Human genes and protein synthesis
Ü Human genes: They are units of DNA sequences that
containing information which determine the composition of an RNA molecule and
most often translated to a protein.
Ü Every three nucleotides "triplet"
represent a single codon, coding for a particular amino acid. Some
codons act as a “start” signal, whereas others serve as “stop”
signals that terminates translation .
Protein synthesis steps (From gene to protein)
1. DNA replication
ü Replication is semiconservative, i.e. each
daughter molecule receives one strand from the parent DNA molecule.
ü Unwinding proteins, DNA-directed RNA
polymerase, DNA polymerase and ligase are also required.
ü DNA polymerases synthesize the new strand
in a 5' to 3' direction.
ü Discontinuous replication, i.e. one or both
DNA strands may be synthesized in pieces known as Okazaki fragments, which are
then linked together to yield a continuous DNA chain.
2. Transcription
ü Synthesis of complete RNA molecules from
DNA by the enzyme RNA polymerase.
ü Transcription yields three types of RNA:
mRNA, tRNA and rRNA.
ü Each nucleotide in the mRNA is
complementary to one in the DNA template.
3. Post-transcriptional processing: the
initial transcript is edited to remove introns and splice exons together by
means of an RNA-protein complex called the spliceosome. Multiple different
transcripts may be produced (alternative splicing).