Biology Reference
In-Depth Information
The Cell as a
Signal Processor
(Recognizer/Receiver, Transducer, and Effector/Constructor)
1
0
Messengers ---> 2
0
Messengers -------> Signal
(
Input
)
1
/\
2
Transducing
| Proteins
| |
| |
|
5
|
3
| |
| |
6
|
4
\/
Output
<--- Gene Expression <------ Transcription
Factors
Approximate correspondence between the two figures:
1
= (19)
2
= (5) + (6) + (7) + (8) + (9)
3
= (8)
4
= (10) + (1) / (2) + (3) + (4)
5
= (12) + (13) + (14) + (15) + (16) + (17) + (18) +(19)
6
= (11) + (20)
Fig. 12.37 The living cell as a signal-transducing machinery. The overall signal transduction
process carried out by the cell can be decomposed into six major steps. Step 1
¼
transmembrane
signaling; Step 2
¼
intracellular signal processing (also called molecular computing); Step 3
¼
activation or inhibition of protein factors that bind to DNA; Step 4
interaction between
processed transcription factors and target DNA regions, including promoters, enhancers and
silencers; Step 5
¼
¼
feedback interactions between the genome and membrane receptors; and
Step 6
cell outputs, including secreted proteins and small molecules, and mechanical processes
such as cell shape changes and cell migration
¼
has many layers (i.e., digital logic, microarchitecture, instruction set architecture,
operating system machine, assembly, and problem-oriented languages (Tanenbaum
2003)), so the cell language appears to have multiple layers:
1. DNA language
¼
DNese
2. RNA language
¼
RNese
3. Protein language
¼
proteinese
4. Metabolite language
¼
metabolese
(e.g., ATP, ADP, glucose, H+, metal ions)
5. Intercellular
language
¼
intercellese
(e.g., hormones, cytokines, PGs,
ion
gradients)
Of these cell sub-languages,
proteinese
is unique because it is the only
autono-
mous (or active) language
in the sense that only proteins acting as enzymes (except
for some RNAs acting as ribozymes) can utilize the chemical free energy locked up
in small molecules such as glucose, NADH, and ATP. Therefore, we can state that
proteinese
is the primary engine of the cell language and the other sub-languages
are
secondary
and
passive
. So, to understand how the
cell language
works, it would
be essential to understand how
proteinese
is constructed and works.
Proteinese and the human language (or briefly
humanese
) are compared at five
structural levels in Table
12.18
.
