BIO130: Genes and Cellular Functioning

A comprehensive vocabulary review of BIO130 covering DNA structure, chromatin organization, the genetic code, transcription, translation, DNA replication, and the cell cycle including mitosis and cytokinesis.

Deoxyribonucleic acid (DNA)

A long, thread-like molecule of uniform diameter and varied length that carries genetic instructions for protein synthesis; most human cells contain $46$ DNA molecules (chromosomes) in the nucleus, averaging about $2\text{ inches}$ in length.

Nucleotide

The monomer building block of nucleic acids, consisting of three components: a sugar (deoxyribose in DNA), a phosphate group, and a nitrogenous base.

Purines

A class of nitrogenous bases characterized by a double-ringed chemical structure; includes adenine (A) and guanine (G).

Pyrimidines

A class of nitrogenous bases characterized by a single-ringed chemical structure; includes cytosine (C), thymine (T), and uracil (U).

Law of complementary base pairing

The structural rule stating that the sequence of one strand of DNA dictates the sequence of the other; adenine binds with thymine via $2$ hydrogen bonds, and guanine binds with cytosine via $3$ hydrogen bonds.

Base triplet

A sequence of $3$ consecutive DNA nucleotides in the template strand that codes for one specific amino acid in a synthesized protein.

Gene

An information-containing segment of DNA that codes for the production of an RNA molecule that most often plays a role in synthesizing one or more proteins; humans have approximately $20{,}000$ genes, which make up about $2\%$ of total DNA.

Noncoding DNA

The remaining $98\%$ of total human DNA that does not code for proteins; plays critical roles in chromosome structure and regulates gene activity.

Chromatin

Fine, filamentous DNA material complexed with structural proteins called histones; exists as $46$ chromosomes in most human cells.

Histones

Proteins around which DNA winds to form core particles, facilitating the organized packaging and compaction of chromatin within the nucleus.

Core particle

An $11\text{ nm}$ structural unit of chromatin formed when the DNA double helix winds around a cluster of histone proteins.

Sister chromatids

Two parallel, identical filaments of DNA produced when a cell replicates its nuclear DNA prior to cell division, joined together at a constricted centromere.

Centromere

The constricted, narrow region of a duplicated chromosome that holds two sister chromatids together.

Kinetochores

Protein plaques located on each side of the centromere that serve as attachment sites for spindle fibers during cell division.

Ribonucleic acid (RNA)

A nucleic acid typically composed of a single nucleotide chain containing the sugar ribose and the bases adenine, uracil, guanine, and cytosine, functioning primarily in the cytoplasm.

Messenger RNA (mRNA)

A type of RNA that carries genetic code from the nucleus to the cytoplasm and contains a protein cap that functions as a recognition site for ribosomes.

Transfer RNA (tRNA)

A cytosolic RNA molecule that delivers a specific amino acid to the ribosome during translation, featuring a $3$-nucleotide anticodon complementary to an mRNA codon.

Genome

All the DNA contained within one complete set of $23$ human chromosomes, encompassing approximately $3.1\text{ billion}$ nucleotide pairs.

Genomics

The comprehensive scientific study of the whole genome and its functions.

Genetic code

The system that enables $4$ nucleotide bases (A, T, C, G) to code for the amino acid sequences of all proteins made from $20$ different amino acids.

Codon

A $3$-base sequence in mRNA that corresponds to an amino acid or serves as a stop signal; there are $64$ total codons ($61$ coding for amino acids and $3$ stop codons).

Start codon

The mRNA codon AUG, which specifies methionine and initiates the amino acid sequence of a protein.

Stop codons

The three mRNA codons (UAG, UGA, and UAA) that signal the termination of protein translation, acting like a period at the end of a sentence.

Transcription

The nuclear process of copying genetic instructions from DNA into a complementary strand of messenger RNA (mRNA).

RNA polymerase

The enzyme that binds to start sequences in DNA, unwinds the double helix, reads bases from the template strand to synthesize complementary mRNA, and rewinds the DNA behind it.

