Chapter 5 Gases

Chapter 5 Gases

Chapter 10 Control of Gene Expression Cengage Learning 2016 10.1 Between You and Eternity Cancer is a multistep process in which cells grow and divide abnormally, disrupting physical and metabolic functions More than 200,000 new cases of breast cancer are diagnosed in the US each year about 5,700 in women and men under 34 years

of age Mutations in genes that control cell growth and division predispose individuals to develop certain kinds Cengage Learning 2016 Breast Cancer Cells Right, this light micrograph shows irregular clusters of cancer cells that have infiltrated milk ducts in human breast tissue. Diagnostic tests revealed abnormal cells such as these in Robins body when she was

just seventeen years old. Cengage Learning 2016 10.2 Switching Genes On and Off All body cells contain the same DNA with the same genes Differentiation The process by which cells become specialized In multicelled organisms, most cells differentiate when they start expressing a unique subset of their genes Which genes are expressed depends on the type of organism, its stage of

development, and environmental conditions Cengage Learning 2016 A stem cell that has become specialized will have most of its genes switched off and only the genes associated with the particular specialization switched on. For example, a liver cell will have

the genes that code for form and function of a liver cell switched on, Cengage Learning 2016 as shown on the Cengage Learning 2016 Gene Controls Govern the kinds and amounts of substances in a cell at any given time Various control processes regulate all steps between gene and gene

product Gene controls start, enhance, slow, or stop the individual steps of gene expression Gene controls can operate at any step in the path of protein production Cengage Learning 2016 Points of Control Over Gene Expression DNA Not Pictured: Gene availability (i.e. Epigenetics)

Tr a n s c r i p t i on PRIMARY MODE OF GENE EXPRESSION RNA mRNA P ro c e s s i n g a n d Tr a n s p o r t mRNA Tr a n s l a t i o n Splicing, capping, tail,

and alternative splicing Sped up or slowed/inhibited by regulator (miRNA) polypeptide PostTr a n s l a t i o n a l M o d i fi c a t i o n Cengage Learning 2016 active protein Proteins can be tagged, chopped

up, modified in RER Transcription Transcription factors Regulatory proteins that affect the rate of transcription by binding to special nucleotide sequences in DNA Activators speed up transcription when bound to a promoter; or may bind to distant enhancers Repressors slow or stop transcription Chromatin structure also affects transcription (againepigenetics) Cengage Learning 2016 HOW DO CELLS KNOW TO

TURN ON AND OFF GENES????? Transcription factors acting on signals from hormones, environment and other cells act to switch genes on or off. Cengage Learning 2016 Genes can be switched on or off by promotors or repressors based on cell information Cengage Learning 2016

Enhancers Enhancers can be located upstream of a gene, within the coding region of the gene, downstream of a gene, or thousands of nucleotides away! enhancer promoter exon1 intron exon2 enhancer transcription start site transcription end When a DNA -bending protein binds to the enhancer, the shape of the DNA changes,

which allows interactions between the activators and transcription factors to occur (see diagram next slide). Cengage Learning 2016 Transcription Factor: a protein that binds to specific DNA sequences, thereby controlling the flow (or transcription) of genetic information from DNA to mRNA promoter: the section of DNA that controls the initiation of RNA transcription (contains TATA Box) enhancer: a short region of

DNA that can increase transcription of genes (binding sequence for TF) activator: any chemical or agent which regulates one or more genes by increasing the rate of transcription at the promoter site repressor: any protein that binds to DNA and thus regulates the expression of genes by decreasing the rate of transcription Cengage Learning 2016 How do repressors

work? Cengage Learning 2016 Many genes are controlled by several different transcription factors, with a specific combination needed to turn the gene on; this is particularly true in eukaryotes Cengage Learning 2016 Control of Transcription Chemical modifications and chromosome duplications affect RNA polymerases access to genes

Enzymes that acetylate histones encourage transcription Adding a methyl group to a histone prevent transcription Polytene chromosomes (many copies) increase transcription rates in some organisms (ex: fruit flies have polytene chromosomes resulting from DNA replication without cell division) Cengage Learning 2016 mRNA Processing and Transport mRNA processing

-Splicing controls products of translation mRNA transport controls delivery of transcripts Passage through nuclear pores Delivery within cytoplasm (mRNA localization) Cengage Learning 2016 Translation Point of control over mRNA stability Depends on base sequence, length of poly-A tail, and which proteins are attached to it

RNA interference Expression of a microRNA complementary to a gene inhibits miRNA: Noncoding expression RNA of the gene thought to be made from introns spliced out of pre-mRNA Cengage Learning 2016

