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Chapter 2

BIOB34H3 Chapter Notes - Chapter 2: Lipid Bilayer, Cell Membrane, Ion Channel

Biological Sciences
Course Code
Ted Petit

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Chapter 2 Cells
Cell basics
- about 100 trillion cells in a human
- size and shape related to function
- in general very small, but a range of sizes
1. 8 - 140 m in diameter, but typically 10 - 20 m (m=1/1000 mm or 1/25,000 inch)
- the Generalized Cell and its major parts
1. plasma membrane separates inside from outside
a. intracellular fluid (ICF)
b. extracellular fluid (ECF)
1. nucleus is the control center
2. cytoplasm is everything between the nucleus and the plasma membrane
a. cytosol - semiliquid portion (ICF), which suspends the other parts and is a site of chemical
b. organelles - specialized structures with specific functions
c. inclusions - temporary storage structures
The Plasma Membrane
- Structure
1. phospholipid bilayer is the basic structure
a. important for fluidity
b. is a barrier
2. cholesterol
a. fluidity and stability
3. proteins
a. integral proteins span the membrane, may be channels, transporters, receptors
b. peripheral proteins are on one side only, may be enzymes or anchors for cytoskeleton
4. carbohydrates
a. on outer surface only, includes glycoproteins and glycolipids (collectively called
glycocalyx), important for recognition of self, attachments to other cells
- Basic functions
1. communication within body and with foreign cells
2. defines boundaries and protects
3. maintains chemical and electrical gradients
4. selective permeability - controls what gets in and out
- Membrane Transport
1. Passive (cell does not use up its own energy)
a. diffusion - molecules move down their concentration gradient from greater lesser
concentration, charged molecules move down electrochemical gradients
1) simple diffusion - moves through bilayer or protein channel
2) osmosis - water moves across bilayer
3) facilitated diffusion - uses a protein carrier
b. filtration - water and solutes forced through membrane by hydrostatic pressure
2. Active (requires the cell to use its ATP)
a. carrier proteins transport substance against its concentration gradient
b. endocytosis - substance brought into cell
1) piece of membrane surrounds substance and pinches off inside cell (vesicle)
2) pinocytosis (cell drinking) and phagocytosis (cell eating)
c. exocytosis - opposite of endocytosis
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