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BIOLOGY GLOSSARY 3

Chapter 3 glossary terms

QuestionAnswer
Adenine one of the two purine nucleobases. Used in forming nucleotides of the nucleic acids. In DNA, adenine binds to thymine via two hydrogen bonds to assist in stablising the nucleic acid structures. In RNA, adenine binds to uracil
Anticodon the three nucelotides on a transfer RNA (tRNA) molecule that join in codons on mRNA my complementary base pairing during the process of translation
Antiparallel running in opposite directions with one strand in the 5' to 3' direction, and the other in 3' to 5' direction (two strands of DNA molecules)
Base one of the 5 nitrogenous chemicals present in the nucleotides of nucleic acids (DNA or RNA). These 5 bases are adenine, guanine, thymine, cytosine (DNA only), and uracil (RNA only)
Coding strand the strand of DNA that has the same nucleotide base sequence as the mRNA strand produced by transcription (uracil in the mRNA in place of the thymine in DNA)
Codon basic unit of the genetic code. A sequence of 3 nucleotides on mRNA that codes for a particular amino acid, or indicates the beginning or end of translation
Complementary base pairing the pairing in DNA and RNA molecules of the nitrogenous bases between two strands. In DNA adenine always pairs with thymine, and cytosine with guanine
Constitutive genes a gene or protein that is always expressed or active
Cytosine a nitrogenous base (or prymidine) that occurs in nucleotides of DNA and RNA
Degenerate more then one codon may code for a particular amino acid
Di-nucleotide two nucleotides joined through a condensation polymerisation reaction that joins phosphate of one nucleotide to the 3' end of the other nucleotides sugar molecule. Water is removed in the process
Double helix the double-stranded, coiled structure of a DNA molecule
Exon the region of a gene that codes for a protein
Gene a specific sequence of nucleotides that codes for a particular protein of RNA molecule. It is the unit of hereditary
Gene expression the process that leads to the transformation of the information stored in a gene product (usually a protein or RNA structure)
Gene regulation processes that control gene expression, turning genes on or off
Guanine a nitrogenous base (or purine) that occurs in nucleotides of DNA and RNA
Induced to promote or to activate. When a gene is induced its transcription is activated
Inducible operon an operon that is under the control of regulatory proteins (transcription factors)
Intron section of DNA that does not code for proteins and is spliced during mRNA processes in eukaryotes
Lac operon contains the genes that code for three proteins involved in the metabolism of lactose in E. coli and a few other bacteria. It is an inducible operon and its genes are transcribed only when lactose is available
Lac repressor a DNA-binding protein that binds to the operator site of the lac operon, inhibiting the transcription of the genes in it
LacI a regulatory gene that codes for the lac repressor
Messenger RNA (mRNA) RNA molecule transcribed from DNA in the nucleus, which passes into the cytoplasm and binds to a ribosome. At the ribosome, RNA is translated into a polypeptide
Nucleotide monomer, or building block, of the nucleic acids DNA and RNA. Consists of a phosphate, a sugar, and a nitrogenous base
Operator the segment of DNA that is the binding site of the transcription factor
Operon a unit of DNA under the regulation of a single promotor that codes for several proteins
Phosphodrester bond the bond that joins nucleotides into a chain of DNA and RNA by linking the phosphate group of one nucleotide and the sugar of another
Poly-A tail a long trail of adenine nucleotides (100-250) that is added to the end of mRNA during processing. This increases the stability of the mRNA
Polynucleotide a polymer of nucleotides joined together through a condensation polymerisation reaction. Can be DNA or RNA
Promoter upstream region of a gene (a specific DNA sequence) to which RNA polymerisation attaches, initiating transcription
Protein synthesis the production of a protein through the processes of gene expression, which, in eukaryotes, comprises of transcription, RNA processing, and translation
Purine a nitrogenous base that has a double ring structure (adenine and guanine). Each purine base pairs with a specific pyrimidine base (cytosine, thymine and uracil)
Pyrimidine a nitrogenous base that has a single ring structure (cytosine, thymine and uracil). Each pyrimidine base pairs with a specific purine base (adenine and guanine)
Regulatory gene a gene that codes for transcription factors (which in turn control gene expression at the transcription stage)
Repressed describes a gene that is inhibited and cannot be transcribed
Ribosomal DNA a nucleic acid synthesised in the nucleolus that forms part of a ribosome
RNA polymerase an enzyme that catalyses the synthesis of RNA, using an existing strand of DNA as a template
RNA processing the removal of introns from the primary transcript produced in transcription. The exons are joined to form mRNA, ready for translation. This stage of gene expression occurs only in eukaryotes
Spliceosome enzyme that removes the introns from the primary transcript produced in transcription. The exons are joined to form mRNA, ready for translation
Splicing the removal of introns from the primary transcript to create mRNA during RNA processing (in eukaryotes)
Structural gene a gene that codes for proteins and RNA molecules that are not involved in gene regulation (eg. enzymes)
TATA box a name given to a common sequence of bases in eukaryotic genes, which it TATAAA, that codes for the promoter region
Template strand a strand of DNA or RNA used as a template for building a complementary strand of a precise nucleotide sequence
Thymine a nitrogenous base (pyrimidine) found in the nucleus of DNA
Transcription process by which a base sequence in DNA is used to produce a base sequence in RNA
Transcription factor proteins that control gene expression at the transcription stage by binding to DNA sequences close to the promoter region of a gene or to RNA polymerase to induce or repress the expression of specific genes
Transfer RNA (tRNA) an RNA molecule that brings a specific amino acid to a ribosome so it can be joined to another amino acid during translation
Translation the process in which the base sequence of a mRNA molecule is used to produce the amino acid sequence of a polypeptide
Triplet sequence of the 3 nucleotides in DNA that carries the genetic information for the sequence of amino acids in a protein. Each triplet usually codes for one amino acid
Uracil a nitrogenous base (purine) found in the nucleotides of RNA. It forms a base pair with adenine
Created by: emmawalton05