Transcript cell theory - George Washington High School

Topic 2: Cells
2.1 Cell Theory
Introduction:
The smallest unit of life is a cell.
Organisms range in size from a single
cell to thousands of cells.
2.1 Cell Theory
★Outline the cell theory
★Discuss the evidence for the cell theory
Over hundreds of years, scientists have
developed the following 3 main principles of the
CELL THEORY:
All organisms are composed of one or more
cells
Cells are the smallest units of life
All cells come from pre-existing cells
2.1 Cell Theory
What does a THEORY mean?
Cell theory, theory of evolution, gravity
Theory: A hypothesis that has been
supported many times over a long period
of time
Theories are developed after the
accumulation of a ton of data.
Sometimes, theories are completely
abandoned because of conflicting
2.1 Cell Theory
Evidence for the Cell Theory:
Louis Pasteur in the 1860s boiled
chicken broth (thus killing all living cells).
Pasteur showed that living organisms do
not "spontaneously" reappear. Only
after exposure to pre-existing cells was
life able to re-establish itself in the
chicken broth.
Cells can only come from cell division mitosis/meiosis!
2.1
Cell
Theory
★State that unicellular organisms carry out all the
functions of life
Remember CARL GREW? That is an easy
freshman version of what you actually need to
know
All organisms (uni or multicellular) carry out all the
FUNCTIONS OF LIFE:
Metabolism: includes all the chemical reactions
that occur within an organism. Chemical
reactions inside the cell.
Growth: may be limited but is always evident in
one way or another (think on the cellular level cells grow to get ready for mitosis). Increasing
2.1 Cell Theory
Reproduction: Involves hereditary molecules that
can be passed to offspring. Produce offspring.
Response: important in an environment for the
survival of an organism. Reacting to stimuli.
Homeostasis: maintaining a constant internal
environment. Examples: constant internal
temperature, constant acid-base levels. Controlling
conditions inside the cell.
Nutrition: providing a source of compounds with
many chemical bonds which can be broken to
provide the organism with the energy and the
2.1 Cell Theory
Question #1:
Which of the following will contribute to the
cell theory?
I. Living organisms are composed of
cells.
II. All cells come from pre-existing cells
by mitosis.
III. Cells are the smallest units of life.
Answer: I and III only
2.1 Cell Theory
Question #2:
Which of the following characteristics found in
a structure necessarily indicates that it is
alive?
A. The presences of genetic material.
B. The presence of a lipid bilayer
C. Metabolism
D. Movement
Answer: C, Metabolism
2.1 Cell Theory
Question #3:
Which functions of life are found in all
unicellular organisms?
A. growth, response and nutrition
B. differentiation, response and nutrition
C. metabolism, meiosis and homeostasis
D. growth, metabolism and differentiation
Answer: A: growth, response and nutrition
2.1 Cell Theory
★Comparing relative sizes of the following
(starts of large and continues to decrease
in size):
cells (largest)
bacteria
viruses
membranes
molecules (smallest)
2.1
Cellactual
Theory
★Calculating
size of a specimen:
1. Need to know diameter of
microscope's field of vision.
If not given to you, can simply put a
ruler on the stage of a light
microscope.
2. Conversions:
1 millimeter (1mm) = 1000
micrometers (1000µm)
2.1
Cell
Theory
Work Example 1 (actual size of a
specimen):
Most light microscopes have a field of
vision at low power of about 1.4
millimeters. If you are looking at a cell
that has a diameter of close to 60% of the
field of vision at low power, what would be
the diameter of the cell in micrometers?
Solution: Since the field of vision is
1.4mm, or 1400µm, multiply 1400µm
by 0.60:
2.1 Cell Theory
Work Example 2 (actual size of a
specimen):
A red blood cell is 8µm in diameter. If
drawn 100 times larger than its actual
size, what diameter will the drawing be in
mm?
Remember 1mm = 1000µm
8µm x 100 = 800µm
800µm x 1mm/1000µm = 0.8mm
2.1 Cell Theory
★Calculating the magnification of images
or drawings.
1. Scale bars are often used with
images from microscopes or drawings so
that actual sizes can be determined,
because images are often enlarged.
2. To calculate the magnification you
need this formula:
Magnification = size of image ÷ size of
2.1 Cell Theory
2.1
Cell
Theory
Work Example 3 (calculating magnification):
A micrograph of a cell is accompanied by a scale
bar that shows it to be 10 micrometers in
diameter. The scale bar, which is the same length
as the cell diameter in the micrograph, is 10
millimeters long. What is the magnification of this
cell?
Solution: The image size is 10 mm or
10,000µm and the specimen size is 10µm.
size of image ÷ size of specimen: 10,000µm
÷ 10µm
2.1 Cell Theory
Work Example 4 (calculating magnification):
If a mitochondrion has a length of 5µm and a
student's drawing of the mitochondrion is 10
mm, what is the magnification of the drawing?
