Important ions
Laura Armstrong
Teacher
Contents
Recall Questions
This topic requires knowledge of Biological molecules covered so far in module 1. You can test your knowledge on these below.
What biological molecules contain phosphate ions?
DNA, RNA, ATP / ADP and phospholipids.
How do hydrogen ions (H⁺) affect enzyme activity?
Hydrogen ion concentration determines pH, which affects enzyme structure by altering hydrogen and ionic bonds in the tertiary structure of proteins.
Why is haemoglobin described as having a quaternary structure?
It consists of more than one polypeptide chain. (It has 4 polypeptide chains).
Topic Explainer Video
Check out this @LauraDoesBiology video that explains important ions or read the full notes below. Once you've gone through the whole note, try out the practice questions!
Ions are essential in many biological processes. Below are four key ions and their functions:
Phosphate Ions (PO₄³⁻) and Their Role in DNA, RNA, and ATP
- Structure of Nucleic Acids:
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Phosphate groups form part of the sugar-phosphate backbone in DNA and RNA, providing stability and allowing nucleotide bonding via phosphodiester bonds.
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- ATP (Adenosine Triphosphate):
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ATP consists of three phosphate groups.
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The removal of a phosphate group via hydrolysis releases energy, which is used in active transport, muscle contraction and protein synthesis, as well as many other metabolic reactions.
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Once hydrolysed, the inorganic phosphate can be used to phosphorylate other molecules, making them unstable and more reactive.
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Hydrogen Ions (H⁺) and Their Role in pH
pH and Enzyme Activity:
pH is a measure of H⁺ concentration:
Low pH (acidic) = High H⁺ concentration.
High pH (alkaline) = Low H⁺ concentration.
H⁺ ions interact with hydrogen and ionic bonds in proteins, affecting enzyme structure and function.
Example: If pH deviates from the optimum, enzyme active sites may denature as the bonds holding the tertiary structure are broken, reducing reaction rates.
Calculating pH
We can calculate pH using this formula:
H+ is the concentration of the hydrogen ion in moles per litre.
Just type into the calculator.
Example:
To find the pH of a solution with a hydrogen ion concentration of 0.001 M
- log (0.001) = 3
This solution has a pH of 3 and so is acidic.
No answer provided.
Sodium Ions (Na⁺) and Their Role in Co-Transport
- Co-Transport in the Small Intestine:
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Step 1: Na⁺ is actively transported out of epithelial cells into the blood by the sodium-potassium pump.
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Step 2: This creates a concentration gradient for Na⁺ to diffuse back into the cell from the lumen of the small intestine via co-transport proteins.
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Step 3: As Na⁺ moves in, glucose or amino acids are transported against their concentration gradient into the cell.
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Step 4: Glucose then moves into the bloodstream by facilitated diffusion.
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You will learn more about co-transport in module 2.
Iron Ions (Fe²⁺) and Their Role in Haemoglobin
- Oxygen Transport in the Blood:
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Haemoglobin in red blood cells contains iron ions (Fe²⁺).
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Each haemoglobin molecule contains four Fe²⁺ ions in each of the four haem groups, each binding to one O₂ molecule.
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Reaction: Fe²⁺ + O₂ → Fe³⁺ (oxygen binds to iron in haemoglobin).
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This allows oxygen transport around the body, delivering oxygen to tissues for aerobic respiration.
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Key Terms
- Phosphate ion (PO₄³⁻): Forms the sugar-phosphate backbone in DNA and RNA and plays a key role in ATP.
- Hydrogen ion (H⁺): Determines pH and affects enzyme activity and protein structure.
- Sodium ion (Na⁺): Involved in co-transport of glucose and amino acids in the small intestine.
- Iron ion (Fe²⁺): Binds to oxygen in haemoglobin, enabling oxygen transport in the blood.
No answer provided.
Exam Tip
When answering ion-related questions, always link the ion to a biological function and give a specific example (e.g., Fe²⁺ → haemoglobin → oxygen transport).
No answer provided.
Describe the roles of phosphate ions, hydrogen ions, sodium ions, and iron ions in biological processes. (6 marks)
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Phosphate ions (PO₄³⁻) form the sugar-phosphate backbone in DNA and RNA.
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Phosphate ions (PO₄³⁻) are part of ATP, which releases energy via hydrolysis.
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Hydrogen ions (H⁺) determine pH,
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Changes in Hydrogen ion (H⁺) concentration affects enzyme activity by altering the tertiary structure of active sites.
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Sodium ions (Na⁺) are involved in co-transport in the small intestine, helping glucose and amino acids enter epithelial cells.
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Iron ions (Fe²⁺) bind to oxygen in haemoglobin, allowing oxygen transport in the blood.
(Each ion is linked to a specific biological role, ensuring a complete and structured answer.)
Practice Question 1
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!
Practice Question 2
If you want to try out another one, check this video out and see how you do!