Post-Translational Modification Can inhibit, activate, or stabilize many molecules, including enzymes that participate in transcription and translocation Cengage Learning 2016 10.3 Master Genes Cascades of gene expression govern the development of a complex, multicelled body Master genes encode products that affect the expression of many other genes Pattern formation is the process by which a

complex body forms from local processes in an embryo Cengage Learning 2016 Gene Expression Control Makes a Fly 90 minutes 100 minutes 120 minutes 140 minutes B By 165 minutes after fertilization,

the products of several master genes, including the two shown here in green and blue, have confined the expression of even-skipped (red) to seven stripes. (pink and yellow areas are regions in which red fluorescence has overlapped with blue or green.) Cengage Learning 2016 A 100 minutes after fertilization, the master gene even-skipped is expressed (in red) only where two transcription fac-tors (green and blue) overlap. The transcription factors are the protein products of maternal mRNAs.

165 minutes C One day later, seven segments have developed. The position of the segments 13 hours corresponds to the position of the even- Homeotic Genes Master genes that control differentiation of specific tissues and body parts in an embryo

Encode transcription factors with a homeodomain Protein region of about 60 amino acids that can bind to a promoter Control development by same mechanisms as in all multicelled eukaryotes Many are interchangeable among different species Hox genes are a type of homeotic Cengage Learning 2016 Hox genes code for proteins that attach to molecular switches on DNA, turning other genes on and off. The DNA-binding

piece of a Hox protein is called the homeodomain, and it's encoded by the homeobox. Cengage Learning 2016 Some Effects of Homeotic Gene Mutations A model of the protein product (in gold) of the homeotic gene antennapedia attached to a promoter. The homeodomain is the

region that binds to the DNA. Expression of antennapedia in embryonic tissues of the insect thorax causes legs to form. Cengage Learning 2016 Antennapedia FYI- Legs and antennae are related to one another as much as molars are to incisors, fingers are to toes, and arms are to legs. Antennapedia is a gene that controls leg development, first discovered in Drosophila Loss-of-function mutations in the regulatory region of this gene result in the development of the second leg pair into ectopic antennae.

By contrast gain-of-function alleles convert antennae into ectopic legs. Cengage Learning 2016 Knockout Experiments Researchers inactivate a gene by introducing a mutation into it, then compare the differences with normal individuals and similar genes in humans Uses include studies for obesity, heart disease, cancer, diabetes Cengage Learning 2016

Eyeless and PAX6 eyeles s eye Cengage Learning 2016 eyeless 10.4 Examples of Gene Control in Eukaryotes Selective gene expression gives rise to many traits X chromosome inactivation In cells of female mammals, either the

maternal or paternal X chromosome is randomly condensed (Barr body) and is inactive Occurs in an early embryonic stage, so that all descendants of that particular cell have the same inactive X chromosome, resulting in mosaic gene expression Cengage Learning 2016 Dosage Compensation The theory that X chromosome inactivation equalizes expression of X chromosome genes between the sexes Mechanism of X inactivation XIST gene on one X chromosome transcribes an RNA molecule, which

coats the chromosome and causes it to condense, forming a Barr body Cengage Learning 2016 Cengage Learning 2016 X Inactivation Notice the red dots, those are Barr Bodies in the nuclei XX Cells above! What are calico cats? Why are

they only female? What is happening in the gene expression for fur color? Cengage Learning 2016 In these XY cells to the left, there are no Barr Bodies present. Cengage Learning 2016

Male Sex Determination in Humans Most of the genes on the X chromosome determine nonsexual traits The Y chromosome carries 307 genes, including SRY the master gene that triggers formation of testes Testes produce testosterone that causes formation of male genitalia and secondary sexual traits In the absence of testosterone, female genitalia form Cengage Learning 2016 Flower Formation The ABC model

Three sets of master genes (A,B,C) encode products that initiate cascades of expression of other genes to accomplish intricate tasks such as flower formation Master genes are expressed differently in tissues of floral shoots Cengage Learning 2016 Control of Flower Formation B C

A 1 4 2 3 peta carpe l l sepa stame l n

mutation: none whorl sepal 1: petal whorl stame 2: n whorl carpel 3: whorl 4:

A gene carpel stamen stamen carpel B gene sepal sepal carpel carpel C gene

sepal petal petal new flower Sequential expression of A, B, and C floral identity genes gives rise to four whorls of tissue in a floral shoot. Each whorl produces one floral structure: sepals, petals, stamens, or carpels. Expression of A genes causes sepals to develop in the outer whorl. A and B gene expression together triggers petals to form in the second whorl. B and C gene expression together triggers stamens to form in the third whorl, and C gene expression alone triggers carpel development in the inner whorl. Cengage Learning 2016

