Molecular Biology: DNA, Protein Synthesis, and Genetics

nucleotide

The basic building block of DNA, consisting of a sugar, a phosphate group, and a nitrogenous base.

purine

A type of nitrogenous base in DNA, specifically adenine and guanine.

pyrimidine

A type of nitrogenous base in DNA, specifically thymine and cytosine.

replication bubble

A region of unwound DNA where replication occurs during DNA replication.

semiconservative

A method of DNA replication where each new DNA molecule consists of one old strand and one new strand.

primer

A short strand of RNA that provides a starting point for DNA synthesis.

telomere

The protective cap at the end of eukaryotic chromosomes that shortens with each cell division.

gene

A segment of DNA that codes for a specific polypeptide.

promoter

A region of DNA that initiates transcription of a particular gene.

terminator

A sequence of DNA that signals the end of transcription.

polypeptide

A chain of amino acids that forms a protein.

transcription

The process of copying a segment of DNA into RNA.

codon

A sequence of three nucleotides in mRNA that codes for a specific amino acid.

translation

The process of synthesizing a protein from an mRNA template.

mutation

A change in the DNA sequence that can lead to changes in protein structure and function.

DNA

Deoxyribonucleic acid, a biochemical component of cells that carries genetic information.

DNA helicase

An enzyme that unwinds the DNA double helix during replication.

DNA topoisomerase

An enzyme that alleviates the tension in DNA strands during replication.

DNA primase

An enzyme that synthesizes RNA primers for DNA replication.

DNA polymerase

An enzyme that assembles nucleotides to form a new DNA strand.

DNA ligase

An enzyme that fuses DNA fragments together during replication.

telomerase

An enzyme that adds nucleotides to the ends of telomeres to prevent shortening.

Transcription

The process that occurs in the nucleus of eukaryotic cells where RNA polymerase assembles the mRNA transcript based on the DNA template of the gene.

RNA polymerase

The enzyme that assembles the mRNA transcript during transcription.

pre-mRNA

The initial RNA transcript in eukaryotes that is modified to remove introns and add a 5' cap and a 3' poly A tail.

Translation

The process that occurs on a ribosome where tRNAs add amino acids one at a time as directed by the mRNA triplet codons.

tRNA

Transfer RNA that acquires specific amino acids and is chemically charged by ATP via the enzyme aminoacyl-tRNA synthetase.

Peptide bond

The bond that connects amino acids into a polypeptide chain.

Start codon

The codon AUG that enters the P (peptidyl site) of the ribosome to initiate translation.

Aminoacyl-tRNA synthetase

The enzyme that chemically charges tRNA with its specific amino acid.

Stop codon

The codon that signals the termination of translation and leads to the disassembly of the ribosome.

Mutation

Changes in the nucleotide base sequence of a gene that can alter the sequence of amino acids in a protein.

Point mutation

A mutation that affects a single nucleotide base pair in the DNA sequence.

Silent mutation

A point mutation that does not change the amino acid sequence of the protein.

Missense mutation

A point mutation that results in the substitution of one amino acid for another in the protein.

Nonsense mutation

A point mutation that creates a premature stop codon in the mRNA sequence.

Frameshift mutation

A mutation that involves the addition or removal of nucleotide base pairs, altering the reading frame of the gene.

Sickle cell disease

A disease caused by a missense mutation in codon 6 of the HBB gene, leading to symptoms like anemia and blood circulation blockages.

Germ line of cells

Cells that give rise to gametes and can pass mutations to offspring.

Somatic line of cells

Cells that do not give rise to gametes and mutations in these cells are not inherited.

Mutagen

An agent that causes mutations in the DNA.

Thymine dimer

A type of DNA damage caused by UV light that results in the bonding of two adjacent thymine bases.

Oncogene

A gene that has the potential to cause cancer when mutated or expressed at high levels.

Tumor suppressor gene

A gene that protects a cell from one step on the path to cancer; mutations can lead to cancer development.

Apoptosis

The process of programmed cell death that can be triggered by mutations or cellular stress.

Germ cell mutations

Mutations in germ cell lines are transmitted to all cells of the developing embryo.

Somatic cell mutations

Mutations in somatic cell lines are expressed only in the effected cells.

