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Learning objectives

  • Explain the distinguishing characteristics of eukaryotic cells
  • Describe internal and external structures of prokaryotic cells in terms of their physical structure, chemical structure, and function
  • Identify and describe structures and organelles unique to eukaryotic cells
  • Compare and contrast similar structures found in prokaryotic and eukaryotic cells

Eukaryotic organisms include protozoans, algae, fungi, plants, and animals. Some eukaryotic cells are independent, single-celled microorganisms, whereas others are part of multicellular organisms. The cells of eukaryotic organisms have several distinguishing characteristics. Above all, eukaryotic cells are defined by the presence of a nucleus surrounded by a complex nuclear membrane. Also, eukaryotic cells are characterized by the presence of membrane-bound organelles in the cytoplasm. Organelles such as mitochondria, the endoplasmic reticulum (ER), Golgi apparatus, lysosomes, and peroxisomes are held in place by the cytoskeleton , an internal network that supports transport of intracellular components and helps maintain cell shape ( [link] ). The genome of eukaryotic cells is packaged in multiple, rod-shaped chromosomes as opposed to the single, circular-shaped chromosome that characterizes most prokaryotic cells. [link] compares the characteristics of eukaryotic cell structures with those of bacteria and archaea.

A diagram of a large cell. The outside of the cell is a thin line labeled plasma membrane. A long projection outside of the plasma membrane is labeled flagellum. Shorter projections outside the membrane are labeled cilia. Just under the plasma membrane are lines labeled microtubules and microfilaments. The fluid inside the plasma membrane is labeled cytoplasm. In the cytoplasm are small dots labeled ribosomes. These dots are  either floating in the cytoplasm or attached to a webbed membrane labeled rough endoplasmic reticulum. Some regions of the webbed membrane do not have dots; these regions of the membrane are called smooth endoplasmic reticulum. Other structures in the cytoplasm include an oval with a webbed line inside of it; this is labeled the mitochondrion. Spheres in the cytoplasm are labeled peroxisome and lysosome. A pancake stack of membranes is labeled golgi complex. Two short tubes are labeled centrosomes. A large sphere in the cell is labeled nucleus. The outer membrane of this sphere is the nuclear envelope. Holes in the nuclear envelope are called nuclear pores. A smaller sphere in the nucleus is labeled nucleolus.
An illustration of a generalized, single-celled eukaryotic organism. Note that cells of eukaryotic organisms vary greatly in terms of structure and function, and a particular cell may not have all of the structures shown here.
Summary of Cell Structures
Cell Structure Prokaryotes Eukaryotes
Bacteria Archaea
Size ~0.5–1 μM ~0.5–1 μM ~5–20 μM
Surface area-to-volume ratio High High Low
Nucleus No No Yes
Genome characteristics
  • Single chromosome
  • Circular
  • Haploid
  • Lacks histones
  • Single chromosome
  • Circular
  • Haploid
  • Contains histones
  • Multiple chromosomes
  • Linear
  • Haploid or diploid
  • Contains histones
Cell division Binary fission Binary fission Mitosis, meiosis
Membrane lipid composition
  • Ester-linked
  • Straight-chain fatty acids
  • Bilayer
  • Ether-linked
  • Branched isoprenoids
  • Bilayer or monolayer
  • Ester-linked
  • Straight-chain fatty acids
  • Sterols
  • Bilayer
Cell wall composition
  • Peptidoglycan, or
  • None
  • Pseudopeptidoglycan, or
  • Glycopeptide, or
  • Polysaccharide, or
  • Protein (S-layer), or
  • None
  • Cellulose (plants, some algae)
  • Chitin (molluscs, insects, crustaceans, and fungi)
  • Silica (some algae)
  • Most others lack cell walls
Motility structures Rigid spiral flagella composed of flagellin Rigid spiral flagella composed of archaeal flagellins Flexible flagella and cilia composed of microtubules
Membrane-bound organelles No No Yes
Endomembrane system No No Yes (ER, Golgi, lysosomes)
Ribosomes 70S 70S
  • 80S in cytoplasm and rough ER
  • 70S in mitochondria, chloroplasts

Cell morphologies

Eukaryotic cells display a wide variety of different cell morphologies . Possible shapes include spheroid, ovoid, cuboidal, cylindrical, flat, lenticular, fusiform, discoidal, crescent, ring stellate, and polygonal ( [link] ). Some eukaryotic cells are irregular in shape, and some are capable of changing shape. The shape of a particular type of eukaryotic cell may be influenced by factors such as its primary function, the organization of its cytoskeleton, the viscosity of its cytoplasm, the rigidity of its cell membrane or cell wall (if it has one), and the physical pressure exerted on it by the surrounding environment and/or adjoining cells.

