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).
- Introduction
- Macronutrients
- Micronutrients
- Importance of metal ions
- Na-K pump
- Na-glucose pump
- Metal toxicity
Bioinorganic chemistry is the branch of study that deals with the interaction of inorganic substances (mainly metal ions) and biological systems (living tissues) and their roles in life processes.
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
- What is bioinorganic chemistry? 1
Macronutrients
Macronutrients are chemicals required in large amounts in the range of grams in our daily diet for the proper functioning of the body.
- 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
- 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.
- 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.
- 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.
Micro Nutrients
Micronutrients are the substances required in small amounts, much less than 1g, for the proper functioning of the body(metabolism) and the prevention of diseases.
- 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.
- 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
- What are micro nutrients? 1
Importance of Metal Ions in Biological Systems
Sodium (Na):
The predominant extracellular cation in both animals and human beings.
Biochemical functions:
- maintains osmotic pressure and cellular fluid balance
- Controls nerve impulse transmission
- Helps muscle contraction
Effects of deficiency:
A low level of sodium in our blood may cause
- Confusion, seizures, coma (severe cases)
- Muscle cramps, nausea.
Main source: table/common salt, salted processed foods
Most people get more sodium than needed, often unknowingly, from processed/salted foods.
Potassium (K):
An electrolyte mineral as important as sodium.
Most of the potassium in our bodies is located in the muscle cells.
Biochemical functions:
- Helps regulate fluid and electrolyte balance in the body and maintains osmotic pressure.
- Adequate potassium intake helps lower blood pressure, hence reducing the risk of stroke, osteoporosis, and kidney stones.
Effects of deficiency:
- Fatigue and weakness in muscles.
- Abnormal/irregular heartbeat(arrhythmia)
Main sources: bananas, vegetables, legumes, etc.
Unlike sodium, most people don’t get enough potassium
Magnesium (Mg):
Magnesium is an important mineral for humans and plants.
99% of magnesium is located in intracellular fluids and bones.
Biochemical role
- Acts as a cofactor for many enzymes involved in protein synthesis and metabolism
- Essential for the stability and proper functioning of DNA and RNA.
- An essential component of chlorophyll in plants, hence important for photosynthesis
Effects of deficiency:
- Muscle cramps, weakness, abnormal heartbeat (arrhythmia)
- Can cause low levels of potassium (hypokalemia) and calcium (hypocalcemia)
Main source: Leafy green vegetables, nuts, whole grains
Calcium (Ca):
An essential element in all animals and human beings.
~ 99% of calcium exists as phosphate in the bones and teeth.
Biochemical role:
- essential for the development, growth, and maintenance of bone, along with vitamin D
- Required for blood clotting
- muscle contraction, nerve signalling
Effects of deficiency:
- Weak bones, osteoporosis
- Poor dental structure
Main source: dairy products; leafy green vegetables
Iron (Fe):
The average human has about 4-5 g of Fe. About 60-70% is found in the haemoglobin (oxygen transporter) of red blood cells. About 3-5% is present in the muscle myoglobin (an oxygen carrier in the muscles). About 15% is stored as ferritin in the liver, spleen, and bone marrow.
Biochemical role:
- transport of oxygen to the different parts of the body.
- Acts as a cofactor of enzymes, where it helps in the catalytic role of the enzyme.
Effects of deficiency:
- Anemia
Main sources: red meat, poultry, spinach, legumes, etc.
Copper (Cu):
found in all body tissues and is an essential nutrient for human survival.
found mainly in the liver, kidney, heart, and brain.
Biochemical role:
• Helps in the formation of red blood cells
• Maintains nervous and immune systems
• Functions as part of enzyme systems
Effects of deficiency:
• Weak immune system, low energy
• Can lead to anaemia and neurological problems
Main source: chicken, meats, nuts, seeds, etc
Zinc (Zn):
located largely in the liver, bone, and muscles.
Biochemical role:
- Activation of T cells that attack the cancerous cells.
- Healing of wounds
- Growth and development
Effects of deficiency:
• Loss of appetite, slow wound healing
• Growth retardation, hair loss, diarrhoea
• Impaired reproductive function
Main sources: Meat (especially red meat), Fish and seafood, Legumes (beans and lentils
Nickel (Ni):
The biological role of nickel is not yet fully established.
Biochemical role:
- May influence enzyme activity and nucleic acid metabolism
- May assist in glucose metabolism
Effects of deficiency:
- May affect the absorption of iron and hence lead to anemia.
Main sources: legumes, grains, meat, fish, eggs, etc.
Cobalt (Co):
Component of Vitamin B12
Biochemical role of cobalt:
• Required for red blood cell formation
• Involved in the metabolism of fatty acids and amino acids
Effects of deficiency:
Due to the lack of vitamin B12, it causes anemia.
Main sources: meat(liver), fish, milk
Chromium (Cr):
An adult human has about 4-6 mg of chromium.
Biochemical role:
• Enhances insulin action (glucose metabolism)
• Helps regulate blood sugar levels
Deficiency of chromium:
• Impaired glucose tolerance
• Weight loss, poor coordination
Main sources: whole-grains (e.g., wheat, oats), meat (especially liver), vegetables (e.g., broccoli, potatoes)
- Mention the biological importance of calcium and magnesium. 2
Answer – Calcium is required for proper bone growth, and magnesium is required for the formation of chlorophyll.
Sodium Potassium Pump
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.
- 3 Na⁺ ions from inside the cell bind to the carrier (pump) protein.
- ATP is broken into ADP + Pi (phosphate)
Energy causes the pump protein to change shape
- The shape change forces 3 Na⁺ ions to move outside the cell
- Now, 2 K⁺ ions from outside bind to the pump
- The phosphate group is removed
Pump returns to its original shape
- 2 K⁺ ions are released into the cell
The mechanism of the Na-K pump is explained in four steps:
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
Elaborate the phenomenon of the Na-K pump with the help of a labelled diagram. (no description required). 2
Sodium-Glucose Pump
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?
Inside the cell, Na⁺ moves down its gradient, providing energy, and both molecules are released; the carrier resets.
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.
Biological Importance of Na-gl 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
Metal toxicity
Heavy metal toxicity is the accumulation of toxic amounts of metals in the soft tissues of the body, leading to harmful effects
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 discolouration (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