DNA, RNA and Proteins

Question 1

Which type of mutation does not change an organism’s phenotype despite changing its genotype?
Silent

Nonsense

Missense

Frameshift

Answer 1

Silent

Explanation:
Silent mutations will change a DNA sequence without affecting the phenotype of the organism. This can occur either in an intron, which will not be translated, or by replacing a single nucleotide with another nucleotide without changing the amino acid recruited by the codon. Silent mutations often result from the degenercy of codons.

Frameshift, missense, and nonsense mutations, however, change both an organism’s genotype and phenotype by altering its DNA. A frameshift mutation results from the insertion or deletion of a nucleotide, causing a shift in the codon reading frame for every codon read after the mutation. Missense mutations replace one amino acid with another, and nonsense mutations result in a premature stop codon, terminating translation and resulting in a shortened protein.

Question 2

What would be an immediate consequence for a cell with a mutant version of DNA polymerase III that has lost its proofreading function?

Inability to replicate DNA

Inability to complete the cell cycle

A higher rate of mutations during replication

Cancer

Answer 2

Correct answer:
A higher rate of mutations during replication

Explanation:
Proofreading is a function of DNA polymerase III that helps prevent errors during replication. An immediate consequence of a cell that cannot proofread would be a higher rate of mutations during replication. The other options could potentially happen later in the cell’s life, but they would only occur as indirect results of the new mutations.

Question 3

Which of the following proteins are not situated within the core of the nucleosome?

H4

H2A

H2B

H3

H1

Answer 3

Correct answer:
H1

Explanation:
Histones are composed of several proteins, and are used to compact DNA within the nucleus. When DNA is wrapped around a group of eight histones, the resulting structure is a nucleosome.

The histone protein H1 is affixed on top of the nucleosome beaded structure, so as to keep the DNA that has wrapped around the nucleosome in place. It is not found in the core of the nucleosome.

H2A, H2B, H3, and H4 are very similar in structure and form the core of the histones

Question 4

Which of the following classes of proteins are essential for DNA mismatch repair?

All of these answers

DNA polymerase

DNA ligase

Nuclease

Answer 4

Correct answer:
All of these answers

Explanation:
For correct mismatch repair all three of the choices are essential. A nuclease is required to remove the damaged DNA. DNA polymerase is required to synthesize new DNA. DNA ligase is essential for synthesizing a phosphodiester bond between the newly synthesized DNA and the original DNA.

Question 5

Which enzyme is not involved in DNA replication?

Gyrase

Ligase

Lipase

Helicase

DNA polymerase

Answer 5

Correct answer:
Lipase

Explanation:
Lipase is the general name for an enzyme that breaks down lipids. Ligase joins the Okazaki fragments on the lagging strand of the DNA during replication. DNA polymerase is the enzyme that catalyzes the polymerization of nucleotides in the 5’ to 3’ direction. Helicase separates the two strands of the double helix to facilitate formation of the replication bubble. Gyrase relieves strain on the DNA while it is being unwound by helicase.

Question 6

Which enzyme has a proofreading ability during DNA replication?

Primase

DNA polymerase

DNA gyrase

DNA helicase

Answer 6

Correct answer:
DNA polymerase

Explanation:
Proofreading is an important part of the DNA replication process to ensure that if mismatched base pairs are incorporated into the newly synthesized DNA strands, they get replaced with correct base paired nucleotides. Mismatched base pairs have the potential to cause disease. DNA polymerases have proofreading abilities. They are able to remove mismatched nucleotides from the end of a newly synthesized strand. Post-replication repair mechanisms also exist to prevent damage and error.

Question 7

You are trying to perform in vitro DNA replication on a small circular piece of DNA. You have DNA polymerase, Primase, Helicase, DNA ligase and all of their accessory proteins. You can get DNA replication to initiate but it never goes for very long without stopping. You visualize your small piece of DNA under an electron microscope and notice that after the initiation of replication, it looks all knotted up. What enzyme can you add to remedy this problem?

Topoisomerase

Knottase

Reverse Transcipase

RNA polymerase

Telomerase

Answer 7

Correct answer:
Topoisomerase

Explanation:
As the replication fork of DNA proceeds and continues to unwind the double helix, the DNA upstream of the fork gets over wound and knotted up which will eventually arrest replication as the fork will not be able to proceed any further. The enzyme topoisomerase corrects for this overwinding ahead of replication forks by swiveling and rejoining DNA strands

Question 8

Which of the following characteristics is NOT seen in both DNA and RNA?

A double helix

Adenine

A pentose sugar

Read in the 5’-to-3’ direction

Answer 8

Correct answer:
A double helix

Explanation:
DNA and RNA share many characteristics. They are both composed of nucleotide monomers and are read in the 5’-to-3’ direction. They also share the same complementary base pairs, except RNA uses uracil in place of thymine; both contain adenine.

RNA does not present in a double helix structure, and is typically single stranded.

Question 9

A section of mRNA is composed of 28% guanine bases. What percentage of the RNA strand is cytosine bases?

More information is needed in order to answer this question.

22%

11%

28%

Answer 9

Correct answer:
More information is needed in order to answer this question.

Explanation:
Remember that mRNA is not a double helix like DNA; RNA is only one single strand of nucleotides. This means that we are unable to say that there are just as many cytosine bases as guanine bases, even though they would be able to form nucleotide pairs in DNA. For all we know, there could be zero cytosine bases! More information is needed before we can make a conclusion as to how many cytosine bases are in the RNA section.

Question 10

Which of the following statements is correct about the differences between DNA and RNA?

