CELL STRUCTURECELL STRUCTURE((細胞的結構細胞的結構 ))

A. Terms

• 1. Cell - the basic unit of structure • and function in living organisms.• 2. Cytology - the study of cells, • especially by microscopy.• 3. Light microscope • 4. Electron microscope

Cell Structure• Cell wall ( 細胞壁 )• Cell membrane ( 細胞膜 )• Protoplast ( 原生質 )- the living contents within the cell: nucleus ( 細胞核 ) and cytoplasm ( 細胞質 )

Cell membrane ( 細胞膜 )• Chemical

components :consists of 60% protein (蛋白質 ) , 35% phospholipid (磷脂 ) and 5% polysaccharides (多糖 )

• Two models:Unit membrane model(單位膜模型 )

Fluid mosaic model (流體鑲嵌模型 )

The Structure of Cell membrane

Fluid mosaic model ( 流體鑲嵌模型 ). a three-layered ( trilaminar 三層 ) structure

        - Hydrophobic tails of two layers of phospholipid molecules point inward to form a phospholipid bilayer (磷脂分子雙層 ) , while the protein molecules is embedded in the phospholipid bilayer (嵌於磷脂分子之間 ) or transmembrane (跨膜 ).

 Fluidity (流動 ): due to the lateral movement (橫向 ) of phospholipid molecules.•  Mosaic(鑲嵌 ) : protein molecules are interspersed

(散佈 ) among phospholipid molecules. •  

Under electronic microscope

• The upper and lower darker regions in the 3 layered image of cell membrane corresponds to the_______ molecules and __________ portions of phospholipids whereas the middle light region corresponds to the ____________ tails of the phospholipid bilayer.

Protein molecule• The protein molecules were in form of g_________

protein which can be embedded in the phospholipid molecules or transmembrane.  

• (1) membrane g___________ - as markers, recognition sites 

• (2) ________ proteins – transmembrane, have ________ / ionic channel that allows __ molecules and ions to pass through. They are for facilitated diffusion. 

• (3) ________ proteins - for facilitated diffusion•  • (4) membrane bound proteins - single enzyme or

aggregated to form multi-enzyme complexes • to speed up chemical reactions.

Function of cell membrane• (i) Compartmentalization ( 分室作用 )• (ii) Control exchange of substances between two sides of

membrane by selective / differentiate permeability ( 控制物質進出 )• (iii)Site of membrane-bound enzyme reaction ( 提供酶反應的位置 )• (iv) For recognition of stimuli ( 記認刺激 ), e.g insulin

( 胰島素 )• (v)For cell identity e.g. antigen • (vi) For endocytosis ( 胞吞 ) and exocytosis ( 胞吐作用 )• Provides electrical insulation ( 提供絕緣作用 )

How these components affect the permeability to different substances

( 這成分如何影響不同物質的透性 )• Phospholipid bilayer allows lipid soluble

molecules / non-polar molecules to diffuse more readily across membranes

• ( 雙磷脂層讓脂溶分子 / 非極性分子易於擴散過膜 )

How these components affect the permeability to different substances

(這成分如何影響不同物質的透性 )

• Hydrophobic inner zone forms a physical barrier to polar molecules which are polar / hydrophilic / ions ( 疏水的內層對極性的 / 親水的分子 / 離子形成物理屏障 )

• Channel proteins ( 通道蛋白 / 蛋白質形成孔道 , 讓離子 / 極性分子擴散 )

How these components affect the permeability to different substances

(這成分如何影響不同物質的透性 )• Carrier proteins / proteins bind with specific

molecules and bring them to the opposite side of membrane ( 載體蛋白 / 蛋白質與特定分子結合 ,將其運至膜的另一邊 )

• Carrier proteins facilitate diffusion of some molecules e.g glucose ( 載體蛋白 將某些分子易化擴散 , 如葡萄糖

• Carrier proteins allow active transport of molecules ( 載體蛋白容許分子進行主動運輸 )

Nucleus ( 細胞核 )

• 1. In all eukaryotic cells , bounded by nuclear

• membrane (envelope) • 2. Contains chromatin ( 染色質 ) and

nucleolus ( 核仁 ) 3. DNA + histone short and thickened chromosomes

Structure of Nucleus ( 細胞核的構造 )

• Nucleolus is a conspicuous rounded structure inside the nucleus. There may be one or more in number, its function is to make ribosomes ( 核糖體 ) by combining rRNA with proteins.

