Introduction to Cell
Cell
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All organisms are made of cells
The cell is the simplest collection of
matter that can live
Basic structural and functional unit of life
To study cells, biologists use microscopes
and the tools of biochemistry
Cytology
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It is the study of the structure and function
of cells.
The cell is the basic structural and
functional unit of life so therefore cytology
is the fundamental most important topic
in all of biology.
Importance
An understanding of cell biology is
important in many areas of study, for
the cell is the building block of all living
forms. This course complements
studies in any area of applied biology
including human health and fitness,
horticulture, agriculture and wildlife
management.
How do we observe cells?
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Light microscopes (LM.s)
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Pass visible light through a specimen
Magnify cellular structures with lenses
Electron microscopes (EM.s)
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Focus a beam of electrons through a
specimen (TEM) or onto its surface (SEM)
People who were important in
early cell discovery
Robert Hooke (1665)
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Observed dead cork - called them
“cells“
Compound Microscope
Anton Von Leeuwenhoek
(1674)
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- living cells in pond water; one celled
organisms -- animalcules
Robert Brown (1831)
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identifies the nucleus of a cell
Mattias Scleiden (1838)
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stated that plants are made up of cells
Theodor Schwann (1839)
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stated that animals are made up of
cells
Rudolph Virchow (1858)
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2.
Studied the pathology of cells. (ability to cause
disease)
All cells arise from preexisting cells.
New cells can only arise from other living
cells by the process of cell division or
reproduction
Cell Theory
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1. All living things are made of cells. (basic
structure).
2. All cells carry out life functions. (basic
function)
3. All cells come from pre-existing cells.
All living things are composed of cells.
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Prokaryote – a cell without membrane bounded organelles
Eukaryote – cell with defined membrane bounded organelles
Unicellular - composed of one cell
Multicellular - composed of more than one cell.
Levels of organization
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Cell- basic unit of life.
Tissue- group of cells performing the same
function. Lung tissue
Organs- group of tissues performing the
same function. Lung, heart
Organ system- group of organs that perform
the same function.ex. Respiratory system
Organism- group of organ systems working
together.
PROCESSES OF CELLS
All life processes involve energy changes.
1. Nutrition - food is needed for energy and building
materials.
2. Digestion - breaking down reactions of food into
usable parts.
3. Absorption - water, food, ions and other materials
4. Biosynthesis - cells organize many organic
substances for cell activity.
5. Respiration - cell energy is released when certain
organic molecules are split - energy is used for cell
activity.
6. Excretion - waste materials passed from cell to
environment
7. Secretion - synthesized molecules which are passed
out of a cell and which affect the activities of other
cells (vitamins, hormones)
8. Reproduction - cells divide; unicellular - more
organisms, multicellular - more cells.
9. Movement - motion of all types; cellular contractions,
flowing substances within the cell
10. Egestion - elimination of insoluble compounds and
nondigestible particles
Prokaryote
Eukaryote
Eukaryotic cells – advanced cells
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Have nucleus
Plasma membrane
Cytoplasm - everything between plasma
membrane and nucleus
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Organelles
Fluid
Cytoskeleton – threads of microtubules
and microfilaments in cytoplasm
Differences between plant and animal cell
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Plant cell
Cell wall
No centrioles
1 Large vacuole
(Tonoplast)
Chloroplast
(chlorophyll)
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Animal cell
No cell wall
Centrioles present
Many small
vacuoles
No chloroplasts
Plant parts
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Cell wall- rigid, made of cellulose and
gives support and structure.
Chloroplasts- contain chlorophyll,
photosynthetic organ
Tonoplast- large vacuole that gives
plant support.
Cell Size
Largest cell in the world
The egg
from an
ostrich
15cm
Other parts of a Cell
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Ribosome- synthesis proteins
Nucleus- controls cell activity
Cell membrane- regulates what enters
and leaves the cell
Mitochondria- carries out cellular
respiration to release energy.
Endoplasmic reticulum- system of
channels that transport materials.
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Smooth ER- without ribosome
Rough ER- with embedded ribosome.
Lysosomes- digestive enzymes to break
down substances.
