Biochemistry 221 (BIOC202) Lecture 1: Levels of Structure in Nucleic Acids

Vocabulary-style practice flashcards covering levels of nucleic acid structure, chemistry, and base pairing from Biochemistry 221 (BIOC202) Lecture 1.

Primary Structure of Nucleic Acids

The linear sequence of nucleotide bases in a nucleic acid chain.

Secondary Structure of Nucleic Acids

The three-dimensional shape or conformation of the polynucleotide backbone.

Tertiary Structure of Nucleic Acids

The complex $3$D shape of the molecule resulting from the higher-order folding and interactions of its secondary structure elements.

Quaternary Structure of Nucleic Acids

The higher-order structural arrangements formed when nucleic acid molecules interact with other macromolecules (primarily proteins).

Genetic Code

The order of bases ($A$, $T(U)$, $G$, $C$) along the $DNA$ or $RNA$ polymer which specifies the amino acid sequence of proteins.

Mutation

A small change in sequence that can alter the encoded genetic information.

$DNA$ Secondary Structure

The double helix where two strands are coiled around each other in an antiparallel fashion.

Antiparallel Orientation

The structural arrangement where one $DNA$ strand runs $5' \text{ to } 3'$ and the complementary strand runs $3' \text{ to } 5'$.

$RNA$ Secondary Structure

Typically single-stranded but can fold back on itself to form local double-helical regions.

Stem-loop structures

Local double-helical regions in $RNA$ formed when it folds back on itself; also called hairpin loops.

$DNA$ Tertiary Structure

A more compact and organized structure formed through supercoiling where the double helix twists further.

Supercoiling

The process where the $DNA$ double helix twists and coils further to create tertiary structure.

$RNA$ Tertiary Structure

Formed when helices and unpaired regions in secondary structure interact to create an intricate, functional form.

Transfer $RNA$ ($tRNA$) Secondary Structure

A structure that resembles a cloverleaf.

Transfer $RNA$ ($tRNA$$) Tertiary Structure

An inverted $L$-shaped structure resulting from interactions between unpaired nucleotides in the loops.

Nucleic Acid–Protein Complexes

The most prevalent form of quaternary organization in nucleic acids, exemplified by ribosomes.

Ribosomes

Functional units essential for protein synthesis consisting of ribosomal $RNA$ ($rRNA$) complexed with numerous proteins.

Nucleic Acid–Nucleic Acid Complexes

Structured complexes formed by interactions between different nucleic acids, such as $tRNA$ pairing with $mRNA$ during translation.

Transient Nucleic Acid Hybrids

Short-lived $DNA-RNA$ or $RNA-RNA$ structures formed during replication and transcription.

Monomer

The smallest single unit of a polymer; in nucleic acids, these are nucleotides.

Nucleotide

A monomer consisting of a nitrogenous base, a sugar, and a phosphoric acid residue covalently bonded together.

Nitrogenous Bases

Nitrogen-containing biological molecules (nucleobases) that form the building blocks of $DNA$ and $RNA$.

Purines

Larger, two-ring nitrogenous base structures consisting of Adenine ($A$) and Guanine ($G$).

Pyrimidines

Smaller, one-ring nitrogenous base structures consisting of Cytosine ($C$), Thymine ($T$), and Uracil ($U$).

Adenine ($A$)

A purine base found in both $DNA$ and $RNA$.

Guanine ($G$)

A purine base found in both $DNA$ and $RNA$.

Cytosine ($C$)

A pyrimidine base found in both $DNA$ and $RNA$.

Thymine ($T$)

A pyrimidine base found specifically in $DNA$.

Uracil ($U$)

A pyrimidine base found specifically in $RNA$.

Nucleoside

A molecule consisting of a nitrogenous base and a pentose sugar.

Pentose Sugar

A $5$-carbon sugar, either ribose (in $RNA$) or deoxyribose (in $DNA$).

Glycosidic Linkage

The covalent bond between the $C-1'$ carbon of a sugar and the nitrogen of a base ($N-1$ for pyrimidines or $N-9$ for purines).

$C-1'$ carbon

The specific carbon on the pentose sugar that forms a linkage with the nitrogenous base.

$N-1$ nitrogen

The position on pyrimidine bases that bonds to the pentose sugar.

$N-9$ nitrogen

The position on purine bases that bonds to the pentose sugar.

Adenosine

A nucleoside formed from the base adenine and the sugar ribose.

Deoxyribose

A sugar found in $DNA$ that lacks an oxygen at the $2'$ position.

Ribose

A sugar found in $RNA$ that retains an oxygen at the $2'$ position.

Phosphoric acid ($H_3PO_4$)

The chemical residue that esterifies to the sugar of a nucleoside to form a nucleotide.

Esterification

The chemical process by which phosphoric acid is attached to the hydroxyl group of a sugar portion of a nucleoside.

$5'$ carbon

The carbon on the pentose sugar where phosphate groups are typically attached.

-monophosphate

The suffix added to the parent nucleoside name to identify a nucleotide with one phosphate group.

$$AMP$$

Adenosine monophosphate, consisting of adenosine plus one phosphate group.

$$5'-AMP$$

Adenosine $5'$-monophosphate, indicating the phosphate ester is at the $5'$ carbon hydroxyl group.

$$3'-AMP$$

Adenosine $3'$-monophosphate, indicating the phosphate ester is at the $3'$ carbon hydroxyl group.

Phosphodiester Bonds

The linkages that connect the $3'$ hydroxyl ($–OH$) group of one sugar to the $5'$ phosphate group of the next sugar.