Function of Nucleus ( 細胞核的功能 )

• Controls all the activities and functions of the cell ( 所有細胞活動 ), cell division ( 細胞分裂 ) and carries genetic information for heredity ( 盛載遺傳訊息 )

• Stores genetic material e.g. DNA• Site of synthesis of rRNA (formation of

ribosome[ 核糖體 ]) and mRNA (for protein synthesis[ 蛋白質製造 ])

Nuclear membrane ( 核膜 )• Double membrane (雙層 )• Similar structure as cell

membrane• Continuous with endoplasmic

reticulum(E.R.) (與內質膜相連 )• With nuclear pores (核膜孔 )

for exchange of materials between nucleus and cytoplasm

Nucleoplasm

• Nuclear sap • Gel-like ( 黏稠性液體 )• Denser than cytoplasm • Contains proteins, enzymes and RNAs

Chromatin ( 染色質 )

• Consists of DNA and protein ( histone, 組蛋白 )• Condense to rod-shape chromosome ( 緊縮成棒狀染色體 ) just prior to nuclear division ( 核分裂前 )• Carry genetic materials which determine

organisms’ characteristics ( 特徵 ) and transmit these characteristics to next generations ( 遺傳至下一代 )

Nucleolus ( 核仁 )

• Composed of DNA mainly• Act as the manufacturing site of ribosomal rRNA

(rRNA) and ribosomes ( 核糖體 )

Ribosomes ( 核糖體 )• Particles synthesis in

nucleolus and then pass through the nuclear pores to the cytoplasm

• Made of protein and rDNA• The site for protein synthesis

( 合成蛋白質的地點 )• Made of two subunits ( 亞基 )• Non-membrane bound

Endoplasmic Reticulum ( E.R.)( 內質網 )

• Membrane-bound structure ( 膜包圍 )• A system of parallel flattened membrane-bounded

sacs ( 扁平片狀囊 ) called cisternae ( 瀦泡 / 池 ) • Continuous with the outer membrane of the

nuclear envelope• Act as an intracellular transport system ( 胞內運輸系統 )• There are two types of E.R - Rough ER ( 粗糙內質網 ) and smooth ER ( 平滑內質網 )

Rough E.R. ( 粗糙內質網 ) • Ribosomes are attached to

its surface ( 表面附核糖體 )• Transports proteins made

by the ribosomes through the cisternae to smooth ER and then to Golgi appartus ( 高爾基體 ) for further modification ( 加工 )

Smooth E.R. ( 平滑內質網 )

• Without ribosomes attached to its surface

• Transport lipids• Synthesis of lipids and

steriod ( 類固醇 ) and glycogen metabolism ( 糖原的代謝 )

Diagram of Golgi apparatus

Golgi Apparatus• Usually located near the nucleus ( 近細胞核 )• Consists of stacks of flattened membrane bounded sacs

called cisternae and many vesicles ( 多單層膜組成的球囊和小泡 )• At one end of the stacks new cisternae are constantly

formed by fusion of vesicles pinched from smooth ER; at the other end, small Golgi vesicles ( 泡囊 ) are pinched off constantly

• Transport in vesicles of many cell materials, such as enzymes( 酶 ) from ER

• Involved in secretion ( 分泌作用 )and lysosome formation ( 形成溶酶體 )

Lysosomes ( 溶酶體 )• A spherical sac bounded by a

single membrane ( 單膜 )• Contain digestive (hydrolytic)

enzymes ( 水解酶 )• Intracellular digestion ( 胞內消化 )of food materials eg. Amoeba

( 變形蟲 )• Destroy the worn-out organelles

inside cell ( 分解衰老的細胞器 )• For self-destruction of cells in

developmental process ( 自體溶解 )

Mitochondrion ( 線粒體 )• Surrounded by an envelope

of two membranes( 兩層膜 ), the inner being folded to form cristae ( 嵴 / 脊膜 / 脊 )

• Contains a matrix ( 基質 ) with respiratory enzymes for the Krebs cycle ( 克雷伯氏循環 )

• Rich in cell which require large amount of energy such as sperm ( 精子 ), muscle cell ( 肌肉細胞 )

cristae

matrix

outer membrane

inner membrane

Mitochondion

• The cristae increase the surface area ( 表面積 ) for attachment of respiratory enzymes, in form of spherical stalked particles ( 球形有柄小體 ),

• In aerobic respiration, cristae are the sites of oxidative phosporylation ( 氧化磷酸化作用 ) and electron transport ( 電子傳遞鏈 )

