Sindh Mdcat Exclusive Course Biology Biological Molecules — Solved MCQs

Question 1

Which of the following are not polymer?

Accepted Answer

C. Lipids — The correct answer is Lipids. Unlike proteins, polysaccharides, and nucleic acids, lipids do not consist of repeating monomer units and therefore are not classified as polymers. Proteins are polymers because they are made up of amino acids linked in chains. Polysaccharides are polymers of monosaccharides, and nucleic acids are polymers of nucleotides, each consisting of a series of repeated structural units.

Question 2

Which of the following is the least likely to be involved in stabilizing the three­ dimensional folding of most proteins?

Accepted Answer

D. Ester Bonds — Protein folding is the process by which a protein structure assumes its functional shape or conformation by allowing interaction between amino acids by various bond formations. All protein molecules are heterogeneous unbranched chains of amino acids. Different types of weak interactions hold the interacting segments together in protein. Hydrophobic interaction, H bonds, and electrostatic interactions are the weak ones and stabilize the tertiary structure of proteins, while ester bonds are covalent bonds and are least likely to be involved in stabilizing the three-dimensional folding of most proteins.

Question 3

Which one of the following statements is wrong?

Accepted Answer

B. Glycine is a sulfur-containing amino acid — Option A: Uracil is a pyrimidine: This statement is correct. Uracil is one of the four nitrogenous bases found in RNA. It is a pyrimidine base, along with cytosine and thymine. Pyrimidines are a type of organic molecule characterized by a six-membered ring structure.Option B: Glycine is a sulfur-containing amino acid: This statement is incorrect. Glycine is the simplest amino acid and does not contain sulfur. It is the only amino acid that is not chiral and has a hydrogen atom as its side chain. Some amino acids, such as cysteine and methionine, do contain sulfur in their structures.Option C: Sucrose is a disaccharide: This statement is correct. Sucrose is a disaccharide composed of glucose and fructose units joined by a glycosidic bond. It is commonly known as table sugar and is found in various plant sources, including sugarcane and sugar beets.Option D: Cellulose is a polysaccharide: This statement is correct. Cellulose is a polysaccharide and one of the main structural components of plant cell walls. It is composed of long chains of glucose units linked by βglycosidic bonds. Cellulose is indigestible by humans but serves as a valuable dietary fiber

Question 4

The chitinous exoskeleton of arthropods is formed by the polymerisation of _?

Accepted Answer

A. N-acetyl glucosamine — Option A: N-acetyl glucosamine is a monosaccharide and a derivative of glucose. It is a key component in the formation of the chitinous exoskeleton of arthropods. Chitin, which is the primary component of the exoskeleton, is a polymer of N-acetyl glucosamine. Option B: Lipoglycans are not directly involved in the formation of the chitinous exoskeleton of arthropods. They are a class of molecules that consist of both lipid (fat) and glycan (sugar) components. They have diverse functions in various biological systems but are not responsible for the structure of arthropod exoskeletons.Option C: Keratin sulfate and chondroitin sulfate are not involved in the formation of the chitinous exoskeleton of arthropods. Keratin sulfate is a component of certain tissues like hair and nails in vertebrates, while chondroitin sulfate is a major component of cartilage. Option D: D glucosamine is a form of glucosamine, which is a naturally occurring amino sugar. While glucosamine plays a role in the synthesis of certain molecules like glycosaminoglycans found in cartilage, it is not directly involved in the polymerization process of chitin to form the chitinous exoskeleton of arthropods.

Question 5

Uridine, present only in RNA is a _.

Accepted Answer

A. Nucleoside — Option A: A nucleoside consists of a nitrogenous base (either a purine or a pyrimidine) bonded to a sugar molecule (ribose or deoxyribose) via a glycosidic bond. Uridine is a nucleoside because it contains the pyrimidine base uracil bonded to the sugar ribose.Option B: A nucleotide, on the other hand, is a nucleoside with one or more phosphate groups attached to the sugar molecule. Nucleotides are the building blocks of DNA and RNA, and they play crucial roles in various cellular processes. Uridine alone does not have any phosphate groups attached to it, so it is not considered a nucleotide.Option C: Purines are a class of nitrogenous bases that include adenine and guanine. Uridine contains the pyrimidine base uracil, not a purine base, so it is not a purine.Option D: Pyrimidines are a class of nitrogenous bases that include cytosine, thymine (in DNA), and uracil (in RNA). Uridine contains the pyrimidine base uracil, making it a pyrimidine.

