Cell Membrane, Cell
Transport & Cell Division
Chapter 7: Membrane Structure and Function
Chapter 12: The Cell Cycle
Plasma Membrane
Plasma Membrane
Structure

Boundary that separates the

Phospholipids are the
 Arranged in a



• hydrophobic region (tails)
• hydrophilic region (heads)
Exhibits
, allowing some
substances to cross it more easily than others
The
states that a membrane is
a fluid structure with a “mosaic” of various proteins
embedded in it
Phospholipid Structure
Selective Permeability



A cell must
process controlled by the plasma membrane
Regulates what enters and leaves the cell
Hydrophobic (nonpolar) molecules, such as
hydrocarbons,

Polar molecules, such as sugars,

Maintains
Allows for

inside the cell
of cells in same organism
,a
Fluid Mosaic Model

Phospholipid
molecules can

Makes the
membrane act
like a

Fluid Mosaic
Model
Animation
Membrane Cholesterol
Cholesterol is a
 Adds
to plasma membrane
 Helps keep fatty acid tails of phospholipids
separated

Membrane Proteins
Different proteins are
in the fluid
matrix of the lipid
bilayer
 They determine most
of the

Spread throughout
the membrane like
raisins in raisin bread
 Allow membrane to
“
” with
its environment

Membrane proteins
are bound to the surface

of the membrane
penetrate the

hydrophobic core


Integral proteins that span the membrane are
called
The hydrophobic regions of an integral
protein consist of one or more stretches of
nonpolar amino acids, often coiled into
Membrane proteins
 Six
major functions of membrane
proteins:



Signal transduction
*




Intercellular joining
Attachment to the cytoskeleton and
extracellular matrix (ECM)
*Includes a carbohydrate chain
Carbohydrate chains

Carbohydrates on the external side of the plasma
membrane

Attached to phospholipids (
proteins (
)
 These
a cell
 Individual (Mr. Fusco cell)
 Species (Human cell)
 Type (kidney cell)
) or

•
Cells recognize each other by
, often carbohydrate chains, on the plasma
membrane
LABEL THESE PARTS
Cholesterol
Glycolipid
Phospholipid
Glycoprotein
Integral protein
Carbohydrate chain
Peripheral protein
Inside/Outside of cell
Cell Transport
Because of the
numerous amount of
activities associated
with the cell,
substances must
constantly move in
and out of the cell
 There are 2 types of
cell transport:



Passive versus Active
Passive
Active


the
concentration
gradient (
 From random
molecular motion


)
the
concentration
gradient (
)
Concentration Gradient

From High  Low
 NO energy needed
Substances diffuse down their
concentration gradient easily
No work must be done to move
substances
the
concentration gradient
Work is required to move
substances
the
concentration gradient
From Low  High
 Energy Needed
Transport Types
Passive
 Diffusion
 Osmosis
 Facilitated Diffusion
Active
 Active Transport
 Endocytosis
 Exocytosis
Diffusion

Diffusion is the tendency for molecules to

Although each molecule moves randomly, diffusion
of a population of molecules

the concentration gradient:
 HIGH  LOW
require energy
Results in
(as many
molecules cross one way as cross in the other
direction)
Diffusion Animation



Osmosis

Osmosis is the

Water diffuses across
a membrane from the
region of lower solute
concentration to the
region of higher
solute concentration
Simple Rule for Osmosis
Salt
is a
When it is concentrated inside or outside
the cell, it will
Tonicity
is the ability of a solution to cause
a cell to gain or lose water
 Three types of solutions:




solution
solution
solution
Hypertonic or hypotonic environments create
osmotic problems for organisms

, is a
necessary adaptation for life in such
environments

Isotonic Solutions


Dynamic Equilibrium
 Water in = water out

Cells keep normal shape
Solute concentration is the
same as that inside the cell
across
the plasma membrane


Hypotonic Solutions




Since salt sucks, water
will move into the cell
Solute concentration is
less than that inside the
cell
(swells) and may
burst
Plant Cells in Hypotonic
Solution
is the pressure inside plant

cells
 Cell walls help maintain water balance
 A plant cell in a hypotonic solution swells until the
wall opposes uptake


Cell is now
If a plant cell and its surroundings are isotonic,
there is no net movement of water into the cell

