Cell Membranes

1. Cell Membranes

2. Cell (plasma) membrane • Functions • separate cell from its environment • regulate flow of materials in and out of cell (“gate keeper”) • maintain homeostasis within the cell IN food - sugars - proteins - fats salts O2 H2O OUT waste - ammonia - salts - CO2 - H2O products - proteins

3. Building a Cell Membrane • The cell membrane is made of phospholipids. • A phospholipid is a specialized lipid made of a phosphate “head” and two fatty acid “tails.” • The phosphate head is polar and is attracted to water. (hydrophilic) • The fatty acid tails are nonpolar and are repelled by water. (hydrophobic)

4. Because there is water inside and outside the cell, the phospholipids form a double layer called the phospholipid bilayer. • The nonpolar tails, repelled by water, make up the interior of the lipid bilayer. • The polar heads are attracted to the water, so they point toward the surfaces of the lipid bilayer. One layer of polar heads faces the cytoplasm, while the other layer is in contact with the cell’s immediate surroundings.

5. inside cell outside cell Building a Cell Membrane • Membrane is made of special kind of lipid • phospholipids • “split personality” • Membrane is a double layer • phospholipid bilayer “attracted to water” Head - Polar end Tail – Nonpolar end “repelled by water”

6. Semi-permeable membrane • Cell membrane controls what gets in or out • Need to allow some materials — but not all — to pass through the membrane • semi-permeable • only some material can get in or out So what needs to get across the membrane? lipids aa O2 H2O salt sugar waste

7. inside cell outside cell Crossing the cell membrane • What molecules can get through the cell membrane directly? • fats and oils can pass directly through lipid salt waste but… what about other stuff? sugar aa H2O

8. How do you build a semi-permeable cell membrane? • Need to make “doors” through membrane • protein channels allow substances in & out • specific channels allow specific material in & out • H2O channel, salt channel, sugar channel, etc. inside cell H2O aa sugar salt outside cell waste

9. Protein channels • Proteins act as doors in the membrane • channels to move specific molecules through cell membrane • known as transport proteins – embedded in membrane

10. Other Components • Other proteins – • Receptors – transmit signals to inside of cell • Enzymes • Cell surface markers – have carbohydrate attached • Carbohydrates – attached to proteins on outside of cell membrane • Cholesterol – nonpolar lipid that prevents tails from sticking • Allows membrane to remain fluid

11. Plasma Membrane

12. Fluid Mosaic Model • phospholipid bilayer behaves like a fluid more than it behaves like a solid. • phospholipids in the bilayer create a “sea” in which other molecules can float. • described by FLUID MOSAIC MODEL • Fluid = lipids move side-to-side • Mosaic = other molecules embedded in the membrane

13. Nucleus • Controls most of the cell processes and contains the hereditary information (DNA) • Parts of the nucleus • Chromatin and chromosomes • Nucleolus • Nuclear envelope

14. Chromatin • The granular material visible within the nucleus • Consists of DNA bound to proteins • Chromosomes • Chromatin condenses into chromosomes before cell division • Contain genetic information • Nucleolus • Assembly of ribosomes begins here

15. Nuclear envelope • Double membrane layer surrounding the cell • Has pores which allows material into and out of the cell

17. Mitochondria • “Powerhouse of the cell” • Cellular respiration occurs here to release energy for the cell to use • Bound by a double membrane • Folds of inner membrane called cristae • Has its own strand of DNA

18. Ribosomes • Site of protein synthesis • Composed of RNA and protein • Found attached to rough ER or floating free in cytoplasm • Produced in a part of the nucleus called the nucleolus

19. Endoplasmic Reticulum • A.k.a. “ER” • Connected to nuclear membrane • Highway of the cell • Rough ER: studded with ribosomes; it makes proteins • Smooth ER: no ribosomes; it makes lipids

20. Golgi Apparatus • Looks like a stack of plates (system of flatten sacs) • Stores, modifies and packages proteins • Molecules transported to and from the Golgi by means of vesicles • Small , spherical shaped sacs that are surrounded by a membrane.

21. Lysosomes • Small organelles filled with digestive enzymes • Function: break down lipids, carbohydrates and proteins from food particles • Break down old organelles and other cellular debris

22. Protein Synthesis • The rough ER, Golgi apparatus, and vesicles work together to transport proteins to their destinations inside and outside the cell.

24. cytoplasm jelly-like material holding organelles in place nucleolus produces ribosomes lysosome food digestion garbage disposal &recycling vacuole & vesicles transport inside cells storage nucleus protects DNA controls cell chromosomes DNA centrioles cell division ribosomes builds proteins mitochondria make ATP energy from sugar + O2 Golgi apparatus finishes, packages & ships proteins cell membrane cell boundary controls movementof materials in & out recognizes signals ER helps finish proteins makes lipids & membranes