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Protein Synthesis
Transcription
Transcription
• Producing an mRNA
(messenger RNA) molecule
from DNA template
• Occurs in nucleus
There are 3 steps to
transcription:
1) Unzipping of DNA
• DNA helicase breaks the
hydrogen bonds
between the bases of
specific section
2. Complimentary base pairing (cbp)
• RNA nucleotides bind
with DNA nucleotides by
cbp on ONE of the DNA
strands
• RNA polymerase
catalyzes this rxn
3) Joining of adjacent nucleotides
The sugar from one
nucleotide bonds with
the phosphate of the
next, making a single
stranded mRNA chain
Done by enzyme RNA
ligase
Hydrogen
Bonds
Before mRNA leaves the nucleus
• When the mRNA molecule is created, there are 2
sections of the molecule, INTRONS and EXONS.
• Exons = the code that is useful for transcripting into
proteins
• Introns = are not useful
• An enzyme splices the introns, puts together the
useful sections (exons)
Splicing of mRNA
Coding on mRNA
• Genetic code is read by
the order of the bases
on the mRNA
• These bases are read in
groups of 3 and are
called CODONS
• Each codon codes for a
specific amino acid
• There are 43 ( = 64) codons possible -->
therefore there are easily enough codons to
code for all the necessary amino acids.
• The same amino acid is often specified by
more than one codon. However, the reverse is
never true.
• that is, any one codon only specifies ONE
amino acid
Do not
need to
write!!
Example of codons and aa’s
• Codon CCU codes for the amino acid =
Proline
• There is a special start codon
AUG (with aa methionine)
• There are special stop codons
UAA, UAG, UGA (do not have aa’s)
This code is read and translated into
polypeptide/protein at the ribosome (rRNA) with the
help of a third type of RNA, transfer RNA (tRNA)
Done 1st half of protein synthesis!
Now review!
YAY!!!
Which of the following occurs during
complementary base pairing?
A. Bonds form between uracil and thymine.
B. Bonds form between cytosine and guanine.
C. Bonds break between phosphates and sugars.
D. Bonds break between amino acids and
phosphates.
Which of the following is produced as a
result of replication?
A. DNA
B. protein
C. mRNA
D. ribosomes
In which of the following are both helicase and
DNA polymerase active?
A. X only
B. Y only
C. Z only
D. X and Z
• The sequence of bases in one strand of a DNA
molecule is C C G T A C. Which of the following
represents the sequence of bases that attach
to this strand during replication?
A. G G C A T G
B. G G C U T G
C. C C G T AC
D. G G C A U G
• One structural difference between DNA and
tRNA is that
A. DNA has uracil and tRNA does not.
B. tRNA contains more bases than
DNA.
C. DNA contains deoxyribose and
tRNA does not.
D. tRNA contains more hydrogen
bonds than DNA.
• Which of the following bonds have
formed during this process?
• A. W and Y
• B. W and Z
• C. Y only
• D. Z only
Woot woot! Now worksheet!