▶️ Answer/Explanation
(a)
- Proteins are made up of amino acids, which are small organic molecules.
- There are 20 different amino acids, each with a central carbon, an amino group, a carboxyl group, and a side chain (R group).
- Amino acids are joined by peptide bonds to form polypeptides.
- A protein may consist of one or more polypeptides that fold into a specific three-dimensional shape.
- This shape determines the protein’s function, such as binding to other molecules or catalyzing reactions.
(b)
- Each gene contains the instructions to build a specific protein.
- The genetic code is read in triplets (codons), with each codon coding for one amino acid.
- In transcription, a gene’s DNA sequence is copied into messenger RNA (mRNA).
- mRNA exits the nucleus and travels to the ribosome.
- In translation, the ribosome reads mRNA codons, and transfer RNA (tRNA) brings the matching amino acids.
- Each tRNA has an anticodon that pairs with the mRNA codon.
- The amino acids are joined by peptide bonds to form a polypeptide chain.
- The sequence of amino acids is determined by the DNA sequence, and different combinations lead to many different proteins.
- Mutations can also cause variations in protein sequences.
(c)
- Enzymes are proteins that speed up chemical reactions by lowering activation energy.
- Hormones like insulin are proteins that regulate physiological processes.
- Transport proteins in membranes help move substances across the cell membrane.
- Hemoglobin is a protein that carries oxygen in red blood cells.
- Structural proteins like actin and myosin give support and help with movement in cells and tissues.
- Some proteins function in cell recognition and adhesion, helping cells communicate and stick together.
- Histones help package and organize DNA in the nucleus.
Markscheme:
a. Protein Structure [3]
• Formed from amino acids (20 different types)
• Linked by peptide bonds
• May consist of one or more polypeptides
• Have specific 3D shape/conformation
• Shape determines function
b. Protein Synthesis [7]
• Gene expression initiates protein production
• Genetic code consists of nucleotide triplets (codons)
• DNA transcribed to mRNA (transcription)
• mRNA exits nucleus to ribosomes
• mRNA translated into polypeptide chain (translation)
• Each codon specifies one amino acid
• tRNA delivers specific amino acids
• tRNA anticodon matches mRNA codon
• Amino acids joined by peptide bonds
• Sequence determined by DNA/mRNA code
• Variety created through amino acid combinations/mutations
c. Protein Functions [5]
• Enzymes catalyze metabolic reactions
• Hormones act as chemical messengers
• Membrane transport proteins (channels/pumps)
• Hemoglobin transports oxygen
• Cell recognition/adhesion proteins
• Structural proteins (muscle fibers/spindle fibers)
• Histones package DNA
▶️ Answer/Explanation
(a)
(b)
- One protein that acts as a hormone: Insulin
(c)
- Lactase enzyme is used to break down lactose.
- The enzyme is immobilized, often bound to alginate beads.
- When milk is passed over these beads, the lactose is hydrolyzed into the monosaccharides glucose and galactose, which can be digested by lactose-intolerant individuals.
Markscheme:
a.
b. insulin/glucagon/ADH/oxytocin/leptin / other verified example;
c.
a. the enzyme lactase acts on lactose;
b. the enzymes are immobilised / are bound to alginate beads;
c. (pouring milk over the immobilised enzymes) causes lactose to be hydrolysed/broken down into monosaccharides/glucose and galactose;