Science 9 – Chapter 2.2 Cell Structures
Involved in Cell Division (Pg. 39-40)
Name: _______________ Block: ________ Date: ____________
Review all cell parts and organelles. Be able to label a diagram of a
plant or animal cell. Also, know the function of each organelle and the
difference between a plant and animal cell. (Gr. 8 review)
The Nucleus controls the functions of life.
NUCLEUS:
 The nucleus controls all the activity in a cell. But how does it do this?
 Every cell in your body contains the exact same DNA, so how do
different cells know to perform different functions?
-nucleus contains the master set of instructions (stored in your DNA)
-different parts of these instructions will be read in order to determine
what each cell will become, how it will function, when it will grow and divide,
and when it will die
-why your nail cells look and function as they do; this differs from
your skin cells
Chapter 2.3 From DNA to Proteins (Pg. 42-46)
DNA (master set of instructions that controls all cell function):
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Deoxyribonucleic acid
Two-stranded molecule found in the nucleus
Looks like a twisted ladder (Figure 3 Pg. 43)
o this called a “double helix”
Sides of ladder are made from sugar-phosphate molecules
The rungs (steps) of the ladder are made up of nitrogen bases.
There are 4 kinds of nitrogen bases: adenine (A), guanine (G),
cytosine (C), and thymine (T).
Only certain bases with “pair up” with one another. Therefore, each
rung of the ladder is a specific pairing (like in a puzzle). Figure 2 Pg.
42
For example:
A only pairs to T  A-T or T-A
G only pairs to C  G-C or C-G
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A strand of unwound DNA is extremely long and would not be able
to fit into the nucleus. Thus, most of the time(when not in use), it
is stored in a condensed form called CHROMATIN (basically think
of it as “wound up DNA” with proteins).
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When a cell is growing, then DNA is uncoiled and helps the cell
make the proteins it needs.
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Chromatin would still take up too much room in the nucleus,
therefore the chromatin is further folded up and condensed into
X-shaped structures called CHROMOSOMES.
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Every organism has a unique number of chromosomes.
We have 46 chromosomes organized into 23 pairs.
In males, the 23rd pair is the XY chromosomes and in females it is
the XX chromosomes.
WHAT are GENES? See Figure 5 Pg. 44
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Genes are small segments of DNA located at specific places on the
chromosome.
Genes are specific segments of DNA that contains the information
needed to make approx. 100,000 proteins used in the cells.
The arrangement and order of the bases in the genes (which is DNA)
will determine which proteins are made.
WHICH genes are “read” and WHICH proteins are made?
 Every cell in the human body contains 46 chromosomes.
 But only certain genes (segments of DNA) are uncoiled and “read” in
order to produce specific proteins that will carry out specific
functions.
 This makes sense, right? For example a skin cell has different
functions that a nail cell, therefore skin cells will want to make
specific and different proteins than nail cells. So skin cells will “read”
different genes than nail cells. (analogy: think about a chef and an
electrician. Would they have the same tools? Why or why not? If
these two were looking for books related to their work, would they be
reading the same book?)
As a result:
Cells (e.g. skin cells) that all perform the same function come together to
form TISSUE (e.g. skin tissue) and tissues come together to form organs
(e.g. skin). And all organs work together to ensure our survival.
Refer to Table 1. Pg. 45 Common Proteins and their functions