Cell : The Unit Of Life

unicellular

having or consisting of a single cell

multicellular

consisting of many cells

(i)independent existence and
(ii) performing the essential functions of life

Unicellular organisms are capable of

Independent living

Anything less than a complete
structure of a cell does not ensure

cell

which is the fundamental structural and functional unit of all living organism ?

Anton Von Leeuwenhoek

first saw and described a live cell

Robert Brown

discovered the nucleus

Robert Hooke

First observed dead cork cell

Matthias Schleiden, a German botanist

examined a large number of plants and observed that all plants are composed of different kinds of cells which form the tissues of the plant

Theodore Schwann (1839), a British Zoologist

studied different types of animal cell

Theodore Schwann

reported that cells had a thin outer layer which is today known as the
‘plasma membrane’.

Theodore Schwann

The presence of cell wall is a unique character of the plant
cells.

Theodore Schwann

proposed the hypothesis that the bodies of animals and plants are composed of cells and products of cell

Schleiden and Schwann

formulated the cell theory

Rudolf Virchow

first explained that cells divided and new cells are formed from pre-existing cells (Omnis cellula-e cellula)

Rudolf Virchow

modified the hypothesis of Schleiden and Schwann to give the cell theory a final shape

(i) all living organisms are composed of cells and products of cells.
(ii) all cells arise from pre-existing cells

Cell Theory

Chromosomes ----> Chromatids ----> DNA

Genetic heirarchy

cytoplasm

the protoplasm of a cell excluding the nucleus;
is full of proteins that control cell metabolism;
semi-fluid matrix; main arena of cellular activity

prokaryotic cells

having cells that lack membrane-bound nuclei

ribosome

an organelle in the cytoplasm of a living cell both eukaryotic and prokaryotic;
they attach to mRNA and move down it one codon at a time and then stop until tRNA brings the required amino acid;
non-membrane bound

mycoplasma

smallest cell 0.3μm in length;
lack cell walls and can survive without oxygen

3 to 5μm

Bacteria size

RBC

7.0 μm in diameter

WBC

Columnar epithelial cells

Nerve cell

Some of the longest cells

Traceid

Mesophyll cells

ostrich egg

largest isolated single cell

function they perform

The shape of the cell may vary with the

Bacteria, blue-green algae, mycoplasma and PPLO (Pleuro Pneumonia Like Organisms)

The prokaryotic cells are represented by

bacillus (rod like), coccus (spherical), vibrio (comma
shaped) and spirillum (spiral)

The four basic shapes of bacteria

plasmid

a small cellular inclusion consisting of a ring of DNA that is not in a chromosome but is capable of autonomous replication; senn in prokaryotes

resistance to antibiotics

The plasmid DNA confers certain unique phenotypic characters to such bacteria, One such character is

ribosomes

No organelles except

Mesosome

infoldings of cell membrane

glycocalyx
cell wall
plasma membrane

outermost ____________ followed by the __________ and
then the _____________; act together as a single protective unit.

Gram positive

take up the gram stain

Gram negative

do not take up the gram stain

Slime layer
capsule

Glycocalyx differs in composition and thickness among different
bacteria. It could be a loose sheath called the ____________ in some, while in others it may be thick and tough, called the ___________.

cell wall

a rigid layer of polysaccharides enclosing the membrane of plant and prokaryotic cells; determines the shape of the cell and provides a strong structural support to prevent the bacterium from bursting or collapsing

Mesosome

These extensions are in the form of vesicles, tubules and lamellae . They help in cell wall formation, DNA replication and distribution to daughter cells. They also help in respiration, secretion processes, to increase the surface area of the plasma membrane and enzymatic content.What are they ?

Chromatophores

In some prokaryotes like cyanobacteria, there are other membranous extensions into the cytoplasm called ____________ which contain pigments.

filament, hook and basal body

Bacterial flagellum is composed of three parts –

Pili and Fimbriae

_________ and ______________are also surface structures of the
bacteria but do not play a role in motility

pili

The _____ are elongated tubular
structures made of a special protein

fimbriae

The_______ are small bristle like
fibres sprouting out of the cell ; they are known to help
attach the bacteria to rocks in streams and also to the host tissu

Ribosomal size in prokaryotes

They are about 15 nm by 20 nm in size;

50S and 30S units which when present together form 70S

qRibosomal subunits in prokaryotes

protein synthesis

Ribosomes are the site of

polyribosomes or polysome ;The ribosomes of a polysome translate the mRNA into proteins

Several ribosomes may attach to a single mRNA and form a chain called

inclusion body

Reserve material in prokaryotic cells are stored in
the cytoplasm in the form of.These are not bound by
any membrane system and lie free in the cytoplasm, e.g., phosphate
granules, cyanophycean granules and glycogen granules

Gas vacuole

__________are found in blue green and purple and green photosynthetic bacteria.

plant cell
Animal cell

_________ possess cell walls, plastids and a large central vacuole which are absent in__________ cell.

centrioles

Animal cells have _________ which are absent in almost all plant cells

human red blood cells (RBC)

chemical studies on
the cell membrane, especially in ____________ ), enabled
the scientists to deduce the possible structure of plasma membrane`.