Magnification = size of image ÷ size of
specimen
Convert 10mm to µm, 10mm x 1,000µm =
10,000µm
10,000µm ÷ 5µm = x2000 magnification
2.1 Cell Theory
Work Example 5 (calculating magnification):
If a Sequoia tree is 100 m tall and a drawing of
it is 100 mm tall, what is the magnification of
the drawing?
Magnification = size of image ÷ size of
specimen
Convert 10m to mm, 1000mm=1m, 10m =
100,000mm
100mm ÷ 100,000mm= x0.001
2.1 Cell Theory
★Explain the importance of the surface area to
volume ratio as a factor limiting cell size.
Cells do not carry on growing indefinitely - even
though growth is one of the functions of life.
There is a factor called the surface area to volume
ratio that effectively limits the size of cells.
In the cell, the rate of heat and waste/resource
productions depends on the cell's volume.
Most of the chemical reactions occur in the interior
of the cell and its size affects the rate of these
reactions.
2.1 Cell Theory
As the width of an object such as a cell
increases, the surface area also increases
but at a much slower rate than the volume.
This means that a large cell has relatively
less surface area to bring in needed
materials and to rid the cell of waste, than a
small cell.
Large animals do not have larger cells,
they have MORE small cells!
2.1 Cell Theory
Cell Volume
Rate of heat
production, waste
production,
resource
consumption
Rate of exchange
Cell Surface Area of materials and
energy (heat)
2.1 Cell Theory
Question #4:
In a cell, what is the effect of a large surface
area to volume ratio?
A. Slower rate of exchange of waste
materials
B. Faster heat loss
C. Faster rate of mitosis
D. Slower intake of food
Answer: B, faster heat loss
2.1 Cell Theory
Question #5:
How does the surface area to volume ratio
change with an increase in cell size?
Answer: C, as cell size increases,
surface/volume ratio decreases
2.1 Cell Theory
★State that multicellular organisms show
emergent properties
This means that the whole organism is
greater than the sum of its parts,
because of the complex interactions
between cells.
Discuss: Living vs. Non Living Things
Discuss: Problems defining death in
medical decisions
2.1 Cell Theory
★Explain that cells in multicellular
organisms differentiate to carry out
specialized functions by expressing some
of their genes but not others.
Multicellular organisms like ourselves
usually start out as a single cell (zygote)
after some type of sexual reproduction.
This single cell has the ability to
reproduce at a very rapid rate, and the
resulting cells then go through a
differentiation process to produce all the
required cell types that are necessary for
the well-being of the organism.
2.1
Cell
Theory
So each cell contains all the genetic
information for the production of the
complete organism.
However each cell becomes a specific
type of cell dependent on which DNA
segment becomes active.
Once a pathway of development has
begun in a cell, it is usually fixed and the
cell cannot change to follow a different
pathway. The cell is said to be
committed.
2.1
Cell
Theory
★State that stem cells have the capacity to
divide and have the ability to differentiate
along different pathways.
After the combination of an egg and a
sperm in the formation of a new human
being, the first cells formed are all exact
copies of one another.
None have started changing into any of
the specialized cells that will later
become the tissues of the body.
2.1
Cell
Theory
Stem cells!
Why are they so awesome?
Stem cells can be "told" what cells to
become
Think Alzheimer's disease, caused by
loss of brain cells - it is hoped that if
you implant stem cells into the brian,
they could replace many of the lost
brain cells and stop the disease from
getting worse, or maybe even reverse
Microscopic view of a colony of
undifferentiated human
embryonic stem cells being
studied in a research lab:
2.1
Cell
Theory
Ethical Issues:
To get their hands on stem cells, the
easiest/fasted place to get it is in an EMBRYO.
In other words - earliest form of LIFE. Human
embryos consist entirely of stem cells in their
early stages - before differentiation.
To gather these stem cells involves death of
the embryo, opponents argue that this
represents the taking of a human life.
Others argue that this research could result in
the significant reduction of human suffering,
Cells being extracted from the
early embryo for stem cell
production:
2.1 Cell Theory
★Outline one therapeutic use of stem cells.
Stem cells are cells that retain the
capacity to divide and have the ability to
differentiate along different paths into all
types of cells.
Stem cells are derived from human
embryos, left over from IVF (in-vitro
fertilization), placenta/umbilical cord
blood, and even some adult tissues.
2.1 Cell Theory
New techniques rely on replacing diseased or
dysfunctional cells with healthy, functioning ones.
1. Need to identify the desired type of stem cell
and grow in a culture (petri dish filled with nutrients
for the cells) under controlled conditions.
2. Develop biochemical solution that will cause the
cells to differentiate into desired cell type.
3. Develop means of implants/integrating the cells
into a patient's own tissues so that they function
with the body's natural cells.
2.1
Cell
Theory
4. There is a danger of rejection, therefore
there is a need to suppress the immune
system from attacking the new cells.
