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Replication Origin (chapter 5)

def: Site on a chromosome at which DNA replication begins

Replication Fork (chapter 6)

def: Y-shaped region of a replication DNA molecule at which the two daughter strands are formed and separate.

Retrotransposon (chapter 6)

def: Type of mobile genetic element that moves by being first transcribes into an RNA copy that is reconverted to DNA by reverse transcriptase and inserted elsewhere in the chromosomes.

Retrovirus (chapter 6)

def: RNA-containing virus that replicated in a cell by first making a double-stranded DNA intermediate. This DNA is inserted into the cell's chromosome, where it can be maintained for a long time and its transcribed to produce new viral genomes and mRNAs that encode viral proteins.

Reverse Transcriptase (chapter 6)

def: Enzyme that makes a double-stranded DNA copy from a single-stranded RNA template molecule. Present in retroviruses and as part of the transposition machinery of retrotransposons.

RNA (Ribonucleic Acid) (chapter 6)

def: A (usually) single-stranded polynucelotide in the form of a chain of covalently linked ribonucelotide subunit. It is synthesized when an RNA polymerase copies the nucleotide sequence of DNA. RNA serves a variety of functions in cells. for example messenger RNA, microRNA, ribosomal RNA, transfer RNA

Rab Protein (chapter 15)

def: A family of small GTP-binding proteins present on the surfaces of transport vesicles and organelles that serve as molecular markers identifying each membrane type.; Rab proteins help to ensure that transport vesicles fuse only with the correct membrane.

Receptor-mediated Endocytosis (chapter 15)

def: Mechanism of selective uptake of material by animal cells in which a macromolecule binds to a receptor in the plasma membrane and enters the cell in a clathrin-coated vesicle.

Rough ER (chapter 15)

def: Region of the ER associated with ribosomes and involved in the synthesis of secreted and membrane-bound proteins.

Ras (chapter 16)

def: One of a large family of small GTP-binding proteins (also called the monomeric GTPases) that help relay signals from cell-surface receptors to the nucleus. Named for the Ras gene, first identified in viruses that cause rat sarcomas.

Receptor Protein (chapter 16)

def: Protein that detects a stimulus, usually a change in concentration of a specific molecule and then initiates a response in the cell. Cell-surface receptors, such as the acytlcholine receptor and the insulin receptor, are located in the plasma membrane, with their ligand-binding site exposed to the external medium. Intracellular receptors, such as steroid hormone receptors , bind ligands that diffuse into the cell across the plasma membrane.

Receptor Serine/Threonine Kinase (chapter 16)

def: Enzyme-coupled receptor with an extracellular signal-binding domain and an intracellular kinase domain that phosphorylates signaling proteins on serine or threonine.

Receptor Tyrosine Kinase (chapter 16)

Enzyme-coupled receptor in which the intracellular domain has tyrosine kinase activity, which is activated by ligand binding to the receptor's extracellular domain.

Rho Protein Family (chapter 16)

def: Family of small GTPases involved in in signaling that causes a rearrangement of the actin cytoskeleton.

Reading Frame (chapter 7)

def: The set of successive triplets in which a string of nucleotides is translated into protein. An mRNA molecule is read in one of three possible reading frames, depending on the starting point.

Ribosomal RNA (rRNA) (chapter 7)

def: Any one of a number of specific RNA molecules that form part of the structure of a ribosome and participate in the synthesis of proteins. Often distinguished by their sedimentation coefficient, such as 28S rRNA or 5S rRNA.

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