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a) A micrograph of a cross section of a flagellum showing a ring of 9 sets of structures that are made of smaller rings. In the center are two more complete smaller rings. B)  A micrograph showing a flagellum. This shows a star shaped structure in the cell attached to the long lines that make up the filament of the flagellum. A diagram shows the triplet centriole in the cell as part of the basal body that attaches the filament to the cell. The diagram also shows a cross section of the filament. The outer ring is made of 9 sets of the following: a ring labeled subfiber A, a ring labeled subfiber B, a projection labeled radial spoke with a small end labeled spoke head, a projection towards the center labeled inner dynein, and a projection towards the outside labeled outer dynein. Each of these 9 sets are connected to the ones next to it via a line called nexin. These 9 sets form a ring; in the center of this ring are 2 small circles labeled central singlet microtubule. These two are attached to each other by a line labeled central bridge. C) A cell with flagella on either end. D) A cell with many small cilia along the outside and an indentation labeled mouth.
(a) Eukaryotic flagella and cilia are composed of a 9+2 array of microtubules, as seen in this transmission electron micrograph cross-section. (b) The sliding of these microtubules relative to each other causes a flagellum to bend. (c) An illustration of Trichomonas vaginalis , a flagellated protozoan parasite that causes vaginitis. (d) Many protozoans, like this Paramecium , have numerous cilia that aid in locomotion as well as in feeding. Note the mouth opening shown here. (credit d: modification of work by University of Vermont/National Institutes of Health)
  • Explain how the cellular envelope of eukaryotic cells compares to that of prokaryotic cells.
  • Explain the difference between eukaryotic and prokaryotic flagella.


Since amoxicillin has not resolved Barbara’s case of pneumonia, the PA prescribes another antibiotic, azithromycin, which targets bacterial ribosomes rather than peptidoglycan. After taking the azithromycin as directed, Barbara’s symptoms resolve and she finally begins to feel like herself again. Presuming no drug resistance to amoxicillin was involved, and given the effectiveness of azithromycin, the causative agent of Barbara’s pneumonia is most likely Mycoplasma pneumoniae . Even though this bacterium is a prokaryotic cell, it is not inhibited by amoxicillin because it does not have a cell wall and, therefore, does not make peptidoglycan.

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Key concepts and summary

  • Eukaryotic cells are defined by the presence of a nucleus containing the DNA genome and bound by a nuclear membrane (or nuclear envelope ) composed of two lipid bilayers that regulate transport of materials into and out of the nucleus through nuclear pores.
  • Eukaryotic cell morphologies vary greatly and may be maintained by various structures, including the cytoskeleton, the cell membrane, and/or the cell wall
  • The nucleolus , located in the nucleus of eukaryotic cells, is the site of ribosomal synthesis and the first stages of ribosome assembly.
  • Eukaryotic cells contain 80S ribosomes in the rough endoplasmic reticulum ( membrane bound-ribosomes ) and cytoplasm ( free ribosomes ). They contain 70s ribosomes in mitochondria and chloroplasts.
  • Eukaryotic cells have evolved an endomembrane system, containing membrane-bound organelles involved in transport. These include vesicles, the endoplasmic reticulum, and the Golgi apparatus.
  • The smooth endoplasmic reticulum plays a role in lipid biosynthesis, carbohydrate metabolism, and detoxification of toxic compounds. The rough endoplasmic reticulum contains membrane-bound 80S ribosomes that synthesize proteins destined for the cell membrane
  • The Golgi apparatus processes proteins and lipids, typically through the addition of sugar molecules, producing glycoproteins or glycolipids, components of the plasma membrane that are used in cell-to-cell communication.
  • Lysosomes contain digestive enzymes that break down small particles ingested by endocytosis , large particles or cells ingested by phagocytosis , and damaged intracellular components.
  • The cytoskeleton , composed of microfilaments , intermediate filaments , and microtubules , provides structural support in eukaryotic cells and serves as a network for transport of intracellular materials.
  • Centrosomes are microtubule-organizing centers important in the formation of the mitotic spindle in mitosis.
  • Mitochondria are the site of cellular respiration. They have two membranes: an outer membrane and an inner membrane with cristae. The mitochondrial matrix, within the inner membrane, contains the mitochondrial DNA, 70S ribosomes, and metabolic enzymes.
  • The plasma membrane of eukaryotic cells is structurally similar to that found in prokaryotic cells, and membrane components move according to the fluid mosaic model. However, eukaryotic membranes contain sterols, which alter membrane fluidity, as well as glycoproteins and glycolipids, which help the cell recognize other cells and infectious particles.
  • In addition to active transport and passive transport, eukaryotic cell membranes can take material into the cell via endocytosis , or expel matter from the cell via exocytosis.
  • Cells of fungi, algae, plants, and some protists have a cell wall, whereas cells of animals and some protozoans have a sticky extracellular matrix that provides structural support and mediates cellular signaling.
  • Eukaryotic flagella are structurally distinct from prokaryotic flagella but serve a similar purpose (locomotion). Cilia are structurally similar to eukaryotic flagella, but shorter; they may be used for locomotion, feeding, or movement of extracellular particles.


