BIOL 112 - LECTURE 8: Cell Size and Endomembrane System

How many cells are in the human body?

The human body contains about 40 trillion cells (4x10¹³).

Why are cells small in size?

Cells are small to ensure efficient diffusion. Diffusion is only effective over small distances, and large cells would make it too slow for essential processes like glycolysis and neurotransmitter diffusion.

Why are eggs an exception to the cell size rule?

Eggs can be large because they store resources and do not require the same level of diffusion efficiency as other cells.

What are prokaryotes and why are they smaller than eukaryotes?

Prokaryotes are simpler organisms without a membrane-bound nucleus. They are much smaller than eukaryotes and have great metabolic diversity.

What distinguishes eukaryotic cells?

Eukaryotic cells are distinguished by a "real nucleus," which is surrounded by a nuclear envelope, and they have compartmentalization through internal membrane systems.

What unique features do plant cells have?

Plant cells have a cell wall, chloroplasts, and a modified lysosome called a vacuole.

How do plant cells differ from animal cells in terms of osmotic regulation?

Plant cells do not need a sodium-potassium pump because their cell wall provides structural support and prevents excessive water influx.

What is the endomembrane system?

The endomembrane system consists of membrane-bound organelles like the nucleus, ER, Golgi apparatus, vesicles, and lysosomes, which compartmentalize the cell.

What is the significance of the lumen in organelles like the ER and Golgi?

The lumen of organelles like the ER and Golgi is equivalent to the extracellular space, as substances within these organelles are transported in vesicles that fuse with the cell membrane.

What is the structure of the nucleus?

The nucleus is surrounded by a double membrane called the nuclear envelope. It contains DNA in the form of chromosomes and a nucleolus, where ribosomal RNA (rRNA) is produced.

What role do ribosomes play in the rough ER?

Ribosomes attached to the rough ER synthesize membrane proteins. These proteins are inserted into the ER membrane during translation via a signal sequence.

What happens in the smooth ER?

The smooth ER is involved in the synthesis of lipids and the detoxification of harmful substances, often through oxidation reactions.

What does the Golgi apparatus do?

The Golgi modifies, sorts, and packages proteins and lipids received from the ER. It adds sugar side chains to proteins and directs them to their final destinations.

What are pulse-chase experiments used for?

Pulse-chase experiments trace the movement of proteins through the endomembrane system by labeling them with radioactive amino acids (pulse) and then tracking them over time (chase).

How do substances enter the cell?

Substances enter the cell via receptor-mediated endocytosis, where molecules are recognized by receptors and internalized in vesicles, or via phagocytosis for larger organisms.

What happens in the lysosome?

The lysosome is responsible for digesting internalized molecules and cellular debris through a low pH and the action of digestive enzymes.

What is autophagy?

Autophagy is the process where lysosomes surround and digest damaged or unneeded organelles and cellular components, like muscle fibers, during times of stress or starvation.

How do ribosomes become attached to the rough ER?

Ribosomes are initially cytosolic, but when translating a membrane protein, they attach to the rough ER where the protein is inserted into the membrane during translation.

How are proteins sorted to their correct destinations?

Proteins are sorted based on specific amino acid sequences (tags) that direct them to the appropriate vesicle, such as those targeting the lysosome or the cell membrane.

What is the function of vesicles in the endomembrane system?

Vesicles transport proteins and lipids between organelles like the ER, Golgi, lysosomes, and the cell membrane, ensuring the correct distribution of cellular components.