Chapter
4 –Part II
Eucaryotic
Cell Structure and Function
The Nucleus and Cell Division
Ø Constant feature in eukaryotic cells
Ø Place where the cell’s genetic information
and its control center
Nuclear Structure
Ø Nuclei are membrane-delimited spherical bodies
Ø Containing Chromatin: Dense fibrous
material
-
In non-dividing cells,
chromatin exists in a dispersed condition, but condenses during mitosis to
become visible as Chromosomes.
-
Euchromatin: loosely organized and contains genes that
expressly themselves actively.
-
Heterochromatin: is coiled more tightly and is not
genetically active most of the time.
Nuclear Envelope
Ø Complex structure of both inner and outer
membrane separated by an perinuclear
space that bounds the nucleus.
-
Continuous with the ER
at several points
-
Outer membrane is
covered with ribosomes
Ø Nuclear
lamina: a network of intermediate filaments lie against the inner surface
of the envelope and supports it. Chromatin is usually associated with
the inner membrane.
Ø Nuclear
pores: penetrate the envelope
Functions:
serve as a transport route between the nucleus and surrounding cytoplasm
-
pores are formed by a
fusion of the outer and inner membrane
-
occupy 10 – 25% of the
nuclear surface
-
Annulus: complex ringlike arrangement of granular and
fibrous material located at the edge of each pore.
-- Function is not
understood, it may regulate or aid the movement of material through the pores.
The Nucleolus
Functions:
plays a major role in ribosome synthesis.
Ø The most noticeable structure within the
nucleus
Ø Nucleus may contain one to many nucleoli
Ø Not membrane enclosed
Ø Complex organelle with separated granular
and fibrillar regions.
Ø Present in non-dividing cells, but
disappears during mitosis
Ø After mitosis, reforms around the nucleolar organizer: a particular part of a specific chromosome.
Ø Nucleolar
organizer:
- NO DNA directs the production of ribosomal
RNA
- rRNA then combines
with the ribosomal proteins to form partially completed risosomal subunits.
- Immature ribosomal
subunits then leave the nucleus, by way of the envelope pores and mature in the cytoplasm
Mitosis
and Meiosis
Mitosis:
Ø When the genetic material must be duplicated
and then separated to ensure that each new nucleus possess a complete set of
chromosomes in eukaryotic reproduction (nuclear division and chromosomes
distribution).
Ø Occupies a small portion of a
microorganism’s life
Ø Can be seen in the Cell Cycle
Cell
Cycle: total sequence of events in the
growth-division cycle between the end of one division and the end of the next.
(1) Interphase:
- Cell growth takes place ,
portion of the cycle between periods of mitosis.
Composed of three parts:
1. G1 Period (gap 1 period)
Ø Active synthesis of RNA, ribosomes, and other
cytoplasmic constituents accompanied by considerable growth.
2. S Period (synthesis
period)
Ø DNA is replicated and doubles in quantity
Ø Distributed equally to two (2) new nuclei so
that each has a full set of genes.
3. G2 (gap 2 period)
Ø Cell prepares for mitosis (the M Period) by
the synthesis of special division protein.
Ø Cycles different length of time differ due
to the G1.
Four Phases of Mitosis:
1. Prophase
Ø Chromosomes (having two chromatids) become
visible and move toward the equator of the cell.
Ø Mitotic spindle forms
Ø Nucleous disappears
Ø Nuclear envelope begins disappeared
2. Metaphase
Ø Chromosomes are arranged in the center of
the spindle
Ø Nuclear envelope has disappeared.
3. Anaphase
Ø Chromatids in each chromosome separate and
move toward the opposite poles of the spindle.
4. Telophase
Ø Chromatids become less visible
Ø Nucleolus reappears
Ø Nuclear envelope reassembles around each set
of chromatids to form two new nuclei.
In mitosis:
Ø The original number of chromosomes is the
same after division
Ø Diploid organism will remain or 2N (still
has two copies of each chromosome)
Ø Microorganisms reduces its chromosome number
by half, from 2N to 1N,
from Diploid to Haploid (a
single copy of each chromosome).
