Chapter 9: DNA Structure and Genetics Practice

Vocabulary flashcards created from the lecture notes on introductory genetics, DNA structure, base pairing rules, and basic probability concepts.

Genetic Information

Information contained in genes which, when passed on to a new generation, influences the form and characteristics of the offspring.

Histones

Nuclear proteins that scientists originally believed carried genetic information prior to discovering that DNA is the primary genetic material.

Transcription

The biological process in the nucleus where DNA is copied into an RNA molecule.

Translation

The biological process occurring in the cytoplasm where messenger RNA (mRNA) is read by a ribosome to physically build a protein.

Nucleotide

The fundamental building block of DNA consisting of three components: a five-carbon deoxyribose sugar ring, a phosphate group, and a nitrogenous base.

Phosphodiester bond

The chemical bond that links adjacent nucleotides together between the $5'$ phosphate group and the $3'$ hydroxyl group to form the side backbone of a DNA strand.

Chardroff's rule

The rule stating that adenine always pairs with thymine, and guanine always pairs with cytosine in double-stranded DNA.

Pyrimidine

A class of nitrogenous bases made up of a single six-carbon ring, consisting of cytosine and thymine in DNA.

Purine

A class of nitrogenous bases made up of two rings (a six-carbon ring and a five-carbon ring), consisting of adenine and guanine.

Hydrogen bond

The type of chemical bond holding complementary base pairs together in DNA, with two bonds between A and T, and three bonds between G and C.

Nucleoside

A subunit of DNA consisting of only two components: a five-carbon pentose sugar and a nitrogenous base, lacking the phosphate group.

Antiparallel

The structural orientation of double-stranded DNA where the two complementary strands run in opposite directions relative to their $3'$ and $5'$ ends.

UVR gene

A gene that turns on during REM sleep to scan and repair DNA damage or mismatch bulges in skin cells caused by exposure to ultraviolet light.

Independent events

Separate probability events whose outcomes do not influence each other, calculated by multiplying their individual probabilities together.

Genetic Information

Information contained within genes that, when transmitted to the next generation, influences the physical traits and developmental form of the offspring.

Four Key Properties of Genetic Material

1. Replication: must accurately duplicate itself. 2. Storage: must hold complex genetic instructions. 3. Expression: must direct cellular functions. 4. Variation/Mutation: must allow occasional structural changes to produce diversity.

Histone Hypothesis (Pre-1944)

The historical, incorrect belief that nuclear proteins (histones) served as the hereditary material because of their abundance, while DNA was assumed to be merely a structural scaffold holding proteins together.

Cellular Uniformity

The biological principle that every somatic cell in an organism contains an identical nucleus and chromosome set regardless of its specialized anatomical location.

Differential Gene Regulation

The mechanism by which cells selectively activate or repress specific genes according to their tissue identity and physiological role, despite possessing identical genomic sequences.

Transcription

The enzymatic process occurring in the nucleus during which double-stranded genomic DNA is copied into a complementary single-stranded RNA molecule.

Translation

The cytoplasmic process in which ribosomes decode an mRNA sequence to synthesize a polypeptide chain (protein), thereby manifesting the physical phenotype.

Primary Classes of RNA

mRNA (messenger RNA, transports coding information to the cytoplasm), rRNA (ribosomal RNA, structural/catalytic ribosome component), and tRNA (transfer RNA, carries amino acids to ribosomes during protein assembly).

Nucleotide

The monomeric building block of nucleic acids consisting of three parts: a pentose sugar (deoxyribose), a phosphate group, and a nitrogenous base.

Nucleoside

A structural subunit consisting solely of a pentose sugar and a nitrogenous base, lacking a phosphate group.

Pentose Sugar Carbon Numbering

Carbons labeled $1'$ through $5'$: the base attaches at the $1'$ carbon, an $-H$ atom resides at the $2'$ carbon, a free hydroxyl group ($-OH$) resides at the $3'$ carbon, and the phosphate group bonds to the $5'$ carbon.

Phosphodiester Bond

A covalent linkage connecting adjacent nucleotides formed when the $5'$ phosphate group of an incoming nucleotide reacts with the $3'$ hydroxyl group of the prior pentose sugar.

Purines vs. Pyrimidines

Purines are double-ring nitrogenous bases consisting of Adenine ($A$) and Guanine ($G$). Pyrimidines are single-ring bases consisting of Cytosine ($C$), Thymine ($T$), and Uracil ($U$ in RNA).

Chargaff's Rules

In double-stranded DNA, the quantity of Adenine equals Thymine ($A = T$) and Guanine equals Cytosine ($G = C$); purines always bind specifically to complementary pyrimidines.

Hydrogen Bonding in DNA

Non-covalent bonds stabilizing complementary base pairs: Adenine and Thymine share $2$ hydrogen bonds, whereas Guanine and Cytosine share $3$ hydrogen bonds.

Antiparallel Strands

The spatial arrangement of the two complementary strands in a DNA double helix running in opposite chemical directions (5'
ightarrow 3' opposite 3'
ightarrow 5').

Dimensional Measurements of the Double Helix

Helical width is $20\,\text{\AA}$, distance between adjacent base pairs is $3.4\,\text{\AA}$, one complete $360^\circ$ turn spans $10$ base pairs, and the length of one complete turn is $34\,\text{\AA}$.

