Copyright © 2009 Pearson Education Inc. 4.5 What Roles Do Membranes Play In Eukaryotic Cells? The endoplasmic reticulum forms channels within the cytoplasm

Copyright © 2009 Pearson Education Inc.

4.5 What Roles Do Membranes Play In Eukaryotic Cells?

The endoplasmic reticulum forms channels within the cytoplasm

Fig. 4-7

(a) (b)Endoplasmic reticulum may be rough or smooth Smooth and rough ER

ribosomessmooth ERsmooth ER

rough ER

rough ER

vesicles



The _______ ER is studded with ribosomes• the site where proteins are made.

The _______ ER lacks ribosomes• makes phospholipids and

cholesterol.

Together, the rough and smooth ER are the sites of new membrane synthesis for the cell.



The Golgi apparatus sorts, chemically alters, and

packages important molecules.

• This organelle looks like a stack of flattened sacs.• Its membranes are derived from the ER.• Vesicles containing preformed molecules from the ER are

transferred to the Golgi for further processing. • Once the molecular work of the Golgi has been done, new

vesicles bud off and travel elsewhere in the cytoplasm, where they fuse with membranes of other organelles, such as the plasma membrane.

• A major role of the Golgi is to add sugar molecules to proteins formed in the ER and to pass them on to other places in the cell.

•


4.5 What Roles Do Membranes Play In Eukaryotic Cells? The Golgi apparatus

Fig. 4-8

Golgiapparatus

Protein-carrying vesicles from theER merge with theGolgi apparatus

Vesicles carryingmodified proteinsleave the Golgiapparatus



An antibody protein is synthesized on ribosomes of the rough ER.

Formed antibody is packaged into vesicles that travel to the Golgi, where carbohydrates are attached to protein to make an antibody.

The vesicle containing antibody leaves the Golgi and goes to the plasma membrane, where it fuses with it.

The antibody inside the vesicle is released to the outside of the cell (to the blood), where it helps defend the body against infection.



Lysosomes are vesicles that serve as the cell’s ______________ system.

• They are formed as buds from the Golgi.

• Lysosomes contain digestive enzymes that they receive from Golgi during their production.

• In the cytoplasm, they digest defective organelles or pieces of membrane into component parts that can be recycled.


4.6 What Other Structures Play Key Roles In Eurkaryotic Cells?

Vacuoles regulate _________ and store substances.

• They are fluid-filled sacs surrounded by a single membrane.

• Many plant cells have a large central vacuole.

• Vacuoles hold water and help maintain the proper water balance of the cell.

• Vacuoles can also serve as dump sites for hazardous waste that can’t be excreted.

• They can also store sugars and amino acids, which can be used for energy.



Mitochondria extract ________ from food molecules.

• Mitochondria provide the energy needed for all cellular processes.

• Energy is obtained from ________ molecules in mitochondria and is stored in _______ molecules.

• Once formed, ATP can be used anywhere in the cell where energy is needed.

• Mitochondria have a complex set of outer and inner membranes, used in the process of energy production.


4.6 What Other Structures Play Key Roles In Eurkaryotic Cells? Chloroplasts capture _______ energy.

• Only _______ cells contain chloroplasts.

• Chloroplasts capture energy from __________ and store it in ________ molecules.

• They are the site of ________________, the process upon which all life depends.

• Like mitochondria, chloroplasts contain both outer and inner membranes.



The cytoskeleton provides shape, support, and movement.

• All organelles in the cell do not float about the cytoplasm, but instead, are attached to a network of protein fibers called the cytoskeleton.

Several type of protein fibers make up the cytoskeleton.

• Microfilaments: thin fibers• Intermediate filaments: medium-sized fibers • Microtubules: thick fibers



The cytoskeleton

Fig. 4-9

plasma membrane

microfilaments

mitochondrion

intermediatefilaments

ribosomes

endoplasmicreticulum

microtubule

vesicle

(a) Components of the cytoskeleton (b) Cell with stained cytoskeleton

microtubules (red)

nucleus

microfilaments (blue)



__________ move fluid past the cell __________ move the cell

• Cilia and flagella are slender, movable extensions of the plasma membrane.

• They contain microtubules that extend along their length.• They may be used to move small animals (flagellum) or

particle-containing fluids past a surface (cilia).• Differences between cilia and flagella lie in their length,

number, and the direction of force generated.



Cilia provide force parallel to the plasma membrane, which can be described as a “rowing” motion.

Fig. 4-10a

return stroke

cilia liningthe trachea

plasma membranepower stroke

(a) Cilium

propulsion of fluid



Flagella provide a force perpendicular to plasma membrane, like the engine on a motorboat.

flagellumof humansperm

continuous propulsion

direction of locomotion

(b) Flagellum

propulsion of fluid

Fig. 4-10b


4.7 What Are The Features Of Prokaryotic Cells? Prokaryotic cells:

• are much smaller than eukaryotic cells, are more abundant, and are very reproductively successful.

• have a simple internal structure.• are surrounded by a stiff cell wall, which provides shape

and protection.• some move with a whiplike flagellum.• have a single, circular strand of DNA attached to the

plasma membrane, concentrated in an area called the nucleoid, which lacks a membrane.

• no membrane-enclosed organelles.• cytoplasm contains ribosomes used for protein synthesis.


4.7 What Are The Features Of Prokaryotic Cells? A generalized prokaryotic cell

chromosome(nucleoid region)

ribosomes

food granule

prokaryoticflagellum

cell wall

plasma membranecytoplasm

Fig. 4-11

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Copyright © 2009 Pearson Education Inc. 4.5 What Roles Do Membranes Play In Eukaryotic Cells? The endoplasmic reticulum forms channels within the cytoplasm