Questions & Answers

How many types of MICROORGANISMS do we have?
Hope Reply
Hello friends
Hope
What's pathogenesity
Usman Reply
something that causes disease
Anietie
who is the father of microbiology?
Hope
no it is not it also dealt withe fermentation techniques, downstream processing of isolated products etc
Ramchandra Reply
hy
Abdul
hy
Roshan
you from
Abdul
I'm from Bangalore, India
Shanu
in banglore
Prabhat
what group is Indian
Abdul
I'm from pune
Vitthal
ok
Abdul
Why scientists is not studies the drungs or vaccines of a virus, based on common characterstics of virus as living and non-living organisms?
demisew
what are the examples of viruses and their causing agent
kolawole Reply
coronavirus in the family of Coronaviridae and the causing agent is common cold where it spread easily compared to hot region.you can correct me if I am wrong.
nyakaraitta
👍
Puja
what
nkechi
okay there are major 3 groups (1.Enterovirus=poliovirus, cocksakievirus A&B,echovirus,endovirus etc causing poliomyelities,meningitis, fever,respiratory disease, acute hemorrhagic conjunctivitis, 2.Hepatitis virus- infectious hepatitis , 3.Rotavius incl.coronavius =vomiting, diarrhoea and common co
nyakaraitta
isthe another virus are coronaviridae
anuush
Hai Puja
Shanu
g
Abdul
corona virus is not dangerous but not care is very dangerous..............
Abdul
👍
Puja
he means if we take care we will not be infected
abel
yeah
Abdul
for the question thing first let's classify viruses then it would be easier to deal with zem
abel
Where you all from?
Shanu
Pakistan
Abdul
what are five elements that are needed for bacteria to grow?
Florence
proper acidity (ph)
Abdi-fatah
salt level
Abdi-fatah
Temperature
Bejide
osmotic pressure,oxygen,light
abel
but zey are not only five n we can classify zem as physical and chemical
abel
air in hydrogen and carbon and niterogin
Abdul
1. Possible complications and outcomes for cutaneous anthrax:
Firoj Reply
chlamydia can it be viral disease?
nyakaraitta Reply
noh
Vitthal
what is microbiology
Sohel Reply
is the study of tiny organisms with the use of microscopes
Bejide
Is the study of microorganisms
Usman
is the biological science of identification and charaterization of micro organisms surrounding the environment
Jojo
what are the major groups of archae bacteria
Brian Reply
methanogens, halophiles, thermophiles
Mahalakshmi
Right, mali
vivek
yeah!!
Mahalakshmi
yes
nyakaraitta
right
Jojo
how can get information
Raage Reply
how i study microbiology
Raage
By Reading About It
Rajat
quickest form
Raage
why do our brain needs glucose?
Bijay Reply
b/c our brain works glucose as the other body use insulin
Cabdi
of course why do hairs obtain nutrients yet there is no blood?
nyakaraitta
can I get a diagram of paramicium
nyakaraitta
what is the meaning of the term microbiology
Mary Reply
 study of all living organisms that are too small to be visible with the naked eye.
Nnamdi
yahh it right
Stavan
wow lovely
Psalm
Well said.
Shanu
study of microscopic organism like protozoa, bacteria, fungi, algea ,viruses betc
Dr
what are the career opportunities in microbiology
Anietie
I don't understand the explanation
Nancy Reply
ok
Cabdi
virus can also culture?
anuush
ya same doubt.. virus can also culture?
Prabhat
prabhat explain More
Prince
yes we can culture virus. virus culture is a laboratory test in which samples are placed with a cell type that the virus being tested for is able to infect.
Feby
the topic is telling us on how the first microscope is been invented by van Lee...., & his own still remains the best although he's was a simple one with one lens while the compound one that was invented by Hooke with two lenses is the one commonly used now.
Esumeh
sorry! Hooke didn't invent it rather he used it in the writing of his book .
Esumeh
what is microbiology
Sohel
microbiology is the study of microrganisms (unicellular,multicellular) which can be seen under the microscope
Andrre
is the test involving use of serum to identify the presence of any pathogens or antibodies
John Reply
Hello everyone here..
Tean Reply
Pseudomonus
How can I contribute to this noble institution?
Tean
is just by reading & understanding the topic & try to ask questions that you don't understand.
Esumeh
Size of colony is measures in what term ?
Aftab Reply
Size of colony is measures in wich term?
Aftab
How Degree/amount of light transmitted through colony is described ?
Aftab

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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