Protein Synthesis, Inheritance, and the Human Genome

Comprehensive vocabulary flashcards covering muscle protein balance, DNA transcription and translation, protein disposal mechanisms, patterns of inheritance, meiosis variation, epigenetics, and the human genome.

Net Protein Balance

The counterbalanced fluctuation between muscle protein synthesis (MPS) and muscle protein breakdown (MPB), defined mathematically by the relationship $\text{NP Balance} = \text{MPS} - \text{MPB}$.

Sarcopenia

The progressive loss of muscle mass and functional strength that occurs after approximately $50$ years of age when muscle protein breakdown exceeds muscle protein synthesis.

Deoxyribonucleic Acid (DNA)

A double-stranded nucleic acid composed of pairs of deoxyribose nucleotides joined by hydrogen bonds between complementary nitrogenous bases and wound into a double helix.

Triplet Code

The genetic arrangement in DNA where a linear sequence of $3$ nitrogenous bases represents the code required to specify a single amino acid.

Messenger RNA (mRNA)

A single-stranded RNA anti-copy of a DNA strand in which uracil replaces thymine, synthesized to transport genetic instructions from the nucleus to ribosomes.

Gene

The functional unit of heredity, composed of a specific sequence of nucleotides on a DNA strand that dictates the sequence of amino acids needed to manufacture a protein.

Chromatin

The loosely coiled, tangled network of DNA wound around histone proteins present within the nucleus of a non-dividing cell.

Transcription

The enzymatic transfer of genetic information from a gene's DNA template strand to a complementary strand of messenger RNA, occurring in the nucleus.

RNA Polymerase

The enzyme responsible for binding to the gene promoter, separating the two strands of DNA, and aligning complementary RNA nucleotides to synthesize an mRNA transcript.

Introns

Non-protein-coding nucleotide sequences that span approximately $30\%$ of the genome and are excised from pre-mRNA transcripts by spliceosomes prior to translation.

Exons

Protein-coding sequences that account for only $1\%$ to $2\%$ of the human genome and are spliced together into mature mRNA to direct protein assembly.

Translation

The biological process in which ribosomes in the cytosol read mRNA codons and assemble corresponding amino acids into a polypeptide chain.

Transfer RNA (tRNA)

A carrier RNA molecule featuring a specific amino acid attached to its tail and a complementary three-base anticodon at its loop end that delivers amino acids to the ribosome.

Codon

A three-base sequence on mRNA that corresponds to a specific DNA triplet and specifies one of $20$ amino acids or a termination signal.

Autophagy

A cellular clearance pathway ('self-eating') in which cytoplasm and worn-out organelles are enclosed within autophagosomes and delivered to lysosomes for degradation.

Ubiquitin-Proteasome Pathway

A protein degradation mechanism that attaches ubiquitin proteins to unneeded soluble proteins, tagging them for recognition and destruction by proteasomes.

Apoptosis

A controlled programmed cell death pathway activated by mitochondrial permeabilization and cytosolic leakage of cytochrome c, which stimulates caspases to digest cell components without lysosomes.

Genotype

The complete set of inherited genes and alleles contained within an individual's chromosomes, serving as the biological instructions for the organism.

Phenotype

The observable physical, anatomical, and physiological characteristics displayed by an individual, resulting from the expression of their genotype.

Allele

Any of the alternative versions or forms of a specific gene located at an identical locus on paired homologous chromosomes.

Homozygous

The condition of carrying two identical alleles for a specific gene across a pair of homologous chromosomes, true for an estimated $80\%$ of human genes.

Heterozygous

The condition of possessing two different alleles for a specific gene on a pair of homologous chromosomes.

Autosomes

The $22$ homologous pairs of chromosomes in human somatic cells that possess matching structural morphology and determine somatic phenotype traits.

Sex Chromosomes

The $23\text{rd}$ pair of human chromosomes consisting of X and Y, where the larger X chromosome contains approximately $1400$ genes and the smaller Y chromosome contains approximately $200$ genes.

Simple Inheritance

A genetic pattern where a phenotype trait is governed by a single pair of alleles reflecting strict dominant or recessive interactions.

Co-dominance

A mode of inheritance in which a heterozygous individual expresses both distinct alleles and manifests both corresponding phenotypes simultaneously, as seen in AB blood type.

Polygenic Inheritance

The additive interaction of multiple separate genes to determine a single continuous phenotypic trait (such as skin color or height), producing a characteristic bell-shaped population distribution.

Independent Assortment

The random segregation and distribution of maternal and paternal homologous chromosome pairs during meiosis I, yielding $2^n$ possible gametic combinations ($2^{23} \approx 8.5 \times 10^6$ in humans).

Crossing Over

The meiotic process during synapsis where non-sister chromatids of a tetrad cross over, form chiasmata, and exchange corresponding gene segments to generate recombinant chromosomes.

Epigenetics

The study of modifications to chromatin structure and DNA (such as methylation or acetylation) that switch genes on or off without altering the primary DNA sequence.

DNA Methylation

An epigenetic modification involving the covalent attachment of methyl groups to DNA nucleotides, which typically acts to repress or silence gene transcription.

Teratogen

Any external environmental factor, chemical, or substance (such as nicotine, alcohol, or pollutants) capable of disrupting normal fetal development and causing congenital birth defects.

Mitochondrial DNA (mtDNA)

A circular molecule of DNA located within mitochondria consisting of $16{,}569$ base pairs and $37$ genes that is inherited exclusively through the maternal lineage.

Human Genome

The total collective DNA sequence across all $46$ human chromosomes, encompassing approximately $3.2 \times 10^9$ base pairs and an estimated $19{,}000$ to $20{,}000$ protein-coding genes.

Karyotype

An organized visual display of condensed metaphase chromosomes arranged in homologous pairs according to size and structure to detect aneuploidies or structural defects.