Nucleic Acids and Their Components

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Questions and Answers

What type of bond connects a nucleobase to the sugar in a nucleoside?

β-N-glycosidic bond (correct)

hydrogen bond

phosphodiester bond

α-N-glycosidic bond

What is a nucleotide composed of?

A monosaccharide and a phosphoric acid

A nucleobase and a monosaccharide

A nucleoside and a phosphate group (correct)

A nucleoside only

Which of the following correctly describes the sugar found in RNA?

2-deoxy-D-ribose

D-mannose

D-glucose

D-ribose (correct)

Which type of nucleic acid does not contain a phosphate group?

Nucleoside Signup and view all the answers

What type of linkage occurs during the polymerization of nucleotides to form nucleic acids?

3’,5’-phosphodiester bond Signup and view all the answers

What is the primary function of Class I topoisomerases?

Cut the phosphodiester backbone of one strand, pass the end through, and reseal Signup and view all the answers

What structure is formed when DNA is wrapped around histones?

Chromatin Signup and view all the answers

Which statement about DNA denaturation is true?

Its midpoint is referred to as Tm. Signup and view all the answers

Which component is associated with the stabilization of supercoiling in chromatin?

Histone proteins Signup and view all the answers

What effect does an increased percentage of G-C pairs have on Tm?

Increases Tm Signup and view all the answers

What type of DNA structure is circular DNA?

Double-stranded DNA with joined ends Signup and view all the answers

Which class of topoisomerase is DNA gyrase classified as?

Class II Signup and view all the answers

What is hyperchromicity in the context of DNA denaturation?

Increased absorbance at 260 nm Signup and view all the answers

What is the primary structure of DNA comprised of?

The sequence of bases along the polynucleotide backbone Signup and view all the answers

How many hydrogen bonds are present in a G-C base pair?

3 Signup and view all the answers

Which type of DNA is considered the physiological form?

B-DNA Signup and view all the answers

Which of these forms of DNA is left-handed?

Z-DNA Signup and view all the answers

Which of the following base pairs forms two hydrogen bonds?

T-A Signup and view all the answers

What defines the secondary structure of nucleic acids?

The ordered arrangement of nucleic acid strands Signup and view all the answers

What is supercoiling in the context of DNA?

The further coiling and twisting of DNA helix Signup and view all the answers

Which sugar is found in DNA as opposed to RNA?

2-deoxyribose Signup and view all the answers

What type of sugar is found in RNA?

β-D-ribose Signup and view all the answers

Which statement is true regarding tRNA?

tRNA has intramolecular hydrogen bonding. Signup and view all the answers

What is the primary function of mRNA?

To carry coded genetic information from DNA to ribosomes. Signup and view all the answers

Which of the following is not a type of RNA mentioned?

pRNA Signup and view all the answers

Which of the following describes ribosomal RNA (rRNA)?

It constitutes the majority of ribosome structure. Signup and view all the answers

What is the significance of snRNA in eukaryotic cells?

It helps process initial mRNA transcripts. Signup and view all the answers

What aspect differentiates RNA from DNA?

RNA contains uracil instead of thymine. Signup and view all the answers

Which component of ribosomes is analyzed by analytical ultracentrifugation?

Both rRNA and proteins. Signup and view all the answers

Study Notes

Nucleic Acids

Nucleic acids are biopolymers composed of monomers containing three molecular components: a base (purine or pyrimidine), a monosaccharide (D-ribose or 2-deoxy-D-ribose), and phosphoric acid.
There are two primary types of nucleic acids: RNA (Ribonucleic Acid) and DNA (Deoxyribonucleic Acid).

Pyrimidine & Purine Bases

Pyrimidine and purine are the building blocks of nucleic acids.
Pyrimidines include cytosine, thymine (DNA only), and uracil (RNA only).
Purines include adenine and guanine.

Other Bases

There are less common bases found primarily in transfer RNAs (tRNAs).

Nucleosides

Nucleosides are composed of a D-ribose or 2-deoxy-D-ribose sugar covalently bonded to a nucleobase via a β-N-glycosidic bond.
Nucleosides lack phosphate groups.

Nucleotides

Nucleotides are nucleosides with a phosphate group esterified to the monosaccharide's 3'-OH or 5'-OH.
They are named after the parent nucleoside, followed by "monophosphate".
Polymerization of nucleotides leads to nucleic acids.

DNA - 1° Structure

DNA is a biopolymer with a backbone of alternating 2-deoxy-D-ribose and phosphate units.
The 3'-OH of one 2-deoxy-D-ribose is linked to the 5'-OH of the next 2-deoxy-D-ribose by a phosphodiester bond.
The primary structure is the sequence of bases along the pentose-phosphodiester backbone.
The sequence is read from the 5' end to the 3' end.
DNA strands are often denoted using single-letter abbreviations (A, G, C, T, and U).

