A&P1 part 5

Purine

A nitrogenous base with a double-ring structure, including adenine and guanine.

Pyrimidine

A nitrogenous base with a single-ring structure, including cytosine, thymine, and uracil.

Adenine

A purine nitrogenous base common to DNA and RNA that pairs with thymine or uracil.

Guanine

A purine nitrogenous base common to DNA and RNA that pairs with cytosine, forming three hydrogen bonds.

Cytosine

A pyrimidine nitrogenous base that pairs with guanine in DNA and RNA.

Thymine

A pyrimidine nitrogenous base found only in DNA that pairs with adenine.

Uracil

A pyrimidine nitrogenous base found only in RNA that replaces thymine.

Law of complementary base pairing

A principle stating that in DNA, adenine pairs with thymine and cytosine pairs with guanine.

Nitrogenous base

Organic bases that contain nitrogen and are part of nucleotide units.

Deoxyribose

A five-carbon sugar that makes up the backbone of DNA.

Ribose

A five-carbon sugar that is part of RNA and ATP.

Double helix

The twisted ladder structure of DNA formed by two strands of nucleotides.

Histone

A basic protein rich in lysine and arginine that DNA winds around for packaging.

Nucleosome

The basic structural unit of chromatin, consisting of DNA wrapped around a histone core.

Core particle

The histone octamer core that wraps around approximately 147 base pairs of DNA.

Linker DNA

The segment of DNA that connects two adjacent nucleosome core particles.

Chromatin

A loose fiber network made up of DNA, RNA, and histones found in the cell nucleus.

Heterochromatin

Highly condensed and inactive chromatin that appears darkly stained.

Euchromatin

Less tightly packed chromatin that is active in transcription and appears lightly stained.

Chromosome

A visible rod-like body formed by condensed chromatin during cell division.

Chromatid

One of the identical copies of DNA formed by replication that are connected at the centromere.

Sister chromatids

Identical chromatids connected at the centromere, formed from the same chromosome during replication.

Centromere

The narrow region of a chromosome where sister chromatids are joined.

Kinetochore

A protein complex associated with the centromere, serving as the attachment point for spindle fibers.

Telomere

The protective cap at the ends of linear chromosomes made of repetitive non-coding sequences.

Gene

A segment of DNA encoding a specific RNA or polypeptide with a particular function.

Genome

The total sum of all DNA sequences constituting the hereditary material of an organism.

Genetic code

The set of rules that defines the correspondence between nucleotide sequences and amino acids.

Base triplet

A sequence of three nucleotides that codes for a single amino acid.

Stop codon

A codon in mRNA that signals the termination of translation, including UAA, UAG, UGA.

Start codon

The codon that signals the start of translation and encodes methionine, typically AUG.

Messenger RNA (mRNA)

The single-stranded RNA that carries genetic information from the nucleus to ribosomes.

Transfer RNA (tRNA)

The cloverleaf-shaped RNA responsible for transporting specific amino acids to the ribosome.

Ribosomal RNA (rRNA)

The structural RNA that combines with proteins to form the ribosomal subunits.

Alternative splicing

The process by which RNA is edited to produce multiple protein isoforms from a single gene.

Spliceosome

A large complex of RNA and proteins that removes introns from precursor mRNA.

Promoter

A DNA sequence located upstream of a gene that is recognized and bound by RNA polymerase to initiate transcription.

Template strand

The DNA strand that RNA polymerase reads to synthesize complementary RNA during transcription.

Coding strand

The DNA strand whose sequence corresponds to the mRNA transcript produced.

Termination sequence

A specific sequence in the DNA template that signals RNA polymerase to stop transcription.

A site (Aminoacyl site)

The ribosomal site that accepts the incoming tRNA carrying a new amino acid.

P site (Peptidyl site)

The ribosomal site where the tRNA carrying the growing polypeptide chain resides.

E site (Exit site)

The ribosomal site where tRNA exits after donating its amino acid.

Polyribosome

A cluster of ribosomes that translates a single mRNA strand simultaneously.

Chaperone protein

A protein that assists in the correct folding of nascent polypeptides.

Posttranslational modification

The chemical modification of a polypeptide chain after its translation, such as phosphorylation or glycosylation.

Signal peptide

A short sequence at the N-terminus of a protein that directs the ribosome to the ER membrane.

Replication fork

The area where the DNA double helix is unwound and replicated during DNA replication.