Cell becomes
and the plant may wilt
Hypertonic Solutions


Water sucked out of the cell

Solute concentration is
greater than that inside the
cell

Cells in Hypertonic Solutions
Animal Cells

Plant Cells
 Turgor pressure drops
 In a hypertonic
environment, plant cells
lose water
 Eventually, the
membrane pulls away
from the wall, a usually
lethal effect called
Facilitated Diffusion
 Some molecules are so small that they pass through the
membrane with little resistance


(even though very large) also pass easily
 In
speed the passive
movement of molecules across the plasma membrane

(transmembrane) provide
corridors that allow a specific molecule or ion to cross the
membrane


, for facilitated diffusion of water
that open or close in response to a
stimulus (gated channels)
Active Transport
Moves substances
their concentration
gradient: (Low  High)
Requires energy in the form
of
Active transport is
performed by
Protein Pumps



Protein 'pump' requires energy (ATP) to function
Allows cells to maintain concentration gradients that
The
is one type of active
transport system
 Exchanges
in animal
cells
 Transported molecules enter the
in the
membrane
 The energy causes a shape change in the protein that
allows it to move the molecule to the other side of the
membrane
Endocytosis

Ability of a cell to
Ex. large molecules, groups of
molecules, or whole cells
Requires Energy
Cell takes in macromolecules by




There are three types of
endocytosis:
 Phagocytosis (“
”)
 Pinocytosis (“
”)
 Receptor-mediated endocytosis
Types of Endocytosis



In
a cell engulfs a particle in a
vacuole
 The vacuole fuses with a lysosome to digest the
particle
In
, molecules are taken up when
extracellular fluid is “gulped” into tiny vesicles
In
, binding of
ligands to receptors triggers vesicle formation
 A ligand is any molecule that
Phagocytosis
Pinocytosis
Receptor-Mediated
Endocytosis
Exocytosis
 Opposite of

endocytosis
To expel wastes or secrete hormones
 Requires
energy
 Transport vesicles
 Many secretory
 Endocytosis
cells use exocytosis to
and Exocytosis Animation
Cell Division
Life
is based on the
ability of cells to
Rudolf Virchow
(German physician)
stated “omnis cellula e
cellula” meaning
“
”
cell division =
Why Cells Divide

Unicellular organisms
 cell division =

Multicellular organisms

(single cell to trillions)


Cell division is an integral part of the
Cell Cycle - Eukaryotes

Defined nucleus houses

Most cell division results in daughter cells with

A special type of division produces nonidentical daughter
cells (gametes, or sperm and egg cells)
Goal:
 Chromosomes are
from 1
parent cell (before division) to each daughter cell
(after division)
Includes:




Cell Cycle - Eukaryotes
Cell Cycle





Interphase (
) can be
divided into 3 subphases:

(“first gap”)

(“synthesis”)

(“second gap”)
The cell grows during all three phases
 Makes proteins
 Copies organelles
Chromosomes are duplicated only during the S
phase
Mitosis is the
Cytokinesis is the
Eukaryotic Chromosomes

Chromatin
 Long strands of DNA
 In preparation for cell division, DNA is replicated and
condenses to form chromosomes
 Each duplicated chromosome has


The centromere is the
Chromosomes must be copied
 Each new cell must have a complete set
 Contain thousands of genes

Vital for organisms to properly function
Human Example
 23 pairs of chromosomes


1 originally from mom, 1 from dad
 Every
time our body cells (
reproduce

Each NEW cell must also
)
Chromosome Duplication

One chromosome =

2 sister chromatids =


Exact copies
Attached by a

Cell division

Each new cell gets one copy of
each chromosome
Mitotic Phase

Mitosis is conventionally divided into five phases:






Cytokinesis is well underway by late telophase
*Some texts do not recognize this as a separate phase
Mitosis
Prophase
Pro = “before”


Chromosomes
Nucleolus and nuclear envelope



Microtubules that
during mitosis
Includes the centrosomes, the spindle microtubules,
and the asters
•
During prophase, assembly of spindle microtubules
begins in the
, the microtubule
organizing center
Prophase
Prometaphase
 Nuclear
envelope completely gone
 Mircotubules
 Some
spindle microtubules attach to
the
of chromosomes
and begin to move the chromosomes
•
Prometaphase
Metaphase
Meta = “with” (middle)

Chromosomes line up
at
 Also called the

Microtubules attach
Anaphase
Ana= “upward” or “back” (apart)

