FUNBIO 7 - Cell Ultrastructure: Mitochondria and ER

Question 1

Describe Mitochondria.

Answer 1

Mitochondria are the most prominent cellular organelle. They are found in all eukaryotic cells and can take a round or rod shape. They are 0.5-1.0 micrometers in diameter and 5-10 micrometers in length. They are not static and like to move throughout the cytoplasm to areas of high metabolic activity. Mitochondria are bound by two membranes, a smooth outer mitochondrial membrane and an inner mitochondrial membrane that is folded into thin plates called cristae.

Question 2

Describe Cristae.

Answer 2

Cristae span wall to wall of the mitochondria, having a large surface area that allows for sequential chemical reactions to take place. The number of cristae in the mitochondria is a good indicator of the activity in the cell.

Question 3

What is the interior of the mitochondria called?

Answer 3

The matrix.

Question 4

Explain ATP production.

Answer 4

The mitochondria are the powerhouse of the cell and are responsible for the production of ATP, which is used to drive many metabolic processes.

• The inner mitochondrial membrane is lined with F1FO particles that act as ATP synthase, in part with a respiratory chain (electron transport chain) composed of protein subunits.
• ATP is produced from the conversion of electrochemical energy (H+ concentration gradient between intermembrane space and matrix) to mechanical energy (FO base turning to respiration chain), to chemical energy (oxidative phosphorylation of ADP to ATP).

Question 5

Explain Mitochondria Reproduction.

Answer 5

During cell division, mitochondria are split equally between the daughter cells, however, to increase the number mitochondria are reproduced from pre-existing mitochondria.

Question 6

Explain Mitochondria Origins.

Answer 6

The Serial Endosymbiotic Theory:

1. There was an original prokaryotic cell host
2. Aerobic bacteria were introduced and multiple plasma invaginations occurred.
3. Aerobic bacteria turned into mitochondria, while plasma invaginations developed into the endoplasmic reticulum and the nuclear envelope.
4. Eukaryotic cells are formed. Plant and protists were introduced to photosynthetic bacteria which became chloroplasts.

Question 7

Describe the Rough Endoplasmic Reticulum.

Answer 7

• May take up 10% of cell space, by spanning from the nuclear envelope to almost the plasma membrane
• Tubules often become flattened discs called cisternae
• After cell division, nuclear envelope forms from remnants of the rough ER
• ER is rough because ribosomes are attached
• cells with rough ER are engaged in protein synthesis of digestive enzymes, lysosomal enzymes, hormones, neurotransmitters, plasma membrane enzymes
• Water-soluble proteins: cross the rough ER and enter the lumen to be released elsewhere
• Transmembrane proteins: stay embedded in the rough ER