Gene Expression and Regulation

Nucleotide

Nucleotide

The basic building block of nucleic acids, consisting of a phosphate group, a five-carbon sugar (ribose or deoxyribose), and a nitrogenous base

Five-carbon sugar

A sugar molecule with five carbon atoms; in DNA, it's deoxyribose, and in RNA, it's ribose

Phosphate

A chemical group consisting of phosphorus atoms bonded to four oxygen atoms, forming the backbone of DNA and RNA

Nitrogenous base

An organic molecule that contains nitrogen and forms the rungs of the DNA ladder, such as adenine, guanine, cytosine, thymine (DNA), or uracil (RNA)

Deoxyribose

A five-carbon sugar found in DNA

Adenine, Guanine, Cytosine, Thymine

Four nitrogenous bases found in DNA

Plasmids

Small, circular DNA molecules found in bacteria, separate from the bacterial chromosome, often used in genetic engineering

Phosphodiester bonds

The chemical bonds that link nucleotides in DNA and RNA

Double helix

The twisted-ladder structure of DNA

Watson, Crick, and Franklin

Scientists credited with the discovery of the structure of DNA

Base pairing

Specific

hydrogen bonding between complementary nitrogenous bases (A-T and G-C in DNA)

Complementary

Two strands of DNA that match up according to base pairing rules

Antiparallel

The arrangement of DNA strands in opposite directions

Hydrogen bonds

Weak bonds between hydrogen atoms and other atoms, important in holding DNA strands together

Gene

A segment of DNA that contains the instructions for making a specific protein or RNA molecule

Genome

The complete set of an organism's DNA, including all of its genes

Chromosome

A DNA molecule with associated proteins, carrying part of an organism's genetic information

Histone

Proteins around which DNA wraps, organizing chromosomes

Nucleosome

A structural unit of a eukaryotic chromosome, consisting of DNA wrapped around histone proteins

Euchromatin

Loosely packed chromatin, allowing for gene expression

Heterochromatin

Highly condensed chromatin, often transcriptionally inactive

DNA replication

The process of copying DNA before cell division

Helicase

Enzyme that unwinds the DNA double helix during replication

Replication fork

The Y-shaped region where DNA is replicated

Origins of replication

Sites where DNA replication begins

Topoisomerase

Enzyme that relieves the tension caused by unwinding DNA

DNA polymerase

Enzyme that synthesizes new DNA strands during replication

RNA primase

Enzyme that synthesizes RNA primers during DNA replication

RNA primer

Short RNA sequence that initiates DNA replication

Leading strand

The DNA strand is synthesized continuously during replication

Lagging strand

The DNA strand is synthesized discontinuously during replication, in short fragments called Okazaki fragments

Okazaki fragments

Short DNA fragments on the lagging strand

DNA ligase

Enzyme that joins Okazaki fragments

Semiconservative

DNA replication mechanism where each new DNA molecule consists of one old strand and one newly synthesized strand

Telomeres

Repeated DNA sequences at the ends of chromosomes, protecting them from degradation

Transcription

The process of synthesizing RNA from a DNA template

Translation

The process of synthesizing proteins from mRNA

Central Dogma of Biology

The flow of genetic information from DNA to RNA to protein

Ribose

A five-carbon sugar found in RNA

Uracil

A nitrogenous base found in RNA, replacing thymine

Messenger RNA (mRNA)

RNA molecule that carries genetic information from DNA to the ribosome for protein synthesis

Ribosomal RNA (rRNA)

RNA component of the ribosome, essential for protein synthesis

Transfer RNA (tRNA)

RNA molecule that carries amino acids to the ribosome during protein synthesis

RNA interference (RNAi)

