Download PROTEIN SYNTHESIS

PROTEIN
SYNTHESIS
Proteins are responsible for
controlling many different
processes in our bodies. As
enzymes they break things
down, put things together,
catalyze chemical reactions,
they make pigments, they form
antigens and antibodies, give
structure to cells and
membranes, transport
substances in cells and across
membranes, and they perform
hundreds of other functions.
So, HOW ARE PROTEINS
MADE?
PROTEIN SYNTHESIS
Proteins are made of building blocks called AMINO
ACIDS.
There are 20 different amino acids.
A protein can have as few as 8 aa’s or as many as
50 000 aa’s.
Each protein is made by ONE GENE.
PROTEIN SYNTHESIS
How does DNA, which has only 4 bases (A, T, C, and G) code
for 20 different amino acids?
A single base cannot code for an amino acid itself
(4 bases = 4 amino acids)
In pairs?
Only 16 possibilities (42)
AA, AT, AC, AG, TA, TT, TC, TG,
CA, CT, CC, CG, GA, GT, GC, GG
In triplets? 64 possibilities (43)
3 bases of DNA code for one amino acid on proteins. This is
called a DNA CODON
TRANSCRIPTION
DNA cannot leave the nucleus and proteins are made
outside the nucleus. First the DNA must make a copy to
messenger RNA (mRNA).
RNA is slightly different than DNA:
DNA
Sugar is DEOXYRIBOSE
Bases:
C, G, A, T
Double stranded
RNA
Sugar is RIBOSE
Bases: C, G, A, URACIL
(U replace T)
Single stranded
TRANSCRIPTION
TRANSCRIPTION is a lot like DNA replication - the DNA
unzips - but only the leading strand of DNA is copied and not
as another DNA strand but as an mRNA strand.
STEPS:
1) INITIATION – RNA polymerase binds to a promotor on the
DNA telling it where to start transcribing. DNA is unwound.
TRANSCRIPTION
STEPS:
2) RNA nucleotides are added with C matching with G and A
now matching with U. This is done by an RNA POLYMERASE
enzyme and is called ELONGATION.
TRANSCRIPTION
STEPS:
3) Once a piece of RNA has been made, it disconnects, leaves
the nucleus, and goes to the ribosomes to code for proteins.
TRANSCRIPTION
SO IF A STRAND OF DNA HAS THE SEQUENCE:
DNA = T A C C C G A A T C G G G T C C G A T T A C A G A T C
mRNA = A U G G G C U U A G C C C A G G C U A A U G U C U A G
THE STRAND OF COMPLIMENTARY mRNA WILL BE:
TRANSCRIPTION
The codons (3 nucleotides) in mRNA can code for a
specific amino acid, can act as INITIATORS (START
codons), or TERMINATORS (STOP codons) or they can
code for the same amino acid as another codon (ie.
leucine has 6 different codons). This is called
REDUNDANCY.
TRANSCRIPTION ANIMATION
TRANSLATION
The newly transcribed mRNA molecule can now detach and
diffuse out of the nucleus to the cytoplasm. Once the mRNA
has left the nucleus, the following steps occur:
1) mRNA binds to a RIBOSOME starting at an INITIATOR
codon
TRANSLATION
2) transfer RNA (tRNA) brings specific amino acids to the
ribosome.
- specialized RNA called tRNA has two parts: one end
binds to a specific amino acid. The other end has 3 nucleotides
which bind to the codon on the mRNA. This end is the
ANTICODON.
TRANSLATION
3) as the tRNA brings in an amino acid, everything shifts
over one codon in the ribosome. The next tRNA brings in
the next amino acid which is connected to the first with a
PEPTIDE BOND and everything shifts.
TRANSLATION
4) amino acids are continually added until a TERMINATOR
codon is reached on the mRNA which signals the ribosome to
release the mRNA and the protein.
TRANSLATION
One mRNA can be translated many times, even in a
consecutive manner to produce many protein copies at once.