Question 6

The given diagrammatic representation shows one of the categories of small molecular weight organic compounds in the living tissues. Identify the category is shown and the blank component “X” in it.

Accepted Answer

D. Nucleoside: Uracil — The structure depicted in the diagram illustrates a pentose sugar (ribose) attached to uracil, which classifies it as a nucleoside. Nucleosides consist of a sugar and a nitrogenous base but lack a phosphate group. The other options are incorrect for the following reasons:Option A: Cholesterol is a sterol and not related to nucleic acids.Option B: Amino acids are building blocks of proteins, not nucleic acids.Option C: Nucleotides must contain a phosphate group; since this structure does not, it cannot be classified as a nucleotide.Thus, the correct identification of the structure is a nucleoside with uracil.

Question 7

Which one of the following biomolecules is correctly characterized?

Accepted Answer

A. Lecithin a phosphorylated glyceride found in the cell membrane. — Lecithin is a triglyceride lipid where one fatty acid is replaced by phosphoric acid, which is linked to an additional nitrogenous group called choline. It is a common membrane lipid. It is an amphipathic phospholipid, having both hydrophilic polar and hydrophobic nonpolar groups. The hydrocarbon chains of two fatty acids function as hydrophobic non­polar tails, whereas the phosphate and choline behave as a hydrophilic polar head group of the molecule. Palmitic acid is a saturated fatty acid (as it does not possess double bonds in its carbon chain) and contains 16 carbon atoms with formula C 16 H 32 O2. Adenylic acid or adenosine monophosphate is a nucleotide formed by the union of adenine (nitrogenous base), ribose (pentose sugar), and phosphate. It is formed through phosphorylation of nucleoside as phosphate combines with sugar molecule at its 5 carbon atom. Amino acids are organic acids with a carboxylic group (–COOH) having an amino group (– NH 2) generally attached to a­ carbon or carbon next to a carboxylic group. Alanine is a nonpolar and neutral amino acid having one methyl group and having an amino group attached to the carbon next to the carboxylic group.

Question 8

Carbohydrates are commonly found as starch in plants storage organs. Which of the following five properties of starch make it useful as a storage material?(1) Easily translocated(2) Chemically non­reactive(3) Easily digested by animals(4) Osmotically inactive(5) Synthesized during photosynthesisThe useful properties are?

Accepted Answer

D. (2) and (4) — Starch is the major storage carbohydrate of plants. In most plant species it is accumulated in the chloroplast of leaves, whereas in storage organs it accumulates in the amyloplast as reserve starch. It is the osmotically inactive form of photosynthetic product and is a hexosan polysaccharide made of a large number of glucose units so it is chemically non-reactive.

Question 9

About 98 percent of the mass of every living organism is composed of just six elements including carbon, hydrogen, nitrogen, oxygen and :

Accepted Answer

B. Phosphorus and Calcium — The correct answer is Phosphorus and Calcium. In the context of biological molecules, the six elements that make up about 98% of the mass of living organisms are carbon (C), hydrogen (H), nitrogen (N), oxygen (O), phosphorus (P), and sulfur (S). Although phosphorus is included, calcium is more of a structural element in bones and is not one of the primary elements constituting the majority of living organism mass.Option A (Carbon and Sulfur) is incorrect because, while carbon is essential, sulfur is not one of the six key elements. Option C (Sulfur and Magnesium) is incorrect as magnesium is a trace element and not one of the primary six. Option D (Magnesium and Sodium) is also incorrect for similar reasons: both are trace elements and do not account for the bulk of the mass of living organisms.

Question 10

The major role of minor elements inside living organisms is to act as?

Accepted Answer

A. Co­factors of enzymes — Minor elements are those which are required in the quantity of less than milligram/gram of dry matter, but they are essential for proper growth and development of an organism e.g., Cl, Mn, B, Zn, Cu, Mo, etc. These elements work as non­protein cofactor in enzymes e.g., Zn, Cu, etc. They also take part in oxidation-reduction reactions, e.g., Cu, with variable valency. Chloride ion enhances the activity of salivary amylase. Zinc is required for the activity of carbonic anhydrase and alcohol dehydrogenase, etc.

