Omics-C3

Question 1

4) Starch and cellulose ________.
A) are polymers of glucose
B) are cis and trans isomers of each other
C) are used for energy storage in plants and animals
D) are structural components of the plant cell wall

Answer 1

The correct answer is A) are polymers of glucose.

Both starch and cellulose are polysaccharides made up of glucose monomers. However, the glucose units are linked differently:

Starch consists of glucose molecules linked by α-1,4-glycosidic bonds, which makes it digestible by humans and used for energy storage in plants.
Cellulose is composed of glucose molecules linked by β-1,4-glycosidic bonds, which gives it a rigid structure and makes it a key component of the plant cell wall, but it is indigestible for humans due to the β-linkages.
Clarification on other options:

B) is incorrect because starch and cellulose are not cis-trans isomers but differ in the type of glycosidic linkage.
C) is incorrect because cellulose is not used for energy storage but is a structural component.
D) is partially correct as cellulose is a structural component of the plant cell wall, but starch is not used structurally.
Thus, A is the most accurate choice.

Question 2

5) Which of the following statements is true for lipids?
A) Lipids are true polymers.
B) Waxes and pigments are not lipids.
C) Lipids mix poorly with water.
D) Lipids are true polymers and mix poorly with water.

Answer 2

The correct answer is C) Lipids mix poorly with water.

Explanation:
Lipids are hydrophobic molecules, meaning they do not mix well with water due to their non-polar nature. This is why lipids, such as fats, oils, and waxes, separate from water.
A) Lipids are true polymers is false because lipids are not considered true polymers. Polymers are made of repeating monomer units, but lipids do not have this structure. Instead, they are formed from smaller, non-repeating molecules like fatty acids and glycerol.
B) Waxes and pigments are not lipids is false because waxes and certain pigments, like carotenoids, are considered lipids.
D) Lipids are true polymers and mix poorly with water is also false because, while lipids mix poorly with water, they are not true polymers.

Question 3

6) What makes lipids/fats hydrophobic?
A) their long carbon skeleton
B) the carboxyl group at one end of the molecule
C) the glycerol moiety
D) presence of relatively nonpolar C—H bonds

Answer 3

The correct answer is D) presence of relatively nonpolar C—H bonds.

Explanation:
Lipids and fats are hydrophobic because their molecular structure is dominated by long hydrocarbon chains (C—H bonds), which are nonpolar. These nonpolar bonds do not interact well with water, which is polar. This lack of interaction causes lipids to be insoluble in water, making them hydrophobic.

A) their long carbon skeleton: While this contributes to their structure, it’s specifically the nonpolar nature of the C—H bonds that make them hydrophobic.
B) the carboxyl group: This is part of fatty acids, but it is polar and interacts with water, so it does not cause hydrophobicity.
C) the glycerol moiety: Glycerol itself is hydrophilic, meaning it can mix with water, so it does not make lipids hydrophobic.
The key factor in the hydrophobic nature of lipids is the nonpolar C—H bonds found in their long hydrocarbon chains.

Question 4

7) For lipids to be fluid at room temperature, they should have ________.
A) single bonds only
B) a higher number of glycerol molecules
C) a higher number of cis double bonds
D) a longer carbon chain

Answer 4

The correct answer is C) a higher number of cis double bonds.

Explanation:
Lipids that remain fluid at room temperature, such as oils, typically have cis double bonds in their fatty acid chains. These double bonds create “kinks” in the structure, preventing the molecules from packing tightly together. This loose packing results in the lipid remaining liquid at room temperature.

A) Single bonds only: Single bonds (saturated fats) lead to straight chains that can pack closely, making the lipid more likely to be solid at room temperature (e.g., butter).
B) A higher number of glycerol molecules: Glycerol is part of the triglyceride structure but does not directly affect the fluidity of the fat.
D) A longer carbon chain: Longer chains without double bonds tend to increase the melting point, making the fat more solid at room temperature.
Thus, cis double bonds are key in maintaining the fluidity of lipids at room temperature.

