Download Figure 1. View of a hypothetical protein at three levels. (A) The

Habashi and Whitlock
A
Complete
protein
Amino acids
Magnified
view of
one
portion of
the protein
B
H
C
H
H
N
H
C
R
O
C
O
Magnified
view of
one amino
acid
Figure 1. View of a hypothetical protein at
three levels. (A) The complete protein. (B)
A magnified view of one part of the
protein, showing three amino acids linked
together by chemical bonds. (C) A
magnified view of a single amino acid,
showing how the individual atoms are
bonded together. C, carbon; N, nitrogen;
H, hydrogen; O, oxygen; R, the
composition here varies for different
amino acids.
Habashi and Whitlock
A
GENE
Transcription
B
mRNA
Translation
C
PROTEIN
Figure 2. Traditional view of the flow of
genetic information in a cell. (A) A gene is
a segment of DNA that carries the
instructions for producing a single protein.
(B) A messenger RNA (mRNA) molecule is a
temporary copy of the instructions for
making a protein. It is produced during
transcription. (C) The final protein is
produced during translation.
Habashi and Whitlock
DNA
A
mRNA
B
Figure 3. Transcription: the first step in
protein synthesis. (A) In transcription,
which occurs in the nucleus of a cell, a
gene is copied into a messenger RNA
(mRNA) molecule. (B) mRNA molecules
leave the nucleus to enter the main fluidfilled interior (cytosol) of the cell.
Habashi and Whitlock
Nucleotides
A
Amino acid #1
Amino acid #2
tRNA
w/amino
acid
B
Growing
protein
Ribosome
mRNA
Figure 4. Translation: the second step in
protein synthesis. (A) In translation, an
mRNA molecule is read three nucleotides
at a time. Each set of three nucleotides
specifies a particular amino acid. (B)
Ribosomes in the cytosol act as a
workbench for protein assembly. Transfer
RNA (tRNA) molecules deliver the
necessary amino acids one at a time.