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The cell
Topic 1
Introduction
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The study of cells is called Cytology
The cell is the smallest functional unit of life
Cell theory
Prokaryote vs Eukaryote
Cell parts and their functions
Normal cell reproduction
1.1 Cell Theory
1. All organisms are composed of one or more
cells.
2. Cells are the smallest units of life.
3. All cells come from pre-existing cells
Contributors to part 1
• Robert Hooke first described cells in 1665
using microscope he built.
• A few years later, Antonie van Leeuwenhoek
sees living cells and calls the animalcules.
• In 1838, Matthias Schleiden states that plants
are made of cells.
• In 1839, Theodor Schwann states that animals
are made of cells.
Contributors to part 3
• Louis Pasteur, in the 1880’s, chicken broth
experiment showed that living organisms
would not spontaneously appear.
Functions of life
• All organisms, whether single cell (unicellular)
or multicellular, carry out all the functions of
life.
• Metabolism
nutrition
• Growth
excretion
• Reproduction
• Response
• Homeostasis
• Metabolism – all the chemical reactions that
occur in an organism. Energy conversion
• Growth may be limited but is always there.
• Reproduction involves hereditary molecules
being passed to offspring.
• Responses to stimuli in the environment.
• Homeostasis is maintenance of constant
internal environment.
• Nutrition provides compounds to convert to
energy.
• Excretion is the release of unneeded or toxic
chemicals from an organism.
Cells and Size
• Cells are small enough to usually need a
microscope to study them.
• Light microscope is the most common and
used light passing through the cells to see
them.
• Electron microscopes use electrons to form an
image and have greater magnification than
light microscopes.
Relative size
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Cells (eukaryotes) 100 micrometers um
Organelles
10 um
Bacteria
1 um
Viruses
100 nanometers nm
Membranes
10 nm
Molecules
1 nm
Calculating size
• Formula
Magnification = size of the image / actual size
Limiting cell size
• The surface area of a cell, compared to the
volume of the cell, limits how large a cell will
get.
• The amount of resources a cell needs to take
in, as well as the amount of waste and heat
that a cell needs to get rid of, depends on the
volume of the cell.
• The surface of the cell, the cell membrane,
controls how fast this can occur.
• As a cell gets larger in volume, its surface area
also increases, but at a much slower rate.
• Volume involves cubing the radius while
surface area involves squaring the radius.
• This means that the larger a cell gets, the
smaller the surface area to volume ratio.
• Eventually, the volume gets so large that the
surface area can’t handle the traffic in and out
and the cell stops growing.
Cell reproduction and Differentiation
• Single cell (unicellular) organisms need to
reproduce to create new organisms.
• Multicellular organisms need to create new
cell to grow and replace damaged or old cells.
• New cells in multicellular organisms need to
differentiate, which means change into a
particular type of cell.
• All cells have the same DNA, but they use or
express different parts of it to become different
types of cells.
• Once they become specialized, some cells (nerve,
muscle) lose the ability to reproduce themselves.
• Different types of cells can accomplish more as a
group than they could as individuals, the group
can do more than the sum of its parts.
• This is referred to as an Emergent Property
Stem Cells
• There are cells within organisms that retain
their ability to divide and differentiate into
different types of cells.
• These cells are called Stem Cells
• Scientists discovered pluripotent or embryonic
stem cells in the early 1980s.
• Stem cells can produce different types of cells
and also more stem cells.
Stem Cell Research
• Therapeutic cloning is using stem cells to
grow cells to replace cells damaged through
disease or accident.
• Parkinson’s and Alzheimer’s are two diseases
being treaded with nerve cells grown from
stem cells.
• Pancreatic cells are being grown to treat
Diabetes
Tissue specific Stem Cells
• Certain tissue types have their own stem cells.
• Leukemia treated with blood stem cells
• Stargardt’s disease with photo receptor cells
in the eye.
Ethical issues
• Pluripotent stem cell research is being done
using stem cells from embryos through in vitro
fertilization.
• Some argue that this is taking a life.
1.2 Cell Structure
Prokaryotes
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Much smaller than eukaryotes- 1 um or less
Much simpler than eukaryotes- no organelles
Appeared on Earth first
Bacteria are the major members of this group
Prokaryote structures
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Cell wall
Plasma membrane
Flagella – not all have them
Pili
Ribosomes
Nucleoid region
Cell Wall and Plasma Membrane
• Cell wall protects and maintains shape of cell
• Made of a carbohydrate-protein material
called peptidoglycan.
