4-3 DNA
Name _________________________________
All cells use a chemical molecule code called _______________________________ ___________ that is
stored in its hereditary material otherwise known as ___________. It contains information about a cell’s
growth and ___________________. As early as the mid-1800’s scientists knew that the _____________ of
cells contained molecules called _____________ ___________ and by 1950 learned what the nucleic acid
__________ was made of. Not until1953 did scientists know what the _________ molecule looked like. Two
famous scientists named James ______________ and Francis ____________ made a model of this molecule
which looks like a twisted ladder. Their model showed each side of the ladder is made up of sugar-phosphate
molecules; the sugar is called __________________. The rungs of the ladder are made up of other molecules
called ____________________ _____________. DNA has ____________ kinds of __________________
____________. These four are usually referred to using their first initials: “A” = _______________, “G” =
________________, “T” = _______________ and “C” = _______________. These _________________
___________ ALWAYS occur in pairs to form the rungs on the ladder. Any one DNA ladder rung is formed
pairs with
by a pair of nitrogen bases. “A”; ____________ always forms a rung by pairing with a “T”; _____________
pairs with
OR by pairing a “C”; _____________ with a “G”; ______________ . Like pieces of a ________________,
each base bonds only with its correct
________________.
AT THIS TIME, COMPLETE
YOUR TEXT NOTES DIAGRAM
OF FIGURE 14 SHOWN HERE
(continued on back of this page),
THEN CONTINUE WITH THE
NEXT PAGE.
4.3 DNA / Figure 14 (continued)
1. Properly match the base pairs by putting the missing letters into the diagram (empty boxes on the twisted
ladder rungs) and then fill the captions.
2. Color this diagram using the colors as displayed in the text book; complete the color key to identify the parts.
Copying DNA
Name __________________________
When DNA is duplicated (copied), a special enzyme separates the DNA molecule down the middle much like a
zipper unzipping! Each side then becomes a ________________ on which a __________ side forms.
The new _________ (after copying) has base pairs that are ________________ to those of the
__________________ DNA and are in the same _____________.
AT THIS TIME, COMPLETE YOUR TEXT NOTES DIAGRAM OF FIGURE 15 (back of this page),
THEN RETURN HERE TO CONTINUE.
Genes
Most of your _______________________ depend on the kinds of _______________ your cells make. DNA
stores the ______________________ for making __________________. Proteins build cells and
_______________ or work as _________________. The instructions for making a protein are found in a
_____________ which is a section of DNA on a ________________________. Each chromosome contains
hundreds of these.
COMPLETE FIGURE 16 INCLUDING CAPTION
Controlling Genes
In many-celled organisms like you, each kind of cell uses only _____________ of the ___________________
of genes that it has in it’s nucleus to make _______________; each kind of cell uses only the _____________
that direct the making of _______________ that it needs. If the ____________________ proteins are produced,
the organism cannot __________________ properly.
Mutations
Sometimes mistakes happen when the DNA is __________ which changes the code. If DNA is not copied
________________, the _______________ made from the instructions might not be made correctly. These
mistakes, called ____________________, are any ___________________ change in the DNA sequence of a
____________ or chromosome of a cell. This includes cells that receive an entire _____________ chromosome
or are __________________ one. Outside _______________ such as ____________, sunlight and some
___________________ have been known to cause ______________________.
Results of a Mutation
A change in a _____________ can change the ________________ of an organism. Mutations in body cells
might or might not be life ______________________. However, if a mutation occurs in a __________ cell, all
the cells that come from that cell will have that ___________________. Some mutations can even be
_______________________ and help an organism to survive better = SURVIVAL OF THE FITTEST.