Transcript Protein Synthesis

DNA
DNA is located in the nucleus of a cell. It is
a double helix shape and contains
sequences of nucleotides.
Each nucleotide has one of the 4 bases:
Adenine (A) which always bonds with
Thymine (T), and Cytosine (C) which always
bonds with Guanine (G). Each stand of DNA
is complementary to the other.
The order of these nucleotides determines
holds the genetic code for a protein.
Nucleotides
DNA UNWINDS
The section of DNA that
codes for the protein
being synthesized is
unwound and unzipped
by the enzyme helicase.
Helicase
TWO STRANDS OF DNA
One half of the DNA is the
template strand. This is the strand
that will be transcribed into
mRNA.
The other strand is the coding
(anti-sense) strand. This has a
complementary sequence of
bases as in the template stand so
contains the same sequence of
nucleotides as will be in the
mRNA that will be produced.
Template
Strand
Coding
Strand
RNA SYNTHESIS
RNA
Polymerase
Coding
Strand
Template
Strand
mRNA
RNA polymerase
attaches to the template
strand and creates a
complementary length
of mRNA. This is the
primary mRNA.
The coding stand of DNA
is not used.
DIFFERENCES BETWEEN RNA AND DNA
DNA:
- Has the bases
Adenine, Cytosine,
Guanine and Thymine
- Very long
- The sugar-phosphate
backbone is made of
deoxyribose sugar
- Double stranded
RNA:
- Has the bases
Adenine, Cytosine,
Guanine and Uracil
- Relatively short
- The sugar-phosphate
backbone is made of
ribose sugar
- Single stranded
RNA PROCESSING
Primary mRNA
During RNA processing,
which occurs in the
nucleus, the introns in
the primary mRNA are
spliced out leaving only
the exons in the
mature mRNA.
Exon
Intron
LEAVING THE NUCLEUS
mRNA
The mature mRNA leaves
the nucleus through a
nuclear pore to go into the
cytoplasm.
Nuclear
Pore
Nucleus
Cytoplasm
TRANSLATION
Amino
Acid
The ribosome attaches to the
mRNA in the cytoplasm.
It reads the codons (3 bases) in
the mRNA that each code for
a specific amino acid.
The tRNA with the
complementary anticodon to
the codon will carry the
specific amino acid.
tRNA loaded
with Amino
Acids
Ribosome
mRNA
TRANSLATION
Binding Site
Loaded
tRNA
Polypeptide
Chain
Unloaded
tRNA
Ribosome
mRNA
The tRNA with the
correct anticodon will be
attracted to the binding
site in the ribosome.
The ribosome will add
the amino acid it carries
to the growing
polypeptide chain and
the tRNA will be released.
The unloaded tRNA will
be reattached to another
of the same amino acid.
PRIMARY PROTEINS
The completed chain of
amino acids, called a
polypeptide chain, is a
primary protein.
Polypeptide
chain - Primary
protein
SECONDARY PROTEINS
The polypeptide chain
arranges into two
common shapes to form
a secondary protein: the
alpha helix (left) and the
beta-pleated sheet
(right). These are held in
place by hydrogen bonds.
TERTIARY PROTEINS
The alpha helix and beta
pleated sheets fold into a
complex 3 dimensional
shape which is called a
tertiary protein. For some
proteins, this is the end of
the road and the protein
goes away to do what is was
synthesized to do.
QUATERNARY PROTEINS
Quaternary proteins are
clusters of tertiary proteins
which bind together to
form one protein that does
a specific job.