1. CH 12.3
RNA & Protein Synthesis

2. Genes are coded
DNA instructions
that control the
production of proteins
within the cell…

3. …by copying the nucleotide sequence of DNA into RNA: ribonucleic acid!
…just how are those
instructions decoded???
Step 1:
…by copying the nucleotide
sequence of DNA into
RNA: ribonucleic acid!

4. 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.

5. Types of RNA
Messenger RNA

6. Messenger RNA
Carries copies of gene instructions (to synthesize proteins out of amino acids) from DNA to the rest of the cell.

7. Ribosomal RNA Proteins are assembled
on ribosomes, which are made up of many
proteins as well as ribosomal RNA.

8. Transfer RNA
Transfer RNA delivers each amino acid coded for by messenger RNA to the ribosome for protein
assembly.

9. Transcription
…In the nucleus, part of the nucleotide sequence of DNA is copied into a complementary sequence of RNA.

10. • 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.

11. 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!

12. 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.

13. 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.

14. 64 possible codons (4 bases3)
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.
…some amino acids
can be coded for
by more than one
codon…
…can you
give an example?

15. 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:
U C G - C A C - G G U
The codons represent different amino acids:
U C G - C A C - G G U
(Serine - Histidine – Glycine)

16. 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…

18. Transcription AND Translation!

20. Videos for Review Replication
Transcription
Translation