BIG IDEA 3 Living Systems store retrieve transmit

BIG IDEA #3 Living Systems store, retrieve, transmit, and respond to information essential to life processes

DISCOVERY OF DNA Important Researchers § Frederick Griffith: transformation of bacterial cells § Avery, Mc. Carty, Mac. Leod: transforming agent is DNA § Hershey and Chase: confirmed DNA is transforming agent by using phages § Chargaff: base pairing rules § Wilkins and Franklin: used x-ray crystallography to photograph DNA § Watson and Crick: discovered double helix structure of DNA § Meselson and Stahl: semi-conservative replication of DNA § Beadle and Tatum: one gene: one enzyme

STRUCTURE OF DNA is a polymer made of nucleotide monomers Each nucleotide is made of a phosphate group attached to a five carbon sugar and one of four possible nitrogen bases: A, T, C, or G. § § Sugar in DNA is deoxyribose Sugar in RNA is ribose Bases are divided into purines (A, G) and pyrimidines (C, T) A always pairs with T: C always pairs with G (Hydrogen bonds hold them together) § U replaces T in RNA § RNA is single-stranded: DNA is double-stranded § Two strands are described as antiparallel and complementary

DNA REPLICATION Semiconservative replication: DNA separates and each old strand serves as a template for a new strand. Enzymes involved: § Helicase: enzyme that unzips DNA at the replication fork § DNA polymerase: adds free DNA nucleotides to the 3’ end of the leading strand the lagging strand. § Lagging strand is synthesized in sections called Okasaki fragments § DNA ligase seals the gaps between the Okasaki fragments

CELL DIVISION Binary Fission: used by bacteria Mitosis: Used by eukaryotes to increase cell number in multicellular organisms and for reproduction in unicellular eukaryotes. Produces two daughter cells with a full set of chromosomes Meiosis: Used by eukaryotes to make reproductive cells for sexual reproduction. Produces four gamete cells with half the number of chromosomes.

CELL CYCLE Three phases of the cell cycle: § Interphase: § G 1: Cell grows and carries out metabolic activities § S: DNA is copied § G 2: Cell growth continues and organelles are copied § Mitosis § Division of the nucleus: Prophase, Metaphase, Anaphase, Telophase § Cytokinesis § Cytoplasm divides

STAGES OF MITOSIS

STAGES OF MEIOSIS

FUNDAMENTALS OF GENETICS Gregor Mendel: father of modern genetics Worked with pea plants Law of Segregation: Individuals have two alleles for each trait and these randomly separate during the formation of gametes Alleles can be dominant or recessive § Heterozygous: two different alleles § Homozygous: two identical alleles Genotype: the actual genetic make-up Phenotype: the physical expression of alleles

EXCEPTIONS TO MENDEL’S GENETICS Multiple alleles: more than two alleles in the population Incomplete Dominance: neither allele is dominant Ex: Pink Red flowers x white flowers = pink flowers Codominance: both alleles expressed individually Ex: Spotted animals Polygenic traits: several genes interact for one trait Ex: skin color Epistasis: allele at one locus affects allele at a different locus Ex: Yellow, black and brown labs Sex-linked traits: traits are located on the X or Y chromosome. More common in men. Ex: color blindness, hemophilia, whiteeyed fruit flies Linked genes: genes located on same chromosome will be inherited together

GENE REGULATION IN PROKARYOTES Operons regulate gene expression in prokaryotes. An operon is a part of a DNA strand that includes a promoter site, operator site and the structural gene to be expressed. Proteins called repressor proteins can bind to the operator site. When a repressor is attached to the operator, the gene is turned off. When a repressor is absent, the gene is turned on. § Inducible operons: usually turned off and only become active when the repressor is lifted. § Repressible operons: usually turned on and only become inactivated when the repressor binds.

GENE REGULATION IN EUKARYOTES Many different mechanisms control which genes are expressed in eukaryotic cells. § Some areas of DNA are so tightly condensed around histone proteins that they can not unwind and be expressed (heterochromatin) § DNA methylation: methyl groups can be added to nucleotides. These will block RNA polymerase from binding and make the genes inactive. (plays a role in genomic imprinting) § Histone acetylation: acetyl groups are added to the histones in the chromosomes. This loosens the DNA, making it uncoil farther and increasing the rate of gene activity.

MORE GENE REGULATION IN EUKARYOTES Control elements include TATA boxes and CAAT boxes; which are regions of DNA near the promotor site. Proteins can bind to these sites and either block or increase gene activity. Poly A tail and a 5’cap are added to an RNA message before it leaves the nucleus. Sometimes, these end caps can be removed to reduce gene activity. Alternative splicing: occurs when different introns (noncoding regions of DNA) are spliced out as the RNA message is being modified before it leaves the nucleus. After translation of a protein, chaperone proteins can be blocked to prevent proper folding. Excess polypeptides can be tagged with ubiquitin so that a proteasome will break them up and reduce gene activity.

