Lecture 3 – MEMBRANES, IONS, WATER AND PROTEINS Flashcards
1
Q
Polarity
A
- Basic meaning: ends/ sides are different
- Epithelial cell: structural polarity
- Magnet: magnetic polarity
- Membrane: electrical polarity
2
Q
Water
A
- All life exists in an aqueous environment
- Molecular properties of water influence the structure and behaviour of cells
- Neurones are directly linked to water
3
Q
Hydrogen bonds
A
- Electronegativity allow ‘hydrogen bonds’ to occur between adjacent/ neighbouring water molecules allowing it to form a lattice when in ice form
- Oxygen ‘sucks’ electrons away
- Hydrogen atom is shared between two electronegative atoms
- Relatively weak
- Highly directional
4
Q
Water is unique
A
- Hydrogen bonds allow water to be a liquid at room temperature
- Compounds with similar, or greater RMM than water are gases
- In liquid state, it’s a loose lattice
- In a solid state, the arrangement of H-bonds are much more ordered
- Ice is less dense than water
5
Q
The Ions
A
- An ion is any atom or molecule that has gained or lost one or more electrons and are defined by a charge
- Carry signals around the body in the form of action potentials
- Act as an energy store which is secondary active transport
- Interact biochemically with proteins and other molecules:
1. Ca2+/ troponin C in muscle contraction
2. Mg2+/ ATP
6
Q
Biologically Important Ions
A
- Physiologically useful ions act as charge carriers and energy stores
- Biochemically useful ones take part in enzyme reaction or form part of proteins
7
Q
Ions in an aqueous solution
A
- Can form electrostatic interactions with water
- Water molecules align themselves to maximise these interactions so the negative oxygens can interact with the ion
- The layer of water molecules immediately in contact with the ion is termed primary hydration shell/ layer
- Negatively charged ions, the hydrogen interacts with the ion and forms the opposite way around
- Looser shell is the secondary hydration shell/layer
8
Q
Ionic ‘size’ = Ionic Radius?
A
- The size of the hydration shell depends on the charge density of the ion
- Smaller the ion, the higher the charge density and the larger the shell
- Smaller ions have lower mobility in solution than larger metal ions with the same charge
- Hydration shell affects interactions/ mobility with proteins
9
Q
Membranes
A
- polar heads of phospholipids interact with water which drives the formation of the bilayer
- charged substances such as ions, and even moderately sized uncharged polar molecules like glucose, find it almost impossible to pass through bilayers
- very small molecules like ethanol, water and gases find it easier to pass through
- membranes are essentially impermeable to ions
10
Q
Membrane Proteins
A
- allow cells to establish ion gradients and use them – impermeable to ions
- form pathways for ions
11
Q
Pumps/ ATPase
A
- concentration of ions against gradients REQUIRES energy
- The Sodium Pump
- Basic features of pumps:
12
Q
Ion Gradients as ‘batteries’
A
- Gradients represent a source of energy
- Can be used to power cellular processes like the transport of other ions via carriers (2nd class)
Can be used to transmit information by signalling via ion channels
13
Q
Secondary Active Transport Carriers
A
Carrier refers to a general class of proteins that bind a substrate on one side of the membrane to undergo a conformational change which leads to the protein moving and releasing the substrate on the other side (inside)
14
Q
Carriers can be very effective
A
- Couple downhill flow of ions to uphill flow of a different ion
- Don’t use energy from ATP directly – energy comes from gradient of downhill ions
- Antiporters
- Symporters
- Not all involved in active transport – many are passive and serve to transport polar substrates down their concentration gradient
15
Q
Ion Channels
A
ROLE – mediate ion flux through membranes
DISTRIBUTION – everywhere from bacteria to humans
EVOLVED FOR ALL MAJOR PHYSIOLOGICAL IONS – Na+/ K+/ Ca2+/ Cl- channels
