Lecture BIOD 5: Eukaryotic Cell Structure

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Lecture BIOD 5 Eukaryotic Cell Structure
Function
- The cell is the basic unit of life.
- Based on their cellular structures, all living
cells can be divided into 2 groups prokaryotic
and eukaryotic.
- Only bacteria have prokaryotic cell types.
- Animals, plants, fungi, protozoans, and algae
all possess eukaryotic cell types.
- Fungi, protozoans, and algae are Eukaryotic
microorganisms.

• These microorganisms are very complex and
  prominent members of the ecosystem.

- Fungi ( some algae) are useful in industrial
microbiology.
- Many fungi and protozoa are major human
pathogens e.g. Malaria and African sleeping
sickness.
- Prokaryotic cells are generally much smaller
and more simple than eukaryotic.
- Prokaryotic cells are, in fact, able to be
structurally more simple because of their small
size.
- In the first part of this section, the focus is
on the structure and function of the eukaryotic
cell.
- At the end of the section, prokaryotic and
eucaryotic cells will be compared.
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• Overview of Eucaryotic Cell Structure

- The most obvious difference between Pro. Euc.
Is their use of membranes.
- Eucaryotic cells have membrane-delimited
nuclei, and have a variety of complex membranous
organelles in the cytoplasmic matrix (organelles
are intracellular structures that perform
specific functions in cells).
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• Cytoplasmic Matrix

- Large part of it is water (70-85).
- The environment of the organelles, and
location of important biochemical processes.
- Cell is not "just a bag in a bubble". Lots of
internal fibers internal skeleton capable of
being assembled, broken down in minutes involved
in cell movement, shape changes division.
- Fibers include microfilaments, microtubules
(e..g. form Cilia and Flagella) and Intermediate
filaments.
- Cell Walls also, provide a rigid structure
around cells. Made of cellulose in the case of
plants and fungi.
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• Endoplasmic Reticulum (ER)

- ER is a maze of parallel membranous tubules and
flattened sacs surrounding the nucleus that
connects with the nuclear membrane and runs
throughout the cytoplasm.
- ER provides a surface area for protein and
lipid synthesis
- forms a pathway for transporting molecules
within the cell and
- provides a storage area for molecules the cell
has synthesized.
- There are two distinct regions of the ER the
rough ER and the smooth ER.
- ER with ribosomes attached is called rough ER
and is involved in protein synthesis, production
of new membrane, modification of newly formed
proteins, and transport of these proteins and
membrane to other locations within the cell.
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- ER without ribosomes is called smooth ER and
contains enzymes for lipid biosynthesis,
especially the synthesis of phospholipids and
steroids. The smooth endoplasmic reticulum forms
transition vesicles to transfer molecules
produced in the rough ER to the Golgi apparatus
and other parts of the cell

• Golgi Apparatus

- The Golgi apparatus (GA) consists of 3-20
flattened and stacked saclike structures called
cisternae. A complex network of tubules and
vesicles is located at the edges of the cisternae.
- GA sorts proteins and lipids received from the
ER
- modifies certain proteins and glycoproteins
and
- sorts and packages these molecules into
vesicles for transport to other parts of the cell
or secretion from the cell.
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• Lysosomes and Endocytosis

- Lysosomes, synthesized by the ER and the GA,
are membrane-enclosed spheres typically about 500
nm in diameter that contain powerful digestive
enzymes.
- They function to digest materials that enter by
endocytosis.
- During endocytosis, the cytoplasmic membrane
invaginates and pinches off placing the ingested
material in a vesicle or vacuole called an
endosome.

• Ribosomes

- Ribosomes are composed of rRNA and protein and
consist of 2 subunits.
- Subunits have densities of 60S and 40S, but the
complete ribosome (2 subunits joined together
during translation) has a density of 80S.
- The ribosomes are both attached to the ER and
free in the cytoplasm.
- They serve as a workbench for protein
synthesis, that is, they receive and translate
genetic instructions for the formation of
specific proteins or polypeptides.
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• Mitochondria

- Mitochondria are rod-shaped structures ranging
from 2 to 8 nm in length.
- Found throughout the cytoplasm up to 20 of
the cell's volume.
- Mitochondria are surrounded by two membranes.
- They have their own DNA and ribosomes
- Frequently called the powerhouses of the cell
- They are the centers for respiratory
catabolism, during which oxygen is combined with
chemicals to break down foods, and generate cell
energy.

• Chloroplasts

- Chloroplasts are disk-shaped structures ranging
from 5 to 10 ?m in length.
- Like mitochondria, chloroplasts are surrounded
by an inner and an outer membrane.
- Contain stacks of thylakoids, where green
pigmented chlorophyll is embedded in membrane to
trap light.
- Use light energy to convert CO2 and water to
carbohydrates and O2, that is Photosynthesis.
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• Nucleus

- is a membrane-delimited spherical body filled
with dense fibrous material called chromatin.
- DNA is organized as multiple chromosomes
located within a nucleus.
- The nucleus is separated from the cytoplasm by
a nuclear membrane.
- The nuclear membrane has pores that connect
with the ER.
- Nucleolus is the most noticeable structure
within the nucleus, where ribosomal subunits are
assembled.
- The nucleus divides by mitosis, a process that
ensures each daughter cell receives the same
number of chromosomes as the original parent
cell.
- Haploid sex cells are produced from diploid
cells by meiosis,
- Meiosis is the nuclear division that occurs as
a part of sexual reproduction wherein the
daughter cell receives the haploid number of
chromosomes.
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• Flagella and Cilia

- Flagella are long and few in number whereas
cilia are short and numerous.
- Both consist of 9 fused pairs of protein
microtubules with side arms of the motor molecule
dynein that originate from a centriole.
- These form a ring around an inner central pair
of microtubules that arise from a plate near the
cell surface.
- Flagella and cilia function in locomotion.
Cilia also function to move various material that
may surround a cell.

• Prokaryotic (P)Vs EuKaryotic (E) Cells

- P nuclear body is called nucleoid not bound by
membrane E bound by membrane called nucleus.
- P one circular chromosome composed of DNA
histone-like proteins E 1 or more paired
linear chromosomes composed of DNA histone
proteins.
- P no nucleolus E nucleolus present.
- P divide by binary fission E divide by
mitosis (diploid) sex cells produced by meiosis.
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- P cytoplasmic membrane (CM) is a fluid
phospholipid bilayer without carbohydrates,
contains sterol-like molecules called hopanoids,
incapable of endocytosis exocytosis.
- E CM is a fluid phosphate bilayer, containing
sterols carbohydrates, capable of endocytosis
exocytosis.
- P Ribosomes 50S 30S E Ribosomes 60S 40S
- P Mitochondria, ER, GA, Vacuoles, Lysosomes,
chloroplasts are absent. No cytoskeleton.
- P cell walls composed of peptidoglycan E CW
composed of cellulose or Chitin.
- P no cilia, flagella is composed of single
rotating fibril E flagella cilia involved in
locomotion, consist of a distinct arrangement of
sliding microtubules.
Representative organisms
- P Bacteria (Eubacteria Archaebacteria)
- E Algae, Protozoans, and Fungi. And of course
Animals and Plants.