Nucleolus – synthesize ribosome.
Cytoplasm- liquid portion of the cell
Vacuoles – storage bins of the cell.
Structure of cell wall
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Cell wall is present only in plant cells.
Cell wall is non-protoplasmic. It is considered as
metabolic byproduct of the protoplast.
Cell wall provides support and protection to cell. It
also plays an important role in absorption,
translocation and secretion.
Typical component of plant cell that fixes the size
and shape of the mature plant cell.
The kind of cell wall present determines the texture
of a tissue.
Functions
Mechanical functions
–Like a skeleton around each cell
–Determine shape and size of cell
–Determines the limits of expansion and water uptake
•Metabolic Activity
–Living part of cell
–Receives signals such as hormones.
–Wall signals transmitted through plasmalemma into cytoplasm,
-biochemical response
•Absorption or secretion–root hairs, rhizoids.
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Cell wall is divided into different layers. Cell walls
vary greatly in composition and morphology. It is
composed of different layers:
The cell walls vary much in thickness in relation to
age and type of cells. Young cells have thinner cell
walls than the fully developed ones.
•The cell wall is complex in its structure and usually
consists of three layers:
•Primary cell wall( usually consists of one layer
•Intercellular substance(middle lamella) cements
together primary wall of two adjacent cells.
Secondary cell wall((made up of one-many layers ,
frequently three)
1. Middle lamella
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It is the outer most layer of cell wall.
The cell wall of the adjacent cells is
joined by middle lamella. Middle lamella
is a thin layer.
Cellulose is absent in it. It is mainly
composed of pectic compounds.
Middle lamella acts as an intercellular
substance. It holds the cell together.
2. Primary wall
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Primary wall is elastic and transparent. It
is the first wall formed in the developing
cell. It remains primary in many types of
mature cells. It is present only in the living
cells like meristems and other living
tissues. But it is absent in non-living cells
like tracheids, sclerenchyma etc.
Primary wall undergoes extensive growth
with the increase in size of cell. It is chiefly
formed of cellulose and hemicelluloses and
pectic material.
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The increase of thickness of primary layer
occurs due to deposition of successive layers of
cellulose towards the inner side of the cell.
Lignin is deposited between the primary wall
and middle lamella in mature tissues.
Therefore, primary wall cannot be differentiated
from the middle lamella. The primary
wall in many cells has lamellae like
structures called microfibrils. These microtibrils
are arranged in criss cross manner.
(3) Secondary wall
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The increase of surface area of primary
wall stops with the growth of cell, now
secondary wall is formed inner to the
primary wall.
secondary wall has no surface growth.
It has compounds like pectin, silica, gum
etc. Unequal lignification produces
following thickenings in the cell wall:
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Annular: These are ring like thickening. In this
case, ring of lignin are deposited one above the
other.
Scalariform: These are ladder like lignin thickenings
Spiral: In this case, thickenings are arranged in
spiral bands.
Reticulate: In this case, lignin thickenings form
networks.
Pitted: The entire cell wall is thickened. It has only
few tin areas called pits.
Plasmodesmata
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The plasmodesmata are cytoplasmic strands
that extend through the pores in adjacent cell
walls.
The protoplasts of the adjoining cells are not
completely separated by the cell walls. The
protoplasts of adjoining cells are connected by
fine strands. These strands pass through pores
and form plasmodesmata.
Plasmodesmata are concerned with the
transport of material & stimuli from cell to cell.
Plasma Membrane
OUTSIDE OF CELL
Sugar Chain
Lipid Bilayer
Protein Marker
Cholesterol
INSIDE OF CELL
Proteins
Embedded
Protein
Cell Membrane Side Profile
Different membranes
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All have similar functions & structures
Plasma membrane separates inside of cell from
outside of cell
Other membrane define organelles to form
compartments of eukaryotic cells
Forms a selectively permeable layer
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Lets some things in or out but not all
Like a window screen
Nucleus - Structures
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Envelope
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Chromatin
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Double membrane
Pores to get messages in and out
DNA threads
Protein balls called histones - wrapping
Nucleolus - site of ribosome production
Ribosomes
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Consists of 2 parts, which are made in nucleus
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Make protein in the Cytoplasm
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Produce proteins from ‘recipes’ in the nucleus
copied into mRNA
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Some (proteins) will remain in cytoplasm
Some will be exported out of cell
Some will attach to membranes in cell
Ribosomes are found on the endoplasmic
reticulum and in the cytoplasm
Endoplasmic Reticulum
Rough
ER
Smooth
ER
Rough Endoplasmic Reticulum
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Rough ER - attached to nucleus
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Ribosomes stud surface
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Produces
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Membrane proteins - stay in cell
Secretory proteins - exported from cell
RER makin’ Proteins!
