RNA and Protein Synthesis
DNA to RNA to Protein
• Focus Questions:
– How does the message coded in the base sequence
of DNA eventually create a protein?
– How does the code get out of the nucleus?
– What happens at the ribosome that causes amino
acids to eventually join to form a protein?
One Gene One Protein
• Genes: each gene is responsible for the
production of a single protein (or part of a
protein)
– Human DNA contains over a 100,000 different genes
• Proteins: determine the structure and function
of an organism
– Polypeptides of long chains of amino acids bonded
together by peptide bonds
• Ex: Enzymes, Structural proteins
RNA
RNA:
– Sugar is ribose instead of
deoxyribose
– Has nitrogenous base
URACIL instead of
thymine (U instead of T)
• Uracil also would pair with
adenine (U-A)
– Only single stranded
3 Types of RNA
1. Messenger RNA:
(mRNA):
– Copies genetic code
from the DNA inside
the nucleus
(Transcription)
– Leaves nucleus and
goes to ribosome
where is the
message is read
(Translation)
2. Ribosomal RNA: (rRNA)
– Form the different parts of
the ribosome
3. Transfer RNA: (tRNA)
– Transfers different amino
acids to the ribosomes
where they are eventually
assembled into protein
chains
– Each amino acid is coded for
by a different triplet codon
on mRNA
– tRNA has an anticodon that
will pair up with codon on
mRNA
Translation of
Genetic Code at
Ribosome
3 types of RNA work
together
How do Genes Code for Proteins?
Transcription: (Information goes from DNA to mRNA)
• Happens in nucleus
• Enzymes unzip the portion of the DNA to be copied in
the middle of the strand
• A single stranded mRNA strand is created from the DNA
template
– Enzyme RNA polymerase helps this happen
• mRNA leaves nucleus through pores and goes to
ribosome
•
http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html
• If the DNA template strand to be copied is
• ATTGCATG
• What would be the sequence of bases in
the mRNA strand?
– Remember it has U instead of T
• Triplet Codon: set of 3 nitrogenous bases
on a mRNA strand
– Each set of 3 can code for a different amino acid
– There are 20 different amino acids
There are 64 ways you can combine the four
Nitrogenous bases in sets of 3
– AAA, GCC, ATA, ATC, GTA etc.
– Sometimes more than one codon can code for
the same amino acid
• Ex: AAA and AAG both code for phenylalanine
– 3 codons signal protein synthesis to stop
– 1 codon signals protein synthesis to start
(AUG)
Translation: (from mRNA to protein)
• Occurs at ribosomes
• Process of converting information
coded in mRNA into sequence of
amino acids
• Involves transfer RNA
– Bring specific amino acids to
ribosomes so they can be assembled
into proteins
– Has “anticodon” that matches up with
each triplet codon on mRNA
– Bottom of tRNA has anticodon triplet
Translation Process:
– 1st triplet codon of mRNa attaches to ribosome
– tRNA carrying amino acid pairs with mRNA codon
– Usually mRNA at start is AUG (“start codon”)
– mRNA slides along ribosome to next codon
– New tRNA with amino acid pairs to mRNA codon
– Amino acids get joined by enzyme by a peptide bond
– Process continues and chain of amino acids form until
a stop codon on mRNA is reached
– Protein detached from ribosome
Transcription Video: (really good watch this!!)
• http://www.hhmi.org/biointeractive/media/DNAi_transcription_vo1lg.mov
Translation Video: (really good watch this!!)
• http://www.hhmi.org/biointeractive/media/DNAi_translation_vo1lg.mov
Transcription and Translation Activity:
• Game where you make a Protein
• http://learn.genetics.utah.edu/content/begin/dna/transcribe/