ALIGARH COLLEGE OF

NURSING

Name: Huma Anwar

Subject: Anatomy&
Physiology

Discipline: BSN- Generic

(Batch 2)

Presented To:

Sir Nadeem Gauri

Date: 19th March 2020

CELL ,TISSUE & MEMBRANE

 Cell, Tissues and Membrane

Describe the structure and functions of a cell

The cell is the basic functional unit in a human meaning that it is a self-contained and operational
living entity. Humans are multicellular organisms with various different types of cells that work
together to sustain life. Other non-cellular components in the body include water, macronutrients
(carbohydrates, proteins, and lipids), micronutrients (vitamins, minerals) and electrolytes. A
collection of cells that function together to perform the same activity is known as tissue e.g. blood,
muscle, bone. Masses of tissue work collectively to form an organ that performs specific functions
in the body e.g. heart, stomach, brain. Organs are grouped together to form systems, each of which
performs a particular function that maintains homeostasis and contributes to the health of the
individual. For example, the digestive system is responsible for taking in, digesting and absorbing
food and involves a number of organs, including the stomach and intestines.

The human body develops from a single cell called the zygote, which results from the fusion of the
ovum (female egg cell) and the spermatozoon (male sex cell). Cell division follows and, as the
fetus grows; cells with different structural and functional specializations develop, all with the same
genetic make-up as the zygote.

Parts of the Human Cell

The cell contains various structural components to allow it to maintain life, which are known as
organelles. All the organelles are suspended within a gelatinous matrix, the cytoplasm, which is
contained within the cell membrane. One of the few cells in the human body that lacks almost all
organelles are the red blood cells. The main organelles are as follows:

 Cell membrane
 Endoplasmic reticulum
 Golgi apparatus
 lysosomes
 Mitochondria
 Nucleus

1|Pa g e
  Ribosomes
 Perioxisomes
 Microfilaments and microtubules
 Centrosome
 Cell extensions
 Cytoskeleton

The Cell

2|Pa g e
Cell Membrane
The cell membrane is composed of almost entirely proteins and lipids. It is about 55% protein by
weight, 25% phospholipids, 17% cholesterol and other lipids, and 3% carbohydrate.
Phospholipids have a phosphate hydrophilic end, and a fatty acid hydrophobic end.

|G|
|L|
|Y|---Fatty Acid
Phosphate----|C|
|E|
|R|---Fatty Acid
|O|
|L|
Hydrophilic Hydrophobic

The hydrophobic parts oppose one another, and the hydrophilic parts are exposed to the intra- and
the extracellular fluid. The membrane itself is water insoluble and is only permeable to fat soluble
substances. However, numerous channels allow passage of water and other substances into the
cell.

The proteins are anatomically classified into integral and peripheral proteins. Difference between
integral & peripheral proteins: Integral proteins penetrate the membrane, and peripheral proteins
are just attached to one side. Integral proteins can act as channels or pores and others act as carriers
and transporters of various substances. Peripheral proteins serve a number of functions, and in

3|Pa g e
many cases serve to activate the integral proteins. Some of the proteins are enzymes, others serve
as second messengers.

Cholesterol is found in varying amounts in the membrane. It tends to be found between the
triglyceride 'stalks' of the phospholipids, and serves to make the membrane less porous.

Most proteins and many lipids are glycoprotins or glycolipids, and the -ve carbohydrate end of
the molecule is presented to the extracellular fluid. This carbohydrate layer is referred to as the
Glycocalyx of the cell. These carbohydrates serve several important functions such as:

 Many have a negative electrical charge, which repels other negatively charged ions.
 They serve to attach cells to one another, and to the basement membrane
 Many act as receptor sites for hormones such as Insulin
 They enter into immune reactions

Cell Membrane Proteins

Cell membrane proteins may be functionally classified into four groups:

 Structural Proteins: On the interior of the cell, these serve as anchors for the actin and

tubulin micro fibrils. On the exterior they serve to bind cells together into tissues
 Enzymes: In the small intestine, many of the digestive enzymes are embedded in the cell

wall.
 Receptors: These act as receptors for the messenger system of the cell. For example,

Insulin exerts its effects on the cell by binding onto a special receptor.
 Transporters: these serve to transport molecules in and out of the cell. They may be

either channels, or carriers.