DNA differs from RNA

DNA contains the sugar 2'-deoxyribose, while RNA contains ribose.
DNA uses the pyrimidine base thymine, while RNA uses uracil.
DNA is often denoted with a "d" prefix to indicate deoxyribose.

DNA - 2° Structure

The secondary structure of DNA involves the arrangement of nucleic acid strands.
The most prominent structure is the double helix, proposed by Watson and Crick in 1953.
The double helix consists of two antiparallel polynucleotide strands coiled around the same axis in a right-handed manner.
The structure is based on X-ray crystallography.

Base Pairing: T-A and G-C

Base pairing is complementary, with T-A and G-C pairs.
T-A base pairs have 2 hydrogen bonds.
G-C base pairs have 3 hydrogen bonds.

Other Forms of DNA

A-DNA: a right-handed helix, thicker than B-DNA, with 11 base pairs per turn.
B-DNA: the most common form in vivo, with a diameter of 11 angstroms and 10 base pairs per turn.
Z-DNA: a left-handed double helix that may play a role in gene expression.

Comparison of A, B, and Z Forms of DNA

A-DNA and B-DNA are right-handed helices.
Z-DNA is left-handed and usually consists of alternating purine-pyrimidine bases.
Methylated cytosine is also found in Z-DNA.

DNA - 3° Structure

The tertiary structure of DNA involves the three-dimensional arrangement of all atoms, specifically supercoiling.
Circular DNA: a type of double-stranded DNA where the 5' and 3' ends of each strand are joined by phosphodiester bonds.
Supercoiling: further coiling and twisting of the DNA helix.

Topoisomerases

Topoisomerase Class I: cuts one DNA strand, passes an end through, and reseals the cut.
Topoisomerase Class II: cuts both strands, passes some of the remaining DNA helix between the cut strands, and reseals.
DNA gyrase: a bacterial topoisomerase.

Supercoiling in Eukaryotic DNA

Histone: a protein rich in lysine and arginine, associated with eukaryotic DNA.
Chromatin: DNA wrapped around histone particles in a bead-like structure.
Supercoiling is accommodated by the histone-protein component of chromatin.
Each "bead" is a nucleosome, which consists of DNA wrapped around a histone core.

Denaturation of DNA

Denaturation disrupts the secondary structure of DNA.
Heat denaturation (melting) causes strands to separate.
Increasing absorbance at 260 nm during denaturation is called hyperchromicity.
The midpoint of the denaturation (melting) curve is designated as Tm.
Higher G-C content results in a higher Tm.
Renaturation is achievable by slow cooling.

Denaturation of DNA (cont.)

The double helix unwinds during denaturation.
The process can be reversed with slow cooling and annealing.

Principal Types of RNA

RNA is composed of long, unbranched chains of nucleotides linked by phosphodiester bonds between the 3'-OH and 5'-OH of adjacent sugars.
The sugar in RNA is β-D-ribose.
RNA contains the pyrimidine bases uracil and cytosine.
RNA is typically single-stranded.

Information Transfer in Cells

Information encoded in DNA is transcribed into RNA.
The RNA sequence is dictated by the DNA sequence.
This process is known as the Central Dogma of biology.

RNA (types)

RNA molecules are classified by structure and function.

1. tRNA

Transfer RNA (tRNA) is the smallest type of RNA.
It is a single-stranded polynucleotide chain with 73-94 nucleotide residues.
tRNA carries an amino acid at its 3' end.
Intramolecular hydrogen bonding occurs within tRNA.

2. rRNA

Ribosomal RNA (rRNA) is found in ribosomes, where protein synthesis occurs.
Only a few types of rRNA exist in cells.
Ribosomes are composed of 60-65% rRNA and 35-40% protein.
Ribosomes have two subunits with different sizes, defined by their sedimentation coefficients in Svedberg units (S).

3. mRNA

Messenger RNA (mRNA) carries genetic information from DNA to ribosomes for protein synthesis..
mRNA is present in small amounts and is short-lived.
mRNA is single-stranded.
Its biosynthesis is directed by DNA information.
A complementary mRNA strand is synthesized along one DNA strand, starting from the 3' end.

4. snRNA

Small nuclear RNA (snRNA) is found in the nucleus of eukaryotes.
It is small (100-200 nucleotides long) and forms complexes with proteins called small nuclear ribonucleoprotein particles (snRNPs).
snRNPs are involved in the processing of initial mRNA transcribed from DNA.

Biosynthesis of Nucleic Acids: Replication

Replication is the process of duplicating DNA.

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Description

Explore the fundamental concepts of nucleic acids, including their structure and classification. This quiz covers the differences between DNA and RNA, the roles of purine and pyrimidine bases, and the essential components of nucleosides and nucleotides.