Nucleic Acids Structure

Question 1

What are the three components of nucleic acids?

Answer 1

(1) Sugar (S)- Ribose in RNA or Deoxyribose in DNA
(2) Phosphate (P) that joins sugar molecules to make a chain
(3) Bases (B) adenine, guanine, cytosine and thymine (in DNA) or
Uracil (in RNA) that are attached to the sugar molecule

Question 2

What are the differences between RNA and DNA?

Answer 2

Sugar Type:
* DNA: Contains deoxyribose.
* RNA: Contains ribose.

Bases:
* DNA: Has thymine.
* RNA: Has uracil (no thymine).

Strand Structure:
* DNA: Typically double-stranded.
* RNA: Usually single-stranded.

Question 3

What is the difference between purines and pyrimidines

Answer 3

Purines: Consist of two
rings made of carbon
and nitrogen.
* Pyrimidines: Have just
one such ring.

Question 4

What are the purines?

Answer 4

Adenine and guanine

Question 5

What are the pyrimidines?

Answer 5

Uracil, thymine, and cytosine

Question 6

How is a nucleoside formed?

Answer 6

A nitrogenous base attaches to the 1′ carbon of a sugar (ribose or deoxyribose).

Question 7

What type of sugar do nucleic acids contain?

Answer 7

A pentose sugar (5-carbon sugar).

Question 8

What sugar is found in RNA?

Answer 8

Ribose

Question 9

What sugar is found in DNA?

Answer 9

Deoxyribose

Question 10

How do ribose and deoxyribose differ?

Answer 10

Ribose has an OH group at the 2′ carbon, whereas deoxyribose has just H (lacks the OH) at the 2′ carbon.

Question 11

What is a nucleoside?

Answer 11

A base linked to a sugar molecule.

Question 12

What is a nucleotide?

Answer 12

A nucleoside with one or more phosphate groups attached to the 5′ carbon of the sugar.

Question 13

What is the difference between a nucleoside and a nucleotide?

Answer 13

Nucleoside = sugar + base

Nucleotide = nucleoside + phosphate(s)

Question 14

What is the balance of bases in DNA?

Answer 14

Balance of bases, matching pairs, and the total number of purines (A + G) equals the total number of pyrimidines (C + T).

Question 15

How do the amounts of specific bases match in DNA?

Answer 15

Adenine (A) = Thymine (T) and Guanine (G) = Cytosine (C).

Question 16

Why are these base pair matches important?

Answer 16

They are key to base pairing and the formation of the DNA double-helix structure.

Question 17

What are nucleic acids made of?

Answer 17

Long chains of nucleotides.

Question 18

How do nucleotides connect to form a DNA strand?

Answer 18

The phosphate of one nucleotide links the 5′ carbon of one sugar to the 3′ carbon of the next sugar.

Question 19

What is the name of the bond between phosphates and sugars?

Answer 19

Phosphodiester bond

Question 20

What is the name of the bond between the base and the sugar?

Answer 20

Glycosidic bond

Question 21

What does the 5′ → 3′ direction of a DNA strand indicate?

Answer 21

The direction of the chain, which tells which way the genetic information is read.

Question 22

Which part of the nucleotide attaches to the base?

Answer 22

The 1′ carbon of the sugar.

Question 23

What roles do the 3′ and 5′ carbons of the sugar play?

Answer 23

They connect to other sugars via phosphate bridges, forming the backbone of the DNA chain.

Question 24

What is the overall shape of DNA?

Answer 24

A double helix, resembling a twisted ladder or spiral staircase.

Question 25

What does it mean that DNA strands are complementary?

Answer 25

The two strands fit together because specific bases pair with each other (A with T, G with C).

Question 26

What does “antiparallel” mean in DNA structure?

Answer 26

The two strands run in opposite directions: one 5′ → 3′ and the other 3′ → 5′.

Question 27

How many base pairs are there per complete turn of the DNA helix?

Answer 27

Approximately 10.4 base pairs per turn

Question 28

What is the length of one complete turn of the DNA helix?

Answer 28

About 3.4 nanometers (nm)

Question 29

What forms the “rungs” of the DNA ladder?

Answer 29

Pairs of nitrogenous bases held together by hydrogen bonds.

Question 30

What are the three major types of DNA sequences in eukaryotes?

Answer 30

Unique sequences Moderately repetitive sequences Highly repetitive sequences

Question 31

What are the unique sequences in eukaryotic DNA?