DNA is not present in prokaryotes, while RNA is

The sugar molecule in RNA has one more hydroxyl group than the sugar molecule in DNA

DNA is present as a single-stranded molecule while RNA is double-stranded

RNA contains the same bases as DNA, except uracil is present instead of guanine

RNA is synthesized from DNA during transcription, but DNA can never be synthesized from RNA

Answer 10

Correct answer:
The sugar molecule in RNA has one more hydroxyl group than the sugar molecule in DNA

Explanation:
The only correct statement here is the one regarding the types of sugar in the two molecules. RNA stands for “ribonucleic acid,” which is a simple way to remember that it contains the sugar ribose. DNA, on the other hand, stands for “deoxyribonucleic acid.” Its sugar is deoxyribose, which is identical to ribose except it is missing a hydroxyl (-OH) group on its second carbon. In total, RNA contains three hydroxyl groups, while DNA contains only two.

In RNA, uracil replaces thymine, not guanine. DNA is generally double-stranded and RNA is generally single-stranded (though both can exist in either form). Prokaryotes contain both DNA and RNA. Finally, DNA is transcribed to RNA in most biological organisms, but RNA can be reverse transcribed to DNA by the protein reverse transcriptase, which is found in some viruses.

Question 11

Which of the following statements is false?

DNA is a polyanion, while RNA is a not

DNA is typically double-stranded, while RNA is typically single-stranded

DNA uses thymine, while RNA uses uracil

DNA and RNA utilize different sugars in their sugar-phosphate backbones

Answer 11

Correct answer:
DNA is a polyanion, while RNA is a not

Explanation:
Both DNA and RNA are polyanions. This is just a fancy way of saying that they are polymers of negatively charged molecules. The phosphate groups in the sugar-phosphate backbone account for this, as phosphate groups generally carry a charge of negative three.

DNA uses thymine and deoxyribose sugar, while RNA uses uracil and ribose sugar. While DNA is usually molded into a double-stranded helix, RNA is usually single-stranded, which allows for the binding of anticodons during translation.

Question 12

Which of the following is characteristic of RNA?

RNA is a permanent molecule in most cells

RNA is less stable than DNA

RNA is typically double-stranded

RNA has a hydroxyl group on the 2’ carbon of ribose

Answer 12

Correct answer:
RNA has a hydroxyl group on the 2’ carbon of ribose

Explanation:
RNA and DNA are very similar in composition, but differ in structure and function. DNA is used to code for genetic material, while RNA is used to generate protein products. Since DNA has a long-term goal of storing information and RNA has a short-term goal of increasing production, it makes sense that DNA is a permanent molecule and RNA is transient. Soon after translation, mRNA is degraded by ribonuclease (RNase). The transient nature of RNA is also linked to its stability. DNA must be very stable to avoid problems with gene storage. DNA is double-stranded to help enhance stability. In contrast, RNA can afford to be less stable and is easily degraded, partially due to its single-stranded structure.

Another key difference between DNA and RNA is the sugar component of the nucleic acid backbone. DNA uses deoxyribose, which lacks a hydroxyl (-OH) group on the 2’ carbon. RNA uses ribose, in which this hydroxyl group is present on the 2’ carbon.

Question 13

Which of the following is not a true characteristic of an RNA molecule?

It can be double stranded

It can be single stranded

It contains deoxyribose sugar

It contains the nucleotide uracil

Answer 13

Correct answer:
It contains deoxyribose sugar

Explanation:
RNA molecules are most commonly found in a single stranded form (e.g. mRNA), but they can also be found in a double stranded form (e.g. viruses). It has four base pairs—uracil, adenine, guanine, and cytosine—and a ribose sugar-phosphate backbone. DNA molecules contin a deoxyribose sugar in their sugar-phosphate backbone; thus, this answer is incorrect.

Question 14

Which of the following types of RNA is double stranded?

Viral RNA

rRNA

tRNA

mRNA

Answer 14

Correct answer:
Viral RNA

Explanation:
Many types of RNA exist within cells, some are single stranded and others are double stranded. The following are among the types of single stranded RNA: mRNA (messenger RNA), tRNA (transfer RNA), and rRNA (ribosomal RNA). Messenger or mRNA carries genetic information from DNA to ribosomes for protein synthesis. Transfer or tRNA carries amino acids to ribosomes that match with mRNA codons. Last, ribosomal or rRNA codes for ribosomes, which are necessary for protein synthesis. An example of a double stranded RNA molecule is viral RNA. Viral RNA is the genetic material of many viruses and has a structure of two complementary strands.

Question 15

Which of the following choices is an element common to both DNA and RNA molecules?

Both are often single-stranded

They can both be found in the nucleus

There is deoxyribose sugar in both of their sugar-phosphate backbones

Both contain the nucleotide uracil

Answer 15

Correct answer:
They can both be found in the nucleus

Explanation:
DNA is a macromolecule that has a double helical form. It has four nitrogenous base pairs (thymine, adenine, cytosine, and guanine) and a deoxyribose-phosphate backbone. The two strands of the helix are joined by hydrogen bonds. On the other hand, RNA molecules can be double-stranded (e.g. viruses) or single-stranded (e.g. mRNA), but RNA most commonly exists in a single-stranded form. RNA contains four base pairs (uracil, adenine, cytosine, and guanine) and a ribose sugar-phosphate backbone. Despite their differences, these molecules share one similarity: both DNA and RNA molecules can be found in the nucleus. DNA molecules reside solely within the nucleus. RNA is transcribed in the nucleus and, once targeted and post-transcriptionally modified, can leave via nuclear pores.

Question 16

Which of the following are correct regarding the central dogma of biology?

RNA signals DNA to activate protein production

DNA directs the synthesis of mRNA, which in turn directs the production of polypeptides

RNA encodes the information for the assembly of ribosomes, which are the sites of protein production

RNA assists with the replication of DNA which encodes information for proteins

Answer 16

Correct answer:
DNA directs the synthesis of mRNA, which in turn directs the production of polypeptides

Explanation:
DNA encodes information for the production of messenger RNA which then interacts with the cell’s protein-synthesizing machinery to produce proteins. Ribosomes are the sites of polypeptide synthesis but are not coded for by RNA. The central dogma of biology is DNA → RNA → protein

Question 17

Which of the following are properties of RNA?