UVR Gene Repair Mechanism

A repair mechanism active during REM sleep that forms a donut-shaped protein complex with an internal diameter of $20\,\text{\AA}$ to scan DNA strands and excise structural distortions or mismatched bases caused by solar UV radiation.

Xeroderma Pigmentosum

A genetic pathology resulting from a non-functional UVR gene; affected individuals cannot repair UV-induced DNA lesions, requiring complete avoidance of daytime sunlight.

Product Rule for Independent Events

A statistical rule stating that the joint probability of independent occurrences equals the product of their individual probabilities (e.g., rolling two $6$s: $P = \frac{1}{6} \times \frac{1}{6} = \frac{1}{36}$).

Suicide Jack Probability

A standard $52$-card deck contains $2$ suicide jacks (jacks depicted with a blade through the head), giving a probability of $P = \frac{2}{52} = \frac{1}{26}$ on a single draw.

Independence of Historical Events

The probability principle stating that prior outcomes of independent trials (such as coin tosses or roulette wheel spins) have zero influence on future outcomes.

Discovery of DNA Molecular Structure

In $1953$, James Watson and Francis Crick determined the double-helix structure of DNA, building directly upon key X-ray diffraction images generated by Rosalind Franklin and Maurice Wilkins.

Growth Hormone Gene Variation

A key biological example of how minor structural variations or mutations in a specific gene determine observable physical phenotypes, such as tall or short stature.

DNA Structural Polarity

The inherent chemical directionality of a nucleic acid strand, which runs from an exposed $5'$ phosphate group at one terminus to a free $3'$ hydroxyl group ($-OH$) at the opposite terminus.

Pyrimidine Identification Mnemonic

A memory aid noting that pyrimidines are single-ring nitrogenous bases whose names contain the letter 'y' (Cytosine and Thymine; Uracil in RNA), whereas purines do not.

Major and Minor Grooves

The alternating outer structural indentations that spiral along the DNA double helix as a consequence of the asymmetric helical geometry and angles of paired bases.

Right-Handed Helical Configuration

The Watson-Crick spatial geometry of DNA in which both antiparallel strands wind upward around the central axis in a clockwise (right-handed) direction.

Gene Segment Length Calculation

Because adjacent base pairs are spaced exactly $3.4\,\text{\AA}$ apart, gene length is calculated as the base-pair count multiplied by $3.4\,\text{\AA}$ (e.g., a $100$-base-pair segment equals $100 \times 3.4\,\text{\AA} = 340\,\text{\AA}$).

Human Somatic Genome Size

The total genetic content inside a human somatic cell nucleus, comprising approximately $3.6 \times 10^9$ ($3,600,000,000$) base pairs that must be copied prior to cell division.

Mitotic Replication Dynamics

The rapid cellular process observed during fast-dividing mitosis wherein chromosomes condense, replicate, and segregate in under $20\,\text{s}$.

REM Sleep UVR Activation

The physiological timing during which the UVR repair gene activates to excise solar ultraviolet radiation damage and structural mismatches accumulated during daytime waking hours.

Mismatch Bulge Formation

A physical distortion in the DNA helix caused by improper base pairings (such as Thymine pairing with Guanine), which halts the $20\,\text{\AA}$ UVR ring complex until repaired.

Chi-Square Test ($\chi^2$)

A statistical goodness-of-fit test used in genetics laboratory analysis to determine whether observed phenotypic counts statistically match expected Mendelian inheritance ratios.

Yahtzee Probability ($5$ Independent Dice)

The compound probability of rolling five identical designated values simultaneously on a single roll: $P = \left(\frac{1}{6}\right)^5 = \frac{1}{7776}$.

Standard Card Deck Composition

A full deck containing $52$ cards split into $2$ colors (Red and Black), $4$ suits (Hearts, Diamonds, Spades, Clubs), and $13$ ranks per suit ($1$ through $10$, Jack, Queen, King).

Red Card Single-Draw Probability

The probability of randomly drawing a red card from a standard $52$-card deck: $P = \frac{26}{52} = \frac{1}{2}$.

Heart Suit Single-Draw Probability

The probability of randomly drawing a heart from a standard $52$-card deck: $P = \frac{13}{52} = \frac{1}{4}$.

Ace Single-Draw Probability

The probability of randomly drawing an ace from a standard $52$-card deck: $P = \frac{4}{52} = \frac{1}{13}$.

Compound Card Draw with Replacement

The compound probability of sequentially drawing a Red card, Heart, Ace, and Suicide Jack with replacement: $P = \frac{1}{2} \times \frac{1}{4} \times \frac{1}{13} \times \frac{1}{26} = \frac{1}{2704}$.

Gambler's Fallacy in Independent Events

The incorrect belief that past trials alter future independent odds (e.g., after $10$ consecutive black roulette spins, the $11$th spin still has an independent probability of $P = \frac{1}{2}$).

Darwin's Tenets (Frogs in the Pond Lab)

Foundational principles of population genetics and natural selection covering phenotypic variation, differential survival, and trait inheritance in populations.

CRISPR Research Project Scope Rule

The course requirement that student groups must narrow broad molecular topics to a single target organism (e.g., CRISPR/Cas application in bananas rather than general plants).

Laboratory Exam Testing Materials

The mandatory exam policy requiring a standard, non-programmable calculator, while explicitly prohibiting cell phones, laptops, and programmable devices.