• Plasma membrane is just inside the cell wall.
• Controls movement of material in and out of
the cell and plays a role in binary fission.
• Inside the membrane is the cytoplasm. No
compartments in cytoplasm.
Pili and flagella
• Pili are hair like growths on the outside of the
cell, used for attachment as well as
reproduction.
• Some prokaryotes have a flagellum or flagella
(plural) which are longer than pili and are used
for movement
Ribosomes
• All Prokaryotes have them
• Site of protein synthesis
• Smaller than Eukaryote ribosomes, 70s vs 80s
Nucleoid Region
• The area (no compartment) where the single
circular DNA chromosome is located.
• Prokaryote DNA is not attached to proteins like
eukaryote DNA are.
• Some prokaryotes also contain plasmids, small
circular pieces of DNA that are separate from the
main chromosome.
• Plasmids replicate independently of the main
chromosome and are not needed for day to day
activities.
Binary Fission
• Prokaryotes divide by process called binary
fission.
• First the chromosome (DNA) is copied.
• The two daughter chromosomes attach to
different areas of the plasma membrane.
• The cell elongates, fibers called FtsZ fibers
separate the two chromosomes, then the cell
divides into two identical daughter cells.
Eukaryote Animal Cell
Eukaryotes
• Size ranges from 5-100 um
• Contain organelles, membrane bound
structures which perform specific functions
for the cell.
Eukaryote Plant Cell
Eukaryote Organelles
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Endoplasmic reticulum
Ribosomes
Lysosomes ( not usually found in plant cells)
Golgi apparatus
Mitochondria
Nucleus
Chloroplasts ( only in plants and algae)
Centrosomes
vacuoles
• Cytoplasm – the area inside the plasma
membrane. The fluid part is called the
cytosol.
• Endoplasmic Reticulum (ER) – A series of
tubes/channels that transport materials
throughout the cell.
• Two types – Smooth ER and Rough ER
Smooth ER
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Contains enzymes on its surface which:
Production of lipids and phospholipids
Production of sex hormones
Detoxification of drugs in the liver
Storage of calcium ions in muscle cells
Release of glucose by liver
Rough ER
• Contain ribosomes on their surface which give a
rough appearance.
• The ribosomes of the Rough ER make proteins to
be transported out of the cell.
• There are ribosomes not attached to the Rough
ER which float freely in the cytosol.
• These free ribosomes make proteins to be used
by the cell.
• Ribosomes are composed of two units of RNA
that are made in the nucleolus
Lysosomes
• Lysosomes – sacs of digestive (hydrolytic)
enzymes, made by the Golgi apparatus, that
help break down proteins, carbohydrates,
lipids and nucleic acids.
• They attach to old organelles or materials
brought into the cell by phagocytosis.
Golgi Apparatus
• Made of flattened sacs called cisternae.
• It collects, modifies, packages and distributes
materials made by the cell.
• The cis side of the Golgi apparatus is near the
Rough ER and it receives products of the ER.
• These products leave the Golgi Apparatus in
small sacs called vesicles, at the trans side.
Mitochondria
• Rod shaped organelle close in size to a bacteria
• Contain their own DNA, a single circular
chromosome, similar to bacterial cells.
• Contain their own ribosomes that are 70s, similar
to bacteria.
• They have a double membrane, the outer being
smooth and the inner having many folds called
cristae.
• Inside the inner membrane is called the Matrix.
Mitochondria
• The area between the two membranes is
called the inner membrane space.
• The folds (cristae) allow for increased surface
area for the reactions of the mitochondria to
take place.
• The reactions of the mitochondria are called
cellular respiration and create molecules
called ATP.
Mitochondria
Nucleus
• Double membrane enclosed area, called the
nuclear envelope, where the DNA is located.
• Contains pores to allow movement into and
out of the nucleus.
• DNA is in pieces called chromosomes.
• Different species have different numbers of
chromosomes.
• DNA is the genetic material of the cell and
allows traits to be passed to offspring.
• When not dividing, DNA is in a form called
chromatin, which is DNA and proteins called
histones.