5. Also a need to make sure the new cells
do not become overgrown or develop into
cancerous tumors.
Recent evidence that some types of
cancer may be caused by stem cells
undergoing a malignant transformation.
Definite possible risk in the implantation
2.1 Cell Theory
Specific examples of therapeutic use of stem cells
1. Retinal cells
Replace dead cells in retina to cure presently
incurable diseases such as glaucoma and macular
degeneration
2. Graft new skin cells
To treat serious burn victims
3. Nerve tissue
Help repair spinal injuries, victims of paralysis can
2.1
CellCommunication
Theoryon Stem Cell
International
Research:
Stem cell research has depended on the
work of teams of scientists in many
countries, who share results and so speed
up the rate of progress.
However, ethical concerns about the
procedures have led to restrictions on
research in some countries.
National governments are influenced by
local, cultural and religious traditions, which
2.1 Cell Theory
Former President George W. Bush permitted
federal funding for embryonic stem cell research
(ESCR) only if the stem cells were obtained from a
limited number of previously existing stem cell
lines.
In 2009, President Barack Obama issued an
executive order expanding the opportunities for
federally funded ESCR by permitting the use of
embryonic stem cells other than those obtained
from the previously designated stem cell lines.
However, legislation to protect this expansion in
research opportunities has never been signed into
law, which gives future administrations the
Question
#6: How
can cells in a
2.1
Cell
Theory
multicellular organism differentiate?
A. They express some of their genes but
not others.
B. They all have a different genetic
composition.
C. Different cells contain a different set
of chromosomes.
D. Different cells do not have some of
the genes.
2.2 Prokaryotic
Cells
Cells are divided into 2 groups:
Prokaryotic (bacteria) and Eukaryotic
(plants/animals)
Prokaryotic cells are much smaller and
simpler than Eukaryotic cells.
Prokaryotes are thought to have
appeared on Earth first.
Greek pro means 'before', and karyon
means 'kernel', referring to the nucleus.
2.2 Prokaryotic
Cells
★Draw/label/annotate a diagram of the
structure of Escherichia coli (E. Coli) as an
example of a prokaryote.
2.2 Prokaryotic
Cells
STRUCTURE
Cell Wall
Plasma Membrane
Cytoplasm
FUNCTION
Forms a protective outer
layer that prevents damage
from outside and also
bursting if internal pressure is
high.
Controls entry and exit of
substances
Contains enzymes that
catalyse the chemical
reactions of metabolism and
contains DNA in a region
called the nucleoid.
2.2 Prokaryotic
Cells
STRUCTURE
Ribosomes
Flagella
FUNCTION
Small granular structures that
synthesize proteins by
translating mRNA. Some
proteins stay in the cell and
others are secreted.
Solid protein structures, with a
corkscrew shape, projecting
from the cell wall, which rotate
and cause locomotion
Hair-like structures projecting
from the cell wall, that can be
ratcheted in and out; when
4.
3.
5.
6.
7.
1.
2.
2.2 Prokaryotic
Cells
★Identify structures in an electron
micrograph of E. Coli
1.
2.
3.
4.
5.
2.2
Prokaryotic
★State that prokaryotic cells divide by BINARY
FISSION.
Cells
1. DNA is copied
2. The 2 daughter chromosomes become
attached to different regions on the plasma
membrane
3. The cell now divides into 2 genetically
identical daughter cells.
Some types of bacteria go through binary
fission every 20 minutes when conditions
are ideal - this means huge populations and
higher risk for infections!
2.2 Prokaryotic
Cells
Question
#7:
A cell has cytoplasm, a cell wall, naked DNA
and ribosomes. Based on this information,
what type of cell would this be?
A. A cell form a pine tree
B. A grasshopper cell
C. A human red blood cell
D. A bacterium
2.2 Prokaryotic
Cells
Question #8:
How do prokaryotic cells divide?
A. By mitosis
B. By meiosis
C. By binary fission
D. By budding
Answer: C, binary fission
2.2 Prokaryotic
Question
#9:
Cells
A cell has cytoplasm, a cell wall, naked DNA
and ribosomes. Based on this information,
what type of cell would this be?
A. A cell form a pine tree
B. A grasshopper cell
C. A human red blood cell
D. A bacterium
Answer: D, a bacterium
2.2 Prokaryotic
Cells
Question #10: The diagram below shows a
bacterium.
What structure is labelled X?
A. Nucleus
B. Nucleoid
C. Nucleolus
D. Nuclear Membrane
Answer: B, Nucleoid
2.2 Prokaryotic
Question #11: What is the function of the plasma
Cells
membrane of this bacterium?
A. To produce ADP
B. To form the only protective
layer preventing damage
C. To control entry and exit
of substances
D. To synthesize proteins
Answer: C
2.3 Eukaryotic Cells
★Draw/label/annotate a structure of a plant
and animal cell.