Ribose, uracil, and a linear structure

Ribose, thymine, and a linear structure

Deoxyribose, uracil, and a globular structure

Deoxyribose, thymine, and a linear structure

Deoxyribose, ribose, and uracil

Answer 17

Correct answer:
Ribose, uracil, and a linear structure

Explanation:
Remember that the sugar for DNA is deoxyribose, and that for RNA is ribose. The nitrogenous bases adenine, guanine, and cytosine in DNA and RNA are the same. However, DNA which contains thymine and RNA that contains uracil. The structure of DNA is a double helix. There are three different structures of RNA: linear, clover-leaf, and globular. Also note that RNA is single stranded and DNA is double stranded

Question 18

The entire collection of DNA in a cell is called the __________.

chromatin

genome

DNA ladder

chromosome

nucleus

Answer 18

Correct answer:
genome

Explanation:
The genome is defined as the total genetic library of a cell. It is estimate that in humans, the genome codes for about 25,000 different genes.

Question 19

DNA with its associated protein scaffold forms a complex called __________.

chromatid

centromere

chromosome

chromatin

nucleotide

Answer 19

Correct answer:
chromatin

Explanation:
Chromatin is the DNA-protein complex and is organized as a long, thin fiber. Chromosomes are densely-packed chromatin, wrapped around proteins called histones. The centromere is the region of a condensed chromosome that connects sister chromatids to each other, and is the site at which the spindle fibers attach during mitosis in order to move them about the cytoplasm.

Question 20

In DNA adenine (A) bonds to thymine (T) and guanine (G) bonds to cytosine (C). What is the bonding scheme in RNA?

A-C and G-U

A-G and C-U

A-U and C-G

A-T and C-G

None of these

Answer 20

Correct answer:
A-U and C-G

Explanation:
In RNA, thymine is substituted by uracil. So adenine will bond to uracil instead of thymine when RNA interacts with DNA and when RNA folds with itself to make a 3-dimensional structure.

Question 21

Which of the following molecules is not present in DNA?

Thymine

Uracil

Deoxyribose sugar

All of these

Phosphate

Answer 21

Correct answer:
Uracil

Explanation:
Uracil is a nitrogenous base that is only found in single-stranded RNA—it is not found in DNA. Thymine pairs with adenine in DNA, whereas in RNA, uracil pairs with adenine.

Question 22

Which of the following base pairs is found only in RNA?

Thymine

Uracil

Adenine

Guanine

Cytosine

Answer 22

Uracil

Explanation:
Uracil is the base pair that is used in ribonucleic acid (RNA) in the place of thymine. The other three bases adenine, guanine and cytosine are found in both DNA and RNA.

Question 23

All of the following bases are found in RNA except __________.

uracil

guanine

cytosine

adenine

thymine

Answer 23

Correct answer:
thymine

Explanation:
Uracil is only found in RNA under normal conditions. It replaces thymine, which is only found in DNA. Therefore, thymine, adenine, cytosine, and guanine are the bases found in DNA, and uracil, adenine, cytosine, and guanine are the bases found in RNA.

Question 24

Who were the two scientists who developed the model of DNA as a double helix in 1953?

Pauling and Corey

Pasteur and Mitterand

Gilbert and Maxam

Watson and Crick

Answer 24

Watson and Crick

Explanation:
Watson and Crick were the two scientists who developed the model of DNA as a double helix in 1953.

Question 25

In the messenger RNA, with which base on DNA does uracil pair?

Cytosine

Thymine

Guanine

Adenine

Answer 25

Adenine

Explanation:
Uracil in RNA bonds to adenine on the DNA template during transcription. These two nitrogenous bases form two hydrogen bonds.

Question 26

What would be the sequence of mRNA translated from the DNA segment 5’ - ACGTCA - 3’ ?

5’ TACTTU 3’

5’ UGCAGU 3’

5’ TGCAGT 3’

5’ UCGAGU 3’

5’ UGACGU 3’

Answer 26

Correct answer:
5’ UGACGU 3’

Explanation:
mRNA contains uracil instead of thymine, therefore your answer should not contain the base thymine. Remember, DNA is read in the 3’ to 5’ direction and the corresponding strand is created in the 5’ to 3’ direction. It is important to pay attention to polarity of the strands. Adenine pairs with thymine, and/or uracil. Guanine pairs with cytosine.

Question 27

Which of the following RNA molecules transports amino acids to ribosomes to be used to assemble the protein molecule?

rRNA

snRNA

mRNA

pre-mRNA

tRNA

Answer 27

Correct answer:
tRNA

Explanation:
mRNA is messenger RNA, it carries the genetic code that determines the protein. snRNA directs splicing of pre-mRNA. tRNA transports the amino acids used for assembling proteins. rRNA is a component of ribosomes (the other component is protein). pre-mRNA- single strand of RNA processed to form mRNA.

Question 28

The most prevalent negative charge on DNA can be found on which of the following molecular components?

Hydroxyl residues

Ribose sugar ring

Hydrogen bonds between base pairs

Phosphate backbone

Phosphodiester linkage

Answer 28

Phosphate backbone

Explanation:
The phosphate backbone of DNA is negatively charged due to the bonds created between the phosphorous atoms and the oxygen atoms. Each phosphate group contains one negatively charged oxygen atom, therefore the entire strand of DNA is negatively charged due to repeated phosphate groups.

Question 29

Nitrogen : Nucleic Acids :: Phosphorous : ______________.

All answer choices

ATP

DNA

Phospholipids

ADP

Answer 29

Correct answer:
All answer choices

Explanation:
Nitrogen is essential to create all the nucleic acids, and phosphorous is essential to create phospholipids (an obvious choice), ATP and ADP (they are the same class of molecule, and the P stands for phosphate), and DNA (for the phosphate-sugar backbone).

Question 30

Which of the following is not true of a DNA molecule?

