IB Biology: Nucleic Acids and Proteins

Comprehensive vocabulary flashcards covering the structure, properties, and functions of nucleic acids and proteins based on the IB Biology syllabus.

DNA (Deoxyribonucleic acid)

The genetic material of all living organisms, located within chromosomes and encoding information for organismal and cellular growth and development.

Characteristics of Life

The suite of essential traits shared by all living organisms: possessing at least one cell, metabolizing, maintaining homeostasis, responding to stimuli, reproducing, growing and developing, and storing genetic information as DNA.

Virus

A biological entity consisting of genetic material (DNA or RNA) enclosed in a protein coat that is not considered alive because it lacks cellular organization, metabolic pathways, homeostasis, and autonomous replication.

Nucleotide

The fundamental monomer of nucleic acids, consisting of three components: a phosphate group, a five-carbon pentose sugar, and a nitrogenous base.

Sugar–Phosphate Backbone

A continuous chain of alternating covalently bonded pentose sugars and phosphate groups in DNA and RNA formed through condensation reactions.

Deoxyribose

The five-carbon pentose sugar found in DNA nucleotides, distinctively possessing a hydrogen atom ($-\text{H}$) bonded to the $2'$ carbon.

Ribose

The five-carbon pentose sugar found in RNA nucleotides, distinctively possessing a hydroxyl group ($-\text{OH}$) bonded to the $2'$ carbon.

Double Helix

The three-dimensional conformation of DNA formed by two complementary polynucleotide strands twisted around each other.

Complementary Base Pairing

The specific hydrogen bonding between nitrogenous bases in nucleic acids: adenine pairs with thymine (or uracil in RNA) via two hydrogen bonds, and cytosine pairs with guanine via three hydrogen bonds.

Antiparallel

The structural property of DNA where the two complementary polynucleotide strands run side-by-side in opposite chemical directions ($5' \rightarrow 3'$ and $3' \rightarrow 5'$).

Directionality ($5'$ to $3'$)

The fixed orientation in which nucleic acids are synthesized, where polymerizing enzymes add new nucleotides only to the $3'$ carbon end of an existing strand.

Universal Genetic Code

The conservation of identical triplet codon assignments for specific amino acids across nearly all forms of life, providing evidence of universal common ancestry.

Tetranucleotide Hypothesis

An early hypothesis proposed by Phoebus Levene stating that DNA is composed of repeating units containing equal quantities of adenine, thymine, cytosine, and guanine.

Chargaff's Rule

The discovery by Erwin Chargaff that in any sample of double-stranded DNA, the ratio of adenine equals thymine ($\%A = \%T$) and guanine equals cytosine ($\%G = \%C$), which falsified the tetranucleotide hypothesis.

Certainty of Falsification

A philosophical principle formulated by Karl Popper stating that while scientific hypotheses cannot be conclusively proven true by inductive observations, they can be conclusively proven false by experimental evidence.

Hershey–Chase Experiment

A 1952 experiment using T2 bacteriophages with radioactively labeled sulfur ($^{35}\text{S}$) in protein and phosphorus ($^{32}\text{P}$) in DNA to prove that DNA, not protein, enters bacteria to act as genetic material.

Purines

Double-ring nitrogenous bases found in nucleic acids, comprising adenine and guanine.

Pyrimidines

Single-ring nitrogenous bases found in nucleic acids, comprising cytosine, thymine, and uracil.

Nucleosome

A eukaryotic chromosome packaging structure composed of negatively charged DNA wound twice around an octamer of eight positively charged histone proteins, held together by an additional linker histone (H1).

Amino Acid

The fundamental monomer of proteins, featuring a central alpha carbon ($\alpha\text{-carbon}$) bonded to an amine group ($-\text{NH}_2$), a carboxyl group ($-\text{COOH}$), a hydrogen atom, and a variable side chain ($R$ group).

Peptide Bond

A covalent bond formed between the carbon of a carboxylic acid group of one amino acid and the nitrogen of an amine group of an adjacent amino acid via a condensation reaction.

Dipeptide

A compound formed from the condensation reaction of two amino acids linked by a single peptide bond, with the release of one water molecule.

Polypeptide

A continuous, unbranched chain of amino acids joined together by peptide bonds synthesized at ribosomes during translation.

Essential Amino Acids

The nine amino acids required by humans that cannot be synthesized internally and must be consumed through the diet.

Non-Essential Amino Acids

The eleven amino acids required by humans that can be synthesized internally by the body from other metabolic precursors.

Denaturation

A conformational change in the three-dimensional shape of a protein resulting in the irreversible loss of its biological function, caused by extremes in temperature or pH.

Primary Protein Structure

The specific linear sequence and total number of amino acids in a polypeptide chain, determined directly by the nucleotide sequence of the corresponding gene.

Secondary Protein Structure

The regular local folding pattern of a polypeptide chain into alpha-helices or beta-pleated sheets, stabilized by hydrogen bonds between $C=O$ and $N-H$ backbone groups at uniform intervals.

Tertiary Protein Structure

The three-dimensional folding of a single polypeptide chain governed by chemical interactions among variable $R$ groups, including ionic bonds, hydrogen bonds, disulfide bridges, and hydrophobic interactions.

Disulfide Bridge

A strong covalent bond formed between the sulfur atoms of two cysteine amino acid side chains located in close proximity within a folded polypeptide.

Quaternary Protein Structure

The structural assembly of a protein that consists of two or more distinct polypeptide chains held together by intermolecular bonds and interactions.

Conjugated Protein

A complex protein composed of one or more polypeptide chains joined to a non-polypeptide prosthetic group, such as the haem groups in haemoglobin.

Prosthetic Group

A non-polypeptide chemical group permanently incorporated into the structure of a conjugated protein that is essential to its biological function.

Non-Conjugated Protein

A protein composed exclusively of amino acid residues in polypeptide chains without any attached prosthetic groups, such as insulin and collagen.

Globular Protein

A functional class of proteins with a rounded, spherical conformation, high water solubility, and a core of hydrophobic amino acids shielded by hydrophilic surface residues (e.g., insulin).

Fibrous Protein

A structural class of proteins with elongated, repetitive amino acid sequences, low water solubility, and high tensile strength (e.g., collagen).

Cryogenic Electron Microscopy

An advanced microscopy technique that visualizes individual protein molecules and complex molecular assemblies at cryogenic temperatures with atomic-level resolution.