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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

information for blood vessels
Sumit Reply
helps pump blood through body
arteries carry blood away from the heart while veins return it to the heart
veins have thinner outer walls because blood pressure in them is very low compared to arteries with thicker outer walls to withstand the higher blood pressure.
cell, tissue, organ, organism, organ system,
Gheida Reply
please what are the characteristics of a good respiratory system?
Salomon Reply
thin wall ,a moist inner surface ,a huge combined surface area and a rich blood supply.
Help me am confused what is the cell membrane as a partially permeable membrane
Janelle Reply
it is the ability of a molecules to cross a cell membrane depending on their both size and chemical properties.
Based on my previous understanding of biological systems, a cell membrane is a semi-permeable membrane made up of a phospholipids bi-layer. The polar head consisting of phosphate and the hydrophobic end made up of lipids.
Smallest bone of rabbit is
Sahrukh Reply
difference between catebolism and anebolism
Anthvanath Reply
identify the causes of infertility in human beings
Rodrick Reply
Describe how a healthy pregnancy could be maintained
Huaman largest bone
How I can test DNY
Salamin Reply
Samllest bone
How can I determine my child
AlfredOfficial Reply
by DNA tests
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How many bones of 1 year childrean
R.k Reply
A baby's body has about 300 bones at birth. These eventually fuse (grow together) to form the 206 bones that adults
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A baby's body has about 300 bones at birth. These eventually fuse (grow together) to form the 206 bones that adults h
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it's 300 bones because it a baby
babies have 300 bones in which it fuses to become 206 as an adult.
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figure of male reproduction
Rani Reply
front view of male reproductive system
front view of male reproductive system
what is Actin? I don't understand this definition
Rhonda Reply
Actin is a family of globular multi-functional proteins that form microfilaments. 
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what is the difference between a vaccine and a antiserum
Silver Reply
An antiserum contains antibodies already produced and is used to pass on immune responses. A vaccine contains a substance that stimulates the production of antibodies to create an immune response.
A vaccine a preparation of antigens for one (or more) diseases that is given to stimulate active immunity and protect against the disease (s). while an antiserum either neutralizes the "infection " or stimulates your immune system to attack an infection.
what is deoxyribonucleic acid
Carlene Reply
A negatively charged molecule; polymer of nucleotides found in the nucleus of a cell ... DNA.
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DNA is genetic material which is present in cell DNA is made up of nitrogen base,phosphate group and pentose sugar.
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to maintain certain biological activities of cell
jeeni Reply

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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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