DNA AND PROTEIN SYNTHESIS

TRANSCRIPTION-PRODUCTION OF PRE-mRNA

TRANSCRIPTION TAKES PLACE IN THE NUCLEUS OF THE CELL.
THE ENZYME DNA HELICASE UNZIPPS THE TWO DNA STRANDS, EXPOSING THE NUCLEOTIDE BASES.
FREE NUCLEOTIDES IN THE NUCLEUS PAIR WITH THEIR COMPLEMENTARY BASES ON THE DNA STRANDS.
RNA POLYMERASE MOVES ALONG THE NEWLY FORMED STRAND OF NUCLEOTIDES AND JOINS THEM TOGETHER TO FORM A PRE-mRNA MOLECULE.
AS THE RNA POLYMERASE IS JOINING NUCLEOTIDES, THE TWO STRANDS OF DNA REJOIN BEHIND IT SO ONLY ABOUT 12 DNA BASE PAIRS ARE EXPOSED AT A TIME.
WHEN THE RNA POLYMERASE REACHES A 'STOP' CODON IT DETACHES AND THE PRODUCTION OF PRE-RNA IS FINISHED.

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STRANDS OF DNA FROM EUKARYOTIC CELLS ARE MADE UP OF EXONS(CODES FOR PROTEINS) AND INTRONS (DON'T CODE FOR PROTEINS)
THE INTRONS INTERVEIN AND PREVENT THE SYNTHESIS OF A POLYPEPTIDE.
SO IN THE PRE-mRNA, THE BASE SEQUENCE CORRESPONDING TO INTRONS ARE REMOVED AND THE EXONS ARE JOIED TOGETHER. THIS IS CALLED SLPICING.

Image result for splicing of pre-mrna (http://www.rnaxploration.com/_Media/pre-mrna_maturation-2_med.png)

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THE NEWLY FORMED mRNA LEAVES THE NUCLEUS OUT OF A NUCLEAR PORE.
A RIBOSOME ATTACHES TO THE 'START' CODON (AUG) AT ONE END OF THE mRNA MOLECULE.
A tRNA MOLECULE WITH A COMPLEMENTARY ANTICODON SEQUENCE (UAC) MOVES TO THE RIBOSOME AND PAIRS UP WITH THE COMPLEMENTARY CODON ON THE mRNA. THIS tRNA CARRIES A SPECIFIC AMINO ACID WITH IT.
A tRNA MOLECULE WITH A COMPLEMENTARY ANTICODON TO TH NEXT CODON OF THE mRNA MOLECULE ATTACHES, BRINGING ANOTHER SPECIFIC AMINO ACID.
THE RIBOSOME MOVES ALONG THE THE mRNA , BRINGING TOGETHER TWO tRNA MOLECULES AT A TIME.
THE TWO AMINO ACIDS ON THE tRNA MOLECULES ARE JOINED BY A PEPTIDE BOND USING AN ENZYME AND ATP TO PROVIDE THE ENERGY
THE RIBOSOME MOVES TO THE THIRD CODON AND LINKS THE 2ND AND THIRD AMINO ACIDS TOGETHER.
SIMULTANEOUSLY THE FIRST tRNA MOLECULE IS RELEASED FROM ITS AMINO ACID AND IS FREE TO COLLECT ANOTHER FROM THE AMINO ACID POOL IN THE CELL.
THE SYNTHESIS OF A PLOYPEPTIDE CONTINUES UNTIL A RIOSOME REACHES A 'STOP' CODON. THE mRNA, tRNA AND RIBOSOMES ARE ALL SPEPARATE AT THIS POINT.

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A SINGLE POLYPEPTIDE CHAIN CAN BE A FUNCTIONAL PROTEIN, MOST OFTEN A NUMBER OF THEM ARE LINKED TOGETHER.
THE POLYPEPTIDE IS COILED OR FOLDED, PRODUCING THE SECONDARY STRUCTURE.
THE SECODARY STRUCTURE IS FOLDED PRODUCING THE TERTIARY STRUCTURE.
DIFFERENT POLY PEPTIDE CHAINS, ALONG WITH ANY NON-PROTEIN GROUPS, ARE LINKED TO FORM THE QUATERNARY STRUCTURE.

Image result for PROTEIN STRUCTURES (http://tse1.mm.bing.net/th?id=OIP.KyOH-KSeAK-6RnOCunDfRAETEs&pid=15.1)

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