Biology 107Biology 107

Cell IIICell III

September 29, 2003September 29, 2003

Cell IIICell III

Student Objectives:Student Objectives: As a result of this lecture and the assigned As a result of this lecture and the assigned reading, you should understand the following:reading, you should understand the following:

1.1. The The mitochondriamitochondria carry out cellular respiration in which the carry out cellular respiration in which the chemical energy of foods, such as sugars, is converted to “useful” chemical energy of foods, such as sugars, is converted to “useful” chemical energy in the form of the molecule ATP. Mitochondria chemical energy in the form of the molecule ATP. Mitochondria are double membrane containing structures.are double membrane containing structures.

a.a. The inner membrane encloses a fluid-filled space called The inner membrane encloses a fluid-filled space called the the mitochondrial matrixmitochondrial matrix..

b.b. The space between the inner and outer membrane is the The space between the inner and outer membrane is the intermembrane spaceintermembrane space..

Cell IIICell IIIc.c. The intermembrane space contains one set of enzymes, The intermembrane space contains one set of enzymes, while while the mitochondrial matrix contains a different set of the mitochondrial matrix contains a different set of enzymes. enzymes. Also, the inner cell membrane is highly folded Also, the inner cell membrane is highly folded and contains and contains enzymes that are responsible for ATP production. enzymes that are responsible for ATP production. Each fold is Each fold is called a called a cristacrista (plural, cristae) and the folding (plural, cristae) and the folding increase the increase the membrane surface area for the enzymes.membrane surface area for the enzymes.

d.d. Mitochondria contain circular DNA and prokaryote-like Mitochondria contain circular DNA and prokaryote-like ribosomes, suggesting they arose from symbiotic ribosomes, suggesting they arose from symbiotic

association association between aerobic organisms (the precursors of between aerobic organisms (the precursors of mitochondria) mitochondria) and anaerobic organisms (the precursors of the and anaerobic organisms (the precursors of the cell in which cell in which the mitochondria reside).the mitochondria reside).

Cell IIICell III2.2. Like mitochondria, Like mitochondria, chloroplastschloroplasts are double membrane structures are double membrane structures

with their own DNA and ribosomes. Like mitochondria, with their own DNA and ribosomes. Like mitochondria, chloroplasts are fuel processors, but they convert solar energy chloroplasts are fuel processors, but they convert solar energy into chemical energy, while mitochondria convert one form of into chemical energy, while mitochondria convert one form of chemical energy into another form of chemical energy. The chemical energy into another form of chemical energy. The membranes partition the chloroplast into three major membranes partition the chloroplast into three major compartments involved in photosynthesis.compartments involved in photosynthesis.

a.a. The intermembrane space is between the outer and inner The intermembrane space is between the outer and inner chloroplast membranes.chloroplast membranes.

b.b. The space enclosed by the inner membrane, the The space enclosed by the inner membrane, the stromastroma, , contains the contains the thylakoid membranes,thylakoid membranes, a the network of a the network of

tubules tubules and hollow discs.and hollow discs.

c. The space inside thylakoid membranes.c. The space inside thylakoid membranes.

Cell IIICell III3. The cytoskeleton is a supportive network of intracellular linear

polymers. These cytoskeletal elements are important in maintaining cell shape and motility of cells and their organelles.

a. Microfilaments are long polar filaments composed of actin. These filaments are involved in cell shape changes; through interaction with other proteins (e.g., myosin), they participate in cellular contractility.

b. Intermediate filaments constitute a class of proteins rather than a single protein species. Intermediate filaments are very stable linear, rope-like structures that help to anchor structures.

c. Microtubules are composed of tubulin that forms long straight polymers that are easily assembled and disassembled. These dynamic structures are involved in the movement of organelles around the cell.

Cell IIICell III4. Cells are dynamic structures - they are continually moving

components around and transferring substances between compartments and regions. Examples of how cells segregate materials include protein sorting and vesicular transport.

a. Protein sorting relates to the different regions specific proteins must localize to provide proper functioning in the cell. Some proteins must enter the nucleus, others enter membranous organelles such as mitochondria, lysosomes, or chloroplasts, and still others become integral membrane proteins or secreted proteins.

b. Vesicular transport carries vesicle contents and membrane to intracellular sites or to sites on the plasma membrane for release to the outside of the cell. The various vesicular transport and secretion pathways use molecular signals or "tags" to designate the proper sorting.

Structure of a Mitochondrion

Mitochondria are Double-membrane Structures

Chloroplasts are Double-membrane Structures

Chloroplast

Cytoskeleton Consist of Three Elements

Examples of Microfilament

Function

Micrographs of Microfilaments and

Intermediate Filaments

Intermediate filamentsIntermediate filaments

Microtubules and Accessory Proteins are Involved with Intracellular Movement of Organelles

Cells are Dynamic Structures

Example of Pathway for Movement of Proteins and Membranes