Page 139 - 86 human physiology part-2

Chapter 18

1985 Alec Jeffreys discovers genetic finger printing
1989 The first human gene is sequenced by Francis Collin and Lap-Chee Tsui. It encodes the
CFTR protein. Defect in this gene causes Cystic Fibrosis
1995 The genome of Haemophilus influenza is the first genome of a free living organism to be
sequenced.
1996 Saccharomyces cerevisiae is the first eukaryote genome sequence to be released.
1998 The first genome sequence for a multicellular eukaryote, C. elegans is released.
2001 First draft sequences of the human genome are released simultaneously by the Human
Genome Project and Celera Genomic
2003 (14 April) Successful completion of Human Genome Project with 99% of the genome
sequenced to a 99.99% accuracy
2006 Marcus Pembrey and Olov Bygren publish Sex-specifics, male line trans-generational
responses in humans, a proof of epigenetics

Transcription and Translation

Transcription is the process of making RNA. In response to an enzyme RNA polymerase breaks
the hydrogen bonds of the gene. A gene is a segment of DNA which contains the information for
making a protein. As it breaks the hydrogen bonds it begins to move down the gene. Next the RNA
polymerase will line up the nucleotides so they are complementary. Some types of RNA will leave the
nucleus and perform a specific function.

Translation is the synthesis of the protein on the ribosome as the mRNA moves across the
ribosome. There are eleven basic steps to translation.

1. The mRNA base sequence determines the order of assembling of the amino acids to form
specific proteins.
2. Transcription occurs in the nucleus, and once you have completed transcription the mRNA will
leave the nuecleus, and go into the cytoplasm where the mRNA will bind to a free floating
ribosome, where it will attach to a small ribosomal subunit.
3. Methionine-tRNA binds to the nucleotides AUG. AUG is known as the start codon and is found
at the beginning of each mRNA.
4. The complex then binds to a large ribosomal subunit. Methionine-tRNA is bound to the P site of
the ribosome.
5. Another tRNA containing a second amino acid (lysine) binds to the second amino acid. Binding
to the second condon of mRNA (on the A-site of the ribosome).
6. Peptidyl transferase, forms a peptide3 bond between the two amino acids (methionine and
lysine)
7. The first amino tRNA is released and mRNA is translocated one codon carrying the second
tRNA (still carrying the two amino acids) to the P site.
8. Another tRNA with attached amino acid (glutamine) moves into the A site and binds to that
codon.
9. It will now form a peptide bond with lysine and glutamine
10. Now the tRNA in the P site will be let go, and mRNA is translocated one codon, (the tRNA
with three amino acids) to the P site.
11. This will continue going until it reaches the stop codon (UAG) on the mRNA. Then this codon
will tell it to release the polypeptide chain.
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354 | Human Physiology