<< Chapter < Page Chapter >> Page >

Lysosomes

In animal cells, the lysosomes are the cell’s “garbage disposal.” Digestive enzymes within the lysosomes aid the breakdown of proteins, polysaccharides, lipids, nucleic acids, and even worn-out organelles. In single-celled eukaryotes, lysosomes are important for digestion of the food they ingest and the recycling of organelles. These enzymes are active at a much lower pH (more acidic) than those located in the cytoplasm. Many reactions that take place in the cytoplasm could not occur at a low pH, thus the advantage of compartmentalizing the eukaryotic cell into organelles is apparent.

Lysosomes also use their hydrolytic enzymes to destroy disease-causing organisms that might enter the cell. A good example of this occurs in a group of white blood cells called macrophages, which are part of your body’s immune system. In a process known as phagocytosis, a section of the plasma membrane of the macrophage invaginates (folds in) and engulfs a pathogen. The invaginated section, with the pathogen inside, then pinches itself off from the plasma membrane and becomes a vesicle. The vesicle fuses with a lysosome. The lysosome’s hydrolytic enzymes then destroy the pathogen ( [link] ).

In this illustration, a eukaryotic cell is shown consuming a bacterium. As the bacterium is consumed, it is encapsulated into a vesicle. The vesicle fuses with a lysosome, and proteins inside the lysosome digest the bacterium.
A macrophage has phagocytized a potentially pathogenic bacterium into a vesicle, which then fuses with a lysosome within the cell so that the pathogen can be destroyed. Other organelles are present in the cell, but for simplicity, are not shown.

Vesicles

Vesicles are membrane-bound sacs that function in storage and transport. Vesicles can fuse with other membranes within the cell system.

Art connection

This figure shows the nucleus, rough ER, Golgi apparatus, vesicles, and plasma membrane. The right side of the rough ER is shown with an integral membrane protein embedded in it. The part of the protein facing the inside of the ER has a carbohydrate attached to it. The protein is shown leaving the ER in a vesicle that fuses with the cis face of the Golgi apparatus. The Golgi apparatus consists of several layers of membranes, called cisternae. As the protein passes through the cisternae, it is further modified by the addition of more carbohydrates. Eventually, it leaves the trans face of the Golgi in a vesicle. The vesicle fuses with the cell membrane so that the carbohydrate that was on the inside of the vesicle faces the outside of the membrane. At the same time, the contents of the vesicle are released from the cell.
The endomembrane system works to modify, package, and transport lipids and proteins. (credit: modification of work by Magnus Manske)

Ribosomes

Ribosomes are the cellular structures responsible for protein synthesis. When viewed through an electron microscope, free ribosomes appear as either clusters or single tiny dots floating freely in the cytoplasm. Ribosomes may be attached to either the cytoplasmic side of the plasma membrane or the cytoplasmic side of the endoplasmic reticulum. Electron microscopy has shown that ribosomes consist of large and small subunits. Ribosomes are enzyme complexes that are responsible for protein synthesis.

Because protein synthesis is essential for all cells, ribosomes are found in practically every cell, although they are smaller in prokaryotic cells. They are particularly abundant in immature red blood cells for the synthesis of hemoglobin, which functions in the transport of oxygen throughout the body.

Mitochondria

Mitochondria (singular = mitochondrion) are often called the “powerhouses” or “energy factories” of a cell because they are responsible for making adenosine triphosphate (ATP), the cell’s main energy-carrying molecule. The formation of ATP from the breakdown of glucose is known as cellular respiration. Mitochondria are oval-shaped, double-membrane organelles ( [link] ) that have their own ribosomes and DNA. Each membrane is a phospholipid bilayer embedded with proteins. The inner layer has folds called cristae, which increase the surface area of the inner membrane. The area surrounded by the folds is called the mitochondrial matrix. The cristae and the matrix have different roles in cellular respiration.

In keeping with our theme of form following function, it is important to point out that muscle cells have a very high concentration of mitochondria because muscle cells need a lot of energy to contract.

