BIOLOGY I

TUTORIAL 2
BASIC MOLECULES OF CELLS II

(Source: Final examination, Dec 2012)
Q1. (a) Amino acids are the building blocks of proteins. Figure 1.1 shows the dipeptide molecule.

[pic]
Figure 1.1

i) Briefly explain the formation of dipeptide from two amino acids. (3 marks)

ii) Name the molecular unit that could determine the structure of a protein. (1 mark)

(Source: Final examination, Apr 2012)
Q2 (a) Figure 2.1 shows a representation of a phospholipid molecule and Figure 2.2 shows the detailed structure of a fat molecule.
[pic] [pic]
Figure 2.1 Figure 2.2

(i) Based on Figure 2.1, name the parts of the molecule labeled as A, B and C. (3 marks)

(ii) Based on Figure 2.1 and 2.2, briefly describe the chemical structure of lipids that account for their insolubility in water. (1 mark)

(iii) During a practical session, Ms. Chan demonstrated to the students that when water and oil were added to a test tube, the two liquids formed two separate layers. She then added a solution of phospholipids to the mixture of water and oil. With justification, predict where the phospholipids would have dissolved. (3 marks)

(b) Figure 2.3 shows part of a DNA molecule. [pic] Figure 2.3

(i) Name the TWO components that make up the part of the DNA molecule labeled as P. (2 marks)

(ii) Name the bond labeled as Q. (1 mark)

iii) Describe how DNA monomers, nucleotides, join to form a polymer. (2 marks)

(c) David learnt that when an egg was fried, the clear egg white surrounding the yolk became solid, white and opaque. He claimed that peptide bonds