Smooth Endoplasmic
Reticulum
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No ribosomes, so not protein factories
Makes steroids, lipids
Liver cells have lots of smooth ER
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Detoxify chemicals
Supply and demand
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Increases tolerance to drug
So higher doses needed for same effect
Golgi apparatus – the Post
Office of the Cell
Golgi apparatus – what it does
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Refines, stores and marks molecules for
shipment
Looks like stack of hollow pancakes
Products of ER arrive & leave via transport
vesicles
Moving from one sac to the next
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Molecules get modified
Labeled and / or stored
Called the cell “Post office” because it marks
and directs products in the cell
Lysosome
Lysosome
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Greek for breakdown body
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Sac of strong digestive enzymes
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Recylcer
Compartmentalized for safety
Can release to breakdown entire cell – “suicide
sack”
Functions
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Digest food vacuoles
Digest invading bacteria
Digest old organelles
Lysosome
Lysosomal diseases
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Genetic disorders
‘Recipe’ is messed up so protein doesn’t work
If recipe for lysosome enzyme
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What should get broken down doesn’t
Ex. Tay Sachs
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Lipids aren’t broken down
Build up occurs
Eventually causes death
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Usually in before age 5
Mitochondria
Mitochondria
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Site of cellular respiration
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Conversion of food into energy (ATP)
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Double membrane
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ATP is what cells use to make things happen (drive
chemical reactions)
Big bag stuffed in smaller bag
Folds of inner bag called cristae
Space inside inner bag called matrix
Also once free living bacteria
Efficiency - gasoline engines converts 25% of energy
mitochondria converts 54% of energy
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contains some of its own DNA (amount
varies within organisms)
believed to evolved from a primitive
cell engulfing it and creating a
symbiotic relationship
DNA in mitochondria obtained only
from mother of organism.
Plant Organelles Chloroplasts - in
plants
Chloroplast
1. chlorophyll is green chemical that releases
electrons, working like a solar panel in sunlight
2. forms glucose
3. photosynthesis
6CO2 + 6H2 O ---> C6H12 O6 + 6O2
Chloroplasts
Structure of Chloroplast
 Double membrane
 Grana
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Stack of thylakoids
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Stroma
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Hollow disk
Where sunlight energy is captured and converted to
chemical energy
Thick fluid filling chloroplast
Contains some DNA
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Once free-living bacteria
Cytoskeleton
Role of the Cytoskeleton
Network of fibers
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Give shape to cells
Allow movement of cell
Move organelles around
Made of microtubules and
microfilaments
Centrioles
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Cell reproduction; goes
to poles of cell during
cell division and helps
cell divide
Centrioles at Work in Cell Division
Cell Specialization
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Different kinds of cells suited for a
different activity.
Division of Labor
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Different cells divide their labor each
has a specific function and supports
each other.
Levels of structure
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1.
2.
3.
4.
5.
Cell
Tissue
Organ
Organ system
Organism
Tissue Level
A group of cells that are alike in structure and
activity in an organism muscles
- Skeletal muscle cells – motion
- Cardiac muscle cells – heartbeat
- Bones - support
- Nerve cells - coordination, perception
and automatic body functions
Organ Level
several tissues working as a unit
Animals
heart
brain
stomach
Plants
roots
stem
leaf
Organ System
many organs involved in carrying out a function
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digestive
nervous
skeletal
excretory
respiratory
endocrine – (hormones)
circulatory
muscular
reproductive
Organism
complete living thing
cell
tissue
organ
organ system
organism