Biochem Lec _ Midterm MLS-2F

A) N-acetyl-β-D-glucosamine & D-glucoronate

Explanation: Hyaluronic acid is composed of alternating units of N-acetyl-β-D-glucosamine and D-glucoronate, which are essential for its structure and function.

B) Alpha

Explanation: The storage form of glucose is alpha, while cellulose, which is a structural polysaccharide, is classified as beta.

C) They are needed for the formation of polysaccharides

Explanation: Hexoses, such as glucose and galactose, are biologically important as they are essential for the formation of polysaccharides, which are crucial for energy storage and structural functions.

B) Right

Explanation: In the Fischer projection of D-glucose, the -OH group on the chiral carbon starts on the right side, which is a defining characteristic of D-isomers.

B) Energy reserve

Explanation: Carbohydrates serve as an energy reserve in the body, with polysaccharides like starch in plants and glycogen in humans acting as storage forms of glucose.

C) Carbohydrates

Explanation: Carbohydrates are prominent constituents of DNA and RNA, with DNA containing deoxyribose and RNA containing ribose.

B) Muscles and liver

Explanation: Glycogen is primarily stored in muscles, where it supplies energy for muscle activity, and in the liver, where it provides glucose for the entire body.

B) Major component of synovial fluid and skin

Explanation: Hyaluronic acid is recognized as a major component of synovial fluid, which lubricates joints, and is also a significant component of skin, contributing to its hydration and elasticity.

D) Ribose

Explanation: Ribose is a pentose sugar (C5H10O5), while galactose, glucose, and fructose are all hexoses (C6H12O6).

C) They are used in glycolipids and glycoproteins

Explanation: Carbohydrates are integral to cell communication, being components of glycolipids and glycoproteins in the cell membrane that facilitate cell-to-cell interactions.

A) C(H₂O)

Explanation: The general formula for carbohydrates is represented as C(H₂O), indicating that they are composed of carbon and water molecules.

B) Retains moisture

Explanation: One of the primary functions of hyaluronic acid is its ability to retain moisture, making it crucial for maintaining skin hydration and joint lubrication.

B) Blue-black or purple

Explanation: The iodine test for starch yields a positive result indicated by a blue-black or purple color, confirming the presence of starch.

B) The spatial arrangement of atoms in carbohydrates

Explanation: The Haworth projection is used to depict the spatial arrangements of atoms within carbohydrates, illustrating how different groups are oriented in three-dimensional space.

B) C5H10O5

Explanation: Pentoses are five-carbon sugars, and their chemical formula is C5H10O5, which distinguishes them from hexoses and other carbohydrates.

D) Amylose

Explanation: Amylose is the unbranched form of starch that is linear and readily digested, making up 15-20% of stored starch in plants.

B) Energy storage

Explanation: Glycogen serves as the primary energy reserve for animals, storing excess glucose for energy needs, particularly in muscles and the liver.

A) They are sweet

Explanation: Polysaccharides, also known as glycans, are generally not sweet. The more monosaccharide units that are linked together, the less sweet the compound becomes, as seen with starch.

B) Forming the rigid coating of exoskeletons

Explanation: Chitin is the second most abundant polysaccharide and is primarily known for forming the rigid exoskeletons of arthropods, such as shrimp.

C) Glucose

Explanation: Hexoses are the most biologically important monosaccharides in humans, with glucose being a primary example.

A) Flavin adenine dinucleotide

Explanation: FAD stands for flavin adenine dinucleotide, which is an important coenzyme involved in various biochemical reactions.

A) α-D-glucose units

Explanation: Starch is primarily made up of α-D-glucose units, which distinguishes it from other carbohydrates like cellulose, which is made of β-glucose units.

B) In fruits

Explanation: Pectin is a major component found in fruits and is crucial for binding cells together in the middle lamella and primary cell walls.

C) Glycogen

Explanation: Glycogen is the polysaccharide that serves as an energy reserve in humans, storing glucose for energy use when needed.

B) Downward

Explanation: In the Haworth projection, groups that are on the right side of the Fischer projection are projected downward, while those on the left side are projected upward.

B) As a blood thinner

Explanation: Heparin is a highly sulfated polysaccharide that acts as an anticoagulant, making it effective for treating thrombotic events by preventing blood clots.

B) It gives a brick-red precipitate

Explanation: A reducing sugar, such as all monosaccharides and some disaccharides like maltose and lactose, will produce a brick-red precipitate when heated with Benedict's solution, indicating its reducing properties.

B) Lipid formation

Explanation: Glyceraldehyde is involved in glycerol formation, which is essential for lipid formation in the body.

C) 1,4 linkage

Explanation: Straight-chain polysaccharides are primarily linked by 1,4 linkages, where carbon 1 of one monosaccharide is linked to carbon 4 of the next.

