11. Bioinorganic Chemistry
🎯 Learning outcomes
Learners should be able to:
- Explain bioinorganic chemistry and compare it with other branches of chemistry.
- Define micro and macro nutrients with examples.
- State and explain the importance of metal ions in biological systems (ions of Na, K, Mg, Ca, Fe, Cu, Zn, Ni, Co, Cr).
- Elaborate ion pumps (sodium-potassium and sodium-glucose pumps).
- Explain metal toxicity (toxicity due to iron, arsenic, mercury, lead, and cadmium).
It explains things like:
- How metal ions function in enzymes and proteins
- How ions regulate biological activities like nerve transmission, oxygen transport, and metabolism
- How imbalance or toxicity of metals affects health
Macronutrients are chemicals required in large amounts in the range of grams in our daily diet for the proper functioning of the body.
💧 1. Water
- Inorganic polar compound, the most abundant component of the human body (~60-70%)
- Universal solvent, essential for metabolic reactions
- Maintains body temperature
- Helps in the transport of nutrients and waste removal
- Acts as a lubricant (joints, eyes) and a shock absorber
- Maintains osmotic pressure and cell structure
🍞 2. Carbohydrates
- Polyhydroxy aldehydes or polyhydroxy ketones, or compounds that hydrolyse to form such substances.
- Primary energy source of the body.
- Excess is stored as glycogen or fat.
- Sources: cereals, potatoes, bananas, honey, etc.
🥚 3. Proteins
- Long-chain polymers of amino acids.
- Main body building nutrients essential for growth, repair, and maintenance of tissues.
- Form enzymes, hormones, antibodies, and transport molecules
- Sources: Pulses, beans, legumes, meat, egg, fish, etc.
🥑 4. Fats
- Provide high energy (double the carbohydrates)
- Stored in adipose tissue for energy reserve
- Help in absorption of fat-soluble vitamins (A, D, E, K)
- Important for hormone synthesis and organ protection
- Sources: Almond, walnut, pumpkin, sunflower, mustard seeds, etc.
Micronutrients are the substances required in small amounts, much less than 1 g, for the proper functioning of the body (metabolism) and the prevention of diseases.
💊 1. Vitamins
Organic micronutrients. Essential to regulate metabolism, support immunity, and help growth and tissue repair. Act as cofactors or coenzymes in various biochemical reactions.
- Water-soluble (Vitamins B complex and C): not stored in the body (must be taken regularly)
- Fat-soluble (Vitamins A, D, E, & K): stored in fat and liver tissues.
⚛️ 2. Minerals
Minerals are the inorganic micronutrients that are required by the body in very small quantities.
Ex: Na, K, Mg, Ca, P, S, Fe, Zn, Cu, Mn, Co etc. Classified as micro and macro minerals.
- Macro minerals are required in relatively large concentrations. E.g., Na, K, Mg, Ca, P, S, Cl, etc.
- Micro-minerals are required in relatively small quantities. E.g., Fe, Zn, Cu, Mn, etc.
Main functions of minerals:
- Enzyme activation
- Oxygen transport
- Nerve and muscle function
- Hormone regulation
The sodium–potassium pump is a membrane protein (carrier protein) that actively transports:
- 3 Na⁺ ions out of the cell
- 2 K⁺ ions into the cell
using energy from the conversion of ATP to ADP.
➢ An example of primary active transport
Inside and outside the cell, ion concentrations are different:
- Outside cell: High Na⁺, low K⁺
- Inside cell: High K⁺, low Na⁺
But the cell must maintain this imbalance for:
- Nerve impulse transmission
- Muscle contraction
- Cell volume control
- Electrical stability (membrane potential)
So the pump works continuously to maintain this balance.
The mechanism of the Na-K pump is explained in four steps:
1. 3 Na⁺ ions from inside the cell bind to the carrier (pump) protein.
2. ATP is broken into ADP + Pi (phosphate). Energy causes the pump protein to change shape.
3. The shape change forces 3 Na⁺ ions to move outside the cell.
4. Now 2 K⁺ ions from outside bind to the pump.
5. Phosphate group is removed. Pump returns to original shape.
6. 2 K⁺ ions are released into the cell.
Think of it like a “door system”:
- First door opens → Na⁺ goes OUT
- Then reset → K⁺ comes IN
But the pump is unequal (3 out, 2 in) → this creates an electrical charge difference
Why is the Na-K pump important?
1. Maintains resting membrane potential
- Inside the cell, the potential becomes more negative
- Needed for nerve impulse firing
2. Helps nerve signal transmission
- Without it, neurons cannot reset
3. Controls cell volume
- Prevents cell swelling or bursting
4. Supports muscle contraction
- Especially the heart and skeletal muscles
What?
An example of secondary active transport. Uses Na⁺ gradient energy. Glucose is transported into the cell against its concentration gradient.
Why?
Glucose is very important for energy production, but in many cases:
- Glucose concentration inside the cell is already high
- So, glucose must enter against its concentration gradient
But glucose cannot do this alone.
How?
- The Na⁺/K⁺ pump maintains a gradient with high Na⁺ outside and low Na⁺ inside the cell.
- A carrier protein (symporter) in the membrane has binding sites for both Na⁺ and glucose.
- Na⁺ binds first, which helps glucose also bind to the same carrier protein.
- Binding causes a shape (conformational) change, allowing both Na⁺ and glucose to enter the cell.
- Inside the cell, Na⁺ moves down its gradient, providing energy, and both molecules are released; the carrier resets.
Biological Importance of Na-Glucose Pump
1. Absorption in the intestine
Helps absorb glucose from food in the small intestine
2. Kidney function
Reabsorbs glucose from the filtrate in the kidneys
3. Energy supply
Ensures glucose is efficiently taken into cells for respiration
Iron Poisoning
Most common cause of fatal metal poisoning in children (<6 years)
Symptoms
- Chronic fatigue
- Joint and abdominal pain
- Liver disease (cirrhosis)
- Diabetes mellitus
- Heart failure
- Skin discoloration (bronze/grey tone)
Arsenic Toxicity
Source: Contaminated groundwater
Acute exposure
- Vomiting
- Abdominal pain
- Watery (sometimes bloody) diarrhea
- Encephalopathy
Chronic exposure
- Skin thickening and darkening
- Numbness
- Heart disease
- Cancer risk
Mercury Poisoning
Key disease: Minamata disease
Symptoms
- Muscle weakness
- Poor coordination
- Numbness in hands and feet
- Memory problems
- Anxiety
- Kidney damage
- Intellectual impairment
Lead Poisoning
Symptoms
- Abdominal pain and constipation
- Headache, irritability
- Memory problems
- Tingling in hands and feet
Severe cases
- Anaemia
- Seizures
- Coma or death
Cadmium Poisoning
Acute exposure (inhalation)
- Flu-like symptoms (fever, chills, muscle pain)
- Lung damage
Chronic exposure
- Kidney damage
- Bone weakness (osteoporosis)
- Lung disease
Test your understanding
Take a short quiz on bio-inorganic chemistry.