Question 5

9

Answer 5

The correct answer is C
A) is a saturated fatty acid: This is incorrect if there are double bonds. Saturated fatty acids have no double bonds between carbons.
B) stores genetic information: This remains incorrect. Fatty acids do not store genetic information.
C) will be liquid at room temperature: This could be correct for unsaturated fatty acids, particularly if the double bonds are in the cis configuration. These double bonds create kinks in the fatty acid chains, preventing tight packing and making the lipid more likely to be liquid at room temperature (e.g., olive oil).
D) is a carbohydrate: Still incorrect, as this is clearly a lipid (fatty acid), not a carbohydrate.
Given the new information about the double bonds, the correct answer would likely be C) will be liquid at room temperature, as unsaturated fats with double bonds are often liquid at room temperature.

Note:
Carbohydrates typically have a ring structure or a chain of carbon atoms connected to hydroxyl groups (-OH) with the formula (CH₂O)n, where n is the number of carbon atoms.
The molecule shown in the figure is a fatty acid, which has a long hydrocarbon chain and a carboxyl group (-COOH) at one end, which is characteristic of lipids, not carbohydrates.

Question 6

10

Answer 6

B) The molecule shown in the figure is a steroid.

Explanation:
The structure consists of four fused rings, which is characteristic of a steroid. Steroids have a structure made of three six-carbon rings and one five-carbon ring.
Examples of steroids include cholesterol, testosterone, and estrogen.
Breakdown of the options:
A) fatty acid: Incorrect. Fatty acids have long hydrocarbon chains, not the ring structure shown here.
B) steroid: Correct. The molecule in the figure has the typical four-ring structure of steroids.
C) triacylglycerol: Incorrect. Triacylglycerols (triglycerides) consist of glycerol linked to three fatty acids, and do not have a ring structure.
D) phospholipid: Incorrect. Phospholipids contain two fatty acids, a phosphate group, and glycerol, but no ring structure like the one shown.
Thus, the correct answer is B) steroid.

Question 7

14) Which of the following statements is true about proteins?
A) Denaturation leads to bond disruption, and the molecule turns into liquid
B) Denaturation is always irreversible
C) Final folded structure can reveal the steps of protein folding
D) Some proteins form a complete 3-D structure only when they interact with their targets

Answer 7

The correct answer is D) Some proteins form a complete 3-D structure only when they interact with their targets.

Explanation:
A) Denaturation leads to bond disruption, and the molecule turns into liquid: This is incorrect. Denaturation disrupts the protein’s structure (breaking hydrogen bonds, disulfide bridges, etc.), but it doesn’t turn the protein into a liquid; it merely loses its functional shape.

B) Denaturation is always irreversible: This is incorrect. Denaturation can sometimes be reversible, depending on the conditions. For example, if the denaturing agent is removed, some proteins can refold into their functional structure.

C) Final folded structure can reveal the steps of protein folding: This is incorrect. The final folded structure doesn’t necessarily reveal the pathway by which the protein folds, as folding can involve intermediates that are not evident from the final structure.

D) Some proteins form a complete 3-D structure only when they interact with their targets: This is correct. These are called intrinsically disordered proteins (IDPs), which remain partially or fully unstructured until they interact with their specific binding partners or targets. This conformational flexibility allows them to perform a variety of functions.

Thus, D is the accurate statement.

Question 8

15) You have just sequenced a new protein found in mice and observe that sulfur-containing cysteine residues occur at regular intervals. What is the significance of this finding?
A) Cysteine residues are required for the formation of α helices and β pleated sheets.
B) It will be important to include cysteine in the diet of the mice.
C) Cysteine residues are involved in disulfide bridges that help form tertiary structure.
D) Cysteine causes bends, or angles, to occur in the tertiary structure of proteins.

Answer 8

The correct answer is C) Cysteine residues are involved in disulfide bridges that help form tertiary structure.