Spontaneous mutations

Mutations that can result from mistakes by DNA polymerase, toxic metabolic products, changes in nucleotide structure, and transposons.

Induced mutations

Mutations that can be induced by chemical and physical agents, or mutagens.

Ultraviolet radiation

Can lead to an induced mutation, such as in cases of skin cancer.

Cancer development

A multistep process that evades DNA repair mechanisms.

Oncogene

A gene that can promote cancer development.

Tumor suppressor gene

A gene, such as p53, that protects a cell from one step on the path to cancer.

p53 protein

Initiates a process that halts cell division at the G1 checkpoint of the cell cycle if the DNA is damaged.

Thymine dimer

A mutation in the p53 gene induced by ultraviolet radiation that can lead to skin cancer.

Mutant p53 protein

Prevents apoptosis and does not regulate the rate of mitosis, allowing tumor development.

Cell cycle

The series of phases including interphase, mitosis, and cytokinesis that a cell goes through to divide.

Mitosis

One of two modes of cell division in sexually reproducing organisms, and the only mode in asexually reproducing organisms.

Diploid

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

Haploid

A cell that contains a single set of unpaired chromosomes.

Homologous chromosomes

Chromosomes that are similar in shape, size, and genetic content.

Sexual reproduction

A mode of reproduction that involves the combination of genetic material from two parents.

Asexual reproduction

A mode of reproduction that does not involve the fusion of gametes.

Interphase

The phase of the cell cycle where the cell prepares for mitosis by replicating its DNA.

Cytokinesis

The final step of the cell cycle where the cytoplasm divides, resulting in two daughter cells.

Mitosis phases

Includes prophase, metaphase, anaphase, and telophase.

Sister chromatids

Identical copies of a chromosome that are joined together at the centromere.

Anaphase

The stage of mitosis where sister chromatids pull apart and migrate to the poles of the cell.

Telophase

The stage of mitosis where the nuclear membrane reforms and the two daughter cells begin to separate.

Cytokinesis

The process during which the daughter cells separate after mitosis.

Meiosis

A type of cell division that produces four genetically unique haploid daughter cells.

Gametes

Haploid cells produced by meiosis that are involved in sexual reproduction.

Haploid

A cell that contains one set of chromosomes (n).

Diploid

A cell that contains two sets of chromosomes (2n).

DNA replication

The process of copying DNA before cell division.

Interphase

The phase of the cell cycle where DNA replication occurs before meiosis I.

Meiosis I

The first round of cell division in meiosis where homologous pairs of chromosomes separate.

Meiosis II

The second round of cell division in meiosis where sister chromatids separate into haploid gametes.

Independent assortment

The random distribution of homologous chromosomes during meiosis, contributing to genetic variation.

Crossing over

The exchange of alleles between homologous chromosomes, contributing to genetic variation.

Fertilization

The union of gametes that creates genetic variation in a population's gene pool.

Homologous pair of chromosomes

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

Gene

A segment of DNA that codes for a specific trait.

Allele

Different forms of a gene that can exist at a specific locus.

Dominant trait

A trait that is expressed when at least one dominant allele is present.

Recessive trait

A trait that is expressed only when two recessive alleles are present.

Monohybrid cross

A genetic cross that involves one trait.

Dihybrid cross

A genetic cross that involves two traits.

Homozygous

An organism with two identical alleles for a trait.

Heterozygous

An organism with two different alleles for a trait.

F1 and F2 generations

The first and second generations of offspring in a genetic cross.

Sex-linked inheritance

Inheritance of traits that are determined by genes located on sex chromosomes.

Particulate Theory of Inheritance

Mendel's theory that traits are inherited as discrete units.

Law of Segregation

Mendel's law stating that allele pairs separate during gamete formation.

Law of Independent Assortment

Mendel's law stating that genes for different traits assort independently during gamete formation.

Particulate Theory of Inheritance

The theory that alleles for a gene on a pair of homologous chromosomes are the 'particles' of inheritance.

Homozygous

An individual with two copies of the same allele for a gene (AA or aa).

Heterozygous

An individual with different alleles for a gene (Aa).

Genotype

The sequence of DNA nucleotides that comprise the alleles for a gene.

Phenotype

The physical, physiological, or behavioral expression coded by the genotype.