Endoplasmic Reticulum

The endoplasmic reticulum(ER) is a membranous structure that contains a network of tubules and
vesicles. Its structure is such that substances can move through it and be kept in isolation from the
rest of the cell until the manufacturing processes conducted within are completed. There are two
types of endoplasmic reticulum –rough (granular) and smooth (a granular).

4|Pa g e
The rough endoplasmic reticulum(RER / granular ER) contains a combination of proteins and
enzymes. These parts of the endoplasmic reticulum contain a number of ribosomes giving it a
rough appearance. Its function is to synthesize new proteins.

The smooth endoplasmic reticulum(SER / a granular ER) does not have any attached ribosomes.
Its function is to synthesize different types of lipids (fats). The smooth ER also plays a role in
carbohydrate and drug metabolism.

Golgi Apparatus

The Golgi apparatus is a series of stacked membrane enclosed sacs, usually six or more. It is a
polarized structure with a cis and a trans side. The cis side faces the endoplasmic reticulum and
the trans side the cell membrane. Its job is to process and package substances, both protein and
non-protein, from the endoplasmic reticulum. The Golgi apparatus modifies the oligo-saccharide
attachments of the glyco-proteins that have been initially prepared in the ER.

Membranous protein containing vesicles pinch off from the endoplasmic reticulum and are
transported across to the cis Golgi apparatus. Substances are exchanged between one layer of the
Golgi apparatus and another by a similar process. The vesicles that pinch off from the trans side
shuttle to lysosomes or to the cell exterior. Those destined for the cell exterior are follow either
constitutive or non-constitutive (also known as regulated) pathways. Those following
constitutive pathways are immediately secreted; those following a non-constitutive pathway either
form an excretory vesicle, or are shunted to an existing vesicle, where further processing may be
carried out

Lysosomes

Lysosomes are one type of secretory vesicle with membranous walls, which are formed by the
Golgi apparatus found in the cytoplasm. The contents of the Lysosome are acidic in nature and
contain a variety of enzymes involved in breaking down fragments of organelles and large
molecules (e.g. RNA, DNA, carbohydrates, proteins) inside the cell into smaller particles that are
either recycled, or extruded from the cell as waste material. They act as the digestive system of the

5|Pa g e
cell. Lysosomes in white blood cells contain enzymes that digest foreign material such as
microbes.

The following enzymes are present in most lysosomes:

Mitochondria

Mitochondria is known as the powerhouse of the cell, producing the majority - about 95% - of the
ATP that is used in cell metabolism. Mitochondria come in various shapes and sizes -from round
or spheroid to sausage or obloid in shape. The more active a cell is the more mitochondria they
have.

They have a double bilayer membrane, an outer and in inner membrane. The inner membrane is
folded into cristae, and the walls of these cristae are studded with enzyme rich proteins which are
involved in the production of ATP. Between the two membranes is the gel of the outer matrix -
rich in enzymes for the processing of high-energy hydrogen to ATP. In the inner space is the inner
matrix that contains numerous enzymes involved in the breakdown of Glucose, fats and proteins
for energy.

6|Pa g e
Mitochondria have several anomalies. They are self-replicating and in fact have their own unique
DNA. When a mitochondria replicates, a new one buds off from an old one, similar in fashion to
the way a bacteria replicates. This process is under the control of the mitochondria's own DNA.
Most of the proteins and enzymes of mitochondria - over 98% - are in fact manufactured by the
cell’s DNA, but many of the enzymes and proteins involved in oxidation and phosphorylation are
manufactured by the mitochondria's DNA.

