CELL%20MEMBRANE,%20DIFFUSION%20AND%20ACTIVE%20TRANSPORT

1
CELL MEMBRANE, DIFFUSION AND ACTIVE TRANSPORT
2
Cell Membranes are phospholipid bilayers, in fact
all cellular membranes are phospholipid bilayers
3
(No Transcript)
4
Some substances are able to move through the cell
membrane, others cannot
5
In part this is due to the phospholipid nature of
the membrane.
6
The phosphate end of the molecule is hydrophilic
and the lipid end is hydrophobic.
7
The phospholipid molecules naturally form a cell
membrane.
8
(No Transcript)
9
Small molecules such as water can move between
the phospholipid molecules into or out of the cell
10
Other molecules must be brought in or out of the
cell by transmembrane proteins
11
Molecules can move through the cell membrane
because of their kinetic molecular motion
12
Kinetic molecular motion is the movement of
molecules because of temperature and molecular
size. The higher the temperature the faster the
movement.
13
Molecules move in a straight line until they hit
another molecule.
14
Because of this random movement molecules travel
farther in areas of low concentration and tend to
spread out
15
This movement of molecules from areas of high
concentration to areas of low concentration is
called diffusion
16
If the molecule has enough energy it will pass
through the fluid nature of the membranes
phospholipids
17
If the molecule has enough energy it will pass
through the fluid nature of the membranes
phospholipids
18
Because not all molecules have enough energy to
get through the cell membrane it is called a
selectively permeable membrane
19
Molecules are moving in and out through the cell
membrane because of molecular movement
20
Concentration is the comparison of the number of
the solute to the number of molecules of the
solvent.
21
(No Transcript)
22
If the blue circles represent water than water is
the solvent
23
If the blue circles represent water than the
yellow circles are the solute
24
Over time diffusion will cause the solutions on
both sides of the membrane to have the same
number of molecules. This condition is called
equilibrium.
25
(No Transcript)
26
(No Transcript)
27
The greater the concentration gradient the more
rapid the rate of diffusion
28
(No Transcript)
29
(No Transcript)
30
(No Transcript)
31
If sucrose cannot move through the membrane than
the solution on the right has a higher
concentration of water (100)
32
The water will move from an area of high water
concentration to an area of low water
concentration
33
Water will move from an area of high water
concentration to an area of low
water concentration (if the solute cannot move
through the membrane)
34
If there is a lower concentration of water
in the cell than water will move
into the cell
35
Until the concentration of water reaches
equilibrium
36
(No Transcript)
37
Osmosis is the diffusion of water molecules
38
through a semi-permeable membrane
39
If the concentration of solute is the same inside
the cell and outside the cell, the cell is said
to be isotonic
40
(No Transcript)
41
If a cell is in a solution with a greater
concentration than the cell, the solution is said
to be hypertonic
42
If the concentration of the solute of the
solution is greater than the concentration inside
the cell, then the concentration of water in the
solution is less than in the cell
43
If the solution outside the cell has a lower
concentration than inside the cell, the solution
is said to be hypotonic
44
If the concentration of the solution is
hypotonic, then the solution has a greater
concentration of water than in the cell.
45
(No Transcript)
46
Water will move into a cell in a hypotonic
solution because the solution has a greater
concentration of water.
47
Water will move out of the cell in a hypertonic
solution, because the solution has a greater
concentration of water than the cell
48
When water moves through a semi-permeable
membrane into a cell, it increases the volume of
the water
49
If a cell is in a hypotonic solution, it will
swell
50
(No Transcript)
51
Diffusion of NaOH into an agar cube with
phenophthalein
52
(No Transcript)
53
Rate distance/time
54
Rate distance/time Distance 0.2 cm 2 mm
55
Rate distance/time Distance 0.2 cm 2
mm Time 12 minutes 12minutes/60 minutes 0.2
hr
56
Rate distance/time Distance 0.2 cm 2
mm Time 12 minutes 12minutes/60 minutes 0.2
hr Rate 2mm / 0.2hr 10 mm/hr
57
Volume of diffused area Volume
of entire cube Volume of
the cube without diffusion produces
58
Volume of diffused area VD Volume
of entire cube VT Volume of cube without
diffusion VN
59
Volume of diffused area VD VD
60
(No Transcript)
61
(No Transcript)
62
(No Transcript)
63
(No Transcript)
64
(No Transcript)
65
(No Transcript)
66
(No Transcript)
67
The cell phospholipid bilayer is selectively
permeable.
68
Water, gases and some small organic molecules can
move through the cell membrane because of
molecular kinetic motion.
69
The Fluid-Mosaic Model of the cell membrane
identifies the cell membrane as a selectively
permeable membrane.
70
(No Transcript)
71
(No Transcript)
72
Imbedded in the membrane are channel proteins
that funnel molecules through the membrane
73
The channel proteins provide a place for ions to
go through the membrane because of the charge and
kinetic molecular motion of the ion
74
Passive diffusion and Facilitated diffusion
requires no use of energy on the part of the cell
75
(No Transcript)
76
Some transmembrane proteins require the use of
ATP energy to pull certain molecules into the
cell
77
(No Transcript)
78
(No Transcript)
79
(No Transcript)
80
(No Transcript)
81
(No Transcript)
82

• Exocytosis-- Secretion from the cell by fusing
  the membrane of a vesicle with the cell membrane

83
Endocytosis

• Taking in a substance through the formation of a
  vesicle
• Three types Phagocytosis, Pinocytosis,
  Receptor-Mediated Endocytosis

84
Phagocytosis

• Taking in a large food particle through the
  formation of a vesicle

85
Pinocytosis

• Forming a vesicle around a liquid or a number of
  small particles

86
Receptor-Mediated Endocytosis

• A form of pinocytosis which uses receptor
  proteins to bind the molecules first

87
The kidney is an organ made up of thousands of
filters called nephrons
88
The filtering process begins when plasma is
forced out of the blood in the network of small
blood vessels called the glomerulus
89
The pressure of going from a wide artery to long,
narrow capillaries forces water and small
molecules through the cells into the glomerular
capsule.
90
The water and small solutes then passes through
the glomerulus of the tubules of the nephron
91
Because the loop of the nephron is longer in the
kangaroo rat is able to absorb almost all the
water in urine
92
As the liquid from the blood moves down the
tubules water and important molecules are
reabsorbed
93
The solution in the tubules is hypotonic, thus
the water moves back into the blood by osmosis.
94
(No Transcript)
95
In the descending loop water diffuses out of the
solution forced from the blood into the Bowmans
capsule.
96
(No Transcript)
97
Many large molecules, such as glucose, amino
acids and hormones, are reabsorbed by active
transport
98
In the proximal convoluted tubule salt is pumped
back into the blood, making the blood hypertonic.
The water moves by osmosis back into the blood.
99
Glucose and amino acids are returned to the blood
by carrier proteins. If the blood is hypertonic
for glucose, then the glucose remains in the
urine.
100
(No Transcript)
101
(No Transcript)
102
Dialysis uses high pressure to force small
molecules through the dialysis membrane.
103
Depending on the size of the holes in the
membrane waste products can be forced out and
then by making the holes smaller, smaller
molecules can diffuse back into the blood.
104
The main difference between dialysis and kidney
function is that the kidneys can remove
molecules, such as potassium ions, from the blood
and urine by active transport against the
concentration gradient.
105
(No Transcript)
106
(No Transcript)
107
http//www.ksu.edu/biology/pob/osmosis.qt