nucleic acid

Genetic material

The biological material that stores hereditary information and allows it to be transmitted between generations of cells or organisms.

DNA

The primary genetic material of all cellular organisms; it stores hereditary information and contains sequences used in gene expression.

DNA full name

Deoxyribonucleic acid.

RNA

A nucleic acid involved in gene expression and other cellular functions; some viruses use it as their genetic material.

RNA full name

Ribonucleic acid.

Four major biological molecules

Carbohydrates, lipids, proteins, and nucleic acids.

Nucleic acid

A polymer made from chains of nucleotides.

Nucleotide

The monomer of nucleic acids, consisting of a pentose sugar, phosphate group, and nitrogenous base.

Polymer

A large molecule composed of repeating smaller units called monomers.

Monomer

A smaller molecular unit that can be joined to other units to form a polymer.

Two main nucleic acids

DNA and RNA.

Primary function of DNA

To store and transmit hereditary information and provide information used in gene expression.

Molecule of heredity

The molecule that stores and transmits genetic information; in cellular organisms this is DNA.

Genetic information

Information encoded in the sequence of nucleotides that can be inherited and used in cellular processes.

Information storage in DNA

The order of nitrogenous bases along a DNA molecule.

DNA information capacity

The enormous capacity to store information because four different bases can be arranged in an extremely large number of sequences.

Gene

A region of DNA containing information for a functional product, such as a polypeptide or functional RNA.

Gene sequence

The particular order of nucleotides within a region of DNA.

Gene expression

The processes through which information in a gene is used to produce a functional product.

Central dogma

The general flow of genetic information from DNA to RNA to protein.

Transcription

The synthesis of an RNA molecule using a DNA strand as a template.

Translation

The synthesis of a polypeptide using the information carried by mRNA.

DNA replication

The process of copying DNA before cell division so genetic information can be passed to daughter cells.

Semi-conservative replication

A replication mechanism in which each daughter DNA molecule contains one original strand and one newly synthesized strand.

Complementary base pairing

The specific pairing of bases that allows nucleic-acid strands to interact accurately; A pairs with T in DNA, A pairs with U in RNA, and C pairs with G.

DNA as genetic material

DNA is capable of storing, accurately copying, and transmitting hereditary information and providing instructions used in gene expression.

Evidence that DNA is genetic material

The Hershey–Chase experiment provided evidence that DNA, rather than protein, is the hereditary material of bacteriophages.

Hershey–Chase experiment

A 1952 experiment using bacteriophages that provided evidence that DNA is the genetic material.

Bacteriophage

A virus that infects bacteria and can contain DNA and protein.

Purpose of Hershey–Chase experiment

To determine whether DNA or protein enters bacterial cells and carries the genetic information during phage infection.

Radioactive phosphorus-32

An isotope used to label DNA because phosphate groups in DNA contain phosphorus.

Radioactive sulfur-35

An isotope used to label proteins because some amino acids contain sulfur while DNA does not normally contain sulfur.

Why phosphorus labels DNA

Phosphorus is present in the phosphate groups of DNA.

Why sulfur labels protein

Sulfur occurs in certain amino acids found in proteins but is not a normal component of DNA.

Hershey–Chase DNA result

Radioactive phosphorus associated with DNA was detected with the bacterial cells after infection.

Hershey–Chase protein result

Most radioactive sulfur associated with protein remained outside the bacterial cells.

Hershey–Chase conclusion

The results supported DNA as the molecule carrying hereditary information into bacterial cells.

Universal DNA

DNA is the genetic material used by all known cellular organisms.

Cellular organisms

Organisms composed of cells, including bacteria, archaea, and eukaryotes.

RNA genomes in viruses

Some viruses use RNA rather than DNA as their genetic material.

Coronavirus genetic material

Coronaviruses have RNA genomes.

Why viral RNA does not contradict DNA universality

Viruses are acellular and are generally not classified as living organisms in IB Biology.

RNA world hypothesis

A hypothesis proposing that early life may have used RNA as both genetic material and a catalyst before DNA became the main genetic-storage molecule.

Ribozyme

An RNA molecule capable of catalyzing a chemical reaction.

Why DNA may have replaced RNA as genetic material

DNA is chemically more stable and better suited for long-term storage of genetic information.

Genetic code

The set of rules relating nucleotide triplets to amino acids or stop signals during protein synthesis.

Nearly universal genetic code

The same basic correspondence between codons and amino acids is used across almost all forms of cellular life.

Evidence from the genetic code

Similar genetic coding across organisms supports the hypothesis that they share a common ancestor.