The mitochondrial DNA is not stored in a nucleus, but is in the form of a double circular molecule
containing 16,569 base pairs (compared with over a billion base pairs in the cells nucleus). This is
similar to the way DNA is stored in bacteria. There are other features similar to bacteria, which
has led to the postulation that mitochondria evolved from an aerobic bacterium that got ingested
by a eukaryotic cell and then learned to live in symbiosis with it.

Nucleus

Every cell in the body has a nucleus, with the exception of mature erythrocytes (red blood cells).
Skeletal muscle and some other cells contain several nuclei. The nucleus is the largest organelle
and is contained within the nuclear envelope, a membrane similar to the plasma membrane but
with tiny pores through which some substances can pass between it and the cytoplasm, i.e. the cell
contents excluding the nucleus.

7|Pa g e
The nucleus contains the body’s genetic material, which directs all the metabolic activities of the
cell. This consists of 46 chromosomes, which are made from deoxyribonucleic acid (DNA). Except
during cell division, the chromosomes resemble a fine network of threads called chromatin.

Within the nucleus is a roughly spherical structure called the nucleolus, which is involved in
manufacture (synthesis) and assembly of the components of ribosomes.

Ribosomes

These are tiny granules composed of RNA and protein. They synthesize proteins from amino acids,
using RNA as the template. When present in free units or in small clusters in the cytoplasm, the
ribosomes make proteins for use within the cell. These include the enzymes required for
metabolism. Metabolic pathways consist of a series of steps, each driven by a specific enzyme.
Ribosomes are also found on the outer surface of the nuclear envelope and rough endoplasmic
reticulum where they manufacture proteins for export from the cell.

Perioxisomes

These organelles are very similar to the lysosomes and contain enzymes that act together in the
form of hydrogen peroxide to neutralize substances that may be toxic to the cell. Perioxisomes
are formed directly from the endoplasmic reticulum rather than from the Golgi apparatus like
lysosomes.

Microfilaments and Microtubules

Cells contain an extensive network of microtubules and microfilaments which act as both a cyto-
skeleton and a means for transport of substances.

Microfilaments

Right under the cell membrane and attached to it is a framework of microfilaments made up of
actin strands. Actin easily polymerizes and de-polymerizes into longer or shorter strands. It is a
very common molecule and is usually found in a double stranded helical form.

8|Pa g e
Microtubules

Microtubules are made up of α-tubulin and β-tubulin molecules. These arrange themselves in
strands, and usually 13 strands complete the tubule. Microtubules usually function for transport
in cells. They are particularly numerous in the long axons of nerve cells.

Centrosome

This directs organization of microtubules within the cell. It consists of a pair of centrioles (small
clusters of microtubules) and plays an important role during cell division.

Cell extensions

These projects from the plasma membrane in some types of cell and their main components are
microtubules, which allow movement. They include:

 Microvilli – tiny projections that contain microfilaments. They cover the surface of
certain types of cell, e.g. absorptive cells that line the small intestine. By greatly
increasing the surface area, microvilli make the structure of these cells ideal for their
function – maximizing absorption of nutrients from the small intestine.

9|Pa g e
  Cilia – microscopic hair-like projections containing microtubules that lie along the free
borders of some cells. They beat in unison, moving substances along the surface, e.g.
mucus upwards in the respiratory tract.
 Flagella – single, long whip-like projections, containing microtubules, which form the
‘tails’ of spermatozoa that enable their movement along the female reproductive tract.

Cytoskeleton

The cytoskeleton is a network of fibers. These fibers consist of a complex mesh

of protein filaments and motor proteins that aid in cell movement and stabilize the cell.

Cytoskeleton Function

The cytoskeleton extends throughout the cell's cytoplasm and directs a number of important
functions.

 It helps the cell maintain its shape and gives support to the cell.

 A variety of cellular organelles are held in place by the cytoskeleton.

 It assists in the formation of vacuoles.

