T1L4 - Cell physiology

Question 1

Solvent [3]

Answer 1

fluid present
Biological systems - it is water
Organic fluids in lab

Question 2

Solute [3]

Answer 2

particles dissolved in solvent
Can be atoms & molecules
DNA, sugars, proteins & H+ ions

Question 3

Important ions

Answer 3

Na+, K+, Ca2+, H+, Mg2+, OH-, Cl-, HCO3_, SO4-, PO4-& charged proteins

Question 4

PO4-

Answer 4

is important for reactions involving ATP (enzyme) & structurally in bone

Question 5

SO4-

Answer 5

is important structurally in glycosaminoglycan (connective tissue )

Question 6

Ionic imbalance causes [8]

Answer 6

Trauma 
Haemorrhage
Diabetes
Hormonal imbalances
Dehydration
Kidney dysfunction
Poisons 
Extensive D & V

Question 7

Fluid compartments: plasma

Answer 7

Na+ based

Question 8

Fluid compartments: interstitial

Answer 8

~ plasma & lacks blood proteins

Question 9

Fluid compartments: Intracellular

Answer 9

K+ based & lots of protein

Question 10

Fluid compartments: Transcellular

Answer 10

In the lumen of tubes and organs

Question 11

Methods of transport

Answer 11

Channels 
Pumps 
Transporters
Exchangers
Leak

Question 12

Role of ions

Answer 12

Start cellular processes and act as secondary messengers - transmit information across cell membrane

Second messengers are molecular mechanisms for transmitting chemical signals from outside cell (usually a hormone or neurotransmitter)
Create energy (as ATP), activate enzymes (protein kinase C),  move water (kidney) & control transmembrane voltage (voltage = information in neurones)

Question 13

Wrong ion concentration of ions can lead to

Answer 13

cardiac arrhythmias, bone deformities, oedema & seizures

Question 14

Voltage

Answer 14

The difference in potential energy between 2 points in an electric field. The electric potential or driving force for charged particles (ions) to move.

V= IR 
V = I/G

Question 15

Chemical force

Answer 15

Called diffusional force
Based upon the difference in concentration across membrane
10X as much Na+ outside, 30X as much potassium in intracellular fluid than extracellularly

Question 16

Electrical force

Answer 16

Based on Vm (membrane potential -> varies over time)

Based on a few positive charges

Question 17

Blood fluids and ions

Answer 17

• Na+ gets pumped or moves through ion channels
• Cl- tends to follow Na+
Water follows Cl-

Question 18

Plasma and ions

Answer 18

• Highest in Na+ concentration

Slightly more negative in electric potential than extracellular fluid

Question 19

Intracellular Fluid and ions

Answer 19

Highest in Highest in proteins
Highest electrolyte concentration (milliEquivalents)
Most negative voltage

Question 20

Extracellular space and ions

Answer 20

Highest chloride concentration (lac

Question 21

Excitable

Answer 21

• Cells that can propagate an action potential
• An action potential is a specific kind of amplified voltage response
Neurons and muscle cells are excitable

Question 22

Non-excitable

Answer 22

Cells without action potentials
Not muscle or nerve
Skins & liver (especially epithelial cells

Question 23

Hypocalcaemia

Answer 23

(insufficient free calcium in blood) leads to paraesthesia -> over-reactive tendon reflexes

ECG abnormalities and risks of arrhythmia of heart

Question 24

Free calcium

Answer 24

Calcium ions that are ionised and in solution -> free to activate enzymes

Calcium found in bone -part of an insoluble solid that will not react with enzymes

It can be bound to proteins
It can be sequestered inside cellular organelles

Question 25

Free calcium concentration

Answer 25

○ ~ 100 nanoM (that is, one tenth of a micromolar conc)

Cf. extracellular free Ca2+ = 1.2 milliM, > 10,000X

Question 26

Actin & Myosin

Answer 26

Myosin = a golf-club shaped motor protein with a hinge. The myosin head bends (and generates force) by breaking ATP

Actin = a structural protein that myosin grabs onto

Question 27

Second messenger

Answer 27

Calcium, kinases, phospholipases

Question 28

Rules

Answer 28

The concentration of positive and negative ions must “nearly” balance
Any ion that leaves the cell must be replaced soon by another ion of that type coming into the cell
Energy is always being used to re-establish the ionic gradients across membranes

Question 29

The concentration of positive and negative ions must “nearly” balance

Answer 29

○ If a positive ion moves across the membrane, the charge imbalance must be corrected

Either a negative ion will shortly follow to correct the imbalance, or another positive charge must go in the opposite direction

“Nearly” means that there can be tiny amounts of unbalanced cations on one side of a membrane that are near to anions on the other side of the membrane

Question 30

Any ion that leaves the cell must be replaced soon by another ion of that type coming into the cell

Answer 30

This is fundamental to homeostasis, otherwise the salivary cells would run out of K+ ions
Often the replacement happens at opposite ends of the cell, so when chloride enters the cell at the basolateral membrane, it may leave the cell at the apical membrane

Question 31

Energy is always being used to re-establish the ionic gradients across membranes

Answer 31

Example: Na+ / K+ pump (ATPase) exchanges 3 Na+ outward for 2 K+ inward, and consumes ATP to pump these ions against their concentration gradients
Without energy (eg after death) the ionic gradients dissipate and equalise.  This is an example of entropy.