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Protein Synthesis
The code must be carried from the
nucleus to the ribosomes of the
cell.
• When a specific protein is needed the cell
must make the protein through protein
synthesis – occurs in ribosomes
• DNA can not leave the nucleus of the cell
• Code must be carried from nucleus
through the cytoplasm to ribosomes
• RNA carries DNA’s instructions
• RNA is a link between DNA and proteins
• RNA differs from DNA in 3 different ways
– Ribose sugar
– Has uracil instead of thymine
– Single stranded structure
• Two parts to protein synthesis:
– Transcription
– Translation
replication
transcription
translation
Transcription
• Copies DNA to make a strand of mRNA.
• DNA code is transferred out of nucleus
and into cytoplasm through our messenger
RNA.
• Chemical signals turn gene for a specific
protein on.
• Enzymes attach to DNA at the gene’s
location and unzip only where that gene is
on the DNA.
– DNA
A
T
C
G
RNA
U
A
G
C
• Nucleotides of RNA bond together, form
single strand of RNA and peels away from
DNA.
• DNA zips back up.
• RNA molecule is called mRNA or
messenger RNA.
DNA
• mRNA leaves the nucleus and goes
through nuclear membrane into the
cytoplasm of the cell.
RNA
Replication and Transcription are
similar but different
• Transcription and replication both involve
complex enzymes and complementary base
pairing.
• The two processes have different end results.
– Replication copies
all the DNA;
transcription copies
a gene.
– Replication makes
one copy;
transcription can
make many copies
one
gene
growing RNA strands
DNA