Complementary strands are held together by hydrogen bonds

A purine or pyrimidine is bound to each sugar-phosphate group

Uracil is not a component of the molecule

Adenine and thymine are held together by phosphodiester bonds

Answer 30

Correct answer:
Adenine and thymine are held together by phosphodiester bonds

Explanation:
DNA is a polymer composed of nucleotide monomers. Each nucleotide is formed from a deoxyribose sugar, a phosphate, and a nitrogenous base. There are two types of nitrogenous bases: purines and pyrimidines. The purines are adenine and guanine, while the pyrimidines are thymine and cytosine (and uracil). Adenine will always bind thymine and cytosine will always bind guanine. Uracil is only found in RNA, and is absent from DNA.

During DNA replication and synthesis, nucleotides align so that the nitrogenous bases are correctly paired. The bases bind to one other via hydrogen bonding to secure the nucleotide to the template strand. The protein DNA ligase then fuses the sugar-phosphate groups of adjacent nucleotides to create the DNA backbone. These bonds are known as phosphodiester bonds.

The only false statement concerns the identity of bonding between nitrogenous bases. Bases are held together by hydrogen bonds, and the DNA backbone is held together by phosphodiester bonds.

Question 31

A __________ bond between the sugar of one nucleotide and the phosphate of an adjacent nucleotide stabilizes the backbone of the DNA.

weak

hydrogen

covalent

metallic

ionic

Answer 31

Correct answer:
covalent

Explanation:
The bond formed between the sugar of one nucleotide and the phosphate of an adjacent nucleotide is a covalent bond. A covalent bond is the sharing of electrons between atoms. A covalent bond is stronger than a hydrogen bond (hydrogen bonds hold pairs of nucleotides together on opposite strands in DNA). Thus, the covalent bond is crucial to the backbone of the DNA.

Question 32

Which of the following nitrogenous bases is used to produce RNA, but not DNA?

Adenine

Guanine

Thymine

Uracil

Answer 32

Correct answer:
Uracil

Explanation:
Uracil is bound to adenine in the production of RNA, while thymine is used in its place in the production of DNA. Adenine, guanine, and cytosine are all used in the production of both RNA and DNA.

Question 33

How many total hydrogen bonds would there be between base pairs of a piece of DNA if the sequence of one side was CGTTTGAC?

22

18

8

20

22

Answer 33

Correct answer:
20

Explanation:
Cytosine and guanine form three hydrogen bonds between each other, while tyrosine and adenine form two hydrogen bonds. We simply need to count how many of each base we have and multiple cytosine and guanine by three, and thymine and adenine by two.

CGTTTGAC has 2 cytosine, 2 guanine, 3 thymine, and 1 adenine.

3(2C)+3(2G)+2(3T)+2(1A)=20

Question 34

What element would you NOT find in either DNA, or RNA?

Hydrogen

Nitrogen

Carbon

Potassium

Phosphorus

Answer 34

Correct answer:
Potassium

Explanation:
DNA and RNA are made of nucleotides, which contain oxygen, hydrogen, nitrogen, carbon, and phosphorus. The nucleic acid backbone is comprised of sugars, made of carbon, hydrogen, and oxygen, and phosphate groups, made of phosphorus, hydrogen, and oxygen. The backbone binds to bases, which contain a nitrogen element.

Potassium is not found in nucleic acid structure, and is used in other parts of the body like muscles and nerves for signal propagation.

Question 35

What are the components of a nucleoside?

A nitrogenous base and a phosphate

A nitrogenous base and a ribose or deoxyribose sugar

A nitrogenous base, a ribose or deoxyribose sugar, and a phosphate group

A ribose or deoxyribose sugar and a phosphate

Answer 35

Correct answer:
A nitrogenous base and a ribose or deoxyribose sugar

Explanation:
This question is mostly about the differentiations between a nucleoside and a nucleotide. A nucleoside is composed of a nitrogenous base and a ribose or deoxyribose sugar. A nitrogenous base, a ribose/deoxyribose sugar, and a phosphate describe a nucleotide. Remember that nucleosides are incomplete nucleotides, and lack a phosphate group.

Question 36

Which of the following is a reason that cytosine pairs more favorably with guanine than thymine or adenine?

Maximized number of hydrogen bonds

Ionic interactions between the bases

A covalent bond is formed

Bond energy is maximized

Answer 36

Correct answer:
Maximized number of hydrogen bonds

Explanation:
Cytosine and guanine, when base paired, have three hydrogen bonds between them. Adenine and thymine only have two. This extra hydrogen bond helps make the cytosine-guanine pair favorable because it increases stability, and reduces bond energy.

Ionic and covalent bonds do not occur between nitrogenous bases in DNA. Covalent bonds are found in the DNA backbone (known as phosphodiester bonds).

Question 37

Chargaff is credited with which of the following discoveries about DNA base pairs?

The ratio of adenine to cytosine is close to 1:1 and the ratio of guanine to thymine is close to 1:1

A+T=G+C

The ratio of adenine to thymine is close to 1:1 and the ratio of guanine to cytosine is close to 1:1

A⋅T=C⋅G

The ratio of adenine to guanine is close to 1:1 and the ratio of cytosine to thymine is close to 1:1

Answer 37

Correct answer:
The ratio of adenine to thymine is close to 1:1 and the ratio of guanine to cytosine is close to 1:1

Explanation:
Due to DNA’s double-helical structure, the nucleotide bases are paired. Adenine is paired with thymine and guanine is paired with cytosine. Chargaff found that there is typically an equivalent number of adenine and thymine bases, and an equivalent number of guanine and cytosine bases. In a given sample of DNA, all adenine residues will have thymine counterparts on the complementary strand, and all cytosine residues will have complementary guanine counterparts. As a result, there will be equal numbers of each residue of the base pair in any sample of double-stranded DNA.

Question 38

Which of the following choices displays complementary DNA strands?