Explanation:
Cysteine contains a sulfur atom, and when two cysteine residues come close together within a protein, they can form disulfide bridges (also called disulfide bonds). These covalent bonds help stabilize the tertiary structure of the protein by linking different parts of the protein chain together.
Breakdown of the options:
A) Cysteine residues are required for the formation of α helices and β pleated sheets: This is incorrect. Cysteine is not specifically required for forming secondary structures like α helices or β sheets. Those structures are stabilized primarily by hydrogen bonds, not disulfide bridges.

B) It will be important to include cysteine in the diet of the mice: While cysteine is an important amino acid, this statement is not relevant to the formation of protein structure or the regular occurrence of cysteine residues in the sequence.

C) Cysteine residues are involved in disulfide bridges that help form tertiary structure: Correct. Disulfide bridges between cysteine residues play a crucial role in stabilizing the tertiary structure of proteins, particularly those that are secreted or need structural rigidity.

D) Cysteine causes bends, or angles, to occur in the tertiary structure of proteins: While cysteine can influence the structure through disulfide bonds, it does not directly cause bends or angles like proline does. Cysteine’s role is more about stabilization through disulfide bridges.

Thus, C is the most accurate answer.

Question 8

18) Which of the following provides the information necessary to stipulate a protein’s 3-D shape?
A) peptide bonds between different amino acids
B) sequence of amino acids in the polypeptide chain
C) side chains of various amino acids
D) number of water molecules in the vicinity

Answer 8

The correct answer is B) sequence of amino acids in the polypeptide chain.
Explanation:
The sequence of amino acids (also called the primary structure) in a polypeptide determines how the protein will fold into its specific 3-D shape. This sequence dictates how the protein forms secondary structures (such as α-helices and β-sheets), which then fold into a more complex tertiary structure and, for some proteins, further into quaternary structure if multiple polypeptides are involved.
Breakdown of the options:
A) peptide bonds between different amino acids: While peptide bonds hold the amino acids together in a chain, they do not dictate the 3-D shape of the protein. It’s the specific sequence of amino acids that influences the folding.
B) sequence of amino acids in the polypeptide chain: Correct. The sequence of amino acids provides all the information necessary for the protein to fold into its unique 3-D shape.
C) side chains of various amino acids: While the side chains contribute to the interactions that help stabilize the protein’s folded form, the overall 3-D shape is primarily determined by the sequence of amino acids.
D) number of water molecules in the vicinity: Water molecules can influence folding, but they do not provide the information necessary to determine the protein’s 3-D shape. The shape is encoded in the amino acid sequence.
Thus, B) sequence of amino acids in the polypeptide chain is the correct answer.

Question 9

17) In sickle-cell disease, as a result of a single amino acid change, the mutant hemoglobin tetramers associate with each other and assemble into large fibers. Based on this information alone, we can conclude that sickle-cell hemoglobin exhibits ________.
A) only altered primary structure
B) only altered tertiary structure
C) only altered quaternary structure
D) altered primary structure and altered quaternary structure; the secondary and tertiary structures may or may not be altered

Answer 9

The correct answer is D) altered primary structure and altered quaternary structure; the secondary and tertiary structures may or may not be altered.

Explanation:
Sickle-cell disease is caused by a mutation in the gene that codes for hemoglobin. Specifically, the disease results from a single amino acid substitution in the primary structure of the hemoglobin protein, where glutamic acid is replaced by valine at position 6 in the β-globin chain.

This change in the primary structure causes the mutant hemoglobin (HbS) to behave differently. The valine substitution creates a hydrophobic patch on the surface of the hemoglobin, which leads to altered quaternary structure. Hemoglobin tetramers that contain HbS aggregate and form long fibers, leading to the characteristic sickling of red blood cells.

The secondary and tertiary structures might also be affected by this mutation, but the specific information provided in the question focuses on the changes in primary (the amino acid sequence) and quaternary structure (the assembly of hemoglobin molecules into large fibers).

