Lecture 2: Structures and Characteristics of the Microbial World Flashcards
two fundamental cell types that differ categorically in cellular organization
prokaryotic & eukaryotic
prokaryotic
Prokaryotic cell structure is found within two different groups of organisms we know as Bacteria and Archaea.
Prokaryotic cells have few internal structures, they lack a nucleus, and they typically lack organelles
eukaryotic
eukaryotic cell structure are found in a group of organisms called the Eukarya.
This group includes plants and animals as well as diverse microbial eukaryotes such as algae, protozoa, and fungi. Eukaryotic cells contain an assortment of membrane-enclosed cytoplasmic structures called organelles (F
Genome
The genome is the full set of genes in a cell. A gene is a segment of DNA that encodes a protein or an RNA molecule. The genome is the living blueprint of an organism; the characteristics, activities, and very survival of a cell are governed by its genome.
Cytoplasmic membrane
All cells have a permeability barrier that separates the inside of the cell, the cytoplasm, from the outside.
The cytoplasm
An aqueous mixture of macromolecules (e.g.proteins, lipids, nucleic acids, and polysaccharides), small organic molecules (mostly the precursors of macromolecules), various inorganic ions, and ribosomes.
Cell wall
The cell wall is a relatively permeable structure located outside the cytoplasmic membrane and is a much stronger layer than the membrane itself.
Cell walls are typically found in plant cells and most microorganisms but are not found in animal cells.
Eukaryotic cell
Are found in a group of organisms called the Eukarya.
plants
animals
diverse microbial eukaryotes
- Algae
- Protozoa
- Fungi
DNA in eukaryotic cells
DNA is present as several linear molecules
The genome locates within the membrane-enclosed nucleus
A human cell, for example, contains approximately 3 billion base pairs, which encode about 20,000–25,000 genes
DNA in prokaryotic cells
The genomes of Bacteria and Archaea are typically closed circular chromosomes (though some prokaryotic cells have linear chromosomes).
The chromosome aggregates within the prokaryotic cell to form the nucleoid, which is not enclosed by a membrane.
Most prokaryotic cells have only a single chromosome
Many also contain one or more small circles of DNA distinct from that of the chromosome, called plasmids
The genomes of Bacteria and Archaea are typically small and compact, and most contain between 500 and 10,000 genes encoded by 0.5 to 10 million base pairs
To be competitive in nature, a microorganism must
Metabolism
Cell division
Metabolism
Nutrients are acquired from the environment and transformed into new cellular materials and waste products.
Energy is used to support synthesis of new structures
Cell division
Production of these new structures culminates in the division of the cell to form two cells.
Microbial growth results from successive rounds of cell division.
Genes
Contain information that is used by the cell to perform the work of metabolism.
Proteins
Genes are decoded to form proteins that regulate cellular processes.
Enzymes
Those proteins that have catalytic activity, carry out reactions that supply energy and perform biosynthesis within the cell.
Gene expression
Enzymes and other proteins are synthesized during gene expression in the sequential processes of transcription and translation.
Transcription
The process by which the information encoded in DNA sequences is copied into an RNA molecule
Translation
The process whereby the information in an RNA molecule is used by a ribosome to synthesize a protein.
Gene expression and enzyme activity in a microbial cell are coordinated and highly regulated to ensure that the cell remains optimally tuned to its surroundings.
DNA replication
Microbial growth requires replication of the genome through the process of DNA replication, followed by cell division.
Responsiveness
Microorganisms have the ability to sense and respond to changes in their local environment.
Motility
Many microbial cells are capable of motility, typically by self-propulsion
Motility allows cells to relocate in response to environmental conditions.
Differentiation
Some microbial cells undergo differentiation, which may result in the formation of modified cells specialized for growth, dispersal, or survival.
Cell signaling
Cells respond to chemical signals in their environment, including those produced by other cells of either the same or different species, and these signals often trigger new cellular activities. Microbial cells thus exhibit intercellular communication; that is, they are “aware” of their neighbors and can respond accordingly.
Horizontal gene transfer
Many prokaryotic cells can also exchange genes with neighboring cells, regardless of their species.
Evolution
results when genes in a population of cells change in sequence and frequency over time, leading to descent with modification.
The evolution of microorganisms can be very rapid relative to the evolution of plants and animals.
What structures are universal to all type of cells
Plasma membrane, cytoplasm, DNA, ribosomes, proteins
What processes are universal to all types of cells?
Multiplication
Metabolism
What processes are universal to all types of cells?
Metabolism
replication
What structures can be used to distinguish between prokaryotic cells and eukaryotic cells?
Organelles + nucleus
Morphology
Cell size and shape.
