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

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.



• 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



• 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 head2. 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 head2. A pair of nonpolar, hydrophobic tails



• 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



• 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



• The diagram below shows a representation of the cholesterol molecules intersperses in the phospholipid bilayer

• The diagram below shows a representation of the cholesterol molecules intersperses in the phospholipid bilayer



• 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



• 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



• 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 WallEukaryote 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


• 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).


• 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 ReticulumEukaryotic Membranes: Endoplasmic Reticulum

• Endoplasmic reticulum (ER) is a series of interconnected membranous tubes and channels in the cytoplasm.

• Endoplasmic reticulum (ER) is a series of interconnected membranous tubes and channels in the cytoplasm.


• 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.


• 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.


• 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.


• 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


• 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


• 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.

Documents

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