McArdle disease is a metabolic disorder caused by a mutation in the PYGM gene, which codes for the enzyme muscle glycogen phosphorylase. Under normal conditions, this enzyme breaks down stored glycogen in skeletal muscle cells into glucose-1-phosphate to fuel cellular respiration.
The mutation alters the triplet codes (codons) in the PYGM gene.
Describe how a change to the triplet codes in the DNA can prevent the muscle glycogen phosphorylase enzyme from functioning, and explain how this mutation affects the levels of glycogen and glucose-1-phosphate within the muscle cells.
Glucose is sometimes present in the urine of individuals with untreated diabetes mellitus.
Benedict's reagent can be used to test for the presence of reducing sugars, such as glucose, in urine.
It can also be used to estimate the concentration of glucose in a clinical sample.
Describe how the results of a Benedict's test can be used to obtain a quantitative measure of the concentration of glucose in a urine sample.
184 exam-style questions on OCR GCSE Biology 1.2 What happens in cells (and what do cells need)?, covering 1.2.1 Structure of DNA, 1.2.2 Nucleotides and complementary bases, 1.2.3 Protein synthesis, 1.2.4 DNA structure and the proteins made, 1.2.5 Investigating enzymatic reactions, and 1.2.6 Mechanism of enzyme action. Each one has a worked solution and a mark scheme showing where the marks go.