This transmission electron micrograph of a mitochondrion shows an oval, outer membrane and an inner membrane with many folds called cristae. Inside of the inner membrane is a space called the mitochondrial matrix.
This transmission electron micrograph shows a mitochondrion as viewed with an electron microscope. Notice the inner and outer membranes, the cristae, and the mitochondrial matrix. (credit: modification of work by Matthew Britton; scale-bar data from Matt Russell)

Section summary

Like a prokaryotic cell, a eukaryotic cell has a plasma membrane, cytoplasm, and ribosomes, but a eukaryotic cell is typically larger than a prokaryotic cell, has a true nucleus (meaning its DNA is surrounded by a membrane), and has other membrane-bound organelles that allow for compartmentalization of functions. The plasma membrane is a phospholipid bilayer embedded with proteins. The nucleolus within the nucleus is the site for ribosome assembly. Ribosomes are found in the cytoplasm or are attached to the cytoplasmic side of the plasma membrane or endoplasmic reticulum. They perform protein synthesis. Mitochondria perform cellular respiration and produce ATP. Vesicles are storage and transport compartments.

The endomembrane system includes the nuclear envelope, the endoplasmic reticulum, Golgi apparatus, lysosomes, vesicles, as well as the plasma membrane. These cellular components work together to modify, package, tag, and transport membrane lipids and proteins.

Art connections

[link] Why does the cis face of the Golgi not face the plasma membrane?

[link] Because that face receives chemicals from the ER, which is toward the center of the cell.

Got questions? Get instant answers now!

Questions & Answers

what is the faction of photo receptors in the eye
Mutangana Reply
transduction of light to nervous impulses occurr it is located in the retina
Maureen
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
hg
RC
CO2
Maureen
Bromine
Aaron
what is the dept of respiration plz?
Maureen
Maureen where are you from
Omokaro
mercury
VANESSA
bromine
VANESSA
which of the muscle can work with out getting tired?
nikkita
heart
Anam
Hg
Samiullah
what is the unit of muscles?
Samiullah
acid are organic or inorganic
Samiullah
why is the baby formed in the uterus n not else where?
Ekali Reply
you may help me ,to know why
mar
lo i am inn
mar
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
Maureen
atom, molecules, organelle, cell, tissue, organ, organ system
Cheila Reply
sub atom atom molecular molecules and cells.
Advertus
cells structural level.
Advertus
what is microorganisms I am a laboratory student.
Advertus
a small organism
Rahbliss
small organism that can only be seen under a microscope
Maureen
i am just interested to be part of ,to learn
mar
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 .
Munyah
plasma DNA cytoplasm Ribosome
Pearl Reply
cell, tissue,organ, organ systems,organism
Pearl Reply
cell is the build block of Life
Pearl
also a smallest unit of life
Frankline
sure..
Pearl
consistsof cytoplsm enclosed with in a membrane which contains many biomolecules such as proteins and nucleic acids
Frankline
differences in the effects of infection by HIV and influenza A virus on host genetic variability.
Yo Reply
i dont know
Ubah
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
Maureen
A.I.D.S
Maureen
suggest bioingormatics research article plz
peermehirali
what makes the heart to pumps blood?
Jamer Reply
sa node
Ubah
i do think its the nerve tranmission to the brain
Frankline
The contracting and relaxing of the atria and vertricles but the electrical system of the heart is what makes this possible.
keynia
yes which is called autorhymicity
Maureen
Yes,,by sucking blood leading to the weakening of cells,and finally it will be destroyed....
R0se
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.
Maureen
how do u prove it
Frankline
Maureen is correct ,
Davis
right
Kenn
right
Ubah
hi
horyaal
mxaa lahayaa
horyaal
What is housing?
Baldwin Reply
is where located you
Ubah

Get the best Human biology course in your pocket!





Source:  OpenStax, Human biology. OpenStax CNX. Dec 01, 2015 Download for free at http://legacy.cnx.org/content/col11903/1.3
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Human biology' conversation and receive update notifications?

Ask