Download 12.3 Transcription and Translation PPT

CH 12.3
RNA & Protein
Synthesis
Genes are coded
DNA instructions
that control the
production of proteins
within the cell…
…just how are those
instructions decoded???
Step 1:
…by copying the nucleotide
sequence of DNA into
RNA: ribonucleic acid!
Like DNA, RNA is a long
chain made up of nucleotides.
There are 3 main differences:
- the sugar in RNA is ribose
(not deoxyribose);
- RNA is mostly single-stranded;
- RNA contains uracil instead of
thymine.
Types of RNA
Messenger RNA
Messenger RNA
Carries copies of
gene instructions
(to synthesize proteins
out of amino acids)
from DNA to the
rest of the cell.
Ribosomal RNA
Proteins are assembled
on ribosomes, which
are made up of many
proteins as well as
ribosomal RNA.
Transfer RNA
Transfer RNA delivers
each amino acid
coded for by
messenger RNA to the
ribosome for protein
assembly.
Transcription
…In the nucleus, part of the nucleotide sequence of DNA is
copied into a complementary sequence of RNA.
• RNA polymerase opens up DNA and separates the strands.
• RNA polymerase uses one DNA strand as a template to produce a
strand of RNA.
• RNA polymerase binds only to promoters, special DNA regions with
specific base sequences that indicate where to start and stop transcription.
Can YOU transcribe?
RNA strand: A U U G A C U G A A C U G A
DNA strand: T A A C T G A C T T G A C T
REMEMBER: in transcription, uracil replaces thymine in RNA!
Translation: Breaking the genetic code
Translation is the process
of decoding mRNA
nucleotides into proteins
• Proteins are made by
joining amino acids into
long chains called
polypeptides.
• The order of these
amino acids determines
which protein is made.
• The sequence of
nitrogenous bases in
DNA determines the
order of amino acids,
thus dictating the
protein.
The genetic code is written in a
language that only has four letters:
A,U,G &C!
These letters (nucleotides) combine in
different ways to form the code for
twenty different amino acids.
The genetic code is read three letters (nucleotides)
at a time in groups called codons.
64 possible codons
(4 bases3)
…some amino acids
can be coded for
by more than one
codon…
…can you
give an example?
One codon, AUG, can
specify methionine or
“start” codon for
protein synthesis.
Note the three
“stop” codons that
do note code for any
amino acid – they signal
the end of a polypeptide
chain.
Consider the following mRNA sequence:
U C G C A C G G U
This sequence would be read three bases at a time as:
UCG - CAC -GGU
The codons represent different amino acids:
UCG - CAC -GGU
(Serine - Histidine – Glycine)
Translation
mRNA leaves the
nucleus, attaches to ribosome…
…in the ribosome,
the amino acid is
transferred to the
growing
polypeptide chain.
…starting at AUG, mRNA’s codon
attracts tRNA ‘s anticodon with its
amino acid…
Transcription AND Translation!
Videos for Review
• Replication
http://www.dnalc.org/resources/3d/DNAReplicationBasic_w_FX.html
• Transcription
http://www.dnalc.org/resources/3d/TranscriptionBasic_withFX.html
• Translation
http://www.dnalc.org/resources/3d/TranslationBasic_withFX0.html