BMP 111: ANAT. & PHY. I
TOPIC: HUMAN CELL
BY
BELLO, SA’AD MOHD (RN)

OUTLINE
• INTRODUCTION
• CELL THEORY
• STRUCTURE OF THE HUMAN CELL
• FUNCTIONS OF THE CELL
• TRANSPORT ACROSS CELL MEMBRANE
• CELL DIVISION
• CONCLUSION/EVALUATION

HUMAN CELL
Introduction
The cell is the smallest functional unit of the body. Cells are grouped
together to form tissues, each of which has a specialised function.
Different tissues are grouped together to form organs e.g. stomach,
heart, and brain. Organs are grouped together to form systems, each of
which perform a particular function to maintain stability and contribute
to the health of the individual.
Cell theory
• This refers to the basic generalisation that is universally accepted by
scientist about cell. These generalisations include:
• All living organisms are made up of cells
• Cell is the fundamental structural and functional unit of life
• All cells are produce by pre-existing cells

STRUCTURE OF HUMAN CELL

DESCRIPTION
• A cell is the basic structural and functional unit of life.
• It consists of a plasma membrane inside which are a
number of organelles suspended in a watery fluid
called cytoplasm.
• Organelles are literally small organs; have individual
and highly specialised functions are often enclosed in
their own membrane within the cytoplasm.
• They include: Nucleus, Mitochondria, Ribosomes,
Endoplasmic Reticulum, Golgi apparatus, and
lysosome.

Nucleus
• The nucleus is the largest organelle in the cell and is
contained within nuclear envelope, a membrane
similar to plasma membrane but with tiny pores
through which some substances can pass between it
and the cytoplasm.
• 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).

Mitochondria
• This is a membranous sausage-shaped structure in the
cytoplasm, sometimes described as the ‘power house’
of the cell.
• They are involved in aerobic respiration, the process
by which chemical energy is made available in the cell.
• This is in the form of Adenosine triphosphate (ATP),
made available in the cell.
• The most active types have the greatest number of
mitochondria.

Ribosomes
• These are tiny granules composed of Ribonucleic acid
(RNA) and protein.
• They synthesise protein from amino acid using RNA.
When present in free units or in small clusters in the
cytoplasm, the ribosomes make proteins for use
within the cell. These include enzymes required for
metabolism.
• When found on the outer surface of the nuclear
membrane and rough endoplasmic reticulum they
synthesise protein for use outside the cell.

Endoplasmic reticulum
• It is an extensive series of interconnecting canals.
There are two types: smooth and rough.
• The smooth synthesises lipid and steroids hormones
and is also associated with detoxification of some
drugs.
• Some of the lipids are used to replace and repair the
plasma membrane and membranes of organelles.
• The rough ER synthesises protein for use outside the
cell which are exported as enzymes and hormones
that leave the parent cell by exocytosis.

Golgi apparatus
•These consist of stacks of closely folded flattened
membranous sacs. It is present in all cells but larger in
those that synthesises and export proteins.
•The proteins move from the rough endoplasmic
reticulum (where they are synthesised) to Golgi
apparatus where they are packaged into membrane-
bound vesicles.
•The vesicles are stored and when needed they move
to the cell membrane fuse with it and secrete/release
their content out of the cell by exocytosis.

Lysosomes
• They are small membranous vesicles pinched of from
the Golgi apparatus.
• They Contain variety of enzymes involve in breaking
down fragments of organelles and large molecules
inside the cell into smaller particles (e.g.
Carbohydrates, Proteins RNA, DNA,) which are either
recycled or extruded from the cell as waste material.
• It also releases chemical substances that digest
particles taken into the cell by endocytosis,
particularly ingested bacteria, viruses and toxins.

CELL MEMBRANE
• The cell membrane (also called plasma
membrane or cytoplasmic membrane, and historically
referred to as the plasmalemma) consists of two layers of
phospholipids with proteins and sugars embedded in them.
• The phospholipid molecule have head which is electrically
charged and is hydrophilic (water loving), and tail which has
no charge and is hydrophobic (water hating).
• The phospholipid bilayer is arranged like a sandwich with the
hydrophilic heads aligned on the outer surfaces of the
membrane and the hydrophobic tails forming a central water
repelling layer.
• These differences influence the transfer of substances across
the cell membrane.

