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-associating3. RNA Primase – Synthesizes RNA primers, required to

initiate DNA nucleotide insertion4. DNA Polymerase III – Responsible for synthesis of lagging

strand & leading strand5. 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 three-

nucleotide 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 September 17 & 18, 2012

*Baking a Cake Analogy

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 ribosomea)UAG, UGA, UAAb)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