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Cell membrane and the nucleus
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Section 1, Chapter 3Cells
CellsOverview
Basic unit of life75 Trillion cells in human bodyVary in size and shapes
Over 260 types of cells in body i.e. neurons, muscle, bone, blood cells All types are derived from just 1 fertilized egg
DifferentiationForming specialized cells from unspecialized cells
Major Parts of a CellNucleus
Cell Membrane
CytoplasmCytosol = fluidOrganelles
Cell MembraneOverview
The cell membrane maintains integrity of cell
Membrane is a fluid structure – flexible
Selectively permeable- allows only select substances into and out of cell
Signal transduction – communication between cell & environment
The cell membrane is composed of three major components
1. Bilayer of phospholipids 2. Cholesterol 3. Membrane proteins
Polar region (hydrophilic)
Nonpolar region(hydrophobic)
Phospholipid bilayer
Phospholipid Bilayer
Nonpolar Hydrocarbon tailsPhospholipids align so that tails are hidden from water
Nonpolar tails form the interior of membrane
Polar Phosphate headsPolar groups align to face water
Polar heads are exposed to surfaces of membrane
Phospholipid bilayer forms a fluid, yet stable boundary.
The interior the cell membrane is hydrophobic
Permeable to nonpolar molecules Steroids, Oxygen, Carbon Dioxide can easily cross the membrane
Impermeable to polar moleculesProteins, Water, Sugars, ect. Cannot easily cross membrane
Cholesterol= rigid rings of hydrocarbons
Contributes to the nonpolar nature of membrane
Stabilizes the cell membrane
Increases rigidity of cell membrane
Membrane Proteins1. Integral Proteins
Spans cell membrane
Forms ion channels & pores
Examples include: Na+ channels and K+ channels Aquaporins = water channels
Transmembrane ProteinsIntegral protein, where one end extends outside cell, and the other end dips into cytoplasm.
Many function as receptors
Membrane Proteins2. Peripheral Proteins
Projects from surface of membrane
May be a glycoprotein (protein + sugar)
Includes Cellular Adhesion Molecules (CAM)
Membrane Proteins
Cellular Adhesion Molecules (CAM)
Guides moving cells to targets
Establishes cell-to-cell connectionsForms new neural connections in learning and memoryGuides cells surrounding an embryo towards uterusGuides white blood cells to injury
Selectin
• Covers the surface of white blood cells (WBC)
• Selectin binds to carbohydrates on surface of damaged capillaries
• Allows circulating WBCs to anchor near site of injury
CAM Protein
Transmembrane Protein Receptor
A molecule (ligand) binds to portion of receptor outside cell
Transmembrane Protein changes conformation
Portion inside cell sends a signal into cell
1. Nuclear Envelope
2. Nucleolus
3. Chromatin
3 Parts of the nucleus
• Double-layered membrane = 2 lipid bilayers.
• Nuclear Pores• Channel proteins allow specific
molecules across nuclear envelope
• Ribosomes & RNA leaves nucleus through pores
Nuclear Envelope
Nucleolus “little nucleus”
• Dense body of RNA & Proteins
• Produces Ribosomes
Chromatin “Colored substance”
Chromosome “colored body”
Condenses into chromosomes during mitosis
DNA wrapped around histone proteins
End of Section 1, Chapter 3