Function of Mitochondrion

• Act as power house of a cell (site of respiration) ( 進行呼吸作用的地點 )

• The energy releasing reactions of respiration occur in matrix and on the cristae

Centrioles ( 中心粒 )

• Adjacent to nucleus, outside nuclear membrane• Internal structure of a centriole is similar to that of

basal body of a cilium ( 纖毛 ), with 9 micotubules ( 微管 )

• Forming the spindle fibres ( 紡錘絲 ) and microtubules during nuclear division to control the separation of chromosome ( 染色體分離 )

Microtubule ( 微管 )

• Act as cytoskeleton ( 細胞骨架 ) which support the cell ( 支持細胞 )

• Involves in the movement of substances inside the cell ( 物質運動 )

• Forming the spindle fibres which involve in the separation of chromatids and chromosome

Cell wall ( 細胞壁 )• Only found in plant cells• Rigid and rather

permeable ( 通透 )• Made of cellulose ( 纖維素 )• Usually modified by

lignin ( 木質素 )• with pores which are

penetrated by plasmodesmata ( 胞間連絲 )

Function of Cell wall

• Provides mechanical support and protection of the cell

• Allows a pressure potential ( 壓力勢 / 壓力潛能 ) to be developed which aids in support

• Prevent osmotic bursting ( 脹破 )of the cell

Chloroplast ( 葉綠體 )• Large plasmid ( 質粒 )

containing chlorophyll ( 葉綠素 ) which absorb light for photosynthesis

• Bounded by two membrane ( 兩層膜 )

• Consists of chloroplast envelope, stroma ( 基質 ), lamella ( 薄片 ) and granum ( 基粒 )

Vacuole ( 液泡 )

• Absence or small in animal cells• Common and large in plant cells• The enclosing membrane is called

tonoplast ( 液泡膜 )• Contain the internal cell sap ( 細胞液 ) which is a concentrated

solution consists of water, sugar, salts, fat, oils, proteins and pigment( 色素 )

Function of Vacuole

• Store various substances eg. Food and wastes

• Maintenance of turgor ( 硬脹 ) for support• Contain hydrolytic enzymes ( 水解酶 ) to

acts as lysosomes during life and cause autolysis ( 自體溶解 ) after death

Plant Histology ( 組織學 )

• Parenchyma ( 薄壁組織 )• Collenchyma ( 厚角組織 )• Sclerenchyma ( 厚壁組織 )• Xylem Tissue ( 木質部 )• Phloem Tissue ( 韌皮部 )

Parenchyma ( 薄壁組織 )

• Plant cells with thin cell wall and living protoplasm

• Roughly isodiametric( 等徑 ) (spherical, 圓形 ) with intercellular spaces

• Found in cortex ( 皮層 ) and pith ( 髓 ) of stems and root, mesophyll of leaves ( 葉肉 ) and packing tissues in xylem and phloem

Function of Parenchyma• Act as packing tissues between more specialized tissues• Turgidity ( 硬脹度 ) of these cells can provide support ( 支持作用 ) in herbaceous plant ( 草本植物 )• Store food ( 貯藏食物 )• Intercellular air spaces ( 細胞間隙 ) allow gaseous exchange• Metabolically active for biochemical processes such as

photosynthesis and synthesis ( 代謝活動較活躍可進行光合作用及合成 )• Their cell walls are important pathway for the water and

mineral salts through the plant (for absorption of water)

Leaf epidermis ( 葉表皮 )• Protective tissue[保護組織 ] (usually single layer)• Modified from parenchyma [由薄壁細胞而形成 ]• Elongated cell with thin cell wall [長形 ]• Mainly colourless (except guard cells[保衛細胞 ])• Compact in arrangement without intercelluar space (排列緊密沒有細胞間隙 )• Presence of stoma (氣孔 ) for gaseous exchange(氣體交換 )• Presence of cuticle ( 角質層 )to reduce transpiration

(蒸騰作用 )

Collenchyma ( 厚角組織 )• Characterized by the deposition of extra

cellulose at the corners of the cells so have thickening cell wall of their corners (只在角隅處加原 )

• They are living cells ( 有生命 )• Cell are capable of stretching ( 有彈性 )• Found in regions beneath the epidermis

of stem (hypodermis[ 下皮 ]) and near the vascular tissues, eg, midrib of leaves [ 葉的中脈 ]

• Mechanical tissue for support ( 支持組織 )

Sclerenchyma ( 厚壁組織 )

• Plant cells with evenly thickened cell wall (均厚的細胞壁 ) which is usually lignified ( 木質化 )

