lecture2

Biol 1F25 SP
Biology: A Human Perspective
Lecture 2
Cell Life Cycle Part 1
Ron Ninniss
rninniss@brocku.ca

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Back to the cel again
* Central to our understanding of cancer, is the cel , and
the types of communication that it receives and how it
deals with them
* We haven't had a chance to discuss cel communication
methods, and we don't have enough time to do that here
* We talked about how they require energy to do just
about everything, and the form of this available energy
source in al of these cel s
* We never talked about how a cel decides to be
whatever it is, nor did we talk about the fourth common
chemical of life - the nucleic acids
Biology 1F25 SP
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Back to the beginning...or future
* Even though we looked at the cel and had to be able to
identify the various things found in it.
* We never dove much further than this
* We need to get on the diving board now, because we
need to take what we know about cel s and how they talk
to each other and apply this to why a cel might get the
message wrong
* But first we need to talk about how cel s decide to be
what they are
* What makes a neuron, a neuron and not an adipocyte?
* ...Genes
Biology 1F25 SP
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The nucleus and the nucleic acids
* In any diagram of the eukaryotic cel , there is a big, dark. roundish
thing that is always identified as the nucleus
Nucleus
Biology 1F25 SP
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The nucleus and the DNA
* But what is in there that is so important?
* It's the DNA of course, the deoxyribonucleic acid, which is the
information containing molecule that is contained, monitored, read,
replicated, etc, inside the nucleus
* In lecture two, when we briefly talked about the cel structure, we
referred to the nucleus as "the library"
* There are lots of analogies that could be used, but for me this is the
best one - except that we are talking about a library from ancient
times were books were not borrowed, so they stayed in the library
and under the control of the librarians
* The librarians wil also be an analogy for the proper functioning of
the cel - but we'l get to that later
* For now let's imagine the DNA molecules are the books in this
library
Biology 1F25 SP
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The library
* In this library are al of the books (genes), that make up you -
organised in chromosomes - not the Dewey Decimal system.
* Some of the books are like blueprints that are a complete set of
instructions on how to make you
* Other books might be like day planners that schedule when you
should do something or make something
* Some books, for the immune system, are constantly being shuffled
to increase the variability
* The reading of these books is control ed and that's why it's like the
library of Alexandria and not a modern public library - no borrowing.
* Only specific reading operations are permitted, which can be
control ed by other books (schedules) or from the cytoplasm, or by a
message received from outside the cel .
* And these differences in what is read, by whom and when, are the
ways cel s differ, even though every cel contains a complete library
Biology 1F25 SP
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Oops, I lied, not every cel has a nucleus
*
I should point out that there is a cel that does not
contain a library, or many of the organel es identified
in the generalised cel diagram - the red blood cell
*
Once mature, the erythrocyte sheds just about
everything,and ends up being just a bag of
haemoglobin - the molecule that ships oxygen around
the circulation and helps remove the carbon dioxide
*
The shape and the fact that the cel has plenty of
room means it can carry about 270,000,000
haemoglobin molecules
*
We make about 200 bil ion a day of these red
beauties, and have about 25 tril ion at any given time.
*
This gives a red blood cel a life expectancy of about
120 days on their suicide mission of oxygen and
carbon dioxide delivery.
*
With this mostly singular function, they don't need to
be ready to take on other duties, hence they don't
need blueprints...
Biology 1F25 SP
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What is DNA and this book business
* It's easy to assume that everyone knows what DNA is
* It's mentioned on every police drama, especial y the one
in "Florida" with the sunglasses and the, "DNA match" to
the perp within 30 seconds of the last commercial.
* But how it works, when and why it's actively being read,
what reading does, and how DNA is expressed as far as
the rest of the cel is concerned, that is what we need to
know to get a better understanding of how cancer can
happen
* So let's start from the molecule up
* ...because this time... it's personal (queue up "The Who")
Biology 1F25 SP
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DNA - the discovery
*
Many of you may have heard of Watson and Crick,
the great discoverers of the the DNA double helix
*
They're discovery was in part due to the
unheralded work of a bril iant scientist named
Rosalind Franklin, and her X-ray diffraction study
leading to the famous Photo 51 (on the right)
*
This photo (which I won't interpret for you) gave
Watson and Crick the details they needed to
finalise the DNA structure
*
Dr. Franklin was not recognised for her
contribution at the time - or with the Nobel Prize
(due in part to the fact she died a few years later
from - Cancer)
*
Fortunately Dr. Franklin has since been widely
accepted as a major contributor
*
If I sound like I feel this was an injustice...I'l just
say that since I read about this, I've not been able
to say the names "Watson and Crick", without
feeling a bit disappointed in the scientific
community, and leave it at that.
Biology 1F25 SP
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DNA as an elegant solution to life's
information management problem
* What is it about DNA that al ows it store information like
a blue print?
* It would obviously need some organisation and be stable
in order for information to be legible and last long
enough to be passed down from our ancestors - in some
cases be unchanged for 100s of mil ions of years
* It is an elegant molecule, and you can see some of the
details on the next two slides (not real y shown in your
textbook)
Biology 1F25 SP
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