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How are proteins made?
How are proteins made?
A structure found within the cytoplasm of cells,
made up of protein and RNA, that serves as the
site of protein synthesis.
http://sun.menloschool.org/~cweaver/cells/e/ribosomes/ribosomes.gif
Where is DNA stored?
Where are proteins built?
Even bacteria need to build
proteins
To make an enzyme that it needs, the chemical mechanisms
inside an E. coli cell make a copy of a gene from the DNA
strand and use this template to form the enzyme. The E. coli
might have thousands of copies of some enzymes floating
around inside it, and only a few copies of others. The
collection of 1,000 or so different types of enzymes floating in
the cell makes all of the cell's chemistry possible. This
chemistry makes the cell "alive" -- it allows the E. coli to sense
food, move around, eat and reproduce.
http://static.howstuffworks.com/gif/cellecoli.gif
http://static.howstuffworks.com/gif/evolutiontranscribe.gif
Building A Protein
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How Life Works: DNA and Enzymes
To understand a gene pool, you need to know a little bit about genes.
If you have read How Cells Work, then you are familiar with the inner
workings of the E. coli bacteria and can skip this section. Here's a
quick summary to highlight the most important points in How Cells
Work
·A bacterium is a small, single-celled organism. In the case of E. coli,
the bacteria are about one-hundredth the size of a typical human cell.
You can think of the bacteria as a cell wall (think of the cell wall as a
tiny plastic bag) filled with various proteins, enzymes and other
molecules, plus a long strand of DNA, all floating in water.
·The DNA strand in E. coli contains about 4 million base pairs, and
these base pairs are organized into about 1,000 genes. A gene is
simply a template for a protein, and often these proteins are enzymes.
Sexual Reproduction
Bacteria reproduce asexually. This means that, when a bacteria cell
splits, both halves of the split are identical -- they contain exactly the
same DNA. The offspring is a clone of the parent.
As explained in How Human Reproduction Works , higher organisms like
plants, insects and animals reproduce sexually, and this process makes
the actions of evolution more interesting. Sexual reproduction can create a
tremendous amount of variation within a species. For example, if two
parents have multiple children, all of the children can be remarkably
different. Two brothers can have different hair color, different heights,
different blood types and so on. Here's why that happens:
·Instead of a long loop of DNA like a bacterium, cells of plants and animals
have chromosomes that hold the DNA strands. Humans have 23 pairs of
chromosomes, for a total of 46 chromosomes. Fruit flies have five pairs.
Dogs have 39 pairs, and some plants have as many as 100.
Chromosomes come in pairs.
Each chromosome is a tightly
packed strand of DNA. There
are two strands of DNA
joined together at the
centromere to form an Xshaped structure. One strand
comes from the mother and
one from the father. Because
there are two strands of DNA,
it means that animals have
two copies of every gene,
rather than one copy as in an
E. coli cell.
When a female creates an egg or a
male creates a sperm, the two
strands of DNA must combine into a
single strand. The sperm and egg
from the mother and father each
contribute one copy of each
chromosome. They meet to give the
new child two copies of each gene.
To form the single strand in the
sperm or egg, one or the other copy
of each gene is randomly chosen.
One or the other gene from the pair
of genes in each chromosome gets
passed on to the child.
Because of the random nature of gene selection, each child
gets a different mix of genes from the DNA of the mother and
father. This is why children from the same parents can have
so many differences.
A gene is nothing but a template for creating an enzyme.
This means that, in any plant or animal, there are actually
two templates for every enzyme. In some cases, the two
templates are the same (homozygous), but in many cases
the two templates are different (heterozygous).