Download Cell Membrane and Transport PPT

The Cell (Plasma) Membrane
• The cell membrane is made up of three
organic parts: lipids, proteins, and
carbohydrates. It has many parts but is still
very flexible: a fluid mosaic model.
The Cell (Plasma) Membrane
• Made of a phospholipid bilayer
- a double layer of lipids
The Cell (Plasma) Membrane
• Proteins serve as channels or pumps
- “doors” that things can pass through
Transport proteins provide larger
openings in the plasma membrane through
which particles can pass…
The Cell (Plasma) Membrane
• Carbohydrates act like chemical “ID tags”
- how cells recognize one another
Why is the cell membrane so important?
• The membrane provides structure and
controls what enters and leaves the cell.
Why is the cell membrane so important?
• The cell membrane is said to be
semipermeable, or selectively permeable,
because some substances can pass through
easily while others cannot.
– It regulates homeostasis between the solutions
on each side of the membrane.
Solutions, Solutes, and Concentration
• A solution is a mixture of two or more
substances.
• Solutes are the substances dissolved in a
solution.
– Example: In a solution of Kool-aid, our solutes are
Kool-aid mix and sugar.
Solutions, Solutes, and Concentration
• Concentration refers to the amount of solutes
dissolved in a solution.
• One packet of Kool-aid mix dissolved in a glass
of water is more concentrated, while one
packet of Kool-aid mix dissolved in a gallon of
water is less concentrated.
Passive Cell Transport
• In passive transport, no energy is
required. There are three kinds of passive
transport:
–Diffusion
–Osmosis
–Facilitated diffusion
Passive Cell Transport
• In passive transport, no energy is
required. There are three kinds of passive
transport:
–Diffusion
–Osmosis
–Facilitated diffusion
Passive Cell Transport: Diffusion
• Diffusion is the movement of molecules from
areas of
to
concentration.
Passive Cell Transport: Diffusion
• If a substance CAN cross the membrane,
it tends to move towards the area where
it is LESS concentrated until the two
areas reach EQUILIBRIUM (equal
concentrations).
– Think of people filling up a movie theater
Passive Cell Transport: Osmosis
• Osmosis is the diffusion of WATER through a
semi-permeable membrane.
– Water also moves from areas of HIGH to LOW
concentrations (think of a waterfall).
– If a solute is too large to diffuse, water molecules
will diffuse instead until the two solutions reach
equilibrium.
Osmosis: movement (diffusion) of
water / solvent
Passive Cell Transport:
Facilitated Diffusion
• Facilitated diffusion occurs when protein
“doors” in the cell membrane help larger
molecules move across the membrane.
– Still passive transport because solutes move from
high to low concentration gradients.
A form of passive transport using transport
proteins
Passive, aided diffusion
Passive Transport
• When molecules move with the concentration
gradient, it means molecules move from HIGH
to LOW concentrations. This does not require
energy (ATP). Think of a waterfall.
– Is it easy or hard for water to flow down a
waterfall? Does it take a lot of energy?
Types of Solutions
• Hypertonic- concentration of solute outside of
cell is greater than inside of cell, water flows out,
cell shrivels
Types of Solutions
• Hypotonic- concentration of solute inside cell is
greater than outside of cell, water flows in, cell
swells
Types of Solutions
• Isotonic- concentration of solution is the same
inside and outside of cell, water flows equally in
and out, cell remains same size
A:
Hypertonic
B:
Hypotonic
C:
Isotonic
Active Cell Transport
• In active transport, energy IS required.
Active Cell Transport
• Protein pumps within the membrane “pump”
molecules and solutes such as calcium,
sodium, and potassium across membranes.
– Changes in the shape of the protein allow
molecules to move in specific directions.
Active Cell Transport
• Endocytosis is the process of creating
“pockets” in the membrane which are then
pinched off and taken inside the cell.
• Exocytosis is opposite process --- vacuoles
within the cell merge with the cell membrane
and deposit their contents outside of the cell.
Active Cell Transport
• When cells move molecules against the
concentration gradient, it means molecules
move from LOW to HIGH concentrations. This
does require energy (ATP). Think of paddling
upstream, or trying to go up a waterfall.
Active Cell Transport
• A lot of the energy used our cells is devoted to
active transport – we need certain
concentrations of molecules in order for
specific parts of our bodies to function.
For example, unequal concentrations of
Na+ and K+ ions help our nerve cells function.
Active Cell Transport
• Therefore, both passive and active transport
help us maintain homeostasis.
Chemical Energy and ATP
• A T P (adenosine triphosphate) is the main
chemical compound in cells that stores and
releases energy
How does it work?
• ADP is ATP with one less phosphate
• Energy is stored in the bond between the
three phosphates
• ATP must lose a phosphate to become ADP
How does it work?
• When the phosphate bond is broken, energy is
released
– Like breaking a glow stick or a hot/cold pack
How does it work?
*[ATP] breaks down to [ADP + Phosphate] and
releases energy to carry out life processes
Why do we need ATP?
• ATP is “energy currency” in the cell
• When ATP breaks down into ADP, it provides
energy for cellular processes:
– Making proteins
– Energy for photosynthesis
– Active transport
Why do we need ATP?
• Our cells store a limited amount of ATP
– only enough for a short period of activity
• cells regenerate ATP from ADP as needed
• ***like recharging and using a cell phone