CHEMICAL REGULATORS OF GENE EXPRESSION Chemical messages can serve as regulators of gene expression Local Regulators § Synaptic signaling: Ex: Neurotransmitters § Paracrine signaling: Ex: Cell secretes a chemical that travels to a nearby cell (growth factors) § Autocrine signaling: Ex: Cell secreted a chemical that targets the same cell Long Distance Regulators § Amino acid derivative (Protein Hormones: insulin): Cannot diffuse through lipid membranes. Must bind to surface receptors § Steroid Hormones (Estrogen and Testosterone): Can diffuse through lipid membranes. Bind to interior target molecules

GENETIC VARIATION Processing of genetic information is imperfect and a source of genetic variation DNA Replication Errors (mutations) § Point (gene) Mutations: affect a single gene or protein. Examples include § Substitutions § Insertions § Deletions See diagram next slide

TYPES OF GENE MUTATIONS

DNA REPLICATION ERRORS (CONTINUED) § Chromosomal Mutations: affect a large portion of a chromosome or an entire chromosome. § Nondisjuctions: Chromosomes fail to separate properly during meiosis I or meiosis II resulting in Aneuploidy (one extra or one to few chromosomes). Ex: Down Syndrome (extra 21 st chromosome) § Polyploidy: One or more extra sets of chromosomes § Deletions: Large section of chromosome is broken off § Inversion: sequence of genes are shuffled § Translocation: piece of one chromosome becomes attached to another

OTHER MECHANISMS FOR GENETIC DIVERSITY Mutations are only one mechanisms for genetic diversity. Others include: § § § Independent assortment during meiosis Crossing over during meiosis Random fertilization Transformation in bacteria cells Conjugation in bacteria cells Transduction in bacteria cells: involves viruses

CELL COMMUNICATION Cell junctions: directly connect the cytoplasm of adjacent cells § Gap junction (animal cells) § Plasmodesmata (plant cells) Cell-to-cell recognition involves direct contact between cell surface molecules Other communication involves chemical messages released by a secretory cell and received by a target cell § Local regulators: short distance messenger molecules § Paracrine signaling: Ex: growth hormone § Synaptic signaling: Ex: neurotransmitters § Long distance regulators: Ex: Hormones

THREE STAGES OF CELL SIGNALING: RECEPTION, TRANSDUCTION, RESPONSE Reception: Involves ligands binding to receptor proteins in the cell membrane. Three main types of membrane receptor proteins: § G coupled: “On/Off” switch. GDP is bound = off/ GTP is bound = on. Once the switch is turned on, Enzymes are activated to set off the response. § Receptor tyrosine kinases: membrane receptors that attach phosphates to tyrosines. They can trigger multiple signal transduction pathways at once § Ion channel receptors: act as gates when receptors changes shape Intracellular receptors: located inside cells and receive messages from molecules that can easily pass through the cell membrane. They often act as transcription factors. Ex: testosterone is received by an intracellular receptor that then enters the nucleus and acts as a transcription factor to turn on specific genes.

THREE STAGES OF CELL SIGNALING: RECEPTION, TRANSDUCTION, RESPONSE Transduction: the message becomes amplified and then travels throughout the cell § Usually involves either phosphorylation cascades or second messengers § Common second messengers include c. AMP and Ca+ Response: usually involves some sort of cytoplasmic activity or the regulation of genes (transcription)

TRANSCRIPTION FACTORS Transcription factors are responsible for turning genes on and off and therefore control their expression Homeotic genes: involved in the patterns and sequences of embryonic development (i. e. they determine when, how and where major body parts will develop) Ex: Hox gene In general, transcription factors bind to a DNA molecule and allow it to open up and be transcribed into an m. RNA message. If they do not bind, then the m. RNA message will not be made and the gene will not be expressed as a protein.

INTERNAL MOLECULAR SIGNALS IN PLANTS Phototropism: plants grow towards light. Involves photosensitive receptors called phototropins. They stimulate the production of the plant hormone, auxin. Auxin causes cells on the dark side of the plant to grow faster than the light. This side will thus get longer and the plant will start to bend toward the short (light) side. Photoperiodism: plants have seasonal changes that cause them to flower. § Long day vs. short day plants

INTERNAL MOLECULAR SIGNALS IN ANIMALS Circadian rhythms: 24 hr. cycles Hibernation (state of inactivity and decreased metabolism during winter) Estivation (state of inactivity and decreased metabolism during summer) Migration (physical movement from one area to another) Phermonal signaling