Answer 31

DNA sequences present only once or a few times in the genome.

Question 32

What do unique sequences usually encode?

Answer 32

Protein-coding regions (genes).

Question 33

What is the typical length of moderately repetitive DNA sequences?

Answer 33

Usually 150–300 base pairs (bp).

Question 34

How many times are moderately repetitive sequences repeated?

Answer 34

Many thousands of times in the genome.

Question 35

Give examples of genes found in moderately repetitive sequences.

Answer 35

rRNA genes and tRNA genes

Question 36

What are tandem repeats?

Answer 36

Repeated DNA sequences that occur one after another in a row.

Question 37

What are interspersed repeats?

Answer 37

Repeated DNA sequences scattered throughout the genome.

Question 38

What are SINEs?

Answer 38

Short Interspersed Elements, usually less than 500 bp long and present in more than 10⁵ copies

Question 39

What is an example of a SINE in humans?

Answer 39

Alu elements (~300 bp long).

Question 40

How abundant are Alu elements in the human genome?

Answer 40

More than one million copies, making up about 11% of the human genome.

Question 41

What are LINEs?

Answer 41

Long Interspersed Elements, usually longer than 5 kb and present in more than 10⁴ copies.

Question 42

What is an example of a LINE in humans?

Answer 42

LINE-1 (L1).

Question 43

What is the typical length of highly repetitive DNA sequences?

Answer 43

10 bp or less.

Question 44

How abundant is LINE-1 in the human genome?

Answer 44

About 500,000 copies, making up roughly 17% of the human genome

Question 45

How often are highly repetitive sequences repeated?

Answer 45

Hundreds of thousands to millions of copies.

Question 46

Where are highly repetitive sequences commonly found?

Answer 46

Clustered around centromeres and telomeres.

Question 47

What is another name for highly repetitive DNA?

Answer 47

Satellite DNA.

Question 48

What is a hairpin structure in nucleic acids?

Answer 48

A structure formed when a single strand of DNA or RNA folds back onto itself and base-pairs internally.

Question 49

How does a hairpin structure form?

Answer 49

It forms when a nucleotide sequence is followed later in the strand by its inverted complementary sequence. This is known as an inverted sequence

Question 50

Why do inverted sequences lead to hairpin formation?

Answer 50

Because the inverted complementary sequences can base-pair with each other, causing the strand to fold and form a stem-loop (hairpin) structure.

Question 51

What is the biological significance of hairpin structures?

Answer 51

Hairpin structures play important roles in gene regulation and have various biological functions.

Question 52

What happens when complementary sequences are continuous in a nucleic acid strand?

Answer 52

The hairpin structure forms a stem but no loop.

Question 53

Can RNA molecules contain more than one hairpin structure?

Answer 53

Yes, RNA molecules may contain numerous hairpins within the same strand.

Question 54

What is the result of RNA having multiple hairpin structures?

Answer 54

Multiple hairpins allow RNA to fold into complex three-dimensional structures

Question 55

What is used to measure nucleic acids quantitatively when determining melting temperature (Tm)?

Answer 55

A spectrophotometer

Question 56

Which absorbs more light at 260 nm: single-stranded DNA (ssDNA) or double-stranded DNA (dsDNA)?

Answer 56

Single-stranded DNA (ssDNA) absorbs more light than double-stranded DNA (dsDNA).

Question 57

What happens to DNA during heat denaturation?

Answer 57

Heat breaks the hydrogen bonds between bases, converting double-stranded DNA into single-stranded DNA

Question 58

What happens to DNA absorption at 260 nm as DNA denatures?

Answer 58

Absorption increases as DNA becomes single-stranded.

Question 59

What is the melting temperature (Tm) of DNA?

Answer 59

The temperature at which 50% of the DNA has changed from double-stranded to single-stranded.

Question 60

How can genomes be differentiated using melting temperature (Tm)?

Answer 60

Genomes can be distinguished based on differences in their Tm values, which reflect differences in base composition (especially GC content).

Question 61

Why are GC base pairs stronger than AT base pairs?

Answer 61

GC base pairs have three hydrogen bonds, while AT base pairs have only two.

Question 62

Why does GC-rich DNA require more energy to denature?

Answer 62

Because the three hydrogen bonds in GC pairs require more heat to break than the two hydrogen bonds in AT pairs.

Question 63

How does GC content affect melting temperature (Tm)?

Answer 63

Higher GC content increases the Tm because more heat is needed to separate the strands.