BIOL126 Lecture 3: Lecture 3
10 Jun 2018
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Cells
2.1 What is a cell?
• Basic unit of life: self-sustaining and self-replicating
• Outer boundary of cell is a thin, phospholipid bilayer membrane
•Body cells contain fluid (cytoplasm) & surrounded by extracellular fluid (interstitial fluid, blood,
lymph)
2.2 The cell membrane
•Phospholipid bilayer
•Fluid mosaic model
•Contains phosphate, lipids, proteins and carbohydrates.
2.2.1 its structure
•Integral/transmembrane proteins span bilayer; peripheral proteins attached to surface (inner or
outer)
•Glycolipids and glycoproteins have range of functions in cluding acting as enzymes, receptors,
self recognition molecules
•Major function to lubricate and protect membrane surface
•Conditions inside cell very different to external environment; membrane important in maintaining
cell homeostasis
2.2.2 its functions
1. Physically isolates cell from external environment
2. Regulates exchange with environment
3. Sensitivity to environment
4. Structural support
2.2.3 different methods of transport across the cell membrane, with examples:
2.2.3.1 diffusion and osmosis
Diffusion:
•Molecules move (have kinetic energy) so bump into and bounce off other molecules = even
distribution of solutes through solution
•Net movement from areas of high concentration across a membrane to areas of low
concentration i.e. “down” the concentration gradient; process known as diffusion (or osmosis with
movement of water)
Osmosis:
•diffusion by water molecules across a membrane through water channels (aquaporins), to the
side with the higher concentration of dissolved solutes (solutes diffuse in an opposite direction to
water)
•Osmotic pressure and hydrostatic pressure determine which way water moves; hydrostatic
pressure opposes osmotic pressure
•Osmotic pressure: force with which water moves into a solution due to it’s dissolved solute
concentration
• Hydrostatic pressure: force generated by pushing against a fluid; created by heart
2.2.3.2 carrier mediated: facilitated diffusion, active transport, secondary active
transport
Carrier mediated transport:
•Requires specialised integral/transmembrane proteins
•Passive or active process depending on substance transported, and nature of transport
mechanism
•Integral proteins bind specific ions or organic molecules, and transport them across the
membrane
•Receptor for an integral protein is typically a glycoprotein
•All carrier-mediated transport mechanisms have 3 things in common:
1. Specificity: each integral protein only binds and transports certain molecules (eg. glucose
transporter will not transport other sugars)
2. Saturation limit: when all relevant carrier proteins are utilised, they are saturated
3. Regulation: Binding of other molecules such as hormones can affect activity
Document Summary
2. 1 what is a cell: basic unit of life: self-sustaining and self-replicating, outer boundary of cell is a thin, phospholipid bilayer membrane, body cells contain uid (cytoplasm) & surrounded by extracellular uid (interstitial uid, blood, lymph) 2. 2. 2 its functions: physically isolates cell from external environment, regulates exchange with environment, sensitivity to environment, structural support. 2. 2. 3 different methods of transport across the cell membrane, with examples: 2. 2. 3. 2 carrier mediated: facilitated diffusion, active transport, secondary active transport. Secondary active transport: (picture) here glucose will only be transported once 2 na+ ions have also bound to the carrier protein. Greater protein and k+ concentration inside cell than outside. Less na+ concentration inside cell than outside. Many enzymes to catalyse reactions (some also om membrane) Energy molecules and amino acids may be stored eg. liver & muscle cells. 2. 4. 1 why cells vary in structure and function: cell organelles = internal structures with speci c tasks within the cell.
