本期的內(nèi)容是第十一章第一節(jié)：膜傳輸?shù)哪芰?。如果有不太明白的或者有錯誤的地方隨時來找UP主喔~ 文集本部分的參考文獻Essential Cell Biology, 5th ed. Alberts, et al. 2019. 部分內(nèi)容來自khanacademy與維基百科。

11a Membrane Transport Energetics

Membrane Transport - movement across the bilayer

????- Size: small molecules diffuse into small gaps between lipids;

????- Polarity: charged molecules must break contacts with water first;

What can cross a bilayer by itself?

????- Hydrophobic / non-polar molecules: can always enter, can be any size; Eg: O2, CO2, N2, steroid hormones, etc.

????- small uncharged polar molecules: can diffuse but slowly; Eg: H2O, ethanol, glycerol, etc.

????- Large uncharged polar molecules: too big to enter; Eg: sugars (C6H12O6), etc.

????- Ions: cannot enter, regardless of the size.

Electrochemical Gradient

????Electrical: different amounts of charges

????Chemical: different concentrations

????In the process shown in the picture below:

????Start with sodium ions on the left side of the container and not on the right. In the end, the sodium ions will be evenly distributed throughout the container.?

????Net movement follows the gradient, but random movement for each molecule;?

????Entropy is increasing throughout the process, and this is a downhill reaction with a negative ?G.

Ion flow can be used as an Energy Source for the cell.

????Ion gradients in human cells: unequal distributions, see the picture below:

????- The cell is more negative inside;?

????- There are about 30 times more of Na+ ions outside of the cell; when Na+ ions move into the cell, they move down the concentration & electrical gradients?

????- very favorable to move in Na+, can be used to power other reactions.?

????- There are about 30 times more of K+ ions inside of the cell; when K+ ions move out of the cell, they move down the concentration gradient but up the electrical gradient;

????- little favorable to move out K+, cannot be used to power other reactions.?

????- The pH outside of the cell is higher, so there are more H+ inside the cell.

????- Ca2+ is very low concentration in the cell cytoplasm. It has high concentrations outside the cell and stored in the ER.?

????- Anions: to balance cations, but not balanced out: voltage across the membrane - attracts positive ions towards the inside of the cell & attracts negative ions towards the outside of the cell.

本次內(nèi)容到此結(jié)束，感謝閱讀！下一期內(nèi)容將開始講述膜通道與膜轉(zhuǎn)運蛋白。

作者：離久-張所長