Introduction to the cell

1. Pravin V Jadhav, PhD
Assistant Professor, MB & GE
Biotechnology Centre
Dr. Panjabrao Deshmukh Krishi Vidyapeeth ,Akola
GP 508 [2+1]
Cell Biology and Molecular genetics

2. Why study cells?
• Cells → Tissues → Organs → Bodies
– bodies are made up of cells
– cells do all the work of life!
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3. ATP
– “breathe”
• gas exchange: O2 in vs. CO2 out
– eat
• take in & digest food
– make energy
• ATP
– build molecules
• proteins, carbohydrates, fats, nucleic acids
– remove wastes
– control internal conditions
• homeostasis
– respond to external environment
– build more cells
• growth, repair, reproduction & development
The Work of Life
What jobs do cells have to do for an organism to live…?
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4. • Cells have 3 main jobs
– make energy
• need energy for all activities
• need to clean up waste produced
while making energy
– make proteins
• proteins do all the work in a cell,
so we need lots of them
– make more cells
• for growth
• to replace damaged or diseased cells
The Jobs of Cells
Our organelles
do all these
jobs!
ATP
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5. The cell is the smallest unit of matter that can carry on all the processes of life
The invention of the microscope enabled Robert Hooke, (1665) and
Anton van Leuwenhoek (1675) to see and draw the first ‘cell’, a word coined by
Hooke
‘Cell Theory’ put forward – 1885
Cell Theory consists of three principles:
a. All living things are composed of one or more cells.
b. Cells are the basic units of structure and function in an organism.
c. Cells come only from the replication of existing cells.
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6. CELL DIVERSITY
Not all cells are alike.
Even cells within the same organism show enormous diversity in size, shape, and internal
organization.
Around 1013
to 1014
cells in human body , of around 300 different cell types
CELL SIZE
A few types of cells are large enough to be seen by the unaided eye.
Most cells are small for two main reasons:
The cell’s nucleus can only control a certain volume of active cytoplasm.
Cells are limited in size by their surface area to volume ratio.
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7. CELL SHAPE
Cells come in a variety of shapes – depending
on their function:-
The neurones from your toes to your head
are long and thin;
Blood cells are rounded disks, so that they
can flow smoothly
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8. Basic Cell Organization
All cells contain:
1.Cell membrane that keeps the inside and
outside separate.
2.DNA-containing region that holds the
instructions to run the processes of life.
3.Cytoplasm: a semi-fluid region containing
the rest of the cell’s machinery.
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9. Prokaryotes v. Eukaryotes
A Prokaryotic cell (bacterium) A Eukaryotic cell (plant)
Prokaryotes Eukaryotes
Typical organisms bacteria fungi, plants, animals
Typical size ~ 1-10 µm ~ 10-100 µm (sperm cells) apart from the tail, are smaller)
Type of nucleus Nuclear body [No nucleus] real nucleus with nuclear envelope
DNA circular (ccc DNA) linear molecules (chromosomes) with histone proteins
Ribosomes 70S 80S
Cytoplasmatic structure very few structures highly structured by membranes and a cytoskeleton
Cell movement Flagellae/cilia made of flagellin flagellae and cilia made of tubulin
Mitochondria none 1 - 100 (though RBC’s have none)
Chloroplasts none in algae and plants
Organization usually single cells single cells, colonies, higher multicellular organisms with specialized
cells
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10. B. CELL ORGANEELS
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11. Cell Organelles
• Organelle= “little organ”
• Found only inside cells
• All the stuff in between the organelles
is cytosol
• Everything in a cell except the nucleus
is cytoplasm
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12. Organelles of the cell1. Cell wall
2. Cell membrane
3. Nucleus
-Chromosomes
1. Cytomembrane system
2. Endoplasmic reticulum
3. Golgi bodies
4. Lysosome
5. Vacuoles
6. Centioles
7. Ribosome
8. Mitochondria
9. Plastids
a. Chloroplast
b. Amyloplast
c. Chromoplast 12

