2. Cell membranes are gatekeepers.
Every cell is bordered by a plasma membrane. 2

3. 5.1 The Nature of the Plasma Membrane

4. Plasma membranes are complex structures
They perform several critical functions.
take in food & nutrients
dispose of waste products
build & export molecules
regulate heat exchange
regulate flow of materials in & out of cell 4

5. hydrophilic = water loving
hydrophobic = water fearing
Spilt Personalities…

6. The Plasma Membrane is a “Fluid Mosaic”
Molecules embedded within the plasma membrane help it perform its functions.
Membrane contains:
Carbohydrates
glycocalyx
cell adhesion & binding
Lipids
cholesterol
flexibility
Proteins
peripheral or integral
The Plasma Membrane is a “Fluid Mosaic” 6

7. The Plasma Membrane glycocalyx phospholipids cholesterol proteins
cell exterior
cytoskeleton
integral
protein
cell interior
peripheral
protein
Phospholipid
bilayer: a double
layer of
phospholipid
molecules whose
hydrophilic “heads”
face outward, and
whose hydrophobic
“tails” point inward,
toward each other.
Cholesterol
molecules that act
as a patching
substance and
that help the cell
maintain an
optimal level of
fluidity.
Proteins, which
are integral,
meaning bound to
the hydrophobic
interior of the
membrane, or
peripheral,
meaning not
bound in this way.
Glycocalyx: sugar
chains that attach
to proteins and
phospholipids,
serving as protein
binding sites and
as cell lubrication
and adhesion
molecules.
Figure 5.1

8. Proteins (a) Structural support (b) Recognition (c) Communication
(d) Transport
cell exterior
cell interior
Membrane proteins
can provide structural
support, often when
attached to parts of
the cell’s scaffolding
or “cytoskeleton.”
Protein fragments
held within
recognition proteins
can serve to identify
the cell as “normal” or
“infected” to immune
system cells.
Receptor proteins,
protruding out from
the plasma membrane,
can be the point of
contact for signals
sent to the cell via
traveling molecules,
such as hormones.
Proteins can serve
as channels
through which
materials can pass
in and out of
the cell.
Figure 5.3

9. The Plasma Membrane is a “Fluid Mosaic” of molecules
Phospholipid bilayer
Carbohydrates
Lipids
Proteins

10. Facilitated Diffusion
Movement of Molecules
Active Transport
Primary
Secondary
Passive Transport
Diffusion
Osmosis
Simple Diffusion
Facilitated Diffusion

11.
Crash Course

12. 5.2 Diffusion, Gradients, and Osmosis

13. Facilitated Diffusion
Movement of Molecules
Active Transport
Primary
Secondary
Passive Transport
Diffusion
Osmosis
Simple Diffusion
Facilitated Diffusion

14. Passive transport is the spontaneous movement of molecules across a membrane.
2 types:
Diffusion –
molecules move from an area of high concentration to an area of low concentration. 14

15. Diffusion, Gradients, & Osmosis
Concentration gradient: difference btwn highest & lowest concentrations of a solute within a given medium.
- In diffusion, compounds naturally move from high to low (down their concentration gradients)
- Energy not needed
High
Low

16. Diffusion, Gradients, and Osmosis
(a) Dye is dropped in.
(b) Diffusion begins.
(c) Dye is evenly distributed.
water
molecules
dye
molecules
Figure 5.4

17. Diffusion, Gradients, and Osmosis
Osmosis - net movement of water across a semipermeable membrane from an area of low solute concentration to an area of high solute concentration
Semipermeable - some compounds pass freely while others are blocked

18. 2. Osmosis – diffusion of water molecules
Cell will swell
Cell will shrivel 18

19. Facilitated Diffusion
Movement of Molecules
Active Transport
Primary
Secondary
Passive Transport
Diffusion
Osmosis
Simple Diffusion
Facilitated Diffusion

20. 5.3 Moving Smaller Substances In and Out

21. Simple Diffusion vs Facilitated Diffusion
Neither one requires Energy!
Simple Diffusion – small molecules pass through membrane easily.
Facilitated Diffusion – requires both a concentration gradient and a
protein channel 21

