genetics terms 3

5’ end

The end of a DNA or RNA strand that has a free phosphate group attached to the fifth carbon of the sugar.

3’ end

The end of a DNA or RNA strand that has a free hydroxyl (-OH) group attached to the third carbon of the sugar.

DNA replication

The biological process where a cell makes two identical copies of its DNA before dividing.

Template

A single strand of DNA or RNA that serves as a guide for building a matching new strand.

DNA polymerase

An enzyme that builds new DNA strands by adding matching nucleotides in the 5' to 3' direction.

Helicase

An enzyme that untwists and unzips double-stranded DNA by breaking the hydrogen bonds between base pairs.

Lagging strand

The newly made DNA strand built in short, separate pieces moving away from the replication fork.

Leading strand

The newly made DNA strand built smoothly and continuously toward the replication fork.

Ligase

An enzyme that seals breaks and glues DNA fragments together into a continuous strand.

Okazaki fragment

Short, separate pieces of DNA made on the lagging strand that are later joined together.

Primase

An enzyme that builds short RNA primers to provide a starting point for DNA polymerase.

Primer

A short starter sequence of RNA required for DNA polymerase to begin building a new strand.

Replication fork

The Y-shaped region where the double-stranded DNA splits into two single strands during copying.

Replication bubble

An unwound opening in double-stranded DNA where copying happens in both directions.

Single-strand binding protein

Proteins that bind to separated single DNA strands to keep them from snapping back together.

Telomere

A protective cap of repetitive, non-coding DNA found at the ends of linear chromosomes.

Telomerase

An enzyme that adds repetitive DNA to chromosome ends using its own built-in RNA guide to prevent chromosome shortening.

Topoisomerase

An enzyme that cuts and rejoins DNA to relieve tension and prevent tangling ahead of the replication fork.

Gene expression

The process of using information in a gene to build functional RNA molecules or proteins.

Sense DNA

The coding strand of DNA that has the same sequence as the RNA transcript, substituting thymine for uracil.

Antisense DNA

The non-coding DNA strand that RNA polymerase reads as a template to build an RNA molecule.

Sigma factor

A bacterial protein that helps RNA polymerase recognize and bind to the correct promoter.

TATA box

A common DNA sequence in eukaryotic promoters that shows RNA polymerase where to start transcription.

Transcription factors

Proteins that bind to specific DNA sequences to control whether genes are turned on or off.

Downstream

The direction along a DNA or RNA strand toward the 3' end, following the path of synthesis.

Upstream

The direction along a DNA or RNA strand toward the 5' end, opposite the path of synthesis.

Exon

A segment of an RNA transcript that is kept and joined together to form the mature mRNA.

Intron

A non-coding segment of an RNA transcript that is cut out and discarded during RNA processing.

Spliceosome

A large molecular machine made of RNA and proteins that cuts out introns and splices exons together.

Exon junction complex (EJC)

A group of proteins attached where exons are spliced together to help export mRNA from the nucleus.

Poly-A tail

A long chain of adenine bases added to the 3' end of mRNA to protect it from breakdown.

Promoter

A specific DNA sequence upstream of a gene where transcription machinery binds to start RNA synthesis.

Termination

The final step of making DNA, RNA, or protein where synthesis stops and the machinery comes apart.

5’ cap

A specially modified guanine nucleotide added to the 5' end of eukaryotic mRNA for protection and ribosome recognition.

Transcription

The process of making an RNA copy of a gene using a DNA strand as a guide.

mRNA

A single-stranded RNA copy of a gene that carries instructions from DNA to ribosomes for making proteins.

Transcription initiation

The starting step of transcription where RNA polymerase binds the promoter and starts building RNA.

Transcription elongation

The middle step of transcription where RNA polymerase moves along DNA adding RNA nucleotides.

Termination signal

A DNA sequence that instructs RNA polymerase to stop copying and release the completed RNA.

Rho proteins

Bacterial proteins that climb along newly made RNA to knock RNA polymerase off and end transcription.

RNA polymerase

An enzyme that reads a DNA template to synthesize a complementary strand of RNA.

Alternative splicing

A process that splices RNA exons in different combinations to make multiple distinct proteins from a single gene.

Translation

The cellular process where ribosomes read mRNA codons to assemble a specific sequence of amino acids into a protein.

Template

A biological molecular guide used to direct the synthesis of a matching complementary strand.

Sense RNA

An RNA transcript that contains the exact sequence needed to be translated into a functional protein.

Antisense RNA

An RNA strand that base-pairs with a target mRNA to block its translation or trigger its destruction.

Genetic Code

The universal set of rules where groups of three mRNA letters match specific amino acids.

Reading frame

The specific way an mRNA sequence is divided into non-overlapping groups of three letters to be read.

Gene

A basic unit of heredity made of DNA that contains instructions for making a functional RNA or protein.

Kozak sequence

A sequence surrounding the start codon in eukaryotes that guides the ribosome to the right place to begin translation.

