Unit 3: Genetics
From Gene to Protein
The bulk of the DNA sequence in most
codes for the production of
is made of one or more
, which are linear polymers of
, and which are folded into specific shapes. In other words, the DNA sequence specifies the
sequence of proteins.
is an important component in this process. Proteins ultimately determine an organism's
RNA is structurally similar to DNA, but differs in three key respects.
, unlike the double-stranded structure of DNA.
RNA nucleotides contain a
rather than the deoxyribose of DNA.
RNA does not contain the base thymine (T), but instead contains the base
with adenine (A) of DNA.
The flow of information from genes to proteins involves a
The DNA message of a gene is first
within the cell nucleus using the
starting at the
and ending at the
. Similar to
the direction of
Other enzymes remove noncoding sequences of RNA called
and splice the
to produce the
which exits the nucleus through the
The mRNA is then
within the cytoplasm using the
to form the sequence of
that makes up a
is made of triplets of bases called
for amino acids. The code is
: many amino acids can "wobble": they are encoded by more than one codon.
The actual assembly of proteins occurs in the cytoplasm on
, which consist of many proteins and
(rRNA). A 3rd kind of RNA,
at the start codon. The tRNA carries a specific amino acid and an
to the codon on the mRNA. The complex forms
until a stop codon terminates the process, releasing the
of one or more wild-type
Since many tRNAs can "wobble", some substitution mutations are
and do not exhibit a change in amino acids, but many substitution mutations do result in
and are called
mutations. Insertions and deletions cause a
of the decoding sequence and usually result in a
Unit 3: Genetics
Knowledge about the molecular nature of genes provides
DNA sequences can be studied by cutting DNA into specific segments using
can be used to insert fragments of DNA from other sources.
The segments can then be sorted by
. These technologies can be combined in
Length Polymorphism (RFLP) to
genetic diseases such as
Alleles can also be identified by
, using radioactively labeled, single-stranded DNA segments called DNA
that can base-pair with specific DNA sequences.
Segments of DNA can be isolated and
by two techniques.
enzymes and DNA
to construct a
in bacteria with vectors such as
, then identifying and culturing the bacteria in the
carrying the desired
Use the enzyme DNA
and known DNA
to synthesize large quantities of a gene
Cloned DNA can be used as
Isolated genes can be
and then inserted back into organisms through a
Other applications of DNA technologies include
Feb 21, 2006