13. Cell wall
• Each plant cell is surrounded by a rigid
cell wall made of cellulose and
polysaccharides.
• The cell wall is outside of the cell
membrane.
• In woody plants, the cell walls can
become very thick and rigid.
• The cell wall, giving the cell its strength.
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14. Cell Walls
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15. Cell membrane
cell boundary
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16. • Function
– separates cell from outside
– controls what enters or leaves cell
• O2, CO2, food, H2O, nutrients, waste
– recognizes signals from other
cells
• allows communication between cells
Cell membrane
lipid “tail”
phosphate
“head”
•Structure
 double layer of fat
• phospholipid bilayer
 receptor molecules
• proteins that receive signals
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17. Cell Membrane, pt. 2
• The molecules in the membrane can move about like ships
floating on the sea: the membrane is a two-dimensional fluid
• In some cells, the membrane proteins are held in fixed
positions by a network of proteins just under the membrane,
a cytoskeleton.
• Only water, a few gasses, and a few other small non-polar
molecules can move freely through a pure phospholipid
membrane. Everything else must be transported into the cell
by protein channels in the membrane.
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18. Transport Across the Cell Membrane
 Basic rule: things spontaneously move from high concentration to low
concentration (downhill). This process is called diffusion.
 To get things to move from low to high (uphill), you need to add energy. In
the cell, energy is kept in the form of ATP.
 Three basic transport mechanisms: passive transport for downhill, active
transport for uphill, and bulk transport for large amounts of material in either
direction.
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19. Passive and Active Transport
• Passive transport uses protein channels through
the membrane that allow a particular molecule
to go through it, down the concentration
gradient.
• The speed and direction of movement depends
on the relative concentrations inside and
outside. Glucose is a good example: since cells
burn glucose for energy, the concentration
inside is less than the concentration outside.
• Active transport uses proteins as pumps to
concentrate molecules against the
concentration gradient. The pumps use ATP for
energy.
• Ex: calcium pump, which keeps the level of
calcium ions in the cell 1000 times lower than
outside, by constantly pumping calcium ions
out.
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20. Nucleus
• The nucleus issues instructions to build and
maintain the cell, respond to changes in the
environment, and to divide into 2 cells.
• The nucleus is surrounded by a double membrane
called the nuclear envelope.
• The cell’s instructions are coded in the DNA,
which is the main part of chromosomes.
• Each instruction in the DNA is called a gene.
The genes issue their instructions, get
expressed, as RNA copies.
• The RNA copy of a gene is called messenger
RNA (mRNA). The mRNA instructions move out
of the membrane into the cytoplasm, where
they are translated into proteins.
• The translation of RNA messages into proteins
is accomplished by ribosomes.
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21. Cytomembrane System
• The cytomembrane system is a
group of organelles that has 3 basic
functions:
– to manufacture new lipids and
membranes,
– to modify polypeptides into their final
proteins, and
– to synthesize and package proteins and
other molecules for export.
• Organelles as part of this system:
– the endoplasmic reticulum (ER),
– the Golgi bodies,
– the lysosomes, and
– the peroxisomes
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22. Endoplasmic Reticulum
• “Reticulum” means
network
• Connected to nuclear
membrane
• Highway of the cell
• Rough ER: studded with
ribosomes; it makes
proteins
• Smooth ER: no
ribosomes; it makes
lipids 22

23. Endoplasmic Reticulum…
• Two types, connected together: rough ER and
smooth ER
• Rough ER looks rough because it is studded
with ribosomes, the cellular machines that
synthesize proteins.
• Ribosomes on the rough ER make the
proteins that go into the membrane, using
the instructions from messenger RNA.
• Smooth ER has no ribosomes.
• It is used to synthesize the lipids of the
membrane. It is also used in liver cells to
detoxify harmful chemicals in the blood.
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24. Golgi Body and Secretion
• Proteins that are synthesized in the rough ER get
finished in the Golgi body: sugars and phosphates
added.
• Golgi looks like a series of stacked plates.
• Vesicles carry proteins from the ER to the Golgi, and
then from the Golgi body to the cell membrane.
Secretion to the outside world occurs by exocytosis.
• Proteins synthesized into the membrane of the ER
end up in the cell membrane by the same mechanism
• Basic mechanism of secretion (Next Fig):
– genes are copied into messenger RNA in the nucleus
– mRNA leaves the nucleus and attaches to ribosomes in
the cytoplasm.
– the ribosomes move to the rough ER and synthesize
new proteins
– proteins are transported by vesicles to the Golgi for
finishing
– proteins are transported in other vesicles to the cell
membrane, where they are released from the cell.
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25. DNA
RNA
ribosomes
endoplasmic
reticulum
vesicle
Golgi
apparatus
vesicle
Protein
on its way!
protein finished
protein
TO:
TO:
TO:
TO:
nucleus
25Cytomembrane system & Making protein

