2.2.1Inquiry Process
Formation of Proteins — IB Biology HL Revision Notes & Topical Questions
5 min read 6 parts Lesson 43 of 160
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 6Amino Acid Structure
All amino acids share the same basic arrangement, written as H₂N-CHR-COOH.
Central carbon
- Central carbon Each amino acid has a central alpha carbon to which all the other groups are attached by covalent bonds.
Amino group
- Amino group A -NH₂ group on the central carbon acts as a base and can take part in forming peptide bonds.
Carboxyl group
- Carboxyl group A -COOH group acts as an acid and reacts with an amino group of the next amino acid.
R group
- R group A variable side chain distinguishes the 20 amino acids and controls how each behaves chemically.
| Part | Formula | Role |
|---|---|---|
| Amino group | -NH₂ | Joins to the carboxyl group of the next amino acid |
| Carboxyl group | -COOH | Joins to the amino group of the previous amino acid |
| R group | Variable | Determines properties of the amino acid |
Section 2 of 6Forming a Peptide Bond
Peptide bonds form by condensation, the same type of reaction used for other biological polymers.
1
The carboxyl group of one amino acid is positioned next to the amino group of another.
2
A hydroxyl group from the carboxyl and a hydrogen from the amino group are removed together as water.
3
A covalent peptide bond forms between the carbon of one and the nitrogen of the other.
4
The product is a dipeptide with a free amino end at one side and a free carboxyl end at the other.
5
Further amino acids are added at the carboxyl end, extending the chain into a polypeptide.
Section 3 of 6Where Proteins Are Made
Where Proteins Are Made
Ribosomes
- Ribosomes Ribosomes catalyse peptide bond formation during translation, reading the mRNA message one codon at a time.
tRNA
- tRNA Transfer RNA molecules bring each amino acid to the ribosome in the order specified by mRNA.
Direction
- Direction The chain grows from its amino end toward its carboxyl end as each new amino acid is added.
Result
- Result The finished polypeptide folds into a specific shape and may be joined with others to make a functional protein.
Section 4 of 6Proteins as Polymers
Polypeptide
- Polypeptide A chain of amino acids joined by peptide bonds, which may be hundreds of units long.
Protein
- Protein One or more polypeptides folded into a functional three-dimensional shape.
Sequence
- Sequence The order of amino acids is fixed by the gene and decides how the chain will fold.
Breakdown
- Breakdown Hydrolysis of peptide bonds by proteases returns amino acids that can be reused.
Section 5 of 6Worked Example
Question
- A tripeptide is made from glycine, alanine and serine.
- How many peptide bonds are formed and how many water molecules are released?
- Three amino acids in a straight chain are joined by 3 - 1 = 2 links.
- Each peptide bond forms through one condensation reaction.
- Each condensation releases one molecule of water.
Answer Two peptide bonds are formed and two water molecules are released.
Section 6 of 6Exam Checklist & Tips
2.2.1 – Key Points for the Exam
- Amino acid A monomer of proteins with an amino group, carboxyl group, hydrogen and R group on one carbon.
- Peptide bond The covalent bond between the carboxyl group of one amino acid and the amino group of the next.
- Dipeptide Two amino acids joined by one peptide bond.
- Polypeptide A chain of many amino acids joined by peptide bonds.
- Translation The process in which ribosomes build a polypeptide using the sequence of mRNA.
Common Mistakes
- Saying peptide bonds form between two R groups; they link the backbone groups.
- Writing that water is used when the bond forms; it is released.
- Confusing protein and polypeptide; a protein can contain several polypeptides.
- Thinking the R group takes part in every peptide bond.
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