Download DNA Synthesis (Replication)

Processes of Nucleic Acids
September 17 & 18, 2012
DNA Synthesis (Replication)
1. Helicase – Separates parental DNA strands (unwind
double helix)
2. ssB (single-stranded Binding) proteins – Prevents
single strands from re-associating
3. RNA Primase – Synthesizes RNA primers, required to
initiate DNA nucleotide insertion
4. DNA Polymerase III – Responsible for synthesis of
lagging strand & leading strand
5. DNA Pol I – Removes RNA primers & Fills lagging
strand gaps (Exonuclease Activity)
6. DNA Ligase – Forms Phosphodiester bond joining 2
adjacent DNA strands
Processes of Nucleic Acids
September 17 & 18, 2012
Processes of Nucleic Acids
September 17 & 18, 2012
Processes of Nucleic Acids
September 17 & 18, 2012
Processes of Nucleic Acids
September 17 & 18, 2012
rRNA (Ribosomal RNA) – in nucleolus gives rise
to ribosomal precursors; makes Ribosome, and
is the central component of the Ribosome’s
protein-manufacturing machinery.
Processes of Nucleic Acids
September 17 & 18, 2012
mRNA (Messenger RNA) - encodes chemical
"blueprint" for protein (The Genetic Code); carries
coding information from Nucleus to Ribosomes
(sites of protein synthesis).
Details of mRNA:
 Encoded in sequence of nucleotides
(AUCG), which are arranged into codons
consisting of three bases each
 Each codon encodes a specific amino acid,
except the stop codons
 Stop codons terminate protein synthesis
Processes of Nucleic Acids
September 17 & 18, 2012
tRNA (Transfer RNA) - adaptor molecule composed of RNA used
to bridge the genetic code (AUCG) in mRNA with the twenty
amino-acids code in proteins.
Details of tRNA:
 The role of tRNA is to specify which sequence from the genetic
code corresponds to which amino acid
 One end of the tRNA complements the genetic code in a threenucleotide sequence called the anticodon
 On the other end of the tRNA is a covalent attachment to the
amino acid that corresponds to the anticodon sequence
 Each type of tRNA molecule can be attached to only one type
of amino acid
o The genetic code contains multiple codons that specify the same
amino acid; therefore, there are many tRNA molecules, each bearing
a different anticodon, which also carry the same amino acid.
Processes of Nucleic Acids
*Baking a Cake Analogy
September 17 & 18, 2012
Processes of Nucleic Acids
September 17 & 18, 2012
Processes of Nucleic Acids
September 17 & 18, 2012
Processes of Nucleic Acids
September 17 & 18, 2012
Processes of Nucleic Acids
September 17 & 18, 2012
Translation
*AUG (Methionine) – Start Codon
*UAG, UGA, UAA – Stop Codons
Processes of Nucleic Acids
September 17 & 18, 2012
Initiation:
 Binding of mRNA to small ribosomal subunit
containing tRNAimet
 mRNA is scanned for AUG start codon
 First amino acid is Methionine
Processes of Nucleic Acids
September 17 & 18, 2012
Processes of Nucleic Acids
September 17 & 18, 2012
Elongation:
 Met-tRNAi already bound to (P) site
1.mRNA codon in (A) site determines
which aminoacyl-tRNA binds to (A) site
2.Methionine binds (peptide bond) to
aminoacyl1 at (A) site
3.Methionine & aminoacyl1 translocate to
(A) site, which now is (P) site – freeing
(A) site for a new aminoacyl-tRNA
 Steps 1-3 repeat until termination
Processes of Nucleic Acids
September 17 & 18, 2012
Processes of Nucleic Acids
September 17 & 18, 2012
Termination:
 A termination (stop) codon is placed into the (A)
site on the ribosome
a)UAG, UGA, UAA
b)There are NO tRNA anticodons that bind
Stop Codons
 Release Factors (RF) bind to ribosome
 Newly peptide chain is released from ribosome
Processes of Nucleic Acids
September 17 & 18, 2012