3’-AUUGC-5’

5’-UAACG-3’

3’-ATTGC-5’

5’-ATTGC-3’

3’-ATTGC-5’

3’-TAACG-5’

3’-ATTGC-5’

5’-TAACG-3’

Answer 38

Correct answer:
3’-ATTGC-5’

5’-TAACG-3’

Explanation:
When determining complementary strands, there are a few important points to consider. First, remember that uracil is only found in RNA. We can eliminate any answer choices that contain uracil. Second, remember that DNA is anti-parallel. This means that the 3’ end of the template strand must match up with the 5’ end of the complementary strand. Flip any answers that have both 3’ ends together. Finally, make sure that the bases align correctly. Adenine and thymine should always pair and cytosine and guanine should always pair.

Template strand: 3’-ATTGC-5’

Complementary strand is antiparallel: 5’-_ _ _ _ _-3’

Complementary strand must have right base pairs: 5’-TAACG-3’

An alternate way of writing this answer would be 3’-GCAAT-5’. This answer would still be correct! It would simply need to be flipped, as in the second step outlined above.

Question 39

Which of the following could be a segment of DNA?

5’-GTCGAT-3’

3’-GATCTC-5’

5’-CTAGAG-3’

3’-GATCTC-5’

5’-AGATAG-3’

3’-GATCTC-5’

5’-CTCGTG-3’

3’-GATCTC-5’

5’-CTCGTG-3’

3’-AATGTA-5’

Answer 39

Correct answer:
5’-CTAGAG-3’

3’-GATCTC-5’

Explanation:
DNA is a double stranded molecule that is antiparallel, meaning the 5’ end of one strand matches up with the 3’ end of the other strand. Nitrogenous bases hold the strands together via hydrogen bonding. These bases are adenine (A), thymine (T), guanine (G), and cytosine (C). Adenine (A) can only pair with thymine (T), and guanine (G) can only pair with cytosine (C).

The correct answer presents two strands that are antiparallel and show proper binding patterns.

5’-CTAGAG-3’

3’-GATCTC-5’

All other answers have an error in base pairing or ordering.

Question 40

Which of the following describes the components of a nucleotide?

ATP, a hexose sugar, and an amino acid

A phosphate group, a pentose sugar, and a nitrogenous base

A phosphate group, a pentose sugar, and an amino acid

A phosphate group, a hexose sugar, and a nitrogenous base

ATP, a pentose sugar, and a nitrogenous base

Answer 40

Correct answer:
A phosphate group, a pentose sugar, and a nitrogenous base

Explanation:
Nucleic acids are one of the main biological macromolecules, and include DNA and RNA. A nucleotide is a DNA monomer, while a ribonucleotide is an RNA monomer. Numerous nucleotides are bonded together by phosphodiester bonds to form a single molecule of DNA. The pattern of nucleotides is used to store and transmit hereditary information. A nucleotide is composed of a phosphate group, a nitrogenous base, and a pentose sugar (deoxyribose).

Question 41

Which of the following DNA primers has the lowest melting point?

GCCACAGGTGGA

AGGTGGACACCG

TGACAAACTTGT

CATGCGTAGATC

GCGGATGTGTCC

Answer 41

Correct answer:
TGACAAACTTGT

Explanation:
Cytosine and guanine form three hydrogen bonds with each other, while adenine and tyrosine only form two hydrogen bonds. This means that strands of DNA with a higher percentage of cytosine and guanine will have higher melting points.

Since we are looking for the sequence with the lowest melting point, we want the lowest percentage of cytosine and guanine, and the highest percentage of adenine and thymine.

Question 42

A section of double-stranded DNA is composed of 35% adenine bases. What is the percentage of cytosine bases in the section of DNA?

65%

15%

20%

30%

Answer 42

15%

Explanation:
Since we know that 35% of the bases in the section of DNA are adenine, we can conclude that 35% of the bases are thymine. This is because adenine will always pair with thymine, so there will be just as many thymine bases as adenine bases. Together, adenine and thymine compose 70% of the segment.

This means that 30% of the section is composed of guanine-cytosine pairs.

Since these two bases will be equal in quantity, 15% of the DNA section will be cytosine bases.

Question 43

In a sample of DNA, 30% of the bases are found to be guanine. What percentage of the bases in the sample are thymine?

60%

30%

20%

25%

40%

Answer 43

Correct answer:
20%

Explanation:
Guanine will pair with cytosine. From this knowledge, we can assume that there will be an equal number of guanine and cytosine residues in the sample. Each guanine must have a cytosine counterpart.

The total composition of the DNA sample must be accounted for by the sum of all the bases.

Use the known values for guanine and cytosine to find the sum of adenine and thymine.

Like cytosine and guanine, adenine and thymine must be present in equal amounts in order to form proper base pairs. We can reasonably assume that half of the remaining DNA will consist of each residue.

Question 44

An analysis of a DNA sample indicates it contains 35% adenine. What percent of the sample would be cytosine?

25%

35%

30%

15%

20%

Answer 44

Correct answer:
15%

Explanation:
There are four nitrogenous bases found in DNA: adenine, thymine, cytosine, and guanine. Adenine always binds with thymine, and cytosine always binds with guanine.

Since certain bases always appear in pairs, they will have equal percentages of the DNA composition. The percentage of adenine will equal the percentage of thymine, and the percentage of cytosine will equal the percentage of guanine. Together, these percentages will add to 100%.

A=T, C=G, A+T+C+G=100

We know that the sample is 35% adenine, which tells us that it is also 35% thymine.

A=T=35, 35+35+C+G=100

C+G=30

We know that cytosine and guanine pair together and will be present in equal amounts, so we can divide this final total by 2 to find our answer.

30÷2=15, C=G=15

The sample is 35% adenine, 35% thymine, 15% guanine, and 15% cytosine.

Question 45

A strand of DNA was measured to contain 22% adenine. What is the DNA’s composition of the other bases?

