Cells - Structure and Function

Important Events in the Discovery of Cells

1665 - Robert Hooke looks at cork under a microscope. Calls the chambers he see "cells"1665 - 75 Anton van Leeuwenhoek, the person incorrectly given credit for the invention of themicroscope (actually, he was just damn good at making and using them, and his scopes soon becamethe standard, and history has just given him credit as the inventor of the microscope), studies organismsliving in pond water (like you did in lab). He calls them "Animalcules."1830 - German scientists Schleiden and Schawann summarize the findings of many scientists andconclude that all living organisms are made of cells. This forms the basis of the Cell Theory of Biology

The Cell Theory of Biology

All organisms are composed of cellsThe cell is the structural unit of life - units smaller than cells are not aliveCells arise by division of preexisting cells - spontaneous generation does not existCells can be cultured to produce more cells

in vitro = outside organism or cellin vivo = inside organism or cell

Properties of Cells

Cells are complex and highly organized

They contain numerous internal structuresSome are membrane bound (organelles) while others do not

Cells contain a genetic blueprint and machinery to use it

Genes are instructions for cells to create specific proteinsAll cells use the same types of information

The genetic code is universalThe machinery used for synthesis is interchangeable

However, for this to function properly, information transfer must be error freeErrors are called mutations

Cells arise from the division of other cells

Daughter cells inherit the genes from the mother cellsBinary fission - cell division in bacteriaMitosis - the genetic complement of each daughter cell is identical to the other and to the mother cell.This is asexual reproductionMeiosis - the genetic complement of each daughter cell is reduced by half and each daughter cell is

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genetically unique. This is used in sexual reproductionDaughter cells inherit cytoplasm and organelles from the mother cells

Asexual - organelles from mother cellSexual - organelles predominately from one parent

In eukaryotes, the chloroplasts and mitochondria come from the egg cellThis can be used to trace the evolutionary origin of the organism

Cells acquire and utilize energy

Plant cells undergo photosynthesisconvert light energy and CO2 to chemical energy (ATP and glucose)

Most cells respirerelease energy found in organic compoundsconvert organic compounds to CO2 and O2make ATP

Cells can perform a variety of chemical reactions

Transform simple organic molecules into complex molecules (anabolism)Breakdown complex molecules to release energy (catabolism)Metabolism = all reactions performed by cells

Cells can engage in mechanical activities

Cells can moveOrganelles can moveCells can respond to stimuli

chemotaxis - movement towards chemicalsphototaxis - movement towards lighthormone responsestouch responses

Cells can regulate activities

Cells control DNA synthesis and cell divisionGene regulation - cells make specific proteins only when neededTurn on and off metabolic pathways

Cells all contain the following structures:

Plasma membrane - separates the cell from the external environmentCytoplasm - fluid-filled cell interiorNuclear material - genetic information stored as DNA

Types of Cells

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Prokaryotes

Pro = before; karyon = nucleusrelatively small - 5 to 10 umlack membrane-bound organellesearliest cell type

Archaea

Originally thought to be prokaryotesrelatively small - 5 to 10 umlack membrane-bound organellesUsually live in extreme environments(thermophiles, halophiles, etc)

Eukaryotes

Eu = true; karyon = nucleuscontain membrane-bound organellesEvolved from prokaryotes byendosymbiotic association of two ormore prokaryotesInclude Protists, Fungi, Animals, andPlants

Features of Prokaryotic Cells

Capsule - outer sticky protectivelayerCell Wall - rigid structure whichhelps the bacterium maintain itsshape

this is in NO way the same asthe cell wall of a plant cell

Plasma membrane - separates the cellfrom the environmentMesosome - infolding of plasmamembrane to aid incompartmentalizationNucleoid - region where nakedDNAis foundCytoplasm

semi-fluid cell interiorno membrane-boundorganelles

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location for metabolic enzymeslocation of ribosomes forprotein synthesis

Properties of Eukaryotic Cells

Features shared with Prokaryotic cellsRigid cell wall

Plant cells, some Fungi, some Protists

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Animal cells lack cell wallPlasma membraneCytoplasm with ribosomesNuclear material

Cytoskeleton - flexible tubular scaffold of microfilamentsmaintains cell shape and provides supportanchors organelles & enzymes to specific regions of the cellcontractility and movement (amoeboid movement)intracellular transport - tracks for vesicle and organelle movement by motor proteins

