1. Nucleic Acid and Protein

Myoglobin is a protein formed by one polypeptide chain bound with a heme group. Which of protein structure would best describe myoglobin?

• Primary Structure

• Secondary Structure

• Tertiary Structure

• Quaternary Structure

Which of the following situations describes active transport of a substance across a semi-permeable membrane?

• Carbon dioxide leaves the tissue fluid around active muscle cells and enters the blood vessels.

• A unicellular amoeba gains water from its natural surroundings.

• In the kidney, glucose in the blood is filtered out then reabsorbed into the blood through transport proteins.

• Glucose is taken up by cells in the human intestine immediately after a carbohydrate-rich meal.

The structure of the endoplasmic reticulum is composed of a

• network of membranous sheets and tubule channels enclosing a lumen.

• system of fused sacs used for the synthesis, modification and transport of lipids.

• system of membrane-enclosed sacs filled with enzymes found only in animal cells.

• collection of ribosomes for protein synthesis and modification.

This process is made possible by

• a steep concentration gradient between the contents within the vesicle and that of the extracellular environment.

• integral and transmembrane proteins allowing for the movement of substances in and out of cells.

• dissociation of phospholipid molecules in both membranes and recombining upon fusion.

• cholesterol particles in the membrane moderating the membrane fluidity and adding resistance to membrane deformation.

A segment of double-stranded DNA contains the same numbers of adenine and thymine bases. The best explanation for this is

• thymine always follows adenine on each strand.

• adenine and thymine bases alternate on the strands of DNA.

• the number of all bases in a DNA strand are always identical.

• adenine on one strand will pair with thymine on the second strand.

The chemical structure of DNA molecules is distinct from that of RNA molecules in that DNA molecules contain

• a sugar-phosphate backbone.

• deoxyribose sugars.

• ribose sugars.

• uracil bases instead of thymine bases.

The first step of gene expression is

• packaging of proteins into vesicles for fusion with the plasma membrane.

• modification of RNA in the nucleus.

• transcription of DNA into RNA in the nucleus.

• translation of DNA at the ribosome.

At the ribosome, a polypeptide chain is synthesised. During this process

• the primary structure of the peptide is formed.

• a growing chain is formed by amino acids joined together by complementary pairing.

• peptide bonds form between tRNA molecules to form a growing chain.

• anticodons in tRNA molecules pair with the corresponding triplet in DNA.

Serine is an amino acid that can be encoded for by six different codons. This demonstrates that the genetic code is

• degenerate.

• susceptible to mutations.

• universal.

• specific.

Gene expression in prokaryotic and eukaryotic organisms differs in that

• prokaryotes do not have regulatory proteins that assist with the turning off of genes.

• transcription and translation occurs at a much faster rate in prokaryotes than eukaryotes.

• eukaryotes often have entire clusters of genes that are regulated by a single promoter.

• regulatory and structural genes are always located on the same chromosomes in eukaryotes.