Leading strand

The DNA strand that is synthesized continuously in the direction of the replication fork.

Lagging strand

The DNA strand that is synthesized discontinuously in segments away from the replication fork.

Okazaki fragments

The short segments of DNA synthesized on the lagging strand during replication.

DNA ligase

The enzyme that joins adjacent Okazaki fragments by forming phosphodiester bonds.

RNA primer

A short RNA segment synthesized by primase that provides a free 3'-OH end for DNA polymerase.

Primase

An enzyme that synthesizes a short RNA primer during DNA replication.

Mutation

Any heritable change in the nucleotide sequence of DNA.

Point mutation

A mutation affecting a single nucleotide pair in the DNA sequence.

Silent mutation

A mutation that does not alter the amino acid sequence of a protein due to redundancy in the genetic code.

Missense mutation

A mutation that results in a different amino acid being incorporated into a protein.

Nonsense mutation

A mutation that creates a premature stop codon, leading to truncated proteins.

Frameshift mutation

A mutation caused by insertions or deletions that shift the reading frame of the genetic code.

Base excision repair

A repair mechanism for damaged bases, involving removal and replacement by the correct nucleotide.

G0 phase

The phase where cells exit the active cell cycle and enter a quiescent state.

G1 phase

The phase following mitosis where the cell grows and synthesizes proteins and organelles.

S phase

The phase of the cell cycle where DNA is replicated.

G2 phase

The phase following DNA replication where the cell prepares for mitosis.

M phase (Mitotic phase)

The phase of the cell cycle where cell division occurs.

Cell cycle checkpoint

Regulatory points in the cell cycle that ensure proper division and integrity of DNA.

G1/S checkpoint

The checkpoint that assesses whether a cell should proceed to DNA replication.

Cyclin

A regulatory protein whose concentration fluctuates throughout the cell cycle and activates cyclin-dependent kinases.

Cyclin-dependent kinase (CDK)

A protein kinase that requires cyclin to be activated and phosphorylates target proteins to drive the cell cycle.

Mitotic spindle

The structure formed by microtubules that segregates chromosomes during mitosis.

Spindle fiber

Individual microtubules that make up the mitotic spindle.

Aster

A star-shaped arrangement of microtubules radiating from the centrosome.

Equatorial plate

An imaginary plane where chromosomes align during the metaphase of cell division.

Cleavage furrow

The indentation that begins to divide animal cells during cytokinesis.

Contractile ring

A ring of actin filaments that constricts to separate the two daughter cells during cytokinesis.

Contact inhibition

A regulatory mechanism that stops cells from dividing when they come into contact with each other.

Apoptosis

Programmed cell death that occurs in a regulated and controlled manner.

Necrosis

Uncontrolled cell death resulting from injury or disease.

Autophagy

The process by which cells degrade and recycle their own components.

Oncogene

A mutated gene that has the potential to cause cancer by promoting uncontrolled cell growth.

Proto-oncogene

A normal gene that can become an oncogene due to mutations or increased expression.

Tumor-suppressor gene

A gene that protects cells from becoming cancerous by regulating cell growth and promoting DNA repair.

Allele

Different variants of a gene that can occupy the same locus on homologous chromosomes.

Dominant allele

An allele that manifests its phenotype even when present in just one copy.

Recessive allele

An allele whose phenotype is expressed only in homozygous condition.

Genotype

The genetic makeup of an organism, specifically the alleles it carries.

Phenotype

The observable physical and biochemical characteristics of an organism.

Homozygous

Having two identical alleles for a particular gene.

Heterozygous

Having two different alleles for a particular gene.

Carrier

An individual who carries one copy of a recessive allele but does not exhibit the associated phenotype.

Autosome

Any chromosome that is not a sex chromosome.

Sex chromosome

The chromosome that determines an individual's sex, namely X and Y chromosomes.

Karyotype

The number and visual appearance of the chromosomes in the nucleus of a eukaryotic cell.

Diploid

A cell that contains two complete sets of chromosomes, one from each parent.

Haploid

A cell containing a single set of unpaired chromosomes.

Homologous chromosomes

Pairs of chromosomes that are similar in shape, size, and genetic content.

Gene locus

The specific physical location of a gene on a chromosome.

Polygenic inheritance

A mode of inheritance where multiple genes determine a single phenotype.

Pleiotropy

The phenomenon where a single gene influences multiple phenotypic traits.