Nucleic acids

Nucleic Acids

Unbranched polymers containing nucleotide monomer units.

DNA

Deoxyribonucleic acid, a nucleotide polymer with deoxyribose, phosphate group, and adenine, cytosine, guanine, or thymine bases.

RNA

Ribonucleic acid, a nucleotide polymer with ribose, phosphate group, and adenine, cytosine, guanine, or uracil bases.

Friedrich Miescher

Discovered nucleic acids in 1869 while studying the nuclei of white blood cells.

James Dewey Watson and Francis Crick

Coined the term "DNA" and described it as a three-dimensional double helix structure.

Double Helix

DNA structure with anti-parallel and complementary strands.

Single Strand

RNA structure.

Longer Strands

DNA strands.

Shorter Strands

RNA strands.

Location of DNA

Found in the nucleus, with a small amount also present in mitochondria.

Location of RNA

Forms in the nucleolus and then moves to specialized regions of the cytoplasm.

Primary Function of DNA

Replicates and stores genetic information.

Primary Function of RNA

Converts genetic information from DNA to build proteins.

Sugar Unit in DNA

Deoxyribose.

Sugar Unit in RNA

Ribose.

Nucleotide Building Blocks

Pentose sugar, nitrogenous bases, and phosphate.

Nucleotide Formation

Nucleoside (sugar + base) and then nucleotide (nucleoside + phosphate).1. Nucleic acid structure:The arrangement and bonding of nucleotides in a nucleic acid molecule.

Sugar-phosphate backbone

The alternating chain of sugar and phosphate molecules that make up the backbone of a nucleic acid molecule.

3', 5'-phosphodiester linkage

The bond between the phosphate group of one nucleotide and the sugar molecule of another nucleotide in a nucleic acid chain.

Directionality

The orientation of a nucleotide chain, with a 5' end that carries a free phosphate group and a 3' end that has a free hydroxyl group.

Charge of phosphate group

Each nonterminal phosphate group in a nucleic acid carries a -1 charge.

Base pair

Two nucleotide bases that are bonded together by hydrogen bonds, such as A-T and G-C.

Complementary base pairing

The specific pairing of nucleotide bases in DNA, where A pairs with T and G pairs with C.

DNA double helix

The twisted ladder-like structure formed by two complementary strands of DNA.

Base stacking

The interaction between adjacent nucleotide bases in a DNA double helix, which stabilizes the structure.

B-DNA

The most common form of DNA double helix found in nature.

A-DNA

A form of DNA double helix with a different structure than B-DNA, characterized by fewer residues per turn and more similar dimensions of major and minor grooves.

Z-DNA

A less common form of DNA double helix that occurs naturally under certain circumstances, characterized by a zigzag appearance of the phosphodiester backbone.1. Prokaryotic DNA:DNA found in the cytoplasm of prokaryotic cells and circular plasmids, not found inside organelles.

Eukaryotic DNA

DNA found in the nucleus of eukaryotic cells, inside the chloroplast and mitochondria.

Circular chromosomes

Small amount of DNA in the form of a single, circular chromosome found in prokaryotic DNA.

Linear chromosomes

More DNA arranged in multiple, linear chromosomes found in eukaryotic DNA.

Introns

Absent in prokaryotic DNA, present in eukaryotic DNA.

Genes

Prokaryotic DNA contains a small number of genes, while eukaryotic DNA contains a large number of genes.

DNA replication

Occurs in the cytoplasm for prokaryotic DNA, occurs in the nucleus for eukaryotic DNA.

Nucleoid

Prokaryotic DNA condenses to form a nucleoid, not packed with histones.

Chromatin

Eukaryotic DNA is packed with histones to form chromatin.

Plasmids

Small, circular, extrachromosomal DNA molecules found in most species of bacteria (prokaryotes).

A-DNA

A form of DNA with a right-handed helix turn and narrow and deep major groove.

B-DNA

A form of DNA with a right-handed helix turn and wide and deep major groove.

Z-DNA

A form of DNA with a left-handed helix turn and narrow and deep major groove.

Supercoiling

Underwound DNA forms negative supercoils, overwound DNA forms positive supercoils.

Topoisomerase

Enzymes involved in changing the supercoiled state of DNA.

Class I topoisomerases

Cut the phosphodiester backbone of one strand of DNA, pass the other end through, and then reseal the backbone.

Class II topoisomerase

Cut both strands of DNA, pass some of the remaining DNA helix between the cut ends, and then reseal.

