Transcription and Translation
Getting Genetic Information
out of DNA
I.
Transcription (DNA  RNA)
A.
Background
1. DNA codes for protein production
a. cannot leave nucleus
b. must send out a “messenger”
RNA – the chemical messenger
1. differences from DNA:
a. single stranded
b. ribose sugar
c. Uracil (U) instead of (T)
B.
I.
Transcription (DNA  RNA)
B.
RNA – the chemical messenger
2. RNA’s Role...
a. get DNA code to ribosome for
protein synthesis
3. Types of RNA
a. Messenger RNA (mRNA)
1. RNA copy of DNA code
2. takes copy to ribosome
I.
Transcription (DNA  RNA)
B.
RNA – the chemical messenger
3. Types of RNA
b. Transfer RNA (tRNA)
1. transfers amino acids
(protein building blocks)
to protein construction
site (ribosome)
I.
Transcription (DNA  RNA)
B.
RNA – the chemical messenger
3. Types of RNA
c. Ribosomal RNA (rRNA)
1. structural RNA
component of ribosomes
2. Ribosomes =
rRNA and Protein
I.
Transcription (DNA  RNA)
B.
RNA – the chemical messenger
DNA | RNA
DNA
Template
A
C
T
G
–
–
–
–
U
G
A
C
RNA Copy of
DNA Message
I.
Transcription (DNA  RNA)
C.
Process of Transcription
1. Enzymes unzip DNA (just like in
replication)
2. RNA nucleotides bind to the
exposed DNA nucleotides
a. AGC TAA CCG  (DNA)
UCG AUU GGC  (RNA)
3. RNA strand breaks free, leaves
nucleus, heads to ribosome
II. Translation (RNA  Protein)
* mRNA is translated into polypeptide (protein)
*amino acids are joined together by peptide
bonds
*polypeptide continues growing until a “stop
codon” is reached
II. Translation (RNA  Protein)
A.
Translating the Message
1. every 3 letters in RNA codes for
ONE amino acid
a. 3 letters = “codon”
2.
every tRNA molecule is carrying
ONE amino acid
a. 3 exposed bases at the bottom
are called “anticodons”
II. Translation (RNA  Protein)
B.
Steps in Translation
1. mRNA binds to the ribosome
2. tRNA brings amino acid to ribosome
3. exposed mRNA codon attracts
complementary tRNA anticodon
4. mRNA and tRNA join, ribosome
holds both in place
II. Translation (RNA  Protein)
B.
Steps in Translation
5. ribosome slides down to next codon
6. the next tRNA joins, ribosome
creates a peptide bond between the
two amino acids of the 2 adjacent
tRNA molecules.
*polypeptide (protein) continues growing until
a “stop codon” is reached