Parts of the Cell Assignment
Nucleus: The nucleus is like the “brain” of the cell, it controls the cell’s activity and aids in
cell division. It is a double-membraned and the largest organelle in the cell, which contains
the cell's chromosomes. The chromosomes are made from a molecule of DNA and an equal
mass of protein. The DNA within these chromosomes store and replicate the genetic
information of the eukaryotic cell.
Nucleolus: The nucleolus is found within the nucleus, and it is a non-membrane-bound
organelle. There can be one or more of these structures, which consists of RNA, protein, and
chromatin, and is the site of rRNA production and assembly within the nucleus.
Smooth Endoplasmic Reticulum: The ER serves as the transport system of the cell, and is a
system of membranous tubular canals. The ER can be found throughout the cytoplasm,
starting outside of the nucleus. The shape of the endoplasmic reticulum allows for an increase
in surface area, for chemical reactions. Specifically for the smooth ER, there are no
ribosomes attached to the endoplasmic reticulum. This makes its function synthesizing lipids
as well as detoxifying drugs and chemicals from the cell. Lipids that are synthesized such as
phospholipids and cholesterol are the main components of membranes. For example, large
amounts of smooth ER would be found in liver cells, as the liver detoxifies.
Rough Endoplasmic Reticulum: The rough ER has ribosomes attached to the endoplasmic
reticulum, changing its function to protein synthesis. The rough ER consists of cisternae,
tubules, and vesicles, which are throughout the cell and help with the function of protein
synthesis. The rough ER processes and folds the proteins and then packs them into vesicles,
which are then sent off to the Golgi body.
Golgi Body: Also known as the Golgi apparatus, the Golgi body is a single-membrane
organelle, which has the shape of many sacs. These sacs are flattened, hollowed, and stacked,
which are known as cisternae, and are enclosed by the membrane. It is mainly involved in the
processes of secretion and is like the “post office” of the cell. The Golgi body modifies,
assembles, packages, processes, and secretes substances, such as proteins and lipids from the
endoplasmic reticulum. For the proteins, the carbohydrate regions of glycoproteins are
removed, added, or modified. For the lipids, phosphate groups and glycoproteins are added to
lipids to create the phospholipid bilayer for the membrane. Vesicles from the endoplasmic
reticulum can merge with the Golgi body, and then their contents are modified by the
enzymes within the Golgi bodies. Usually, the proteins modified and packaged by the Golgi
bodies are for use outside of the cell, as the Golgi body packs them into vesicles before
sending the secretory vesicle out for secretion.
Mitochondria: The mitochondria is an oval-shaped, double-membrane-bound organelle,
which is usually referred to as the “powerhouse” of the cell. They are the main sites of
cellular respiration and produce energy by breaking down organic molecules when oxygen is
present, leaving the waste products to be water and carbon dioxide. This reaction results in
the production of energy from glucose is converted into energy in the form of ATP, adenosine
triphosphate. The outer membrane is semi-permeable and allows for small molecules to
freely pass through. The outer membrane also consists of many protein-based pores, porins,
which allow for the passage of molecules such as proteins. The outer membrane also consists
of enzymes, with various functions. In between the inner and outer membrane, there is the
intermembrane space, which is the area between the two. The inner membrane does not have
the porins, making it impermeable to most molecules, and a molecule can only cross this
membrane in special membrane transporters. The ATP is mainly produced in the inner
membrane. The inner membrane consists of many folds, known as cristae, which increase the
surface area, increasing the space for chemical reactions. The space within the inner
membrane contains an abundance of enzymes, which is extremely important for the
production of energy. This space is known as the matrix, and it also is where the
mitochondrial DNA is located.
Cell Membrane: The cell membrane is a selectively permeable membrane, made of a
phospholipid bilayer. This controls the transport of materials and in and out of the cell, and
functions in recognition, communication, and homeostasis. Homeostasis is the process of
maintaining internal conditions, despite changes in the external environment. In an animal
cell, the cell membrane provides shape and protects the inner contents of the cell. In a plant
cell, the cell membrane is surrounded by a cell wall. The cell membrane is regarded as the
fluid mosaic model, as the membrane is fluid and contains several different components
embedded in it. The fluid nature of the membrane means that the components of the
membrane can move sideways, small tears in the membrane easily repair themselves so the
tails can avoid water contact, and the two membranes can fuse very easily. As well as this, the
mosaic component comes from the fact that the membrane contains proteins with a variety of
functions such as channels to allow substances in and out, transferring substances across the
membrane by pumps, hormone receptors, and binding adjacent cells.
