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Cell Structure and taxonomy, Lecture notes of Microbiology

Ateneo de Naga University (ADNU)Microbiology

An overview of the structure and classification of cells. It explains the differences between prokaryotic and eukaryotic cells, and describes the structures and functions of various organelles found in eukaryotic cells, such as the nucleus, mitochondria, and ribosomes. It also covers the structures and functions of prokaryotic cells, including the cell membrane, chromosome, and cytoplasm. The document concludes with a discussion of the Gram stain and glycocalyx.

Typology: Lecture notes

2021/2022

Available from 06/26/2023

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CELL
STRUCTURE
AND
TAXONOMY
What is a cell?
The fundamental living unit of any organism.
A cell is the basic unit of life.
All living organisms are composed of one or
more cells.
Cells are classified as:
PROKARYOTES – do not have complex system
of membranes and organelles. Examples are:
Bacteria and Archaea.
EUKARYOTES – More complex cells,
containing true nucleus and many membranes
bound organelles. Examples are algae,
protozoa, fungi, plants, animals, and humans.
EUKARYOTIC CELL
eu=true; karyo=nucleus
Have true nucleus, DNA is enclosed by a
nuclear membrane.
10X larger than most prokaryotic cells.
EUKARYOTIC CELL STRUTCURES:
Cell Membrane
- Enclosed and keep the cell intact.
- Composed of large molecules of
proteins and phospholipids.
- Like a “skin”
- Regulates passage of substances
in and out.
- Selective permeability
Nucleus
- Controls the functions of the
entire cell.
- “Command center”
4 components:
1. Nucleoplasm
2. Nuclear membrane
3. Chromosomes
4. Nucleolus
Cytoplasm
- Semifluid, gelatinous nutrient
matrix
- Contains the “organelles”
- Organelles has highly specific
functions which maintains the
cells and allow it to properly
perform its activities.
Endoplasmic Reticulum
- Highly convoluted system of
membranes that are
interconnected to form a
transport network tubules and
flattened sacs within the
cytoplasm.
1. Smooth ER
2. Rough ER
Ribosomes
- 18 to 22 nm in diameter
- Consists of rRNA
- play important part in protein
synthesis.
- free or attached in the ER.
Golgi Complex
- Stack of flattened membranous
sacs.
- Packages newly synthesized
proteins into small, membrane-
enclosed vesicles for storage
within the cell or export outside
the cell (exocytosis).
- “Packaging plants”
Lysosomes & Peroxisomes
1. Lysosomes
- contains lysozyme and other
digestive enzymes
-phagocytosis and autolysis
2. Peroxisomes
- where hydrogen peroxide is both
generated and broken down.
- found in mammalian liver cells.
Mitochondria
- Where most of the ATP (energy
carrying molecules) are formed by
cellular respiration.
- Energy is released from glucose
molecules and other nutrients to
drive other cellular functions.
Plastids
- Contains various photosynthetic
pigments.
- Chloroplasts - one type of plastid,
contain a green, photosynthetic
pigment called chlorophyll.
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CELL

STRUCTURE

AND

TAXONOMY

What is a cell?  The fundamental living unit of any organism.  A cell is the basic unit of life.  All living organisms are composed of one or more cells. Cells are classified as:PROKARYOTES – do not have complex system of membranes and organelles. Examples are: Bacteria and Archaea.  EUKARYOTES – More complex cells, containing true nucleus and many membranes bound organelles. Examples are algae, protozoa, fungi, plants, animals, and humans.

