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Chapter 3
Cell Diversity
Cell TheoryCells 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 CellPlasma membrane
Outer limiting barrierDetect chemical signals,
and recognize self from not
NucleusControl center
Cytoplasm (cytosol)Intracellular fluid
including organelles (excluding)
Plasma Membrane’s Role Physical isolation
Separates intracellular from extracellular environment
Regulates exchange with environmentSelective permeability
Polarity (hydrophobic vs. hydrophilic) Charge (charged vs. uncharged) Size (large vs. small)
Ions & nutrient enter, wastes & secretions exitAllows a concentration gradient to develop
Maintains homeostasis
The Fluid Mosaic ModelIntegral proteins
Channels, carriers, and signal transduction
Peripheral proteinsEnzymes, cell-cell recognition, and
structurePhospholipid bilayer (unsaturated)
Hydrophilic endsHydrophobic ends
Cholesterol
Types of Transport
Energy not requiredMovement ‘down’ a
concentration gradientSpecific types
Diffusion Simple Facilitated
OsmosisFiltration
Energy requiredMovement against a
concentration gradient
Passive Active
Simple DiffusionMovement of MOLECULES ‘down’ their
concentration gradientSmall, nonpolar molecules
E.g. O2 in and CO2 out in red blood cellsEach substance is independent
Continues until equilibrium = no NET movement
OsmosisMovement of WATER ‘down’ its concentration
gradientWater binds to solute in solution
More solute = less free water = less water available to move
Depends on TOTAL solute concentrationSelective permeability has a role too
watermolecules
glucosemolecules
Ability of a solution to cause a cell to gain or lose waterDepends on [solutes] that can’t cross PM relative to those in the
cellHypotonic solutions have a ___?__ [solute] than the cell
Water moves in Cells lyse
Hypertonic solutions have a ___?__ [solute] than the cellWater moves out
Cells crenate
Isotonic solutions have ___?__ [solute] as the cellWater shows no NET movement
Tonicity
Other Passive Transport TypesFacilitated diffusion FiltrationMovement same as
simpleLarger, water soluble
substancesGlucose, water, & ions
Protein carriers or channels
Water and solutes move ‘down’ a pressure gradientWater forced, solutes
chosen by sizeBulk movement
Active TransportMovement of MOLECULES against their
concentration gradientATP is energy sourceMaintains disequilibrium
Vesicular TransportExocytosis: removes
from inside the cellGolgi vesicles to PM
Endocytosis: brings into the cellPM pinches in to form
vesicles3 types
Phagocytosis Pinocytosis Receptor-mediated
Plasma Membrane SpecializationsMicrovilli
Folds of PM to increase surface areaMembrane 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 CytosolMembranous 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
Lysosomes 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
NucleusControl center of the cellNuclear envelope
Double membrane continuous with rough ER
Maintains shapeNuclear pores for transport; selectively permeable
NucleoliBuild ribosome subunits
ChromatinDNA and proteinCoils/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 ReplicationHelicase
2 templates formedDNA polymerase
Complementary base pairingDaughter strands
Leading strandLagging strand
DNA ligase
Semiconservative modelChromatid 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
AnaphaseSister chromatids separate
Single chromosomes move toward opposite ends of the cellMicrotubule ‘tug of war’
TelophaseDaughter nuclei form
Nuclear envelope reforms
Chromosomes begin to uncoil
Mitosis is complete
CytokinesisDivision of cytoplasm
Begins at the end of telophase (late anaphase too)
Cleavage furrow formsPinch plasma membrane
in 2 2 identical daughter
cells formed
MeiosisSimilar to mitosisReduces genetic material of each daughter
cell by halfDiploid (2n) adult produces haploid (n) gametes
n = # different chromosomes, paired = homologous Autosomes (22) and sex chromosome (X or Y)
Event occurs in 2 cyclesMeiosis I
Most variation from mitosisMeiosis II
Protein SynthesisDNA RNA protein
Genes instruct, but don’t buildNucleotides and amino
acids are different ‘languages’
RNA connects themTranscription: same
languageTranslation: different
language
Reviewing DNA and RNA
DNA RNA
Sugar is deoxyriboseHas –H
Bases are A,C, G, and TDouble-stranded helixOnly in nucleusModified only by
mutations1 type
Sugar is riboseHas -OH
Bases are A, C, G, and USingle-strandedNot confined to nucleusLots of processing and
modifications3 types (mRNA, tRNA,
rRNA)
TranscriptionSimilar to replication
Only 1 template used Occurs in the nucleus
RNA polymerase Complementary bases added
Steps Initiation at promoter Elongation Terminator sequence reached
Pre-mRNAProcessing
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 codons43 = 64 (plenty)
Demonstrates redundancy, but not ambiguity
Nearly universal across species
TranslationRibosome binds mRNA
In cytoplasmtRNA with complementary
anticodon bindsCarries start AA (from
chart) into P site2nd tRNA to A sitePeptide bond forms
Ribosome translocatesNew tRNA to A siteP site with 1st & 2nd AA
Stop codon terminatesPolypeptide folds =
protein
Summary of Protein Synthesis