Transcript cell membrane

‫بـسـم هللا الرحـمن الرحـيم‬
Cell Physiology.
-study of cell is called Cytology (cyte=cell, logy=study)
- Cell represents the basic unit of life.
-human body develops from a single cell called the
Zygote ( ovum + spermatozoa).
-Zygote undergoes multiplication giving trillion (75-I00
trillions) of cells.
-Cells are grouped
a tissue (e.g. blood,muscle
and bone)
organs(e.g. heart , stomach and
brain)
system (e.g. digestive system).
-cells size, shape and structure:smallest units of the body
- are microscopic, ranging from l0- 30 um in diameter.
-
-The largest cell is ovum, approximately 500 um in
diameter, and visible to the naked eye. .
-the smallest cell is the erythrocyte (RBC) of blood
about 7.2 -_7.5 um in diameter.
-The longest cell is the neuron (neur=nerve) up to about
1- meter in length.
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Different types of cells human body
LIke nerve cell,muscle cell, bone cell, gland
cells,
blood cells,and reproductive cells.
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Each type adapted to perform one particular
function.
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e.g. the red blood cells transport oxygen from
the lung to the tissues.
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Almost all cells have the ability to reproduce
Structure of the cell
Cell is the structural and functional unit of living body.
Each cell is formed by cell body and a membrane
covering the body called cell membrane.
The cell membrane separates the cell
body from the fluid surrounding the cell.
The cell body has two parts namely the nucleus and the
cytoplasm that surrounds the nucleus.
The nucleus is separated from the cytoplasm by
nuclear membrane,and the cytoplasm is separated from
the surrounding fluid by the cell membrane.
MICROSCOPIC EXAMINATION OF HUMAN CELL
Each cell has
- cell membrane .
- cytoplasm .
-nucleus .
NUCLEUS
- In center of the cell.
- is spherical or oval in shape.
- Its average diameter is about 5um.
- Nucleus is present only in those cells which
divide and produce enzymes.
- cells with nucleus are called Eukaryotes (e.g.
WBC). Cells without nucleus are called
Prokaryotes (e.g. RBC).
STRUCTURE OF THE NUCLEUS
-Nuclear Membrane .
-separates the nuclear contents from the
surrounding cytoplasm.
-has Nuclear Pores .
-allowing the selectively permeable movement of
material from the nucleus to the cytoplasm and
vise versa.
-nucleoplasm
-gel fluid within the nucleus.
-contains the genetic material as deoxyribonucleic
acid (DNA). which makes up the genes.
-
DNA appears in form of thread like material
known as chromatin (means color) .
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just before cell division, the Chromatin becomes
tightly coiled as short, rod like structures called
Chromosomes.
-number of chromosome is 46 except mature
sex cells, is only 23 chromosomes.
-Each chromosome consists of (DNA + protein ).
-Chromosomes carry the Genetic information
about the hereditary and individual
characteristics of the person.
-DNA is responsible for the formation of ribonucleic
acid (RNA).
RNA regulates the synthesis of proteins by ribosomes.
Functions of the nucleus
1 : controls all the activities of the cell.
2: sends genetic information in form of RNA to
the cytoplasm for the synthesis of specific
protein.
3: The genes present in the nucleus control the
cell division.
Nucleolus
-densely stained small structures inside the
nucleus , not covered by the membrane.
- contains RNA, and small amount of proteins.
-This RNA later on forms Subunits of Ribosomes,
which are transported to the cytoplasm to form
matureribosomes.
-Mature ribosomes play an essential role in the
formation of proteins .
Three types of RNA
1-Messenger RNA (mRNA)
-DNA synthesis RNA by a process called
Transcription. Then RNA passes through the
nuclear pores and carries the gene code
(Genetic information) , to the cytoplasm for
controlling the formation of proteins.
 Transfer
RNA (tRNA)
-it present in cytoplasm .
-It transfer activated amino acids to the ribosomes
to be used in assembling protein molecules
according to the mRNA code by a process called
Translation.
Ribosomal RNA (rRNA)
-It is present with in the ribosomes
-it is responsible for the assembling of protein
molecules from the amino acids.
-cells of human being have over 100,000 gene
pairs.
-It means that as many as 100,000 different
protein are formed as enzymes or structural
proteins .
CYTOPLASM
- present between the cell membrane and the
nucleus and has two parts:
- Ectoplasm or cortex. just under the cell
membrane and contains a network of
Microfilaments to provide support to the cell
membrane.
-Endoplasm or cytosol fluid in nature extend from
the cortex up to the nuclear membrane
containing Dispersed Particles as dissolved
proteins, electrolytes, glucose, and small amount
of lipids.
