Name:_______________________________________________ Date ________________ Period ____
CP Biology
Journey into Human DNA
Introduction: Chances are you've seen an illustration of DNA's double-helix
structure and even pictures of the chromosomes that make up the human
genome. But where and how does the famous double helix fit into chromosomes,
and how do chromosomes relate to the human body? Travel into the tiny world
of DNA, all the way down to the level of the atoms that make up a single DNA
base.
1. Log onto a computer, and using Google Chrome as your browser, follow this link to the NOVA
website:
http://www.pbs.org/wgbh/nova/body/journey-into-human-dna.html
2. Complete the following paragraphs as you take a journey to the molecular level of heredity.
The human body contains about _________________cells, each working together in
a complex symphony of interactions. With the exception of___________________,
which contain no nucleus and no nuclear DNA, every one of these cells contains the
___________________-- a string of three billion A's, C's, G's, and T's. And, in every
one of the 100 trillion cells, the sequence of these four letters, or bases, is
nearly_________________.
Although the _________ __________ from cell to cell is the same, there are many
different types of cells within the body, each with a specific function. For example,
the long, narrow ______________cell is designed to contract, the branching
_________________is designed to send and receive electrochemical impulses, and
the square-shaped cell that lines the wall of the ________________ is designed to
filter nutrients from food.
These cells and others in the body are _________ ____________of their parent cells -they formed when their parent cells divided. But sometimes cells need to
____________________, or become specialized. Within the first month of embryonic
development, cells are changing into____________ _______. If they didn't, all of the
body's cells would be exactly like the single egg cell from which they all originated. This
production of new types of cells is the result of_________"turning on" and "turning off"
different sections of the _______________ it stores.
Within every cell of our bodies (except red blood cells) is a ___________________ -- a
sphere-like structure separated from the rest of the cell by a membrane. This organelle
acts as the cell's control center, regulating its__________, _______________,
and__________________. At the heart of this control center is the ____________
______________.
The human genome is comprised of ______sets of ______ chromosomes -- 46
chromosomes in all. Each parent contributes a set. About _______ percent of the
genome consists of sequences that don't code for proteins and have no known
function. Within the rest of the genome are an estimated ____________ genes.
The single __________________ displayed here and those on the previous screen are
shown in their most compacted state -- they're about to divide, along with the cell,
through the process of __________. When we see pictures of chromosomes, this is
usually what we see. The reason is that chromosomes are most visible during this time.
When________________, chromosomes show bands of light and dark areas. The dark
bands indicate areas where the structure of the chromosome is __________. Each of the
23 chromosome types has a unique ___________ __________. (A chromosome pair has
_______________ banding.) In fact, scientists can __________________ a chromosome
based solely on its banding pattern.
_______________ determine whether you have brown eyes or blue, long toes or short,
and much, much more. Genes also _______________everything from how your cells
_________ to how they ____________ with one another. A single gene can range in
length from as few as ___________ DNA bases to as many as ________________
_______________.
There's a lot of DNA within the ________________ -- about six feet if you could
___________ it and _____________ it out end to end. To fit such a long molecule
within the tiny space of the nucleus, DNA __________ and ____________ in several
ways. The largest of these loops results from the _______________________________
of chromatin (the thick line in this illustration). This coiling causes the chromosome to
resemble a ___________________.
The chromatin scaffold refers to _______________ that help _______________ the
long DNA molecule. The protein shown here _________________ and
__________________ small loops of DNA.
We've now zoomed in enough to see portions of the DNA strand. The DNA is wrapped
around __________ -- protein structures that are sometimes depicted as discs.
Histones carry a slight __________ charge, and DNA carries a slight _____________
charge. Since _________ charges attract, the DNA is pulled in toward the histones. A
________________ is a segment of the DNA wrapped around a core of histones.
Here is a view of the ____________ helix -- the subject of Rosalind Franklin's
___________. With the help of her photograph, ________________ and
________________ were able to piece together the first accurate model of
_________. Shown here is the structure of naked DNA -- DNA without all of the
proteins that organize it into chromatin. Note how its structure resembles a
_________________. Note also that DNA with a "left-handed" twist, as this has, is a
special kind of DNA known as Z-DNA.
The DNA molecule is made up of four __________ -- ______________(A),
_____________ (C), _____________ (G), and ______________ (T). Each rung of the
DNA ladder consists of _____________. In the DNA molecule, A always pairs up with
______, and C always pairs up with _______.
The sides of the DNA ladder consist of a long string of ____________ and
________________ molecules, to which the bases are attached. Each sugar-phosphatebase combination is called a __________________.
A ____________________________ is made up of 30 atoms, plus or minus a few,
depending on the base. It's no wonder that determining the sequence of bases in the
human genome -- all ___________________________of them -- was such a
monumental accomplishment. And though the task of determining the sequence is
over, that of understanding the sequence is just beginning. Figuring out how these
three billion bases code for a human being will keep researchers busy for many
decades to come.