1.
Cell Compostion and structure
Course_ Microbial Physiology
Lec. no_ first lecture
3rd Grade – Fall Semester 2021-2022
Instructor´s name_ Heshu J. Ahmed
Instructor´s email_ heshu.jalal@tiu.edu.iq
Date_ 13/Oct./2021

2.
 What is microbial physiology?
 Define microbial physiology
 What is the significance of microbial physiology?

3.
What is Microbial physiology?
 Microbial physiology is defined as the study of how microbial cell structures, growth and metabolism
function in living organisms.
 It covers the study of viruses, bacteria, fungi and parasites.
 It is also conveyed as the study of microbial cell functions which includes the study of microbial growth,
microbial metabolism and microbial cell structure.

4.
 In this lecture basic structure and function of the components that make up eukaryotic
and prokaryotic cells will be discussed in detail.

5.
Eukaryotic cell structure
 The Nucleus
 The nucleus contains the cell’s genome.
 It is bounded by a membrane, which is composed of two lipid bilayer membranes: the
inner and the outer membrane.
 The nuclear membrane exhibits selective permeability because of pores, which consist
of a complex of several proteins whose function is to import substances into and export
substances out of the nucleus.

6.
 Eukaryotic DNA macromolecules are associated with basic proteins called histones
that bind to the DNA by ionic interactions.
 A structure often visible within the nucleus is the nucleolus, an area rich in RNA that is
the site of ribosomal RNA synthesis

7.
Cytoplasmic Structures
 The cytoplasm of eukaryotic cells is characterized by the presence of an ER, vacuoles, self-reproducing
plastids, and an elaborate cytoskeleton composed of microtubules, microfilaments, and intermediate
filaments.
 The endoplasmic reticulum (ER):
 Two types
Rough ER is a major producer of glycoproteins as well as new membrane material that is transported
throughout the cell
Smooth ER participates in the synthesis of lipids.

8.
 The Golgi complex
consists of a stack of membranes that to chemically modify and sort products of the ER to be secreted or to
become membranous structures of the cell.
 Lysosomes
are membrane-enclosed vesicles that contains digestive enzymes that the cell uses to digest macromolecules
such as proteins, fats, and polysaccharides.

9.
 The peroxisome
Functions to produce H2O2 from the reduction of O2. The H2O2 produced in the
peroxisome is subsequently degraded to H2O and O2 by the enzyme catalase.
 The cytoskeleton : is a three-dimensional structure that fills the cytoplasm.

10.
Prokaryotic cell structure
nucleoid
 Prokaryotes have no true nuclei;
 instead they package their DNA in a structure known as the nucleoid.
 Nucleoid-associated proteins exist in bacteria and are different from histones in
eukaryotic chromatin.

11.
 The nucleoid of most bacterial cells consists of a single continuous circular molecule.
 However, a few bacteria have been shown to have two, three, or even four dissimilar
chromosomes.

12.
Ribosomes
 The most numerous intracellular structure in most bacteria is the ribosome,
 the site of protein synthesis in all living organisms.

13.
The Cell Envelope
 Prokaryotic cells are surrounded by complex envelope layers that differ in composition
among the major groups.
 These structures protect the organisms from hostile environments, such as extreme
osmolarity, harsh chemicals, and even antibiotics.

14.
The Plasma Membrane
 The plasma membrane, also called the bacterial cytoplasmic membrane
 composed of phospholipids and upward of 200 different proteins. Proteins account for
approximately 70% of the mass of the membrane
 The membranes of prokaryotes are distinguished: from those of eukaryotic cells by
the absence of sterols (with some exceptions, eg, mycoplasmas, which also lack a cell
wall)

15.
Bacterial plasma membrane structure. This diagram of the fluid mosaic model of
bacterial membrane structure shown the integral proteins (green and red) floating in a
lipid bilayer. Peripheral proteins (yellow) are associated loosely with the inner
membrane surface. Small spheres represent the hydrophilic ends of membrane
phospholipids and wiggly tails, the hydrophobic fatty acid chains.

16.
Functions:
The major functions of the cytoplasmic membrane are
(1) selective permeability and transport of solutes;
(2) electron transport and oxidative phosphorylation in aerobic species;
(3) excretion of hydrolytic exo-enzymes;
(4) contain the enzymes and carrier molecules that function in the biosynthesis of DNA,
cell wall polymers, and membrane lipids;
(5) bear the receptors and other proteins of the chemotactic and other sensory transduction
systems.