ORGANELLES
They are the essential components of the cell present in
the cytoplasm. Each organelle has a specific function.
Generally they are responsible for the maintenance of
normal cell structure and its metabolism.
Two types of organelles are present in the cytoplasm:
I: Organelles covered by the membrane (Limiting
Membrane) :- as Endoplasmic Reticulum Golgi
Apparatus, Lysosomes, Secretory, Vesicles,
Peroxisomes, and mitochondria.
II: Organelles not covered by the membrane:- as
Ribosomes, Centrioles and Centrosomes,
Microtubules and Microfilaments,
I: Organelles Covered By the Membrane
A: endoplasmic reticulum
-Endoplasm( =cytoplasm), Reticulum(= network).
- At center of the cell.
- 2 parts:
a) Tubules makes a network of cavities named
Cisternae.
b) Vesicles expanded terminal portions.
-Both the tubules and vesicles are inter-connected
with each other.
- are made up of lipid bilayer membranes .
-The space inside the tubules and vesicles is
called Endoplasmic Lumen.
-It is filled with a fluid named Endoplasmic-Matrix
Rough/ Smooth Endoplasmic Reticulum
TYPES OF ENDOPLASMIC RETICULUM
1- Rough and smooth Endoplasmic Reticulum
l-Rough (granular) Endoplasmic Reticulum
- granular ribosomes are attached to it, giving its
"rough appearance
2-Smooth (A-granularEndoplasmicReticulum
1-The part of endoplasmic reticulum to which the granular
ribosomes are not attached is called smooth or granular
reticulum.
Many enzymes are present at the outer surface of smooth 
ER. These enzymes are responsible for various metabolic
processes of the cell.
Smooth endoplasmic reticulum is also responsible for the 
synthesis of non-protein substances like Steroid Hormones,
Sebum, and Cholesterol.
Functions of endoplasmic reticulum :1-ER forms the link between the nucleus and cell

membrane
2-ER provides the mechanical support for the even distribution 
of the cytoplasm in the cell.
3-ER forms an intracellular circulatory system in side the cell. 
This system is responsible for the transport of various cellular
products from one region of the cell to other region of the cell,
as well as out side the cell.
4-Cisternae of the ER act as temporary store house for 
specifically synthesized chemicals such as glycogens, lipids
and proteins.
5-An important function of ER is the catabolism of harmful 
such as drugs and carcinogens (material
substances
which can produce cancers).
•
B: Colgi apparatus or Golgi body :- present in all the cells expect red blood cells.
- near the nucleus facing the plasma membrane.
-consists of 4-8 flattened membranous sacs,
named Cisternae.
-Function:1-responsible for processing, sorting, modifying
and delivering the protein molecules mainly, as
well as lipid and carbohydrate molecules to the
various parts of the cell.
-The proteins synthesized in ER
transported
to Golgi apparatus
processed, sorted out
and packed in the form of Secretory-Granules
and are converted into modified compounds like
Lipoproteins and Glycoproteins
transported
to the surrounding tissue fluid via the process of
Exocytosis.
2- Some of the Golgi material is responsible for
the production of organelles and their enzymes
within the cell
Enlargement of Golgi apparatus to show Vacuoles and Cisternae
C: LYSOSOMES (vesicles )
- form by the Golgi-apparatus
- dispersed in the cytoplasm.
- spherical or oval in shape
- Its diameter about 250-750 nm.
- surrounded by a lipid bilayer membrane and
are filled with large numbers of small Granules
about 5 - 8 nm in diameter.
These granules contain(more than 40 different
lysosomal digestive enzymes, synthesized in
rough endoplasmic reticulum named as
Catalytic Hydrolases.)
-function:1-digestivefunction :- by Catalytic Hydrolases
- as nucleases
break down of nucleic acid
lipases
break down of lipids
proteases
break down of protein
carbohydrases break down of carbohydrates.
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2-Apart from the digestive functions, lysosomes are responsible
for the removal of unwanted substances like bacteria and
toxins out of the cell
For Example, white blood cells (WBCs) contain great number of
lysosomes. When a bacteria or other foreign particle enters the
cell, the lysosomes of WBCs are ruptured and the digestive
enzymes are released into the cytoplasm. These enzymes
immediately digest the bacteria or the foreign particles.
LYSOSOME
D: SECRETORY VESICLES:- formed in endoplasmic-reticulum
- then processed and packed in Golgi apparatus.
- Later on these are released in the cytoplasm.
-When it is necessary, the secretory vesicles are
ruptured and the secretory substances are
released through outer cell membrane
-e.g secretory granules( secretory vesicles) in
acinar cells of pancres.
E: PEROXISOMES
- They are derived from endoplasmic reticulum.
