Organelle Functions

ANIMAL CELL MODEL ORGANELLE FUNCTIONS

Cell membrane:
Separating the interior of the cell from the outside environment, the cell wall is selectively permeable, only letting certain things through. It is involved in a variety of cellular processes, such as cell adhesion and cell signalling.

Cytoplasm:
The fluid that fills the cell, cytoplasm uses its dissolved enzymes to break down larger molecules. The products can then be used by the organelles that are suspended in the cytoplasm.

Cytoskeleton:
Both a muscle and a skeleton, the cytoskeleton is responsible for cell movement, cytokinesis (the process where the cytoplasm of a cell is divided to form two daughter cells) and organisation of organelles. It is there for movement and stability, and is made of 3 parts – the microfilaments, the microtubules and the intermediate filaments.

Nucleus:
This is the control centre of the cell. The nucleus regulates cell activity – such as metabolism, growth and reproduction – by controlling the enzymes. It also contains most of the cell’s DNA (genetic material)

Nucleolus:
Positioned in the centre of the nucleus, the nucleolus contains DNA. It also produces ribosomes, and sends them out of the nucleus through nuclear pores.

Nuclear membrane:
Separating the nucleus from the cytoplasm, the nuclear membrane encloses the nucleus, controlling what enters and exits.

Golgi Apparatus:
Located very near the rough endoplasmic reticulum, the Golgi apparatus is involved in a variety of processes. It builds lysosomes and, in plant cells, it creates complex sugars to send off in secretory vesicles. Its membrane surrounds an area of fluid where complex molecules (eg. Proteins, sugars etc) are stored and changed. The Golgi apparatus also gathers simple molecules and combines them to make them more complex. It then packs them in vesicles and stores them for further use, or sends them out of the cell.

Smooth Endoplasmic Reticulum (SER):
The SER looks like rows of tubes connected to the nuclear membrane and acts as a storage organelle for the cell. It is very important in the creation and storage of steroids. The SER also stores ions for quick access.

Rough Endoplasmic Reticulum (RER):
Similar to the smooth endoplasmic reticulum, the RER looks like sheets of bumpy membranes as it has ribosomes attached. It is located around the nucleus, and plays an important role in the synthesising and packaging of proteins.

Mitochondrion (plural Mitochondria):
A part of the digestive system, the mitochondria create cell energy in a process called cellular respiration. They may also be involved in the controlling of calcium in muscles. These organelles are tiny, and there may be thousands in a single cell. The numbers vary depending on what the cell needs to do. Mitochondria have two membranes – the outer membrane covers and contains the organelle and the inner membrane folds over on itself many times. This is because most of the reactions happen on the inner membrane which, when folded over, provides more surface area for the reactions to happen on.

Vacuole:
The vacuole stores food, water, minerals and nutrients needed by the cell to survive. It can also store waste products to prevent the cell from contamination. Its membrane surrounds a mass of fluid. In plant cells, the vacuole is much larger, and located in the centre of the cell (known as the central vacuole), whereas in animal cells, there are multiple smaller-sized ones.

Ribosomes:
These make proteins to be used within the cell. mRNA is created in the nucleus and sent to the ribosomes. The two subunits – 40-S (small) and 60-S (large) – combine with the mRNA to create the protein which is then sent around the cell.

Lysosome:
This single-membrane organelle digests everything – from food to other organelles. It is the organelle that breaks the cell down when it dies, but until it is needed, it simply floats around in the cytoplasm.

Peroxisomes:
These organelles are very similar to the lysosomes. They differ in that peroxisomes hold on to enzymes that require oxygen. Lysosomes have enzymes that work in oxygen-poor areas and have a low pH. Peroxisomes absorb nutrients the cell has acquired and digests fatty acids.

Centrioles/Centrosome:
These are found in pairs, usually at right angles. They are located next to the nucleus, but when the cell isn’t dividing, they cannot be seen. Instead, you can see a condensed and darker area of the cytoplasm, called the centrosome. During division, one pair of centrioles move in each direction towards opposite ends of the nucleus. Mitotic spindles of threads appear and connect to the now-apparent chromosomes (called prophase). The chromosomes are then split and pulled towards each centriole (called anaphase). Finally, the chromosomes begin to unravel and new nuclear envelopes begin to appear (telophase).