Thus, the most comprehensive answer is D, since it acknowledges both the primary mutation and the resulting quaternary structural changes.

Question 10

22) When nucleotides polymerize to form a nucleic acid, ________.
A) a covalent bond forms between the sugar of one nucleotide and the phosphate of a second
B) a hydrogen bond forms between the sugar of one nucleotide and the phosphate of a second
C) covalent bonds form between the bases of two nucleotides
D) hydrogen bonds form between the bases of two nucleotides

Answer 10

The correct answer is A) a covalent bond forms between the sugar of one nucleotide and the phosphate of a second.

Explanation:
When nucleotides polymerize to form a nucleic acid (like DNA or RNA), a phosphodiester bond is formed. This is a type of covalent bond that links the phosphate group of one nucleotide to the sugar (specifically the 3’-OH group) of another nucleotide.
This bond forms the backbone of the nucleic acid strand, with the sequence of bases extending out from this backbone.

Question 11

25) If one strand of a DNA molecule has the sequence of bases 5′-ATTGCA-3′, the mRNA synthesized following the template will be ________.
A) 5′-TAACGT-3′
B) 5′-TGCAAT-3′
C) 3′-UAACGU-5′
D) 5′-UGCAAU-3′

Answer 11

The correct answer is C) 3′-UAACGU-5′.

Explanation:
During transcription, the DNA template strand is used to synthesize a complementary strand of mRNA.

Question 12

26) The central rule of molecular biology states that ________.
A) DNA is transcribed into RNA, which is translated into protein
B) DNA is translated into protein
C) DNA is translated into RNA, which is transcribed into protein
D) RNA is transcribed into protein

Answer 12

A

Question 13

27) Homo sapiens have 23 pairs of chromosomes. This implies that ________.
A) 46 double-stranded DNA molecules are present in each somatic cell
B) 23 single-stranded DNA molecules are present in each somatic cell
C) 23 double-stranded DNA molecules are present in each somatic cell
D) several hundreds of genes are present on DNA but not on the chromosomes

Answer 13

The correct answer is A) 46 double-stranded DNA molecules are present in each somatic cell.

Explanation:
Humans have 23 pairs of chromosomes, which totals 46 chromosomes in each somatic (non-reproductive) cell.
Each chromosome consists of a double-stranded DNA molecule. Therefore, in each somatic cell, there are 46 double-stranded DNA molecules.

Question 14

Which polysaccharide has the greatest number of branches?
cellulose
chitin
amylose
amylopectin
glycogen

Clicker questions-05

Answer 14

Glycogen is the most highly branched polysaccharide. It is a storage form of glucose in animals and fungi. The branching occurs every 8 to 12 glucose units, allowing for rapid release of glucose when energy is needed.

Amylopectin is also a branched polysaccharide (found in plants), but its branches occur less frequently than in glycogen (about every 24 to 30 glucose units).

Cellulose is an unbranched polysaccharide used for structural support in plant cell walls. It has a straight-chain structure with β(1→4) glycosidic bonds.

Chitin is similar to cellulose and is also unbranched, providing structural support in the exoskeletons of arthropods and fungal cell walls.

Amylose is a component of starch (along with amylopectin) and is largely unbranched, forming a helical structure.

Thus, glycogen has the greatest number of branches among these polysaccharides, which allows it to be more efficiently broken down into glucose.

Question 15

A polysaccharide you are studying contains unbranched β glucose molecules and cannot be digested by humans. Which polysaccharide are you studying?
cellulose
DNA
chitin
starch
glycogen

Answer 15

The correct answer is: cellulose

Explanation:
Cellulose is a polysaccharide made up of unbranched β-glucose molecules linked by β(1→4) glycosidic bonds. Humans lack the enzyme cellulase, which is necessary to break down these β-glycosidic bonds, so cellulose cannot be digested by humans. It serves as a structural component in the cell walls of plants.

DNA is not a polysaccharide; it is a nucleic acid made up of nucleotides.