 The cytoskeleton is not a static structure but is able to disassemble and reassemble its parts

in order to enable internal and overall cell mobility. Types of intracellular movement
supported by the cytoskeleton include transportation of vesicles into and out of a
cell, chromosome manipulation during mitosis and meiosis, and organelle migration.
 The cytoskeleton makes cell migration possible as cell motility is needed
for tissue construction and repair, cytokinesis (the division of the cytoplasm) in the
formation of daughter cells, and in immune cell responses to germs.
 The cytoskeleton assists in the transportation of communication signals between cells.

 It forms cellular appendage-like protrusions, such as cilia and flagella, in some cells.

10 | P a g e
Cytoskeleton Structure

The cytoskeleton is composed of at least three different types of fibers:

Microtubules, microfilaments, and intermediate filaments. These fibers are distinguished by

their size with microtubules being the thickest and microfilaments being the thinnest.

Protein Fibers

 Microtubules are hollow rods functioning primarily to help support and shape the cell and

as "routes" along which organelles can move. Microtubules are typically found in all
eukaryotic cells. They vary in length and measure about 25 nm (nanometers) in diameter.
 Microfilaments or actin filaments are thin, solid rods that are active

in muscle contraction. Microfilaments are particularly prevalent in muscle cells. Similar

to microtubules, they are typically found in all eukaryotic cells. Microfilaments are
composed primarily of the contractile protein actin and measure up to 8 nm in diameter.
They also participate in organelle movement.
 Intermediate filaments can be abundant in many cells and provide support for

microfilaments and microtubules by holding them in place. These filaments form keratins
found in epithelial cells and neuro filaments in neurons. They measure 10 nm in diameter.

Motor Proteins

A number of motor proteins are found in the cytoskeleton. As their name suggests, these proteins
actively move cytoskeleton fibers. As a result, molecules and organelles are transported around
the cell. Motor proteins are powered by ATP, which is generated through cellular respiration.
There are three types of motor proteins involved in cell movement.

 Kinesins move along microtubules carrying cellular components along the way. They are

typically used to pull organelles toward the cell membrane.

 Dyneins are similar to kinesins and are used to pull cellular components inward toward

the nucleus. Dyneins also work to slide microtubules relative to one another as observed in
the movement of cilia and flagella.

11 | P a g e
  Myosins interact with actin in order to perform muscle contractions. They are also

involved in cytokinesis, endocytosis (endo-cyt-osis), and exocytosis (exo-cyt-osis).

The Process of cell division i.e. Mitosis and Meiosis

Cell division consists of two phases— nuclear division followed by cytokinesis. Nuclear
division divides the genetic material in the nucleus, while cytokinesis divides the
cytoplasm. There are two kinds of nuclear division—mitosis and meiosis.

Actively dividing eukaryote cells pass through a series of stages known collectively as the
cell cycle: two gap phases (G1 and G2); an S (for synthesis) phase, in which the genetic
material is duplicated; and an M phase, in which mitosis partitions the genetic material and
the cell divides.

 G1 phase. Metabolic changes prepare the cell for division. At a certain point - the

restriction point - the cell is committed to division and moves into the S phase.

12 | P a g e
  S phase. DNA synthesis replicates the genetic material. Each chromosome now consists

of two sister chromatids.

 G2 phase. Metabolic changes assemble the cytoplasmic materials necessary for mitosis

and cytokinesis.
 M phase. A nuclear division (mitosis) followed by a cell division (cytokinesis).

The period between mitotic divisions - that is, G1, S and G2 - is known as interphase.

Mitosis

Mitosis is a form of eukaryotic cell division that produces two daughter cells with the same genetic
component as the parent cell. Chromosomes replicated during the S phase are divided in such a
way as to ensure that each daughter cell receives a copy of every chromosome. In actively dividing
animal cells, the whole process takes about one hour.

The replicated chromosomes are attached to a 'mitotic apparatus' that aligns them and then
separates the sister chromatids to produce an even partitioning of the genetic material. This
separation of the genetic material in a mitotic nuclear division (or karyokinesis) is followed by a
separation of the cell cytoplasm in a cellular division (or cytokinesis) to produce two daughter
cells.