EUKARYOTIC CELL

 eu=true; karyo=nucleus  Have true nucleus, DNA is enclosed by a nuclear membrane.  10X larger than most prokaryotic cells. EUKARYOTIC CELL STRUTCURES:  Cell Membrane

  • Enclosed and keep the cell intact.
  • Composed of large molecules of proteins and phospholipids.
  • Like a “skin”
  • Regulates passage of substances in and out.
  • Selective permeability  Nucleus
  • Controls the functions of the entire cell.
  • “Command center” 4 components:
  1. Nucleoplasm
  2. Nuclear membrane
  3. Chromosomes
  4. Nucleolus  Cytoplasm
  • Semifluid, gelatinous nutrient matrix
  • Contains the “organelles”
  • Organelles has highly specific functions which maintains the cells and allow it to properly perform its activities.  Endoplasmic Reticulum
  • Highly convoluted system of membranes that are interconnected to form a transport network tubules and flattened sacs within the cytoplasm. **_1. Smooth ER
  1. Rough ER_**  Ribosomes
  • 18 to 22 nm in diameter
  • Consists of rRNA
  • play important part in protein synthesis.
  • free or attached in the ER.  Golgi Complex
  • Stack of flattened membranous sacs.
  • Packages newly synthesized proteins into small, membrane- enclosed vesicles for storage within the cell or export outside the cell (exocytosis).
  • “Packaging plants”  Lysosomes & Peroxisomes 1. Lysosomes
  • contains lysozyme and other digestive enzymes
  • phagocytosis and **_autolysis
  1. Peroxisomes_**
  • where hydrogen peroxide is both generated and broken down.
  • found in mammalian liver cells.  Mitochondria
  • Where most of the ATP (energy carrying molecules) are formed by cellular respiration.
  • Energy is released from glucose molecules and other nutrients to drive other cellular functions.  Plastids
  • Contains various photosynthetic pigments.
  • Chloroplasts - one type of plastid, contain a green, photosynthetic pigment called chlorophyll.
  • Found in plant cells and algae.  Cytoskeleton
  • System of fibers present throughout the cytoplasm.
  • Strengthen, support, and stiffen the cell, giving its shape.
  1. Microtubules - slender, hallow tubules (tubulins).
    • Slender, thread-like contractile structures which facilitate cell contraction.  Cell Wall
  • External structures that provide rigidity, shape, and protection.
  • May contain cellulose, pectin, lignin, chitin and some mineral salts.
  1. Cellulose - polysaccharide, present in algae and plants.
  2. Chitin - present in fungi and exoskeleton of arthropods.

 Flagella and Cilia

  1. Flagella - relatively long, thin structure, the organelle of locomotion.
  2. Cilia - tend to be more shorter (hair- like), thinner and more numerous

PROKARYOTIC CELLS

 10X smaller than eukaryotic cells  Very simple cells than eukaryotic cells  Do not contain membrane-bound organelles  Reproduce by binary fission  Includes bacteria and archaeans

PROKARYOTIC CELL STRUCTURES:

 Cell Membrane o Enclosed and keep the cell intact.

o Composed of large molecules of proteins and phospholipids. o Like a “skin” o Regulates passage of substances in and out. o Selective permeability

 Chromosome o Consists of a single, long, supercoiled, circular DNA molecule. o Serves as the control center of the bacterial cell. o Capable of replicating itself, guiding cell division, and directing cellular activities.  Plasmid o Small, circular molecules of double- stranded DNA that are not part of the chromosome. o May contain 10 to hundred genes. o May or may not be present in bacterial cell.  Cytoplasm o Semi-fluid consists of water, enzymes, dissolved oxygen, waste products, essential nutrients, proteins and carbohydrates, and lipids. o No organelles.  Cytoplasmic particles o Many tiny particles in the bacterial cytoplasm. o Most of these are clusters of ribosomes- polyribosomes or polysomes. o Site of protein synthesis.  Bacterial Cell Wall o Rigid exterior cell wall that defines the shape of bacteria. o Consist of a complex macromolecule known as peptidoglycan.

  1. Gram positive bacteria - thick layer
  2. Gram negative bacteria- thinner layer GRAM STAIN  The most widely used procedure for staining bacteria.  Developed over a century ago by Dr. Hans Christian Gram.  Bacteria are grouped as Gram- negative and Gram-positive  Glycocalyx o Slimy, gelatinous material produced by the cell membrane and secreted outside the cell wall.