CHAPTER 8 MEMBRANE STUCTURE AND FUNCTION

1. CHAPTER 8MEMBRANE STUCTURE AND FUNCTION How things get into and out of the cell Active Transport النقل النشط

2. Active transport is the pumpingضَخ of solutes against their concentration gradients عكس الإنحدارالتركيزى • This active transport requires metabolic energy via ATP. • Active transport is critical بالغ الأهمية for a cell to maintainتحافظ its internal concentrations التركيزات الداخليةof small molecules. • Active transport is performed يتم by specific proteins embedded موجودةin the membranes (transport protein). Fig. 8.14b, Page 148

3. T. protein High conc. ofK+ Low conc. ofK+ Low conc. ofNa+ High conc. ofNa+ 1)- Small molecules (Ions) Outside the cell Na Na Na • The sodium-potassium pump مضخة الصوديوم والبوتاسيومactively maintains the gradient of sodium (Na+) and potassium ions (K+) in the cell. • The sodium-potassium pump uses the energy الطاقةof one ATP to pump 3 Na+ ions out and 2 K+ ions in. Na Protein molecule Na Na ATP Cellular membrane Na 1ATP 2 Inside the cell 3

4. Fig. 8.15, Page 149

5. Two roles of membrane protein Fig. 8.16, Page 150 Both diffusion and facilitated diffusion are forms of passive transport of molecules down their concentration gradient, while active transport requires an investment of energy to move molecules against their concentration gradient.

6. 2)- Large molecules (macromolecules)الجزيئات الكبيرة Large molecules are transported by Exocytosis and endocytosis • Large molecules, such as polysaccharidesالسكريات العديدةand proteins, cross the membrane by vesiclesأوعية. • Exocytosisالإخراج الخلوي: A vesicle is budded from ينشأ من the Golgi apparatus is moved by the cytoskeleton to the plasma membrane. When the vesicle and plasma membrane come in contact تلامس, they fuse يندمج and spill يُفرغthe contents المحتوىto the outside. 2-Endocytosisالإدخال الخلوى, a cell brings in macromolecules by forming new vesicles from the plasma membrane and include the following:

7. A)- Phagocytosisالإبتلاع الخلوى: Called “cellular eating”. The cell engulfs تـَبْلَع a particle by extending pseudopodia أقدام كاذبة around it and packaging it تـُغلفها in a large vacuole. Fig. 8.19a, Page 152

8. B)- Pinocytosis,الشرب الخلوى “cellular drinking”, A cell creates a vesicle around droplets نقاط of extracellular fluid السائل الموجود خارج الخلية. Fig. 8.19b, Page 152

9. C)-Receptor-mediated endocytosis: الإدخال الخلوى عن طريق المستقبلات المتخصصة • It is triggered تـُستـَحث when extracellular substances bind to special receptors مُستقبـِلات خاصة, on the membrane surface. This triggers the formation of a vesicle وعاء • It enables تسمح للخليةa cell to take large quantitiesكميات كبيرة of specific materials that may be in low concentrations تركيز قليلin the environmentالبيئة . Fig. 8.19c, Page 152

10. Transport Active Passive Facilitated diffusion Diffusion Large molecules Small Molecules/ions (Membrane) (Membrane) (T. protein) (T. protein) Exocytosis Endocytosis Pinocytosis Receptor-mediated endocytosis Phagocytosis Cellular eating Cellular drinking Selective eating