DNA: Structure and Replication
What does DNA stand for?__________________________________________
DNA is a long fiber, like a hair, only thinner and longer. It is made from _____________________ strands
that stick together with a slight twist.
Proteins attach to the DNA and help the strands coil up into a ________________________ when the
cell gets ready to divide during ___________________________.
The DNA is organized into pieces called ______________________. The genes carry the instructions
for making all the thousands of ________________ that are found in a cell. The proteins in a cell
determine what that cell will look like and what jobs that cell will do. The genes also determine how the
many different __________________ of a body will be arranged. In these ways, DNA controls how many
fingers you have, where your legs are placed on your body, and the color of your eyes.
So, what's the difference between DNA and a chromosome?
A chromosome is made up of __________________ and the proteins attached to it. There are 46 in a
human cell. DNA is a particular bio-molecule that is the material to make chromosomes. All of the DNA
in a cell is found in individual pieces, called __________________________. DNA is like the cookie
dough and chromosomes are the individual cookies.
Scientists found that DNA consists of long strands of ____________________. Each nucleotide contains
a ______________________ (five carbon) sugar called deoxyribose, a __________________________
group and one of the four compounds called __________________________________ bases.
The phosphate group bonds to the deoxyribose forming a backbone of sugars and phosphates.
Each nucleotide is attached to each sugar, perpendicular to the backbone.
B. Watson and Crick’s ______________________________ is now accepted as the correct structure for
DNA. It looks like a twisted _____________________. The nitrogeneous bases face inward toward the
center and meet each other in __________________.
The weak electrical attractions of _________________________ bonds hold the pairs of bases together.
The bases are: _______________________________________________
In DNA:
1. Adenine always pairs with ________________________.
2. Cytosine always pairs with ________________________.
The two strands of DNA are said to be _____________________________ to each other.
The process by which DNA makes copies of itself is called _______________________. At the beginning
of replication, the double helix _________________________. The hydrogen bonds that hold the base
pairs together are broken by ________________________. This separates the two strands of the molecule,
somewhat like unzipping a zipper.
Each single strand of parent DNA
serves as a pattern, or _______________________, for a new complementary strand.
The new strands are assembled from free floating nucleotides that have been made earlier in the nucleus.
An enzyme called DNA _____________________________ moves along the separated parent DNA
strands, matching the bases on each ______________, or original strand to new
__________________________ bases on the free nucleotides.
Along each strand, adenine bonds to ____________________________ and cytosine bonds to
_____________________________________. Eventually because the parent DNA has two strands, two
new ______________________double helixes are formed.
When we make new chromosomes, its very, very important that the new chromosomes are exactly like the
old ones. Otherwise, you might have your nose coming out of your ear!