| A | B |
|---|
| gene expression | the information in DNA is transcribed and translated into a protein |
| structural genes | genes in a metabolic pathway that are grouped on a chromosome and transcribed at the same time |
| regulator gene | normally located outside the operon, codes for a DNA binding protein that acts as a repressor |
| repressor | a protein that controls whether the operon is active or not |
| promoter | a short sequence of DNA where RNA polymerase first attaches to begin transcription |
| operator | a short portion of the DNA located before the structural genes where the repressor binds |
| repressible operons | in the presence of a particular molecule, these operons are turned off (trp Operon and tryptophan) |
| inducible operons | in the presence of a particular molecule, these operons are turned on (lac Operon--lactose) |
| inducer | the presence of a molecule brings about the expression of genes-->lac Operon and lactose |
| chromatin | DNA in eukaryotes is always associated with a variety of proteins, and together they make up this stringy material |
| euchromatin | more loosely packed and transcriptionally active chromatin, histones are acetylated |
| heterochromatin | more tightly packed and transcriptionally inactive chromatin, histones are methylated |
| nucleosome | a portion of DNA wrapped around a group of histone proteins |
| chromatin remodeling complex | unpacks the histone portion of the nucleosome so that access to DNA is not blocked and transcription can begin |
| Barr body | an inactive X chromosome, highly packed heterochromatin, does not produce gene products |
| epigenetic inheritance | variations in the pattern of inheritance are not due to changes in the sequence of the DNA nucleotides |
| transcriptional control | most critical--involves availability of DNA-chromosome structure, participation of transcription factors, activators, and repressors |
| transcription factors | proteins that help to regulate transcription by assisting in the binding of RNA polymerase to the promoter |
| transcription activator | a DNA binding protein critical for transcription |
| enhancers | regions of DNA upstream from the promoter where activators bind |
| posttranscriptional control | occurs in the nucleus and includes alternative mRNA splicing and controlling the speed with which the mRNA leaves the nucleus |
| alternative pre-mRNA splicing | allows organisms to recombine their genes in novel ways to create a great variety of proteins |
| small RNS (sRNAs) | regulate gene expression at multiple levels |
| microRNAs (miRNA) | a type of sRNA that can bind to and disable the translation of mRNA in the cytoplasm |
| small-interfering RNAs (siRNA) | join with an enzyme (RISC) to form an active silencing complex that targets specific mRNAs in the cell for breakdown, preventing them from being expressed |
| RNA interference | Both miRNAs and siRNAs interfere with normal gene expression |
| translational control | begins when the processed mRNA molecule reaches the cytoplasm and before there is a protein product, involves the activity of mRNA for translation at the ribosome |
| posttranslational control | begins once a protein has been synthesized and has become active |
| proteases | enzymes that break down proteins |
| proteasomes | special structures where proteases are confined |
| gene mutation | a permanent change in the sequence of DNA |
| spontaneous mutations | arise as a result of abnormalities in normal biological processes (such as replication errors, transposons) |
| induced mutations | result from exposure to toxic chemicals or radiation |
| mutagens | environmental factors that alter the base composition of DNA |
| carcinogens | cancer-causing mutagens |
| DNA repair enzymes | constantly monitor DNA and fix any irregularities |
| point mutations | a change in a single DNA nucleotide |
| substitution | one DNA nucleotide is replaced with another |
| silent mutations | change a base in DNA but do not affect the amino acid sequence (redundancy of the genetic code) |
| frameshift mutations | occur most often when one or more nucleotides is either added or deleted from DNA |
| carcinogenesis | begins with either the loss of tumor suppressor activity and/or the gain of oncogene activity |
| RISC | an RNA-induced silencing complex that is activated by joining with siRNAs |