In some single-celled organisms, mitosis forms the basis of asexual reproduction. In diploid
multicellular organisms, sexual reproduction involves the fusion of two haploid gametes to
produce a diploid zygote. Mitotic divisions of the zygote and daughter cells are then responsible
for the subsequent growth and development of the organism. In the adult organism, mitosis plays
a role in cell replacement, wound healing and tumor formation.

Mitosis, although a continuous process, is conventionally divided into five stages: prophase,
prometaphase, metaphase, anaphase and telophase.

13 | P a g e
 The Phases of Mitosis

Prophase

Prophase occupies over half of mitosis. The nuclear membrane breaks down to form a number of
small vesicles and the nucleolus disintegrates. A structure known as the centrosome duplicates
itself to form two daughter centrosomes that migrate to opposite ends of the cell. The centrosomes
organize the production of microtubules that form the spindle fibers that constitute the mitotic
spindle. The chromosomes condense into compact structures. Each replicated chromosome can
now be seen to consist of two identical chromatids (or sister chromatids) held together by a
structure known as the centromere.

Prometaphase

14 | P a g e
The chromosomes, led by their centromeres, migrate to the equatorial plane in the mid-line of the
cell - at right angles to the axis formed by the centrosomes. This region of the mitotic spindle is
known as the metaphase plate. The spindle fibers bind to a structure associated with the
centromere of each chromosome called a kinetochore. Individual spindle fibers bind to a
kinetochore structure on each side of the centromere. The chromosomes continue to condense.

Metaphase

The chromosomes align themselves along the metaphase plate of the spindle apparatus.

Anaphase

The shortest stage of mitosis. The centromeres divide, and the sister chromatids of each
chromosome are pulled apart - or 'disjoin' - and move to the opposite ends of the cell, pulled by
spindle fibers attached to the kinetochore regions. The separated sister chromatids are now referred
to as daughter chromosomes. (It is the alignment and separation in metaphase and anaphase that
is important in ensuring that each daughter cell receives a copy of every chromosome.)

Telophase

The final stage of mitosis and a reversal of many of the processes observed during prophase. The
nuclear membrane reforms around the chromosomes grouped at either pole of the cell, the
chromosomes uncoil and become diffuse, and the spindle fibers disappear.

Cytokinesis

The final cellular division to form two new cells. In plants, a cell plate forms along the line of the
metaphase plate; in animals there is a constriction of the cytoplasm. The cell then enters interphase
- the interval between mitotic divisions.

Meiosis

Meiosis is the form of eukaryotic cell division that produces haploid sex cells or gametes (which
contain a single copy of each chromosome) from diploid cells (which contain two copies of each

15 | P a g e
chromosome). The process takes the form of one DNA replication followed by two successive
nuclear and cellular divisions (Meiosis I and Meiosis II). As in mitosis, meiosis is preceded by a
process of DNA replication that converts each chromosome into two sister chromatids.

Meiosis I

Meiosis I separates the pairs of homologous chromosomes.

16 | P a g e
  Prophase I begins like prophase of mitosis. The nucleolus disappears, chromatin
condenses into chromosomes, the nuclear envelope breaks down, and the spindle
apparatus develops. During prophase I, homologous chromosomes pair, a process
called synapsis. These pairs of homologous chromosomes are called tetrads (a group of
four chromatids) or bivalents. During synapsis, corresponding regions form close
associations called chiasmata (singular, chiasma) along non-sister chromatids.
Chiasmata are sites where genetic material is exchanged between non-sister homologous
chromatids, a process called crossing over. The result contributes to a mixing of genetic
material from both parents, a process called genetic recombination.
 At metaphase I, homologous pairs of chromosomes are spread across the metaphase
plate. Microtubules extending from one pole are attached to kinetochores of one member
of each homologous pair. Microtubules from the other pole are connected to the second
member of each homologous pair.
 Anaphase I begins when homologues within tetrads uncouple as they are pulled to
opposite poles.
 In telophase I, the chromosomes have reached their respective poles, and a nuclear
membrane develops around them. Note that each pole will form a new nucleus that will
have half the number of chromosomes, but each chromosome will contain two
chromatids. Since daughter nuclei will have half the number of chromosomes, cells that
they eventually form will be haploid.
 Cytokinesis occurs, forming two daughter cells. A brief interphase may follow, but no
replication of chromosomes occurs. Instead, part II of meiosis begins in both daughter
nuclei.