Sister chromatids

Chromatids now
chromosomes
Other microtubules
elongate cell


Move along
microtubules
Telophase
Telos = “end”

Reverse of
 Begins when chromosomes
reach poles



Chromosomes “
condensed)
” (less


daughter
nuclei form at opposite ends of
the cell
Cytokinesis

Division of cellular
contents



In animal cells,
cytokinesis occurs
by a process known
as
Cytokinesis

In plant cells, a

Formed from
move along
microtubules, and
join in the middle of
the cell
Some Animations

Mitosis Animation

Mitosis and Cytokinesis Animation

Mitosis Animation 2
Mitosis Ho-Down
MITOSIS is a process that helps one cell become two
It happens when a cell dies or makes some brand new
This is how a cut heals and how a baby grows
It works all o’er the body from your head down to your toes
PROPHASE is the first phase where chromosomes you'll see
Then comes METAPHASE where they line up perfectly
After that is ANAPHASE where they are pulled apart
Finally is TELOPHASE, cells split then go back to start
Cell Cycle Controls
The sequential events of the
cell cycle are directed by a
distinct
, which is
similar to a clock
 The cell cycle control system
is regulated by both


The clock has specific
where the
cell cycle stops until a goahead signal is received

G1, G2, M checkpoints
Cell Cycle Controls

G1 checkpoint seems to be
 A go-ahead signal at the G1 checkpoint allows cell to
complete the S, G2, and M phases and divide
 No go-ahead signal and the cell will exit the cycle,
switching into a

G2 checkpoint
 Assesses success of


Mitosis checkpoint
 Assesses accuracy of
 Occurs during
Cell Cycle Controls

Two types of regulatory proteins are involved in cell cycle
control:
Activity of cyclins and Cdks fluctuates during the cell
cycle
 MPF (maturation-promoting factor)
 A cyclin-Cdk complex
 Triggers a cell’s passage

Also called “
Cell Cycle Control Animation


”
Cancer



Disease of cell cycle
DNA mutation changes genes that normally control
growth


Cancer cells do not respond normally to the body’s control
mechanisms
Features of Cancer Cells
”
“

Normal cells divide about 50 times before dying


Aging, toxins (smoking), mutagens (UV light), DNA
replication errors


Instead of “sticking” to neighbors, cancer cells
become “round”, allowing for metastasis (spread)


Keep growing after touching neighbor
Tumors

Cancer cells form



Abnormal mass of essentially normal cells





Invade surrounding tissues
Can
• Move to other sites and create a new tumor
(secondary)
Cells send out signals for blood vessel production
• Gives them food, oxygen, escape route
Review Questions
1. Identify and describe the parts of the fluid mosaic model of the plasma
membrane.
2. Describe the various regions of a phospholipid molecule as they apply to the
arrangement of the plasma membrane.
3. Explain the role of cholesterol in the membrane.
4. Describe the 2 main types and 6 various functions of membrane proteins.
5. Differentiate between passive and active transport.
6. Explain the idea of a concentration gradient, along with moving down and
against it.
7. Define tonicity and explain hypertonic, isotonic, and hypotonic solutions.
8. Define osmoregulation and turgor pressure.
9. Differentiate between diffusion, osmosis, and facilitated diffusion, naming the
parts of the membrane that help these transports.
10. Differentiate between protein pumps, endocytosis, and exocytosis, naming that
parts of the membrane that help these transports.
11. Name and describe 3 types of endocytosis.
12. Explain the importance of cell division.
13. Name the parts of the cell cycle and state the events that occur in each stage.
14. Differentiate between chromatin, chromosome, and chromatid.
Review Questions
15. Define somatic cells.
16. Name the 5 steps to the cell cycle.
17. Define cytokinesis and explain how it differs in plant and animal cells.
18. Describe the 3 events that occur in prophase.
19. Name 2 events that occur in prometaphase.
20.Name 2 events that occur in metaphase.
21. Name the main event of anaphase.
22. Name 3 events that occur in telophase.
23. Explain how the cell plate forms in plant cell cytokinesis.
24. Name the 3 checkpoints of the cell cycle control system and explain what occurs
in each step.
25. Differentiate between the roles of cyclins and cyclin-dependent kinases.
26. Define the importance of MPF.
27. Relate the formation of cancer to the cell cycle.
28.Name 4 major features of cancer cells.
29. Define tumor and differentiate between benign and malignant.
30.Define metastasis.