Question 11

Which of the following is a reducing sugar?

Accepted Answer

A. Galactose — All those sugars which have free aldehyde or ketone group are called reducing sugars. These are able to reduce cupric ions (Cu+2) into cuprous ions (Cu+). Sucrose and starch are non-­reducing sugars.

Question 12

Which of the following have carbohydrates as a prosthetic group?

Accepted Answer

A. Glycoprotein — Glycoproteins are proteins that contain sugars like carbohydrates as a prosthetic group. In most glycoproteins, the linkage is between asparagine and N­-acetyl­ D-­glucosamine. Some glycoproteins are immunoglobulins, membrane proteins, and muscle proteins. Lipoproteins are protein complexed with lipids like triglycerides, phospholipids, etc. Nucleoproteins are proteins associated with nucleic acids and chromoproteins are proteins associated with pigments e.g., cytochrome, phytochrome.

Question 13

Cellulose, the most important constituent of the plant cell wall, is made up of:

Accepted Answer

B. Unbranched chain of glucose molecules linked by b­1, 4 glycosidic bond — Cellulose is the most abundant carbohydrate. Cellulose molecule is composed of 1600 to 6000 glucose molecules joined together. Those polymers form long-twisting macromolecules of cellulose. The chains are unbranched and linear. The successive glucose residues are joined together by B-1,4 linkages.

Question 14

Which of the following nucleotide sequence contain 3 pyrimidine bases?

Accepted Answer

C. UAGCGGUAA — In DNA and RNA, these bases form hydrogen bonds with their complementary purines. Thus, in DNA, the purines adenine (A) and guanine (G) pair up with the pyrimidines thymine (T) and cytosine (C), respectively.Normally the Nucleotides contain Nitrogenous base,pentose sugar,phosphate groups.

Question 15

How many water molecules will be released upon the formation of a trisaccharide?

Accepted Answer

B. 2 — To form a trisaccharide, three monosaccharides are linked together. Each link between two monosaccharides is a glycosidic bond, which releases one water molecule. Thus, two glycosidic bonds are formed to link three monosaccharides, releasing two water molecules in total. Option B is correct because it reflects the correct number of water molecules released during this process. Options A, C, and D are incorrect because they represent the number of water molecules released when forming disaccharides, tetrasaccharides, and pentasaccharides, respectively.

Question 16

How many carbon atoms are present inside the ring of fructose?

Accepted Answer

B. 4 — Frustose is an keto hexose, it has keto group on carbon no 2 so when it forms an Ring the oxygen from carbon no 2 forms an bond with carbon no 5 and form ring, due to this bonding there's only 4 carbon atoms inside the ring while 2 carbon atoms remains outside the ring.Four carbon atoms are present inside the ring of fructose, while two carbon atoms are present outside of the ring.

Question 17

Which of the following is an amino acid and part of phospholipids?

Accepted Answer

A. Serine — Serine and aspartic acids are examples of amino acids, while choline and ethanolamine are Nz-containing bases. Serine can be a constituent of phospholipids and can act as a nitrogenous base.

Question 18

Myelin sheath of neuron is composed of:

Accepted Answer

A. Sphingolipids — The myelin sheath is an essential part of the nervous system, acting as an insulating layer around nerve fibers to facilitate efficient transmission of electrical signals. It is primarily composed of lipids, with sphingolipids being a major component. Sphingomyelin, in particular, is a crucial sphingolipid in the myelin sheath, comprising a combination of a fatty acid, sphingosine, and a phosphate group. This structure allows it to effectively insulate nerve fibers. Other options, such as ethanolamine, choline, and waxes, play different roles in lipid metabolism or cellular functions but do not form the myelin sheath.

Question 19

How many amino acids are present in the cell?

Accepted Answer

A. 170 — About 170 types of amino acids have been found to occur in cells and tissues. Of these, about 25 are constituents of proteins. Most of the proteins are, however, made of 20 types of amino acids.

Question 20

A protein having secondary structure possesses:

Accepted Answer

D. Both A and B — The correct answer is 'Both A and B' because proteins with a secondary structure rely on hydrogen bonding for the stabilization of structures like alpha-helices and beta-sheets. Peptide bonds, while important, are relevant to the primary structure, linking amino acids in a linear chain. Disulfide bonds, on the other hand, contribute to tertiary and quaternary structures, not secondary.

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