Lìfe

生命的省思
周成功
陽明大學生命科學系
[email protected]
生命是什麼？
地球生命的起源?
來自外太空?
發生於地球?

無論發生地何在，問題仍舊一樣
「生命如何開始？」
「細胞的資訊系統如何形成？」




Harold Urey
1950
Stanley Miller and origin of life
The building blocks of life can be formed from inanimate environment！
生命的單元
具有遺傳系統的細胞
What is life?E. Schrondinger, 1943
Highly organized structure.
How to combat the tendency of increasing entropy in the life system?
Inherited genetic information
How to precisely copy the genetic information from generation to generation?.




自動發生
這樣複雜的結構如何可能發生？
Using physical barrier to isolate internal structure from external aqueous environment
生物有別於非生物的特點

能量的吸收與利用 – 結構的維持與更新

生命的起始：細胞的形成
建構細胞的材料
指揮細胞製備材料的指令
材料自行組合的機制


建構細胞的材料
預鑄式的製備方式
From building block to larger unit！
Why ?


Metabolic reaction network in one single cell to extract energy from the food .
Genetic program ( a set of genes or genome ) instructs the formation of such network ( hardware ) from generation to generation!
生命的單元
具有遺傳系統的細胞
生物有別於非生物的特點
資訊的處理系統 -資訊的遺傳

生命的起始：細胞的形成
建構細胞的材料
指揮細胞製備材料的指令
材料自行組合的機制


細胞
電腦
硬體
硬體
細胞像電腦？電腦像細胞？
May 21, 1953 at Cambridge
密碼系統
TGTGCCACT
ACA
CGG
UGA
C
A
T
遺傳密碼
DNA
RNA
胺基酸
摩斯密碼
-.-. .- -
C A T
貓
電腦碼
11000011 01000001 11010100
43 41 54
C A T
貓
Human Genome
- 30,000 – 40,000 genes
- 3,000,000,000 genetic codes
- 23 chromosome
- In almost every single human cells except red blood cells

生命的兩個基本面
硬體（蛋白質）
執行化學催化作用
形成組成與結構
軟體（核酸）
儲藏與複製訊息
指揮與控制硬體
這樣複雜的結構如何可能發生？
Arguments against
Boeing 747
每秒擲一次骰子，連續擲出140次6需要多久時間？
6的140次方秒，比宇宙的歷史還要久！

Argument for
問題出在什麼才叫連續？
如果中間不能出錯，一次不對，前面的努力全功竟棄！那剛才的答案就是對的！
但是如果每擲出一亇6就把它記在紙上，完成連續140次6的紙上記錄，只要花140 x 6 = 840秒!


自由碰撞的石塊，需要多久時間才能形成這樣奇特的結構？
Forever!
Solution
時間加上歷史刻痕的累積，任何特異結構的形成都是可能的。
那些特異結構会存留下，來就得看環境的淘汰或選擇了！
預先存在一亇設計家的假設是不必要的！
“Any living cell carries with it the experiences of a billion years of experimentation by its ancestors”
From “ A physicist looks at biology” by Max Delbruck, 1949
Is biology an autonomous science?
Whether and how biology differs from the physics?

The physics is the paradigm of science
Science reawakened in the work of Galileo and Newton.
Physical law was not in any way restricted in time or space nor subject to any exceptions.
The role of chance in natural processes was completely ignored.
The controlled experiment was the only respectable method.
Observation and comparison were viewed as less scientific.
How the physicist views biology?
“Postage stamp collection”
By Ernest Rutherford
“A mature physicist, acquainting himself for the first time with biology, is puzzled by the circumstance that there are no ‘absolute phenomenon’ in biology. Everything is time-bound and space-bound. The animal or plant or micro-organism he is working with is but a link in an evolutionary chain of changing forms, none of which has any permanent validity.”
By Max Delbruck
For biology-
Life was originated around 3.8 billions years ago and was restricted to the earth!
Always has exceptions.
Explanation usually were not based on universal laws but rather were pluralistic.
Two key questions in biology.
“How?” or “how come?”
“Why?” or “what for?”
What is the cause of bird migration to south in the autumn?
How?
An extrinsic physiological cause
Cold air or short daytime.
An intrinsic physiological cause
Photo- or temperature- sensor tie in with migration
Why?

A genetic cause: an acquired genetic program in the course of the evolutionary history
An ecological cause: insect eater, must migrate before the winter come.
The owl?

Prediction
Is an essential qualification for physical law!
Predict the existence of one unknown planet (Neptune) due to the abnormal movement of Uranes.
Predict the path of light would be curved when it pass through a big mass.
For functional biology: yes!
For evolutional biology: probably no!
It is meaningless to discuss the change of life form in the wild in the future!
Teleology(目的論)
From egg to adult: a process with a purpose or with a predetermined state?
Important question in biology.
Do not discuss “purpose” in physical sciences.
Does the purpose of a pebble to become smooth and round is to make it better laying down in the river bed?
Populations
For physicist: every atoms or molecules are identical.
For biologist: Every individual organisms are unique (different).
Biology: a science with evolutionary history
Future challenge in life science
Understanding of genetic program

A historically evolved genetic program coded in the DNA of the nucleus (genome program)
How the genetic program make every individual unique? (functional genomics).
How the genetic program evolved? (comparative genomics)
How the new properties emerged? (Emergence)
A whole is more than the sum of its parts
Living beings are not just piles of characters or molecules, their function depends on their organization, mutual interrelations, interactions, and interdependencies.
New properties emerge at higher levels of integration which could not have been predicted from knowledge of the lower-level components
“The genetic program is the product of a history that goes back to the origin of life, and thus it incorporates the “experiences” of all ancestors.”
From “Is biology an autonomous science?”
By Ernst Mayr 1985
"Nothing in biology makes sense except in the light of evolution."
T. Dobzhansky 1900 - 1975.