AS Level Biology A H020/02 Depth in biology Monday 4 June 2018 - Afternoon EXAM QUESTIONS AND AMSWERS 100% CORRECT!

Pepsin is a protease enzyme with a polypeptide chain containing 327 amino acids. Titin is the largest known protein. It has a polypeptide chain containing at least 92 times more amino acids than pepsin. (i) DNA sequences in genes code for polypeptide molecules such as pepsin and titin. Explain why a process known as transcription is necessary for polypeptide synthesis - ANSWER DNA, copied to mRNA DNA, is too large to leave nucleus Calculate the minimum length of the DNA base sequence required to code for titin. Show your working - ANSWER 327 x 92 x 3= 90,252 * Titin is a fibrous protein. Pepsin is a globular protein. Compare the properties and functions of fibrous proteins and globular proteins in the human body - ANSWER Properties: Globular-soluble, Fibrous- insoluble Globular- tertiary structure, fibrous-no tertiary structure Globular- Hydrophilic R groups on the outside Fibrous- Hydrophobic R groups , strong flexible Functions: Globular- to transport substances in blood • haemoglobin + role described e.g. carry oxygen to transport substances across cell membranes • carrier / channel / pump + role described Using the traces shown in Fig. 2.1, name the heart rhythm abnormality that the patient is suffering from - ANSWER tachycardia Explain how the heart is controlling the electrical activity at Y on Fig. 2.1(b) - ANSWER The impulse travels to the AV node. Here, the impulse slows for a moment before going on to the ventricles The impulse travels through a pat