Welcome back, bio people! For this week’s
video, we’ll be comparing and contrasting prokaryotes and eukaryotes, then making
it feel more relevant by learning how antibiotics work.
All right! Onwards and upwards! Cells are categorized into two major groups;
Prokaryotes and Eukaryotes. Usually it’s easier to remember the differences if we
look at a couple of examples first. You may already know that Bacteria are
Prokaryotes, but so are Archaea. These ancient microbes are still around and
they’re known as “extremophiles” because they live in environments like deep sea
vents, thermal pools and oil wells. Eukaryotes include plants, animals, fungi,
and protists. The two categories of cells also differ in size, how they pass on
their genetic material, and whether or not they have membrane-bound organelles.
Prokaryotic organisms tend to be smaller, whereas Eukaryotes have the potential to
be much larger. Prokaryotes are almost always unicellular, with the exception of
some bacterial colonies, whereas Eukaryotes can be either unicellular or
multicellular. Prokaryotes do not have a membrane-bound nucleus. Instead they have
something called a nucleoid, which is basically an area where a single DNA
molecule is kept. Eukaryotes not only have a membrane-bound nucleus, but also
organize their DNA into multiple packages known as chromosomes. The most
distinctive feature that separates prokaryotes and eukaryotes is the
presence of membrane-bound organelles. Prokaryotes do not have any membrane-bound organelles. They do have ribosomes, but because ribosomes are not membrane-bound, they don’t count. Eukaryotes have many types of membrane bound organelles.
A few examples include mitochondria, Golgi bodies, and chloroplasts. The
endosymbiotic theory proposes one explanation for how membrane-bound
organelles came to be. Scientists believe that an early Prokaryotic cell engulfed
several others that were capable of photosynthesis, forming the first
Eukaryote. The engulfed bacteria ultimately became chloroplasts, and
scientists believed that a similar process formed mitochondria. This theory
also explains how mitochondria have their own DNA. here’s one reason why all
this stuff is important (besides your test, which is probably TOMORROW
if you’re watching this video!) Have you ever had an ear infection, food
poisoning, pneumonia, strep throat, a staph infection, or a U.T.I? The answer is
probably “yes”. All of these are very common, and they’re caused by bacteria.
Other more serious bacterial infections include cholera, diphtheria, meningitis,
and tuberculosis. Luckily these are pretty rare in most parts of the world.
Bacterial infections are treated with antibiotics. Antibiotics work by
attacking characteristics that Prokaryotic bacterial cells have, but
Eukaryotic human cells do not. Penicillin is one of the most famous antibiotics.
It’s known as a beta lactam, which is a class of antibiotics that attack
bacterial cell walls. Since humans do not have cell walls, penicillin is harmless
to them, but toxic to the Prokaryotic bacteria. Bacterial cell walls are
reinforced by an enzyme called transpeptidase, which
creates cross-linkages between the components. Beta lactams attach to the
active site of this enzyme, preventing them from functioning properly. Without
the cross-linkages, the bacterial cell walls become far less stable. Many
bacteria have high internal osmotic pressure. The weakened cell walls cause
the bacterium to expand until finally it pops. Other antibiotics attack
prokaryote-specific structures in a similar way. Erythromycin is a
type of antibiotic called a Macrolide, and it’s commonly used to treat
respiratory infections. It attacks bacterial ribosomes, which are
slightly different than Eukaryotic ribosomes. Ribosomes are heavily involved
in protein synthesis, and have three active sites; the E site, the P site and
the A site. Usually, an mRNA template enters the ribosome, and is met by a
complimentary tRNA triplet at the A site. The tRNA brings an amino acid along with
it, in this case methionine. The mRNA then advances to the P site, opening up the a
site for a new tRNA, bearing a new amino acid. The amino acids are linked together
using a peptide bond, and ultimately form a long chain called a polypeptide that
will eventually become a protein. Scientists believe that Erythromycin prevents movement forwards from the a site to the P site. Because of this,
it effectively halts bacterial protein synthesis.
That’s it for this week! If you found this video useful, I hope you’ll consider
subscribing to my channel, and checking out some of my other videos. I also
publish content to social media like Twitter, Facebook and Instagram. Thanks
for watching everyone!