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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
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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 TransportPassive• 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. 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
watermolecules
glucosemolecules
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– 9 + 2 orientation
The Cell Cycle (IPMATC) • Interphase about 90%
– Chromosomes not visible yet– G1 phase– S phase– G2 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– 43 = 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– 2nd tRNA to A site– Peptide bond joins AA’s
• Ribosome translocates– P site with 1st & 2nd AA– New tRNA to A site
• Stop codon terminates– Polypeptide folds = protein
Summary of Protein Synthesis