Lysosome: Lysosomes are vesicles found in animal cells, produced by the Golgi body. They
are like the “stomach” of the cells, and they contain digestive enzymes. They are
single-membrane sacs that contain over 40 kinds of hydrolytic enzymes. These enzymes
break down with water, catalyzing hydrolysis reactions, breaking large molecules into small
molecules. The lysosome breaks down the old and useless parts of the cell, as well as foreign
particles and bacteria. Lysosome aids in cellular digestion of food, autodigestion, or breaking
down old cell components like old and damaged mitochondria, and they can break down an
entire cell. However, this is not too likely to happen, as the optimal pH for lysosomes is
around 5, whereas the cytoplasm has a pH of 7.2. This pH difference would cause the enzyme
to denature and lose its function, which would allow the cell to not be broken down if a
lysosome broke and spilled its enzymes into the cytoplasm.
Cytoplasm: The cytoplasm is found in plant and animal cells, and it is the jelly-like
substance in the space between the cell membrane, and the nucleus and organelles. It consists
of water, organic, and inorganic compounds. All the organelles are surrounded and within this
liquid, and some are enclosed by membranes that separate them from direct contact with the
cytoplasm, such as the nucleus.
Chromatin: Within the nucleus are chromosomes, which are made from a molecule of DNA
and an equal mass of protein. Chromosomes are only seen in dividing cells, wherein a
non-dividing cell, the chromosome takes the form of the unfolded state. This unfolded state is
called chromatin. The major protein that helps make up chromatids are called histones, which
function as packaging elements for DNA. Chromatins organize the DNA into nucleosomes,
which are “bead-like” structures, by providing the DNA with a base to be wrapped around.
Chromatin allows for the occurrence of cell processes such as cell division, DNA repair and
replication, genetic recombination, and transcription.
Nuclear membrane: The nuclear membrane is a double-membrane of two phospholipid
bilayers surrounding the nucleus. This separates the nucleus from the cytoplasm and the rest
of the cell. The space between these two layers is called the lumen. The membrane is very
porous, consisting of thousands of nuclear pores, which are groups of proteins that form
openings in the membrane. This allows for the free travel of water and ions and other small
particles to pass through these pores between the cytoplasm and the nucleus, and it regulates
the passing of the larger molecules such as RNA.
Centrioles: Centrioles are a pair of cylindrical bodies found near the nucleus in animal cells.
They help organize microtubules that serve as the cell’s skeletal system, and aid in cell
division. During mitosis, the centrioles organize the spindle fibers, which functions during
cell division. They have a short, barrel-like structure with a 9+0 pattern of microtubular
triplets. They also help form cilia and flagella and contribute to cell movement. Centrioles
give rise to basal bodies, which then form flagella or cilia, which function in cell movement.
Ribosomes: Ribosomes are small organelles without membranes. They are made from rRNA
and proteins and are the site of protein synthesis. They can be found in the rough
endoplasmic reticulum and floating around the cytoplasm, after being made in the nucleolus.
Peroxisomes: Peroxisomes are similar to lysosomes as they are also sacs enclosed by a
membrane that contain enzymes. The enzymes they contain, however, are different.
Peroxisomes contain oxidase which catalyzes redox reactions, breaking down toxic and
biological molecules. They break down organic molecules through oxidation, producing
hydrogen peroxide. Peroxisomes also contain the enzyme catalase, which converts the
harmful hydrogen peroxide into oxygen and water. They break down excess fatty acids,
amino acids, and aid in the synthesis of bile acids derived from cholesterol, which is a key
function in the liver.
Chloroplast: Chloroplasts are double-membrane organelles that are large and oval-like in
shape. They are only found in plant cells, as they produce food for plant cells. They contain
the green pigment chlorophyll, which traps light energy for photosynthesis. This energy is
used to combine carbon dioxide and water, into energy-rich organic molecules, forming
glucose. The inner membrane is filled with a thick liquid called the stroma, and it surrounds
the flat and disk-like structures called thylakoids. These thylakoids contain chlorophyll and
are stacked into piles within the chloroplasts, and each pile is called a granum.
Vacuole: Vacuoles are like storage sacs within the cells. They are found within the cytoplasm
and are single-membrane organelles filled with fluids. They store nutrients, water, food, and
dissolved materials that are essential for a cell’s survival, as well as storing waste. The
content stored inside protects the other organelles and the overall cell from contamination.
The size and number of these organelles vary for plant and animal cells. Animal cells have
much smaller vacuoles, in contrast to a plant cell which has a very large central vacuole.
They are formed by the pinching off of the Golgi bodies, the endocytosis of the cell
membrane, and can be an extension of the membrane from the endoplasmic reticulum, such
as a plant’s large central vacuole.
Vesicle: A vesicle is a small vacuole, a single-membrane organelle, used for transport and
storage of materials.