TPO 12 Conversation 1
Narrator
Listen to a conversation between a student and a professor.
Student
So Professor Tibets, your notes said that you want to see me about my
heavy-weight paper. I have to say that grade wasn’t what I was expecting. I
thought I’d done a pretty good job.
Professor
Oh, you did. But do you really want to settle for pretty good when you can do
something very good?
Student
You think it can be very good?
Professor
Absolutely!
Student
Would that mean you’d…I could get a better grade?
Professor
Oh, sorry! It’s not for your grade. It's…I think you could learn a lot by revising it.
Student
You mean, rewrite the whole thing? I really swamped. There’re deadlines
wherever I turn and… and I don’t really know how much time I could give it.
Professor
Well, it is a busy time, with spring break coming up next week. It’s your call.
But I think with all a little extra effort, you could really turn this into a fine essay.
Student
No… yeah…I mean, after I read your comments, I...I can see how it tries to do
too much.
Professor
Yeah. It’s just too ambitious for the scope of the assignment.
Student
So I should cut out the historical part?
Professor
Yes. I would just stick to the topic. Anything unrelated to the use of nature
EMITRY has no place in the paper. All that tangential material just distracted
from the main argument.
Student
Yeah, I never know how much to include. You know…where to draw the line?
Professor
Tell me about it! All writers struggled without one. But it’s something you can
learn. That will become more clear with practice. But I think if you just cut out
the…emm…
Student
The stuff about history, but if I cut out those sections, won’t it be too short?
Professor
Well, better a short well-structured paper than a long paper that
poorly-structured and wanders off topic.
Student
So all I have to do is to leave those sections?
Professor
Well, not so fast. After you cut out those sections, you’ll have to go back and
revise the rest, to see how it all fits together. And of course, you’ll have to
revise the introduction too, to accurately describe what you do in the body of
the paper. But that shouldn’t be too difficult. Just remember to keep the
discussion focused. Do you think you can get it to me by noon tomorrow?
Student
Wow…emm…I have so much…er…but I’ll try.
Professor
OK, good! Do try! But if you can’t, well, sure for after spring break, OK?
TPO12 Lecture 1 Biology
Narrator
Listen to part of a lecture in a Biology Class.
Professor
As we learn more about the DNA in human cells and how it controls the growth
and development of cells, then maybe we can explain a very important
observation, that when we try to grow most human cells in libratory, they seem
programmed to divide only a certain number of times before they die. Now this
differs with the type of cell. Some cells, like nerve cells, only divide seven to
nine times in their total life. Others, like skin cells, will divide many, many more
times. But finally the cells stop renewing themselves and they die. And in the
cells of the human body itself, in the cells of every organ, of almost every type
of tissues in the body, the same thing will happen eventually.
OK, you know that all of persons’ genetic information is contained on very long
pieces of DNA called Chromosomes. 46 of them are in the human cells that’s
23 pairs of these Chromosomes are of very lengths and sizes. Now if you look
at this rough drawing of one of them, one Chromosome is about to divide into
two. You see that it sort of looks like, well actually it’s much more complex than
this but it reminds us a couple of springs linked together to coil up pieces of
DNA. And if you stretch them out you will find they contain certain genes,
certain sequences of DNA that help to determine how the cells of the body will
develop. When researchers look really carefully at the DNA in Chromosomes
though, they were amazed, we all were, to find that only a fraction of it, maybe
20-30%, converts into meaningful genetic information. It’s incredible; at least it
was to me. But if you took away all the DNA that codes for genes, you still have
maybe 70% of the DNA left over. That’s the so-called JUNK DNA. Though the
word junk is used sort of townies cheek.
The assumption is that even these DNA doesn’t make up any of the genes it
must serve some other purpose. Anyway, if we examine these ends of these
coils of DNA, we will find a sequence of DNA at each end of every human
Chromosome, called a telomere. Now a telomere is a highly repetitious and
genetically meaningless sequence of DNA, what we were calling JUNK DNA.
But it does have any important purpose; it is sort of like the plastic tip on each
end of shoelace. It means not help you tie your shoe but that little plastic tip
keeps the rest of the shoelace, the shoe string from unraveling into weak and
useless threads. Well, the telomere at the end of Chromosomes seems to do
about the same thing--- protect the genes the genetically functional parts of the
Chromosome from being damaged. Every time the Chromosome divides,
every time one cell divides into two. Pieces of the ends of the Chromosome,
the telomere, get broken off. So after each division, the telomere gets shorter
and one of the things that may happen after a while is that pieces of the genes
themselves get broken off the Chromosomes. So the Chromosome is now
losing important genetically information and is no longer functional. But as long
as the telomeres are at certain length they keep this from happening. So it
seems that, when the, by looking at the length of the telomeres on specific
Chromosomes we can actually predict pretty much how long certain cells can
successfully go on dividing. Other some cells just seem to keep on dividing
regardless which mean not be always a good thing if it gets out of control.
But when we analyze the cells chemically we find something very interesting, a
chemical in them, and an enzyme called telomerase. As bits of the telomere
break off from the end of Chromosome, this chemical, this telomerase can
rebuild it, can help resemble the protected DNA, the telomere that the
Chromosome is lost. Someday we may be able to take any cell and keep it
alive functioning and reproducing itself essentially forever through the use of
telomerase. And in the future we may have virtually immortal nerve cells and
immortal skin cells of whatever because of these chemical, telomerase can
keep the telomere on the ends of Chromosomes from getting any shorter.