• They are dead cells (死細胞 )• Support the cells• There are two types: fibres

( 纖維 ) and Sclereids (石細胞 )

Fibre ( 纖維 )

• Long narrow cell shape with tapering ends ( 細長 , 兩端尖銳 ), wall with few pits

• Found in cortex( 皮層 ), pericycle(柱鞘 ) , vascular tissues, surrounding vascular bundles ( 維管束 )

Sclereids (石細胞 )

• Short and relatively spherical in shape ( 圓形 )• Found in almost everywhere in plant body,

especially in cortex, phloem of stems and roots (根及莖的韌皮部 ), in fruit wall (果皮 ) and seed coat (種皮 )

• Act as main cell type for mechanical support (機械性的支持作用 ) and protection (保護 )

Xylem ( 木質部 )

• Consists of tracheary elements (tracheids[ 管胞 ], vessels[導管 ]), fibres ( 纖維 ) and parenchyma ( 薄壁細胞 )

• Tracheary elements are dead and empty cells ( 中空 ) for transporting water and support

Tracheids ( 管胞 )• Narrow elongated (長圓筒形 ) cell with finely

tapering ends ( 兩端尖銳 ) , without protoplasm at maturity, with heavily lignified ( 木質化 )and pitted secondary cell wall (次生細胞壁 )

• Passage of water from cell to cell is facilitated through pit-pairs which allow lateral transport of water

• Act as the only water conducting elements in gymnosperms (裸子植物 ) and primitive vascular plant; (具有維管組織的低等植物 ) small amount in angiosperms (開花植物 )

Xylem vessel ( 木質導管 )

• Long , tubular( 管狀 ) and hollow [ 中空 ] (end walls broken down 端壁 )

• Without protoplasm at maturity• Join each other at end walls to form

longitudinal conducting tubes ( 細胞首尾相連接形成導管 )• Shorter, greater in diameter than tracheids

Xylem vessel

• Water moves from cell to cell • Cell wall lignified ( 木質化 ) and

strengthened to prevent collapse (塌陷 )• More specialized for water conducting than

tracheids ( 較管胞更專門於輸送水 )• Only present in angiosperms (只出現在開花植物 )

Thickening of secondary wall

• Annular thickening ( 環狀加厚 )• Spiral thickening (螺紋加厚 )• Recticulate thickening ( 網紋加厚 )• Pitted thickening (紋孔加厚 )

Diagram of Phloem ( 韌皮部 )

Phloem Tissue ( 韌皮部 )

• Sieve tube elements (篩管分子 ) for conduction of food (e.g. sucrose 蔗糖 )

• Sieve tube elements are elongated cells, end walls (端壁 ) are modified as sieve plates (篩板 )

• Sieve tube elements have no nucleus, tonoplast, decrease in number of ER and ribosomes, with thin layer cytoplasm to facilitate the translocation of food ( 輸導作用 )

Sieve Tube Element (篩管分子 )

• Located on the end walls(端壁 ) called sieve plates (篩板 )

• Connected by sieve plates with each other to form sieve tube (篩管 )

• Present in angiosperms ( 有花植物 )• With companion cell (伴細胞 ) to help metabolic

activities ( 代謝活動 ) of the sieve tube element and translocation of food (輪導作用 )

Short assignment:Discuss the structural adaptations

of xylem and phloem to their functions

Blood cell (血細胞 )

• Is a specialized connective tissue for transportation of materials and body defence (身體防衛 )

• include fluid medium (plasma 血漿 55%) and cellular constituents (red blood cells/erythrocytes [紅血球 ], white blood cells/leucocytes [ 白血球 ], platelets/thrombocytes [血小板 ])

Neurones (神經元 )

• Including cell body ( 細胞體 ) and nerve fibres (神經纖維 )

• located in C.N.S ( 中樞神經系統 )• cell body is stellate in shape• nerve fibres are protoplasmic extensions

( 原生質的伸延 ) of cell body, including dendrons (樹突 ) and axon (軸突 )

Skeletal muscle

• Innervated by the voluntary part of nervous system

• contraction is neurogenic required nervous stimulation

• contract and fatigue rapidly• attached to the skeleton• long, cylindrical with tapering or rounded ends

Functions of skeleton muscle

• for the maintenance of posture• for locomotion and movements of body

parts

Nerve

• a group of nerve fibres bound together by connective tissues lying outside C.N.S

• including sensory nerve, motor nerve and mixed nerve