Download Protein Synthesis (Transcription and Translation)

Protein Synthesis
(Transcription and Translation)
Do You Remember?
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Think back to the cell analogy of a factory.
Do you remember who manufactured proteins?
Can you remember of what proteins are composed?
Who contains the “code” to make proteins?
How does DNA code for proteins?
• The sequence of
nucleotides in each gene
contains information for
assembling the string of
amino acids that make up
a single protein.
• The ribosomes required to
make proteins cannot
read DNA.
• Therefore, for DNA to
code for proteins, an RNA
molecule must be made.
• Ribosomes can read
RNA.
RNA is another Nucleic Acid
Nucleotide Polymer
• RNA differs from DNA
structure in three ways.
– Single stranded
instead of double
stranded
– Ribose sugar
instead of
deoxyribose
– Uracil instead of
thymine nitrogen
base
Ribose sugar
Coding from DNA to RNA
• When proteins are needed
to be made in the cell RNA
must make a copy of the
instructions for the protein
from DNA
• Chargraff’s Rule is still
used, but modified.
• T–A
• C – G, G-C
• A–U
• So wherever RNA comes
across an A, a U will bind
instead of a T.
Three types of RNA
• Messenger RNA (mRNA): carries the DNA code
(message) to the ribosomes
• Ribosomal RNA (rRNA): makes up the
ribosomes that reads the mRNA to build the
correct amino acid sequence
• Transfer RNA (tRNA): brings the amino acids to
the ribosome
Messenger RNA (mRNA)
• Responsible for making a
copy (message) of the DNA
sequence needed to make a
specific protein.
*This process will occur within the
nucleus and the copy is then taken
out of the nucleus to the
cytoplasm of the cell.
• Code the following DNA sequence
into a strand of mRNA.
DNA: T A C C G G A T G C C A
mRNA: A U G G C C U A C G G U
Ribosomal RNA (rRNA)
• Makes the ribosomes needed to
read the mRNA message to make a
protein.
• Remember that ribosomes are
manufactured in the nucleolus of the
nucleus.
Transfer RNA (tRNA)
• Responsible for bringing ribosomes
the amino acids or “ingredients”
needed to make the protein.
• tRNA must take the code read by
the ribosome and bring the
complimentary code of each amino
acid.
– Ex.
mRNA:UCUGCCAAA
tRNA: AGACGGUUU
That’s Notes for Today.
Now Let’s Review and Practice.
Transcription
• The process of building an RNA strand from the
DNA template
Remember A – U
and C – G.
In eukaryotes,
this occurs inside
the nucleus.
In prokaryotes,
this occurs in the
cytoplasm.
Click on image to play the video.
mRNA processing in eukaryotes
• Since much of the DNA code is useless or codes
for multiple proteins, the unnecessary portions of
DNA that were coded into mRNA must be
removed.
• The useless portions of
RNA (introns) are removed.
The coding portions (exons)
are linked together to make
the final mRNA.
mRNA codes for amino acids.
• Three mRNA nucleotides code for one amino
acid, but more than one combination codes for
the same amino acid.
Translation
• The process of ribosomes reading the mRNA
code to properly make an amino acid chain that is
folded into a usable protein. Bind using peptide
bond.
Translation
• Initiation: The ribosome binds to AUG, the
starting code (codon). The ribosome directs the
methionine tRNA to bring the methionine (met)
amino acid.
Translation
* Elongation: The ribosome reads the next
codon and directs the appropriate tRNA to
transfer the amino acid. Bind using peptide
bond.
Translation process
Termination: The ribosome joins the amino
acids together and continues this process until
the codon indicates stop.
The End
That’s all for now!!!
Let’s practice
What happens if there is a mistake
(mutation) in the DNA code?
• Possibly proteins won’t be made or are made
improperly.
• If the mutations occur in the gametes, the
offspring’s DNA will be affected positively,
negatively, or neutrally.
• What can cause a mutation?
– Replication error
– Transcription error
– Cell division error
– Chemical agents (mutagens)
– Spontaneous changes
Point mutation
• A point mutation is a change in a single base pair
in DNA.
• A change in a single nitrogenous base can
change the entire structure of a protein because a
change in a single amino acid can affect the
shape of the protein.
Point mutations
• May change the amino acid code if the mutations
occurs in the right place in the code.
mRNA
Normal
Protein
Stop
Replace G with A
mRNA
Point
mutation Protein
Stop
Frameshift mutations
• Losing a single nucleotide base
• This mutation would cause nearly every amino
acid in the protein after the deletion to be
changed
Deletion of U
mRNA
Protein
Changes to the chromosome
• When a part of a chromosome is left out, a
deletion occurs
A B C D E
F G H
A B C E
F G H
Deletion
• When part of a chromatid breaks off and attaches
to its sister chromatid, an insertion occurs.
A B C D E
F G H
A B C B C D E
Insertion
F G H
Changes to the chromosome
• When part of a chromosome breaks off and
reattaches backwards, an inversion occurs.
A B C D E F G H
A D C B E FGH
Inversion
• When part of one chromosome breaks off and is
added to a different chromosome, a translocation
occurs.
AB C D E F GH
W X AB C DE F GH
WX Y Z
Translocation
Y
Z
Repairing DNA
• Enzymes proofread the DNA and replace
incorrect nucleotides with correct nucleotides.
• The greater the exposure to a mutagen such as
UV light, the more likely is the chance that a
mistake will not be corrected.