Download Genes, Protein Synthesis, and Mutations

Genes, Protein Synthesis, and Mutations
I. Genes and Proteins
A. gene = a small section of DNA code on a chromosome that forms the code for a specific
protein that will be made by the ribosomes.
1. All of the genes on the DNA will determine what an organism is and how each trait
or characteristic will appear in that organism (body structure, looks, and the
products produced by the cells all come from the codes of our genes).
2. The genes control these traits by providing the code (or “recipe”) from which
proteins will be made (the kinds of proteins the genes tell the ribosomes to make will
determine what the traits and products will be ).
B. Proteins are made up of building blocks called amino acids.
1. There are 20 different kinds of amino acids, each identified by its own unique 3-base
(3-letter) code.
a. For example, the code AGC is the code for an amino acid called serine.
2. The genes tell the ribosomes in which order the amino acids should be placed to
make a protein for a particular trait by using the codes for the amino acids needed.
a. Changing the order of the amino acids changes the type of protein made.
3. The proteins that are made act as chemical “triggers” and messengers that control the
various cell processes and the traits that make up an organism.
a. There are several thousands of different proteins constantly at work in the body.
II. How the Codes on the Genes are Read and How Proteins are Made (Protein Synthesis)
A. “Reading” the code from the gene and sending the “message” (the instructions or recipe
for the protein) to a ribosome that will make that protein is the job of the RNA.
1. RNA (ribonucleic acid) is another form of nucleic acid that has the same nitrogen
bases as DNA with one exception—instead of Thymine, RNA has a nitrogen base
called Uracil (which would still match up with Adenine).
2. The steps for reading the code on the DNA’s genes and creating the proteins are:
a. The DNA untwists and separates at the spot where the gene to be read is located.
1. The gene is found on one side of the DNA strand.
b. A certain type of RNA, called messenger RNA (mRNA), is formed by “reading”
the code on the gene.
1. It does this by pairing the proper nitrogen bases to the ones found on the gene
and connecting them into a stand of mRNA.
c. This single strand of properly ordered bases (the mRNA) leaves the nucleus and
attaches one end of itself to a ribosome.
1. The code on the mRNA is read by the ribosome 3 bases at a time.
a. This 3-base group is called a codon.
d. A second type of RNA, called transfer RNA (tRNA), picks up amino acids based
on the amino acid’s 3-base code.
e. As each codon is read from the mRNA, the tRNA brings the proper amino acid
that matches that codon’s bases.
f. After the first amino acid is brought to the ribosome, the next codon is read, that
amino acid is brought to the ribosome, and it attaches to the first one with a bond.
g. This process continues until the entire mRNA strand is read.
1. The strand of attached amino acids makes up the protein the DNA called for.
III. Mutations
A. mutation = any permanent change in the code on the DNA (this changes the code for the
gene on a chromosome).
1. Often these errors occur in the code when a molecule of DNA makes a copy of itself.
a. There are 3 ways mutations can occur:
1. deletion = occurs when a base pair is left out.
2. insertion = occurs when an extra base pair is added.
3. substitution = occurs when the wrong base pair is used instead of the original.
a. Substitution is the most common way mutations form.
2. The change in the code will affect the way the gene is read, the type of protein that will
be produced, and ultimately the way the trait or cell product is formed.
b. The “new” code may cause the organism to have a trait it never had before, cause
it to lose a trait it once had, or change an existing trait.
B. Mutations are not always negative.
1. Negative mutations
a. If the mutation causes a change that does not allow the organism to function well in
its environment, the organism will not survive or will have a difficult time.
1. If it does not live long enough to mate, its DNA and all of its codes will not be
sent on to the next generation and the mutation will die with that organism.
2. Positive mutations
a. If the mutation changes or creates a trait that helps the organism better survive in its
environment, then the organism will be successful and live to adulthood.
1. This organism will mate and the new code for the successful or positive mutation
will be passed on to the next generation and all the generations that follow.
IV. The Role of Mutation in Natural Selection and Evolution
A. natural selection = the process in nature by which organisms that are better adapted to
their environment (because of the stronger genetic traits they possess) will have a much
better chance of surviving, reproducing, and sending their genes on to the next generation
than organisms with “weaker” genes and traits.
1. Organisms with positive mutations are selected “for” in their environment because they
are better able to out compete other organisms for the resources and mates they need.
2. Those organism with negative mutations are selected “against” in their environment,
usually causing them to die or at least making it more difficult for them to survive.
a. This means that negative mutations and their “weaker” genetic codes die out of the
population and only the positive mutations and their “stonger” codes move forward
into the next generation.
3. In this way, natural selection helps keep each type (or species) of organism strong.
B. evolution = the process in which inherited characteristic within a population of one type of
organism change enough over several generations that new species form.
1. A positive mutation that occurs in an individual will be passed on to its offspring,
making them slightly different than the others within their species.
2. Over a many, many generations, changes (mutations) continue to occur, making the two
types of organisms different enough that they can no longer be considered the same
species—the changed organism then becomes a new species.
a. New species are constantly evolving, creating great diversity among organisms.