10.5 Gene Control in Prokaryotes Prokaryotes (bacteria and archaea) are single-celled and do not have master genes Prokaryotes control gene expression mainly by adjusting the rate of transcription in response to shifts in nutrient availability and other outside conditions Cengage Learning 2016 Operons and Operators Inquiry Activity: Using a chromebook, Click Operon Link 1

and watch video and try to figure out the functions of the molecules. Take notes on the Cornell note sheet, ask questions, and draw if needed. Watch Link 2 with class and discuss your findings!! Cengage Learning 2016 Operons and Operators In PROKARYOTES, genes that are used together often occur together on chromosomes Operon A promoter and one or more operators that collectively control

transcription of multiple genes Operators DNA regions that are binding sites for a repressor Cengage Learning 2016 The lac Operon E. coli digest lactose in guts of mammals using a set of three enzymes controlled by two operators and a single promoter Cengage Learning 2016 When Lactose Is Absent

Repressors bind to the operators and inactivate the promoter; transcription does not proceed Repressor protein gene 1 gene 2 gene 3 Lactose absent Cengage Learning 2016

In the absence of lactose, a repressor binds to the two operators. Binding prevents RNA polymerase from attaching to the promoter, so transcription of the operon genes does not occur. When Lactose Is Present Some is converted to another sugar that binds to the repressor and changes its shape; repressors dont bind to operators to inactivate the promoter; transcription proceeds When lactose is present, some is converted to a form that binds to the

repressor. Binding alters the shape of the repressor such that it releases the operators. RNA polymerase can now bind to the promoter and transcribe the operon genes lactose . mRNA RNA polymerase operator

Cengage Learning 2016 promoter operator gene 1 gene 2 gene 3 Compare/Contrast Gene Expression Prokaryotic Transcription: cytoplasm

Uses operons as functional units Regulatory gene causes inhibitor to make repressor which binds to operator No proofreadingmRNA goes directly Cengage Learning 2016 Eukaryotic Transcription: nucleus No operons Regulatory gene recognizes RNA

polymerase and starts transcription Proofreading occurs (prevents mutations) DNA Pre mRNA mRNA Lactose Intolerance Human infants and other mammals produce the enzyme lactase, which digests the lactose in milk The majority of humans begin to lose the ability to produce lactase around age 5, and become lactose intolerant Many people of European ancestry carry a mutation of one of the genes responsible for programmed lactase shutdown

Cengage Learning 2016 Riboswitches Some bacterial mRNAs regulate their own translation with riboswitches small sequences of RNA nucleotides that bind to a target molecule Binding of an end product (such as vitamin B12) changes the shape of the mRNA so that ribosomes no longer attach to it, and translation stops an example of feedback Cengage Learning 2016

inhibition 10.6 Epigenetics Methylations and other modifications that accumulate in DNA during an individuals lifetime can be passed to offspring Methylation in the parental DNA is usually reset but not always This is epigenetic inheritance that does not modify the nucleotide sequence Cengage Learning 2016 Cengage Learning 2016

DNA Methylations Between 3 and 6 percent of DNA in body cells is methylated Methyl groups often attach to a cytosine followed by a guanine, but which cytosines are methylated varies by individual In some cases, a decrease in methylations that results in an increase in expression of a gene may offer a survival advantage Cengage Learning 2016 DNA Methylation Illustrated

cytosin e guanine Cengage Learning 2016 Heritable Methylations Once a base in a cells DNA becomes methylated, it usually stays methylated in all of the cells descendants Methylation patterns in parental DNA is normally reset, with new methyl groups being added and old ones being removed However, not all parental methyl

groups are removed, so methylations acquired during an individuals lifetime can be passed to offspring Cengage Learning 2016 Epigenetic Inheritance Any heritable changes in gene expression that are not due to changes in DNA sequence are said to be epigenetic Epigenetic inheritance can adapt offspring to environmental stressors much more quickly than evolutionary processes Epigenetic marks may persist for generations after an environmental stressor has faded

Cengage Learning 2016 Epigenetic Inheritance Is Sex-Limited Grandsons of boys who endured a winter of famine when they were 6 years old lived about 32 years longer than the grandsons of boys who overate at the same age Effects are sex-limited Boys are affected by lifestyle of male ancestors; Girls by individuals in the maternal line Cengage Learning 2016

Points to Ponder What are the advantages and disadvantages of learning you have a gene that may lead to cancer? Why is gene control research more difficult among eukaryotic species than it is among prokaryotic species? How might alterations in DNA structure be harmful or beneficial to a species? Cengage Learning 2016

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