Download Protein Synthesis

Protein Synthesis:
The Central Dogma of Biology
Chapter 8 in your textbook
RNA: Ribonucleic acid

Used to make proteins
DNA
RNA
Thymine
Uracil
Double – stranded
Single – stranded
1 type
3 types
Deoxyribose sugar
Ribose sugar
Three Types of RNA
Video clip – 2:52
1. mRNA (messenger): copies the information
from the DNA to carry it out of the nucleus
to the ribosomes
2. rRNA (ribosomal): used to make up most of
the ribosomal subunits that decode the
mRNA
3. tRNA (transfer): carries amino acids to the
ribosome to be linked together to form an
amino acid chain (that will become a protein)
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mRNA is linear (forms a line of bases)
tRNA has a “cloverleaf” shape
rRNA + protein make up the ribosome
The Central Dogma of Biology
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DNA carries the genetic code (genes)
The code is a triplet code – 3 nucleotides (grouped
together as a codon) code for one amino acid.
That code is translated into proteins (each gene
codes for one protein)
Each protein results in one trait (or is responsible
for one part of one trait)
Proteins result in the physical characteristics
(traits) or enzymes (controls chemical reactions) of
an organism
Transcription: Making mRNA from DNA
1. One gene in the DNA molecule is opened
Quick-time movie
Transcription
2. RNA polymerase
bonds free-floating
RNA nucleotides to
open bases on the
exposed strand of
DNA
Animation
Transcription
Animation – Click on left hand box in top row
3.The newly made mRNA leaves the nucleus
and travels to the ribosomes in the cytoplasm
Translation: Making an amino acid
chain from RNA -- Animation
1. The ribosomal subunits surround the
mRNA
Translation, cont’d
2. tRNA binds to a
specific amino acid
and brings it to a
specific codon on the
mRNA. One end of
the tRNA has 3 bases
called an anticodon
that is
complementary to the
codon on the mRNA.
Translation, cont’d
3. Amino acids are
joined together
by peptide
bonds
4. tRNA is
released and
reused
Protein Synthesis
Video clip – 3:20
Animation
The Genetic Code

This chart
is used to
determine
which
amino
acid will
be added
based on
the
mRNA
codon.
The Genetic Code, cont’d
To find the amino
acid that goes to a
specific codon
(three-base mRNA
sequence), find the
first base on the
left, the second
base across the
top, and then –
within that box –
the third base on
the right.
Genetic
Code, cont’d

Sometimes
the chart for
translating
mRNA
codons into
amino acids
is displayed
in a circular
format
The Genetic Code, cont’d
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There are 64 possible codons
There are only 20 amino acids
Each codon codes for one amino acid
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Ex: CCC codes for proline
Some amino acids may be coded for by
multiple codons
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Ex: CCU, CCC, CCA, and CCG all code for
proline
Video clip – 3:26
The Genetic Code, cont’d
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There is one “start” codon – AUG – which
codes for the amino acid methionine
There are three “stop” codons
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These codons do not code for any amino acid
When a stop codon is reached, it is a signal that
the amino acid chain is complete.
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This releases the amino acid – or polypeptide –
chain
Also, the mRNA detaches from the ribosome and
the ribosomal subunits come apart
Mutations
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Mutation = any error / mistake in the DNA
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Video clip – 1:47
Two types: point and frameshift
Point mutations: those that affect one
nucleotide – they occur at a single point on
the DNA
Point Mutations
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Substitution:
changing one
nucleotide for
another
May have no
noticeable effect if
the codon still codes
for the same amino
acid
Point Mutation - Substitution
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May have a significant effect if the substituted
codon changes the amino acid – video clip – 0:59
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For instance, sickle cell anemia results from a single
substitution point mutation
The change of one nitrogen base leads to a different
amino acid, causing the range of problems faced by a
person with sickle cell anemia
Deletions

Deletion –
removing one or
more nucleotides

If a set of three
nucleotides is
removed, then
one amino acid
will be missing
from the protein
made by that
gene
The deletion shown above results in
cystic fibrosis.
Deletions, cont’d

If one or two
nucleotides is
deleted (or
anything that is
not a multiple of
three), the deletion
can change the
amino acids for
everything past
the deletion
Insertions
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Insertion – adding one or more nucleotides
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If a set of three nucleotides is added, then the
protein will have an additional amino acid
Insertions, cont’d
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If one or two
nucleotides is
added (or
anything that is
not a multiple of
three), the
insertion can
change the
amino acids for
everything past
the insertion
Frameshift Mutations
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Frameshift mutations: any changes that
add or subtract nucleotides causing a change
in the sequence of every codon after the
mutation.
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This affects the “reading frame” –
AAT/CGG/ACC – if “T” is inserted after the first
“C”, it will now read AAT/CTG/GAC/C…
changing all of the amino acids after the insertion
Frameshift Mutations
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Results when one or
two nucleotides / bases
are inserted or deleted
(or any number of
bases that is not a
multiple of 3)
Causes of Mutations
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bacteria / viruses
environmental / chemical
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Video clip – 1:06
UV radiation
Various pollutants
genetic
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Some types of cancer (which is caused by a
mutation in the DNA of the cells that become
cancerous) can have a genetic predisposition –
making it more likely someone will get that type
of cancer