Chitin is similar to cellulose in that it is also composed of β-glucose units, but it includes a modification with nitrogen-containing groups. It forms the exoskeleton of arthropods and is also indigestible by humans.

Starch (found in plants) is composed of α-glucose and can be digested by humans because we have the enzyme amylase to break down the α-glycosidic bonds.

Glycogen is a highly branched polysaccharide composed of α-glucose and can also be digested by humans.

Thus, the polysaccharide being studied is cellulose, as it is made of unbranched β-glucose and cannot be digested by humans.

Question 16

The chemical bonds present in a molecule contribute to the properties of the molecule. Carbon is an unusual atom in that it can form multiple bonds. Which statement is not true?

A carbon-to-carbon cis double bond is the type found in nature and is associated with cardiovascular health.

A carbon-to-carbon trans double bond that is made artificially in food processing is associated with poor cardiovascular health.

A carbon-to-carbon double bond in the cis configuration creates a bend in the hydrocarbon chain.

Saturated fats are those that have carbon-to-carbon double bonds and are associated with good health.

Answer 16

The statement that is not true is:

Saturated fats are those that have carbon-to-carbon double bonds and are associated with good health.

Explanation:
Saturated fats do not have carbon-to-carbon double bonds. Instead, they have single bonds between the carbon atoms, meaning they are “saturated” with hydrogen atoms. These fats are typically found in animal products and are solid at room temperature. Excessive consumption of saturated fats is associated with increased risk of cardiovascular disease, not good health.

The other statements are true:

A cis double bond creates a bend in the hydrocarbon chain and is the type commonly found in nature, such as in unsaturated fatty acids (e.g., olive oil). Cis fats are generally considered beneficial for cardiovascular health.
Trans fats, which are artificially created through food processing, have trans double bonds and are associated with poor cardiovascular health. They are commonly found in processed foods and are linked to heart disease.
Thus, the incorrect statement is the one regarding saturated fats having carbon-to-carbon double bonds.

Question 17

Sickle-cell disease is caused by a mutation in hemoglobin that changes a charged amino acid to a hydrophobic amino acid. Where in the protein would you expect to find this charged amino acid?
on the exterior surface of the protein
in the interior of the protein, away from water
at the active site, binding oxygen
at the heme-binding site

Answer 17

The correct answer is: on the exterior surface of the protein

Explanation:
Charged amino acids are typically found on the exterior surface of proteins because they interact favorably with the aqueous environment (water) outside the protein. These amino acids can form hydrogen bonds or ionic interactions with water molecules, making them more stable on the protein’s surface.

In sickle-cell disease, a mutation occurs in the hemoglobin protein where the normal glutamic acid (a charged amino acid) is replaced by valine (a hydrophobic amino acid) at position 6 of the β-globin chain. This change from a hydrophilic to a hydrophobic residue causes the mutant hemoglobin molecules to stick together and form fibers, leading to the characteristic “sickle” shape of red blood cells.

Interior of the protein, away from water: Hydrophobic amino acids are typically found in the interior of the protein, away from water, to avoid unfavorable interactions. A charged amino acid is unlikely to be in this location under normal conditions.

At the active site, binding oxygen: The binding of oxygen in hemoglobin occurs at the heme-binding site, not necessarily involving this particular charged amino acid.

At the heme-binding site: The mutation in sickle-cell disease affects the surface of the protein, not the heme-binding site, which is where oxygen binds to the hemoglobin molecule.

Therefore, the charged amino acid would normally be found on the exterior surface of the protein, interacting with the surrounding water molecules.

Question 18

How does RNA differ from DNA?
DNA encodes hereditary information; RNA does not.
DNA forms duplexes; RNA does not.
DNA contains thymine; RNA contains uracil.
all of the above

Answer 18

The correct answer is: DNA contains thymine; RNA contains uracil.

Explanation of Each Statement:
DNA contains thymine; RNA contains uracil: This is true. In DNA, the nitrogenous base thymine (T) pairs with adenine (A). In RNA, uracil (U) replaces thymine and pairs with adenine. This is one of the primary differences between the two nucleic acids.