22. ATP Passive transport Active transport simple diffusion
facilitated diffusion
ATP
Materials move down
their concentration
gradient through the
phospholipid bilayer.
The passage of materials
is aided both by a
concentration gradient
and by a transport
protein.
Molecules again move
through a transport
protein, but now energy
must be expended to
move them against their
concentration gradient.
Figure 5.7

23. Facilitated Diffusion - transport proteins work as channels for larger hydrophilic substances (b/c of size & electrical charge, can’t diffuse through the hydrophobic portion)
cell exterior
glucose
plasma
membrane
cell interior
1.Transport protein has binding site for
glucose open to the outside of the cell.
2. Glucose binds
4. Glucose passes into the cell & protein
returns to its original shape.
3. This binding
causes the protein
to change shape, exposing glucose
to the inside of the cell.
Figure 5.8

24. Facilitated Diffusion
Movement of Molecules
Active Transport
Primary
Secondary
Passive Transport
Diffusion
Osmosis
Simple Diffusion
Facilitated Diffusion

25. ATP Passive transport Active transport simple diffusion
facilitated diffusion
ATP
Materials move down
their concentration
gradient through the
phospholipid bilayer.
The passage of materials
is aided both by a
concentration gradient
and by a transport
protein.
Molecules again move
through a transport
protein, but now energy
must be expended to
move them against their
concentration gradient.
Figure 5.7

26. Active transport - cells use energy to move small molecules.
Molecules can’t always move freely in and out of cells
Some molecules need to maintain a high concentration – move against the gradient
– membrane proteins act like motorized revolving doors 26

27. Active Transport example
Cells surrounding Stomach
H+ moving
Against Concentration Gradient
Inside Stomach 27

28. 5.4 Moving Larger Substances In and Out

29. Moving Larger Substances In and Out
Endocytosis
Exocytosis
Both mechanisms use vesicles
the membrane-lined enclosures that alternately bud off from membranes or fuse with them

30. Exocytosis
extracellular fluid
protein
plasma membrane
transport vesicle
cytosol
a transport vesicle moves from the inside of the cell to the plasma membrane
fuses with plasma membrane
the contents of the vesicle are released
Figure 5.10

31. Endocytosis
There are two principal forms of endocytosis: pinocytosis and phagocytosis.

32. Pinocytosis movement of moderate-sized molecules into a cell
transport vesicles produced through infolding or “invagination”
clathrin-mediated endocytosis (CME):
cell-surface receptors bind to molecules
- the protein clathrin becomes a
vesicle

33. Phagocytosis
Certain cells use pseudopodia or “false feet” to surround and engulf whole cells, fragments of them, or other large organic materials.

34. 6.1 Energy Is Central to Life

36. Energy Conversions
All life depends on capturing energy from the sun and converting it into a form that living organisms can use.
Two key processes
Photosynthesis
Cellular respiration

37. 6.2 The Nature of Energy

38. What is energy? The capacity to do work Work
Moving matter against an opposing force

39. Energy has two forms. The energy of moving objects Heat energy
Light energy

40. Potential Energy
A capacity to do work that results from the location or position of an object
Concentration gradients and potential energy
Food, chemical energy, has potential energy

41. Energy Conversions
Only ~1% of energy released by the sun that earth receives is captured and converted by plants.
Converted into chemical bond energy
What happens to the other 99%?
reflected back into space (~30%)
absorbed by land, oceans, & atmosphere (~70%),
Mostly transformed into heat

42. The study of the transformation of energy from one type to another
Thermodynamics
The study of the transformation of energy from one type to another
First Law of Thermodynamics
Energy can never be created or destroyed.
It can only change from one form to another.
Second Law of Thermodynamics
Every conversion of energy includes the transformation of some energy into heat.
Heat is almost completely useless to living organisms.

43. Energy Tax!
Every time energy is converted from one form to another the conversion isn’t perfectly efficient.
Some of the energy is always converted to the least usable form of kinetic energy: heat.