Microbial structure and function Flashcards
General structural features of bacterial cells
- Cell shape
- Cell Wall
- Cell membrane(s)
- Capsules
- Pili and/or Fimbriae
- Cytoplasmic inclusions
- Bacterial DNA and nucleic acids
- Ribosomes
- Flagella
- Spores
CHECK DIAGRAM FOR BACTERIA LABELLED
What is Cell membrane / plasma membrane / inner membrane
Thin structure lying inside the cell wall and enclosing the
cytoplasm of the cell.
Role:
1) Selective barrier through which materials exit and enter thecell = selective permeability
2) Large molecules e.g. proteins can not pass through
membrane
3) Allows entry of smaller molecules e.g. H20, CO2 and some simple sugars
What is the Outer Membrane
- Thin structure lying beyond the the cell wall. Only
Gram-negative bacteria.
Role:
1) Selective barrier
2) Contains proteins for transport
3) Lipopolysaccharide – bacterial defence
4) Allows selective uptake and efflux
What do archaea contain but also lack
Archaea contain polysaccharides and proteins but lack
peptidoglycan
- Gram stain used to classify bacteria by cell wall composition:
What is gram positive and negative bacteria
Gram-positive bacteria have simpler walls with a large amount of peptidoglycan
Gram-negative bacteria have less peptidoglycan and an outer
membrane that contains lipopolysaccharides
What is the capsule
Outer layer of polymer made of extracellular
polysaccharide and/or proteins is present in some
prokaryotes.
Role:
1) adherence to a substrate, cells, surface such as
teeth (e.g. Streptococcus mutans)
2) protect bacteria from the host immune system such
as phagocytosis and complement (e.g.
Streptococcus pneumoniae)
What are fimbriae
Hair-like thin appendages
Role: allow attachment to substrates/surfaces or
other cells
What are pili
longer than fimbriae
Role: allow prokaryotes to exchange DNA
(conjugation)
What are flagella
- Flagella are long filamentous appendages consisting of a
filament, hook and motor.
-Composed of 42 different types of proteins.
-Scattered across the surface or concentrated at one or
both ends of the cell.
Role: Movement, Attachment, Secretory apparatus
Flagella & Motility
- Rotates clockwise or counter-clockwise by rotation from
the motor unit. - Bacterial flagella rotate to push the cell.
- Motile bacteria exhibit taxis:
What is positive and negative taxis
positive taxis = movement towards an attractant
negative taxis= movement away from a repellent
Whats Mesosome
Bacterial cells may have one or more large, irregular
folds.
Role:
* Many functions have been proposed: respiration etc
* Still unknown if cell processing artefacts or true cell
structures.
Nucleoid / nuclear body / DNA / chromosome
Prokaryotic genome has less DNA than the eukaryotic genome.
Circular continuous chromosome of dsDNA, not contained in a
nucleus but in nucleoid region with no surrounding membrane.
Most also have smaller rings of independently replicating DNA
called plasmids.
Role:
* DNA replication, transcription.
-Differences between prokaryotes and eukaryotic DNA
replication, transcription, and translation allows use of
antibiotics to inhibit bacterial growth without harming host.
Ribosomes
Cytoplasm of a bacterial cell contains numerous 70S
ribosomes (consisting of 50S and 30S subunits). Consists
of rRNA and protein.
Role:
* Protein synthesis
Endospores
Dormant, tough, non-reproductive structure.
Role:
* Permits survival of nuclear material for later germination.
* To ensure the survival of a bacterium through
environmental stress.
* Resistant to ultraviolet and gamma radiation, desiccation,
lysozyme, temperature, starvation, and chemical
disinfectants.
* Commonly found in soil and water, where they may
survive for long periods of time
Cysts
Dormant cells with thickened cells walls
* Permits survival of nuclear
material for later germination.
* To ensure the survival of a
bacterium through stress.
* Resistant to desiccation and
some chemicals, but cannot
withstand high temperatures
like endospores.
Structure and function: Fungi
- Fungal filaments absorb nutrients from the
soil, transfer them to trees and receive sugars
in return. - Some even transfer sugars between trees of
different species.
What does the body of fungi form
- Body of fungi form networks of branched hyphae
adapted for absorption. - Hyphae have tubular cell walls strengthened with chitin.
What is a septa
- Most fungi have hyphae divided into cells by septa, with
pores allowing cell-to-cell movement of organelles.
- Fungal hyphae form an interwoven mass called
mycelium.
* The structure of a mycelium maximizes surface-to-volume
ratio, making feeding very efficient.
What is a virus
- A virus is an infectious particle consisting of
DNA/genes packaged in a protein coat. - Viruses are much simpler in structure than even
prokaryotic cells. - Viruses cannot reproduce or carry out metabolism
outside of a host cell. - Viruses exist in an area between life-forms and
chemicals, leading a “borrowed life”
Structure and function: viruses
- Viruses are not cells.
- Small infectious particles consisting of nucleic
acids enclosed in a protein coat (in some cases, a
membranous envelope). - Viruses are obligate intracellular parasites =
replicate only within a host cell. - Each virus has a host range, a limited number of
host cells that it can infect.
What is Viral genomes
Double- or single-stranded DNA or RNA.
Viruses are classified as DNA viruses or RNA viruses.
Viruses have between three and 2,000 genes in their
genome.