Membrane proteins
• Proteins make up about half of the plasma membrane by mass and
are responsible for most of the specialised membrane functions.
• There are two types of membrane proteins or proteins in the cell
membrane:
• some proteins extend all the way through the membrane (called
integral proteins) while others are on the surface of the membrane
(called peripheral proteins).
• Those that extend all the way through the membrane provide
channels that allow the passage of electrolyte and non-lipid soluble
substances while those protein molecules on the surface of the
membrane perform the following functions:
• They attached to the branch of carbohydrate molecules to give the
cell its immunological identity
• They act as receptors for hormones and other chemical messengers
• Some are enzymes etc

FUNCTIONS OF THE CELL
• Structural support: every organism is made up of cells, therefore all cells
generally provides structural basic=s for all organism.
• Growth: in complex organism, tissue grows by simple multiplications of
cells. This occurs through the process of mitosis.
• Transport: through active and passive transport cell import nutrients to be
use in various chemical processes that take place inside the cell and also
excrete waste generated through these chemical processes.
• Production of energy: energy is generated in form of ATP through the
process of respiration.
• Metabolism: this includes all the chemical reactions that take place inside
an organism to keep it alive. These reactions may be catabolic or anabolic.
• Reproduction: all cells reproduce through the process of mitosis and
meiosis. In mitosis, cells simply divide to form new cells. This is termed
asexual reproduction. Meiosis takes place in gametes in which there is
mixing of genetic information. This is called sexual reproduction.
• Excretion: waste material generated inside the cell get excreted

TRANSPORT OF SUBSTANCES ACROSS CELL MEMBRANE
• Our body cells are bathed in an extracellular fluid called interstitial
fluid that is derived from the blood.
• Interstitial fluid is nutritiously rich: it contains thousands of
ingredients including amino acids, sugars/glucose, fatty acids,
vitamins and waste products etc.
• To remain healthy, each cell must extract from this mix the exact
amount of substances it needs at specific times.
• The structure of the plasma membrane provides it with property of
selective permeability meaning that not all substances can cross it.
• Those that can do so in different ways depending on their size and
characteristic.

TRANSPORT OF SUBSTANCES ACROSS CELL MEMBRANE cont.
• Substances cross the cell membrane basically by two means namely
• Passive transport & Active transport
• Passive transport: This occurs when substances can cross the
semipermeable plasma and organelle membranes and move down the
concentration gradient (downhill) without using energy.
• This can occur through:
• Diffusion
• Facilitated Diffusion
• Osmosis
• Diffusion: This refers to the movement of molecules from area of high
concentration to an area of low concentration and occurs mainly in gases,
liquid and solutions.
• Lipid-soluble materials e.g oxygen, carbon dioxide and fatty acids cross the
membrane by dissolving in the lipid part of the membrane.
• Water soluble materials e.g. sodium, potassium and calcium cross the
membrane by passing through the water-filled channels.

TRANSPORT OF SUBSTANCES ACROSS CELL MEMBRANE cont.
• Facilitated Diffusion: This passive process is used by substances that are
unable to diffuse through the semi permeable membrane unaided. E.g.
glucose and amino acid
• Specialised protein carrier molecules in the membrane have specific site
that attracts and bind substances to be transferred like lock and key
mechanism
• The carrier changes it shape and deposit the substance on the other side of
the membrane.
• Osmosis: This refers to diffusion of water down its concentration gradients.
This occurs because any other molecules present are too large to pass
through the pores in the membrane. This occurs to ensure equilibrium in
the concentration of solution/fluid within and outside the cell is maintain
• Active transport: Active transport is the movement of molecules across a
membrane from a region of their lower concentration to a region of their
higher concentration—in the direction against the concentration gradient

CELL DIVISION
Mitosis
• This refers to the process of somatic cell division (replication) in which
a cell divide into two daughter cells which are identical and have the
same number of chromosomes as the parent cell.
• Before mitosis begins the cell is in interphase (late G2​ phase) and has
already copied its DNA, so the chromosomes in the nucleus each
consist of two copies called sister chromatids which are connected by
centromere.
• The cell has also made a copy of its centrosome, an organelle that will
play a key role in mitosis.

Mitosis takes place in four stages: PMAT
•Prophase
•Metaphase
•Anaphase
•Telophase

Prophase
• The chromosomes start to condense (making them easier to
pull apart later on).
• The mitotic spindle begins to form: The spindle is a structure
made of microtubules, strong fibers that are part of the cell’s
“skeleton.”
• Its job is to organize the chromosomes and move them
around during mitosis. The spindle grows between the
centrosomes as they move apart.
• The nucleolus (or nucleoli, plural), a part of the nucleus
where ribosomes are made, disappears. This is a sign that
the nucleus is getting ready to break down.

Metaphase
• The chromatid align at the centre of the spindle
attached by the centromeres

Anaphase
• The sister chromatids separate at the centromere, and one
of each pair of sister chromatids (now called chromosomes
again) migrate to each end of the spindle as the microtubule
that form mitotic spindle contract.
• Microtubules not attached to chromosomes elongate and
push apart, separating the poles and making the cell longer.

Telophase
In telophase, the cell is nearly done dividing, and it starts to
re-establish its normal structures as cytokinesis (division of
the cell contents) takes place.
• The mitotic spindle is disappears or is broken down.
• Chromosomes uncoil
• Nuclear envelopes reforms

Cytokinesis
• The cytosol, intracellular organelles and plasma membrane
split forming two identical daughter cells. The division of the
cytoplasm to form two new cells, overlaps with the final
stages of mitosis.
• It may start in either anaphase or telophase, depending on
the cell, and finishes shortly after telophase.
Cytokinesis

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