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生命為什麼如此複雜?
周成功
102年10月1日
這些無數繁複的生命形式從何而來 ?
Charles Darwin
(Feb. 12, 1809 – Apr. 19,1882)
“Probably all the organic beings which have
ever lived on this earth have descended from
some one primordial form, into which life was
first breathed,”
Darwin: On the Origin of Species (1859)
天生萬物都來自一個共同的祖先?
是的!我們都來自一個共同的祖先!
生命怎麼變的如此複雜?
生物演化的三步曲:變異、遺傳與天擇
生物演化的三步曲:變異、遺傳與天擇
遺傳資訊 (genotype) 的變異
變異
蛋白質胺基酸序列的改變
遺傳
蛋白質結構與功能的改變
生命表徵 (phenotype) 的改變
對環境改變時的適應力:天擇
Most diverse single cell organism – procaryotic cells
First cellular life form over 3.5 billion years ago
典型的細菌
1 µM
Prokaryotes lack nuclear membrane
nucleoid
Circular double strand DNA is anchored on the inner membrane as the origin of
replication
Classification of bacteria by its shape
細胞的演化
•第一個原核細胞 (prokaryotes)
–結構簡單、功能原始
•演化的第一步
– 如何對抗水的滲透壓?
–如何從環境中取得食物?
所有原核細胞都配備堅固的細胞壁
and cannot live without it!
Peptidoglycan
Classification of bacteria by dye staining
細菌對抗細菌 — 抗生素
•抗生素
–生物所合成(並分泌),殺死或抑制起它生物的
物質;大都是二級代謝物(一級代謝的衍生物)
–已知約六千種
•約三分之二為鏈黴菌所產生
•生產菌也會對自己的產生的抗生素敏感
–抗藥性基因與合成基因在一起,一起表現
–抗藥性基因擴散到它類細菌(特別是後抗生素期
的病源菌)
Antibiotic Targets
Strategy to Escape
• Antibiotics resistant gene
– Digesting enzyme
– Increase exporter protein
• To change the structure of targets
– Ribosome (rRNA and ribosomal proteins)
– RNA polymerase
• To take alternative way to increase strength of
the cell membrane
– Lost cell wall
– Cytoskeleton under the plasma membrane
– Increase ability to EAT!
Any bacteria produce a novel enzyme can cleavage
this peptide bond will survive!
Eucaryotic Cells
1. Contains structure-forming molecular
complexes (a cytosceleton) responsible for
movements: actin and myosin, their
accompanying regulators, and tubulin.
2. Their genetic information is located on several
molecules of DNA (chromosomal equivalents)
and is stored in a functional unit enclosed by a
membrane, the nucleus.
Eucaryotic Cells (Continue)
3. Mitosis, a mechanism for the distribution
of chromosomes and chromosome
equivalents developed with the help of
tubulin.
4. The ability to take up organic material
led also to their taking up smaller cells, a
process called phagocytosis.
No life can live alone! Compete or cooperation!
Symbiosis!
Origin of eukaroyte
細胞的演化
•第一個原核細胞 (prokaryotes)
–結構簡單、功能原始
•演化的第一步
– 如何對抗水的滲透壓?
–如何從環境中取得食物?
誰為原始生命提供了足夠的食物?
•環境中的有機分子 (葡萄糖)。
•其他有機分子構成的生命體。
•環境中的食物總有用完的一天
•然後呢?
地球生命史中最重要的一次
「基因改造」(約25億年前) !
「僅此一次的偶發事件」
光合作用產生氧氣: 地球上最
嚴重的一次「空氣污染」 !
氧:厭氧生物的第一號殺手!
找地方躲起來!
消滅清除它!
自由基: superoxide dismutase — aerobes and aerotolerant
anaerobes
過氧化物:catalase (nearly all organisms), peroxidase (in
some)
聰明地利用它!
「光合作用」帶來地球生命史上第一
次「工業革命」 (約18-20億年前) :
演化出能控制氧化燃燒產生能量的生
命形態!
細胞的演化
•第一個原核細胞 (prokaryotes)
–細菌
–古生菌
• 15-20 億年前
– 一個全新的生命型態 – 真核細胞eukaryotes
複雜的真核細胞如何從簡單的原核生物(細菌)演化出來?
1, 柔軟的細胞膜 (細胞壁的消失)
2, 複雜的胞器結構 (細胞核、粒腺體等)
原核細胞如何演化成真核細胞?
