Genes, DNA, and Protein Notes

A DNA molecule is made up of four different nitrogen bases:
o Adenine (A)
o Thymine (T)
o Guanine (G)
o Cytosine (C)

The nitrogen bases are like letters in an alphabet. This DNA alphabet only has 4
letters, but combinations of the four letters results in providing the genetic
information for every living thing on this planet. A gene is a sequence of these
nitrogen bases, like ATTGCCTAG. The order and length of each sequence is
critical, as there are only four ‘letters’ to work with. A single gene may be
hundreds to even millions letters long.

As you remember from earlier in the school year, proteins are made up of amino
acids. Your body is mostly made up of protein. When you eat something, your
body breaks down what you eat into amino acids, then reassembles the amino
acids into human protein. DNA is the recipe that is used so that correct proteins
are made from the amino acids.

Each sequence of THREE nitrogen bases codes for one amino acid. The
sequence, CGT, codes for the amino acid, alanine. How many amino acids can be
formed from the following DNA sequence? ATTCGGTATAAAGGA. Hint:
count off three letters at a time.

CHARGAFF’s RULE: Remember that DNA is a double helix which means it has
two strands: Chargaff’s rule states that A=T, and G=C. Adenine always pairs with
Thymine, and Guanine always pairs with Cytosine:
ATTCGGGCCATAGAG
TAAGCCCGGTATCTC

Proteins are formed on ribosomes in the cytoplasm of the cell which is OUTSIDE
of the nucleus. The instructions (DNA) to make the proteins from amino acids are
INSIDE the nucleus. How do the instructions get to the ribosomes? DNA is not
the only nucleic acid. There is another nucleic acid known as RNA, which acts as
a messenger. RNA only has one strand, while DNA is a double helix.

There are two types of RNA.
o Messenger RNA copies the DNA in the nucleus, then carries the
information outside of the nucleus to the ribosomes.
o Transfer RNA carries amino acids to the ribosome for assembly into
proteins.

There are several steps for the process of protein synthesis (making proteins.)
o STEP 1: The DNA molecule unzips down the middle. One of the strands
of DNA helps form the messenger RNA.
o STEP 2: The messenger RNA leaves the nucleus and attaches to a
ribosome. The messenger RNA acts as the recipe for the developing
protein.
o STEP 3: Transfer RNA carry specific amino acids to the messenger RNA.
Each three letter code, CAT, or ATA, or GCA, represents one amino acid.
o STEP 4: The protein chain gets longer and longer as more amino acids are
added to it. There is a special STOP signal amino acid which causes the
protein to be finished and released.
MUTATIONS
 Mutations are mistakes that occur in the DNA. For example a gene that is
supposed to be ATTGCCCAT is now changed to AATGCCCAT. The one letter
difference changes the amino acid, and therefore, the whole gene. If a mutation
occurs in a regular body cell, either nothing may happen, or a tumor or type of
cancer may form.

If a mutation occurs in a sex cell, the mutation may be passed onto the offspring.

There are different types of mutations:
o SUBSTITUTION: A nitrogen base is substituted for the correct base:
Example ATTCGAATTCGG
o INSERTION: An extra nitrogen base is inserted: Example
ATTCGAATTCGTA
o DELETION: A nitrogen base is erased: Example: ATTCGAATCGA


Mutations can be harmful, helpful, or have no effect. Helpful mutations increase
an organism’s chance of survival, while harmful mutations reduce an organism’s
chance of survival.
MUTATIONS ARE THE MAIN REASON WHY WE HAVE GENETIC
VARIETY.