22% Adenine, 22% Uracil, 28% Cytosine, 28% Guanine

22% Adenine, 22% Guanine, 28% Cytosine, 28% Uracil

22% Adenine, 22% Cytosine, 28% Guanine, 28% Thymine

22% Adenine, 22% Guanine, 28% Cytosine, 28% Thymine

22% Adenine, 22% Thymine, 28% Cytosine, 28% Guanine

Answer 45

Correct answer:
22% Adenine, 22% Thymine, 28% Cytosine, 28% Guanine

Explanation:
We can use Chargaff’s rule to find the remaining compositional percentages. Adenine always pairs with thymine, so their percentages will be equal. Cytosine always pairs with guanine, so their percentages will also be equal. The sum of all four percentages must equal 100%.

A=T, C=G, A+T+C+G=100%

We know that the sample is 22% adenine; this tells us it is also 22% thymine.

A=T=22%

22%+22%+C+G=100%

C+G=56%

Since cytosine and guanine are present in equal amounts, we can simply divide their sum by 2.

56%÷2=28%

C=G=28%

The final composition is 22% adenine, 22% thymine, 28% cytosine, and 28% guanine.

Uracil is only found in RNA.

Question 46

A strand of RNA is composed of 20% adenine and 30% guanine.

What is the strand’s composition of the other bases?

20% Adenine, 30% Guanine, 20% Uracil, 30% Cytosine

20% Adenine, 30% Guanine, 30% Thymine, 20% Cytosine

20% Adenine, 30% Guanine, 20% Thymine, 30% Cytosine

Cannot determine from the given information

20% Adenine, 30% Guanine, 30% Uracil, 20% Cytosine

Answer 46

Correct answer:
Cannot determine from the given information

Explanation:
Chargaff’s rule only applies to DNA. RNA is single-stranded, and thus, no base pairing occurs.

Think of a strand of DNA. Each base pairs with a specific partner, allowing us to determine their percentages: adenine and thymine are always equal, and cytosine and guanine are always equal. In RNA, with this pairing absent, there is no correlation between the base percentages. A strand could be 20% adenine, 30% guanine, 5% cytosine, and 45% uracil; we simply cannot draw any conclusions.

Question 47

What are the monomers of DNA?

Nucleotides

Deoxyribose sugars

Phosphate-sugar backbone

Nitrogen atoms

Answer 47

Correct answer:
Nucleotides

Explanation:
A polymer is a macromolecule that is made up of subunits that are repeated or very similar. These subunits are called monomers. DNA is a polymer made up of monomer units called nucleotides. Nucleotides are made up of a phosphate group, a five-carbon sugar (deoxyribose, in the case of DNA), and a variable nitrogenous base. There are four different nucleotides that make up the polymer of DNA: thymine, cytosine, adenine, and guanine. These four nucleotides belong to two different classes based on structure. Adenine and guanine are purines that have two carbon-nitrogen rings. Thymine and cytosine are pyrimidines that have only one carbon-nitrogen ring.

Question 48

Which base pair can be found in a DNA molecule?

Guanine-thymine

Cytosine-thymine

Guanine-cytosine

Adenine-guanine

Answer 48

Correct answer:
Guanine-cytosine

Explanation:
Within a DNA molecule, there are specific nucleotide binding patterns, a phenomenon called “complementary base pairing.” Specific pyrimidine nucleotides can only bind to specific purine bases: cytosine binds to guanine via three hydrogen bonds and adenine binds to thymine via hydrogen bonds. Normally, within a DNA molecule, no other base pair combinations exist. These specific complementary base pairs allow DNA to take the form of a double helix. The double helix can be most simply described as a twisted ladder; the base pairs and their hydrogen bonds represent the rungs, and the sugar-phosphate backbone represents the sides of the ladder.

Question 49

What type of bonding occurs between the two parallel strands of nucleic acids in DNA?

Ionic bonding

Covalent bonding

Double bond

Hydrogen bonding

Single bond

Answer 49

Correct answer:
Hydrogen bonding

Explanation:
The bonding that occurs between two parallel strands of nucleic acids in DNA is hydrogen bonding. As you know, hydrogen bonding occurs between molecules containing fluorine, nitrogen and oxygen with other fluorine, nitrogen and oxygen atoms. This is a fairly weak bond but there are so many hydrogen bonds along a strand of DNA making the attachment between the two quite strong, but the two strands can still be separated as needed (during replication and transcription). Adenine and thymine form two hydrogen bonds, while cytosine and guanine form three hydrogen bonds.

Question 50

What are four possible chromosome structure abnormalities?

Synapsis, duplication, inversion, translocation

Deletion, independent assortment, inversion, duplication

Polyploidy, deletion, inversion, translocation

Nondisjunction, deletion, duplication, inversion

Deletion, duplication, inversion, translocation

Answer 50

Correct answer:
Deletion, duplication, inversion, translocation

Explanation:
Chromosomal related mutations include deletion, duplication, inversion, or translocation. Nondisjunction is a faulty separation event of homologous chromosomes but does not necessarily involve improper chromosome structures. Independent assortment is a mendelian inheritance principle which states chromosomes are divided randomly into two daughter cells. Synapsis is a normal pairing up event of homologous chromosomes in prophase I. Polyploidy is a condition of having more than two sets of chromosomes and is typically a characteristic of a species, not an abnormality.

Question 51

During DNA synthesis, DNA polymerase mistakenly substitutes a purine (adenine or guanine) for a pyrimidine (cytosine or thymine). This is known as what type of mutation?

Inversion

Replacement substitution

Transversion

Transition

Silent mutation

Answer 51

Correct answer:
Transversion

Explanation:
The substitution of a purine for a pyrimidine, or vice versa, is called a transversion. The substitution of one purine for another or one pyrimidine for another is called a transition. Either of these can be referred to as a point mutation, but transversion is the most specific answer to this question.

Question 52

Which of the following is not a component of nucleic acids?

