Transcript Nucleic Acids and Protein Synthesis

Nucleic Acids and Protein
Synthesis
Chromosomes are thread-like structures
found inside the nucleus of a cell. Each body
cell contains 46 chromosomes arranged as
23 pairs. Sex cells (eggs and sperm) contain
only 23 chromosomes in total
Chromosomes are the stuctures
that hold genes. Genes are made
from DNA
What are chromosomes?
• Chromosomes hold genes. Genes are
made of DNA. A gene holds information
that decides our colour of hair, colour of
eyes etc. It also holds information for
making proteins that may become
enzymes or hormone for use within the
body.
Two of these strands become
joined together by weaker
hydrogen bonds forming between
there bases. However this union
is temporary in that hydrogen
bonds can be easily broken when
this becomes necessary e.g
during the process of
transcription
Base pairing rules
• Each base can only pair with one other
type of base: adenine(A) always bonds
with thymine(T), and Guanine(G) always
bonds with Cytosine(C). A-T and G-C are
called Base Pairs. Each member of a pair
are complimentary to its partner.
• This twisted
strand a bit
like a spiral
ladder is called
a double helix
How to carry out protein Synthesis
• In order to make a protein which may be a
globular, fibrous or conjugated protein using the
information from genes, we must start with DNA
use it to make an RNA strand called a
messenger RNA, this in turn is used to make
another RNA strand called a Transfer RNA. The
transfer RNA is used to link amino acids in a
specific order. This in turns forms a polypeptide.
Several polypeptides link together to form our
completed protein
Structure of RNA
• Now that we understand the structure of
DNA, we must now understand the
structure of our second type of nucleic
acid RNA. An RNA molecule is similar to
DNA
Differences between DNA and
RNA
Starting protein synthesis• A single stranded Messenger RNA
(mRNA) must be Transcribed from a
single strand of double stranded DNA.
This process is called Transcription.
Stages of Transcription of a mRNA
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The 2 DNA strands becomes unwound at stage 1
The DNA strands separate as weak hydrogen bonds between the bases are
breaking at stage 2
Free RNA nucleotides join up with exposed bases on one of the DNA
Strands at stage 3. Uracil joins with Adenine, Cytosine with Guanine
Weak hydrogen bonds are forming between the new base pairs at stage 4
The nucleotides on the RNA strand are being linked in a chain by strong
chemical bonds between the sugar of one RNA nucleotide and the
phosphate of the next one in the chain at stage 5. This linking into a chain
is controlled by an enzyme called RNA Polymerase.
At stage 6 the weak hydrogen bonds between the DNA and RNA bases are
breaking allowing the molecule of transcribed mRNA to become separated
from the DNA template.
At stage 7 the transcribed mRNA is ready to begin its journey out of the
nucleus and into the cytoplasm.
At stage 8 the two exposed DNA strands reunite with weak hydrogen bonds
forming between them. The DNA becomes wound into a double helix once
more. This whole process is continuous.
mRNA
• The completed molecule of mRNA leaves
the nucleus through the pore in the
nuclear membrane and enters the
cytoplasm. Each triplet of bases on mRNA
is called a codon
tRNA
• A second type of RNA is found in the cell’s
cytoplasm. This is called transfer RNA
(tRNA). Each molecule of tRNA has a
triplet of bases exposed. This triplet is
known as an anticodon.
Picking up amino acids
• The anticodon corresponds to a particular
amino acid. Each tRNA molecule picks up
the appropriate amino acid from the
cytoplasm at its site of attachment. There
are 20 different amino acids.
Ribosomes
These are small almost spherical structures
found in all cells. Some occur freely in the
cytoplasm, others are found attached to
endoplasmic reticulum
Translation
• Ribosomes are the site of translation of
mRNA into protein. The ribosome
becomes attached to one end of the
mRNA molecule about to be translated.
Inside the ribosome there are sites for
attachment of tRNA molecules, two at a
time.
Stages of translation
• The anticodon of the first tRNA molecule
forms weak hydrogen bonds with the
complimentary codon on the mRNA
Stages of translation
• When the second tRNA molecule repeats
this process, the first two amino acids
molecules are brought into line with one
another.The two amino acids become
joined together by a strong peptide bond.
Stages of translation
• The first tRNA becomes disconnected
from its amino acid and from the mRNA
and leaves the ribosome
Stages of translation
• The amino acids continue to align form
peptide bonds and disconnect. The
growing chain of amino acids is known as
a polypeptide chain.
Stages of translation
• The completed polypeptide chain
consisting of very many amino acids is
then released into the cytoplasm. The
tRNA and mRNA are reused.
• The polypeptide then may be folded and
rearranged to become the final protein.
Sometimes several polypeptide chains
combine to form the protein.
• Protein synthesised in free ribosomes is
for use within the cell. Protein made in
ribosomes attached to endoplasmic
reticulum is for export.
Protein made in
Ribosomes attached
To endoplasmic
Reticulum is for
export
Protein made
In free
Ribosomes is
For use
Within the
cell
Coiling and folding of the
polypeptide
• When a protein is made on the ribosome
that is attached to endoplasmic reticulum,
the polypeptide is ‘injected’ into the ER
and then coiled and folded. The protein is
then passed to the golgi apparatus for
packaging (adding for example a
carbohydrate part to make it into a
glycoprotein which is a conjugated protein)
and secretion from the cell
Function of the nucleus and
nucleolus
• Nucleus- contains DNA which holds the
genetic instructions for the manufacture of
proteins and the control of inherited
characteristics
• Nucleolus- controls the synthesis of RNA
and other components needed to build
ribosomes
Nucleus
Nucleolus