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Ch 12. Gene Expression and Regulation Chapter 12 At a Glance 12.1 How Is the Information in DNA Used in a Cell? 12.2 How is the Information in a Gene Transcribed into RNA? 12.3 How is the Base Sequence of mRNA Translated into Protein? 12.4 How Do Mutations Affect Protein Structure and Function? Case Study: Cystic Fibrosis If all you knew was her music, you’d think Alice Martineau had it made – a young, pretty singer-songwriter under contract with a major recording label. However, like about 70,000 other people worldwide, Martineau had_______, a recessive __________________genetic disorder caused by _______________of a gene that encodes a crucially important protein called _______. CF occurs when a person is homozygous for these defective alleles. Before modern medical care, most people with cystic fibrosis died by age 4 or 5; even now, the average life span is only 35 to 40 years. Martineau died when she was 30. The CFTR protein forms channels that allow chloride to move across plasma membranes down its concentration gradients. CFTR also helps ________ movement in many parts of the body, including the ________ glands, CFTR helps to reclaim sodium chloride form the sweat and transport it back into the blood, so that the body doesn’t _______much salt. Probably the most crucial role of CFTR is in the cells lining the airways are covered with a film, of ___________, which traps bacteria and debris. The bacteria-laden mucus is then swept out of the lungs by ___________ on the cells of the airways. Case Study: Cystic Fibrosis Normally, chloride moves through CFTR channels out of the airway cells into the mucus, and sodium follows. The resulting high concentration of sodium chloride causes _________to move into the mucus by _______, resulting in a thin liquid that can be removed easily by the cilia. However, mutations in the CFTR gene produce a _____________________channel proteins. As a result, chloride and sodium do not move from the cells into the mucus, so water doesn’t move into the mucus, either. The mucus becomes so ________that the cilia can’t move it out of the lungs, leaving the airways partially __________. Bacteria multiply in the mucus causing the ___________________________ In this chapter, we examine the processes by which the instructions in genes are translated into proteins. As you will learn, changes in those instructions – mutations – alter the structure and function of proteins 12. 1 How Is the Information in DNA Used in a Cell? • Information must be translated into action in order for a particular process to work • DNA contains the “____________________________________” of every cell • Proteins = construction ____________________ of the cell • Proteins control cell shape, function, reproduction & synthesis of biomolecules • Must be a flow of information from __________ __________ • DNA provides instructions for protein synthesis via ____________ intermediaries • DNA info must be carried by _________________(RNA) from the nucleus to the cytoplasm • RNA is usually __________ stranded unlike DNA’s double helix • RNA has the sugar _________ rather than deoxyribose in its backbone • RNA contains the nitrogenous base ___________ instead of thymine (T) There are 3 types of RNA involved in protein synthesis: 1. ______________ RNA (mRNA) carries DNA gene information to the ribosome • contains __________ (groups of 3 bases) which specify _________________________ will be incorporated into a protein 2. _______________ RNA (rRNA) is part of the structure of ribosomes • Consist of ___ subunits (made up of rRNA and other proteins) that contain various _______ and catalytic ___________ needed for protein synthesis; carry out translation 3. _________________RNA (tRNA) brings amino acids to the ribosome • contain ____________ (groups of 3 bases) which ________ specific ____________to the ribosome where they are incorporated into a protein. Genetic information is _______________into RNA and then translated into protein. • DNA ______________________________________in a 2-step process 1. Information in a DNA gene is copied into RNA in the process of ____________________ (occurs in __________ of eukaryotic cells) 2. mRNA, together with tRNA, amino acids, and a ribosome synthesize a protein in the process of __________________ of the genetic information contained in mRNA (occurs in ___________________ of eukaryotic cells) 12.2 How Is the Information in a Gene Transcribed into RNA? 1. ______________ – _______________binds to __________region at the beginning of a gene so RNA can be synthesized 2. ___________ – RNA polymerase travels along DNA template strand (_______’) adding RNA bases that are _________________to DNA (as the RNA strand forms; DNA helix re-forms). 3. _________________– transcription stops when RNA polymerase reaches a termination ________________; completed RNA strand is released and detaches from DNA; RNA polymerase free to bind to promoter region on a different gene https://www.youtube.com/watch?v=ztPkv7wc3yU 12.3 How Is the Base Sequence of Messenger RNA Translated into Protein? mRNA synthesis differs btwn prokaryotes and eukaryotes Prokaryotes - ______ nuclear membrane - Transcription/translation ______ separated in space/time - Ribosomes _________________ begin translating the mRNA into protein while still attached to DNA Eukaryotes - DNA contained in _________ and ribosomes reside in ___________________ - Genes not clustered by many disperse among several chromosomes - mRNA molecule formed is _____________________________________that can be immediately translated into protein • In eukaryotes, a _______________________is processed to form mature mRNA that is translated into protein • Pre-mRNA contains _______ (segments of DNA that encode for protein) interrupted by ____________ (segments of DNA that are not