA (better call it noncoding DNA) is a vast amount of nucleic acid lying unused in the nucleus. Actually, only 3% of the 'normal' DNA codes at a given time. Rest of it lies unused.

With me still here? Great. Now, we come to 'jumping genes' or 'transposons'. What initially was considered as a rigid blueprint, the DNA is so not like it. In fact, its a dynamic entity. Genes moving here and there, cutting,copying, and  pasting themselves within the strands.
These frisky genes are the transposons. In experiments conducted by Barbara MC Clintock, it was discovered that when corn plants were subjected to environmental stresses, the genes arranged themselves so as to confer them with a survival benefit. Yes, a sort of intentional mutation was done by the plant itself!
Later, in experiments conducted by Harvard researcher John Cairns on certain lactophobic strains of E coli, where the bacteria were deprived of all the nutrition except for lactose, it was observed that those bugs lost their milk fear rather readily, quicker than mere chance would have allowed to mess with their genetics.
Lamarck doesn't sound too stupid now, does he?!

And now, coming to the most interesting part, does all this magic occur in us, as well? Hell yeah. And wait till I mention the name of the partner in crime - Retroviruses.Yep.You read that right.
These are the viruses which can penetrate the Weissman barrier - a barrier which prevents traits acquired by the parent's somatic cells to pass to the germ cells.The idea is to prevent harmful acquired traits like radiation induced DNA damage from passing to the offspring.

Coming to viruses again,we all know how they work their charm. Using the host machinery and then in the process, sometimes ending up as a part of our own DNA- the junk DNA about which I wrote earlier.Today,it is a known fact that at least 8% of our DNA can be traced back to retroviruses. With this vast noncoding (junk) DNA, the space to play for the jumping genes opens up many folds, and hence a higher number of permutations and combinations become available for an acceptable mutation to occur.

Now what the hell are 'retrotransposons' in the title? Well, a subtype of jumping genes. Normal transposons work by cutting and pasting within the genome, while these retrotransposons are copy pasters.
But more interestingly, their work resembles very, very close to retroviruses. A retrotransposon initially copies itself on an RNA strand, travels,and uses reverse transcriptase to paste itself into a new location on the DNA strand. Does this mean retrotransposons are descended from retroviruses?! You bet!

This has led many to theorize that viruses have actually accelerated human evolution by endowing us with acres of junk DNA and retrotransposons, while we continued to provide them a warm, cozy environ. 
Some thought innit?

LDL Cholesterol- The 'bad' turns good

Hello!

Since long back, the low-density lipoproteins have been linked to high rates of cardiovascular disease and mortality! But is it really so?

USMLE STEP 1: Psychiatry: Malingering and Factitious disorders.

Hey there..! Hello..

 So whenever you come across a clinical vignette in which the patient comes with UNEXPLAINED symptoms or complaints and doesn't seem to have an actual illness, but is either faking it or creating it, the patient is either MALINGERING or has a FACTITIOUS DISORDER.

Alzheimer's due to infections?

Hey awesomites!!!
Could Alzheimers' stem from infections?

Stress and epilepsy

For epilepsy patients Stress and anxiety exacerbate the condition by increasing the frequency and severity of attacks!!

MAC prophylaxis mnemonic

Bonjour!

Mycobacterium avium complex infections need to be prevented in patients with AIDS if their CD4 cell counts are less than 50/microL.

Clinical and radiological features of rickets mnemonic

Hello!

So I had created this video long back but just realized I never uploaded it on the blog. Here it is! :)

Study group discussion: White jaundice

Can anyone explain about what is white jaundice?

I think it refers to cholestasis syndrome (obstruction of bile outflow)

Jaundice (Increased conjugated bilirubin)
Acholia (Pale stools, thus "white jaundice")
Choluria (Dark urine)
May have generalized pruritus (Due to cholesterol)

Here's what someone else wrote:

White Jaundice is not a separate disease, it is a very old term for jaundice.

Jaundice is a condition in which bilirubin, which is a yellow coloured pigment, accumulates in the body and causes the skin to turn bright yellow. In severe cases, the skin can appear brown.

To confirm that someone is jaundiced, and not just dark-skinned, the whites of the eyes are examined, yellow colouration here is a clear sign of jaundice, hence the old expression "white jaundice".

Migraines linked to Vitamin D deficiency

Hey awesomites!

