Transcript protein synthesis and mutations

Mr. Drake
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What organelle makes proteins?
Where do these organelles get their
directions?
What are the monomers of proteins?
Can mistakes occur in the DNA?
What are those mistakes called?
What are the two different types of nucleic
acids?
What are the monomers of nucleic acids?
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DNA is in the form of a
double-helix
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DNA gets split and each old
strand of DNA acts as a template
to make a new strand of DNA.
This is known as
semiconservative replication.
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Protein Synthesis occurs in four steps:
 Transcription – DNA is copied into mRNA
 mRNA is edited
 mRNA leaves the nucleus
 Translation – mRNA is read and a protein is made
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RNA is different from DNA in 3 ways
1) The sugar in RNA is Ribose where in DNA it is
Deoxyribose
▪ RNA = Ribonucleic acid
2) RNA is usually single stranded; DNA is double
stranded
3) RNA includes the nucleotide
Uracil INSTEAD of Thymine
▪ A – U G-C
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Messenger RNA (mRNA)
 Carries the genetic code from the DNA, out of the
nucleus, to the ribosomes
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Ribosomal RNA (rRNA)
 RNA found inside of the ribosomes that make up
their structure
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Transfer RNA (tRNA)
 RNA that carries the amino acids into the
ribosomes to make a protein
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Step 1: Transcription-Copy DNA into mRNA
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Step 2: Unimportant parts of mRNA (introns)
get taken out of mRNA
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Step 3: mRNA leaves the nucleus and goes to
the ribosomes
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Step 4: Ribosomes read the mRNA and hook
on the correct amino acid
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Copy DNA into mRNA
 DNA is opened up
 RNA polymerase hooks onto DNA
 Makes complementary strand of mRNA
▪ A hooks to T
▪ U hooks to A
▪ G hooks to C
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Introns
(unimportant
parts of mRNA)
are removed
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Exons are spliced
back together
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Ribosomes hook onto the mRNA and read
the mRNA code in groups of 3 nucleotides
 Codons-groups of 3 nucleotides
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tRNA anticodon matches up with a START
codon (AUG) on the mRNA sequence and
tRNA begins to bring in the correct amino
acids
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Amino acids
hook
together by
peptide
bonds
Codons are
read until a
stop codon is
reached
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Codons code
for one of 20
amino acids
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Proteins that
are formed
are based on
the amino
acid
sequence
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Figure out the order of amino acids using the
mRNA strand above
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DNA: T T A G C G A A T T C A
mRNA:
Amino Acids:
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The DNA is opened up by RNA polymerase and
the DNA is transcribed into mRNA.
Unimportant pieces of RNA called introns are
removed from the mRNA, and the exons are
spliced together.
The mRNA leaves the nucleus and binds to a
ribosome in the cytoplasm.
The ribosome reads that mRNA code in groups
of 3 called codons, and tRNA hooks on the
correct amino acids that is coded for.
Once a stop codon is read, the polypeptide chain
is released and a new protein is formed.
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Mistakes in the DNA are known as mutations.
 Not all mutations are necessarily bad, but many
are detrimental (harmful)
 Two Types of Mutations
▪ Chromosomal mutations-large pieces of the DNA
▪ Gene mutations-Individual nucleotide errors
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Deletion – loss of a piece of chromosome
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Duplication – an extra piece of an already
existing piece chromosome is produced
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Inversion – the direction of parts of
chromosome are reversed
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Translocation – when part of a chromosome
breaks off and attaches to a different
chromosome
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Nondisjunction- the failure of a chromosome
to separate from its homologous pair during
gamete formation in meiosis.
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Ex: Klinefelter’s syndrome-caused by the
nondisjuction of the XX chromosomes during
egg formation, causing the boy to end up
with XXY
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Point Mutations – gene mutations involving
in one or a few nucleotides.
1) Silent Mutation
2) Nonsense Mutation
3) Frameshift Mutation
4) Missense Mutation
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Single nucleotide changes in the DNA
sequence.
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This nucleotide error, however, does not
make a difference because the codon still
codes for the same amino acid as it would
have before.
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Point mutation in a DNA sequence that
causes a premature stop codon.
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This results in an incomplete protein which
usually cannot complete its function.
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If a nucleotide is added or deleted, the bases
are still read in groups of three, but now
those groupings are shifted for every codon
that follows.
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By shifting the reading frame, frameshift
mutations may change every amino acid that
follows the point of the mutation.
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Mutation that occurs in an amino acid codon
which results in the use of a different, but
sometimes chemically similar, amino acid.
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The similarity between the two is enough
that little or no change is often rendered in
the protein structure.
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Sickle cell anemia is an example of a missense
mutation that DOES change the protein
 Substitutes A for T. Results in a defective form of
the protein hemoglobin (carries oxygen in the red
blood cells(, causing the cells to be sickle shaped.