The Cell Chapter 3

Cell Diversity

Cell Theory All living things are composed of cells Cells are the smallest unit to demonstrate the properties of life Cells are only produced from existing cells

Typical Animal Cell Plasma membrane – Outer limiting barrier – Detect chemical signals and recognize self from non-self 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 – 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 Energy not required Movement ‘down’ a concentration gradient Specific types – Diffusion Simple Facilitated – Osmosis – Filtration Active Energy required Movement against a concentration gradient

Clarifying Solutions Liquid mix of 2+ substances – Aqueous solution when water is solvent Solvent: dissolving agent Solute: substance that is dissolved Reviewing polarity – ‘Like dissolves like’ – Hydrophilic Sugar or salt and water – Hydrophobic Oil and water

Simple Diffusion Movement of MOLECULES ‘down’ their concentration gradient – Small, nonpolar molecules E.g. O 2 in and CO 2 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 Movement same as simple Larger, water soluble substances – Glucose, water, & ions Protein carriers or channels Filtration 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 = impermeable E.g. keep digestive enzymes out of blood – Desmosomes Protein filaments = high tension protection E.g. skin and heart muscle – Gap junctions Integral proteins for communication E.g. heart and smooth muscle

Nucleus Control center of the cell Nuclear envelope – 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

Organelles Within Cytosol Membranous Mitochondria – Produces ATP Endoplasmic reticulum (ER) – Rough – proteins to Golgi – Smooth – lipids & carb production; detoxification Golgi apparatus – Modify and package secretory vesicles Lysosomes – Digestive processes Peroxisomes – Detoxification Nonmembranous 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 – orientation

The Cell Cycle (IPMATC) Interphase about 90% – Chromosomes not visible yet – G 1 phase – S phase – G 2 phase Mitotic (M phase) cell division – Mitosis is nuclear division Prophase Metaphase Anaphase Telophase – Cytokinesis is cytoplasmic division Repeat as needed

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

Prophase Events Sister chromatids condense Nuclear envelope begins to disappear Centrioles appear at opposite ends of cell Mitotic spindles form

Metaphase Events Centrioles at opposite ends of cells Sister chromatids line up with centromere on metaphase plate Microtubules attached to each chromatid at the centromere

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

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

Cytokinesis Division of cytoplasm – 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 Sugar is deoxyribose – Has –H Bases are A,C, G, and T Double-stranded helix Only in nucleus Modified only by mutations 1 type RNA Sugar is ribose – 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)

Transcription Only 1 template used RNA polymerase – Complementary bases added Steps – Promotion – Elongation – Termination Pre-mRNA processing – Introns spliced out – Exons rejoined – mRNA

Decoding Genes 4 nucleotide bases to specify 20 amino acids Based on codons – 4 3 = 64 (plenty) Redundancy, but not ambiguity Nearly universal across species

Translation Ribosome binds mRNA – In cytoplasm tRNA with anticodon binds – Start codon to P site – 2 nd tRNA to A site – Peptide bond joins AA’s Ribosome translocates – P site with 1 st & 2 nd AA – New tRNA to A site Stop codon terminates – Polypeptide folds = protein

Summary of Protein Synthesis