Practise IB Biology SL B1.2 proteins through amino acid structure, peptide bonds, condensation reactions, dietary requirements and structure–function links.
Syllabus
First assessment 2025
Course
Biology SL
Level
SL
Exam points
Identify an amino acid’s alpha carbon, amine group, carboxyl group, hydrogen and variable R-group, and relate protein composition to C, H, O, N and usually S.
Explain amino-acid condensation and peptide-bond formation, identify dipeptide or polypeptide products and water release, and distinguish condensation from hydrolysis.
Distinguish essential amino acids that must come from dietary protein from non-essential amino acids made by the body, and explain limiting supply and protein-deficiency consequences.
Explain how amino-acid type, number and order create a wide variety of polypeptide sequences and proteomes.
Explain how high temperature or unsuitable pH denatures proteins by changing their structure and reducing biological activity.
The diagram shows the molecular structure of the amino acid leucine.
Draw a circle on the diagram to enclose the carboxyl group.
Circle only the COOH group.
No mark if C1 in chain is included
Question 2
[Maximum number: 2]
A short base sequence of mRNA and a table of the genetic code are shown below. Sequence of mRNA AUGAGCCGAAGGUAGCUG Table of the genetic code
Question (a)
(a)
The diagram shows a section of a polypeptide.
[ 2 ]
Question (i)
(i)
Annotate the diagram to show a peptide bond between two amino acids.
[ 1 ]
Any annotation between a C=O and the next NH.
Question (ii)
(ii)
State the type of reaction that removes water while linking amino acids together to form polypeptides.
[ 1 ]
condensation
Question 3
[Maximum number: 2]
Some of the twenty amino acids that are linked together to make polypeptides in human cells are essential in the diet and others are not. Distinguish between essential and non-essential amino acids.
a. essential amino acids cannot be synthesized (by human cells)
OR essential amino acids are required to be obtained by diet / OWTTE;
b. non-essential amino acids can be made (from other amino acids);
Question 4
[Maximum number: 7]
Cells produce a large variety of proteins with different sequences of amino acids. Explain how this is done.
a
protein is produced when a gene is expressed / switched on;
b
genetic code/codons consists of three nucleotides/bases/base triplet;
c
genetic code in DNA is transcribed/transcription (to mRNA);
d
mRNA exits the nucleus;
e
mRNA (code) is translated/translation into a polypeptide/protein;
f
amino acid sequence/polypeptide formation occurs at a ribosome;
g
one codon translates to one amino acid;
h
tRNA carries code for specific amino acids;
i
tRNA anticodon matches with specific codon in mRNA;
j
amino acids joined (by peptide bonds) to form polypeptide;
k
sequence of amino acids determined by order of bases/nucleotides/codons in DNA/mRNA;
l
proteins vary based on which amino acids are used and their order OR protein variety increases by mutations to DNA;
Question 5
[Maximum number: 1]
The diagrams represent the structure of a protein before and after it has become denatured.