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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

why is DNA a genetic material
Mcbeth Reply
DNA is genetic material because it contains chromosome contains the traits which includes characters and behavioral characteristics
chima
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Tanaka
Good
Eddy
what is infection prevention
Muhammed Reply
good hygiene
Dhaqan
way of preventing disease causing germs
henry
maintenance of sterilization
Pooja
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Faustina
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Muhammed Reply
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Nantongo
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Md
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effiong
أ‌) Host factor ب) pathogen ج) environment
Widad
Hello
Kofi
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Widad
hey hi
kalai
The epidemiologic triangle is made up of three parts: agent, host and environment
Princess
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fadumo
history of microbiology
Balqees Reply
Penicillin is caused by what microorganism
Balqees
Penicillin is caused by what microorganism
Balqees
penicillium notatum
Pooja
M sorry I mean penicillin is caused by what Fungi
Balqees
penicillium fungi
Pooja
mention 5 characteristics of prokaryotic cell and also 5 characteristics of euryotic cell
Grace Reply
PROKARYOTES _ does not have nucleus _does not have membrane bound organels like eukaryotes -does not have endoplasmic reticulum _does not have a mitchochondrion _it have plasmid instead of chromosome EUKARYOTE S _have true nucleus _have all membrane bound organels _have mitochondria have
Pooja
continuation _have endoplasmic reticulum _have chromosomes does not have plasmid
Pooja
antigenisity define
kalai
explanation of spores
nahida Reply
what specific types of biological macromolecules do living things require?
Jonathan Reply
define spores its classification
nahida
define spores its structure and classification
nahida
what is a complement
Alecia Reply
something which completes or combine with something else to make it complete.
Kosi
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Kosi
medical microbiology
Kosi
you?
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Amina
Guys who's doing nursing in here
Mumba
I have a question
Mumba
what's the importance of microbiology in nursing
Mumba
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Mumba
microbiology also important for understanding the communicable or non-communicable disease in our hospitals...which is very important for patients and healthy people.
Kiran
what is a microbial flora
Chetan
normal microbial flora
Chetan
Definition of microbiology?
Mohamed Reply
study of microorganisms is known as microbiology
Pooja
no
Mumba
microbiology is the study of small or minute organisms that cannot be seen with our naked eyes but with the aid of a microscope
Mumba
write and explain the infection chain of 6 common disease infections
Adjowa Reply
diphtheria. dysentery. bubonic plague. pneumonia. tuberculosis. typhoid. typhus. Aug 22, 2017
shamim
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Dasaah
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Dasaah
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Dasaah
which bacteria can be isolated from abattoirs ( slaughter houses).
Omoja
bacteria that csn be isolated from abattoirs are- Clostridium Bacteroides Desulfobulbus Desulfomicrobium Desulfovibrio
Yashkin
what is a microscope
Louise Reply
Is an instrument used to magnify object which can not be seen with our naked eyes.
Mohamed
are virus host specific?
koguriyem Reply
are viruses effective in small dose?
koguriyem
structure of the bacteria
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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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