Download MEMBRANES

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 living cell from its
surroundings
Phospholipids are the most abundant lipid
 Arranged in a bilayer



• 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 exchange materials with its surroundings, a
process controlled by the plasma membrane
Regulates what enters and leaves the cell
Hydrophobic (nonpolar) molecules, such as
hydrocarbons, can dissolve in the lipid bilayer and pass
through the membrane rapidly
Polar molecules, such as sugars,
Maintains
Allows for
inside the cell
of cells in same organism
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
embedded 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 vary among species, individuals, and
even cell types in an individual
Attached to phospholipids (
) or
proteins (
)
 These
a cell
 Individual (Mr. Fusco cell)
 Species (Human cell)
 Type (kidney cell)

•
Cells recognize each other by binding to surface
molecules, 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
 Protein pumps
 Endocytosis
 Exocytosis
Diffusion






Diffusion is the tendency for molecules to
into the available space
Although each molecule moves randomly, diffusion
of a population of molecules may exhibit a net
movement in one direction
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
across a selectively
permeable
membrane
 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 draw the water in its
direction
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

, the control of water
balance, is a necessary adaptation for life in such
environments

Isotonic Solutions

water and
solute (salt) concentrations
inside and outside the cell

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

solute
(salt) concentration
outside than inside

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

solute (salt)
concentration outside than
inside

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
 Oxygen & Carbon Dioxide
 Lipid molecules (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 specific
proteins embedded in the
membranes
Protein Pumps



Protein 'pump' requires energy (ATP) to function
Allows cells to maintain concentration gradients that
differ from their surroundings
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
forming vesicles from the plasma
membrane
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
is any molecule that binds
specifically to a receptor site of another molecule
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 = one
cell divides into two
cells
Why Cells Divide

Unicellular organisms
 cell division = asexual reproduction (new
organism)

Multicellular organisms

(single cell to trillions)


Cell division is an integral part of the cell cycle, the
life of a cell from formation to its own division
Cell Cycle - Eukaryotes





Defined nucleus houses DNA as chromosomes, a
condensed form of chromatin
Most cell division results in daughter cells with identical
genetic information (DNA)
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 division of the
Cytokinesis is the division of the
)
Eukaryotic Chromosomes

Chromatin
 Long strands of DNA wrapped around proteins
 In preparation for cell division, DNA is replicated and
condenses to form chromosomes
 Each duplicated chromosome has two
,
which separate during cell division
 The
is the narrow “waist” of the
duplicated chromosome, where the two chromatids are most
closely attached

Chromosomes must be copied before a cell divides
 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 end up with 23 pairs
of chromosomes
Chromosome Duplication

One chromosome =

2 sister chromatids =


Exact copies
Attached by a centromere

Cell division separates sister
chromatids

Each new cell gets one copy of
each chromosome
Mitotic Phase


Mitosis is conventionally divided into five phases:
 Prophase
 Prometaphase*
 Metaphase
 Anaphase
 Telophase
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 controls chromosome movement
during mitosis
Includes the centrosomes, the spindle microtubules,
and the asters
• An aster is a radial array of short microtubules
During prophase, assembly of spindle microtubules
begins in the centrosome, the microtubule
organizing center
Prophase
Prometaphase
 Nuclear
envelope completely gone
 Microtubules
 Some
spindle microtubules attach to
the
of chromosomes and
begin to move the chromosomes
•
Kinetochores are specialized protein
structures at the centromere
Prometaphase
Metaphase
Meta = “with” (middle)


Chromosomes line up
at
 Also called the
metaphase plate
(midway point
between the
spindle’s two poles)
Microtubules attach
Anaphase
Ana= “upward” or “back” (apart)

Sister chromatids
Move along
microtubules
connected to
kinetochore towards
opposite ends of cell
 Chromatids now
chromosomes
Other microtubules
elongate cell


Telophase
Telos = “end”

Reverse of prophase
 Begins when chromosomes
reach poles



Chromosomes “
(less condensed)
”


Genetically identical daughter
nuclei form at opposite ends of
the cell
Cytokinesis
Division of cellular
contents
 Cytoplasm
 Organelles
 In animal cells,
cytokinesis occurs
by a process known
as

Cytokinesis

In plant cells, a

Formed from vesicles
that pinch off of the
Golgi body, 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 internal
and external controls
 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
 Triggers start of mitosis
 Mitosis checkpoint
 Assesses accuracy of mitosis
 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 past the G2 checkpoint into
the M phase
 Also called “mitosis-promoting factor”
 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
 Masses of abnormal cells within otherwise normal
tissue



Abnormal mass of essentially normal cells
Remain at original site




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.