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By the end of this section, you will be able to:
  • Describe the structure of eukaryotic animal cells
  • State the role of the plasma membrane
  • Summarize the functions of the major cell organelles
  • Describe the cytoskeleton and extracellular matrix

At this point, it should be clear that eukaryotic cells have a more complex structure than do prokaryotic cells. Organelles and other cellular components allow for various functions to occur in the cell at the same time. Before discussing the functions of organelles within a eukaryotic cell, let us first examine two important components of the cell: the plasma membrane and the cytoplasm.

Art connection

Part a: This illustration shows a typical eukaryotic cell, which is egg shaped. The fluid inside the cell is called the cytoplasm, and the cell is surrounded by a cell membrane. The nucleus takes up about one-half of the width of the cell. Inside the nucleus is the chromatin, which is comprised of DNA and associated proteins. A region of the chromatin is condensed into the nucleolus, a structure in which ribosomes are synthesized. The nucleus is encased in a nuclear envelope, which is perforated by protein-lined pores that allow entry of material into the nucleus.  The nucleus is surrounded by the rough and smooth endoplasmic reticulum, or ER. The smooth ER is the site of lipid synthesis. The rough ER has embedded ribosomes that give it a bumpy appearance. It synthesizes membrane and secretory proteins. Besides the ER, many other organelles float inside the cytoplasm. These include the Golgi apparatus, which modifies proteins and lipids synthesized in the ER. The Golgi apparatus is made of layers of flat membranes. Mitochondria, which produce energy for the cell, have an outer membrane and a highly folded inner membrane. Other, smaller organelles include peroxisomes that metabolize waste, lysosomes that digest food, and vacuoles. Ribosomes, responsible for protein synthesis, also float freely in the cytoplasm and are depicted as small dots. The last cellular component shown is the cytoskeleton, which has four different types of components: microfilaments, intermediate filaments, microtubules, and centrosomes. Microfilaments are fibrous proteins that line the cell membrane and make up the cellular cortex. Intermediate filaments are fibrous proteins that hold organelles in place. Microtubules form the mitotic spindle and maintain cell shape. Centrosomes are made of two tubular structures at right angles to one another. They form the microtubule-organizing center.
This figure shows a typical animal cell.

The plasma membrane

Like prokaryotes, eukaryotic cells have a plasma membrane    ( [link] ) made up of a phospholipid bilayer with embedded proteins that separates the internal contents of the cell from its surrounding environment. A phospholipid is a lipid molecule composed of two fatty acid chains, a glycerol backbone, and a phosphate group. The plasma membrane regulates the passage of some substances, such as organic molecules, ions, and water, preventing the passage of some to maintain internal conditions, while actively bringing in or removing others. Other compounds move passively across the membrane.

the plasma membrane is composed of a phospholipid bilayer. in the bilayer, the two long hydrophobic tails of phospholipids face toward the center, and the hydrophilic head group faces the exterior. Integral membrane proteins and protein channels span the entire bilayer. Protein channels have a pore in the middle. Peripheral membrane proteins sit on the surface of the phospholipids and are associated with the head groups. On the exterior side of the membrane, carbohydrates are attached to certain proteins and lipids. Filaments of the cytoskeleton line the interior of the membrane.
The plasma membrane is a phospholipid bilayer with embedded proteins. There are other components, such as cholesterol and carbohydrates, which can be found in the membrane in addition to phospholipids and protein. The phrase "fluid mosaic" is used to describe the structure of the plasma membrane because it is dynamic and contains numerous components.

The plasma membranes of cells that specialize in absorption are folded into fingerlike projections called microvilli (singular = microvillus). This folding increases the surface area of the plasma membrane. Such cells are typically found lining the small intestine, the organ that absorbs nutrients from digested food. This is an excellent example of form matching the function of a structure.

People with celiac disease have an immune response to gluten, which is a protein found in wheat, barley, and rye. The immune response damages microvilli, and thus, afflicted individuals cannot absorb nutrients. This leads to malnutrition, cramping, and diarrhea. Patients suffering from celiac disease must follow a gluten-free diet.

The cytoplasm

The cytoplasm    comprises the contents of a cell between the plasma membrane and the nuclear envelope (a structure to be discussed shortly). It is made up of organelles suspended in the gel-like cytosol    , the cytoskeleton, and various chemicals. Even though the cytoplasm consists of 70 to 80 percent water, it has a semi-solid consistency, which comes from the proteins within it. However, proteins are not the only organic molecules found in the cytoplasm. Glucose and other simple sugars, polysaccharides, amino acids, nucleic acids, fatty acids, and derivatives of glycerol are found there too. Ions of sodium, potassium, calcium, and many other elements are also dissolved in the cytoplasm. Many metabolic reactions, including protein synthesis, take place in the cytoplasm.

Questions & Answers

what is the faction of photo receptors in the eye
Mutangana Reply
wat are e constituents of blood
marybertiny Reply
Can a cell be destroyed by the bacteria
Makhanya Reply
anamia. because of loss of blood
fon Reply
Name the element which is liquid
Sandeep Reply
what is the dept of respiration plz?
Maureen where are you from
which of the muscle can work with out getting tired?
what is the unit of muscles?
acid are organic or inorganic
why is the baby formed in the uterus n not else where?
Ekali Reply
you may help me ,to know why
lo i am inn
the womb is to protect the baby because inside the womb the lay in a fluid called the amniotic fluid which keeps the baby warm and it also have the placenta which the baby feeds from
atom, molecules, organelle, cell, tissue, organ, organ system
Cheila Reply
sub atom atom molecular molecules and cells.
cells structural level.
what is microorganisms I am a laboratory student.
a small organism
small organism that can only be seen under a microscope
i am just interested to be part of ,to learn
explain why is it that old peoples as from the age of 60 usually have eye problems?
Kenn Reply
most old people suffere eye problems.because of short sight where individuals with this kind of problems see only near objects clearly but not distance objects, this is cause by elongated eyeball so light from distance is focus infront the retina so the image on the retina is blurred .
plasma DNA cytoplasm Ribosome
Pearl Reply
cell, tissue,organ, organ systems,organism
Pearl Reply
cell is the build block of Life
also a smallest unit of life
consistsof cytoplsm enclosed with in a membrane which contains many biomolecules such as proteins and nucleic acids
differences in the effects of infection by HIV and influenza A virus on host genetic variability.
Yo Reply
i dont know
hiv is direct contact of blood or body fluid and if not treated can break down the immune system faster and lead to acids with complications of pneumonia skin infections inflammation of the brain etc.while influenza A is a air borne virus which can cause the common cold pain fever and can be cured
suggest bioingormatics research article plz
what makes the heart to pumps blood?
Jamer Reply
sa node
i do think its the nerve tranmission to the brain
The contracting and relaxing of the atria and vertricles but the electrical system of the heart is what makes this possible.
yes which is called autorhymicity
Yes,,by sucking blood leading to the weakening of cells,and finally it will be destroyed....
adrenoline action in brains
Frankline Reply
please describe the human heart brefly
Shah Reply
the size of the heart is like a fist. it has four chambers. the left and right upper atrium which push blood in the lower left and right ventricles which in turns pump blood to the lungs or the rest of the body.
how do u prove it
Maureen is correct ,
mxaa lahayaa
What is housing?
Baldwin Reply
is where located you

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Source:  OpenStax, Human biology. OpenStax CNX. Dec 01, 2015 Download for free at http://legacy.cnx.org/content/col11903/1.3
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