2.3 Eukaryotic Cells
STRUCTURE
Nucleus
Ribosomes
Rough Endoplasmic
Reticulum (RER)
Golgi Apparatus
Mitochondrion
FUNCTION
Contains cell's DNA,
surrounded by pores
Small structures, free in the
cytoplasm, associated with
RER, protein synthesis(think
big blob in translation!)
Protein transportation and
processing
Stores, modifies, and
packages proteins
Provide energy , ATP
2.3 Eukaryotic Cells
Ribosomes of eukaryotic cells are larger and
denser than those of prokaryotic cells.
Eukaryotic ribosomes have 2 subunits,
equaling 80S
Prokaryotic ribosomes also have 2 subunits,
but are smaller, equaling 70s
S = Unit of measurement for ribosomes
★Identify structures in an
electron micrograph of liver
cells
2.3 Eukaryotic Cells
★Compare prokaryotic and eukaryotic cells
Feature
Prokaryotic
Eukaryotic
Chromosomes
consisting of
strands of DNA
Type of genetic
Naked loop of DNA
associated with
material
protein. 4 or more
chromosomes are
present.
In the nucleus
DNA free in the
inside a double
Location of genetic
cytoplasm in a
nuclear membrane
material
region called the
2.3 Eukaryotic Cells
Feature
Prokaryotic
Eukaryotic
Ribosomes
Small sized - 70S
Larger sized - 80S
Many internal
membranes that
No internal
compartmentalize
Internal membranes compartmentalizatio
the cytoplasm
n to form organelles including ER, Golgi
apparatuses,
2.3
Eukaryotic
Cells
★State the differences between plant and
animal cells
Feature
Animal
Plant
Cell wall AND
No cell wall, only a plasma
Cell Wall
plasma membrane
membrane
present
Chloroplast
Present in cells that
Not present
s
photosynthesize
Polysaccha
rides
Glycogen is used as a
storage compound
Vacuole
Not usually present, or
small
Starch is used as a
storage compound
Large fluid-filled
vacuole often
present
2.3 Eukaryotic Cells
★Outline 2 roles of extracellular components.
1. The plant cell wall maintains cell shape,
prevents excessive water uptake, and
holds the whole plant up against the force
of gravity
2. Animal cells secrete glycoproteins that
form the extracellular matrix. This
functions in support, adhesion and
movement.
2.3 Eukaryotic Cells
Extracellular Matrix (ECM):
Outside many animal cells
Composed of collagen fibers plus a combo
of sugars and proteins called glycoproteins.
These form fiber-like structures that
anchor the matrix to the plasma
membrane.
This strengthens the plasma membrane
and allows attachment between adjacent
cells.
2.3 Eukaryotic Cells
The ECM allows
for cell to cell
interaction,
bringing about
coordination of
cells within a
tissue.
Researchers
believe the ECM
is involved in
directing stem
cells to
2.3 Eukaryotic Cells
Questions #12: What feature do plant cells
have but not animal cells?
A. Plasma membranes
B. Mitochondria
C. Cell walls
D. 80S ribosomes
Answer: C, cell walls
2.3 Eukaryotic Cells
Questions #13: Which of the following structures does
Escherichia coli have?
I. 70S Ribosomes
II. Pili
III. Nucleus
A. I only
C. II and III only
B. I and II only
D. I, II and III
Answer: B, I and II only
2.3 Eukaryotic Cells
Questions #14: Which of the following
structures are found in all cells?
A. Mitochondria
B. Cell walls
C. Chloroplasts
D. Ribosomes
Answer: D, Ribosomes
2.3 Eukaryotic Cells
Questions #15: What can the extracellular matrix of
cells be made of?
I. Polysaccharide
II. Glycoprotein
III. Phospholipid
A. I only
C. II and III only
B. I and II only
D. I, II and III
Answer: B, I and II only
2.3 Eukaryotic Cells
Questions #16: What is the difference between the
structure of ALL prokaryotes and ALL eukaryotes?
•
Prokaryotes
Eukaryotes
A
cell wall
no cell wall
B
chloroplasts
no chloroplasts
C
flagellum
no flagellum
nucleoid
nuclear envelope
D
Answer: D
2.3 Eukaryotic Cells
Questions #17: What do prokaryotic cells
have that eukaryotic cells do not?
A. Mitochondria
B. 70S ribosomes
C. Histones
D. Internal membranes
Answer: B, 70S ribosomes
2.3
Eukaryotic
Cells
Questions #18: Which of the following are features
prokaryotes and eukaryotes?
DNA
70S
80S
associated
Naked DNA
ribosomes ribosomes
with
proteins
A prokaryote eukaryote prokaryote eukaryote
B
•C
eukaryote prokaryote eukaryote prokaryote
Answer: A
eukaryote prokaryote prokaryote eukaryote
D prokaryote eukaryote
eukaryote prokaryote
2.3 Eukaryotic Cells
Questions #19: Which pair of features is correct for
both a human liver cell and an Escherichia coli cell?
