Nucleic Acid Biochemistry

nucleic acids

Large molecules that store and transmit genetic information.

nucleotides

Building blocks of nucleic acids, consisting of a phosphate, a sugar, and a nitrogen base.

nucleosides

Combinations of a sugar and a nitrogen base.

DNA

A polymer of nucleotides that carries genetic information.

RNA

A nucleic acid involved in protein synthesis and gene expression.

chromosome

Structures within cells that contain DNA and genetic information.

chromatin

A complex of DNA and proteins found in the nucleus, which condenses to form chromosomes.

gene

A segment of DNA that contains the instructions for making a specific protein.

deoxynucleoside

The combination of a deoxyribose sugar and a nitrogen base.

deoxynucleotide

The combination of a phosphate, a deoxyribose sugar, and a nitrogen base.

nitrogen base

The part of a nucleotide that encodes genetic information, consisting of adenine, guanine, thymine, or cytosine.

purine

A type of nitrogen base with a double-ring structure, including adenine and guanine.

pyrimidine

A type of nitrogen base with a single-ring structure, including thymine and cytosine.

sugar-phosphate backbone

The structural framework of nucleic acids, consisting of alternating sugar and phosphate groups.

transforming principle

The substance that causes genetic transformation, identified as DNA.

(A + G)/(T + C) = 1

Chargaff's rule stating that the ratio of purines to pyrimidines in DNA is equal.

ATP

A molecule used to store and transfer chemical energy in cells.

Griffith's experiment

Demonstrated the concept of transformation in bacteria.

Avery, MacLeod, and McCarty experiment

Showed that DNA is the transforming principle.

Hershey and Chase experiment

Demonstrated that DNA, not protein, carries genetic information.

Mendel's unit character

Described the inheritance of traits through discrete units.

Levene's identification of DNA components

Identified the chemical structure of DNA in the 1920s.

Chargaff's findings

Discovered that the number of purines is not equal to the number of pyrimidines.

Hydrogen bonds

Two hydrogen bonds form between A and T; three hydrogen bonds form between C and G.

Double helix

The structure formed by two polymers of DNA.

Polarity of DNA strands

DNA strands have 5′ to 3′ polarity based on the phosphodiester backbone.

Deoxyribose

The sugar molecule in the backbone of DNA.

Nucleotide bases

Four bases that make up DNA: Adenine (A), Guanine (G), Cytosine (C), Thymine (T).

Purines

A class of nucleotide bases that includes Adenine (A) and Guanine (G).

Pyrimidines

A class of nucleotide bases that includes Cytosine (C) and Thymine (T).

Base composition

The amount of adenine equals the amount of thymine, and the amount of guanine equals the amount of cytosine.

Chargaff's rules

The number of adenines approximately equals the number of thymine, and the number of guanines approximately equals the number of cytosine.

Example of base percentages in human DNA

A=30.9%, T=29.4%, G=19.9%, C=19.8%.

Adenine

Always binds to thymine.

Guanine

Always binds to cytosine.

Self-replication of DNA

DNA can make exact copies of itself during reproduction or cell growth.

Phosphodiester bridges

Each strand of DNA is linked together through phosphodiester bonds.

Antiparallel strands

The 3' carbon of one ribose in one deoxyribonucleotide bonds with the 5' carbon in the ribose of the adjacent deoxyribonucleotide.

Polynucleotide reading direction

A polynucleotide is read from the 5' end to the 3' end.

dATP

Deoxyadenine-triphosphate.

dGTP

Deoxyguanine-triphosphate.

dCTP

Deoxycytosine-triphosphate.

dTTP

Deoxythymine-triphosphate.

DNA vs. RNA

DNA is double-stranded; RNA is single-stranded.

Sugars in DNA and RNA

DNA has deoxyribose sugars; RNA has ribose sugars.

Messenger RNA (mRNA)

Carries genetic information out of the nucleus for protein synthesis.

Ribosomal RNA (rRNA)

Constitutes 50% of a ribosome and is involved in protein synthesis.

Transfer RNA (tRNA)

Decodes the information carried by mRNA during protein synthesis.

Heteronuclear RNA (hnRNA)

Precursor to mRNA that undergoes processing before translation.

Small nuclear RNA (snRNA)

Involved in the splicing of pre-mRNA.

MicroRNA (miRNA)

Regulates gene expression by targeting mRNA for degradation.

Short interfering RNA (siRNA)

Involved in RNA interference and gene silencing.

Double-stranded RNA (dsRNA)

Can be found in some viruses and is involved in RNA interference.

RNA replication

Requires no priming, has many more initiation sites, is slower (50-100 b/sec vs. 1000 b/sec), has lower fidelity, and is more processive.

RNA polymerase

Enzyme that synthesizes RNA from a DNA template.

Promoter

Region where RNA synthesis begins and RNA polymerase assembles on DNA.

Histones

Proteins that DNA wraps around, affecting accessibility for transcription.

Acetylation

A chemical modification of histones that can affect gene expression.

Phosphorylation

A chemical modification of histones that can affect gene expression.

Methylation

A chemical modification of histones that can affect gene expression.

Ubiquitination

A chemical modification of histones that can affect gene expression.

Ribosylation

A chemical modification of histones that can affect gene expression.

Glycosylation

A chemical modification of histones that can affect gene expression.

Diploid

Contain 2 full complements of the human genome, organized into 23 homologous chromosome pairs.

Euchromatin

Genomic regions rich in genes that are less compactly organized.

Heterochromatin

Gene-poor genomic regions that are more densely packed.