DNA gyrase

A bacterial topoisomerase that introduces negative supercoils into DNA.1. Chromatin:a complex of DNA and protein found in eukaryotic nuclei

Histones

basic proteins found complexed to eukaryotic DNA

Nucleosome

a globular structure in chromatin in which DNA is wrapped around an aggregate of histone molecules

Packaging of DNA

the process of condensing DNA into chromosomes after replication

Central Dogma

the process of DNA being transcribed into RNA and then translated into proteins

Telomere

complexes of DNA plus proteins located at the ends of linear chromosomes, used to maintain structural integrity and protect the chromosomes

Reverse Transcription

the process of synthesizing DNA from an RNA template, used by retroviruses

Replication Fork

the point at which the DNA double helix is unwinding during DNA replication

Okazaki Fragments

short segments of DNA synthesized on the lagging strand during DNA replication

Nicks

breaks or gaps in the daughter strand during DNA replication

Leading Strand

the strand that grows continuously during DNA replication

Lagging Strand

the strand that is synthesized in small segments during DNA replication

DNA Helicase

an enzyme that unwinds the DNA double helix during DNA replication

DNA Polymerase III

an enzyme that verifies base pairing and catalyzes the formation of new DNA strands during DNA replication

Primase

an enzyme that synthesizes short stretches of RNA that are complementary and antiparallel to the DNA template during DNA replication

DNA Ligase

an enzyme that connects two strands of DNA together by forming a bond between the phosphate group of one strand and the deoxyribose group on another, used to join Okazaki fragments on the lagging strand

DNA Polymerase I

an enzyme that excises RNA primers from DNA fragments and replaces them with the required nucleotides during DNA replication

RNA Primer

RNA that primes and initiates DNA synthesis during DNA replication1. DNA helicase:An enzyme that unwinds the DNA during replication.

Polymerases

Enzymes that orchestrate the manufacturing of new DNA strands during replication.

Semi-conservative replication

A pattern in which individual strands of DNA are manufactured in different directions, producing a leading and a lagging strand.

Okazaki fragments

Small DNA fragments that are produced during lagging strand synthesis and eventually joined together.

Primer

A small RNA molecule that is used to initiate the synthesis of new DNA strands.

Prokaryotic replication

DNA replication that occurs in the cytoplasm of prokaryotic organisms.

Eukaryotic replication

DNA replication that occurs inside the nucleus of eukaryotic organisms.

Origin of replication

The site where DNA replication begins. Prokaryotes have a single origin, while eukaryotes have multiple origins.

Unidirectional replication

Replication that occurs in one direction. Prokaryotes use unidirectional replication.

DNA polymerase III

The main polymerase responsible for both initiation and elongation during prokaryotic replication.

DNA polymerase α, δ, and ε

Different polymerases involved in the initiation and elongation of DNA strands during eukaryotic replication.

DNA polymerase I and β

Polymerases involved in DNA repair and gap filling during prokaryotic and eukaryotic replication, respectively.

DNA gyrase

An enzyme needed for DNA replication in prokaryotes.

Telomeres

The ends of eukaryotic chromosomes that have a distinct process for replication.

Cell cycle

The series of events that occur in a eukaryotic cell, including DNA replication and cell division.

G1 phase

The period preceding DNA replication in the cell cycle.

S phase

The phase of the cell cycle during which DNA replication occurs.

G2 phase

The period following DNA replication in the cell cycle.

Mitosis

The process of cell division in eukaryotic cells.

Antimetabolites

Anticancer drugs that inhibit DNA synthesis by interfering with the structures required for replication.

Ribonucleic acid (RNA)

The molecule that carries the genetic information from DNA and is involved in protein synthesis.

Heterogeneous nuclear RNA (hnRNA)

RNA formed directly by DNA transcription and converted to messenger RNA through post-transcription processing.

Small nuclear RNA (snRNA)

RNA that facilitates the conversion of hnRNA to messenger RNA.

Methotrexate

An antimetabolite drug that inhibits DNA synthesis by interfering with the conversion of folic acid to a needed derivative.1. Messenger RNA (mRNA):Carries instructions for protein synthesis to the sites for protein synthesis.

Ribosomal RNA (rRNA)

Combines with specific proteins to form ribosomes, the physical sites for protein synthesis.

Transfer RNA (tRNA)

Delivers amino acids to the sites for protein synthesis.

Transcription

The process by which DNA directs the synthesis of hnRNA/mRNA molecules that carry the coded information needed for protein synthesis.

Gene

A short segment of a DNA strand that contains instructions for the formation of a particular hnRNA/mRNA molecule.

Exon

A gene segment that conveys (codes for) genetic information.

Intron

A gene segment that does not convey (codes for) genetic information.

Template Strand

The strand of DNA used for hnRNA/mRNA synthesis.

Informational Strand

The other DNA strand, although not involved in RNA synthesis, gives the base sequence present in the hnRNA strand being synthesized (with the exception of U replacing T).

RNA Polymerase

Enzyme responsible for unwinding the DNA double helix and linking ribonucleotides to the growing hnRNA molecule during transcription.

Splicing

The process of removing introns and joining the remaining exons in the hnRNA molecule.

snRNA

Shortened RNA with genetic information of the transcribed gene, formed in complex with proteins in particles called snRNPs (snurps).

Spliceosomes

Large complexes formed by snurps that are involved in the splicing process.

Transcriptome

The complete set of mRNA molecules produced by a cell, serving as the blueprint for protein assembly.1. Genetic code:The assignment of the 64 mRNA codons to specific amino acids (or stop signals).

Codon

A three-nucleotide sequence in an mRNA molecule that codes for a specific amino acid.

Termination codons

Three combinations of bases (UAG, UAA, and UGA) that signal the end of protein synthesis.