TRANSLATION
DNA = T A C C C G A A T C G G G T C C G A T T A C A G A T C
mRNA = A U G G G C U U A G C C C A G G C U A A U G U C U A G
tRNA = U A C C C G A A U C G G G U C C G A U U A C A G A U C
A.As =
MET – GLY – LEU – ALA – GLU – ALA –ASP – VAL STOP
TRANSLATION
Now YOU do it:
DNA = T A C A G C T A G A A A C T G A C A A T T
mRNA = A U G U C G A U C U U U G A C U G U U A A
tRNA = U A C A G C U A G A A A C U G A C A A U U
A.As =
MET – SER – ISO – PHE – ASP – CYS STOP
TRANSLATION
Now YOU do it, IN REVERSE:
A.As = METH – TRYPTOPHAN– HISTIDINE- LYSINE- TYROSINE STOP
mRNA = A U G
UGG
C A __ A A __ U A __ U A G
DNA =
TAC
ACC
G T __ T T __ A T __ A T C
ATG
TGG
C A __ A A __ T A __ T A G
COMPLEMENTARY
DNA =
TRANSLATION CLIP
What if you get asked about
DNA when given an amino
acid sequence?
What if you get asked about
tRNA anticodons when given
DNA code?
What if …….what else could
you be asked….
Protein synthesis animations
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PBS website
University of Utah website
NCC Transcription animation
NCC - Translation animation
Lewis port website
DNA LEARNING CENTER
F. TRANSLATION TO PROTEIN
With the sequencing of the human genome, molecular biologists have
isolated the genes for many important genes and their resulting proteins.
While most research centers on finding the genes and proteins to help cure
disease (ie. Osteoporosis, cancer, diabetes, etc.), a fringe group lead by Dr.
Dickmeister, focuses their research on isolating genes for aesthetic human
traits (ie. Smooth skin, hairy chest, dimples, and eye colour). It so happens
that this last discovery proved to be helpful in profiling suspects using DNA
evidence. One isolated gene was found to produce a protein causing blue
eyes while the normal form (allele) of the gene caused brown eyes. It was
discovered that the mutant blue-eye colour was the result of any mutation in
the DNA causing three of the SAME amino acid to be produced side by side
in the polypeptide sequence. Amazingly, it did not matter which amino acid
was tripled up or where in the protein this happened – the blue eye colour
would result when three of the same amino acids were side by side. Using
this discovery, forensic scientists took a sample of blood from the knife,
amplified the DNA, cut the DNA at known restriction sites to isolate the eye
colour gene, then sequenced the DNA to elucidate the resulting polypeptide
chain.
PROCEDURE:
- TRANSCRIBE the segment of DNA below into mRNA. Remember: only
the leading strand is transcribed. On this piece of DNA the TOP
strand is the leading strand.
- TRANSLATE the mRNA segment into amino acids. Remember: You
must start translation at the proper START codon. If you start at the
wrong place, you will produce the wrong protein. Translate the
WHOLE polypeptide until you reach a STOP codon.
- Determine the eye colour of the killer – if the polypeptide has three of
the same amino acid in a row, the pigment produced is blue; if not,
the pigment is brown.
DNA SEGMENT:
GGTACGGGGGTTTGCTCCAACATCGCCTGC TTCTAT CAAGTTCGACCACTTACT
CCATGCCCCCAAACGAGGTTGTAGCGGACGAAGATAGTTCAAGCTGGTGAATGA
ANSWER:
DNA SEGMENT:
GGTACGGGGGTTTGCTCCAACATCGCCTGCTTCTATCAAGTTCGACCACTTACT
CCATGCCCCCAAACGAGGTTGTAGCGGACGAAGATAGTTCAAGCTGGTGAATGA
mRNA SEGMENT:
CCAUGCCCCCAAACGAGGUUGUAGCGGACGAAGAUAGUUCAAGCUGGUGAAUGA
PROTEIN:
MET(start)-PRO-PRO-ASP-GLU-VAL-VAL-ALA-ASP-GLU-ASP-SER-SER-SER-TRP-STOP
EYE COLOUR:
The eye colour resulting from the above polypeptide will be: BLUE
THE KILLER OF GRAMPA JIM MUST BE:
LORI – BLUE EYES, DAUGHTER TO NINA AND DENNY,
COULD BE O- AND HAS FLAT FEET.
NOTE: The information contained in this activity is fictitious. Any similarities to actual people, places, or events is purely coincidental. DNA
segments, genes, genetic traits, and proteins may have been fabricated to be representative of actual genes, traits, and proteins. No one
was hurt in the making of this assignment.