1.3 Genetic Control of Protein Synthesis, Cell Function, and Cell Reproduction(1).pptx

Genetic Control of Protein Synthesis, Cell Function, and Cell Reproduction Lecture Outline I. Genetic control of protein synthesis, cell function, and cell reproduction – Central dogma – Nucleotides, DNA, and genetic code II. Transcription- transfer of cell nucleus DNA code to cytoplasm RNA code – R...

Genetic Control of Protein Synthesis, Cell Function, and Cell Reproduction Lecture Outline I. Genetic control of protein synthesis, cell function, and cell reproduction – Central dogma – Nucleotides, DNA, and genetic code II. Transcription- transfer of cell nucleus DNA code to cytoplasm RNA code – RNA • mRNA • tRNA • rRNA • miRNA and siRNA III. Translation- formation of protein on the ribosomes IV. Control of gene function V. The DNA-Genetic System Controls Cell Reproduction – Cell cycle • Mitosis • Interphase – Mutations – Telomeres VI. Cell differentiation and cancer 1 Genetic Control of Protein Synthesis, Cell Function, and Cell Reproduction Objectives 1. Identify the central dogma of biology 2. Compare the basic structures of RNA and DNA 3. Define the terms nucleotide, gene, genome, chromatin, chromosome, & histone 4. Compare transcription and translation 5. List the function of mRNA, rRNA, and tRNA 6. Identify the function of miRNA and siRNA 7. Define the terms centromere, telomere, promoter region/TATA box 8. Identify the phases of the life cycle 9. List the phases of mitosis 10.Compare the function of RNA and DNA polymerase 11.Explain how gene mutations and gene regulation occur 12.Briefly describe how cancer may occur in a cell 2 References Assigned reading from your text: Hall Chapter 3, pages 31-47 3 I. Genetic Control of Protein Synthesis, Cell Function, and Cell Reproduction 17 Central Dogma  Transcription of RNA from DNA (nucleus)  One DNA strand copied and transcribed into pre-mRNA  pre-mRNA modified into messenger RNA (mRNA)  Translation of m-RNA into protein  m-RNA moves from nucleus to cytoplasm where it associates with ribosomes and various t-RNA molecules to synthesize a protein molecule Genetic Control of Cell Function • DNA and RNA – Each gene is made of DNA • • Gene is the functional unit of heredity Contains all the DNA nucleotides needed to produce specific proteins – Controls the formation of another nucleic acid- RNA – DNA contains the information; but RNA does the work • Transcription of the genetic code occurs in nucleus • Transcription and Translation – Translation of the RNA code to form proteins occurs in Nucleotides • Nucleosides contain a sugar linked to a nitrogen-containing base • Physiologically important bases are purines and pyrimidines • Adding an inorganic phosphate forms a nucleotide • Formed via the pentose phosphate pathway – anabolic process parallel to glycolysis • Form the backbone of RNA and DNA and other regulatory molecules (NAD+, ATP) DNA • Phosphoric acid • A pentose sugar • 4 nitrogenous bases – Two purines- adenine, guanine – Two pyrimidines- thymine and cytosine Figure 3-3. The basic building blocks of DNA. DNA and RNA Composition • Primary structure is very similar. • Both have the sugar phosphate backbone with a nitrogenous base attachment • They differ in their sugar component • Comparison • DNA is metabolically stable • Is found in bacteria, nuclei of eukaryotic cells, and mitochondria • RNA is in dynamic equilibrium with the AA pool Chromatin Structure • Gene- fundamental unit of DNA • DNA is compacted in the cell by association with histones- then into chromosomes – A nucleosome is formed when coiled DNA strands wrap around histone molecules • A diploid human cell contains 46 chromosomes 10 Helical, Double-Stranded Structure of DNA • Nucleic acids – DNA , deoxyribonucleic acid- is composed of discrete unitsgenes • DNA • Two helical strands form the backbone of the DNA molecule – Phosphoric acid – Deoxyribose • 4 nitrogenous bases lie between the two strands to connect them – 2 purines – adenine and guanine – 2 pyrimidines- thymine and cytosine Genetic Code – Genome is the collection of genes with the full expression of DNA from an organism – ~20-25,000 different genes code for proteins in each cell – Produces 100,000 different cell types – DNA contains all information to maintain life of cells and controls cell division • Linear DNA found in chromatin material • Circular DNA found only in mitochondria – Mitochondrial reproduction – Codes for mitochondrial proteins II. Transcription – Transfer of Cell Nucleus DNA Code to Cytoplasm RNA Code 17 Transcription – Genetic code consists of successive triplets of bases • Each three successive bases is a code word – Combination of ribose nucleotides with DNA form a molecule of RNA that carries the genetic code from the gene to the cytoplasm – RNA polymerase adds phosphates for polymerization Figure 3-7 Chemical Events in Protein Formation The code that is present in the DNA strand is transmitted in complementary form to the RNA chain DNA Base Guanine Cytosine Adenine Thymine RNA Base Cytosine Guanine Uracil Adenine RNA • • Single strands of nucleotides with ribose in the sugar-phosphate backbone RNA produced by transcription of genes along a strand of DNA Several secondary structures • Main classes of RNA • – Messenger RNA (mRNA)-is a copy of the genetic information in DNA • Carries DNA genetic code from the nucleus to cytoplasm for protein synthesis – Ribosomal RNA- (rRNA) is found in ribosomes • The platform for protein synthesis • Holds mRNA in place and helps assemble amino acids into proteins – Transfer RNA- (tRNA) is a small RNA molecule used to bring the correct amino acids to a site on mRNA that codes for proteins Precursors to mRNA • In eukaryotes, the portions of genes that dictate the formation of proteins are usually broken into several segments (exons) separated by segments that are not translated (introns) • Precursor messenger RNA- (premRNA) is a large, immature