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