17.
The Cell Wall
 The internal osmotic pressure of most bacteria ranges from 5 to 20 atm as a
result of solute concentration via active transport. In most environments, this
pressure would be sufficient to burst the cell were it not for the presence of a
high-tensile strength cell wall.
 The bacterial cell wall owes its strength to a layer composed of a substance
variously referred to as murein, mucopeptide, or peptidoglycan (all,
including “cell wall,” are synonyms).

18.
 Most bacteria are classified as Gram-positive or Gram negative according to
their response to the Gram-staining procedure.
 In addition to providing osmotic protection, the cell wall plays an essential
role in cell division as well as serving as a primer for its own biosynthesis.
 The cell wall is, in general, non selectively permeable; one layer of the
Gram-negative wall, however—the outer membrane—hinders the passage of
relatively large molecules.

19.
A. The Peptidoglycan Layer
 Peptidoglycan is a complex polymer consisting, for the purposes of description,
of three parts:
 a backbone, composed of alternating N-acetyl glucosamine and N-acetyl muramic acid
connected by β1→4 linkages.
 a set of identical tetrapeptide side chains attached to N-acetylmuramic acid;
 a set of identical peptide cross-bridges
The backbone is the same in all bacterial species; the tetrapeptide side chains and the
peptide cross-bridges vary from species to species.

20.
B. Components specific to Gram Positive cell-wall
1. Teichoic and teichuronic acids
There are two types of teichoic acids:
 wall teichoic acid (WTA), covalently linked to peptidoglycan,
 and membrane teichoic acid, covalently linked to membrane glycolipid. Because the
latter are intimately associated with lipids, they have been called lipoteichoic acids
(LTA).
2. Polysaccharides
 neutral sugars such as mannose, arabinose, rhamnose, and glucosamine and acidic
sugars such as glucuronic acid and mannuronic acid has been found in gram positive
cell wall, these sugars exist as subunits of polysaccharides in the cell wall

21.
Gram positive envelope

22.
C. Components specific to Gram Negative cell-wall
 Gram-negative cell walls contain three components that lie outside of the peptidoglycan
layer: lipoprotein, outer membrane, and lipopolysaccharide.
 1. Outer membrane—The outer membrane is chemically distinct
from all other biological membranes.
 It is a bi-layered structure; its inner layer resembles in
composition that of the cell membrane, and its outer layer
contains a distinctive component a lipopolysaccharide (LPS)
This asymmetric composition of the outer membrane helps it to exclude hydrophobic
substances from entering the cell such as bile salt that can kill the cell
Outer membrane has special protein channels Porins that allows passive transmission of
small hydrophilic substances

23.
 2. Lipopolysaccharide (LPS)—
 The LPS of gram-negative cell walls consists of a complex glycolipid, called lipid A,
to which is attached a polysaccharide which is extremely toxic to animals, has been
called the endotoxin of gram-negative bacteria because it is firmly bound to the cell
surface and is released only when the cells are lysed
 3. Lipoprotein—Molecules of an unusual lipoprotein cross-link the outer membrane and
peptidoglycan layers.
 4. The periplasmic space—The space between the inner and outer membranes, called the
periplasmic space

24.
Gram negative envelope

25.
D. The Acid-Fast Cell Wall
 Some bacteria, notably the tubercle bacillus (M tuberculosis) and its relatives
have cell walls that contain large amounts of waxes, known as mycolic acids.

26.
E. Cell Walls of the Archaea
 The Archaea do not have cell walls like the Bacteria. Some have a simple often
composed of glycoproteins.
Some Archaea have a rigid cell wall composed of polysaccharides or a
peptidoglycan called pseudomurein

27.
F. The Mycoplasmas
 The mycoplasmas are cell wall-lacking bacteria containing no peptidoglycan.
 such as Mycoplasma pneumoniae, an agent of pneumonia, contain sterols in their
membranes.

28.
Capsule
 The terms capsule and slime layer are frequently used to describe
polysaccharide layers; the more inclusive term glycocalyx is also used.
 Glycocalyx is defined as the polysaccharide-containing material lying outside
the cell.
 A condensed, well-defined layer closely surrounding the cell that excludes
particles, is referred to as a capsule.
 If the glycocalyx is loosely associated with the cell and does not exclude
particles, it is referred to as a slime layer.