微生物吸收营养物质的方式1

1、单纯扩散(simple diffusion or passive diffusion)
特点： ①扩散是非特异性的营养物质吸收方式：如营养物质通过细胞 膜中的含水小孔，由高浓度的胞外环境向低浓度的胞内扩散； ②在扩散过程中营养物质的结构不发生变化：即既不与膜上的 分子发生反应，本身的分子结构也不发生变化； ③物质运输的速率较慢：速率与胞内外营养物质的浓度差有关 ，即随细胞膜内外该物质浓度差的降低而减小，直到胞内外物 质浓度相同； ④不需要载体参与； 扩散是一个不需要代谢能的运输方式：因此，物质不能进行逆 浓度运输。
Comparison of passive and active transport.
Legend:If uncharged solutes are small enough, they can move down their
concentration gradients directly across the lipid bilayer itself by simple diffusion. Examples of such solutes are ethanol, carbon dioxide, and oxygen. Most solutes, however, can cross the membrane only if there is a membrane transport protein (a carrier protein or a channel protein) to transfer them. As indicated, passive transport, in the same direction as a concentration gradient, occurs spontaneously, whereas transport against a concentration gradient (active transport) requires an input of energy. Only carrier proteins can carry out active transport, but both carrier proteins and channel proteins can carry out passive transport.
促进扩散(facilitated diffusion)
特点：在促进扩散过程中 营养物质本身在分子结构上也不会发生变化
不消耗代谢能量，故不能进行逆浓度运输
运输的速率由胞内外该物质的浓度差决定 需要细胞膜上的载体蛋白（透过酶）参与物质 运输
被运输的物质与载体蛋白有高度的特异性
养料浓度过高时, 与载体蛋白出现饱和效应 促进扩散的运输方式多见于真核微生物中，例如通常在厌氧 生活的酵母菌中，某些物质的吸收和代谢产物的分泌是通过 这种方式完成的。
可以进行逆浓度运输的运输方式
需要载体蛋白参与 对被运输的物质有高度的立体专一性
被运输的物质在转移的过程中不发生任何化学变化
不同的微生物在主动运输过程中所需的能量的来源不同，好 氧微生物中直接来自呼吸能，厌氧微生物主要来自化学能，光 合微生物中则主要来自光能 。 主动运输是微生物吸收营养物质的主要方式。
Embeded protein:
Proteins that act as carriers are too large to move across the membrane. They are transmembrane proteins. They cycle between two conformations in which a solute binding site is accessible on one side of the membrane or the other.
微生物吸收营养物质的方式
1、单纯扩散(simple diffusion or passive diffusion) 被输送的物质，靠细胞内外浓度为动力， 以透析或扩散的形式从高浓度区向低浓度 区的扩散。
Simple diffusion means that the molecules can pass directly through the membrane. Diffusion is always down a concentration gradient. This limits the maximum possible concentration of the molecule inside the cell (or outside the cell if it is a waste product). The effectiveness of diffusion is also limited by the diffusion rate of the molecule. Therefore, though diffusion is an effective enough transport mechanism for some substances (such as H2O), the cell must utilize other mechanisms for many of its transport needs.
三
Facilitated diffusion utilizes membrane protein channels to allow charged molecules (which otherwise could not diffuse across the cell membrane) to freely diffuse in a nd out of the cell. These channels comes into greatest use with small ions like K+, Na+, and Cl-. The speed of facilitated transport is limited by the number of protein channels available, whereas the speed of diffusion is dependent only on the concentration gradient.
⑤可运送的养料有限：限于水、溶于水的气体，及分子
量小，脂溶性、极性小的营养物质。
•smosis
flows towards high salt concentrations
细胞膜外
细胞膜
细胞膜内
单纯扩散模式图
促进扩散 (facilitated diffusion/transport)
营养物通过与细胞膜上载体蛋白（也称作透 过酶permease）的可逆性结合来加快其传递 速度
细胞膜外
细胞膜
恢复原构象 再 循 环
细胞膜内
ห้องสมุดไป่ตู้
结 合结 合
构 象 改 变 移位
促进扩散模式图
or active ansport
主动运输(Active transport)
在代谢能的推动下，通过膜上特殊载体 蛋白逆养料浓度梯度吸收营养物质的过 程
主动运输(Active transport)
特点：物质在主动运输的过程中 需要消耗代谢能