Now Playing Tracks

rhamphotheca:

The Whale Shark (Rhincodon typus)

… is the largest living species of fish, with individuals reaching lengths of 41 feet (12.5 m) or more. Though fearsome in size, Whale Sharks are gentle giants. They feed on plankton and small fish, and are generally quite tame and docile around divers.

Unlike dolphins and whales, which give birth to a single large baby, Whale Sharks are ovoviviparous - they produce up to a few hundred eggs, which the mother incubates within her body. They are fertilized slowly using stored sperm, and babies are birthed with regularity rather than in one large event. When born, young Whale Sharks are dwarfed by their mother, measuring only 16 to 24 inches (40 to 60 cm) long. Individuals take a long time to reach sexual maturity, first starting to breed around 30 years old, but may live to ages of 70 or more years.

They inhabit tropical and sub-tropical oceans worldwide; on North America’s coasts, they are primarily found off California in the Pacific, and sometimes as far north as New York in the Atlantic.

photo by Zac Wolf, borrowed from Wikimedia

(via: Peterson Field Guides)

I Zwicky 18

I Zwicky 18 is a dwarf galaxy located about 59 million light years away and spans about 3,000 light years. It was once thought to be an unusually young galaxy, only about 500 million years old, and much closer. However, recent studies have observed older, redder stars, indicating that the galaxy began star formation at least 1 billion years ago and as much as 10 billion years ago. Additional studies of Cepheid variable stars, which pulse relative to their brightness, clarified the distance of the galaxy.

Still, it appears the rate of star formation in I Zwicky 18 has been much slower than most galaxies, with higher amounts of hydrogen and helium- meaning that stars have not created as much of the heavier elements yet. The galaxy is currently forming many newer stars. The reasons behind this lag, and this new burst of star formation, remain unknown.

Image from NASA, information from ESA.

sciencesoup:

Life from the Ancient Soup: The Miller and Urey Experiment

Alright, so we know how eukaryotes came to be, but how did life arise in the first place? In the early 1950s, an experiment performed by a couple of guys at the University of Chicago gave us a pretty good idea.

Early in Earth’s history, the conditions of the planet were relatively hostile. Temperatures were high, lots of energy was running riot (such as lightning, volcanoes, and UV radiation), and the atmosphere was reducing rather than oxidising, meaning that it was devoid of gaseous oxygen, but had plenty of methane, hydrogen, carbon dioxide, water vapour and nitrogen.

Miller and Urey decided to simulate these early Earth conditions in the lab to see if they could produce some form of life. Basically, their aim was to find out whether these abiotic (lifeless) conditions were conducive to the rise of living organisms.

To do this, they sealed ammonia, methane, hydrogen and water into a closed, sterile system. Then they heated it to form water vapour, and passed electrical sparks through it to simulate lightning.

After a week or two of brewing time, they analysed their mixture and found that up to 15% of the carbon in their system had formed into organic molecules—most noticeably, amino acids. Amino acids are the building blocks of proteins, which are one of the three most important macromolecules of life.

image

(Image Source)

By themselves, amino acids are relatively small and simple, but together they join to build structures far bigger and grander than individual molecules: life.

So, Miller and Urey found that it’s a cinch to synthesise at least the building blocks of life out of some messy soup.

Further resources: Animation

ohstarstuff:

Cosmic pillars of cold molecular gas and clouds of dark dust lie within Sharpless 171, a star-forming region some 3,000 light-years away in the constellation Cepheus. This false-color skyscape spans about 20 light-years across the nebula’s bright central region. Powering the nebular glow are the young, hot stars of a newly formed cluster, Berkeley 59.

(Credit & Copyright: Antonio Fernandez)

sciencesoup:

Nucleic Acids

Nucleic acids are the “genetic software” of the cell, allowing organisms to pass on their complex components to the next generation. You might know them better as DNA (deoxyribonucleic acid) or RNA (ribonucleic acid): the macromolecules responsible for storing and transmitting hereditary information. They’re the reason you have blonde hair, or long fingers, or a gigantic nose. Without them, no organism could produce offspring, so they’re essential for all life.

Nucleic acids are made up of a chain of monomers called nucleotides, which are in turn made up of five-carbon sugars, a nitrogenous base, and one or more phosphate groups. That might seem like an extra level of complication, but we need to know this to understand their structure.

Consider, for example, a DNA molecule:

image

The two strands running down on either side are called the molecule’s “sugar phosphate backbone”, which are connected in the middle by nitrogenous bases that pair up to the adjacent strand.There are four kinds of bases: Adenine and Guanine, which are purines, and Cytosine and Thymine, which are pyrimidines. In RNA, Thymine is replaced with Uracil (a pyrimidine). Purines have two rings and pyrimidines have one ring, so the groupings just refer to structure.

image

(Source)

The bases are almost always shortened to A, G, C, T & U. Their order determines how life is built—they encode a sequence of amino acids, which instruct how proteins are built. We’ll learn more about later.

Nitrogenous bases are hydrophobic, meaning they hate water. This is crucial to the structure of the DNA, because the strands are oriented so the bases face each other rather than the outside world, protecting them from water. The bases pair together using hydrogen bonds—purines always pair with pyrimidines, so A pairs with T (U in RNA), and C with G.  In any given DNA molecule, the amount of A equals the amount of T, and the amount of C equals the amount of G. This is important because it maintains a uniform diameter for the helix of DNA.

image

The person who realised this equality was Austrian biochemist Erwin Chargaff, and he was a contemporary of American biologist James Watson and English physicist Francis Crick, who you might have heard of. In 1953, they were the first to publish the spiralling, double-helix structure of DNA. (See my article on Rosalind Franklin for the reason I’m not a fan of Watson and Crick.)

DNA strands have a polarity, meaning they have a direction—strands are always synthesised from the 5’ (said “five prime”) end to the 3’ end. I’ll talk a whole lot more about how this happens later on. The important thing to know now is that when two strands are connected in a DNA molecule, they run antiparallel—in opposite directions.

So, what about an RNA molecule?

For starters, DNA is located in a different place to RNA:

image

RNA only has a single strand, and it’s made from a different sugar: ribose instead of deoxyribose. Basically, this means it has one more OH group. RNA also has a completely different function. While DNA is the blueprint for life, RNA is the guy who actually gets things done. Different types of RNA are specialised for different functons: mRNA (messenger RNA) carries the blueprints between DNA and ribosomes in order to make proteins; rRNA (ribosomal RNA) essentially makes up the ribosomes; and tRNA (transfer RNA) carries amino acids into the ribosome for synthesis into proteins.

In summary: nucleic acids are made up sugars, phosphate groups, and nitrogenous bases, and their function is to encode, transmit, and express hereditary information. Next article, we’ll take a look at how scientists learned that nucleic acids are the genetic material of life.

Body images sourced from Wikimedia Commons

Further resources: Structure of Nucleic Acids at Educationportal

We make Tumblr themes