cells
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
• A small cell has a greater ratio of surface area to volume than a large cell of the same shape
30 µm 10 µm
Surface areaof one large cube= 5,400 µm2
Total surface areaof 27 small cubes= 16,200 µm2Figure 4.3
Prokaryotic cells - “before nucleus”
- small, relatively simple cells–Single-celled organisms
2 kinds of cells: prokaryotic and
eukaryotic
- true nucleus
- larger: 10-100 microns
- often multicellular
- organelles surrounded by membranes
- usually need O2
Eukaryotic cells - functional compartments
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
polarhead
nonpolartails
P –
hydrophobic molecules
hydrophilic molecules
cytosol
1. Phospholipid bilayer
Plasma membrane components
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Fibers of the extracellular matrix
Figure 5.12
Glycoprotein Carbohydrate (of glycoprotein)
Microfilaments of the cytoskeleton
Phospholipid
Cholesterol
Proteins
CYTOPLASM
Glycolipid
• 2. Cholesterol - adds rigidity
Fluid mosaic model
• 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
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• In passive transport, substances diffuse through membranes without work by the cell
EQUILIBRIUMMolecule of dye
Figure 5.14A & B
Membrane
EQUILIBRIUM
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• water travels from an area of higher concentration to an area of lower water concentration
Osmosis = diffusion of water across a membraneHypotonicsolution
Figure 5.15
Solutemolecule
HYPOTONIC SOLUTION
Hypertonic solution
Selectivelypermeablemembrane
HYPERTONIC SOLUTION
Selectivelypermeablemembrane
NET FLOW OF WATER
Solute molecule with cluster of water molecules
Water molecule
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Osmosis causes cells to shrink in a hypertonic solution and swell in a hypotonic solution
Water balance between cells and their surroundings is crucial
osmoregulation = control of water balance
isotonic solution hypertonic solution hypotonic solution
10 microns
equal movement of waterinto and out of cells
net water movement out of cells
net water movement into cells
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Small nonpolar molecules - simple diffusion
• Many molecules pass through protein pores by diffusion through channels.
• Facilitated diffusion
Passive transport = diffusion across membranes
Figure 5.17
Solutemolecule
Transportprotein
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• against a concentration gradient
• transport proteins needed
• requires energy (ATP)
Active transport
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• Active transport in two solutes across a membrane
• Na+/K+ pump
• Protein shape changeFigure 5.18
Transportprotein
1
FLUIDOUTSIDECELL
Firstsolute
First solute, inside cell, binds to protein
Phosphorylated transport protein
2 ATP transfers phosphate to protein
3 Protein releases solute outside cell
4 Second solute binds to protein
Second solute
5 Phosphate detaches from protein
6 Protein releases second solute into cell
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exocytosis = vesicle fuses with the membrane and expels its contents
Exocytosis and endocytosis transport large molecules
Figure 5.19A
FLUID OUTSIDE CELL
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
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human immune system ingests whole bacteria
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Cholesterol can accumulate in the blood if membranes lack cholesterol receptors
Figure 5.20
LDL PARTICLEPhospholipid outer layer
Protein
Cholesterol
Plasma membraneCYTOPLASM
Receptor protein
Vesicle