Transcript cells and membranes

Cells
Wassily Kandinsky
(1866-1944)
Cell Theory:
- all organisms are composed of cells
- all cells come from other cells
Figure 4.1x
• Scanning
electron
microscope
(SEM)
TEM
Figure 4.1B
• Cell size and
shape relate
to function
• Minimum
• Maximum
Figure 4.2
• A small cell has a greater ratio of surface area to
volume than a large cell of the same shape
30 µm
Figure 4.3
Surface area
of one large cube
= 5,400 µm2
10 µm
Total surface area
of 27 small cubes
= 16,200 µm2
2 kinds of cells: prokaryotic and
eukaryotic
Prokaryotic cells “before nucleus”
- small, relatively
simple cells
– Single-celled
organisms
Eukaryotic cells - functional
compartments
- true nucleus
- larger: 10-100 microns
- often multicellular
- organelles surrounded by membranes
- usually need O2
What do these have in common?
•
•
•
•
•
•
HIV infection
Transplanted organs
Communication between neurons
Drug addiction
Cystic fibrosis
hypercholesteremia
Plasma membrane
• Contact between cell and environment
• Keeps useful materials inside and harmful
stuff outside
• Allows transport, communication in both
directions
Plasma membrane components
1. Phospholipid bilayer
polar
head
P
–
hydrophobic
molecules
nonpolar
tails
cytosol
hydrophilic
molecules
• 2. Cholesterol - adds rigidity
Fluid mosaic model
Glycoprotein
Carbohydrate
(of
glycoprotein)
Fibers of the
extracellular
matrix
Glycolipid
Phospholipid
Cholesterol
Microfilaments
of the
cytoskeleton
Proteins
CYTOPLASM
Figure 5.12
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• 3. Membrane Proteins - span entire
membrane or lie on either side
• Structural Support
• Recognition
• Communication
• Transport
How do molecules cross the plasma
membrane?
• Passive transport
• Active transport
• Endocytosis and exocytosis
• Diffusion and gradients
– Diffusion = movement of molecules
from region of higher to lower
concentration.
– Osmosis = diffusion of water across a
membrane
• In passive
transport, substances
diffuse through
membranes without
work by the cell
Molecule
of dye
Membrane
EQUILIBRIUM
EQUILIBRIUM
Figure 5.14A & B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Osmosis = diffusion of water across a membrane
• water travels from
an area of higher
concentration to
an area of lower
water
concentration
Hypotonic
solution
Hypertonic
solution
Selectively
permeable
membrane
Solute
molecule
HYPOTONIC SOLUTION
HYPERTONIC SOLUTION
Water
molecule
Selectively
permeable
membrane
Solute molecule with
cluster of water molecules
NET FLOW OF WATER
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 5.15
Water balance between cells and their
surroundings is crucial
osmoregulation = control of water balance
• Osmosis causes cells to shrink in a hypertonic
solution and swell in a hypotonic solution
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
10 microns
isotonic solution
equal movement of water
into and out of cells
hypertonic solution
net water movement
out of cells
hypotonic solution
net water movement
into cells
Passive transport = diffusion across membranes
• Small nonpolar molecules - simple diffusion
• Many molecules pass through protein pores by
diffusion through channels.
• Facilitated diffusion
Solute
molecule
Transport
protein
Figure 5.17
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Active transport
• against a concentration gradient
• transport proteins needed
• requires energy (ATP)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Active
transport in
two solutes
across a
membrane
FLUID
OUTSIDE
CELL
Transport
protein
First
solute
1
• Na+/K+
pump
Phosphorylated
transport protein
First solute,
inside cell,
binds to protein
2
ATP transfers
phosphate to
protein
3
Protein releases
solute outside
cell
5
Phosphate
detaches from
protein
6
Protein releases
second solute
into cell
Second
solute
• Protein
shape
change
4
Second solute
binds to protein
Figure 5.18
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Exocytosis and endocytosis transport large
molecules
exocytosis = vesicle fuses with the membrane
and expels its contents
FLUID OUTSIDE CELL
Figure 5.19A
CYTOPLASM
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
– or the membrane may fold inward, trapping
material from the outside (endocytosis)
Figure 5.19B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
human immune system ingests whole bacteria
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Receptor-mediated endocytosis
• Cholesterol can accumulate in the blood if
membranes lack cholesterol receptors
LDL PARTICLE
Phospholipid
outer layer
Receptor protein
Protein
Cholesterol
Plasma membrane
Vesicle
CYTOPLASM
Figure 5.20
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
What do these have in common?
•
•
•
•
•
•
HIV infection
Transplanted organs
Communication between neurons
Drug addiction
Cystic fibrosis
hypercholesteremia