lipids and proteins

studies showed that the cell membrane is mainly composed of

phospholipids
Bilayer

The major lipids are _____________ that are arranged
in a _______

polar head
hydrophobic tails
protected from the aqueous environment

the lipids are arranged within the membrane with the
__________ towards the outer sides and the ________________ towards
the inner part.his ensures that the nonpolar tail of saturated
hydrocarbons is _________________________

cholesterol

In addition to phospholipids membrane also contains _______________

52 per cent
40 per cent

the membrane of the
erythrocyte has approximately ______ protein and _______lipids

Peripheral proteins
integral proteins

___________lie on the surface of membrane while the ____________are partially or totally buried in the membrane.

1.Sugar
2.Peripheral protein
3.Integral protein
4.Phospholopid bilayer
5.Cholesterol

Singer and Nicolson
fluid mosaic model

An improved model of the structure of cell membrane was proposed
by _____________ widely accepted as ________________

lipid
proteins
fluidity

the quasi-fluid nature of _____ enables lateral movement of _______ within the overall bilayer. This ability to move within the membrane is measured as its ______.

cell growth, formation of intercellular junctions,
secretion, endocytosis, cell division

The fluid nature of the membrane is also important from the point of
view of functions like

passive transport

transport of a substance across a cell membrane by diffusion; expenditure of energy is not required

osmosis

diffusion of water through a semipermeable membrane from a place of higher concentration to a place of lower concentration until the concentration on both sides is equal

simple diffusion

Neutral solutes may move across the
membrane by the process of _____________ along the concentration
gradient

polar molecules
facilitate their transport

the _______________ cannot pass through the nonpolar lipid bilayer, they require a carrier protein of the membrane to _________________ across the membrane

active transport

transport of a substance across a cell membrane against the concentration gradient; A few ions or molecules are transported from lower to the higher concentration. Such a transport is an energy dependent process, in which ATP is utilized and is called _________,e.g., Na+/K+ Pump

non-living
rigid
cell wall

a ________ and __________structure called the ______ forms an outer covering for the plasma membrane of fungi and plant

cellulose, galactans, mannans and minerals like calcium carbonate

cellulose, hemicellulose, pectins and protein

algae have cell wall, made of _____________________, while
in other plants it consists of ____________________________.

primary wall
secondary wall

The _________________ is capable of growth, which gradually diminishes as the cell matures and the ______________ is
formed on the inner (towards membrane) side of the cell.

calcium pectate

The middle lamella is a layer mainly of _______________ which holds
or glues the different neighbouring cells together.

plasmodesmata

The cell wall and middle lamellae may be traversed by _______________ which connect the cytoplasm of neighbouring cells.

their functions are coordinated

any of these are considered together as an endomembrane system
because

endoplasmic reticulum (ER), golgi complex, lysosomes and vacuoles

he
endomembrane system include

mitochondria, chloroplast and peroxisomes

Since the functions of ______________ , ______________ and ____________ are not coordinated with the above components, these are not considered as part of the endomembrane system.

luminal (inside ER) and extra luminal (cytoplasm) compartments.

ER divides the intracellular
space into two distinct compartments, i.e.,

rough endoplasmic reticulum (RER)

The endoplasmic reticulun bearing ribosomes on their surface is called _________________________.

smooth endoplasmic reticulum (SER)

In the absence of ribosomes they appear smooth and are called
____________________________.

protein synthesis and secretion

RER is frequently observed in the cells actively involved in

RER

_______________ are extensive and continuous with the outer
membrane of the nucleus.

The smooth endoplasmic reticulum

__________________________ is the major site for synthesis of lipid

SER

In animal cells lipid-like steroidal hormones are synthesised in

Golgi apparatus

densely stained reticular structures near the nucleus

cisternae

flat, disc-shaped sacs of golgi apparatus

Cis face

forming face

Trans face

Maturing face

packaging materials, to be delivered either to the intra-cellular targets or secreted outside the cell.

The golgi apparatus principally performs the function of

cis face
the maturing face

Materials to be packaged in the form of vesicles from the ER fuse with the _____________ of the golgi apparatus and move towards
______________. This explains, why the golgi apparatus remains in
close association with the endoplasmic reticulum.

cisternae of the golgi apparatus
trans face

A number of proteins synthesised by ribosomes on the endoplasmic reticulum are modified in the ____________________ before they are released from its __________________.

Golgi apparatus

__________________ is the important site of formation of
glycoproteins and glycolipids.

lysosome

____________ are membrane bound vesicular structures formed by the process of packaging in the golgi apparatus.

hydrolytic enzymes (hydrolases – lipases, proteases, carbohydrases) acidic
digesting carbohydrates, proteins, lipids and nucleic acids.

The isolated lysosomal vesicles
have been found to be very rich in almost all types of ________________________________________ optimally
active at the ___________ pH. These enzymes are capable of _______________________________________________.

water, sap, excretory product and other materials not useful for the cell

Vacuoles contain

tonoplast

The vacuole is bound by a single membrane called

90 per cent

In plant cells the vacuoles can occupy up to ______________ of the volume of the cell.