Human liver cell
Escherichia coli cell
A
contains DNA associated
with protein
contains naked DNA
B
has 70S ribosomes
has 80S ribosomes
contains
mitochondria
Answer: A
contains mitochondria
•
C
D
contains DNA enclosed by a contains DNA associated
membrane
with proteins
2.4 Membranes
★Draw and label a diagram to show the structure
of membranes.
★Explain how the hydrophobic and hydrophilic
properties of phospholipids help to maintain the
structure of cell membranes.
2.4
Membranes
Phospholipid Bilayer
IS the cell/plasma membrane, surrounds
the cell
A single phospholipid has one
hydrophilic head (water loving) and two
hydrophobic fatty acid tails (water
fearing).
In water, phospholipids form double
layers with the hydrophilic heads in
contact with water on both sides and the
2.4
Membranes
Because the tails do not strongly attract
one another, the membrane tends to be
fluid or flexible.
The phospholipid bilayer is also referred
to as the fluid mosaic model.
This allows animal cells to have a variable
shape and also allows the molecules to
easily pass in and out of the cell.
What maintains the overall structure of the
membrane is the tendency water has to
2.4 Membranes
2.4
Membranes
Cholesterol:
Membranes must be fluid to function
properly - kind of like the consistency of
olive oil.
At various locations in the hydrophobic
region (fatty acid tails) in animal cells are
cholesterol molecules.
Cholesterol helps regulate membrane
fluidity, which changes with
temperature. With cholesterol, the
membrane can function at a wider
2.4 Membranes
Proteins
Proteins of various types are embedded
in the fluid matrix of the phospholipid
bilayer.
They create extreme diversity in
membrane function.
This creates the mosaic effect of the
term fluid mosaic model.
2.4 Membranes
2 major types of protein:
1. Integral protein
Have both hydrophobic and hydrophilic
regions in the same protein.
The hydrophobic region, is in the mid-section
of the phospholipid membrane, holding the
protein in place.
Their hydrophilic region is exposed to the
water solutions on either side of the
membrane.
They completely penetrate the lipid bilayer.
2.4 Membranes
2. Peripheral Protein
Do not protrude into the middle
hydrophobic region, but remain
bound to the surface of the
membrane.
Often these peripheral proteins are
anchored to an integral protein.
2.4 Membranes
Glycoproteins:
Composed of carbohydrate chains
attached to peripheral proteins.
They play a role in recognition of
like cells and are involved in
immune responses.
Glycoproteins
Peripheral
Protein
Integral
Protein
Question #20: The diagram below shoes a plasma
membrane. What is molecule X?
•A. Cholesterol
•B. Peripheral protein
C. Glycoprotein
D. Polar Amino Acid
Answer: A, cholesterol
2.4
Membranes
★List the functions of membrane proteins.
1. Hormone binding sites
Proteins that serve as hormone
binding sites have specific shapes
exposed to the exterior that fit the
shape of specific hormones.
The attachment between the protein
and the hormone causes a change in
shape in the protein and results in a
message being relayed to the interior
2.4 Membranes
2. Enzymatic Action
Cells have enzymes attached to
membranes that catalyze many chemical
reactions.
The enzymes may be on the interior or
exterior of the cell.
Often they are grouped so that a
sequence of metabolic reactions, called
a metabolic pathway, may occur.
2.4 Membranes
3. Cell adhesion
Cell adhesion is provided by proteins
when they hook together in various ways
to provide permanent or temporary
connections.
These connections, referred to as
junctions, may include gap junctions or
tight junctions.
2.4 Membranes
4. Cell to cell communication
Many of the cell to cell communication
proteins include attached molecules of
carbohydrate.
They provide an identification label
representing cells of different types.
2.4
Membranes
5. Channels for passive transport
Some proteins contain channels that
span the membrane providing
passageways for substances to pass
through.
When this transport is passive, a
material moves through the channel from
an area of high concentration to an area
of lower concentration.
Each channel allows one specific
2.4 Membranes
6. Pumps for active transport
In active transport, proteins shuttle a
substance from one side of the
membrane to another by changing
shape.
This process requires the expenditure of
energy in the form of ATP.
2.4 Membranes
★Define diffusion and osmosis
★Explain the role of protein pumps and ATP
in active transport across membranes.
There are 2 general means of cellular
transport - how molecules (sugars, energy,
waste) get into and out of cells.
1. Passive transport (requires no
energy)
2. Active transport (requires energy)
2.4
Membranes
1. Passive
Transport: Diffusion and
Osmosis
a. Diffusion: particles move from a
region of high concentration to a region
of low concentration.
In a living system, diffusion involves a
membrane.
