The Cell Chapter 3

Cell Diversity

Cell Theory Cells are the smallest unit to demonstrate the properties of life Cells are produced from existing cells Organismal activity depends on cells individually and collectively Subcellular structures dictate cellular activity

Typical Animal Cell Plasma membrane Nucleus Cytoplasm (cytosol) Outer limiting barrier Detect chemical signals, and recognize self from not Nucleus Control center Cytoplasm (cytosol) Intracellular fluid including organelles (excluding)

Plasma Membrane’s Role Physical isolation Separates intracellular from extracellular environment Regulates exchange with environment Selective permeability Polarity (hydrophobic vs. hydrophilic) Charge (charged vs. uncharged) Size (large vs. small) Ions & nutrient enter, wastes & secretions exit Allows a concentration gradient to develop Maintains homeostasis

The Fluid Mosaic Model Integral proteins Peripheral proteins Channels, carriers, and signal transduction Peripheral proteins Enzymes, cell-cell recognition, and structure Phospholipid bilayer (unsaturated) Hydrophilic ends Hydrophobic ends Cholesterol

Types of Transport Passive Active Energy not required Movement ‘down’ a concentration gradient Specific types Diffusion Simple Facilitated Osmosis Filtration Energy required Movement against a concentration gradient

Simple Diffusion Movement of MOLECULES ‘down’ their concentration gradient Small, nonpolar molecules E.g. O2 in and CO2 out in red blood cells Each substance is independent Continues until equilibrium = no NET movement

Osmosis Movement of WATER ‘down’ its concentration gradient Water binds to solute in solution More solute = less free water = less water available to move Depends on TOTAL solute concentration Selective permeability has a role too water molecules glucose molecules

Tonicity Ability of a solution to cause a cell to gain or lose water Depends on [solutes] that can’t cross PM relative to those in the cell Hypotonic solutions have a ___?__ [solute] than the cell Water moves in Cells lyse Hypertonic solutions have a ___?__ [solute] than the cell Water moves out Cells crenate Isotonic solutions have ___?__ [solute] as the cell Water shows no NET movement

Other Passive Transport Types Facilitated diffusion Filtration Movement same as simple Larger, water soluble substances Glucose, water, & ions Protein carriers or channels Water and solutes move ‘down’ a pressure gradient Water forced, solutes chosen by size Bulk movement

Active Transport Movement of MOLECULES against their concentration gradient ATP is energy source Maintains disequilibrium

Vesicular Transport Exocytosis: removes from inside the cell Golgi vesicles to PM Endocytosis: brings into the cell PM pinches in to form vesicles 3 types Phagocytosis Pinocytosis Receptor-mediated

Plasma Membrane Specializations Microvilli Folds of PM to increase surface area Membrane Junctions Tight junctions Integral proteins fuse the PM’s of 2 cells together = impermeable E.g. digestive enzymes from blood Desmosomes Protein filaments anchor cells in places of high tension E.g. skin and heart muscle Gap junctions Integral proteins form communication channels for ions and small molecules E.g. heart and smooth muscle

Organelles Within Cytosol Membranous Nonmembranous Mitochondria Produces ATP Lysosomes Produced by golgi apparatus Endoplasmic reticulum (ER) Rough – proteins to Golgi Smooth – lipids & carb production; detoxification Golgi apparatus Modify and package secretory vesicles Digestive processes Peroxisomes Detoxification Cytoskeleton Microtubules, microfilaments, & intermediate filaments Centrioles Formed by microtubules, 9 triplets Microtubules originate in mitosis Ribosomes Small and large subunits Free or attached = dynamic Cilia Move substances or organism Flagella 9 + 2 orientation

Nucleus Control center of the cell Nuclear envelope Nucleoli Chromatin Double membrane continuous with rough ER Maintains shape Nuclear pores for transport; selectively permeable Nucleoli Build ribosome subunits Chromatin DNA and protein Coils/condenses to become visible = chromosomes

The Cell Cycle (IPMATC) Interphase about 90% Chromosomes not visible yet G1 phase S phase = DNA replication occurs G2 phase Mitotic (M phase) cell division Mitosis is nuclear division Prophase Metaphase Anaphase Telophase Cytokinesis is cytoplasm division Repeat as needed

DNA Replication Helicase DNA polymerase Daughter strands 2 templates formed DNA polymerase Complementary base pairing Daughter strands Leading strand Lagging strand DNA ligase Semiconservative model Chromatid  sister chromatids

Prophase Sister chromatids condense Nuclear envelope begins to disappear Mitotic spindles form

Metaphase Sister chromatids line up with centromere on metaphase plate Microtubules attached to each chromatid at the centromere

Anaphase Sister chromatids separate Single chromosomes move toward opposite ends of the cell Microtubule ‘tug of war’

Telophase Daughter nuclei form Nuclear envelope reforms Chromosomes begin to uncoil Mitosis is complete

Cytokinesis Division of cytoplasm Cleavage furrow forms Begins at the end of telophase (late anaphase too) Cleavage furrow forms Pinch plasma membrane in 2 2 identical daughter cells formed

Meiosis Similar to mitosis Reduces genetic material of each daughter cell by half Diploid (2n) adult produces haploid (n) gametes n = # different chromosomes, paired = homologous Autosomes (22) and sex chromosome (X or Y) Event occurs in 2 cycles Meiosis I Most variation from mitosis Meiosis II

Protein Synthesis DNA  RNA  protein Genes instruct, but don’t build Nucleotides and amino acids are different ‘languages’ RNA connects them Transcription: same language Translation: different language

Reviewing DNA and RNA DNA RNA Sugar is ribose Sugar is deoxyribose Has -OH Bases are A, C, G, and U Single-stranded Not confined to nucleus Lots of processing and modifications 3 types (mRNA, tRNA, rRNA) Sugar is deoxyribose Has –H Bases are A,C, G, and T Double-stranded helix Only in nucleus Modified only by mutations 1 type Reviewing DNA and RNA

Transcription Similar to replication RNA polymerase Steps Processing Only 1 template used Occurs in the nucleus RNA polymerase Complementary bases added Steps Initiation at promoter Elongation Terminator sequence reached Pre-mRNA Processing Introns spliced out by spliceosomes Exons rejoined mRNA

Decoding Genes 4 nucleotide bases to specify 20 amino acids Genetic instructions are based on triplet code called codons 43 = 64 (plenty) Demonstrates redundancy, but not ambiguity Nearly universal across species

Translation Ribosome binds mRNA In cytoplasm tRNA with complementary anticodon binds Carries start AA (from chart) into P site 2nd tRNA to A site Peptide bond forms Ribosome translocates New tRNA to A site P site with 1st & 2nd AA Stop codon terminates Polypeptide folds = protein

Summary of Protein Synthesis