Sugar-phosphate Backbone

The stable structural framework of nucleic acids formed by repeating phosphodiester linkages.

Direction of sequence reading

The sequence of bases attached to the backbone is read in the $5' \text{ to } 3'$ direction.

Complementary Base Pairing

The specific hydrogen bonding between bases ($A$ with $T$, $G$ with $C$) that stabilizes the $DNA$ double helix.

$A-T$ pair

A base pairing held together by $2$ hydrogen bonds.

$G-C$ debt

A base pairing held together by $3$ hydrogen bonds, making these regions more thermally stable.

Purine–Pyrimidine pairing

The only base geometry that fits the uniform width of the $DNA$ double helix.

$DNA$ polymerase

An enzyme that can only add nucleotides in the $5' \rightarrow 3'$ direction during replication.

Non-covalent forces

Forces like hydrogen bonding, ionic interactions, hydrophobic effects, and van der Waals forces that mediate quaternary structure.

Hydrogen bonding

Non-covalent force that stabilization base pairing and quaternary interactions.

Ionic interactions

Electrostatic forces that help mediate quaternary structural arrangements in nucleic acids.

Hydrophobic effects

Non-covalent forces contributing to the higher-order structural arrangements of nucleic acids.

Van der Waals forces

Weak, short-range electrostatic attractions that help stabilize quaternary structures.

Hierarchical structure

The organization of nucleic acids into levels (primary, secondary, tertiary, quaternary) similar to protein structure.

$2'$ position

The specific carbon on the sugar molecule that determines if the nucleic acid is $DNA$ (no oxygen) or $RNA$(oxygen present).

Uniform width of helix

Maintained in $DNA$ by pairing a large purine base with a small pyrimidine base.

Accuracy in decoding

Ensured during translation by the pairing of $tRNA$ with $mRNA$, forming an $RNA-RNA$ duplex.

Ribosomal $RNA$ ($rRNA$)

The nucleic acid component of ribosomes that complexes with proteins.

Parent nucleoside

The base plus sugar unit used as the root name when naming a nucleotide (e.g., adenosine in $AMP$).

Genetic information storage

A function of $DNA$ and $RNA$ sequence determined by the order of bases.

$DNA \text{ vs } RNA$ sugar difference

$DNA$ contains deoxyribose; $RNA$ contains ribose.

$DNA \text{ vs } RNA$ base difference

$DNA$ contains Thymine ($T$); $RNA$ contains Uracil ($U$).

Cloverleaf interaction

Interaction of unpaired nucleotides in the loops of $tRNA$ results in folding from cloverleaf to inverted $L$-shape.

Thermal stability

Increases in $DNA$ molecules with higher $GC$ content due to the extra hydrogen bond in $G-C$ pairs.

Backbone protection

The sugar-phosphate backbone is stable and protects the genetic code held in the base sequence.

Complex $3$D shape

The definition of the tertiary structure of $DNA$ or $RNA$.

Glycosidic linkage (Purine)

A bond between the $C-1'$ carbon of the sugar and the $N-9$ nitrogen of the purine base.

Glycosidic linkage (Pyrimidine)

A bond between the $C-1'$ carbon of the sugar and the $N-1$ nitrogen of the pyrimidine base.

Polynucleotide backbone

The chain of sugars and phosphates that defines the secondary structural conformation.

Hairpin loops

Another name for the stem-loop structures found in $RNA$ secondary structure.

Hierarchical levels of DNA

Organized into four levels: primary, secondary, tertiary, and quaternary.

Linear sequence purpose

Encodes genetic information (the genetic code).

Translation accuracy

Mediated by a short-lived $RNA–RNA$ duplex between $tRNA$ and $mRNA$.

Nucleic Acid Monomers

Nucleotides, consisting of three covalently bonded parts: base, sugar, and phosphoric acid residue.

Higher-order folding

The process resulting in tertiary structure elements in $DNA$ or $RNA$.

Base sequence reading convention

Always read from the $5'$ end to the $3'$ end.

Hydrogen bond count (A-T)

$2$ hydrogen bonds.

Hydrogen bond count (G-C)

$3$ hydrogen bonds.

Complexity difference

The distinction between structural levels ranging from linear sequences to intricate protein-complexed units.

Inverted L-shape

The specific tertiary structure adopted by transfer $RNA$ ($tRNA$).

Covalent polymer parts

Nitrogenous base, sugar, and phosphoric acid residue.

Purine structure

A double-ring nitrogenous structure.

Pyrimidine structure

A single-ring nitrogenous structure.

Nucleoside components

Nitrogenous base and a pentose sugar (ribose or deoxyribose).

Transcription hybrids

Transient $DNA–RNA$ complexes formed during the transcription process.

Replication orientation

Crucially requires the antiparallel orientation of $DNA$ strands for enzyme recognition.

Function of Quaternary Structure

Essential for the execution of specific biological functions in living systems.

DNA-RNA hybrids

Transient complexes formed during $DNA$ replication and transcription.

RNA-RNA duplex

A complex formed between $tRNA$ and $mRNA$ during translation.

Local double-helical regions

Regions in single-stranded $RNA$ where the molecule folds back on itself.

Hierarchical description

The description of nucleic acid structure in levels, similar to protein structural hierarchy.

Biochemistry 202 outcome

Understanding how genetic information is stored, accessed, and used based on structural levels.

Nucleic acids purpose

To carry genetic information in the form of $DNA$ and $RNA$.

Stable backbone function

Protects the genetic code held in the base sequence.

Uniform width requirement

In a $DNA$ double helix, a large base (purine) must always pair with a small base (pyrimidine).