Ex: oxygen gas moves from outside
a cell to inside. When you breathe
in, amount of oxygen higher
2.4 Membranes
b. Facilitated diffusion (transport): molecules
moving across a membrane with the help of
proteins.
The carrier protein changes shape to
accomplish this task but it does NOT require
energy.
Facilitated diffusion is very specific and
depends on the carrier protein.
Example of failed facilitated diffusion:
kidneys that have a specific protein absent
in the membrane results in painful kidney
2.4 Membranes
c. Osmosis: passive movement of water
molecules, across a selectively/partially
permeable membrane, from a region of high to
low concentration
2.4 Membranes
Substances that can move across a
membrane passively are influenced by 2
major factors: size and charge.
Small and non-polar substances move
across a membrane with ease.
Ex: oxygen, carbon dioxide, nitrogen
Large and polar substances do not.
Ex: chloride/potassium ions (polar),
glucose/sucrose (large sugars)
2.4 Membranes
★Explain the role of protein pumps and
ATP in active transport across membranes.
2. Active Transport: movement of
substances across a membrane against
a concentration gradient (from a low to
high concentration), energy is required.
Along with energy, a membrane
protein, or protein pump, must be
involved for this active transport to
occur.
2.4 Membranes
Example of failed active transport:
Cystic fibrosis is a human genetic
disease in which the membrane protein
that transport chloride ions is missing.
This causes high concentrations of water
inside the cells that line the lungs and
leads to the production of very thickened
mucus.
The average lifespan for an adult with
2.4 Membranes
★Explain how vesicles are used to
transport materials within a cell between
the rough endoplasmic reticulum, Golgi
apparatus and plasma membrane.
★Describe how the fluidity of the
membrane allows it to change shape,
break and re-form during endocytosis and
exocytosis.
2.4
Membranes
1. Endocytosis:
allows macromolecule
INTO the cell
2. Exocytosis: allows macromolecules to
EXIT the cell
Both processes depend on the fluidity of
the plasma membrane.
What helps with fluidity is the "loose"
connections between the fatty acid
tails of the phospholipids.
Yet the bilayer is stable because of
2.4 Membranes
http://telstar.ote.cmu.edu/biology/animation/
Membranes/membranes.html
2.4 Membranes
Endocytosis: occurs when a portion of the
plasma membrane is pinched off to enclose
macromolecules.
The plasma membrane is pulled
inwards.
A droplet of fluid become enclosed when
a vesicle is pinched off.
Vesicles can then move through the
cytoplasm carrying their contents.
2.4 Membranes
Exocytosis: essentially the reverse of
endocytosis
Usually begins in the ribosomes of the
RER and progresses through a series of
4 steps until the produced substance is
secreted to the environment outside the
cell.
1. Proteins are produced by ribosomes
and then enter the RER
2. Vesicles bud off from the RER and
carry the proteins to the Golgi apparatus.
2.4
Membranes
3. The Golgi apparatus modified the
proteins.
4. Vesicles bud off from the Golgi
apparatus and carry the modified
proteins to the plasma membrane
Vesicles fuse with the plasma
membrane
The contents of the vesicle are
expelled
2.4 Membranes
http://www.johnkyrk.com
click on golgi apparatus
2.4
Membranes
Question
#21: What do diffusion and
osmosis have in common?
A. They only happen in living cells.
B. They require transport proteins in the
membrane.
C. They are passive transport
mechanisms.
D. Net movement of substances is
against the concentration gradient.
2.4 Membranes
Question #22: What does facilitated
diffusion across a cell membrane require?
A pore protein
ATP
A concentration
gradient
A.
yes
no
no
B.
no
no
yes
C.
yes
no
yes
D.
no
yes
no
Answer: C
2.4 Membranes
Question #23: What is the difference
between simple diffusion and facilitated
diffusion?
Simple Diffusion
A.
B.
C.
D.
Facilitated Diffusion
Rate increases with
Rate decreases with increasing
increasing
concentration gradient
concentration gradient
Slower movement of
Faster movement of molecules
molecules
Never involves a
Always involves a membrane
membrane
Answer: D
Uses channels in the
Uses any part of a membrane
2.4
Membranes
Question #24: If someone comes into an
enclosed room wearing a distinctive
perfume, what is the process that allows
the odor to be distributed throughout the
room in a relatively short period of time?
Answer: DIFFUSION - as the molecules of
the perfume originally had a high
concentration close to the wearer, they
collide with one another which causes them
to move outward until they are evenly
distributed throughout the room. At this
2.4
Membranes
Question
#25: While walking through the
produce section of a grocery store, it is
common to see automated sprayers above the
fruit and vegetables, spraying water over them.
What cellular transport process is being used to
maintain healthy-looking vegetables?
Answer: The mist provides a layer of pure
water that covers the outside of the
vegetables. The outer surface of the
veggies acts as a partially permeable
membrane. Because there is a higher
concentration of water outside of the veggie
surface, water will move into the vegetable -
2.5 Cell Division
★Outline the stages in the cell cycle,
including interphase (G1, S, G2) mitosis
and cytokinesis.