Sugar

Phosphate group

Tyrosine

Adenine

Guanine

Answer 52

Correct answer:
Tyrosine

Explanation:
Nucleic acids are made up of nitrogenous bases and a sugar-phosphate backbone. The sugar will vary depending on if it is an RNA or DNA molecule that’s being discussed. RNA has ribose while DNA has deoxyribose. The nitrogenous bases are guanine, adenine, thymine, cytosine and uracil. Tyrosine is an amino acid, therefore not involved in the composition of nucleic acids.

Question 53

Which of the following statements about post-transcriptional processing is true?

A methylguanine cap is added to the 3’ end of the mature mRNA

Post-transcriptional hnRNA processing prevents RNA from degrading as it leaves the nucleus

A poly-A tail is added to the 5’ end of the mature mRNA

Exons are spliced out of hnRNA and are not part of the mature mRNA

Answer 53

Correct answer:
Post-transcriptional hnRNA processing prevents RNA from degrading as it leaves the nucleus

Explanation:
The hnRNA (heterogeneous nuclear RNA) produced from transcription must be processed by several enzymes to create an mRNA (messenger RNA) product that can pass from the nucleus to the cytoplasm without degrading. This involves cutting out introns, which remain in the nucleus, and splicing exons together. Furthermore, a methylguanine cap is added to the 5’ end and a poly-A tail is added to the 3’ end.

Question 54

Which of the following is not an example of a post-transcriptional modification of mRNA molecules?

Addition of a 5-methyl guanosine cap

Splicing of anticodons

Splicing of introns

Addition of a poly-A tail

Answer 54

Correct answer:
Splicing of anticodons

Explanation:
Addition of a 5-methyl guanosine cap, the splicing out and removal of introns, and the addition of a poly-A tail are all processes that are essential to making stable, mature mRNA.

Codons are contained on the exons of mature mRNA and are matched to appropriate anticodons during translation. Anticodons are found on tRNA molecules, and are not involved in mRNA transcription.

Question 55

Which biotechnology method will allow you to distinguish between identical twins?

Southern blot

Restriction fragment length polymorphism (RFLP) Analysis

Standard fingerprinting

DNA fingerprinting

Answer 55

Correct answer:
Standard fingerprinting

Explanation:
Fingerprints are different in all individuals, even identical twins. Due to RNA processing, or post-transcription modification, the grooves of a finger are different even in individuals with identical DNA.

The other techniques are used for DNA analysis between individuals with different DNA. Identical twins will be indistinguishable under these techniques, because their DNA is the same.

Question 56

Which of the following statements is false concerning post-transcriptional modification?

A poly A tail is attached to the 3’ end of the transcript

Spliceosomes remove exons from the transcript and splice together the introns

Both the 5’ cap and poly A tail protect the transcript from degradation

A 5’ cap is added in order to provide an attachment site for ribosomes during translation

Methylation is not part of post-transcriptional modification

Answer 56

Correct answer:
Spliceosomes remove exons from the transcript and splice together the introns

Explanation:
During post-transcriptional modification, spliceosomes can remove introns from the transcript and splice together exons. Introns are the parts that are removed from the transcript, meaning they are not translated. Exons are the portions of mRNA that code for the correct amino acids sequence for the desired gene.

Other modifications involve the poly-A tail, which is added to the 3’ end, and the 5’ cap. Both structures protect the transcript from damage during transport and provide binding sites for various proteins, as well as the ribosome itself. Methylation is a part of epigenetic DNA modification, and is not involved with transcription processes.

Question 57

snRNPs assist in what post-transcriptional modification?

Addition of the 5’ cap

Exporting the transcript to the ribosome

The removal of introns

Addition of the poly-A tail

Answer 57

Correct answer:
The removal of introns

Explanation:
snRNPs, or small nuclear ribonucleoproteins, are an essential part of the spliceosome complex. The spliceosome is responsible for the removal of introns from the primary transcript.

Question 58

Which of the following is not an example of eukaryotic post-transcriptional modification?

The 3’ end of the growing strand is cleaved

A methylguanosine cap is added to the 5’ end

A poly-A tail is added to the 3’ end

Exons, or non-coding regions, are removed via splicing

After splicing, the exons are rejoined to form a final mRNA transcript

Answer 58

Correct answer:
Exons, or non-coding regions, are removed via splicing

Explanation:
Post-transcriptional modifications are changes that are made to the mRNA transcript before it is translated into a protein. The first of these changes is cleavage at the 3’ end to separate the new strand, or “primary transcript,” from the transcription machinery. Next, a protective 5’ cap is added, as is a string of adenine nucleotides at the 3’ end. Finally, noncoding regions, called introns, are spliced out and the exons, or coding regions, are reconnected.

The incorrect statement confuses exons and introns.

Question 59

Which of the following choices is not one of the processes associated with post-transcriptional modification?

5’ capping

Polyadenylation

Protein folding

Splicing

Answer 59

Correct answer:
Protein folding

Explanation:
Post-transcriptional modification is the stage where the recently synthesized primary RNA transcript undergoes changes to become a mature RNA molecule. Post-transcriptional modifications ensure that the correct RNA transcripts are produced and that the correct proteins are translated. Post-transcriptional modification includes the processes of polyadenylation, 5’ capping, and splicing. Polyadenylation is the addition of adenine bases (the poly-A tail) to the 3’ end of the RNA primary transcript. The poly-A tail is important in export, stability, and translation of the transcript. 5’ capping is the addition of guanine bases to the 5’ end of the primary transcript. The 5’ cap aids in export and translation of the transcript and also protects it from degradation. Splicing is the removal of non-coding regions, or introns, from the primary transcript.

Question 60

Which of the following choices is not a true characteristic of spliceosomes?

Most spliceosomes are found in the nucleus

They splice introns from primary RNA transcripts

They are composed of small nuclear RNA molecules (snRNAs)

Both prokaryotes and eukaryotes have spliceosomes

Answer 60

Correct answer:
Both prokaryotes and eukaryotes have spliceosomes

Explanation:
The spliceosome is a complex structure composed of small nuclear RNA molecules (snRNAs) and other proteins. They are often located in the nucleus. The spliceosome splices introns from the primary RNA transcript. This process occurs through splicing at 5’ and 3’ sites that are identified by particular nucleotide sequences. Prokaryotic cells do not contain spliceosomes.