26. small food
particle
vacuole
digesting food
lysosomes
digesting broken
organelles
Lysosomes
# Garbage disposal of the cell
# Contain digestive enzymes that break down wastes
• Function
– digest food
• used to make energy
– clean up & recycle
• digest broken
organelles
• Structure
– membrane sac of
digestive enzymes
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27. Lysosomes and Peroxisomes
• Lysosomes are intracellular stomachs: they are full of
digestive enzymes that operate at low pH.
• Vesicles transport materials to the lysosomes, and the
lysosomes digest them.
• In the process of “programmed cell death”, cells
scheduled to die are destroyed from within by their
lysosomes.
• Example is the tail of a tadpole, which is destroyed to
make a tailless frog.
• Lysosomal storage diseases are caused by genetic defects.
Example: Gaucher disease, certain lipids accumulate
inside of lysosomes instead of being broken down.
It leads to interference with bone marrow function: blood
and bone problems.
• Peroxisomes are membrane-bound sacs used to break
down fatty acids and some other molecules. They
generate hydrogen peroxide, a poisonous molecule, in
the process, which is the source of the name peroxisome.
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28. Vacuoles
• Large central vacuole
usually in plant cells
• Many smaller vacuoles
in animal cells
• Storage container for
water, food, enzymes,
wastes, pigments, etc.
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29. Ribosome
That looks familiar…what is a polypeptide?
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Site of protein synthesis
Found attached to rough ER or
floating free in cytosol
Produced in a part of the
nucleus called the nucleolus

30. Plant Cell Organelles
• Plants have three special structures not found in animals:
the chloroplast, the cell wall, and the central vacuole
• The chloroplast is the site of photosynthesis
• Like the mitochondria, chloroplasts have two membranes
and their own circular DNA.
• Chloroplasts are also thought to have originated from an
ancient mutually beneficial relationship between
photosynthetic bacteria and a primitive eukaryote.
• In some plant cells, chloroplasts are modified to store
starch (as in potatoes) or to contain other pigments (as in
flowers).
Chloroplast
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31. Chloroplast
• Vary in size and shape
• Thylakoids
– where photosynthesis takes
place
• Stroma
– Calvin cycle
– sugar synthesis
• The chloroplast has its own
genome
CHLOROPLAST BIOGENESIS. 31

32. The Mighty
Mitochondrion!
Powerhouse of the Cell
A
T
P
=
e
n
e
r
g
y
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33. Mitochondria
• “powerhouse of the cell”
• ATP production
• Cell “breathing” is called
cellular respiration
• The mitochondrion has its
own Genome
Cellular respiration:
converts sugars to energy (ATP) 33

34. Mitochondria
• The mitochondria are the site where most of the cell’s
ATP is generated, when organic compounds are broken
down to carbon dioxide and water, using oxygen.
• All eukaryotes have mitochondria. The number in a cell
depends on that cell’s energy needs.
• Mitochondria have their own circular DNA, the same kind
found in bacteria.
• Mitochondria have 2 membranes, forming 2
compartments inside. To generate energy, hydrogen ions
are accumulated between the 2 membranes. Then they
flow down the concentration gradient into the inner
compartment through a protein that uses the energy of
their flow to create ATP.
• Genetic defects in the mitochondria affect tissues that
use a lot of energy: nerves, muscles, liver, kidney.
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35. Plastids
• Contain pigments or
storage products
1. Chloroplasts
2. Elioplasts [fat]
3. Amyloplasts [starch]
4. Leucoplast [terpens]
5. Protenoplast [proteins]
• Processing of circular
dsDNA
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36. Quick Review
• Which organelle is the control center of the cell?
Nucleus
• What is the stuff in between the organelles?
Cytosol
• Which organelles are not found in animal cells?
Cell wall, central vacuole, chloroplasts
• Which organelle helps plant cells make food?
Chloroplasts
• What does E.R. stand for?
Endoplasmic reticulum
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