★State that interphase is an active
period in the life of a cell when many
metabolic reactions occur, including
protein synthesis, DNA replication and
an increase in the number of
mitochondria and/or chloroplasts.
2.5 Cell Division
New cells are produced by division of
existing cells.
If many new cells are needed, cells go
through a cycle of events again and
again - this is called the cell cycle.
The cell cycle describes the behavior of
cells as they grow and divide.
Cytokines
is
DNA
Synthesis/Re
plication
2.5 Cell Division
Interphase
Largest/longest part of the cell cycle
Includes 3 phases: G1, S, G2
Interphase
Phases
Major Events
G1
Growth of cell and increase in # of organelles
S
G2
Replication/copying of chromosomes, referred
to as DNA Synthesis
Further growth occurs, organelles increase in
#, DNA condenses to form visible
2.5
Cellis aDivision
Interphase
very active time in a cell's
life.
It involves metabolic reactions, DNA
replication, and an increase in the
number of organelles.
More mitochondria and in plants,
more chloroplasts
Because interphase involves growth, it
is essential that protein synthesis
occurs at a rapid rate during this time.
2.5 Cell Division
Question #26: What happens during the G2
stage of interphase?
A. Homologous chromosomes pair
B. Synthesis of proteins
C. Homologous chromosomes separate
D. Replication of DNA
Answer: B, synthesis of proteins
2.5
Cell
Division
Question #27: What is a difference between a cell in
the G1 phase and a cell in the G2 phase of the cell
cycle?
A. A cell in the G2 phase would be smaller than a
cell in the G1 phase
B. A cell in the G2 phase would have more
mitochondria than a cell in the G1 phase.
C. A cell in the G1 phase would have more DNA in
its chromosomes than a cell in the G2 phase
D. DNA replication occurs in the G1 phase but not in
the G2 phase
2.5
Cell
Division
Question
#28: Which
events occur during
the G1 and S phases of the cell cycle?
G1 Phase
S Phase
A
DNA replicates
cell grows
B
mitosis begins
cell divides
C
cell divides
mitosis begins
D
cell grows
DNA replicates
Answer: D
2.5 Cell Division
★Describe the events that occur in the
4 phases of mitosis (prophase,
metaphase, anaphase and telophase).
★Explain how mitosis produces 2
genetically identical nuclei
2.5 Cell Division
At the end of interphase, the cell begins
mitosis - the process by which the nucleus
divides to form 2 genetically identical nuclei.
Towards the end of mitosis, the cytoplasm
of the cell starts to divide - known as
cytokinesis.
Eventually 2 cells are formed, each
containing 1 nucleus.
These cells are identical, called daughter
cells
The 2 cells begin interphase when
2.5 Cell Division
1 chromosome =
2 sister
chromatids
Sister
chromatids
identical
Centromere
holds sister
chromatids
together
2.5 Cell Division
During G2, chromatin (elongated/relaxed
DNA) begins to condense via a process
called supercoiling.
First the DNA wraps around histones
(proteins) and a final coiling occurs to
produce the chromosome - now ready for
2.5
Cell
Division
4 phases in Mitosis:
1. Prophase
a. Chromatin fibers become more tightly coiled to
form chromosomes
b. Nuclear envelope disintegrates and nucleoli
disappear
c. Mitotic spindle begins to form and is complete
at the end of prophase
d. Centrosomes move toward opposite poles of
the cell due to lengthening of microtubules.
2.5 Cell Division PROPHASE
2.5
Cell Division
2. Metaphase
a. Chromosomes are moved to the middle
or equator of the cell - called the
metaphase plate.
b. Chromosome's centromeres lie on the
plate.
c. Movement of the chromosomes is due
to the action of the spindle which is made
of microtubules.
d. Centrosomes are now at the opposite
2.5 Cell Division METAPHASE
2.5 Cell Division
3. Anaphase
a. Usually the shortest phase of mitosis.
Begins when the 2 sister chromatids of eac
chromosome are split.
b. These chromatids, now chromosomes,
move toward the opposite poles of the cell.
c. The chromatid movement is due to
shortening of the microtubules of the spindl
2.5
Cell
Division
d. Because the centromeres are
attached to the microtubules, they
move towards the poles first.
e. At the end of this phase, each pole
of the cell has a complete, identical
set of chromosomes (from now on,
each chromatid is considered a
chromosome.
2.5 Cell Division ANAPHASE
2.5
Cell
Division
4. Telophase
a. Chromosomes are at each pole
b. A nuclear membrane/envelope begins to reform around each set of chromosomes
c. Chromosomes start to elongate to form
chromatin
d. Nucleoli reappear
e. Spindles disappear
f. The cell is elongated and ready for
2.5 Cell Division TELOPHASE
2.5 Cell Division
Cytokinesis
Once nuclear division has occurred, the cell
undergoes cytokinesis.
cell division = mitosis + cytokinesis
Cytokinesis in animal cells involves an inward
pinching of the fluid plasma membrane to form
cleavage furrows
In plant cells a firm cell wall starts to form called a
cell plate. It occurs midway between the 2 poles of
the cell and moves outward toward the sides of the
cell from the center.