Question 61

Which of the following statements is false?

A codon will always code for the same amino acid

An amino acid can only be produced from one codon

More than one codon can code for the same amino acid

tRNA will always carry one amino acid to the ribosome

Answer 61

An amino acid can only be produced from one codon

The genetic code is degenerative, meaning that multiple codons can code for the same amino acid. It is also unambiguous: a pafticular codonwill always code for one amino acid. That being said, it would be wrong to assume that an amino acid will only have one codon, as an ami o acid can have multiple different codons that code for it.

Question 62

Which of the following statements concerning translationis true?

The poly A tail serves as an attachment site for the ribosome

The growing amino acid chain is found in the P site of the ribosome

The first amino acid, methionkne, is positioned in the A site of the ribosome

mRNA is read by the ribosome in 3’-to-5’ directiln

Answer 62

The growing amino acid chain is found in the P site of the ribosome

In translation, the mRNA is positioned in the ribosome and read in the 5’-to-3’ direction. Initiation of translation is triggered by a tRNA attached to a methionine entering the P site of the ribosome. The mRNA will then be read, and additional amino acids will be added to the chain, which grows in the P site. New tRNA enters the A site and old tRNA exits the E site, but the ami o acid chain is always anchored to the rRNA in the P site.

Question 63

What happens when the ribosome encou ters a stop codon?

A release factor is recruited, which dissociates the translation complex and releases the completed polypeptide chain

An anti-codon pairing is made with a final tRNA that releases the completed polypeptide chain

A chaperone is recruited to help fold the polypeptide chain

A special terminal amino acid is placed on the polypeptide chain

Answer 63

A releases factor is recruited, which dissociates the translation complex and releases the completed polypeptide chain

Stop codons are a signal for the ribosome to recruit a release factor. Release factors are proteins that dissociate the translation complex and release thepolypeptide chain.
There are no tRNAs that match stop codons and there is no ”special” terminal amino acid. Chaperones are involved in folding proteins, but they are not involved in the termination of translation.

Question 64

Where does translation occur

Answer 64

In the cytoplasm

Another possible answer would be the rough endoplasmic reticulum. Both the rough endoplasmic reticulum and cytoplasm contain ribosomes, which are essential for translation.

The mitochondria are essengial foe cellular respiration, and are the site of the citric acid cycle and electron transport chain. The nucleus houses DNA and synthesizes ribosomes (in the nucleolus). The Golgi apparatus modifies and packages proteins in vesicles after translation is complete.

Question 65

Where could translationof RNA occur i the cell?

Answer 65

Ribosomes on the roughendoplasmic reticulum.

After DNA ks transcribe into RNA, the RNA goes through post-traditional modifications and is then sent out of the the nucleus to the cytoplasm.
From there, the mRNAis bought to the ribosomes, some located on the rough endoplasmic reticulum and some free-floating, in order to be translated into proteins. Proteins are then packaged and transported to their respective locations for usage.
The nucleus is responsible for synthesizing and assembling ribosomal subunigs. The nucleus houses DNA and is the site of transcription, but not translation. Mitochondria are essential for cellular respiration and ATP synthesis. Lysosomes digest cellular wastes and defective proteins.

Question 66

During translation, amino acid elongatio n continues until….

Answer 66

Until a stop codon occupies the A-site of the ribosome. The stop codon is a three-base signal present within the mRNA. There ars three stop codons: UAG, UAA, UGA.

Question 67

What is the result of a missense mutation?

Answer 67

Inclusion of a different amino acid.

Missense mutation are point mutations that cause a single amino acic in a lrotein to be changed. Tnis may or may not affect the functionality of the protein. When one amino acic is rellaced by another amino acid from the same class, such as replacing one polar amino acid with another, functionality is usually retained. When an amino acid from a different class is used, such as replacing an acidic amino acid with a basic amino acid, the protein folding may be affected and functionality may fail.

The other answers describe other types of mutations. Silent result in no change to the protein primary structure. Nonsense mutations cause early termination. Frameshift mufations shift the reading frame of the codon sequence, severely qltering the protein composition.

Question 68

Which of the following js not a step for the elongation process of translation?

RNA splicing

Peptide bond formation

Translocation

Codon recognition

All of these are involved inelongatio

Answer 68

RNA splicing

The three steps for the elongation process of translation ars codon regnition, peptide bond formation and translocation. These steps essentially correspond to the different tRNA positions in the ribosome. tRNA enters and matches the codon of the mRNA strand. A peptide bond is then formed between the tRNA amino acid and the ribosomal amino acid chain. The empty tRNA and peptide strand then shift to make room for the next residue to enter the ribosomes structure.

RNA splicing occurs in the nucleus as part of post-transcriptional modification. Introns are removed to generate a mature mrna strand before translation can occur.

Question 69

Which of the following is not involved in the process of translation?

Answer 69

hnRNA
transcription leads to the production of hnrna (heterogenous nuclear RNA), which primarily consists of a pre-mrna And must go through processing and modification to form mrna and leave the nucleus.

Question 70

Which nucleotide in the mrna codon iss called the wobble position?

Answer 70

Third position.
The wobble position refers to the ability of the third position nucleotide of the codon and first position nucleotide of the anticodon tRNA sequence to exhibit non-standrad base pairing. This allows fewer tRNA molecules to exist because a tRNA molecules is able to bind more than one codon, which increases efficiency.

Question 71

Which molecules provides the energy for elongation of the polypeptide chain during translation?

Answer 71

GTP
During the elongation stage of translation, GTP is used to provide the energy to translocate a tRNA molecule from the A-site to the P-site. GTP is also required to move the ribosome down the mRNA strand to the next codon.