Before we move into the course, it's really important
for us to establish what life is.
Some might debate that viruses and prions are non living.
But certainly, cells are living.
So we're going to explore some brief comparisons between
eukaryotic and bacterial or prokaryotic cells.
Yes, there's another division, another type of cells
called archaeas. But they're not really components of human body.
We're going to be dealing primarily with
bacterial cells and eukaryotic cells
and on occasion throughout this course,
we'll be exploring some mechanism of viruses.
So comparing prokaryotic and eukaryotic cells,
they both have ribosomes, they both have DNA.
They both have cell membranes. Bacterial cells have cell walls
whereas eukaryotic cells generally do not have cell walls.
Plant cells have cell walls.
And fungal cells have cell walls.
However, animal cells lack a cell wall at all.
Both cell membranes are composed of phospholipid bilayers.
Both have ribosomes although
prokaryotic and eukaryotic ribosomes are slightly different.
We'll explore those in further lectures.
And then in general, a eukaryotic cell is about
ten times larger than a prokaryotic cell.
And as I mentioned, in addition we'll be visiting
viruses and prions briefly.
Viruses, technically they are non living.
They're composed of a protein capsid, so a protein outer coat
with a nucleic acid or DNA core.
Sometimes an RNA core in the case of retroviruses.
In addition, some virus like the AIDS virus
also have a viral envelope
which has enveloped protein studded over the surface
for recognition purposes.
And finally, prions. Prions have given us
some questions to think about
because they contain no DNA. However, they're contacting
other proteins, can cause them to fold in a different way.
And they seem to have some sorts of genetic capacities,
yet zero DNA.