A new study suggests that migraine attacks are linked to vitamin deficiencies.

The question is - 'Could supplements be the key to fight such attacks?'

Vitamin D in Type - 2 Diabetes Mellitus

Hey awesomites!

Vitamin  D has an important role in overcoming insulin resistance in type 2 diabetes. Here's how...

Why does acute promyelocytic leukemia (M3) cause DIC?

Disseminated intravascular coagulopathy (DIC) is caused by an inappropriate activation of the coagulation cascade

Indications of hypertonic saline

Hey :D

The only indications of hypertonic saline is when there is hyponatremia in the body severe enough to cause symptoms like mental status changes.

Oral hypoglycemic drugs used for diabetes mellitus mnemonic

Hello!

So whenever there is a LOT of things to remember, like a lot of drug classes or a lot of microorganisms, I personify them. I make them real life characters and give them creep personality traits.

Here's a mnemonic kinda thingy on drugs used in diabetes mellitus aka oral hypoglycemics!

Atelectasis

Atelectasis simply means collapse of the lung parenchyma. This includes failure of expansion of the lung parenchyma( Congenital) and a normally inflated lung parenchyma getting collapsed(Acquired).

There are 3 types of Acquired Atelectasis-

1. Resorption Atelectasis

Basically an obstruction in the airway causes collapse of the airway distally. The mediastinum shifts towards the side of the collapsed lung.

2. Compression Atelectasis

The lung collapses due to the compressing force which may be due to hydro thorax/hemothorax etc. The mediastinum shifts to the opposite side of the collapsed lung.

3. Contraction Atelectasis

Due to chronic interstitial fibrosis which makes the lung smaller. The only type of Atelectasis which is irreversible.

Ionotrophy, chronotrophy, dromotrophy, lusirophy and bathmotrophy

The heart is amazing.. Just like we have 5 senses, theheart has 5 properties < 3

They are rhythmicity, conductivity, excitiability, contractility and relaxation. These properties have been given fancy names too!

Hyperthyroidism and hyperdynamic circulation

Hello!

Hyperthyroidism results in a hyperdynamic circulation. This post was created because I attempted to know why :D

The cardiac effects of hyperthyroidism commonly cause increased preload with low systemic vascular resistance, a high heart rate, high cardiac output and increased cardiac muscle oxygen consumption. So that's why, hyperdynamic circulation!

Step 2 CK: Investigating thyroid nodule

Hello! 

If you find a thyroid nodule on clinical examination, the next best step is to get a TSH level.

Why? Because it helps you decide which investigation to order next!

If TSH is low, you need to do a radionucleotide scan first.

Why? Because it helps you decide whether or not you need a fine needle aspiration cytology (FNAC)

If the nodule is functioning, do not do a FNA. It just means hyperthyroidism. Observe or treat depending of FT4, T3 levels.

If the nodule is non functional, however, you must do a FNAC for a possible malignancy.

If TSH is normal or elevated, it means there could be something suspicious in the glad, do FNAC of the nodule.

Why not do a scan? Because the nodule will likely be non functional and will tell you nothing else to change your management,

UpToDate mentions sonographic criteria for biopsy before jumping to a FNA, but Master The Boards says that USG can never exclude malignancy and you must always do a FNAC.

 Investigating thyroid nodule

That's all!

-IkaN

Pendred syndrome mnemonic

Hello!

What is pendrin?
An iodine transporter, pendrin, is located on the apical surface of thyroid cells which mediates iodine efflux into the lumen.

What is pendred syndrome?
Mutation of the pendrin gene causes Pendred syndrome, a disorder characterized by defective organification of iodine, goiter, and sensorineural deafness.

How do I remember this?

Diabetes insipidus and SIADH mnemonics

"Do you have any mnemonics on vasopressin related disorders? I always mix up diabetes insipidus and syndrome of inappropriate anti-diuretic hormone!"

Sorry for replying so late. You are probably in your second year med school because once you get old, you can never mix up the two. Anyway, I made these mini mnemonics for ya, hope they help! :)

Normal sodium, potassium and serum osmolality values mnemonic

Hello!

In my last post, I helped you guys remember normal arterial blood gas values. Now, we are going to remember a few electrolytes. Yaay! :D

Step 2 CK: Conjunctivitis in newborn

Hello! 

These are some points that I felt are high yield while studying conjunctivitis in newborn =)