• Where the DNA wraps around 8 histones, an
area is formed called a nucleosome.
• Most eukaryote cells have a single nucleus.
• Some, like red blood cells, have no nucleus.
• Most nuclei also contain a dark area called a
nucleolus which makes ribosomes.
Chloroplast
• Found only in algae and plant cells
(autotrophs).
• Surrounded by a double membrane and about
the size of a bacteria.
• Has its own DNA and 70s ribosomes, just like
the Mitochondria.
• Contain flattened sacs called thylakoids where
the light absorption part of photosynthesis
occurs.
• Thylakoids are in stacks called Grana/ Granum
• The fluid part of the chloroplast is called
Stroma which contains enzymes for
photosynthesis.
• Like Mitochondria, Chloroplasts can reproduce
themselves independently of a cell.
Chloroplast
Centrosome
• Found in all eukaryotic cells.
• Consists of a pair of centrioles at right angles to
each other.
• Centrioles make microtubules which provide
structure and allow movement.
• Also important for cell division.
• Some higher evolved plants produce
microtubules even though they lack centrioles.
• Located close to the nucleus.
Vacuoles
• Membrane bound storage organelles made by
the Golgi Apparatus.
• Store many different substances including
food, water, waste, and toxins.
• Plant cells have a huge one filled with water
and enzymes, allows rigidity for the plant.
Prokaryote vs Eukaryote
Eukaryote Plant vs Animal cells
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Animal cell
cell wall
no cell wall
chloroplasts
no chloroplasts
Large central vacuole small or no vacuoles
carbs stored as starch carbs stored as glycogen
no centrioles
centrioles
Fixed angular shape
rounded shape
Extracellular Matrix (ECM)
• Surrounds the outside of animal cells,
composed of collagen fibers and
glycoproteins.
• Allows cells to attach to each other.
• Allows communication and coordinated action
between cells
ECM
1.3 Membrane Structure
History
• Since 1915, scientists have known membranes
are made of proteins and phospholipids.
• In 1935, Davson-Danielli model suggested a
phospholipid bilayer covered on both sides by
a thin layer of protein.
• In 1972, Singer-Nicolson model suggested
proteins were inserted into the phospholipid
bilayer and not a continuous layer.
• They believed the phospholipids were fluid,
meaning they were very loosely attached to
each other and could move around, and the
proteins formed a mosaic pattern within the
bilayer.
• Most of the new evidence came from the use
of the electron microscope.
Phospholipids
• The main “backbone” of the membrane is
made of a double layer of phospholipids.
• Each phospholipid is composed of a three
carbon molecule called glycerol
• Two of the carbons have fatty acid (lipid)
molecules attached to them.
• The third carbon is attached to a highly polar
alcohol/phosphate group.
• The fatty acids are non-polar and not soluble
in water. (Hydrophobic)
• The alcohol/phosphate group in polar and
soluble in water. (Hydrophilic)
• This causes the phospholipids to align
themselves with their polar “heads” outward
and their non-polar “tails” inward.
Phospholipid
Cholesterol
• Membranes must be fluid or flexible to
function properly.
• At various locations in the hydrophobic, or tail
region of animal cells, there are cholesterol
molecules.
• They allow membranes to be properly flexible
at a large range of temperatures.
• Plant membranes do not have cholesterol.
Proteins
• It is the proteins found in and on the
membranes that allow for the great diversity
of membrane function.
• There are two major types of membrane
proteins, integral and peripheral.
• Integral proteins are amphipathic, meaning
they have both polar and non-polar regions.
Proteins
• These proteins will have their non –polar
hydrophobic regions near the middle of the
membrane (by the tails) and their polar
hydrophilic regions near the edges.
• Peripheral proteins are attached to the surface
of the membrane, often attached to an
integral protein.
Protein Functions
• There are many different proteins which have 6 general
functions:
• Sites for hormone binding – have a specific shape
exposed to the outside that will only fit a specific
hormone. When hormone attaches, it changes the
shape of the protein, relaying a message inside the cell
• Enzymatic action – proteins act as enzymes to catalyze
reactions, attached to outside or inside of the
membrane
• Cell adhesion – allow cells to attach to each other
permanently or temporarily. Gap and tight junctions
Protein Function
• Cell to cell communication - proteins with
carbohydrates attached that provide
identification for different species.