single strand of RNA produced in the nucleus from the DNA template – The precursor to mRNA contains two types of segments: • Introns are removed by splicing • Exons are retained in final mRNA • Small nuclear RNA (snRNA) directs Messenger RNA • Complementary in sequence to the DNA coding strand • 100s to 1000s of nucleotides per strand • Organized in codons - triplet bases – each codon “codes” for one amino acid (AA) – each AA—except met—is coded for by multiple codons – start codon: AUG (specific for met) – stop codons: UAA, UAG, UGA Transfer RNA • Acts as a carrier molecule during protein synthesis • Each transfer RNA (tRNA) combines with one AA. • Each tRNA recognizes a specific codon by way of a complementary anticodon on the tRNA molecule. Regulation of Gene Expression by miRNA and Small • Micro RNA (mi-RNA) is involved with postInterfering RNA transcriptive regulation of gene expression by affecting protein synthesis, m-RNA degradation and sequestering • Short molecules that bind to regions of m-RNA molecules • mi-RNAs stop synthesis of a specific protein; degrade a specific m-RNA or sequester m-RNA molecules (P bodies); Equivalent to gene silencing • Primary transcripts of DNA are processed in nucleus by microprocesser complex to form pre-miRNA which are processed in cytoplasm by dicer enzyme. • Dicer helps to assemble RISC complex and generates miRNAs. • miRNAs regulate gene expression by binding to complementary region of mRNA and repressing translation or promoting degradation of mRNA. III. Translation- Formation of Proteins on the Ribosomes 17 Translation Translation is the formation of proteins on the ribosomes Polyribosomes Polyribosomes: multiple ribosomes can simultaneously translate a single mRNA IV. Control of Gene Function and Biochemical Activity in Cells 17 Genomics • Genomics—the large-scale study of the genome • Human haploid genome (total genetic message) can code for approximately 30,000 genes. • Each nucleated somatic cell in the body contains the full genetic message – yet there are great differentiation and specialization in the functions of the various types of adult cells • Only small parts of the genetic message are normally transcribed • The genetic message is normally maintained in a repressed state • Humans are 99.8% identical at the genome level, 99.999% identical in the coding regions. Control of Gene Function and Biochemical Activity Genes control both the physical and chemical functions of the cells Two methods of gene control: 1) gene activation and 2) enzyme DNA (genes) Transport to cytosol translation mRNA stability Transcription processing RNA Proteins Structural Enzymes Cell function Protein activity Genetic Regulation • The promoter controls gene expression – at the site of transcription start • The promoter site includes a thymidine-adenine-thymidine-adenine sequence (TATA box) which ensures transcription starts at the proper point • Series of genes and their shared regulatory elements • Gene products contribute to a common process-single nucleotide polymorphisms (SNPs) can have major consequences for gene function Figure 3-13 V. The DNA-Genetic System Controls Cell Reproduction Cell Cycle Life cycle of the cell after mitosis: G1 (Gap 1) A period of cell growth • • Divides end of mitosis and DNA synthesis Common cell arrest point S (Synthesis) phase DNA synthesis • DNA doubled before mitosis G2 (Gap 2) Cell growth ending with chromosome • Condensation and the beginning of mitosis Copyright © 2021 by Saunders, an imprint of Cell Mitosis Copyright © 2021 by Saunders, an imprint of DNA Replication DNA Repair, “Proofreading” and “Mutations” • Gene mutations occur when the base sequence in the DNA is altered from its original sequence. • Following replication and prior to mitosis, DNA polymerase “proofreads” the “new” DNA, and cuts out mismatches. • DNA ligase replaces the mismatches with complementary nucleotides. • Gene mutations occur when the base sequence in the DNA is altered from its original sequence • Approximately 10 DNA mutations are passed to the next generation; however, two copies of each chromosome almost always ensures the presence of a functional gene. Chromosomes and Their Replication • After replication, “New” DNA helices associate with histones to form chromosomes (preventing RNA formation or DNA replication). • Two chromosomes remain temporarily attached at the centromere • The duplicated, attached chromosomes are called chromatids. Image from https://thebiotechnotes.com/2019/04/02/chromosomes-chromatids-and-chromatin/ Control of Cell Growth What determines the rate of cell growth? • growth factors • contact inhibition • cellular secretions (negative feedback) Rapid: bone marrow, skin, intestinal epithelia Slow/never: smooth muscle, neurons, striated muscle Telomeres and Telomerase • Telomeres prevent the degredation of chromosomes • is a region of repetitive nucleotide sequences located at each end of a chromatid- a protective cap • Are gradually consumed during repeated cell division • Telomerase adds bases to the ends of the telomeres so that many more generations of cells can be produced Cell Differentiation Different from reproduction ... • Changes in physical and functional properties of cells as they proliferate • Results not from the loss of genes but from the selective repression/expression of specific genes. • Development occurs in large part as a result of “inductions,” one part of the body affecting another. VI. Cell Differentiation and Cancer Cancer • Dysregulation of cell growth • Caused in all or almost all cases by the mutation or abnormal activation of genes that encode proteins that control cell growth and/or mitosis. • Proto-oncogenes: the “normal” genes • Oncogenes: the “abnormal” gene • Presence of several usually required to cause cancer • Antioncogenes: genes whose product suppresses activation of oncogenes – tumor suppressor cells Copyright © 2021 by Saunders, an imprint of