Shine-Dalgarno sequence

A bacterial RNA sequence just before the start codon that aligns the ribosome for translation.

tRNA

An adaptor RNA molecule that carries a specific amino acid to the ribosome by matching its anticodon to an mRNA codon.

Wobble site

The third position of an mRNA codon where flexible base pairing allows one tRNA to recognize multiple codons.

Aminoacyl-tRNA synthetase

An enzyme that links the correct amino acid to its corresponding tRNA molecule.

fMet

A chemically modified form of methionine used as the first amino acid in bacterial protein synthesis.

Initiation factors

Helper proteins that assemble the ribosome, mRNA, and starting tRNA together to begin translation.

E site

The exit slot in a ribosome where an empty tRNA sits just before leaving.

P site

The middle slot in a ribosome that holds the tRNA connected to the growing protein chain.

A site

The entry slot in a ribosome that receives an incoming tRNA carrying a new amino acid.

5’UTR

The untranslated leader segment of mRNA found between the 5' cap and the start codon.

3’UTR

The untranslated trailer segment of mRNA located after the stop codon that regulates mRNA stability.

EF-Tu

A bacterial protein that uses energy to deliver amino acid-carrying tRNAs into the ribosome's A site.

EF-G

A bacterial protein that uses energy to push the ribosome forward by one codon along the mRNA.

GTP

An energy molecule similar to ATP that powers key movements in protein synthesis.

Peptidyl transferase

The catalytic RNA part of the ribosome that joins amino acids together by making peptide bonds.

Release factor

A protein that binds to a stop codon in the ribosome to end translation and release the finished protein.

Polyribosome

A group of multiple ribosomes translating the same mRNA strand at the exact same time.

rRNA

The RNA molecules that form the core structure of ribosomes and help catalyze peptide bond formation.

Codon

A three-nucleotide sequence in mRNA that codes for one specific amino acid or a stop signal.

Start codon

The three-letter sequence (usually AUG) where the ribosome begins translating a protein.

Stop codon

A three-letter mRNA sequence (UAA, UAG, or UGA) that signals the ribosome to stop building the protein.

Methionine

The specific amino acid coded by the universal start codon AUG.

Amino acids

The small molecular building blocks that link together to make proteins.

Polypeptide

A single unbranched chain of amino acids held together by peptide bonds.

Peptide bond

The covalent chemical bond linking two amino acids together in a protein.

Protein

A functional biological molecule made of one or more amino acid chains folded into a specific 3D shape.

Anticodon

A three-nucleotide sequence on a tRNA that matches and pairs with a complementary codon on mRNA.

Ribosome

A cellular machine made of RNA and proteins that reads mRNA to build protein chains.

Translation initiation

The beginning stage where the ribosome units, mRNA, and first tRNA come together at the start codon.

Translation elongation

The repeating cycle where the ribosome reads codons, adds amino acids, and moves down the mRNA.

Peptide bond formation

The chemical reaction where a new amino acid is bonded to the growing protein chain inside the ribosome.

Translocation

The step where the ribosome shifts forward by three nucleotides along the mRNA.

Translation termination

The final step where a stop codon triggers release factors to detach the finished protein and disassemble the ribosome.

Chaperonin

A barrel-shaped protein complex that gives newly made proteins a protected space to fold properly.

Signal sequence

A short tag of amino acids at the front of a new protein that directs it to a specific cellular organelle.

Ubiquitin

A small regulatory protein attached to worn-out or damaged proteins to mark them for destruction.

Cellular differentiation

The process where generic stem cells turn on specific genes to become specialized cell types.

Chromatin

The combination of DNA wrapped around histone proteins inside eukaryotic cells.

Nucleolus

A dense area inside the nucleus dedicated to making ribosomal RNA and assembling ribosome parts.

rDNA

Repeated sections of DNA that code for ribosomal RNA.

Nuclear envelope

The double-layered membrane that surrounds the nucleus and contains pores to regulate transport.

Acetylation

Adding chemical acetyl groups to histones to loosen DNA packing and allow genes to be transcribed.

Acetyl transferase (HAT)

An enzyme that adds acetyl groups to histones, opening up chromatin to activate transcription.

Deacetylase (HDAC)

An enzyme that strips acetyl groups off histones, tightening chromatin and turning genes off.

Methylation

Adding chemical methyl groups to DNA or histones, which typically packs DNA tightly and silences genes.

CpG islands

Stretches of DNA packed with cytosine and guanine bases, frequently found near gene promoters.

Epigenetics

The study of changes in gene activity that occur without altering the underlying DNA sequence.

Enhancers/activators

Distant DNA sequences and the regulatory proteins that bind them to speed up gene transcription.

Silencers/repressors

Specific DNA sequences and the proteins that bind them to slow down or shut off gene transcription.

Transcription factor

A protein that binds to specific DNA sequences to either turn transcription on or off.