细胞生物学：叶绿体1

1、8. Chloroplasts(叶绿体叶绿体) Plastid is one of peculiar organelles in plant cells, and has many types. OUTLINE Chloroplasts- structure Protein localization in chloroplasts Chloroplasts- function inheritances of mitochondria and chloroplasts Origions of mitochondria and chloroplasts Leeuwenhoek o b s e r

2、v e d chloroplasts in algae plants after microscope was invented in 1600s. Chloroplast is the first organelle discovered by using light microscope 1.Chloroplast (Chl) Structure (1) Morphologic Structure Chl : a spherical or oval organelle with a diameter of 46 m. Each mesophyll cell: 50- 200 chlorop

3、lasts in high plants and one chloroplast in algae. The size and number of chloroplast change with growing environment, for example, the bigger and more chloroplasts are distributed over plant cells growing in full sun. (2) The number and distribution (3）The ultrastructure Outer membrane Inner membra

4、ne Intermembrane space Stroma (基质基质) T h y l a k o i d ( 类 囊 体类 囊 体 ) membrane Thylakoid space chloroplast envelope (叶绿体外被叶绿体外被) the outer and inner membrane- chloroplast envelope, and each layer of membrane is 6-8 nm thick. 1020 nm intermembrane space The outer membrane contains porins. The inner m

5、embrane: lower permeability. The enzymes relative with synthesis of glycolipid(糖脂糖脂) and phospholipid Thylakoid Thylakoid: a set of disc- like sacs (囊囊) enclosed b y a l a y e r o f u n i t membrane. l Lipid/protein is 2:3, and unsaturated fatty acid is rich (about 87%) in the lipid. l lGranum thyla

6、koid(基粒基粒 类囊体类囊体): - - - m a n y d i s c - l i k e thylakoids in stroma usually stack into a cylindrical granule- g r a n u m ( 基 粒基 粒 ) , s o these thylakoids are also called stacked thylakoids (堆积类囊堆积类囊 体体). -A granum consists of 5 3 0 g r a n u m thylakoids, and each chloroplast contains 4080 gra

7、na (基粒基粒). lStroma thylakoid (基质基质 类囊体类囊体): -Granum thylakoids elongate into flattened sacs interconnected (相 通)with adjacent granum thylakoids. -The flattened lumen (囊囊) are unstacked thylakoids(非堆积类囊体). l l Proteins relative with energy conversion: electron- transfer chain, ATP synthase. 类囊体蛋白分布类囊

8、体蛋白分布 lPhotosynthetic pigment(光合色素分子光合色素分子)：All of chlorophyll(叶绿素)and almost all of carotenoid(类胡萝卜 素), which bind with proteins, are embeded in the thylakoid membrane. lThe ratio of chlorophyll and carotenoid is 3 to 1. l l Carotenoid absorb purple light and blue light, and chlorophyll mainly abso

9、rb red light and blue light, no green light. lThe chlorophyll molecules can lead to charge separation after absorption of photons- photochemistry of chlorophyll molecules. lThe thylakoid membrane - photosynthetic membrane Stroma Space between inner membrane and thylakoid Principal component: l The e

10、nzymes relative with carbon assimilation such as ribulose-1,5-bisphosphate carboxylase (60% of all soluble proteins of stroma); lChl DNA and various enzymes of gene expression. l Some starch grains 2. Protein Localization in chloroplast The pre-proteins are transported into chloroplast under the gui

11、dance of transitpeptides (转运肽) at the N-terminus. Eight Eight small subunits of pre-RuBPRuBP carboxylasecarboxylase have have a 4060-AA transitpeptidea 4060-AA transitpeptide at the N-terminus, , which leads each which leads each small subunit into stroma. 2) Chl Function Photosynthesis(光合 作用) is a

12、process that plants, alage（藻类）, and prokaryotes(原核生 物) directly use light energy to combine CO2 and H2O into organic compounds and liberate O2. dark reaction （暗反应）（暗反应） Light reaction （光反应）（光反应） (1)light reaction:(1)light reaction: light reaction:通过叶绿素等光合色素分子吸收光能，并将光能 转化为化学能，形成ATP和NADPH的过程。 absorpti

13、on and transfer of light energy H2O photolysis Formation of ATP and NADPH electric energy conversion into active chemical energy by electron transfer Photosystem(PS-光系统光系统): A fundamental unit of absorption of light energy, consists of chlorophyll, carotenoid(类胡萝卜素类胡萝卜素), lipid and proteins. Each ph

14、otosystem consists of a photochemical reaction center （反应中心）反应中心） complex and light -harvesting complex(捕光复合 物) or antenna （天线色素）天线色素） complex. l light -harvesting complex : consisting of polypeptides bound to a large set of pigment molecules that capture light energy. -Pigment molecules: several hu

15、ndreds chlorophyll molecules per reaction center, some carotene(胡萝卜素胡萝卜素) and phylloxanthine (叶黄素叶黄素) molecules. R Reaction center complex: a complex of transmembrane proteins and pigments that lies at the heart of photosynthesis -a pair of reaction center Chla molecules -a primary donor of electron

16、 and a primary receptor of electron. -The center Chla can not only capture light energy but enable light energy into electric energy. l l According to the difference of the maximal absorption peak, reaction center pigment molecules are grouped into two categories of P700 and P680. l l Photosystems a

17、re also classed into two categories of PSI (P700) and PS (P680) -Photosystem complex (PSPS): - more than ten types of polypeptides, several types of lipids and 250300 pigment molecules (P700, A0 (a specific form of chla) ), A1(VK1), and FeS (FX, FA, FB). PSI由由LHC （1个）个） +反应中反应中 心心P700 -Photosystem c

18、omplex (PS): -PS: at less nine types of polypeptides, several types of lipids connecting closely, many kinds of pigment molecules (chla, chlb, carotenoid, a pair of pheophytin (Ph：褐藻素), P680), cytb559, and one Mn cluster. -The reaction center : the Ph pigment molecules and two relative polypeptides

19、of D1 and D2. PS 由由LHC（2个）个） +反应中心反应中心P680 primary reaction (原初反应): 指叶绿素分子从被光激发至引起第一个光指叶绿素分子从被光激发至引起第一个光 化学反应为止的过程，化学反应为止的过程，namely, absorption, transfer and conversion of light energy. H2O Mn TryZ (原初电子供体原初电子供体) P680 Ph (褐藻素) QA QB 含锰的放氧复合体含锰的放氧复合体 2H2O O2 + 4H+ + 4e- LHC PC(质体蓝素)P700 A0(chla )A1醌(

20、维生素K1)FXFAFBFd Electron transfer lPhotosynthetic electron-transfer chain (光合电子传递链):由类囊体 膜上的电子载体构成， three complexes embedded in the thylakoid membrane are asymmetrically oriented in the membrane: PS, cytb6/f complex, PSI. H2O e- P680-Ph-QA-QB reduced QB2- 2H+ QBH2 (free) e- Cytb6-f PCP700-A0-A1-FeS Fd NADP+ e- e- e- e- H+ NADPH Cytb6/f complex: Consisting of four polypeptides, cytb6 (563nm), cytf(553nm), FeS and a 17kD polypeptide o