There are three general categories of junctions between animal cells.
tight junctions, desmosomes, and gap junctions.
Tight junctions bind the two cells very closely. Tight junctions are barriers to prevent materials
from moving between the cells. Figure 5.7a.
In the example, of the epithelial cells the tight junctions are used at the top surface of the cells to
form a wall to block movement IN BETWEEN the cells. Thus the only way for molecules to
move from one side of the cell layer to the other is through the cells, and this is tightly regulated.
Desmosomes are the next type of connection. Figure 5.7 middle panel. Desmosomes are
designed to keep the two cells linked, but not tightly linked. This type of linkage, allows the
passage of material in between the cells. Thus there are passage-ways still in between the cells.
Gap junctions are the third type of connection. Figure 5.7 lowest panel. Gap junctions are
designed for intimate direct communication between the two cells. Here there is a small gap
between the two cells that is spanned by a channel. Specific chemicals or electric impulses can
move quickly through these channels.
This completes our look at each eukaryotic cell structure.
Which type of junction is most similar in function to the plasmodesmata?
a) Tight junction
c) Gap junction*****
LET’S GET AN OVERVIEW OF ACTIVITY WITHIN A EUKARYOTIC CELL
The hereditary material of the cell is kept within the nucleus and never leaves the nucleus.
Therefore DNA replication (duplicating the genetic material) and transcription(the creation of
RNA) takes place in the nucleus.
But most RNA moves to the cytoplasm. Ribosomal subunits are assembled at the nucleolus
within the nucleus, but the subunits move out to the cytoplasm.
Translation (the synthesis of proteins) occurs in the cytoplasm, either on free ribosomes, or on
the rough ER.
Photosynthesis takes place within the chloroplast. Starches are made from simple sugars in the
leucoplasts of plant cells.
Cellular respiration occurs with the mitochondria, here sugars are broken down to produce ATP.
ATP is the main energy molecule used by proteins to do work.