Mitochondria in eukaryotic cells contain ribosomes that are structurally similar to those found in prokaryotic cells.


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Peroxisomes typically produce _____________, a harsh chemical that helps break down molecules.

hydrogen peroxide

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Microfilaments are composed of _____________ monomers.


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Short answer

What existing evidence supports the theory that mitochondria are of prokaryotic origin?

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Why do eukaryotic cells require an endomembrane system?

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Name at least two ways that prokaryotic flagella are different from eukaryotic flagella.

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Questions & Answers

Can you give an essay of theta model of DNA replication?
ARYA Reply
Actually Bacterial replication is bidirectional process so when replication start in bacterial DNA two dna forks get formed and both replication again meet on same point in termination position ... so therefore in bacterial dna a greek letter (θ) structure formed which is called theta modal.
what are thermophile's bacteria
evon Reply
bacteria which can survive in high temperature.
why do we study microbiology?
Joyce Reply
For the classification, identification of pathogenic microbes ...
what is pathogenicity
diseases causing activity ...
of microbes..
sorry ability not activity..
I think it's the degree of a pathogen to cause infection
what is prokaryotes
are micro-organisms that have no nucleus e.g bacteria
and they do not possess membrane bound organelles e.g mitochondria
they are single cellular organisms,
all the organelles are embedded in cytoplasm of the cell
They don't possess true nucleus
they're unicellular organisms
they are classified as bacteria and. archaea. bacteria have a cell membrane conposed of peptidoglycan and archaea is composed of psuedomu
organelles are non membraneous as the nucleus
What is the biosynthesis of a bacteria cell
Adesina Reply
biosynthesis is multiple step enzymes catalyze process which occur in bacterial cell
biological way of manufacturing food and utilizes it for growth, multiplication and development
what is microbiology
Kiirya Reply
which organism can not be seen necked eyes is knowm as microbiology
micro can be define as d smallest living organisms dat can not be see wit naked eyes only with the aid of a microscope 🔬
bio means life logy means study
biology can b define as the systematic study of living things
microbiology can be define as the study of tiny organisms, that's according to my understanding
Microbiology is the study of living organisms which cannot be seen by the naked eye but only with the aid of a microscope. These microorganisms can be classified as bacteria, fungi, micro-algae, protozoa and virus.
microbes that can't seen in naked eyes. upto 100micrometer we can see in naked eyes but 1 microns or nanometers are invisible in naked eye.
what is a cell
Oteri Reply
cell can be define as smallest indivisible organism in the body
cell is the smallest unit which makes up the whole body
cell is smallest unit and there are two types prokaryotic cell and eukaryote cell. bacteria a prokaryotic cell which works independently.
nice forum
Which parasite competes with the host for vitamin B12 to cause pernicious anaemia
Diphyllobothrium latum for vit B12
it is also fish tapeworm
Diphyllobothrium sp feed vitB 12
recent trends in microbiology of biofertilizer
Ykomalipriya Reply
using nano technology
what is transposors
Junk DNA, jumping gene.
transposon elements are jumping gene as DNA sequence move from one location to anothet
what is microbiology
Usama Reply
Microbiology is the study of organisms, most of which are too small to be seen with the naked eye, including bacteria, algae, protozoa, and fungi, as well as acellular agents, such as viruses and prions.
what is gram +ve and gram - ve bacteria?
gm- contain lipid layer so it take counter stain during gram staining and pink or red in color but gm + does have thick LPS layer.
what year microbiology started
Robert Koch was the first to detect microorganisms
what appears microorganisms
clear the questions please
was it robert koch or robert hooke?
microbiology word came from microns. study microbes that not recognize in naked eyes.
what are the branch of microbiology
Oyemade Reply
We can basically classify into pure and applied microbiology
what is arabinose operon and it's stucture
Pooja Reply
The L-arabinose operon, also called the ara or araBAD operon, is an operon required for the breakdown of the five-carbon sugar, L-arabinose, in Escherichia coli
kya hum operon ko divide kar skate hain
reactions if viruses to physical and chemical agents?
All viruses contain the following two components: 1) a nucleic acid genome and 2) a protein capsid that covers the genome. Together this is called the nucleocapsid. In addition, many animal viruses contain a 3) lipid envelope. The entire intact virus is called the virion.
assume you have performed a gram stain on a sample of pus from a patients urethra. you see red, nucleated cells and purple rods. what can you conclude
Petty Reply
gram negative bacteria hence gonococcal infection
Study of micro organisation which we cannot see with naked eye...
shyam Reply
Despite their bad reputation, microbes are mostly beneficial or have a neutral effect on our lives. Microbiology is the scientific study of these microorganisms. Microorganisms are those organisms that are too small to see with the naked eye and include things like bacteria, fungi, and viruses.
not 'things'...'organisms' like bacterias, viruses and fungi
simi, it's not bacterias but bacteria which is the plural form of the word while bacterium is the singular of it
bacterium is obvio in a singular form but plural of bacterium is bacterias
Richard is right it's bacterium which is the singular form and plural is bacteria. *Bacterias* doesn't exist.
that is microbiology which is deals with microbes only their structure

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