4 - STRUCTURES OF NUCLEOTIDES 2025

Nitrogen bases present in both DNA and RNA

Adenine

Guanine

Cytosine

Nitrogen bases present in DNA only

Thymine

Nitrogen base present in RNA only

Uracil

Methylation of uracil makes this nitrogen base

Thymine

This is the bond formed between nitrogenous base and pentose sugar of a nucleoside

N-glycosidic linkage

This is the bond formed between pentose sugar and phosphoryl group of a nucleotide

Ester bond

This bond allows the addition of more phosphoryl bonds at nucleotides to form di- and triphosphates

Anhydride bond

Most abundant free nucleotide in mammalian cell

Adenosine triphosphate (ATP)

Nucleic acids are polymers of nucleotides that are joined by this bond

3'-5' phosphodiester bond

Sequence of writing the bases of a DNA

From 5' end → 3' end

Determinant of the melting point of DNA

Number of G-C bonds

Orientation of DNA strands

Antiparallel

States that the number of purines = number of pyrimidines

Chargaff's rule

All types of DNA are right-handed except this type of DNA

Z-DNA (left-handed)

Most common form of DNA physiologically (well-hydrated and w/ low salt concentration)

B-DNA

Type of DNA found in low humidity and high salt concentration

A-DNA

Type of DNA mostly seen in 5' end of chromosomes

Z-DNA

Most abundant chromatin protein

Histone

Histone seen in the linker region

H1

Composition of the histone octomer (core histones)

Pairs of H2A, H2B, H3, H4

Source of negative charge of DNA

Phosphate groups

Source of positive charge of histones

Lysine (H3, H4)

Arginine (H2A, H2B)

Represents the "beads on a string" appearance on electron microscopy

10-nm chromatin fibril

DNA is wrapped by around the histone octomer by this amount

1.75 times

Condensation of DNA to form chromosomes occur during this phase of mitosis

Prophase

The highly condensed chromatin seen in electron microscopy, which is transcriptionally inactive

Heterochromatin

The less condensed chromatin seen in electron microscopy, which is transcriptionally active

Euchromatin

Most heterogeneous RNA

mRNA

Most abundant RNA

rRNA

RNA containing significant proportions of nucleosides with unusual bases

tRNA

RNAs responsible for gene expression regulation

snRNA

miRNA

siRNA

lncRNA