Transcript How does this relate to the number of amino acids?

Protein synthesis
Transcription and translation
RNA
can be
Messenger RNA
also called
Ribosomal
RNA
which functions to
mRNA
also called
Carry
instructions
rRNA
which functions to
Combine
with proteins
from
to
to make up
DNA
DNA
Ribosome
Ribosome
Ribosomes
Ribosomes
Transfer
RNA
also called
tRNA
Bring
amino acids to
ribosome
Transcription
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA
polymerase
DNA
RNA
mRNA
• Primary transcript will be edited
– Introns are removed
– Segments may be deleted or rearranged
according to instructions from other
regions of DNA
• Final version of mRNA get a “cap” and
“tail” to mark it as complete.
• Now it can leave the nucleus.
The Genetic Code
• Groups of 3 DNA nucleotides are called
triplets and each represents an amino
acid or an instruction to “start” or
“stop”.
– There are 4 nucleotides, so how many
possible combinations of 3 are there?
– How does this relate to the number of
amino acids?
– The code is redundant.
The genetic code
• When the code is transcribed to mRNA,
the groups of 3 nucleotides are called
codons.
• Each codon represents one amino acid
or a start (AUG) or stop.
– Multiple codons may mean the same thing.
The genetic code
The Genetic
Code
1. Find the 1st base
along the left side
– look only in that
row.
2. Find the 2nd base
along the top –
look only in that
column.
3. Find the 3rd base
along the right
side in the row of
the 1st base.
Translation
Messenger RNA
Messenger RNA is transcribed in the nucleus.
Phenylalanine
Methionine
Ribosome
tRNA
Lysine
mRNA
Transfer RNA
The mRNA then enters the cytoplasm and
attaches to a ribosome. Translation begins at
AUG, the start codon. Each transfer RNA has
an anticodon whose bases are complementary
to a codon on the mRNA strand. The ribosome
positions the start codon to attract its
anticodon, which is part of the tRNA that binds
methionine. The ribosome also binds the next
codon and its anticodon.
Translation, continued
The Polypeptide “Assembly Line”
The ribosome joins the two amino acids—
methionine and phenylalanine—and breaks
the bond between methionine and its tRNA.
The tRNA floats away, allowing the ribosome
to bind to another tRNA. The ribosome moves
along the mRNA, binding new tRNA molecules
and amino acids.
Lysine
Growing polypeptide chain
Ribosome
tRNA
tRNA
mRNA
Completing the Polypeptide
Ribosome
Translation direction
The process continues until the ribosome reaches
one of the three stop codons. The result is a
growing polypeptide chain.