DNA and Protein Synthesis

RNA RECAP!

• RNA stands for RIBONUCLEIC ACID.
• It's made up of Ribose, Phosphate group, organic bases.
• The 4 Organic Bases are: ADENINE, URACIL, CYTOSINE, GUANINE.
• The Pentose sugar is RIBOSE
• A monomer of this molecule is called a NUCLEOTIDE
• The bond that join these monomers together is a PHOSPHODIESTER BOND.
• The bond is a result of a CONDENSATION REACTION.

Similarities of MRNA and TRNA

• -Both Single Stranded
• -Both Have Ribose Sugar
• -Both Have Same bases

Polypeptide Synthesis,DNA terms/concepts

• The Genetic Code is described as Universal, what does this mean?
• -Genetic Code= universal as it appears to be the SAME in all organisms.
• Why do we believe that the genetic code is a triplet code?
• A DNA TRIPLET CODE is the Smallest coding unit that can accommodate the 20 A.A that make up the variety of proteins.
• What are stop codons and how many are there? [Do not code for anything]
• 3 of the possible 3-letter codons fail to specify an A.A; such triplets are STOP CODONS and indicate the end of the genetic message in a gene. In MRNA: [UAA, UAG, UGA]
• What is the significance of the AUG CODON?
• The AUG codon is the START CODON and is found at the start of all the genes.
• Why is the genetic code described as non-overlapping.
• The GC is non-overlapping being read in groups of 3 bases with no overlap between the codons.
• Why is the genetic code described as degenerate?
• An amino acid may be coded for more than 1 triplet code. E.g. ATA|CGG both code for the same amino acid.

3 Types of RNA

• MRNA:
• -Rna mols that Convey genetic info from DNA to Ribosome.
• TRNA:
• -Rna mols-help decode an mrna sequence into a protein.
• Rrna:
• -Rna component of the ribosome.
• Proteome: The full range of proteins a cell is able to produce
• Exon: Section of DNA that codes for amino acids.
• Introns: Section of DNA that does not code for amino acids.

Polypeptide Synthesis -Transcription

• The process of making pre-MRNA using part of the DNA as a template. UTRPRDIL
• 1.) Section of DNA unzips- H bonds being broken by the enzyme DNA HELICASE.
• 2.) One of the exposed strands of DNA becomes a template (template strand) and nucleotides of RNA present in the nucleus attach to complementary DNA nucleotides (T being replaced by U).
• 3.) Enzyme RNA POLYMERASE joins RNA nucleotides together to form a single strand of MRNA.
• 4.) As a strand of pre-MRNA is formed by RNA polymerase moving along the DNA, the DNA zips back up behind the enzyme.
• (only 12 DNA bases exposed at any one time.)
• 5.) When RNA POLYMERASE reaches a STOP CODON, it detaches from the DNA and the production of pre-MRNA is then complete.
• 6.) DNA is constructed from INTRONS (not code for amino acids) and EXONS (Code for amino acids) [Prokaryotes=not have Introns].
• Introns are unnecessary to the structure of the MRNA and would interfere with polypeptide formation, therefore are removed in SPLICING. (exons are joined together when introns are removed)
• 7.) The MRNA leaves the nucleus through a pore in the nuclear membrane (as MRNA mols are too large to diffuse out of the nucleus).
• Outside the nucleus, the MRNA is attracted to the ribosomes, to which it becomes attached, ready for translation.

Translation

• During Translation, the entire message in MRNA is read CODON-BY-CODON [non overlapping] until the polypeptide chain is completely assembled according to the instructions originally encoded in the DNA.
• The process of translation involves MRNA, Amino Acids, Ribosomes, A variety of enzymes, and chemical energy in the form of ATP.
• Translation also requires TRNA that decodes MRNA's message and translates it into the language of proteins. TRNA is referred to as a Decoder Molecule.
• There are a variety of unique TRNA mols that differ from one another in the triplet of bases at one end of the mol called the anticodon.
• 

TRANSLATION

• 1.) Ribosome attaches to start of MRNA mol.
• [3 bases on the MRNA mol form a codon and 2 codons fit into ribosome at once.]
• 2.) TRNA mol with complementary anticodons to the MRNA codons enter Ribosome. They bring their specific amino acids.
• 3.) The 2 A.A carried by the TRNA mols come very close to one another. They join to each other by a peptide bond- this requires energy in the form of ATP.
• 4.) The first TRNA is now released from the A.A. It leaves the Ribosome and can now bring another A.A of the same kind to the Ribosome.
• 5.) The Ribosome moves along the MRNA, and a new TRNA enters the ribosome, bringing its A.A.
• 6.) This process continues until the Ribosome reaches a STOP or non-sense codon which does not code for an amino acid.

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