A1.2 Nucleic Acids

Question 1

State the two primary functions of nucleic acids.

Answer 1

1. Pass genetic information between generations.
2. Code for protein production.

Question 2

State the two types of nucleic acids used in cells.

Answer 2

DNA: deoxyribonucleic acid
RNA: ribonucleic acid

Question 3

Outline the meaning and implication of DNA being the genetic material of all living organisms.

Answer 3

Meaning:

All living organisms use DNA as the genetic material.

Implication:

The use of the genetic code across all forms of life is evidence of universal common ancestry of life. The sequences of DNA in cells can be analyzed and compared to determine evolutionary relationships between organisms. The more similar the sequence, the more closely related the organisms.

Question 4

State why RNA viruses do not falsify the claim that all living things use DNA as the genetic material.

Answer 4

Some viruses use RNA as their genetic material. However, because viruses are not made of cells, they are not considered to be living.

Question 5

List the three components of a nucleotide.

Answer 5

A nucleotide is the monomer subunit of the nucleic acids. A nucleotide has three component parts:

1. a nitrogenous base
2. A 5-carbon “pentose: sugar (ribose or deoxyribose)
3. A phosphate group

Question 6

Identify and label the carbons of a pentose sugar.

Answer 6

The carbons of the sugar component of the nucleotide are numbers clockwise, starting from the oxygen in the ring at the top and the phosphate group to the left.

Question 7

Define “backbone” as related to nucleic acid structure.

Answer 7

The “backbone” is the alternating phosphate-sugar- phosphate-sugar-phosphate… found in a polymer of nucleic acids. The relative strength of the backbone maintains the nucleotides in their specific sequence.

Question 8

Explain how nucleotides can connect to form a nucleic acid polymer.

Answer 8

Nucleotides connect by creating covalent bonds between the sugar of one nucleotide and the phosphate group of another nucleotide in a condensation reaction.

The 5’ phosphate group on one nucleotide forms a new covalent bond with the 3’ carbon on the pentose of the next nucleotide. Water is created as a biproduct.

Question 9

State the names of the nitrogenous bases found in DNA and RNA.

Answer 9

Cytosine (DNA and RNA)
Thymine (DNA only)
Guanine (DNA and RNA)
Adenine (DNA and RNA)
Uracil (RNA only)

Question 10

Outline how the sequence of bases in a nucleic acid serves as a ‘code.’

Answer 10

A code is a system in which one symbol signifies the meaning of another symbol. In the genetic code, a group of three nucleic acid bases signifies for an amino acid.A gene is a specific sequence of DNA nucleotides that codes for the making of a specific protein.

Question 11

Define gene.

Answer 11

A gene is a specific sequence of nitrogenous bases in DNA nucleotides that codes for the making of a protein.

Question 12

Describe the condensation reaction that forms a polymer of RNA from RNA nucleotides.

Answer 12

RNA nucleotides connect by creating covalent bonds between the ribose sugar of one nucleotide and the phosphate group of another nucleotide in a condensation reaction.

The 5’ phosphate group on one RNA nucleotide forms a new covalent bond with the 3’ carbon on the ribose of the next nucleotide. Water is created as a biproduct.

Question 13

Draw a short section of an RNA polymer (using circle, pentagon and rectangle)

Answer 13

Include at least three RNA nucleotides, drawn as circle (phosphate), hexagon (ribose) and rectangle (base).

Be sure the phosphate of one nucleotide is connected to the 2’C of the adjacent nucleotide.

Question 14

Describe the structure of a DNA double helix.

Answer 14

Two polymers of DNA nucleotides, each with a sugar-phosphate backbone, run in antiparallel directions. Complementary DNA nitrogenous bases (A-T, C-G) form hydrogen bonds between them, binding the two polymer stands (“double”) so that they wind around each other (“helix”)

Question 15

Outline the complementary base pairing rule, including the type and number of bonds between bases.

Answer 15

In DNA, the nitrogenous bases of two antiparallel strands form hydrogen bonds with each other. The complementary base pairing rule is that adenine only binds with thymine (with 2 H-bonds) and that guanine only binds with cytosine (with 3 H-bonds).

Question 16

Define antiparallel in relation to DNA structure.

Answer 16

Adjacent molecules are oriented parallel to each other but oriented in opposite directions.

In DNA, one strand runs 5’ to 3’ and the complementary strand runs 3’ to 5’

Question 17

Compare and contrast the structure of DNA and RNA.

Answer 17

Both are nucleic acids formed through condensation of nucleotides. Both DNA and RNA have a sugar-phosphate backbone.

RNA
ribose
single stranded
nitrogenous bases A, G, C, U
Complementary paring A-U, C-G

DNA
deoxyribose
double stranded
nitrogenous bases A, G, C, T
Complementary pairing A-T, C-G

Question 18

Compare and contrast the functions of DNA and RNA.

Answer 18

DNA:

Passes heredity information between generations of cells

Codes for making RNA during transcription

RNA:

Codes for making proteins during translation

Question 19

Compare and contrast the location of DNA and RNA in prokaryotic and eukaryotic cells.

Answer 19

Eukaryotic Cells

Both DNA and RNA are found in the nucleus.

DNA also in mitochondria and chloroplasts.

RNA also in cytoplasm and as part of ribosomes (free or bound to rough ER)

Prokaryotic Cells

Both DNA and RNA are in the cytoplasm.

DNA is clumped in a region called the nucleoid.

Question 20

Explain the role of complementary base pairing in maintaining the DNA sequence during DNA replication.

Answer 20

During DNA replication, the two strands of a “parent” DNA molecule are broken apart. Each of these strands serves as a template for the creation of a new “daughter” strand. Because of the base pairing rule, the parent template strand will always code for the complementary sequence of nucleotides in the daughter strand (A to T, C to G). The complementary base paring will maintain the sequence of the DNA from generation to generation.

Question 21

Outline the role of complementary base pairing in transmitting the genetic code in transcription.

Answer 21

During transcription, one of the the two strands of a DNA molecule is used as a template for the creation of an RNA strand. Because of the base pairing rule, the DNA template strand will always code for the complementary sequence of RNA nucleotides in the (A to U, C to G). The complementary base paring will maintain the sequence of the gene as mRNA is translated into protein.

Question 22

Outline the role of complementary base pairing in transmitting the genetic code in translation.

Answer 22

During translation, an RNA strand is used as a template for the creation of a polypeptide. Because of the base pairing rule, the mRNA codon will only bind with the complementary tRNA anticodon (A to U, C to G). The complementary base paring ensures the correct amino acid are brought in the correct sequence to the ribosome.

Question 23

Outline why there is a limitless diversity of DNA base sequences.

Answer 23

There are four nitrogenous bases in DNA (A, T, C and G). These 4 bases are components of nucleotides that can form a DNA molecule in any order and of any length.

Question 24

Define universal in relation to the genetic code.

Answer 24

Universal means that the characteristic is shared by all life. A universal generic code means that all life uses essentially the same code when translating information stored in genes into a polypeptide.

Question 25

Outline why conservation of the genetic code across all forms of life is evidence of common ancestry.

Answer 25

Using inductive reasoning, it can be concluded that the use of the same genetic code across all forms of life indicates that all organisms inherited the use of the code from a common ancestor. The alternative, that all forms of life independently developed use of the same genetic code, is an illogical hypothesis.