Universal common ancestry

The idea that all modern cellular life ultimately descended from a common ancestral lineage.

LUCA

The last universal common ancestor of all currently living cellular organisms; it was not necessarily the first organism to exist.

DNA sequence comparison

The comparison of nucleotide sequences between organisms to investigate genetic similarities and evolutionary relationships.

Sequence similarity

Evidence that organisms with similar corresponding DNA sequences may share a more recent common ancestor.

Sequence difference

Evidence that organisms with more divergent corresponding sequences may have a more distant evolutionary relationship.

Nucleotide

An individual unit containing a pentose sugar, phosphate group, and nitrogenous base.

Three components of a nucleotide

A pentose sugar, a phosphate group, and a nitrogenous base.

Pentose

A five-carbon sugar.

DNA pentose sugar

Deoxyribose.

RNA pentose sugar

Ribose.

Phosphate group

A negatively charged group containing phosphorus and oxygen that forms part of the nucleic-acid backbone.

Nitrogenous base

A nitrogen-containing molecule attached to the pentose sugar whose sequence carries genetic information.

Five nitrogenous bases

Adenine, guanine, cytosine, thymine, and uracil.

DNA bases

Adenine, thymine, cytosine, and guanine.

RNA bases

Adenine, uracil, cytosine, and guanine.

Adenine

A nitrogenous base found in both DNA and RNA; it is a purine.

Guanine

A nitrogenous base found in both DNA and RNA; it is a purine.

Cytosine

A nitrogenous base found in both DNA and RNA; it is a pyrimidine.

Thymine

A nitrogenous base found in DNA; it is a pyrimidine that pairs with adenine.

Uracil

A nitrogenous base found in RNA; it is a pyrimidine that replaces thymine.

Purine

A nitrogenous base with two fused rings; adenine and guanine belong to this group.

Pyrimidine

A nitrogenous base with one ring; cytosine, thymine, and uracil belong to this group.

Purines

Adenine and guanine.

Pyrimidines

Cytosine, thymine, and uracil.

Purine memory aid

“Pure As Gold” represents adenine and guanine.

Pyrimidine memory aid

“CUT” represents cytosine, uracil, and thymine.

Number of rings in a purine

Two fused rings.

Number of rings in a pyrimidine

One ring.

DNA versus RNA base difference

DNA contains thymine, whereas RNA contains uracil.

Ribose

A five-carbon sugar containing an OH group at the 2′ carbon and found in RNA.

Deoxyribose

A five-carbon sugar containing H rather than OH at the 2′ carbon and found in DNA.

Difference between ribose and deoxyribose

The 2′ carbon has an OH group in ribose but an H in deoxyribose.

Meaning of deoxy

The sugar has one less oxygen at the 2′ position compared with ribose.

Sugar carbon numbering

The five sugar carbons are designated 1′, 2′, 3′, 4′, and 5′.

1′ carbon

The sugar carbon attached to the nitrogenous base.

2′ carbon

The sugar carbon whose attached group distinguishes ribose from deoxyribose.

3′ carbon

The sugar carbon containing the hydroxyl group involved in forming the next phosphodiester bond.

4′ carbon

A carbon within the pentose sugar ring.

5′ carbon

The sugar carbon associated with the phosphate group.

Prime notation

The prime symbol distinguishes carbon numbers in the sugar from numbering within nitrogenous bases.

Nucleic-acid backbone

The repeating sugar-phosphate structure forming the structural framework of DNA and RNA.

Sugar-phosphate backbone

A chain consisting of alternating pentose sugars and phosphate groups.

Backbone sequence

Sugar-phosphate-sugar-phosphate-sugar-phosphate.

Function of the sugar-phosphate backbone

It provides structural support and maintains the ordered arrangement of nucleotides.

Phosphodiester bond

A strong covalent bond linking adjacent nucleotides through the sugar and phosphate groups.

Covalent bond

A strong chemical bond formed by sharing electrons between atoms.

Condensation reaction

A reaction that joins molecules together while releasing a small molecule, commonly water.

Nucleotide condensation

Nucleotides are joined to form a polynucleotide through reactions that create phosphodiester bonds.

Water in condensation

A molecule of water is released during a condensation reaction.

5′ end

The end of a nucleic-acid strand associated with the 5′ carbon and phosphate group.

3′ end

The end of a nucleic-acid strand with a free hydroxyl group associated with the 3′ carbon.

Nucleic-acid directionality

The existence of chemically distinct 5′ and 3′ ends that gives each strand a specific orientation.