-similar to lysosomes but they carry different
group of destructive enzymes. These enzymes
are basically Oxidative-Enzymes,or Oxidases.
function:-destroying Hydrogen Peroxide (H202) resulting
from breakdown of lipids.
-detoxifying certain compounds such as ethanol,
alcohol, and alcoholic beverages in the liver
and in the kidney.
.
PEROXISOME
F: Mitochondria
- rod shaped or oval shaped structures
- about 0.5 to 1.0 u. in diameter
- covered by a bilayer membrane.
-The outer membane is smooth and encloses the
content of mitochondrion. .
-The inner membrane is folded inthe form of
series of shelf like projections called Cristae,
That provide large area for enzymatic reactions.
-function:-The basic function of mitochondria is to
initiate the process of Aerobic Respiration, for
the production of energy.
The energy produced is stored in the form of
Chemical Energy in the form of adenosine
triposphate (A TP) molecules .
- Thus, the mitochondria form the site of ATP
systems. When ever there is need for energy,
the ATP molecules are broken down and
energy is released. .
Thus, the mitochondria is called Power-House of
the cell.
-Number of mitochondria varies from cell to cell
e.g. more than 1000 mitochondria in a single
liver cell.
-
Cutaway Diagram of Mitochondrion Showing Outer and
Inner Membranes, Folded extensions (Cristae) of inner
membrane
II: Organelles Not Covered by the Membrane
A: RIBOSOMES
-Ribosomes are small, bead like structures
-Their size is less than 25nm.
- formation of ribosomal RNA begins in the
nucleus & collect in nucleolus.
- Ribosomes are composed up of two parts :
I: Ribosomal RNA (Synthesized in the nucleolus)
2: Ribosomal Proteins(Synthesized in the
cytoplasm)
- Once the ribosomes are completely developed
in the nucleolus these are transferred to the
cytoplasm, through the pores of the nuclear
membrane, where these are responsible for
protein synthesis. Ribosomes are therefore
known as "Protein Factories.
-Ribosomes are classified into 2 types:
Free Ribosomes
-are freely present in the cytoplasm and make
both structural and functional proteins
(enzymes) used for the cell only.
Fixed Ribosomes
- are bound to endoplasmic reticulum and make
protein for export purposes this means that
protein is used for other structures outside the
cell.
B: Centrioles and centrosome
- Centrioles and the surrounding cytoplasm
constitute the Centrosome of the cell.
-Centrioles are cylindrical structures, made up of
proteins.
-The wall of each centrioles consist of 9 groups of
3 types of microtubules named A, B, and C
from inner to outer. .
-Two centrioles are oriented at right angles to
each other.
-function:- are responsible for the movement of
chromosomes during cell division.
D: CYTOSKELETON
-Within the cytoplasm of most of the cells, various sized
filaments are present which form a flexible framework
known as the cytoskeleton.
-Cytoskeleton determines the shape of the cell. It is
responsible for the movement of the cell. It is also
responsible for the response of the cell to the external
stimuli.
-Cytoskeleton contains 4 types of filaments :
*Microfilaments (the thinnest)
*Intermediate filaments .
* Muscle thick filaments
*Microtubules (the thickest).
1: Microfilaments
-are long non-tubular organelles present throughout the
cell (most prevalent at the periphery).
- very thin structures, about 7nm in diameter.
- composed of a contractile protein called actin.
2- Intermediate filaments
-form a network around the nucleus.
-These filaments help to maintain the shape of the cell.
3- Muscle thick filaments:- Muscle thick filaments are present only in muscle
cells.
- These are made up of a contractile protein named
Myosin.
3: Microtubules
- tubular organelles having a diameter of 20 to 30 nm.
- are made up of a protein called tubulin arranged in
form of bundles.
-function:- maintainence of the shape of cell.
- Movement of secretory vesicles (transport system )
- Their best function is observed in the Nerve Cell.
Function of cytoskeleton structures:-
-determines the shape of the cell.
-movement of the cell.
- response of the cell to the external stimuli.
-act as binding sites for specific enzymes.
CI LIA & FLAGELLA
Some cells of the human body possess hair like short
and numerous (many) projections called Cilia.
(Cilia :-hair like short and numerous (many) projections )
If these projections are few and long in proportion to the
size of the cell, these are called Flagella.
( Flagella :-few and long projections)
- Both Cilia and Flagella contain cytoplasm surrounded
by the cell membrane
Cilia and Flagella of eukaryotic cell contain a group of
microtubules arrange as nine pairs of microtubules
around the circumference and two in the center.
-
functions
- Cilia:- move fluids or substance
along cell surface.
-flagellum:- moves an entire cell.