Meiosis:
Ø
When the number
of chromosomes is reduced in half with each daughter cell receiving one
complete set of chromosomes.
Two stages of meiosis:
Stage I
Ø
Prophase: synapsis occurs homologous chromosomes come together and
lie side by side.
Ø
Anaphase: double stranded chromosomes from each homologous pair move to
opposite poles.
The number of chromosomes in halved in meiosis not mitosis.
Ø
Similar to mitosis in mechanics
Ø
Single stranded chromosomes are separated
Ø
After Meiosis I and II, the 2N has been
transformed into four (4) 1N cells.
Procaryotic and Eucaryotic cells differ with regards to the supporting and protective structure outside of the plasma membrane.
Bacteria have cell walls which provide the shape and protection
In contrast MANY
EUCARYOTES LACK A CELL WALL.
Ø Cell membrane of Eucaryotic contains sterols (cholesterol) in their lipid bilayer making them mechanically strong, reducing the need for external support.
n Some bacterial contain hopanoids which help to strengthened their cell membrane.
NOW ---Many
EUCARYOTIC CELLS DO HAVE a rigid external cell wall.
Ø
Algae: photosynthetic have cell walls that
contain polysaccharides such as cellulose and pectin.
Ø Fungal: nonphotsynthetic, cell wall composition varies, usually cellulose, chitin, or glucan
Ø
The EC cell
walls are much simpler then those of the peptidoglycan cell wall of the PC.
Ø Protozoa and some algae mostly nonphotosynthetic have a different external structure
Pellicle: a rigid layer of components just beneath the plasma membrane
- fairly simple in structure
-
not as strong and rigid as the cell wall, it gives the organism a characteristic
shape.
Example: Euglena
Cilia and Flagella:
Ø Most prominent organelles associated with motility.
Ø Both are whiplike and beat to move the mo along, they are different.
Two Ways they
Differ:
1. Size (cilia are smaller length to the flagella)
Cilia: 2 to 20 um
Flagella: 100 to 200 um
2. Pattern of movement
Flagella
Ø Flagellum movement often takes the form of waves that move through either from the base of the flagellum to its tips or in the opposite direction.
Ø
The motion of the waves propels the organism along.
Cilium
Ø Beat takes place in two different phases:
(1) a stroke represents when the cilium remains fairly stiff as it swings through the water
(2) Followed by a recovery stroke in which the cilium bends and returns to its initial position.
Comparison of the
Procaryotic and Eucaryotic Cells
Eucaryotes have a membrane-enclosed nucleus
Ø Algae, fungi, protozoa, higher plants, and animals
Ø Phagocytosis, pintocytosis, intracellular digestion, etc.
Procaryotes do not. Lack a true nucleus.
Ø Bacteria and Archea are
Ø Normally smaller than EC, often about the size of mitochondria and chloroplasts
Ø PC has a much more simpler structure than EC (no membrane-organelle)
Ø Functionally, PC are much simpler than EC
No Mitosis and Meiosis occurring, have asexual reproduction
Chapter 5
Microbial Nutrition
Nutrients:
Ø
A supply of raw materials needed by organisms to
obtain energy and construct cellular components.
Ø
Substances used in biosynthesis and energy
production, a requirement for microbial growth.
Common
Nutrient Rrequirement:
Ø
Over 95% of the microbial cell dry weight
composition is composed of the following major elements:
n
Carbon
n
Oxygen
n
Hydrogen
n
Nitrogen
n
Sulfur
n
Phosphorus
n
Potassium
n
Calcium
n
Magnesium
n
Iron
Ø C, O, H, N, S, and P are components of Carbohydrates, lipids, proteins, and nucleic acids.
Ø K, Ca, Mg, and Fe are cations and play a variety of roles.
- K required for activity by a number of enzymes, some involved in
protein synthesis
-
Ca contributes to the heat resistant
endospore
-
Mg serves as a cofactor for many
enzymes
Complexes with ATP
Stabilizes ribosomes and cell
membranes
-
Fe is part of the cythchromes
A cofactor for enzymes and
electron-carrying proteins
q
Manganese
q
Zinc
q
Cobalt
q
Molybdenum
q
Nickel
q
Copper