DNA encodes hereditary information; RNA does not: This statement is incorrect. While DNA is the primary molecule for storing hereditary information, RNA does play a role in encoding genetic information during processes like transcription and translation. For example, messenger RNA (mRNA) carries the genetic code from DNA to the ribosomes for protein synthesis.

DNA forms duplexes; RNA does not: This statement is also incorrect. While DNA typically exists as a double-stranded helix (duplex), RNA can also form complex secondary structures, including hairpins and loops, which may resemble duplexes in certain regions. However, RNA generally exists as a single-stranded molecule.

Summary:
The key difference between DNA and RNA is that DNA contains thymine, while RNA contains uracil. The other statements are either incomplete or incorrect.

RNA does encode hereditary information in RNA viruses, and RNA does form intramolecular duplexes: hairpins, pseudoknots, and other complex secondary structures.

Question 19

If you heat a cell to a moderately higher temperature than it is normally used to, which molecule will stop working first?
RNA
DNA
protein
lipid
carbohydrate

Answer 19

The correct answer is: protein

Explanation:
Proteins are highly sensitive to changes in temperature because their function depends on their 3D shape, which is held together by weak non-covalent interactions like hydrogen bonds, ionic bonds, and hydrophobic interactions. A moderate increase in temperature can cause proteins to denature—meaning they lose their shape and, consequently, their function. This happens before other molecules like DNA or lipids are affected.

RNA and DNA are more stable compared to proteins at moderate temperature increases, though at very high temperatures, they can start to break down.

Lipids become more fluid at higher temperatures but do not “stop working” as quickly as proteins do.

Carbohydrates are generally stable at moderate temperature increases and are less likely to be affected.

Thus, proteins will be the first molecules to stop functioning when a cell is exposed to higher temperatures.

Question 20

PROBLEM

If you wanted to extract the heaviest component of a membrane, you would need a protocol to extract
sterols.
phospholipids.
glycerol.
fatty acids.
none of the above.

Answer 20

The correct answer is: none of the above.

Explanation:
The heaviest component of a cell membrane is typically proteins, not the options listed (sterols, phospholipids, glycerol, or fatty acids). Membrane proteins, especially integral membrane proteins, are generally much heavier than lipids or other molecules in the membrane.

Phospholipids, sterols (like cholesterol), glycerol, and fatty acids are lighter compared to the proteins that make up a significant portion of the membrane’s mass.

Thus, none of the options provided (sterols, phospholipids, glycerol, or fatty acids) represent the heaviest component, as that would be proteins.

Question 21

MORE ADVANCED, DO I STUDY IN MORE DETAILS ON MY OWN?

If you substituted alanine for glycine in a protein, how much change to the protein’s structure would you expect?

little change, since these are both hydrophobic amino acids
much change, since one has a large side chain and the other a small side chain
some change, since one contains S and the other does not
little change, since amino acid identity doesn’t have much effect on protein function

Answer 21

A change from glycine to alanine in a protein could potentially cause structural changes, but because both amino acids are nonpolar or hydrophobic, these changes might not significantly disrupt the protein’s overall structure and function. It could, however, have subtle effects depending on the protein’s context.

Explanation:
Substituting alanine for glycine in a protein could potentially cause changes to the protein’s structure, as every protein’s unique sequence is determined by the gene encoding it. This concept is highlighted by cases like sickle cell anemia, where a single amino acid substitution in hemoglobin’s ß chain results in significant structural and functional changes to the protein.

Specifically, alanine and glycine differ primarily in their side chain, with glycine having a hydrogen atom as the R group, being nonpolar or hydrophobic, while alanine has a methyl group as its side chain, also being a nonpolar or hydrophobic amino acid. Therefore, substituting alanine for glycine might not significantly disrupt the protein’s overall structure and function, but it could potentially have subtle effects depending on the protein’s context.