Prokaryotes
(Bacteria)
Eukaryote
(human phagocyte)
“engulfing” bacteria
細菌對抗細菌 — 抗生素
• 生物所合成(並分泌),殺死或抑制其他生物
的物質。
• 已知約六千種。
• 盤尼西林:抑制細胞壁的合成。
• 如何對抗?
– 抽水機
– 製造分解抗生素的酵素
– 不要細胞壁如何?
• How to live without cell wall?
在細胞膜下由骨架蛋白形成的網狀結構支撐:
柔軟的外套,有什麼好處?
DNA
infolding of
plasma
membrane
柔軟的外套:細胞核的形成?
F: food vacuole
L: lysosome
柔軟的外套:吞噬作用(phagocytosis)
整廠輸出的「基因改造」:
吃掉它, 不如共生互利!
共生得到了一個新的生命型式:能利用氧的真核細胞!
共生得到的另一個生命型式:能行光合作用和利用氧
的真核細胞!
Symbiosis Within a Modern Cell
Chlorella, the green, photosynthetic, single-celled algae living
symbiotically within the cytoplasm of the Paramecium.
Methanococcus jannaschii
•古生物
•嗜熱、耐壓、生產甲烷(methane)
•生活在無陽光、無氧氣、無有機物質的深
海中
The third domains — Archeae
• Originally based on rRNA sequences
– Carl Woese
• Bacteria-type morphology and yet different
inside
– Genetic system (Replication, transcription,
translation) - Eukaryotic-like
– Metabolic system - bacterial-like
Structure of ribosome
Eubacteria
Archaeabacteria
Eukaryotes
Tree of life
(based on rRNA sequences)
協力廠群的「基因改造」
多細胞生物的誕生---結合與分工
多細胞生物的特質
• 細胞間的結合 (Association)
– 黏合蛋白還是堅固的細胞壁
• 細胞間的分工:分化 (Differentiation)
– 溝通與協同
– 消化與輸送
– 移動與支撐
– 防禦與保護
• 生殖 (Reproduction)
• 體型的發育(Pattern development)
在這裡還有那一類的多細胞生物沒有被提到?
生命為什麼如此複雜?
Part 2
周成功
101年10月4日
The private life of plants-The seeds of a dandelion begin their flight(p17)
The private life of plants-South African ants hauling the seed of a plant down
into the underground nest, in order to eats its coating(p24)
The private life of plants-The fearsome seed-pod of the African grapple plant (p23)
Storage root
Transverse
section
of root
2-mg phloem
fragments
Fragments
cultured
in nutritive
medium
Free cells in
suspension
A View of Life-fig 8-3 (p199)
“Embryoid”
from
cultured
free cells
Plantlet
Flowering plant
•One hypothesis for origin of animals from a flagellated
protist suggests that a colony of identical cells evolved into
a hollow sphere.
•The cells of this sphere then specialized, creating two or
more layers of cells.
早期動物進化的一些關鍵步驟
Fossilized animal embryos from Chinese sediments 570
million years ago.
Burgess Shale
Burgess Shale Fossils
copyright (c) 1995
by Andrew MacRae,
Anomalocaris - an arthropod-like predator
Burgess Shale Fossils
Olenoides serratus - a
trilobite group of
extinct Arthropods).
Trilobites were the
most successful
Cambrian group.
copyright (c) 1995
by Andrew MacRae,
Burgess Shale Fossils
=
Pikaia - a Burgess
Shale
fossil
from
copyright
(c) UCMP,
530 mya is the
first known Chordate.
The ventral nerve cord
is a precursor to the
vertebrate backbone.
Tree of life
• Unicellular or
multicellular
• Ancestors of
multicellular
Thank you for your attention!
在地球上生命的誕生與演化:
一個偶發的事件?還是一個必然的結局?
Typical protein
N = 100-300
What is the chance to arrange 100 amino acid with correct
sequence into a protein with right structure and function?
在地球上生命的誕生與演化:
一個偶發的事件?還是一個必然的結局?
• Monod: Chance and Necessity 1971
• 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!
在不可能的物理世界中,複雜的
生命如何可能誕生?
• 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!
生物學:一亇帶着歷史經驗的科學
“Any living cell carries with it the
experiences of a billion years of
experimentation by its ancestors”
“ A physicist looks at biology”
Max Delbruck, 1949
"Nothing in biology makes
sense except in the light of
evolution."
T. Dobzhansky 1900 - 1975.
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