transcription translation

1. Transcription and
Translation
From DNA to RNA to protein

2. Overview
• Genes in DNA contain
information to make
proteins.
• The cell makes mRNA
copies of genes that are
needed.
• The mRNA is read at the
ribosomes in the rough
ER.
• Protein is produced.

3. Key Players
• mRNA carries the
information from a gene
in DNA.
• Ribosomes, made of
rRNA, consist of
subunits and carry out
an enzyme-like role.
• tRNA carries specific
amino acids to the
ribosome.

4. Transcription
1. DNA unzipped by helicase.
2. RNA polymerase transcribe DNA into mRNA by
complementary base pairing

5. Transcription
RNA polymerase matches bases in the sense strand with
RNA bases, building a strand of mRNA that carries the
information encoded in the DNA.

6. Transcription
Encoded in DNA is a signal telling RNA polymerase where
to stop. Transcription ends at that point.

7. Transcription
The completed mRNA molecule then moves from the
nucleus to the rough ER for translation.

8. Translation
• On the ribosome,
specific tRNA will bring
in specific amino acid
towards the mRNA by
complementary base
pairing

9. Translation
• The ribosomal unit binds
to mRNA where the
code for met is located
(AUG). The anticodon
(UAC) of the tRNA
matches the “start”
codon on mRNA (AUG).

10. Translation
• Another tRNA carrying
different amino acid will
come in, as the
ribosome reads through
the mRNA sequence

11. Translation
• Ribosome will catalyze
the formation of peptide
bonds between the
adjacent amino acids

12. Translation
• A catalytic site on the
larger subunit binds the
two amino acids
together using
dehydration synthesis,
forming a peptide bond
between them.

13. Translation
• The first tRNA now
detaches and goes of to
find another met in the
cytoplasm. The mRNA
chain shifts over one
codon, placing the
second codon (CAU)
over the second active
site.

14. Translation
• A tRNA with an
anticodon (GUA)
matching the exposed
codon (CAU) moves
onto the ribosome. This
tRNA carries histidine
(his).

15. Translation
• A new peptide bond
forms between val and
his on the catalytic site.
The tRNA that carried
val will detach and find
another val in the
cytoplasm. The mRNA
strand will then shift over
one more codon.

16. Translation
• The process continues
until the ribosome finds
a “stop” codon. The
subunits detach from
one another, the mRNA
is released, and the
polypeptide chain moves
down the ER for further
processing. The initial
met is removed and the
chain is folded into its
final shape.

17. Summary

18. Transcription Animation
• http://learn.genetics.utah.edu/units/basics/tra
nscribe/

19. Mutations
• Any mistakes in the DNA code can result
in a “broken” (non-functional) protein.
• A mutation affecting only a few somatic
cells (body cells) might not have any
effect, unless the mutation turns the cell
cancerous.
• A mutation affecting a sex cell can be
passed on to the offspring.

20. Types of Mutations
• Point mutation: base substitution that may
or may not code for a different amino acid.
• Insertion mutation: one or more bases is
inserted into the DNA strand.
• Deletion: one or more bases is deleted
from the DNA strand.

21. Effects of mutations
• Original: THE FAT CAT SAT
• Point mutation: THA FAT CAT SAT
• Insertion: THE FTT ATC ATS AT
• Deletion: THE FTC ATS AT

22. Hemoglobin mutations
DNA mRNA Amino Acid
Properties of
AA
Effect on protein Disease
Original
codon 6
CTC GAG Glutamic Acid Hydrophilic Normal None
Mutation 1 CTT GAA Glutamic Acid Hydrophilic Neutral None
Mutation 2 GTC CAG Glutamine Hydrophilic Neutral None
Mutation 3 CAC GUG Valine Hydrophobic
Loses water
solubility
Sickle Cell
Anemia