Protein Synthesis-- Transcription and Translation

The product of transcription is RNA There are three major types. 1. messenger RNA (mRNA) 2. transfer RNA (tRNA) 3. ribosomal RNA (rRNA) 4. other types of RNA are found in eucaryotic cells

mRNA contains the genetic information present in DNA therefore mRNAs code for proteins. This is translated in the cytoplasm. tRNA codes for an adapter molecule. This molecule is bifunctional and converts the base code present in DNA and RNA into the amino acid code present in proteins. rRNA is a structural component found in ribosomes.

Ribosomes are intracellular organelles which are directly involved in protein synthesis. They provide a highly organized three dimensional surface on which the various components involved in protein synthesis can be correctly positioned.

RNA is transcribed from only one DNA strand DNA sense strand AGCTGTGTCATCACGA DNA template strand TCGACACAGTAGTGCT RNA strand AGCUGUGUCAUCACGA

Remove introns and splice exons add a cap and add a poly A tail

5’capAAAAAAAAA... Now it is ready to translate.

Requirements for Translation A message Both ribosome subunits all of the transfer RNA’s energy (In this case, it comes from GTP.) a cofactor (Mg 2+ )

Each ribosome contains two subunits: a large and a small subunit. The small subunit binds to the beginning of a mRNA molecule followed by the large subunit.

The Genetic Code

Some Interesting Facts about the Genetic Code It is unambiguous-- each codon codes for one and only one amino acid. It is redundant-- for most of the amino acids, there is more than one codon.

Why are there 3 nucleotides per codon? Why is the code redundant? What makes the code redundant?

Translation  occurs at the ribosome v a cellular particle made of protein and ribosomal RNA (rRNA) v ribosome binds to the 5’ end of the mRNA AUGGUGCACCUGACUCCUGAGGAG...

B - Globin Gene... ATG GTG CAC CTG ACT CCT GAG GAG AAG TCT GCC GTT ACT GCC CTG TGG GGC AAG GTG....TAG... 5

B - Globin mRNA... AUG GUG CAC CUG ACU CCU GAG GAG AGC CGU UAC UGC CCU GUG GGG CAA GGG...………………….UAG.... 5

...AUG GUG CAC CUG ACU CCU GAG NH 3 MET VAL HIS LEU THR PRO GLU GAG AAG UCU GCC GUU ACU GCC CUG GLU LYS SER ALA VAL THR ALA LEU UGG GGC AAG GUG.… UAG... TRP GLY LYS VAL STOP 5

Translation  ribosome binds to the 5 end of the mRNA v begins to read the message codon by codon AUGGUGCACCUGACUCCUGAGGAG...

v at each codon a specific transfer RNA brings the appropriate amino acid to the growing chain AUGGUGCACCUGACUCCUGAGGAG...

 The specificity is determined by anticodon that complements mRNA codon AUGGUGCACCUGACUCCUGAGGAG... UAC NH 3 COOH

 at each codon a specific transfer RNA brings the appropriate amino acid to the growing chain AUGGUGCACCUGACUCCUGAGGAG... NH 3 UAC COOH

 at each codon a specific transfer RNA brings the appropriate amino acid to the growing chain AUGGUGCACCUGACUCCUGAGGAG... NH 3 UAC COOH NH 3 UAC COOH CAC NH 3 COOH

 at each codon a specific transfer RNA brings the appropriate amino acid to the growing chain AUGGUGCACCUGACUCCUGAGGAG... NH 3 CAC COOH

 at each codon a specific transfer RNA brings the appropriate amino acid to the growing chain AUGGUGCACCUGACUCCUGAGGAG... NH 3 CAC COOH NH 3 COOH GUG

 process continues until the protein is complete AUGGUGCACCUGACUCCUGAGGAG... NH 3 COOH GUG