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RNA
• Stands for “Ribose Nucleic Acid”
• Single stranded
• Contains a ribose sugar
• Uracil instead of thymine, so
adenine bases with uracil
RNA’s Purpose
• To take information on how to
build a protein and assemble
amino acids accordingly
• How?: Assembles amino acids
in a long chain which is used to
code for proteins
3 Types of RNA
• mRNA: Messenger RNA – brings
information from the DNA in the nucleus
to the cytoplasm
• rRNA: Ribosomal RNA – clamp onto the
mRNA and use it to assemble the amino
acids in the correct order
• tRNA: Transfer RNA – transports the
amino acids to the ribosome to be
assembled into a protein.
Transcription
• Process in the cell nucleus when
enzymes make an RNA copy of a
DNA strand
• Same process as DNA replication;
with some differences:
• RNA molecule is single-stranded (rather
than double stranded in DNA)
• Uracil instead of Thymine. So in RNA
Adenine binds with Uracil
Transcription…
• Where it takes place:
• Prokaryotic cell – in the
cytoplasm
• Eukaryotic cell – in the nucleus,
then it moves to the cytoplasm
Transcription
DNA
backbone
mRNA
DNA
backbone
We know that amino acids
are the building blocks for
proteins …
But how do we get amino
acids from mRNA?
The Code
• Biochemists started to break the genetic
code when they realized that 3 nucleotides
code for an amino acid!
– This is known as a CODON
• Amino acids are considered the code that
converts the language of mRNA to our
proteins
The Code….
• 20 amino acids total
• 64 different mRNA codons in the genetic
code
• All organisms have the same genetic
code for amino acids and proteins
• Important Codons:
1. Start: AUG
2. Stop: UAA, UAG, & UGA
Amino Acid Chart
How to Read the
Amino Acid Chart
• Start on the left side with the first
letter of the codon
• Then find the second letter of the
codon along the top of the chart
• Then, on the right side, find the
corresponding last letter of the codon
You Try It!!
• Which amino acid
do the following
codons code for?
– CUU
– GAC
– UAC
– CAU
– UAG
– UGA
• Which codons
would code for the
following amino
acids?
– Methionine
– STOP
– Glycine
– Arginine
– Histine
– Proline