CER 6 Vocabulary

Antiparallel

The opposite orientation of the two strands in a DNA double helix; one strand runs in the 5′ to 3′ direction, while the complementary strand runs 3′ to 5′

• Purines

Double-ring nitrogenous bases (Adenine and Guanine) that pair with pyrimidines.

• Pyrimidines

SIngle-ring nitrogenous bases (Cytosine, Thymine, and Uracil) that pair with purines

• Origins of replication

Specific DNA sequences where replication begins and the double helix opens.

• Replication fork

The Y-shaped region formed when helicase unwinds the double helix, serving as the active site for replication.

• Helicase

An enzyme that unwinds and unzips the DNA double helix by breaking hydrogen bonds between base pairs.

• Topoisomerase

An enzyme that relieves over winding strain ahead of the replication fork by breaking, swiveling, and rejoining DNA strands

• Primase

An enzyme that synthesizes a short RNA primer to provide a 3′-OH group for DNA polymerase to begin elongation.

• Primers

Short sequences of RNA required to initiate DNA synthesis.

• DNAP III (DNA Polymerase III)

: The primary enzyme that synthesizes new DNA strands by adding nucleotide to the 3′ end of a pre-existing primer or strand.

• DNAP I (DNA Polymerase I)

An enzyme that removes RNA primers and replaces them with DNA nucleotides.

• Leading strand

The new continuous complementary DNA strand synthesized toward the replication fork in the mandatory 5′ to 3′ direction.

• Lagging strand

A discontinuously synthesized DNA strand that elongates away from the replication fork via short segments.

• Okazaki fragments

Short segments of DNA synthesized discontinuously on the lagging strand.

• DNA ligase

An enzyme that joins Okazaki fragments together by catalyzing the formation of covalent phosphodiester bonds.

• Mismatch repair

A cellular mechanism where enzymes remove and replace incorrectly paired nucleotides missed during proofreading.

• Nuclease

An enzyme that cuts and cleaves nucleic acids, often used in DNA repair to excise damaged segments.

• Telomeres

Repetitive, non-coding DNA nucleotide sequences at the ends of eukaryotic chromosomes that protect genes from eroding during replication cycles.

• Telomerase

An enzyme that catalyzes the lengthening of telomeres in germ cells and cancer cells to prevent chromosome shortening.

• Plasmids

Small, circular, double-stranded extrachromosomal DNA molecules found primarily in prokaryotes, often used as vectors in biotechnology

• DNA

Deoxyribonucleic acid; a double-stranded nucleic acid molecule that stores heritable genetic information using deoxyribose sugar and A, T, C, G bases.

• RNA

Ribonucleic acid; a single-stranded nucleic acid involved in protein synthesis and gene regulation, using ribose sugar and A, U, C, G bases.

• Promoter

A specific nucleotide sequence on DNA where RNA polymerase binds to initiate transcription.

translation

specific nucleotide sequence on DNA where RNA polymerase binds to initiate transcription.

• tRNA: Transfer RNA;

an RNA molecule that carries specific amino acids to the ribosome, matching its anticodon to the mRNA codon.

• Anticodon

A three-nucleotide sequence on a tRNA molecule that is complementary to a specific codon on an mRNA molecule.

• Stop codon

A triplet nucleotide sequence on mRNA (UAA, UAG, UGA) that signals the termination of translation.

• Operons

A cluster of functionally related prokaryotic genes regulated and transcribed together as a single mRNA molecule under the control of a single promoter

• Operator

The DNA sequence within an operon where a repressor protein binds, physically blocking RNA polymerase and turning off transcription.

• Repressible

An operon that is normally turned on but can be inhibited (turned off) when a specific small molecule (co-repressor) binds allosterically to a regulatory protein (e.g., trp operon).

• Inducible

An operon that is normally turned off but can be activated (turned on) when a specific small molecule (inducer) inactivates the repressor protein (e.g., lac operon).

• Control elements

Segments of non-coding DNA (such as enhancers and proximal elements) that serve as binding sites for transcription factors to regulate eukaryotic gene expression.

• Histone acetylation

The attachment of acetyl groups to histone tails, which loosens chromatin structure and promotes/transfers transcription.

• DNA methylation

The addition of methyl groups to DNA bases (usually cytosine), which condenses chromatin and typically represses gene transcription

Epigenetic inheritance

Inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence itself (such as DNA methylation or histone modifications)

• Gene differentiation

The process by which unspecialized cells become highly specialized in structure and function through differential gene expression.

• Cytoplasmic determinants

Maternal substances (proteins, RNA) in the egg's cytoplasm that are distributed unevenly during early cell divisions, influencing the developmental fate of early embryonic cells.

• Induction

A process where signaling molecules from neighboring embryonic cells cause changes in the gene expression of target cells, directing their development.

• Morphogenesis

The cellular and structural processes that give an organism its shape and physical form.

• Pattern formation

The developmental process by which cells and tissues are organized into their proper spatial arrangements along the major axes of an organism.

• Apoptosis

Programmed cell death; a regulated cellular suicide pathway where a cell dismantles itself in a controlled manner, critical for embryonic development and tissue homeostasis