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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

describe the process of platelet formation
Joy Reply
what is parasitic helminths
Sadiya Reply
list three categories of symbiotic relationships.
mary Reply
what's the difference between microbial intoxication and infectious diseases
dranimva Reply
microbial intoxication results when a person ingests a toxin or a poisonous substance that has been produced by a microbe while infectious disease results when a pathogen colonize the body and subsequently cause disease.
mary
weighing balance is needed in lab of microbiology for weighing?
amna Reply
It is mainly used for media preparation and product testing purpose.
Nakaweesi
thank you for your joining
nuur
what is microbiology
Shamsuddeen Reply
study of living organisms that are too small to be visible with naked eye
Marah
yes
Ahmed
microbiology is the study of microscopic organisms, either unicellular(single cell), multicellular( cell colony), or acellular (lacking cell).
munachimso
is the word Atypical or a typical bacteria. .am confused pliz help
MUWANGUZI Reply
typical bacteria
Zulpha
okay thank you what does that mean
MUWANGUZI
atypical means that it has some characters from bacteria not all characters ...but tybical means that it has all the characters that bacteria have
Reham
thank you Zulpha
MUWANGUZI
some examples please
MUWANGUZI
thank you Reham
MUWANGUZI
1) typical bacteria contain a cell wall whereas atypical bacteria usually do not contain a cell . 2) typical bacteria can be either Gram-positive or Gram-negative while atypical bacteria remain colorless with Gram staining. 3) cells of typical bacteria are large ,while cells of the atypical small
Marah
Example of atypical : Mycoplasma pneumoniae , chlamydophila pneumoniae , legionella
Marah
what is micro biology
Jauharah Reply
is the study of organisms which can't be viewed by our necked eyes
Egumat
Because it preexisting causing secondary infection after collateral damage of normal microbota
Rafaa Reply
combinations of drugs that can't be taken together and why
Grace Reply
Antagonism: the combined action is less than that of the more effective agent when used alone). All these effects may be observed in vitro (particularly in terms of bactericidal rate) and in vivo والله اعلم
Lenovo
....fermentros have 1-15litre capacity
AMAR Reply
which of the following microorganisms are classified as eukaryotic?
Semugab Reply
how do I see the list?
Melissa
what are the choices?
Melissa
dear tell us the choices
MUWANGUZI
mr semugab give us the list please
Nambi
Fungi
munachimso
what are the new discoveries of microorganisms
Ezibon Reply
bacteriology,viriology,micrology
Egumat
understanding of contributed to attempts to treat contain disease
james Reply
what is a bacteria
ROSE Reply
yes tell us
Judith
a bacteria is the largest living organisms on the planet Earth
Egumat
oh, sure. we have also one big here nearby!
Maxim
Bacteria is a large group of single-cell microorganisms. some causes infections and disease in animals and humans..
munachimso
do you mean procariots?
Maxim

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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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