A chain of peptide containing linear sequences of amino acid linked by peptide bonds best represent the
- A.Primary structure
- B.Secondary structure
- C.Tertiary structure
- D.Quaternary structure
Correct answer
Explanation
The correct answer is A, Primary structure. The primary structure of a protein is simply the linear order of amino acids joined one after another by peptide bonds.
Proteins are built at four levels. The primary structure is the sequence of amino acids in the polypeptide chain, fixed by the gene that codes for it. This sequence decides how the chain will fold later, so even a single change in it can alter the protein, as in sickle-cell anaemia where one amino acid of haemoglobin is replaced.
B is wrong because the secondary structure is the local folding of the chain into an alpha helix or a beta pleated sheet, held by hydrogen bonds. C is wrong because the tertiary structure is the overall three-dimensional folding of a whole chain. D is wrong because the quaternary structure is the arrangement of two or more polypeptide chains together, as in haemoglobin with its four subunits.
Exam tip: primary means sequence, secondary means helix or sheet, tertiary means 3-D fold, quaternary means several chains.
Practice Questions
View allWhich one of the following features is an indication for modification of stem of a plant?
- A.Presence of 'eye' on potato
- B.'Scale' found in onion
- C.'Tendril' found in pea
- D.'Hair' present in carrot
Show answer
The eyes of a potato are nodes with buds, and only a stem bears nodes and buds, so they prove that the potato is a modified stem.
Read the full explanation →Which one of the following metals is used in the filaments of photo-electric cells that convert light energy into electric energy ?
- A.Tungsten
- B.Copper
- C.Rubidium
- D.Aluminium
Show answer
Rubidium, an alkali metal like caesium, gives off electrons easily when light falls on it, so it is used in photoelectric cells.
Read the full explanation →Tooth enamel is made up of which one of the following calcium compounds ?
- A.Calcium carbonate
- B.Calcium sulphate
- C.Calcium hydroxide
- D.Calcium phosphate
Show answer
Tooth enamel is made mainly of calcium phosphate in the form of a hard crystal called hydroxyapatite. Enamel is the hardest substance in the human body, harder even than bone.
Read the full explanation →Which one of the following viruses used to be responsible for highly infectious disease Smallpox ?
- A.Adenovirus
- B.Variola virus
- C.Aichi virus
- D.Coxsackie virus
Show answer
Smallpox was caused by the variola virus, a large DNA virus of the pox family that spread from person to person through the air.
Read the full explanation →After fertilization, the fruit and the seed are produced by
- A.ovule and ovary, respectively
- B.ovary and ovule, respectively
- C.ovary, no ovule required
- D.ovule, no ovary required
Show answer
After fertilisation the ovary of the flower grows into the fruit, and each ovule inside it develops into a seed.
Read the full explanation →