Lecture 2 Flashcards
(28 cards)
What are prokaryotes
simple cells that don’t have simple membrane bound parts called organelles. No genetic information is located in the organelles called the nucleus
What is the DNA of a prokaryotic cell
DNA of a prokaryotic cell is a circular double-
stranded macromolecule (the bacterial
chromosome) that is not separated by a
membrane barrier from the rest of the cell (the
nucleoid region)
Is there any mitochondria, Golgi apparatus,
endoplasmic reticulum in prokaryotic cells
no
What is the sedimentation rate of ribosomes
70 S (30S and 50 S)
What is the mode of reproduction of prokaryotes
binary fission
What are the similarities and differences in archaea and bacteria
Both groups are similar in size and shape
Archaea have an independent evolutionary
history and show many differences in their
biochemistry. Now, they are classified as a
separate domain.
What is prokaryotic cell structure
Cytoplasmic membrane
cytoplasm with ribosomes (sites of protein synthesis)
Cell wall (except the mycoplasma and ureaplasma)
Structures for the storage of genetic info: bacterial chromosome ( nucleoid, bacterial genome) and plasmids
What are additional structures in prokaryotes
Additional structures:
- capsules
- flagella
- pili (fimbriae)
- endospores (mainly genera Bacillus
and Clostridium)
What is the function of the cytoplasmic membrane and what is it
The primary function of the CM is to
regulate the flow of the material into- or
out of the cell. It is a differentially permeable barrier
What does the cytoplasmic membrane consist of
CM is composed largely of phospholipids
and proteins
What does the inside of the cytoplasmic membrane look like
Phospholipids are molecules made up of two
parts – a hydrophilic phosphate group and a
hydrophobic lipid (16-18 carbon atoms)
CM has a bilipid structure
Proteins are integrated into or associated
with the basic membrane structure
There is a dynamic relation between proteins
and phospholipid molecules (the fluid mosaic
model)
What is the structure and function of the cell wall
A rigid structure outside of the cytoplasmic
membrane that provides structural integrity to
the cell
The primary function of it is to protect the
bacterial cell from expanding and bursting
due to internal turgor pressure
It is relatively porous – it is not considered to
be a permeable barrier for small molecules
Cell wall also establishes the shape of
bacteria
What does the cell wall of almost every bacterial cell contain
peptidoglycan (also known as
murein or mucopeptide)
What is peptidoglycan
Peptidoglycan is biochemically unique and
is not found in any eukaryotic cell
Peptidoglycan is made up of two parts:
- the glycan portion
- the peptide portion
What is the glycan portion made up of
The glycan portion: alternately repeating units
of aminosugars N-acetylglucosamine (NAG)
and N-acetylmuramic acid (NAM), connected
by a β-glycosidic bond
What is the peptide portion made up of
The glycan portion: alternately repeating units
of aminosugars N-acetylglucosamine (NAG)
and N-acetylmuramic acid (NAM), connected
by a β-glycosidic bond
Differences in the cell walls of gram positive and gram negative bacteria
Characteristic Gram-positive Gram-negative
Thickness of the cell wall Thick (20-80 nm) Thin (up to 10 nm)
Cross-linkages in peptido- Present (usually absent (tetrapeptides
glycan pentapeptides) bind directly)
Teichoic acids Present Absent
Outer membrane (with
lipopolysaccharide, LPS) Absent Present
What is the outer membrane
A structure occurring externally to the
peptidoglycan layer in Gram-negative cell wall
It is quite similar to the cytoplasmic membrane in
thickness and biochemical composition (bilipid
structure); it also contains proteins (e.g. porins)
What are very important compounds in the outer membrane
A very important component of the outer
membrane is lipopolysaccharide (LPS) consisting
of lipid A (the toxic component, often referred to as
endotoxin) and a polysaccharide chain (O-specific
polysaccharide) extending outwards (co-called O
antigen)
What is the cellular storage of genetic information in bacteria
Bacterial chromosome – contains most of the genetic
information. Its size is about 5x105 - 5x106 bp (base
pairs)
In addition to the bacterial chromosome, bacteria may
have one or more small, circular macromolecules of
DNA known as plasmids
Plasmids, although contain only limited amount of DNA
(1- 5% of the DNA found in the bacterial chromosome),
often provide a supplementary genetic information -
mating capabilities (F plasmids), resistance to
antibiotics (R plasmids), pathogenic properties
(virulence plasmids) and tolerance to toxic metals
What is a bacterial capsule ( what is its structure and functions)
Capsule is a clear zone that lies outside the cell
wall
It usually consists of polysaccharides (e.g
uronic acids, amino sugars) but also other
materials (polypeptydes and proteins) may be
encountered
Capsule protects the bacterial cell against
phagocytosis, desiccation and some
desinfectants; it also help cells adhere to
surfaces
How is the capsule a virulence factor
Capsule is an important virulence
factor; some bacterial species will
have two variants, one that forms a
capsule and is a virulent pathogen,
and a noncapsulated form that does
not cause disease
What are bacterial flagella and what are the functions of them
Flagella are relatively long,
whiplike projections extending
outward from the cell of some
bacteria
* Bacteria may possess one
flagellum – monotricha (A),
several flagella originating from
one pole – lophotricha (B), two
flagella located on both poles –
ditricha or amphitricha (C) or
many flagella surrounding the
cell – peritricha (D
What are fimbrae (pilli)
These are short, hair-like projections
extending from the cell of some bacteria
Pili are composed of protein called pilin
They are involved in attachment
processes (e.g. to enterocytes or to the
intestine lining) – adhesion fimbriae
A special type of pili (F or sex pili) are
involved in bacterial mating (conjugation)
