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Transcript Ch.22Pt.3_000

Spliceosome attachs to hnRNA
and begins to snip out
non-coding introns
mRNA strand composed of exons
is free to leave the nucleus
TRANSLATION: turning mRNA into a
Group of three nucleotides on mRNA is called a
CODON. 4 types of nucleotides arranged in
multiples of 3 means 43 = 64 possible
Each codon ultimately stands for an amino acid.
Slight variations for the same a.a. are called
There are START and STOP codons:
AUG = start; UAA, UAG, UGA = stop
A hairpin loop is produced when singlestranded RNA doubles back on itself and
complementary base pairing occurs.
A tRNA molecule. The amino acid attachment
site is at the open end of the cloverleaf (the 39
end), and the anticodon is located in the loop
opposite the open end.
An aminoacyl - tRNA synthetase has an active
site for tRNA and a binding site for the particular
amino acid that is to be attached to that tRNA.
tRNA= smallest RNA
Interprets genetic info in
DNA & brings specific
amino acids to ribosome for
protein synthesis.
Only tRNA can translate
genetic info into amino
acids for proteins.
One or more different
tRNAs for each of 20 A.A.
tRNAs are all similar, made
of 70-90 nucleotides.
H bonds between some
bases make loops
The interaction
between anticodon
(tRNA) and codon
(mRNA), which
complementary base
pairing, governs the
proper placement of
amino acids in a
The Universal Genetic Code.
A transfer RNA molecule (tRNA for short) brings
correct amino acid to ribosome & drops it off.
e.g.: AUG (codes for methionine)
tRNA brings methionine to ribosome.
Ribosomes, which contain both rRNA and
protein, have structures that contain two
subunits. One subunit is much larger than the
Initiation of protein synthesis begins with
the formation of an initiation complex.
The process of translation that occurs during
protein synthesis
The process of translation that occurs during
protein synthesis (cont’d)
The process of translation that occurs during
protein synthesis. (cont’d)
Several ribosomes can simultaneously proceed
along a single strand of mRNA one after
another. Such a complex of mRNA and
ribosomes is called a polysome.
at a
•Errors do occur
•Repair enzymes always
making repairs
•Mutations usually are harmful
•Sometimes milder ones lead
to genetic variety
Recombinant DNA is made by inserting a gene
obtained from a cell of one kind of organism into
the DNA of another kind of organism.
Cleavage pattern resulting from a restriction
enzyme that cleaves DNA between G and A
bases in the 5’-to-3’ direction in the sequence G A - A - T - T - C.
The double helix structure is not cut straight across.
The “sticky ends” of the cut plasmid and the cut
gene are complementary and combine to form
recombinant DNA.