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Chapter 10: Control of Gene Expression What Is Gene Control? A typical cell in your body uses only about ____________ of its genes at one time Some genes affect structural features and metabolic pathways and are expressed in __________________ Others genes are expressed only by certain _____________ (e.g., globin in RBCs) Control over __________________allows cells to respond to changes in their environment Gene Expression Control Includes: __________________; ______________________________; __________________; ________________________ The “____________” that turn a gene on or off are molecules or processes that ____________ or ____________ the individual steps of its expression Transcription __________________: bind directly to DNA and affect whether and how fast a gene is transcribed __________________: bind to __________________ or __________________ to shut off or slow down transcription by preventing RNA polymerase from accessing the promoter or by impeding its progress along the DNA strand ________________________bind directly to the promoter, or to a silencer that may be thousands of base pairs away from the gene ____________: in prokaryotes, a binding site in DNA for a repressor _______________: recruit RNA polymerase to a promoter region to enhance transcription ____________: distant DNA binding site for eukaryotic activators ________________________affects DNA transcription: only DNA regions that are ____________from histones are accessible to RNA polymerase Adding __________________ (—COCH3) to a histone loosens the DNA and ________________________ Adding __________________ (—CH3) to a histone tightens the DNA and ________________________ mRNA Processing and Transport Delaying the ______________________________of mRNA delays translation by preventing mRNA from reaching the cytoplasm mRNA must first be ____________, ____________, and finished with a __________________before leaving the nucleus ________________________can affect the form of a protein; different final mRNA’s can be produced from the original mRNA depending on which exons are joined together mRNAs are delivered to organelles or specific regions of cytoplasm via “zip codes” located near the ________________________; this allows translation of an mRNA close to where its protein product is being used Translation A cap on an mRNA “zip code” sequence _____________________until mRNA has reached its final destination, close to where the protein product is being used mRNA stability alters translation rates and is affected by base sequence, the ______________________________, and __________________short lived mRNA enables cells to adjust for their protein needs In eukaryotes, translation of a particular mRNA can be shut down by tiny bits of noncoding RNA called __________________: complementary in sequence to part of an mRNA ___________: microRNAs bind to complementary stretches and mark that mRNA for destruction, no translation occurs and no protein is produced _____________________is also a factor in control over translation in prokaryotes Bacteria can shut off translation of a particular mRNA by expressing an ____________ (complementary) RNA strand With double-stranded RNA, ____________ cannot initiate translation Post-Translational Modification Many newly synthesized polypeptide chains must be ____________ before they become functional Example: some enzymes become active only after they have been phosphorylated Post-translational modifications ____________, ____________, or ____________ many molecules How Do Genes Control Development in Animals? Master Genes As an animal embryo develops, its cells __________________ and form tissues, organs, and body parts; this is driven by cascades of ______________________________ The products of ________________________the ____________of many other genes; final outcome is the completion of an intricate task such as the formation of an eye Orchestration of gene expression during development: __________________are delivered to opposite ends of an _________________ ____________as it forms These mRNA’s are ____________after the egg is fertilized and the ___________ ____________ diffuse away, forming ____________ that span the entire developing embryo The nucleus turns on __________________based on its position relative to the ________________________ __________________products also form__________________, further influencing which additional master genes the nucleus will turn on Eventually, the products of master genes cause __________________ cells to __________________, and specialized structures to form Homeotic Genes A ________________________is a master gene that governs the formation of a __________________- such as an eye, leg, or wing Animal homeotic genes encode for proteins called ______________________that contain a __________________, region of about sixty amino acids, that bind directly to a ____________ and turn on a set of genes Homeotic genes are often named for what happens when a ____________ alters their function (Examples in the fruit fly: Antennapedia gene, Tinman, Wingless) A ____________ is an experiment in which a gene is not expressed due to deliberate__________________by the introduction of a ____________ or a complete ____________ of the gene itself. (Results in a __________________) What Are Some Outcomes of Gene Control in Eukaryotes? X Marks the Spot In humans and other mammals, a female’s cells contain two __________________ In each cell, one __________________is always tightly condensed, termed __________________ Most of the genes on a Barr body are ____________; X chromosome inactivation ensures that only one of the two X chromosomes in a female’s cells is active ________________________: mechanism in which X chromosome inactivation equalizes gene expression between males and females There is ________________________of maternal and paternal X chromosomes in each cell An adult female mammal is a “____________” for the expression of X chromosome genes; some express the maternal X chromosome while some express the paternal X chromosome An X chromosome gene called XIST is transcribed on only one of the two X chromosomes; the gene’s product, a long noncoding RNA, sticks to the chromosome that expresses the gene, causing it to condense into a Barr body Male Sex Determination in Humans The human __________________contains the master gene for male sex determination in mammals, ______ ______ expression in ______ embryos triggers the formation of testes which produce the sex hormone testosterone Mutations in the SRY gene cause ______ individuals to develop external genitalia that appear female What Are Some Outcomes of Gene Control in Prokaryotes? Prokaryotes do not undergo development, so these cells have no need for ____________ Prokaryotes do respond to environmental fluctuations by adjusting __________________ Example: bacteria transcribe certain genes only when a specific nutrient is available; the cell does not waste energy producing gene products that are not needed Bacteria control gene expression mainly by adjusting the ________________________ Genes that are used together often occur ____________ on the chromosome and share a single ____________that precedes genes, so all are ________________________into a single RNA strand ____________: group of genes together with a promoter–operator DNA sequence that controls their transcription The lac Operon An operon called______allows E. coli cells to metabolize lactose The lac operon includes __________________and a ____________ flanked by two ____________ Three genes of the lac operon: One gene encodes a __________________that brings lactose across the plasma membrane Another gene encodes an __________________ that breaks the bond between lactose’s two monosaccharide monomers, glucose, and galactose A third gene encodes an __________________whose function is still being investigated When lactose is not present, a ____________ binds to the two ____________and twists the region of DNA with the ____________ into a loop ________________________cannot bind to the twisted up promoter, so the lac operon’s genes cannot be____________ When ____________ is present, some of it is converted to another sugar that binds to the ____________and changes its ____________ The ________________________releases the ____________and the looped DNA unwinds The promoter is now accessible to ________________________, and transcription of lactose metabolizing genes begins Lactose Intolerance In the majority of human worldwide, the ability to digest ____________ stops at about age five, when expression of the gene for ____________ (enzyme produced by intestinal cells) shuts off When lactase production slows, lactose passes undigested into the ___________ _______, which hosts huge numbers of ____________which switch on their lac operons, resulting in the production of gaseous products – causing distention, pain, and diarrhea Not everybody is lactose intolerant about ____________of human adults carry a mutation that allows them to digest milk; this mutation is more common in some populations than in others Can Gene Expression Patterns Be Inherited? Direct __________________ of DNA suppresses gene expression and once a DNA nucleotide becomes __________________, it will usually stay methylated in all of a ________________________ Methylation is an __________________ modification: heritable changes in gene expression that are not the result of changes in DNA sequence Methylation is influenced by ______________________________ Example: humans conceived during a famine have an unusually low number of methyl groups in certain genes which leads to the expression of hormones that foster prenatal growth and development; may offer a survival advantage in a poor nutritional environment Methylation of __________________is normally “______” in the first cell of the new individual, with new methyl groups being added and old ones being removed. However, reprogramming __________________all methyl groups and these can be passed on to ____________ Example: Grandsons of boys who endured famine in 1944 Nazi-occupied Netherlands, lived about 32 years longer than grandsons of boys who ate well during the same winter.