Grade 12 Life Sciences: DNA, RNA, Protein Synthesis, and Genetic Technology

Comprehensive vocabulary flashcards covering the discovery of DNA, nucleic acid structure, replication, protein synthesis, gene mutations, extraction methods, and DNA technology based on Grade 12 Life Sciences.

Chargaff's Rules

The biochemical principle formulated in 1950 stating that in any double-stranded DNA molecule, the amount of adenine ($\text{A}$) always equals thymine ($\text{T}$) and the amount of cytosine ($\text{C}$) always equals guanine ($\text{G}$).

Photo 51

The famous X-ray diffraction photograph of DNA captured by Rosalind Franklin in 1952, which provided key structural data demonstrating the helical shape, diameter ($20\,\text{Å}$), pitch ($34\,\text{Å}$), and base pair spacing ($3.4\,\text{Å}$) of DNA.

Rosalind Franklin

A physical chemist who utilized X-ray crystallography to produce Photo 51 in 1952, determining DNA's helical dimensions; her critical research data was shown to Watson and Crick without her knowledge or consent.

Maurice Wilkins

A researcher at King's College London who worked on X-ray crystallography, shared Rosalind Franklin's data with James Watson and Francis Crick, and shared the 1962 Nobel Prize in Physiology or Medicine.

James Watson and Francis Crick

Scientists at Cambridge University who pieced together physical model representations in 1953 to publish the correct double-helix structure of DNA in Nature.

Nuclear DNA

The double-stranded, helical chromosomal DNA located within the cell nucleus that binds to histone proteins to form chromatin and encodes genetic traits on chromosomes.

Mitochondrial DNA (mtDNA)

A small, circular DNA molecule found inside mitochondria that codes for mitochondrial proteins and is inherited strictly through the maternal lineage.

Chloroplast DNA

The distinct type of circular DNA found inside chloroplasts in plant cells.

Endosymbiotic Theory

The evolutionary theory proposing that mitochondria originated from primitive, free-living aerobic prokaryotes that were engulfed by ancestral eukaryotic cells billions of years ago and retained their own circular DNA.

Maternal Inheritance

The inheritance pattern of mitochondrial DNA ($\text{mtDNA}$), wherein offspring receive mitochondria solely from the female egg cell while sperm contribute none, leaving the genetic sequence unaltered across generations.

Nucleotide

The basic monomeric building block of nucleic acids, consisting of a phosphate group, a pentose sugar, and a nitrogenous base.

Phosphate Group

A chemical component of a nucleotide that imparts a negative charge to the nucleic acid molecule and links alternating sugar molecules to build the continuous backbone.

Deoxyribose

A five-carbon pentose sugar found in DNA nucleotides that lacks one oxygen atom in comparison to ribose.

Ribose

A five-carbon pentose sugar found in RNA nucleotides that contains an additional oxygen atom missing in deoxyribose.

Purine

A class of nitrogenous bases composed of a double-ring structure; examples found in DNA and RNA include adenine and guanine.

Pyrimidine

A class of nitrogenous bases composed of a single-ring structure; examples include cytosine, thymine, and uracil.

Adenine (A)

A double-ring purine base that pairs with thymine in DNA (or uracil in RNA) via two weak hydrogen bonds.

Thymine (T)

A single-ring pyrimidine base found exclusively in DNA that pairs with adenine via two weak hydrogen bonds.

Cytosine (C)

A single-ring pyrimidine base that pairs specifically with guanine via three weak hydrogen bonds in both DNA and RNA.

Guanine (G)

A double-ring purine base that pairs specifically with cytosine via three weak hydrogen bonds in both DNA and RNA.

Uracil (U)

A single-ring pyrimidine nitrogenous base found in RNA that substitutes for thymine and pairs with adenine.

Antiparallel Strands

The structural arrangement of the two complementary strands in a DNA double helix, where one strand runs in the $5' \rightarrow 3'$ direction and the other runs in the $3' \rightarrow 5'$ direction.

Histones

Basic proteins around which chromosomal DNA wraps in eukaryotic nuclei to form nucleosomes and condense into chromatin.

Nucleosome

The fundamental subunit of chromatin, consisting of a segment of DNA wrapped around a core of histone proteins.

Chromatin

The DNA-containing diffuse network found in the eukaryotic nucleus during interphase (the non-dividing stage of the cell cycle).

Chromatid

One of the two identical individual strands of a replicated chromosome that are joined together at the centromere.

Centromere

The constricted region of a chromosome that holds two sister chromatids together and serves as the attachment point for spindle fibres during cell division.

Chromosome

A condensed, thread-like structure of DNA and protein that carries genetic information organized into genes.

Chromatin Network

Visible thread-like structures composed of DNA and proteins situated in the nucleus of an inactive, non-dividing cell.

Nucleolus

A distinct dense structure within the cell nucleus responsible for transcribing and assembling ribosomal RNA ($\text{rRNA}$).

Nucleoplasm

The fluid protoplasmic substance enclosed within the nuclear membrane surrounding the chromatin and nucleolus.