Translation

The cytoplasmic process in which a ribosome reads the nucleotide sequence of an mRNA molecule and converts it into the amino acid sequence of a protein.

Anticodon

A series of $3$ nucleotides on a loop of a tRNA molecule that is complementary to a specific codon on an mRNA strand.

Ribosome

A cytoplasmic organelle made of a large and small subunit with E, P, and A binding sites that reads the mRNA message and assembles an amino acid chain.

Polyribosome

A cluster of multiple ribosomes attached to and translating the same mRNA molecule simultaneously to produce many copies of a protein.

Indirect genetic control

The mechanism whereby non-protein cellular products (e.g., glycogen, fat, steroids, and pigments) are produced by enzymatic reactions, where the enzymes themselves are proteins encoded by genes.

DNA replication

The process by which a cell duplicates its entire nuclear DNA prior to cell division to ensure each daughter cell receives a full set of genes.

DNA polymerase

The enzyme required to replicate DNA by unwinding the helix, breaking hydrogen bonds, creating a replication fork, reading the original strand, and assembling a new complementary strand from free nucleotides.

Replication fork

The point of unwinding and separation where DNA polymerase breaks hydrogen bonds between complementary strands to allow synthesis of new DNA.

Semiconservative replication

The mode of DNA replication wherein each newly produced double-stranded DNA molecule is composed of one original template strand and one newly synthesized strand.

DNA Damage Response (DDR)

Cellular error-correction mechanisms where DNA polymerase double-checks new base pairs and replaces unstable incorrect pairs, resulting in an error rate of only $1$ mistake per $1\text{ billion}$ bases replicated.

Mutation

A structural change in DNA caused by replication errors or exposure to environmental factors such as radiation, viruses, and chemicals.

Genetic mosaicism

The presence of cells with differing genetic sequences within an individual's body as a result of somatic mutations and replication errors.

Cell cycle

The complete sequence of events through which a cell grows, duplicates its genetic material, and divides; comprised of interphase and the mitotic phase.

Interphase

The non-dividing portion of the cell cycle during which the cell grows and prepares for division; consists of the $G_1$, $S$, and $G_2$ subphases.

$G_1$ phase (First gap phase)

The interval of interphase between cell division and DNA replication during which the cell performs normal metabolic roles and synthesizes proteins and materials for subsequent phases.

$S$ phase (Synthesis phase)

The subphase of interphase during which the cell duplicates its centrioles and replicates all of its nuclear DNA.

$G_2$ phase (Second gap phase)

The subphase of interphase between DNA replication and cell division where the cell repairs replication errors, grows, and synthesizes enzymes that control division.

$G_0$ phase

A quiescent state describing cells that have withdrawn from the active cell cycle and ceased dividing for a long time or permanently.

Mitosis

Cell division resulting in two genetically identical daughter cells; responsible for tissue growth, cell replacement, and embryonic development from a fertilized egg to about $50\text{ trillion}$ cells.

Prophase

The first phase of mitosis in which chromatin condenses into $46$ visible chromosomes (each with two chromatids), the nuclear envelope disintegrates, and centrioles migrate apart while sprouting spindle fibers.

Metaphase

The second phase of mitosis during which chromosomes align along the cell equator (midline) and spindle fibers attach to kinetochores.

Anaphase

The third phase of mitosis in which an enzyme cleaves sister chromatids apart at the centromere, and motor proteins in kinetochores crawl along spindle fibers to pull daughter chromosomes to opposite poles.

Telophase

The final stage of nuclear division in which chromosomes cluster at each pole and uncoil into chromatin, rough ER forms new nuclear envelopes, the mitotic spindle vanishes, and nucleoli reappear.

Cytokinesis

The division of the cytoplasm into two cells, achieved by myosin pulling on actin in the cytoskeleton terminal web to form a cleavage furrow that pinches the cell in two.

Contact inhibition

The cessation of cell division that occurs when cells come into snug physical contact with neighboring cells.