Page 2: Intracellular Membranes

Eukaryotic cells have developed a system of intracellular membranes to increase the total membrane area available for vital functions. This adaptation is necessary due to the relatively small surface area to volume ratio of eukaryotic cells. The endoplasmic reticulum (ER) forms a network of membrane tubules continuous with the nuclear membrane, with rough ER (RER) having ribosomes on its cytosolic face and smooth ER (SER) lacking ribosomes.

Definition: Intracellular membranes are internal membrane systems in eukaryotic cells that increase the total membrane area for cellular functions.

Vocabulary: The endoplasmic reticulum (ER) is a network of membrane tubules continuous with the nuclear membrane.

Highlight: The distinction between rough ER (RER) and smooth ER (SER) is the presence or absence of ribosomes on the cytosolic face.

Page 5: Protein Synthesis and Transport

The synthesis of all proteins begins in cytosolic ribosomes. Cytosolic proteins complete their synthesis there and remain in the cytosol. Transmembrane proteins carry a signal sequence that directs the synthesizing ribosome to dock with the ER, forming rough ER (RER). After synthesis, proteins are transported by vesicles that bud off from the ER and fuse with the Golgi apparatus. As proteins move through the Golgi apparatus, they undergo post-translational modifications, with the addition of carbohydrate groups being a major modification.

Vocabulary: A signal sequence is a short stretch of amino acids that determines the eventual location of a protein in a cell.

Highlight: The Golgi apparatus plays a crucial role in post-translational modifications of proteins, particularly the addition of carbohydrate groups.

Example: Transmembrane proteins are inserted into the ER membrane during synthesis, guided by their signal sequence.