A micrometer
μm or micron: is one-millionth of a meter in length
Prokaryotic cells size
SMALL: Ranging between 0.5 and 10 in μm length, but prokaryotic cells can vary widely in size.
Eukaryotic cell size
LARGE: Between 5 and 100 μm in length
The smallest eukaryotic microorganism known is about 0.8 μm in diameter
The largest eukaryotic cells can be many centimeters in length.
Why are eukaryotic cells large?
owing to their complex intracellular structure and organelles
actively transport molecules and macromolecules within the
Why is it advantageous to have cellular structures when size gets larger?
As cell size increases, it becomes advantageous to have cellular structures that facilitate transport and compartmentalize cellular activities as seen in eukaryotic cells.
How do Prokaryotic cells generate energy for their size?
Rely on diffusion for transport through the cytoplasm and this limits their size.
Diffusion is very fast at small distances
the rate of diffusion increases as the square of the distance traveled
the metabolic rate in a prokaryotic cell varies inversely with the square of its size.
Largest prokaryotic cell:
Epulopiscium fishelsoni
found in the gut of the surgeonfish, can be more than 75μm wide and 600μm long.
**has more than 10,000 copies of its genome distributed throughout its cytoplasm, thereby preventing diffusional limitation between the genome and any region of the cytoplasm.
largest prokaryotic
Thiomargarita
about 750 μm in diameter
**Has a large vacuole that fills the center of the cell
Has many copies of its genome, which are distributed throughout its cytoplasm.
Vaccuole
The cytoplasm occurs as a thin layer squeezed between the cytoplasmic membrane and this central vacuole. In this way, the cytoplasm is never more than 1 μm from the membrane.
Advantages to being small
Small cells have more surface area relative to cell volume and thus have a higher surface-to-volume ratio than larger cells.
the S/V ratio of a coccus is 3/r
The S/V ratio of a cell controls many of its properties
How fast it grows (its growth rate)
Shape
Cellular growth rate
depends in part on the rate at which cells exchange nutrients and waste products with their environment.
- As cell size decreases, the S/V ratio of the cell increases and can exchange nutrients and wastes more rapidly (per unit cell volume).
Cell shapes can increase the overall
membrane area of the cell, such as those having long thin appendages or invaginations, allow bacteria to increase their S/V ratio for a given mass of cytoplasm.
Coccus
A cell that is spherical or ovoid in morphology (plural, cocci).
Rod or a bacillus
A cylindrically shaped cell (plural, bacilli)
Spirillum
A spiral-shaped cell (plural, spirilla)
Vibrio
A cell that is slightly curved and comma-shaped.
Spirochete
A special kind of organism that has a spiral shape but which differs from spirilla because the cells of spirochetes are flexible, whereas cells of spirilla are rigid.
Irregular in shape.
Appendages
such as stalks and hyphae, are used by some cells for attachment or to increase surface area.
Asymmetrical cell division, such as budding, can result in irregular and asymmetrical cell shapes.
The cell morphologies variations for rods:
fat rods
thin rods
short rods
long rods
rods that occur as single cells
rods as pairs of cells
rods that form into filaments
What properties of the cell change as it gets smaller?
No room for organelles, Less DNA
Why is it that eukaryotic cells are typically larger than prokaryotic cells?
Contain organelles
What traits have allowed the bacteria Epulopiscium and Thiomargarita to have such large cells?
vaculoe, lots of dna
domains
Bacteria
Archaea
Eukarya
All known cellular organisms belong to one of these three domains
Bacteria
Archaea
Eukarya
Bacteria
Bacteria have a prokaryotic cell structure
Undifferentiated single cells with a length that ranges from 0.5 to 10μm.
Diverse in appearance, size, and function.
Most bacteria are unicellular
Some bacteria can differentiate to form multiple cell types and others are even multicellular (for example, Magnetoglobus).
Bacterial classification
Phyla
More than 90% of cultivated bacteria belong to one of only four phyla:
Firmicutes
Proteobacteria
Bacteroidetes.
Actinobacteria
The analyses of environmental DNA sequences provide evidence for the existence of at least
80 bacterial phyla
Archaea- eukaryotic or prokaryotic cell structure
Archaea have a prokaryotic cell structure
Phyla of Archea
Euryarchaeota
Crenarchaeota
Thaumarchaeota
Nanoarchaeota
Korarchaeota
Are archea pathogenic?
Archaea lacks any known disease-causing (pathogenic or parasitic) species of plants or animals.
Groups of Eukarya
Plants
Animals
Fungi
lineages of eukarya
6 kingdoms
What phylum of Archaea is common worldwide in soils and in the oceans?
What four bacterial phyla contain the largest number of well-characterized species?
How are viruses different from Bacteria, Archaea, and Eukarya?
