CELL
ORGANNELS
1. Nucleus
a. Nucleus Pores
Large protein complexes that cross the nuclear envelope
Proteins that make up the nuclear pore complex are known as nucleoporins
About on average 2000 nuclear pore complexes in the nuclear envelope of a vertebrate cell, but it varies depending on cell type and throughout the life cycle
Nuclear pores allow the transport of water-soluble molecules across the nuclear envelopeus
The entire nuclear pore complex (NPC) has a diameter of about 120 nm
The diameter of the opening (functional diameter) is about 9 nm wide and its "depth" is about 200 nm
b. Nucleus Membrane (Nucleus Envelope)
Encloses the genetic material in eukaryotic cells and serves as the physical barrier, separating the contents of the nucleus (DNA) from the cystol (cytoplasm)
The nuclear envelope has two membranes, each with the typical unit membrane structure
Each of the two membranes is made up of a lipid bilayer. The outer membrane is continuous with the rough endoplasmic reticulum (ER) and has ribosomes attached
The inner nuclear membrane is connected to the nuclear lamina, a network of intermediate filaments composed of various lamin
Lamina acts as a site of attachment for chromosomes and provides structural stability to the nucleus
Numerous nuclear pores are inserted in the nuclear envelope and facilitate and regulate the exchange of materials (proteins such as transcription factors, and RNA) between the nucleus and the cytoplasm
The outer and inner nuclear membrane are fused at the site of nuclear pore complex insertion
2. Cell Membrane
also called plasma membrane or phospholipid bilayer
contains a wide variety of biological molecules, primarily proteins and lipids, that are involved in a lot of cellular processes such as cell adhesion, ion channel conductance and cell signaling
also serves as the attachment point for both the intracellular cytoskeleton and, if present, the extracellular cell wall
Function
Surrounds the cytoplasm of a cell and separates the intracellular components from the extracellular environment
Plays a role in anchoring the cytoskeleton to provide shape to the cell, and in attaching to the extracellular matrix to help group cells together in the formation of tissues
Movement of substances across the membrane can either be passive, occurring without the input of cellular energy, or active, requiring the cell to expend energy in moving it
Structure
Is made up mainly of ampthipathic phospholipids which spontaneously arrange so that the hydrophobic "tail" regions are shielded from the surrounding polar fluid, causing the more hydrophilic "head" regions to associate with the cytosolic and extracellular faces of the resulting bilayer. This forms a continuous, spherical lipid bilayer
Arrangement of hydrophilic heads and hydrophobic tails of the lipid bilayer prevent polar solutes (e.g. amino acids, nucleic acids, carbohydrates, proteins, and ions) from diffusing across the membrane, but generally allows for the passive diffusion of hydrophobic molecules