The transfer vesicle from RER fuse with which region of golgi complex

The correct option is Cis.

To understand why this is correct, let us break down the pathway of protein transport and the structural organization of the Golgi complex:

1. Synthesis and Packaging in the Rough Endoplasmic Reticulum (RER):
Proteins destined for secretion or for other organelles are synthesized by ribosomes attached to the Rough Endoplasmic Reticulum (RER). Once synthesized, these proteins are packaged into spherical membrane-bound transport vesicles (often called transfer vesicles) that bud off from the transition elements of the RER.

2. Polarity of the Golgi Complex:
The Golgi complex is a highly polarized organelle consisting of flattened membranous sacs called cisternae. It has two distinct faces:
- The Cis face (also known as the forming face, receiving face, or entry face): This face is physically oriented toward the endoplasmic reticulum. It is convex in shape and serves as the receiving department of the Golgi complex.
- The Trans face (also known as the maturing face, shipping face, or exit face): This face is oriented toward the plasma membrane. It is concave and is responsible for packaging modified proteins into secretory vesicles and dispatching them to their final destinations.
- The Medial region: This consists of the cisternae located between the cis and trans faces, where further modifications take place.

3. Fusion of the Transfer Vesicles:
Because the cis region is the entry face that directly faces the endoplasmic reticulum, the transport vesicles carrying newly synthesized proteins from the RER travel to and fuse specifically with the membranes of the cis-Golgi network. This allows the protein cargo to enter the Golgi lumen for sequential post-translational modifications (such as glycosylation) as they move from the cis to the medial and finally to the trans cisternae.