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Ch. 25.4 (part 1)

Ch. 25.4 (part 1). Control of Gene Expression. Target #26- I can state how control of gene expression leads to cell specialization. The human body contains many types of cells which differ in structure and function

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Ch. 25.4 (part 1)

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  1. Ch. 25.4 (part 1) Control of Gene Expression

  2. Target #26- I can state how control of gene expression leads to cell specialization • The human body contains many types of cells which differ in structure and function • Each cell type must contain its own mix of proteins that make it different from all other cell types • Only certain genes are active in cells that perform specialized functions • What that means is that because gene expression is controlled, cells can have specialized functions • Skin cells vs. nerve cells, muscle cells vs. blood cells, etc…

  3. Target #27- I can describe an operon • Operon: a cluster of genes usually coding for proteins related to a particular metabolic pathway • Corresponds to a DNA sequence that controls transcription • Example • The enzymes needed to break down lactose, the sugar in milk, are found encoded together in an operon in bacterial DNA E. Coli

  4. Target #28- I can define the term promoterTarget #29- I can explain the functioning of the lac operon • The structural genes for three enzymes needed for lactose metabolism are under the control of one promoter/operator complex • Remember • Promoter= a region of DNA that contains a special sequence of nucleotides • Operator  aka operon

  5. Target #29- cont. • lac operon the operon used to breakdown lactose • If lactose is absent, a protein called a repressor binds to the operator • Means RNA polymerase cannot transcribe the three structural genes of the operon • The lac operon is encoded by a regulator gene located outside of the operon • If lactose is present, the lactose binds with the lac repressor so that the repressor is unable to bind to the operator • Means RNA polymerase is able to transcribe the structural genes into a single mRNA, which then is used in translation to make the three enzymes needed to break down the lactose

  6. Target #30- I can differentiate between an inducible operon and a repressible operon • Inducible operon: an operon that is only activated when a substance is present • Ex: lactose • Repressible operons: an operon that is active until a repressor turns it off

  7. Ch. 25. 4 (part 2) Control of Gene Expression

  8. Target #31- I can differentiate between gene expression in prokaryotes & eukaryotes • Gene expression is different in prokaryotes & eukaryotes • In a prokaryote, a single promoter serves several genes that make up a transcription unit • In Eukaryotes, each gene has its own promoter where RNA polymerase binds • Rely on a variety of mechanisms to regulate gene expression • Affects whether gene is expressed, the speed of expression, and the length of expression

  9. Target #32- I can describe the 5 different levels of gene expression in eukaryotes • There are 5 different levels of gene expression in eukaryotes • Pre-transcriptional control • Genes can be kept turned off via chromatin packing • Highly condensed portions called heterochromatin are inactive • Active genes are more loosely packed to be transcribed easily • Example • Female Calico cats are both tan and black • One of their x chromosomes is “turned of”, via dense chromatin packing, in each of their hair producing cells, which gives the cat a mosaic fur color pattern

  10. Target #32- cont. • Transcriptional Control • Dependent on the interaction of proteins with particular DNA sequences • Proteins that help RNA polymerase bind to a promoter are known as transcription factors • Proteins that speed up transcription are called transcription activators • Bind to a section of DNA called an enhancer • Posttranscriptional Control • mRNA must first be processed before it can leave the nucleus to be used for translation • A poly-A tail and a guanine cap are added • Poly-A tail= a stretch of nucleotides with only adenine as the nitrogen base • Added to the 3’ end • Guanine cap • Added to the 5’ end • Increases stability

  11. Target #32- cont. • Posttranslational Control • Some proteins are not immediately active after synthesis • Some proteins need to bond in a particular shape, or undergo modifications like phosphorylation before it can be used

  12. Target #33- I can differentiate between introns and exons • Introns vs. exons • Type of post-transcriptional control • Exon - RNA sequences in the primary transcript that are found in the mRNA • Intron - RNA sequences between exons that are removed by splicing

  13. Target #34- I can explain the process of splicing to create mature mRNA • Process • During transcription, all of the genetic information in a gene is initially copied into mRNA • The poly-A tail and guanine cap are added • The mRNA is spliced • the introns are cut out of the sequence, and the exons are joined together • The mature mRNA is ready to leave the nucleus for the cytoplasm

  14. Ch. 2 5 . 5 Gene Mutations

  15. Target #35- I can describe a gene mutation • Gene mutation: a permanent change in the sequence of bases in DNA • Effect can cause a range of consequences from no effect to complete protein synthesis inactivity • Can occur on somatic cells and on sex cells, also known as the germ line • Both can lead to cancer

  16. Target #36- I can explain the three causes of gene mutation • Three causes of gene mutation • Errors in replication • Rare source of mutation • DNA polymerase is responsible for proof-reading the new strand against the old strand • Usually mismatched pairs are replaced with the correct nucleotide • Occurs 1 in every 1 billion nucleotides • Mutagens • Environmental influences • Radiation, certain organic chemicals • Rate of mutation is usually low because DNA repair enzymes constantly monitor and repair damages

  17. Target #36- cont. • Transposons • Specific DNA sequences that have the ability to move to different genes • Can either increase or decrease the expression of the affected gene • Nicknamed “jumping genes” • Example • Indian corn has both white and red/black kernels • Caused by a transposon interrupting the expression of the gene for black kernel pigment

  18. Target #37- I can state how frameshift and point mutations affect protein activity • FrameshiftMutation • Occurs most often • Caused by a deletion of a nucleotide from a sequence or an insertion of a nucleotide in a sequence • May create a new sequence of codons, coding for a new protein • Point Mutation • A single nucleotide changes in a gene • Can alter the type of amino acid being produced, which may result in the wrong protein being synthesized

  19. Target #38- I can explain how gene mutations can lead to cancer • Development of cancer involves a series of accumulating mutations that can be different for each type of cancer • Several genes are involved with the suppression of tumor formation, but when mutated cause cancer • Proto-oncogenes and tumor-suppressor genes • When those genes are mutated, they do not transcribe/translate cell cycle regulating proteins correctly • Results in the cell cycle not being controlled, and/or apoptosis is not occurring • Characteristics of Cancer Cells • Genetically unstable • Do not correctly regulate the cell cycle • Escape the signals for cell death

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