Medical Isozymes, Chromosome Structure, and Epigenetics

Flashcards covering medical isozymes (LDH), GTPase regulation, chromosomal structure and redundancy, DNA compaction, and epigenetic mechanisms based on lecture transcript notes.

Lactate Dehydrogenase (LDH)

A tetramer enzyme participating in the lactic acid fermentation pathway consisting of 4 available isoform units expressed in heart or skeletal muscle.

LDH 1 > 2

A blood test result signifying a heart attack, where the normal ratio of $LDH 2 > 1$ is reversed.

LDH 5 > 4

A blood test result signifying liver damage, where the normal ratio of $LDH 4 > 5$ is reversed.

GTPases

G proteins that hydrolyze GTP by removing a phosphate to put the regulatory nucleotide to work.

GEFs (Guanine nucleotide Exchange Factors)

Factors that regenerate G proteins by replacing spent GDP with fresh GTP.

GAPs (GTPase-Activating Proteins)

Proteins that stimulate G proteins to hydrolyze GTP, which inactivates the enzyme.

Ran

A GTPase that facilitates protein movement between the nucleus and the cytosol.

Endosymbiosis Theory

The theory that eukaryotic organelles originated from an anaerobic archaeon forming a nucleus, followed by the engulfing of an aerobic bacterium (mitochondrion) and a photosynthetic bacterium (chloroplast).

Telomeres

The functional elements found at the ends of linear chromosomes.

Origins of Replication

The specific locations on a chromosome where the Replication Bubble starts.

Centromere

The chromosomal site where sister chromatids connect during mitosis or meiosis; often identified using C-band staining.

Spectral Karyotypes (SKY)

An imaging technique used when genomes are sequenced to paint the chromosomes in color.

Translocations

A chromosomal abnormality involving the swapping of big chunks of chromosomes, often seen in cancer cell karyotypes.

Aneuploidy

The condition of having plus or minus some of the chromosomes, resulting in an abnormal count.

Genetic Redundancy

The presence of redundancies and relics in DNA; in humans, repeated sequences make up $53.94\%$ of the genome.

VNTRs and STRs

Variable Number Tandem Repeats ($15-100\,bp$) and Short Tandem Repeats ($2-5\,bp$) used in DNA fingerprinting; STRs include trinucleotide repeats related to diseases like Huntington's.

SINEs (Short Interspersed Elements)

Transposable elements with less than $500\,bp$ inserts; Alu sequences make up approximately $40\%$ of these.

LINEs (Long Interspersed Elements)

Transposable elements with approximately $6000\,bp$ inserts; L1s make up approximately $60\%$ of these and constitute $20.68\%$ of the human genome.

Satellite DNA

Long tandem repeats with GC content different from the species average, found in heterochromatin (centromeres and telomeres), making up $3.92\%$ of human DNA.

Supercoiling

The primary mechanism needed to compact small, circular genomes like those in most prokaryotes and some viruses.

Nucleosome

The base unit of eukaryotic DNA compaction where $147\,bp$ of DNA wraps around a histone octamer.

Heterochromatin

Highly compacted chromatin with high histone density, located at telomeres and centromeres, where gene expression is repressed.

Euchromatin

Uncoiled chromatin with lower histone density found in protein-coding regions where gene expression is active.

Barr Body

An inactivated X-chromosome that exists entirely as heterochromatin.

Cajal Bodies

Nuclear condensates that assist with the splicing of transcripts.

Histone Tails

Prime sites for modification where lysines can be acetylated/methylated, arginines methylated, and serines phosphorylated.

Writers

Proteins such as HAT (acetyltransferase) or HMT (methyl transferase) that add histone marks.

Erasers

Proteins such as HDAC (deacetylase) or HDM (demethylase) that remove histone marks.

Readers

Proteins that recognize specific combinatorial histone marks to promote gene expression, silencing, or other biological functions.

Barrier (Insulator) Sequence

A DNA sequence that stops a wave of heterochromatin formation through tethering, sheltering, or re-writing marks.

Epigenetics

The study of heritable changes in gene expression that occur without an alteration of the DNA sequence.

DNA Methylation Disorders

Conditions like Angelman and Prader-Willi syndromes (imprinting disorders) or cancer resulting from hypermethylation of tumor suppressor genes like BRCA1.