Cytoskeleton componentsMicrofilaments

solid protein (actin) which is assembled at one end and disassembled at the other endIntermediate filaments - rope-like fibrous proteins

provide structural reinforcementanchor organelleskeep nucleus in place

Microtubules - hollow tubes of tubulin (a globular protein)maintains cell shapeanchor organellesmovement of organellestrack for motor proteins

Cilia and Flagella - involved in cellular movementcomposed of microtubulescilia - short, numerous, complexflagella - longer, fewer, less complexboth arranged in a 9+2 pattern with dynein arms projecting outward

NucleusDouble membrane with poresOuter membrane continuous with ERNuclear matrix - protein-containing fibrilar networkNucleoplasm - the fluid substance in which the solutes of the nucleus are dissolvedChromosomes - protein and DNA complexesNucleolus - involved in the synthesis and assembly of ribosomes

Endomembrane SystemEndoplasmic Reticulum - an extensive membranous network continuous with the outer nuclearmembrane.

Rough ER - has ribosomes and is involved in secreted protein synthesisSmooth ER - lacks ribosomes and is involved in membrane lipid synthesis

Golgi ApparatusFlattened vesicles in stacks which receive protein from ERForm secretory vesicles to transport proteins to different parts of the cell (vacuole,lysosome, etc) or for secretioncis face - "receiving" side of Golgi apparatustrans face - "shipping" side of Golgi apparatus

Lysosomefound only in animal cellscontain enzymes for use in the hydrolytic breakdown of macromolecules

Peroxisome

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Eukaryotic organelle that degrades fatty acids and amino acidsAlso degrades the resulting hydrogen peroxide

Plant Central Vacuole - major storage space in center of plant cell with many functionsDigestive - break down of macromoleculesStorage - ions, sugars, amino acids, toxic wasteMaintain cell rigidity - high ionic concentration generates high water potential

Images of Vesicle Transport Between Endomembrane Organelles

MitochondriaFound in ALL eukaryotic cells (yes, even in plant cells)Site of aerobic respiration

sugars + O2 - - > ATP + CO2 + H2OContain DNA which codes for mitochondrial proteins, ribosomes, etc.Divide by a process similar to binary fission when cell dividesEnclosed in a double membrane system

Inner Membrane forms the Cristae (invaginations into interior region)Site of energy generation

Matrix is the soluble portion of the mitochondiraSite of carbon metabolismLocation of mDNASite of mitochondrial protein synthesis

ChloroplastsFound only in plant cellsSite of photosynthesis

conversion of solar energy to chemical energy in the form of ATP and sugarsContain DNA which codes for chloroplast proteins, ribosomes, etc.Divide when plant cell dividesEnclosed in a double membrane envelope that does not invaginate into the chloroplastThylakoid is a third internal membrane system

contains membrane-bound photosynthetic pigmentssite of photochemistry (the conversion of light energy to ATP)site of O2 generation

Stroma is soluable portion of chloroplastsite of CO2 fixationsite of sugar synthesis (carbon metabolism)location of cpDNAsite of chloroplast protein synthesis

Ribosomes Technically not an organelle, since there is no membrane, but they are prominent cellularstructures and usually lumped in with the organellesThe "factories" of the cell - involved in protein synthesisFacilitate the specific coupling of tRNA anticodons with mRNA codons during protein synthesisMay either be free or bound to ERMade up of two subunits, the large and the small subunitBoth subunits are constructed out of protein and RNA (called rRNA)The ribosomes of prokaryotes and eukaryotes vary slightly with regard to size and shape

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Endosymbiotic Origin of Chloroplasts and Mitochondria

Free-living prokaryote eaten by hostGenes transferred to host nucleusSome genes retained but most lost - can no longer survive outside of hostSymbiotic relationship

photosynthetic symbiont provides sugar - degenerates to form chloroplastaerobic symbiont provides a more efficient energy generation system - degenerates to formmitochondriahost provides stable environment, nutrients, energy, and most proteins

Evidence for Endosymbiotic TheoryChloroplasts and mitochondria have DNA

does not code for all proteinssome genes in nucleusproteins imported rom cytoplasm

Organelle proteins similar to bacterial formRibosome structure and metabolic enzymes more similar to bacterial forms

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