translated) ________________– introns cut out and exons spliced together _________________ __________ help 1) _______ the RNA through the nuclear envelope, 2) _______ mRNA to ribosome, 3) _______________ cellular enzymes from _____________ the mRNA • During translation, ____________________________help to synthesize proteins • 3 steps (initiation, elongation, termination) 1. Initiation – begins when tRNA and mRNA bind to a ribosome • Pre-initiation complex forms • __________________of methionine tRNA binds to mRNA by base paring with _______________________at (5’ end) of mRNA • large ribosomal unit attaches to small subunit, holding mRNA btwn 2 subunits and holding methionine tRNA in its first tRNA binding site (P site) 2) Elongation – _______________________one at a time to growing protein chain • 2nd tRNA anticodon base-pairs with 2nd codon on mRNA • bond holding methionine to its tRNA is broken and forms _______________ btwn amino acid on 1st tRNA and amino acid on 2nd tRNA • Empty _________________and ribosome moves down the mRNA one codon https://www.youtube.com/watch?v=5bLEDd-PSTQ 3) Termination: stop codon (____________________) signals the end of translation https://www.youtube.com/watch?v=itsb2SqR-R0 12.4 How do Mutations Affect Protein Structure and Function? • Mutations – ______________in base sequence of DNA caused by mistakes made during replication or environmental factors • 1-2. ____________________________: when pieces of DNA are broken apart and reattached within a single chromosome or to a different chromosome - These mutations relatively ______________ if entire gene is moved - If gene is split in 2, it won’t code for a complete functional protein • Depending on how many nucleotides are involved, mutations can cause a ____________________ of a gene’s __________________ • Deletions – occurs when 1 or more ________________________ from the sequence • Insertion – occurs when 1 or more _______________________ to the sequence • Substitution (point mutation) – an ___________________ takes the pace of a correct one. • There are about 1,500 different defective alleles of the CFTR gene, all of which can cause cystic fibrosis. The most common defective allele is missing a ______________. The resulting lack of one crucial amino acid causes the CFTR protein to be misshapen. A normal CFTR protein is synthesized by ribosomes on rough endoplasmic reticulum, enters the ER, and then is transported to the plasma membrane. The misshapen CFTR protein, however, is broken down within the ER and never reaches the plasma membrane. Four other common mutant CFTR alleles code for a ____________ in the middle of the protein, so translation ____________ partway through. Still other mutant alleles produce proteins that are completely synthesized and inserted into the plasma membrane, but do not form functional chloride channels. Androgen Insensitivity Sometime between 7-14 yrs of age, a girl usually goes through ________breasts swell, hips widen, and menstruation begins. In rare instances, however, a girl may develop all of the outward signs of womanhood, but without ___________. If her physician performs a chromosome test, in some cases the results seem to be impossible: the girls’ sex chromosomes are ______. The reason she has not begun to menstruate is that she lacks ovaries and a uterus but instead has testes inside her abdominal cavity. She has about the same concentrations of androgens (male sex hormones, i.e. testosterone) circulating in her blood as would be found in a boy her age. In fact, androgens have been present since early in her development. However, her cells cannot respond to them – a condition called _______________ ___________________. The affected gene codes for a protein known as an androgen receptor. In normal males, androgens bind to the receptor proteins, stimulating the___________________of genes that help to produce many male features, including formation of a penis and descent of testes. Androgen insensitivity is caused by defective androgen receptors. There are more than 200 mutant alleles of the androgen receptor gene. The most serious are mutations that create a ___________ __________. Bc the androgen receptor gene is on the X chromosome, a person who is genetically male (XY) inherits a single allele for the androgen receptor. If this allele is seriously defective, the person will _____ synthesize functional androgen receptor proteins. The person’s cells will be unable to respond to __________, and male characteristics will not develop. In many respects, female development is the “default” option in humans, and without functional androgen receptors, the affected person’s body will develop female characteristics. Thus a mutation that changes the nucleotide sequence of a single gene, causing a single type of defective protein to be produced, can cause a person who is genetically male to look like and perceive herself to be female. Why Bruises Turn Colors Bruises typically progress from ______________________.This sequence is visual evidence of the control of ______________. If you bang your shin on a chair, blood vessels break and release red blood cells, which burst and spill their hemoglobin. Hemoglobin and its iron-containing heme group are dark bluish-purple in the _________________ state, so fresh bruises are purple. Heme, which is toxic to the liver, kidneys, brain, and blood vessels, stimulates transcription of the heme oxygenase gene. ____________________is an enzyme that converts heme to ______________, which is green. A second enzyme, which is always present because its gene. A second enzyme, which is always present because its gene is always expressed, converts biliverdin to __________, which is yellow. The bruise finally disappears as bilirubin moves to the liver, which secretes it into the bile. You can follow the detoxification of heme by watching your bruise change color.