2.5 Cell Division CYTOKINESIS
2.5 Cell Division
★State that growth, embryonic development, tissue
repair and asexual reproduction involve mitosis.
When Mitosis is used in Eukaryotes:
1. During growth
2. During embryonic development, when the large
cell produced by fertilization (zygote) divides
repeatedly to produce many smaller cells
3. When tissues have been damaged and need to
be repaired.
4. To reproduce asexually
Question #4
2.
3.
1.
8.
5.
6.
7.
4.
2.5 Cell Division
Question #29: Which of the following does
not occur during interphase?
A. Replication
B. Translation
C. Cytokinesis
D. An increase in the number of
mitochondria
Answer: C, cytokinesis
2.5
Cell
Division
Question
#30: Which
events occur during
the G1 and S phases of the cell cycle?
G1 Phase
S Phase
A
DNA replicates
cell grows
B
mitosis begins
cell divides
C
cell divides
mitosis begins
D
cell grows
DNA replicates
Answer: D
2.5 Cell Division
Question #31: What is the sequence of
stages during the cell cycle?
A. G1→S→G2→mitosis→cytokinesis
B. mitosis→G1→G2→cytokinesis→S
C. G1→G2→S→mitosis→cytokinesis
D. G1→G2→mitosis→cytokinesis→S
Answer: A
2.5 Cell Division
Question #32: During which phase of
the cell cycle do chromosomes
duplicate?
A. G1
B. S
C. G2
D. Mitosis
Answer: B, S phase
2.5
Cell
Division
Question #33: Which of these
processes require mitosis?
A. Cell growth
B. Reducing surface area to volume
ratio
C. Maintaining cell size
D. Embryological development
Answer: D, embryological
2.5 Cell Division
Questions #34: Which of the following take(s)
place during either interphase or mitosis in animal
cells?
I. Re-formation of nuclear membranes
II. Pairing of homologous chromosomes
III. DNA replication
A. I only
C. II and III only
B. I and II only
D. I and III only
cell during mitosis
Stage of mitosis
A
metaphase
B
anaphase
C
anaphase
Answer:
D
D
metaphase
Structure I
chromatid
centromere
chromatid
centromere
Structure II
nuclear membrane
plasma membrane
nuclear membrane
plasma membrane
Questions #36: The graph below represents the
amount of DNA during the cell cycle. Which part
of the graph represents metaphase?
Answer: C
2.5
Cell
Division
★State
that tumors
(cancers) are the
result of uncontrolled cell division and
that these can occur in any organ or
tissue.
Sometimes, cells multiply so rapidly
that they form a solid mass of cells
called a tumor.
It appears that any cell can lose its
usual orderly pattern of division
because we have found cancer in
2.5 Cell Division
Normal cells grow on nutrient agar in the
lab until the petri dish is completely
covered.
If normal cells are removed from the center,
cells will begin to divide to fill the empty
space until the cells touch each other.
This is called contact inhibition.
Ex: cut on skin or broken bone
2.5 Cell Division
Protein regulators (Cyclin) regulate the
timing of the cell cycle of eukaryotes.
If added to a cell in G2, the cell will enter
mitosis
Other proteins make sure that a cell
does not enter mitosis until replication in
S phase is completed.
Prevents the cell from entering
anaphase until chromosomes are
2.5 Cell Division
Cancer occurs when the cells have lost the
ability to control cellular division.
2 types of masses of cells with out-ofcontrol cell reproduction:
1. Benign: abnormal mass of essentially
normal cells (warts, cysts)
2. Malignant: problematic masses from
reproduction of cancer cells.
2.5 Cell Division
Metastasis: the spread of cancer cells beyond
their original site.
2.5 Cell Division
How does a normal cell turn cancerous?
If we knew that, wouldn't it be a whole lot
easier to treat cancers???
Researchers are still trying to figure out
how to prevent healthy cells from turning
cancerous
We do know some environmental factors
increase risk of cancer: smoking, UV
exposure, asbestos
2.5 Cell Division
Cancer Treatments:
Surgery: often times difficult to use this
method alone to remove a tumor, usually
combined with treatment at the cellular
level.
Radiation: exposing tumors to highenergy radiation to disrupt cell division.
Chemotherapy: prevents division by
freezing mitotic spindle fibers.
2.5 Cell Division
Question #37: The DNA of a particular cell
is damager, so that the cell continues to
divide uncontrollably. What is the possible
result?
A. Coronary heart disease
B. AIDS
C. Tumor formation
D. Down syndrome