nuclear envelope chromatin nucleolus nuclear pores rough ER smooth ER

Structure
-The nucleus, a prominent structure in cells.
The nucleus contains chromatin.
Chromatin has a special region called the nucleolus, where rRNA is produced and ribosome subunits are assembled.
The nuclear envelope contains pores that allow substances to enter and exit the nucleus to and from the cytoplasm. The nuclear envelope is attached to the endoplasmic reticulum, which often has attached ribosomes, where protein synthesis occurs
Function stores genetic information

Ribosomes are organelles composed of proteins and rRNA.
Protein synthesis occurs at the ribosomes. Ribosomes are often attached to the endoplasmic reticulum; but they also may occur free within the cytoplasm, either singly or in groups called polyribosomes.
Proteins synthesized at ribosomes attached to the endoplasmic reticulum have a different destination from that of proteins manufactured at ribosomes free in the cytoplasm
.

The endomembrane system.
The organelles in the endomembrane system work together to produce, modify, secrete, and digest proteins and lipids.
The Endomembrane System
The endomembrane system consists of the nuclear envelope, the endoplasmic reticulum, the Golgi apparatus, lysosomes, and vesicles
(tiny membranous sacs) . This system divide the cell so that chemical reactions are regulate to specific regions. The vesicles transport molecules from one part of the system to another.

secretion plasma membrane incoming vesicle enzyme lysosome contains digestive enzymes that break down cell parts or substances entering by vesicles transport vesicle takes lipids to Golgi apparatus
Lipid
Smooth endoplasmic reticulum synthesizes lipids and has various other functions ribosome secretory vesicle
Nucleus
Golgi apparatus modifies lipids and proteins from the ER; sorts and packages them in vesicles transport vesicle takes proteins to
Golgi apparatus protein rough endoplasmic reticulum synthesizes proteins and packages them in vesicles

The endoplasmic reticulum has two portions.
1- Rough ER is studded with ribosomes on the side of the membrane that faces the cytoplasm. Here, proteins are synthesized and enter the ER interior, where processing and modifi cation begin .
Some of these proteins are incorporated into membrane, and some are for export.
2- Smooth ER, continuous with rough ER, does not have attached ribosomes. Smooth ER synthesizes the phospholipids that occur in membranes and has various other functions, depending on the particular cell. In the testes, it produces testosterone. In the liver, it helps detoxify drugs.

The ER forms transport vesicles in which large molecules are transported to other parts of the cell. Often, these vesicles are on their way to the plasma membrane or the Golgi apparatus.

The Golgi apparatus is named for Camillo Golgi,
who discovered its presence in cells in 1898.
The Golgi apparatus consists of a stack of slightly curved saccules, whose appearance can be compared to a stack of pancakes. Here, proteins and lipids received from the ER are modified. For example, a chain of sugars

may be added to them. This makes them glycoproteins and glycolipids, molecules often found in the plasma membrane.
The vesicles that leave the Golgi apparatus move to other parts of the cell. Some vesicles proceed to the plasma membrane, where they discharge their contents. In all, the Golgi apparatus is involved in processing, packaging, and secretion

Lysosomes, membranous sacs produced by the Golgi
apparatus, contain hydrolytic enzymes. Lysosomes
are found in all cells of the body but are particularly numerous in white blood cells that swallow up disease-causing microbes. When a lysosome fuses with such an endocytic vesicle, its contents are digested by lysosomal enzymes into simpler subunits that then enter the cytoplasm. In a process called autodigestion, parts of a cell may be broken down by the lysosomes .

Some human diseases are caused by the lack of a particular lysosome enzyme. Tay–Sachs disease occurs when an undigested substance collects in nerve cells,leading to developmental problems and death in early childhood.

Outer membrane
Inner membrane
Intermembrane space cristae
The structure of a mitochondrion.
matrix

Mitochondria (sing., mitochondrion) are often called the powerhouses of the cell the mitochondria convert the chemical energy of glucose products into the chemical energy of ATP (adenosine triphosphate )molecules .
In the process, mitochondria use up oxygen and give off carbon dioxide. Therefore, the process of producing ATP is called cellular respiration
The structure of mitochondria is appropriate to the task. The inner membrane is folded to form little shelves called cristae. These project into the matrix, an inner space filled
with a gel-like fluid , The matrix of a mitochondrion contains enzymes
The number of mitochondria in cells is highly variable; liver cells contain as many as
2000 mitochondria, whereas inactive cells contain very few.

for breaking down glucose products. ATP production then occurs at the cristae. Protein complexes that aid in the conversion of energy are located in an assembly-line fashion on these membranous shelves. The structure of a mitochondrion supports the hypothesis

that they were originally prokaryotes engulfed by a cell.
Mitochondria are bounded by a double membrane, as a prokaryote would be if taken into a cell by endocytosis. Even more interesting is the observation that mitochondria have their own genes—and they reproduce themselves!

Each mitochondrion consists of four sections
1- The outer membrane is relatively permeable
as it contains a pore-forming protein, known as
porin,which allows free passage of small molecules. The outer membrane contains enzymes that convert certain lipid substrates into forms that can be metabolised within the mitochondrion.

Each mitochondrion consists of four sections
2- The inner membrane, which is thinner than the outer, is thrown into complex folds and tubules called cristae that project into the inner cavity. In some cell types mitochondria typically have tubular
Cristae.

Each mitochondrion consists of four sections
3- The inner cavity filled by the mitochondrial matrix.
The matrix contains a number of dense matrix granules, thought to be binding sites for calcium,
Which is stored in mitochondria
4- The intermembranous space between the two membranes also contains a variety of enzymes.