B) In serums

Explanation: Hyaluronic acid is often included in serums, particularly in skincare products, due to its ability to retain moisture and enhance skin hydration.

B) To act as a stool bulking agent

Explanation: Pectin serves as a stool bulking agent, adding bulk and water to stools, which helps them pass more easily through the intestines.

B) Ribose

Explanation: Ribose is a pentose sugar that is crucial for the synthesis of coenzymes such as NAD and NADP.

C) Monosaccharides

Explanation: Monosaccharides are defined as the smallest unit of carbohydrates and are the simplest sugars, consisting of a single carbon chain.

B) 3

Explanation: Trioses are monosaccharides that consist of 3 carbon atoms, with examples including glyceraldehyde and dihydroxyacetone.

B) Structural material

Explanation: Cellulose serves as a structural material in the cell walls of plants, providing rigidity and support, which is essential for plant structure.

A) Cellulose

Explanation: Cellulose is a homopolysaccharide as it consists of repeating units of a single type of monosaccharide, specifically glucose.

C) Sucrose

Explanation: Sucrose is the only disaccharide listed that is not a reducing sugar, while lactose and maltose are reducing sugars, which can be digested by the body.

B) A diastereomer that differs at one carbon

Explanation: Epimers are a specific type of diastereomer that differ from each other at only one carbon atom, excluding the anomeric carbon, which is a key aspect of their classification.

D) 80-85%

Explanation: Amylopectin makes up 80-85% of stored starch in plants, characterized by its branched structure which allows for efficient glucose release.

B) The type of glycosidic linkage

Explanation: Maltose has an alpha 1,4 glycosidic bond, while cellobiose has a beta 1,4 glycosidic linkage, which is the key difference between these two disaccharides.

B) Down

Explanation: In Alpha-D-Glucose, the OH group on the anomeric carbon is oriented downward, distinguishing it from Beta-D-Glucose where the OH group is oriented upward.

C) It provides a stable 3D structure

Explanation: The chair conformation of Beta-D-Glucose resembles a chair and is significant because it provides a stable three-dimensional structure, which is important for the molecule's stability.

C) Compounds with the same molecular formula but different bonding arrangements

Explanation: Structural isomers are defined as compounds that have the same molecular formula but differ in the arrangement of their atoms, leading to different chemical properties.

C) Maltose

Explanation: Maltose consists of two alpha-D-glucose units linked by an alpha 1,4 glycosidic bond, distinguishing it from other disaccharides.

B) The interconversion of tautomers by relocating a proton

Explanation: Tautomerization refers to the process where tautomers readily interconvert by relocating a proton, which is a key concept in understanding the relationship between different forms of molecules like d-glucose and d-fructose.

B) They differ at one or more points but are not mirror images

Explanation: Diastereomers are characterized by being non-superimposable and non-mirror images of each other, differing at one or more points in their structure.

C) Heteropolysaccharide

Explanation: Heteropolysaccharides are composed of two or more different types of monosaccharide units, such as glucose and galactose.

B) Same molecular formula with different configurations due to asymmetric carbons

Explanation: Stereoisomers have the same molecular formula but differ in their 3D arrangements due to the presence of asymmetric or chiral carbons, leading to different configurations.

B) They are non-superimposable, mirror images of each other

Explanation: Enantiomers are defined as non-superimposable mirror images of each other, which is a fundamental characteristic of this type of stereoisomer.

B) Two monosaccharides

Explanation: Oligomers, specifically disaccharides, are formed by linking two monosaccharide units, which is a fundamental concept in carbohydrate chemistry.

C) Sucrose

Explanation: Sucrose is identified as a non-reducing sugar, while lactose and maltose are classified as reducing sugars, highlighting the different properties of these disaccharides.

B) Beta 1,4

Explanation: Lactose is composed of galactose and glucose connected by a beta 1,4 glycosidic linkage, which is crucial for its structural identity.

B) 6-membered ring

Explanation: Pyranose refers to a 6-membered ring structure in the Haworth Projection, which is a key characteristic of certain monosaccharides.

C) Oxidation-reduction reactions

Explanation: Monosaccharides can undergo several reactions, with oxidation-reduction reactions being the most commonly observed.

C) Glycosidic bond

Explanation: The bond formed between monosaccharides in di/oligosaccharides is called a glycosidic bond, which is created through condensation and can be broken by hydrolysis.

B) Sugar alcohol

Explanation: The reduction of monosaccharides produces sugar alcohols, such as glucitol (commonly known as sorbitol), which is often found in products like chewing gum.

C) Fructose

Explanation: Furanose is a 5-membered ring structure, and fructose, a ketose sugar, is the most important sugar that forms this structure.

B) A weak oxidizing agent that can oxidize C1

Explanation: Aldonic acid is characterized as a weak oxidizing agent that can only oxidize the first carbon (C1) of a monosaccharide.