• Channel for passive transport – allow
substances to travel through the membrane
from high to low concentration.
• Pump for active transport – moves substances
through membrane by changing shape using
ATP for energy. Moves from Low to High
1.4 Membrane Transport
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Passive and Active Transport
Passive Transport
• Does NOT require energy
• Movement is from an area of higher
concentration to an area of lower
concentration.
• Usually referred to as moving down the
concentration gradient.
• Osmosis (water), or diffusion
Simple Diffusion
• Particles moving from high to low
concentration. In biology, usually across a
membrane.
• Examples: Oxygen moving from the blood
into cells, Carbon Dioxide moving from cells
into the blood.
Facilitated Diffusion
• Movement across a membrane is facilitated by
a integral carrier protein.
• Carrier protein changes shape but does not
require energy.
Osmosis
• Osmosis is a type of diffusion that involves the
passive movement of WATER across a partially
permeable membrane.
• Water will move from an area of lower solute
concentration (hypotonic) to an area of higher
solute concentration (hypertonic).
Ease of movement
• The size and polarity of a molecule determines
how easily it can cross a membrane.
• Small non-polar molecules cross easiest
(gases)
• Large polar molecules cross hardest.(ions and
sugars)
Active Transport
• Requires work to be performed and therefor
requires energy (ATP)
• It is the movement of a substance AGAINST
the concentration gradient, from an area of
low concentration to an area of high
concentration.
• Example: animal cells have a high
concentration of P+ inside and high Na+
outside.
Sodium-Potassium Pump
• 5 stages involved in moving Na+ and K+ against
their concentration gradients:
• 1- A specific integral protein binds to 3 sodium
ions inside the cell
• 2. The binding of the sodium to the protein
causes phosphorylation to occur. ATP
becomes ADP
• 3- Phosphorylation causes the protein to
change shape, expelling the Na+ from the cell
• 4- Two Phosphate ions outside the cell bind to
the protein, which causes the release of the
phosphate.
• 5- The loss of the phosphate returns the
protein to its original shape, releasing the K+
into the cell.
• The Na+ P+ pump is used extensively in nerve
signal transport.
Endo and Exocytosis
• These are processes that allow larger
substances in and out of cells.
• Endo is into the cell, while exo is out of the
cell.
• Both processes depend on the fluidity of the
cell membrane.
Endocytosis
• The membrane of a cell surrounds and engulfs
an object, leaving it within a membrane inside
the cell.
Exocytosis
• The opposite of endocytosis, how the cell
exports proteins is a good example of how this
works.
• 1- Proteins produced by ribosomes on the
Rough ER enter the lumen (inside) of the ER
• 2- Protein exits the ER inside a vesicle and
enters the cis end of the Golgi Apparatus.
• 3- As protein moves through Golgi, it is
modified then exits the trans end inside a
vesicle.
• 4. This vesicle moves to the cell membrane
and fuses to release (secrete) the protein from
the cell.
• https://youtu.be/DuDmvlbpjHQ
1.5 The Origin of Cells
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Cell Theory:
All organisms are made of 1 or more cells
Cells are the smallest unit of life
All cells come from other pre-existing cells
• There are some problems with and exceptions
to this theory.
• How did the first cell arise?
• Pasteur showed that cells don’t spontaneously
arise. His experiment:
• He boiled nutrient broth
• He put sterile broth into 3 flasks, one open,
one closed and one with a water trap type
seal. He allow time for incubation
• A sample from each flask was transferred to
solid growth media (petri dish) and incubated.
• The only flask that showed growth was the
open one.
Exceptions to normal
• Multi nucleated cells of striated muscle, fungal
hyphae and giant algae.
• Very large cells with no compartments
• Viruses
• Where did the first cells come from.
• Before that discussion we need to understand
the transition from simple prokaryotes to
complex eukaryotes.
Endosymbiotic Theory
• Presented by Lynn Margulis in 1981
• About 2 billion years ago, a bacterial cell
began living inside another cell that had
engulfed it (endocytosis)
• This eukaryotic cell and the bacterial cell
began a symbiotic relationship.
• Over time, the bacteria cell evolved into a
mitochondria.
Evidence
• Mitochondria: are about the size of bacteria
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divide by binary fission
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divide independently of their cell.
