Eukaryotic Membranes: Plasma Membrane As we discussed when we first mentioned the plasma membrane it is not as simple as pictures make it look. These membranes are complex, heterogeneous structures with different parts performing very distinct functions, and they change dynamically in response to their surroundings. As we discussed when we first mentioned the plasma membrane it is not as simple as pictures make it look. These membranes are complex, heterogeneous structures with different parts performing very distinct functions, and they change dynamically in response to their surroundings.

Eukaryotic Membranes: Plasma Membrane One theory states that the plasma membrane is a fluid mosaic (fluid mosaic model) –An everchanging image of proteins and phospholipids One theory states that the plasma membrane is a fluid mosaic (fluid mosaic model) –An everchanging image of proteins and phospholipids

Eukaryotic Membranes: Plasma Membrane The liquid portion of this mosaic is the phospholipid bilayer, which we have discussed. This is made up of lipids with two distinct parts 1.A polar hydrophilic head 2.A pair of nonpolar, hydrophobic tails The liquid portion of this mosaic is the phospholipid bilayer, which we have discussed. This is made up of lipids with two distinct parts 1.A polar hydrophilic head 2.A pair of nonpolar, hydrophobic tails

Eukaryotic Membranes: Plasma Membrane This barrier encloses the cytoplasm –Which includes all of a cell’s internal contents, including organelles (except the nucleus) The watery medium inside and the watery medium outside cause the spontaneous formation of the lipid bilayer This barrier encloses the cytoplasm –Which includes all of a cell’s internal contents, including organelles (except the nucleus) The watery medium inside and the watery medium outside cause the spontaneous formation of the lipid bilayer

Eukaryotic Membranes: Plasma Membrane In addition to the phospholipids most membranes contain some if not many cholesterol molecules –These make the lipid bilayer stronger –Less fluid –Less permeable to water soluble substances In addition to the phospholipids most membranes contain some if not many cholesterol molecules –These make the lipid bilayer stronger –Less fluid –Less permeable to water soluble substances

Eukaryotic Membranes: Plasma Membrane The diagram below shows a representation of the cholesterol molecules intersperses in the phospholipid bilayer

Eukaryotic Membranes: Plasma Membrane Beyond the cholesterol thousands of proteins are embedded with in or attached to the surface of a membrane’s phospholipid bilayer. These proteins come in many forms and perform many functions Beyond the cholesterol thousands of proteins are embedded with in or attached to the surface of a membrane’s phospholipid bilayer. These proteins come in many forms and perform many functions

Eukaryotic Membranes: Plasma Membrane Transport Proteins – regulate the movement of hydrophilic molecules through the plasma membrane Receptor Proteins – trigger cellular responses when specific molecules in the extracellular fluid, such as hormones or nutrients, bind to them Recognition Proteins – many of which are glycoproteins, serve as identification tags and cell- surface attachment sites Transport Proteins – regulate the movement of hydrophilic molecules through the plasma membrane Receptor Proteins – trigger cellular responses when specific molecules in the extracellular fluid, such as hormones or nutrients, bind to them Recognition Proteins – many of which are glycoproteins, serve as identification tags and cell- surface attachment sites

Eukaryotic Membranes: Plasma Membrane The logistics of how these proteins operate to allow and control transportation will be dealt with later in this course. For now just understand that they are there. The logistics of how these proteins operate to allow and control transportation will be dealt with later in this course. For now just understand that they are there.

Eukaryote Cells: Cell Wall The outer surfaces of the cells of bacteria, plants, fungi and some protists are covered with stiff, nonliving coatings calls cell walls. Plant Cells – cellulose (polysacharide) Fungal Cells – chitin (polysacharide) Bacterial Cells – chitin like coating The outer surfaces of the cells of bacteria, plants, fungi and some protists are covered with stiff, nonliving coatings calls cell walls. Plant Cells – cellulose (polysacharide) Fungal Cells – chitin (polysacharide) Bacterial Cells – chitin like coating

Eukaryote Cells: Cell Wall The two cells then secrete cellulose through their plasma membranes, underneath the middle lamella, forming the primary cell wall. –This process may be repeated to create the secondary cell wall, which could become thicker than the whole cell (this will be inside the primary cell wall). The two cells then secrete cellulose through their plasma membranes, underneath the middle lamella, forming the primary cell wall. –This process may be repeated to create the secondary cell wall, which could become thicker than the whole cell (this will be inside the primary cell wall).

Eukaryote Cells: Cell Wall What are the functions of cell walls? –Support and protect otherwise fragile cells. –Thus allowing plants and mushrooms to resist the power of wind, gravity and rain and stand straight up –Tree trunks Though strong cell walls tend to be porous, preventing cell suffication What are the functions of cell walls? –Support and protect otherwise fragile cells. –Thus allowing plants and mushrooms to resist the power of wind, gravity and rain and stand straight up –Tree trunks Though strong cell walls tend to be porous, preventing cell suffication

Eukaryotic Membranes: Endoplasmic Reticulum Endoplasmic reticulum (ER) is a series of interconnected membranous tubes and channels in the cytoplasm.

Eukaryotic Membranes: Endoplasmic Reticulum Most eukaryotic cells have two forms of ER – rough and smooth. Numberous ribosomes stud the outside of the rough and smooth ER. The different structures of smooth and rough ER reflect different functions. Most eukaryotic cells have two forms of ER – rough and smooth. Numberous ribosomes stud the outside of the rough and smooth ER. The different structures of smooth and rough ER reflect different functions.

Eukaryotic Membranes: Endoplasmic Reticulum Enzymes embedded in the membranes of the smooth ER are the major site of lipid synthesis, including the phospholipids of the ER and other membranes. In other cells smooth ER might synthesize steroid hormones testoterone and estrogen. Enzymes embedded in the membranes of the smooth ER are the major site of lipid synthesis, including the phospholipids of the ER and other membranes. In other cells smooth ER might synthesize steroid hormones testoterone and estrogen.

Eukaryotic Membranes: Endoplasmic Reticulum The ribossomes on the outside of rough ER synthesize proteins, including membrane proteins. There for the ER can produce itself. The ribossomes on the outside of rough ER synthesize proteins, including membrane proteins. There for the ER can produce itself.

Eukaryotic Membranes: Endoplasmic Reticulum These membrane proteins have three directions to move. –Outward to replace membrane of the Golgi complex, lysosomes, or plasma membrane. –Inward to replace nuclear envelope –Or within the ER to replace itself These membrane proteins have three directions to move. –Outward to replace membrane of the Golgi complex, lysosomes, or plasma membrane. –Inward to replace nuclear envelope –Or within the ER to replace itself

Eukaryotic Membranes: Endoplasmic Reticulum Aswell these ribosomes on the outside of the rough ER produce proteins that some secretory cells export into their surroundings. –Digestive enzymes –Protein Hormones Aswell these ribosomes on the outside of the rough ER produce proteins that some secretory cells export into their surroundings. –Digestive enzymes –Protein Hormones

Eukaryotic Membranes: Endoplasmic Reticulum Once these enzymes are produced they are uptakend by the ER and transported up tubes to the end of the ER Here they bud off as membrane bound vescicles and are transported to the Golgi complex. Once these enzymes are produced they are uptakend by the ER and transported up tubes to the end of the ER Here they bud off as membrane bound vescicles and are transported to the Golgi complex.