17 | P a g e
Meiosis II

Meiosis II separates each chromosome into two chromatids.

18 | P a g e
  In prophase II, the nuclear envelope disappears and the spindle develops. There are no
chiasmata and no crossing over of genetic material as in prophase I.
 In metaphase II, the chromosomes align singly on the metaphase plate (not in tetrads
as in metaphase I). Single alignment of chromosomes is exactly what happens in
mitosis—except now there is only half the number of chromosomes.
 Anaphase II begins as each chromosome is pulled apart into two chromatids by the
microtubules of the spindle apparatus. The chromatids (now chromosomes) migrate to
their respective poles. Again, this is exactly what happens in mitosis—except now there
is only half the number of chromosomes.
 In telophase II, the nuclear envelope reappears at each pole and cytokinesis occurs. The
end result of meiosis is four haploid cells. Each cell contains half the number of
chromosomes and each chromosome consists of only one chromatid.

19 | P a g e
20 | P a g e
Meiosis ends with four haploid daughter cells, each with half the number of chromosomes (one
chromosome from each homologous pair). These are gametes—that is, eggs and sperm. The
fusing of an egg and sperm, fertilization (syngamy), gives rise to a diploid cell, the zygote. The
single‐celled zygote then divides by mitosis to produce a multicellular embryo fetus, and after nine
months, a newborn infant. Note that one copy of each chromosome pair in the zygote originates

21 | P a g e
from one parent, and the second copy from the other parent. Thus, a pair of homologous
chromosomes in the diploid zygote represents both maternal and paternal heritage.

The importance of Mitosis and Meiosis

Mitosis

 Genetic stability- Mitosis helps in the splitting of chromosomes during cell division and

generates two new daughter cells. Therefore, the chromosomes form from the parent
chromosomes by copying the exact DNA. Therefore, the daughter cells formed are
genetically uniform and identical to the parent as well as to each other. Thus, mitosis helps
in preserving and maintaining the genetic stability of a particular population.
 Growth- Mitosis help in increasing the number of cells in a living organism thereby

playing a significant role in the growth of a living organism.

 Replacement and regeneration of new cells- Regeneration and replacement of worn-out

and damaged tissues is a very important function of mitosis in living organisms. Mitosis
helps in the production of identical copies of cells and thus helps in repairing the damaged
tissue or replacing the worn-out cells. However, the degree of regeneration and
replacement in multicellular organisms vary from one another. For example, mitosis
process is used in order to regrowth the legs of newts and crustaceans. However, the degree
of regrowth may vary.
 Asexual reproduction- Mitosis is used in the production of genetically similar offspring.

For example budding of hydra and yeast, binary fission in amoeba, etc.

Meiosis

 Meiosis is responsible for the formation of sex cells or gametes that are responsible for

sexual reproduction.
 It activates the genetic information for the development of sex cells and deactivates the

saprophytic information.
 It maintains the constant number of chromosomes by halving the same. This is important

because the chromosome number doubles after fertilization.

22 | P a g e
  In this process, independent assortment of maternal and paternal chromosomes takes

place. Thus, the chromosomes and the traits controlled by them are reshuffled.
 The genetic mutation occurs due to irregularities in cell division by meiosis. The

mutations that are beneficial are carried on by natural selection.

 Crossing over produces a new combination of traits and variations.

23 | P a g e