Contents
The Cell
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A eukaryotic cell.
Note the nucleus in the middle.
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DNA is found
in cells, the smallest living units
in your body or the smallest separate living organisms. Every living
organism is made of cells. Microscopic organisms such as algae, bacteria,
and protozoas are made of only one cell. A person on the other hand
is made of billions of specialized cells. These cells such as skin,
brain and bone cells work together to form organs which make the systems
of the body. Inside every cell is the information that determines
what function the cell performs. This information is in the form
of DNA which is found in chromosomes that exist in the nucleus
of your cells.
There are two types of cells, eukaryotic
and prokaryotic cells.
Eukaryotic cells found in a variety of organisms such as yeast, plants,
and animals have a nucleus while procaryotic cells like bacteria do not.
Eukaryotic cells have a nucleus while prokaryotic cells only have a nuclear
area.
The most important part
of the cell is the nucleus. The nucleus has a nuclear envelope or
a coating to keep its material together. There are pores on this
envelope that allow certain materials like RNA
into the cytoplasm. Inside
this nucleus or nuclear area is a material called a chromosome.
Chromosomes
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| Prokaryotic cell with a circular chromosome in the middle. There
is no nucleus. |
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| Click on the picture to see a chromosome. |
A chromosome is a
long strand of DNA that contains certain genes.
These genes are portions of the DNA strand and carry the genetic information
of the cell. In a eukaryotic cell there are multiple chromosomes,
and each of these is part of a pair. Both of the chromosomes in a
pair contain the genes for the same trait. However, a procaryotic
cell has a long circular chromosome that contains all of the genes of the
cell.
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Organism
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Number of Chromosome Pairs
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| Tomato |
12 Pairs |
| Mouse |
20 Pairs |
| Human |
23 Pairs |
| Dog |
39 Pairs |
Cells in the human body are
eukaryotic and contain twenty-three pairs of chromosomes. Other organisms
have a different chromosome count.
In the disorganized group of 46 chromosomes in your
cells’ nucleus, are twenty three pairs. They can be aligned with
their pairs into a karyotype.
Scientists pair these chromosomes by their size, shape, and bands, or centromere.
These bands are present after the chromosomes have been dyed.
A Point to Ponder
Each chromosome of a pair stands for the same traits as its counterpart.
Genes
Genes are portions of the DNA
strand and tell the body what proteins
to make. These proteins help carry out the functions of the cell.
They form the structure of your skin and hair, act as enzymes to break
down your food, and regulate the different processes of the cell.
A Point to
Ponder
Every cell in your body has the same genes, and DNA.
Your cells have all of the genetic information for your whole body.
Your skin cells have the genetic make up of your skin and your muscles.
Your skin does not use this extra information.
Mitosis
Mitosis
is the name given to basic cell division. Cells divide when hormones
instruct them to; usually to replace dying cells or as part of the healing
process. There are five stages to this division, the first of which
is interphase. During interphase, the cell rests, and the chromosomes
make copies of themselves. After interphase comes prophase, the second
stage of mitosis. During prophase, the chromosomes change shape and
the walls of the nucleus begin to break down. The third phase, metaphase,
is when the chromosomes line up at their centers. During anaphase,
the fourth stage, each forming cell is given its own identical set of chromosomes.
The fifth stage, telophase, occurs when the two newly formed daughter cells
pull away from each other and begin forming new nuclei. When these
new nuclei are formed, the cells re-enter interphase and await their next
division.
Links
Structure and Functions
of DNA:
DNA
the Code of Life
Nucleic
Acids, DNA Replication,
and Transcription.
