Introduction to DNA and Chromosome Structure

Flashcards covering classical DNA identity experiments, structural features of DNA, chromatin packaging mechanisms, and chromosome structure based on lecture notes.

Transforming principle

The concept demonstrated by Griffith showing that dead organisms could pass material to a live organism, allowing it to transform and adopt new characteristics.

Phage

A bacterial virus composed exclusively of protein and DNA that infects bacteria host cells.

Sulfur-35 ($S^{35}$)

A radioactive isotope of sulfur used to selectively label proteins containing cysteine and methionine.

Phosphorus-32 ($P^{32}$)

A radioactive isotope of phosphorus used in Hershey and Chase's experiments to selectively label DNA.

Purines

A class of nitrogenous bases in DNA that possess double-ring structures and are larger than pyrimidines.

Pyrimidines

A class of nitrogenous bases in DNA that possess single-ring structures and are smaller than purines.

Chargaff's rule

The finding that DNA always contains a $1:1$ ratio of purines to pyrimidines across different organisms.

X-ray diffraction

An imaging technique used by Dr. Rosalind Franklin to analyze DNA structure, revealing its double-stranded helical nature with major and minor grooves.

5' end

The top end of a DNA strand named for the fifth carbon position on the sugar molecule.

3' OH group

A hydroxyl group located on carbon three of deoxyribose that must be present for a phosphate bond to form during DNA strand synthesis.

Antiparallel

The structural arrangement of double-stranded DNA where one strand runs $5'$ to $3'$ while the opposite strand runs $3'$ to $5'$.

Nucleosome

A structural unit of DNA packaging consisting of DNA wrapped twice around a core set of histone proteins.

Histones

Positively charged proteins (specifically H2A, H2B, H3, and H4) that attract and bind to negatively charged DNA.

Histone H1

A hydrophobic protein located between nucleosomes that pulls nucleosome complexes together into compact groupings.

Scaffold proteins

Non-histone proteins that provide a structural framework to organize wound-up DNA and nucleosome fibers into higher-order chromosome structures.

p arm

The shorter top portion/arm of a mapped chromosome.

q arm

The longer bottom portion/arm of a mapped chromosome.

Trisomy 18

A chromosomal condition involving an extra copy of chromosome 18 that can result in a live birth lasting from a matter of minutes to hours.

Trisomy 21

A chromosomal condition commonly known as Down syndrome caused by having three copies of chromosome 21.

Turner syndrome

A condition characterized by having only one X chromosome and no second sex chromosome.

LINES

Long Interspersed Elements; long repetitive sequences of non-coding DNA found within the genome.

SINES

Short Interspersed Elements; repetitive non-coding DNA sequences that are less than $400$ base pairs in length.

Telomeres

Repetitive DNA structures found at the physical ends of chromosomes.

Junk DNA

An informal historical term given to the 98\text{\textpercent} of the human genome that does not directly code for mRNAs or proteins.