i want 25 multiple choice questions with their model answer below each question that covers different aspects of : Structure of the cell
1- Cytoplasm (cytosol, organelles and
inclusions).
2- Nucleus.I) The Cytoplasm
➢colloidal solution, called the cytoplasmic matrix
or cytosol, in which some bodies are suspended
----- granular appearance.
The suspended bodies of the cytoplasm (2 groups)
1-the cytoplasmic organoids (organelles)
2-the cytoplasmic inclusions.What is the Cytosol ?
• It is the fluid component of cytoplasm that
contains :
- enzymes like ( enzymes used GLYCOLYTIC
PATHWAY).
- mRNA, transfer RNA, enzymes, Oxygen, CO2.
- (ions & salts), waste products.The cell (cytoplasmic) organoids (organelles)
Definition:
living , essential to the vitality and function of the cell.
Types:
A) Membranous cell organoids (organelles) ...
1- Cell membrane (plasmalemma)
2- Endoplasmic reticulum
3- Golgi apparatus
4- Mitochondria
5- Lysosomes
6-coated vesicles 7- endosomes 8- peroxisomesB) Non-membranoucellorganoids(organelles)...
1- Ribosomes and polyribosomes
2- Microtubules ( centroiles, cilia and flagella)
3- FilamentsMembranous Cell OrganoidsA) Cell membrane
By L/M:
By E/M
MOLECULAR STRUCTURE
FUNCTION in relation to histology1) The cell membrane and the
cell coat
By L/M:
- 7.5 - 10 nm in thickness.
- Too thin to be seen with LM.•By E.M.:
1-Trilaminar or UNITE membrane.
2- Two electron dense layers
separated by a lucent intermediate
one.
3-The outer surface covered by the
cell coat (glycocalyx).The molecular structure of cell
membrane
1) Lipids (Phospholipid molecules
+ cholestrol).
2) Proteins.
3) Glycoproteins & Glycolipid.1) Phospholipid molecules.
- Two rows (BILAYER) of phospholipid
molecules.
- Each phospholipid molecule is composed
of:
➢Polar (hydrophilic) phosphate head:
➢ Non-polar (hydrophobic) tail (two fatty
acid chain)1- hydrophillic polar end (water
attracting):
➢ Directed towards aqueous
solutions.
➢ Arranged at the outer and
inner(cytoplasmic) surfaces.
1- hydrophobic polar end
(water repelling):
➢ located in the middle region
away from water and facing
each other.• N.b : The dark lines (The electron-dense lines)
observed by electron microscope. Caused by the
deposit of Osmium Tetroxide (used in EM
preparation) in the hydrophilic portions of the
phospholipid molecules.2- Cholesterol
Site : Present among the closely –
packed phospholipid fatty acids.
Function: it has a stabilizing
effect on the membrane and
regulating the fluidity of cell
membrane in body temperature
N.B: Without cholesterol, cell
membranes would be to
permeable to some molecules.3) Protein molecules )50%)
1- The lipid in the membrane is incorporated
with Ptns molecules which are of Two types:
a) The integral (intrinsic) membrane proteins.
b) The peripheral (extrinsic) membrane
proteins.a) The integral (intrinsic) membrane
proteins.
1-(transmembrane protein).Span the membrane
from one side to the other
2- Others are small & partly embedded in the
hydrophilic region of lipid bilayer called (=carriers).
3- the integral proteins requires detergent (strong
treatment) to disrupt the lipid & remove them from
the cell membrane.b) The peripheral (extrinsic) membrane
proteins.
- Bound to the one of the 2
membrane surfaces especially the
cytoplasmic side of the lipid bilayer.
- This type of (Ptns) can be removed
easily with salt solution (with mild
treatment)4) Glycoprotein and glycolipids molecules:
- Projecting from the outer surface of the
membrane to form the cell coat (glycocalyx) .
- Fuzzy layer by EM.
Chemically formed of :
a) Glycoptns: oligosaccharide chain+ ptn
molecule.
b) Glycolipids: oligosaccharide chain+
phospholilid molecule.Function of cell coat:
Its integral ptn components act as a
receptors share in important
interactions such as:
Cell adhesion
Cell recognition
Hormones response.What is the function
of cell membrane?1- selective barrier (semipermeable)
• One important role of cell
membrane is to keep constant
the ion content of cytoplasm,
which differs from that of
extracellular fluid2- membrane transport &selective
permeability : (physiology )3- Communication
Cells need to communicate with one
another to regulate their growth,
division, and to coordinate their
functions.
Some of the integral membrane
proteins act as membrane receptors
that recognize signaling molecules
from other cells4- Vesicular transport (bulk
transport)
1)Endocytosis & exocytosis.
2) Receptor-mediated
endocytosisA- Phagocytosis ????? B- Pinocytosis??????
1) Endocytosis ( Fig 2-6 p. 11&12)A- PhagocytosisExocytosis
Bulk movement of substance
from inside outside the cell
by fusion of secretory vesicles
with the plasma membrane
e.g: release of neurotransmitter
By nerve cell.2- Receptor mediated endocytosis
(highly selective transport)
1- Receptors ( some integral membranous Ptns)
for specific molecules( ligands) such as
cholesterol & protein hormones..These
receptor present at cell surface.
2- Binding of these specific molecules (ligands)
to its receptor causes widely dispersed
receptors to accumulate in coated pit
10/9/20233- On other hand the coating on the cytoplasmic
surface is composed of many protiens mainly
clathrin ?????.
4- The coated pit invaginates and pinched off in
the cytoplasm as coated vesicles.
5- So The coated vesicle carries the specific
molecule (ligand) & its receptor into cell.• The clathrine molecule separate from the
coated vesicles & recycle back to the cell
membrane ----- for formation of new coated
pits.• N.b : Endocytosis of low-density lipoproteins
(LDL) is an important mechanism that keeps the
concentration of LDL in extracellular body fluids
low to keep the cholesterol in blood in low level
• Then the LDL is delivered to lysosomes
where it is degraded and its cholesterol is
released for use in the synthesis of
membranes
2-Other vesicles containing ligands may move
to and fuse with cell surface and release the
ligands outside in the process of
(transcytosis)LDL EndocytosisEndocytosis &ExocytosisTranscytosisCapillary Exchange- TranscytosisMembrane trafficking
Portions of the cell membrane become part of
the endocytotic vesicles during endocytosis.
…during exocytsis, membrane is returned to the
cell surface. The process of membrane
movement and recycling is called membrane
trafficking……
This process is important for cell maintenance
& health & preserving membrane area