THE CELL - ENGLISH
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THE CELL
• Cells
are the structural and functional units of all living organisms. Cells were
discovered by Robert hooke in 1665. Some organisms, such as bacteria, are
unicellular, consisting of a single cell. Other organisms, such as humans, are
multicellular, indicating that humans are made up of many cells
• Cells
are the smallest independent units of life with different parts that perform their own function For the cells to survive some fundamental
chemical activities occur within the cell. Each cell is an amazing unit of
life; it can take in nutrients, convert these nutrients into energy, carry out
specialised functions and reproduce as necessary.
• Human
cells consists of-
• Cell
membrane Cytoplasm
• Nucleus Mitochondria
• Ribosome Endoplasmic
reticulum
• Golgi
body Lysosome
• Peroxisome Vacuole
CELL MEMBRANE-
• The
cell membrane is a thin membrane that forms the outermost layer of a cell, and
it is also called the plasma membrane. This membrane ensures the boundary and
integrity of the cell and that its contents are separated from the surrounding
environment. The cell membrane contains a variety of biological molecules, mainly
proteins and lipids
• The
cell membrane is made up of a double layer (bilayer) of phospholipid (fatty)
molecules with protein molecules
interspersed between them.
• The
phospholipid bilayer consists of a polar ‘head’ end, which is hydrophilic
(water loving), and fatty acid ‘tails’, which are hydrophobic (water hating).
The hydrophilic heads are situated on the outer and inner surfaces of the cell,
while the hydrophobic areas point into the cell membrane
FUCNTIONS OF CELL
MEMBRANE-
Ø A
Physical Barrier- The cell membrane surrounds all cells and physically
separates the cytoplasm, which is the material that makes up the
cell, from the extracellular fluid outside the cell. This protects all the
components of the cell from the outside environment and allows separate
activities to occur inside and outside the cell.
Ø Selective
Permeability- cell membranes are selectively permeable (or semi-permeable),
meaning that only certain molecules can pass through them. Water, oxygen, and
carbon dioxide can easily travel through the membrane. Generally, ions (e.g.
sodium, potassium) and polar molecules cannot pass through the membrane.
Ø Endocytosis
and Exocytosis – Endocytosis is when a cell ingests relatively larger contents
than the single ions or molecules that pass through channels. Through
endocytosis, a cell can take in large quantities of molecules or even
whole bacteria from the extracellular fluid. Exocytosis is when the
cell releases these materials.
Ø Cell
Signaling - Another important function of the membrane is to facilitate
communication and signaling between cells. It does so through the use of
various proteins and carbohydrates in the membrane. Proteins on the cell “mark”
that cell so that other cells can identify it.
CYTOPLASM –
• Cytoplasm
refers to the thick solution that fills the cell, which includes
the cytosol along with filaments, proteins, ions and
macromolecular structures as well as the organelles suspended in the cytosol.
The cytoplasm includes all of the material inside the cell and outside of the
nucleus.
NUCLEUS-
• The cell nucleus
is a large organelle of the cell which protects the majority of the
genetic material (DNA) within each cell. The nucleus also produces the
necessary precursors for protein synthesis. The DNA is used to form chromatin/chromosomes.
The human cell contains 23 pairs of chromosomes. chromosomes are thread-like
structures made up of strands of DNA and the histone proteins.
• A
cell nucleus and nucleoplasm is surrounded by a double membrane, known as
the nuclear membrane. This membrane covers and protects the
chromosomes from physical and chemical damage. In a stained nucleus, a dark
spot can be seen. This spot is the nucleolus. Within the nucleolus,
the several different parts of ribosomes are produced and
exported.
MITOCHONDRIA-
• Mitochondria
(singular: mitochondrion) are organelles within cells that produce adenosine triphosphate
(ATP), the main energy molecule used by the cell. For this
reason, the mitochondrion is sometimes referred to as “the powerhouse of the
cell”.
• Mitochondria
have two membranes, an outer membrane and an inner membrane. The outer membrane
covers the surface of the mitochondrion, while the inner membrane is located
within and has many folds called cristae.
• The
amount of mitochondria in a cell depends on how much energy that cell needs to
produce. Muscle cells, for example, have many mitochondria because they
need to produce energy to move the body. Red blood cells, which carry
oxygen to other cells, have none; they do not need to produce energy.
RIBOSOME-
• The
ribosome is a highly complex cellular organelle. It is largely made up of
specialized RNA known as ribosomal RNA (rRNA) and proteins. The
ribosomal proteins and rRNAs are arranged into two distinct ribosomal pieces of
different size, known generally as the large and small subunit of the ribosome.
Ribosomes consist of two subunits that fit together
• Ribosomes
function to synthesize proteins. Proteins are needed for many cellular
functions such as repairing damage or directing chemical processes. Ribosomes
can be found floating within the cytoplasm or attached to the endoplasmic
reticulum. Basically, their main function is to convert genetic code into an
amino acid sequence and to build protein polymers from amino acid monomers.
ENDOPLASMIC RETICULUM-
• The
endoplasmic reticulum (ER) is a large organelle made of
membranous sheets and tubules that begin near the nucleus and extend across
the cell. The endoplasmic reticulum creates, packages, and secretes
many of the products created by a cell.
• There
are two major types of ER within each cell – smooth endoplasmic reticulum (SER)
and rough endoplasmic reticulum (RER). Each has distinct functions, and
often, differing morphology. The SER is involved in lipid metabolism and
acts as the calcium store for the cell. the RER is commonly seen close to the
nucleus. It contains membrane-bound ribosomes that give it the characteristic
‘rough’ appearance. RER is involved in creating proteins.
GOLGY BODY-
• The
Golgi apparatus is an organelle in eukaryotic organisms that
moves molecules from the endoplasmic reticulum to their
destination. The organelle also modifies products of the endoplasmic reticulum
to their final form. The Golgi apparatus is comprised of a series of flattened
sacs that extend from the endoplasmic reticulum.
• The
main function of the Golgi apparatus is the ability to deliver vesicles,
or packets of various cell products, to different locations
throughout the cell.
LYSOSOME-
• Lysosomes
are specialized vesicles within cells that digest large molecules by the use of
hydrolytic enzymes. Vesicles are small spheres of fluid surrounded by a lipid
bilayer membrane, and they have roles in transporting molecules within
the cell. A human cell contains around 300 of them. Not only do
they digest large molecules, they are also responsible for breaking down and
getting rid of waste products of the cell.
• They
can also perform autophagy, which is the destruction of improperly
functioning organelles. In addition, lysosomes have a role in phagocytosis,
in white blood cells.
PEROXISOMES-
• Peroxisomes
are organelles that can vary in shape, size and number depending on the energy
needs of the cell. Peroxisomes are membrane-bound organelles
in most eukaryotic cells, primarily involved in lipid metabolism and the
conversion of reactive oxygen such as hydrogen peroxide into safer
molecules like water and oxygen.
• Their
role in detoxifying and oxidizing a number of molecules, metabolic byproducts
and drugs makes them a prominent part of kidney and liver cells.
VACULE-
• A
vacuole is an organelle in cells which functions to hold
various solutions or materials. This includes solutions that have been created
and are being stored or excreted, and those that have been phagocytized, or engulfed,
by the cell. A vacuole is simply a chamber surrounded by a
membrane, which keeps the cytosol from being exposed to the
contents inside.
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