Ribosome

A cytoplasmic organelle composed of RNA and proteins that reads mRNA codons and serves as the site of protein synthesis (translation).

DNA Replication

The biological process occurring in the nucleus during interphase whereby an original DNA molecule produces two identical double-stranded DNA molecules.

Semi-conservative Replication

The mechanism of DNA copying wherein each newly synthesized double helix is composed of one conserved parental strand and one newly assembled daughter strand.

Template Strand

An original single strand of DNA that provides the complementary nucleotide framework upon which a new DNA or RNA strand is assembled.

Complementary Strand

A newly synthesized polynucleotide strand generated by matching complementary bases against an existing template strand.

DNA Helicase

An enzyme responsible for unwinding the DNA double helix and breaking the weak hydrogen bonds between complementary base pairs to separate the strands.

DNA Polymerase

The enzyme that synthesizes new DNA strands by attaching free nucleoplasmic nucleotides to the exposed complementary bases of a template strand during replication.

DNA Ligase

An enzyme known as the molecular glue that seals breaks in the sugar-phosphate backbone by forming phosphodiester bonds to link DNA fragments.

Central Dogma of Molecular Biology

The fundamental framework stating that genetic information flows directionally within biological systems from DNA to RNA to Protein.

Transcription

The first stage of protein synthesis occurring in the nucleus, in which an RNA polymerase enzyme synthesizes a single strand of mRNA from a DNA template.

RNA Polymerase

The primary enzyme of transcription that separates DNA strands and joins complementary RNA nucleotides to synthesize an mRNA transcript.

Messenger RNA (mRNA)

A single-stranded RNA molecule transcribed in the nucleus that carries the genetic sequence code from DNA out through the nuclear pore to ribosomes in the cytoplasm.

Transfer RNA (tRNA)

A folded, cloverleaf-like RNA molecule in the cytoplasm possessing a specific anticodon at one end and carrying its designated amino acid to the ribosome.

Ribosomal RNA (rRNA)

The structural and functional RNA component synthesized in the nucleolus that associates with proteins to form ribosomes.

Triplet

A sequence of three consecutive nitrogenous bases on a DNA molecule that codes for one specific amino acid in a polypeptide chain.

Codon

A sequence of three adjacent nitrogenous bases situated on an mRNA molecule that directs the placement of a specific amino acid.

Anticodon

A sequence of three adjacent nitrogenous bases situated on a tRNA molecule that pairs complementarily with an mRNA codon to deliver the correct amino acid.

Translation

The second stage of protein synthesis occurring at the ribosome, where the genetic code in mRNA is translated into an amino acid sequence joined by peptide bonds to create a protein.

Gene Expression

The process by which coded information stored within a gene is used to direct the synthesis of a functional protein molecule.

Gene Mutation

A permanent alteration in the nucleotide sequence or arrangement of bases in DNA, which can modify mRNA transcription and alter the resulting polypeptide structure.

Point Mutation

A mutation that affects a single nucleotide within a DNA sequence, typically exemplified by a base substitution.

Substitution Mutation

A type of point mutation where a single nitrogenous base in DNA is swapped for a different base, categorised as silent, missense, or nonsense.

Silent Mutation

A base substitution that produces an altered codon that still encodes the identical amino acid due to the degeneracy of the genetic code, leaving the protein unchanged.

Missense Mutation

A base substitution that changes an mRNA codon such that a different amino acid is incorporated into the growing polypeptide, potentially altering protein structure and function.

Nonsense Mutation

A base substitution that prematurely converts an amino acid-coding codon into a stop codon, terminating translation early and producing a truncated, non-functional protein.

Frameshift Mutation

A mutation caused by the insertion or deletion of one or more nucleotides (not in multiples of three) that shifts the entire triplet reading frame for all subsequent codons.

Insertion Mutation

The addition of one or more nucleotide bases into a DNA sequence, which causes a frameshift and results in abnormal amino acid coding downstream.

Deletion Mutation

The loss of one or more nucleotide bases from a DNA sequence, causing a frameshift that completely alters downstream codon reading and protein formation.

Chemical DNA Extraction

A salt-based isolation procedure that uses detergent to dissolve lipid cell and nuclear membranes, salt to neutralize the DNA backbone charge, and ice-cold ethanol to precipitate intact DNA strands.

Mechanical DNA Extraction

A cell lysis method that utilizes small beads (such as metal, glass, or zirconia) shaken at high velocity to physically shear and shatter tough cell walls and membranes.

Polymerase Chain Reaction (PCR)

A laboratory technique used to amplify trace quantities of DNA millions of times through sequential thermal cycles of denaturation ($\sim 95^\circ\text{C}$), primer annealing ($\sim 55^\circ\text{C}$), and polymerase extension ($\sim 72^\circ\text{C}$).

DNA Fingerprinting

A forensic and diagnostic profiling technique that analyzes highly variable, non-coding repetitive DNA regions to generate a unique banding pattern for an individual.

Non-coding DNA

The approximately $98\%$ of the human genome that does not code for proteins, containing highly variable repetitive sequences known as Short Tandem Repeats (STRs) used in genetic profiling.