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have their own 70s ribosomes
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have their own DNA, single
strand loop like bacteria
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have a double membrane from
being engulfed.
• Chloroplasts also show the same evidence for
endosymbiotic theory.
• The protist hatena gets its energy by ingesting
organic matter. When it eats algae, it starts
photosynthesis to get energy.
• The slug Elysia chlorotica is brown and eats
things for energy when it is young.
• As adults they are green due to eating algae
and using them to do photosynthesis.
• DNA of mitochondria more closely resembles
that of bacteria than eukaryotes.
1.6 Cell Division
• The life of a cell is described by the cell cycle.
• In most cases, a cell will grow, then divide into
two identical cells called daughter cells.
• The cell cycle has a growth part as well as a
division part.
Cell Cycle
Interphase
• Longest phase of most cell cycles
• Composed of three parts, G1 (Gap 1) , S and G2
(Gap 2).
• G1 major event is growth of the new cells.
• S major event is replication of the DNA
• G2 major events are further growth as well as
preparing for Mitosis (M phase). DNA starts
to condense, organelles are copied,
microtubules begin to form.
Cyclins
• Cyclins are proteins that help control a cells
movement through the cell cycle.
• Cyclins bind to cyclin-dependent protein
kinases (CDKs), enabling them to act as
enzymes.
• These enzymes allow the cell to move from G1
to S and from G2 to M.
• Some cells will stop at G1 and stay there (G0),
such as nerve and muscle cells.
Mitosis – Nuclear division
• During Mitosis, the replicated chromosomes
are divided into two identical groups in
preparation for the cell division (cytokinesis).
• The two new cells should be identical to each
other and are called daughter cells.
• Prior to Mitosis beginning, the DNA coils to
form chromosomes.
• Chromatin – nucleosomes- solenoids – looped
domains - supercoil
chromosomes
• During Interphase, each DNA molecule is
wrapped around histone proteins to form
nucleosomes.
• Nucleosomes coil into solenoids, then form
looped domains and finally supercoil to
chromosomes.
• After replication during the S phase of interphase,
each chromosome has an identical twin, attached
to the original by a Centromere. Each molecule is
called a chromatid and together they are called
sister chromatids.
Phases of Mitosis
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Prophase
Metaphase
Anaphase
Telophase
Prophase
• Chromatin fibers continue to supercoil and
form chromosomes.
• Nuclear envelope (membrane) disintegrates
and nucleolus disappears.
• Mitotic spindle (fibers) forms.
• Each chromosome has a region of its
centromere called a kinetochore that the
fibers attach to.
• Centrosomes move to opposite poles
Metaphase
• Chromosomes move to the middle (equator)
of the cell, this is called the metaphase plate.
• The chromosomes centromeres lie on the
plate
• The microtubules, or spindle fibers do this.
• The centrosomes are now at opposite poles.
Anaphase
• The shortest phase begins when the two sister
chromatids of each chromosome split.
• The chromatids, now chromosomes, move
toward opposite poles, toward centrosomes.
• The shortening of the microtubules causes the
movement.
• At the end of this phase, each pole of the cell
has a complete, identical set of chromosomes.
Telophase
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Chromosomes are at the poles
Nuclear envelope reforms
Chromosomes begin to uncoil
Nucleolus reappears
Spindle fibers disappear
The cell elongates and is ready for cytokinesis
Cytokinesis
• In animal cells, a cleavage furrow forms
• In plant cells, a cell plate forms
• Both processes result in the cell being divided
into two daughter cells with identical nuclei
• Growth, development of embryos, tissue
repair and asexual reproduction all involve
Mitosis
Cancer
• Cancer is when the cell cycle runs out of control.
• The mass of cells created is called a tumor.
• A primary tumor is located at the original site of
formation.
• A secondary tumor forms as a result of
metastasis or spreading to other areas.
• Mitotic index is ratio of cells undergoing mitosis
compared to the number not. The larger the
number, the faster the cancer is growing.
Causes of Cancer
• Areas of a gene can change (mutate) to
become oncogenes.
• Oncogenes contribute to cancer formation.
• Oncogenes can be formed by outside agents
called mutagens.
• Cigarette smoke is a mutagen.
• There is a positive correlation between
smoking and cancer.