Mechanism where RNA molecules inhibit gene expression

Polycistronic transcript

mRNA that carries the information for multiple genes

Monocistronic transcript

mRNA that carries the information for a single gene

Promoter

DNA sequence where RNA polymerase binds to initiate transcription

Antisense/non-coding/template strand

DNA strand used as a template for RNA synthesis during transcription

Sense/coding strand

The DNA strand that has the same sequence as the RNA transcript

RNA polymerase

Enzyme that synthesizes RNA from a DNA template during transcription

Start site

The site on DNA where transcription begins

Exons

Coding gene regions that are retained in mature mRNA

Introns

Non-coding regions of a gene that are removed during mRNA processing

Splicing

Process of removing introns and joining exons in pre-mRNA

Spliceosome

Complex of RNA and protein that carries out splicing

Poly(A) tail

A stretch of adenine nucleotides added to the ' end of eukaryotic mRNA

' GTP cap

A modified guanine nucleotide added to the ' end of eukaryotic mRNA

Codon

A three-nucleotide sequence on mRNA that codes for a specific amino acid

Anticodon

A three-nucleotide sequence on tRNA complementary to a codon

Wobble pairing

Flexible base pairing at the third position of a codon-anticodon interaction

Initiation

The beginning of translation, when ribosomes assemble on mRNA

Elongation

The process of adding amino acids to a growing polypeptide chain during translation

Termination

The end of translation, signaled by a stop codon

A site, P site, E site

Three sites on the ribosome where tRNA binds during translation

Start codon

The codon that signals the start of translation (AUG)

Stop codons

Codons that signal the end of translation (UAA, UAG, UGA)

Pre-transcriptional regulation

Regulation of gene expression before transcription

Transcription factors

Proteins that regulate gene expression by binding to DNA and controlling transcription

Epigenetic changes

Changes in gene expression or phenotype that are not due to alterations in DNA sequence

Operon

A unit of genetic regulation in bacteria, consisting of a promoter, operator, and structural genes

Structural genes

Genes that code for proteins or functional RNA molecules

Promoter genes

Genes that control the initiation of transcription

Operator

A DNA sequence that acts as a binding site for regulatory proteins

Regulatory gene

A gene that codes for a protein involved in regulating the expression of other genes

Inducer

A molecule that activates the expression of genes by binding to a regulatory protein

Post-transcriptional regulation

Regulation of gene expression after transcription has occurred

Post-translational regulation

Regulation of gene expression after translation has occurred, typically through protein modifications

Morphogenesis

The process by which an organism develops its shape and form

Zygote

A fertilized egg cell formed by the fusion of gametes during sexual reproduction

Fertilization

The fusion of gametes (sperm and egg) to form a zygote

Homeotic genes

Genes that regulate the development of anatomical structures in multicellular organisms

Hox genes

A subset of homeotic genes that play a crucial role in the development of body structures in animals

Mutation

A change in the DNA sequence of an organism

Base substitution

A type of mutation where one nucleotide is replaced by another

Nonsense mutation

A mutation that introduces a premature stop codon, leading to the truncation of the protein

Missense mutation

A mutation that changes a codon to encode a different amino acid

Silent mutation

A mutation that does not result in any change to the amino acid sequence of a protein

Gene rearrangements

Structural changes in the arrangement of genes on a chromosome

Insertions

Mutations where one or more nucleotides are added to a DNA sequence

Deletions

Mutations where one or more nucleotides are removed from a DNA sequence

Frameshift mutation

A type of mutation where the reading frame of the genetic code is altered, usually by insertions or deletions

Duplications

Mutations where a region of DNA is duplicated

Inversions

Mutations where a segment of DNA is reversed in orientation

Translocations

Mutations where segments of DNA are exchanged between non-homologous chromosomes

Transposons

DNA sequences that can move or "jump" to different positions within the genome

Bacteria

Single-celled microorganisms that can be found in various environments and have diverse metabolic capabilities

Conjugation

A process of genetic transfer in bacteria where DNA is transferred from one cell to another through direct contact

Viruses

Infectious agents that require a host cell to replicate and can cause a range of diseases

Host

An organism that a virus or parasite infects and uses for replication Bacteriophage