Chapter 6 A Tour of the Cell

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Chapter 6
A Tour of the Cell
CAMPBELL AND REECE
Cell Theory
 All living organisms are made of cells
 Cells are the smallest unit of structure &
function in living organisms
 All cells come from other cells
Microscopes
 1665: Hooke sees cell walls
Anton van Leewenhoek
 made best lenses of
his day
 pond water:
animalcules
Light Microscopy
 light goes through specimen and is refracted
by glass lenses so image is magnified as it is
projected toward eye
 magnification: ratio of image size to real size
 resolution: a measure of clarity , the
minimum distance 2 pts can be separated &
seen as 2 pts (can’t do better than 200 nm)
 contrast: accentuate pts in different parts of
specimen
Light Microscopy
Electron Microscopy
TEM
 beam e- thru
specimen
SEM
 beam e- across
surfaces
Size Range of Cells
Cell Fractionation
Common to all cells
1. cytosol
2. ribosomes
3. DNA
4. plasma membrane
Compare & Contrast
Prokaryotic Cell
 DNA concentrated in





nucleoid
smaller
simpler
(-) internal
membranes
older
asexual reproduction
Eukaryotic Cell
 DNA in nucleus
 larger
 more complex
 (+) internal
membranes
 asexual or sexual
reproduction
Images
Prokaryotic
Nucleoid
Eukaryotic
Nucleus
Cell Size Limitations
Prokaryotic Cell Details
Eukaryotic Cell Details: Plant Cell
Eukaryotic Cell Detail: Animal Cell
Nucleus
 contains most of the DNA
 5 microns across on average
 enclosed by dbl membrane: nuclear envelope
Chromatin
Nucleolus
Nucleus
Nucleolus
Ribosomes
 rRNA & proteins
 carry out protein synthesis
 free ribosomes or ribosomes embedded in
membrane
 polysomes: string of ribosomes
Ribosomes
Polysomes
Anatomy of a Ribosome
The Endomembrane System
 includes all membranes in cell
 nuclear
envelope
 Endoplasmic reticulum
 Golgi apparatus
 vesicles, vacuoles
 lysosomes
 plasma membrane
The Endomembrane System
 functions:
 synthesis
of proteins (ribosomes in
membrane)
 transport of proteins into membranes &
organelles (or out of cell)
 movement of lipids
 detoxification of poisons
 all membranes “related” either by
proximity or by transfer of membrane
segments via vesicles
The Endomembrane System
Endoplasmic Reticulum
 >50% of membrane in a cell
 “endoplasmic” means within the cytoplasm”
 “reticulum” means little net
 made of network of tubules & sacs
Endoplasmic Reticulum
 cisternae spaces contiguous with nuclear
envelope
RER & SER Contiguous
RER
 ribosomes on outer surface of membrane
 most proteins made shipped out of cell
 as polypeptide grows (into cisternae) it folds
into its 2’ then 3’ structure
 most secretory proteins are glycoproteins so
that carbohydrate attachment is done by
enzymes in RER membrane
RER
 protein made for use in cytosol kept separate
from those meant for export
 transport vesicles carry new secretory
protein/glycoprotein away from RER
Secretory Vesicles
SER
 functions:
 lipid
synthesis
 metabolism of carbohydrates
 detoxification of drugs & poisons
 storage of Ca++
SER
 cells with lots SER:
 endocrine
glands
synthesize
steroid hormones
 ovaries, testes, adrenals
 hepatocytes
detoxify
by adding –OH, increases solubility
 cleared by kidneys
alcohol, drug abusers (legal or not) have
increased amts of SER in their hepatocytes
(also increases drug tolerance)
Detox by SER
SER Stores Ca++ in Muscle Fibers
Golgi Apparatus
 receives, sorts, packages, ships
 also does a little modifying of proteins
 extensive in cells that secrete
 made of flattened membranous sacs with a
curve (has directionality cis & trans)
 internal space = cisternae
Golgi Apparatus
Golgi Apparatus
 ER products modified on trip thru Golgi
 cisternae
membrane has unique “team”of
enzymes that moves from cis to trans
 modifies the monomers in carb part of
glycoproteins
 modifies phospholipids destined for
membrane
 makes some macromolecules:
polysaccharides
Golgi Apparatus
Golgi Apparatus Vesicles
 when leave trans vesicles have molecular ID
tags that indicates where they are going
 vesicles have receptor proteins on external
surface that “recognize” where vesicle is
supposed to dock (other organelles, plasma
membrane)
Lysosomes
 membranous sac filled with hydrolytic
enzymes
 digests macromolecules
 use acidic pH
 made in RER  Golgi  cytosol
Lysosome Functions
 digest food vacuoles ingested by phagocytosis
in protists or by macrophages (WBCs that
ingest bacteria or debris and recycle
nutrients in them)
 autophagy: hydrolytic enzymes in lysosomes
recycle cell’s own organic material in worn
out organelles
Lysosomes
Lysosmes
Lysosomal Storage Diseases
 autosomal recessive diseases
 lack a functioning hydrolytic enzyme 
whatever that enzyme would have chemically
broken down builds up in lysosome (called a
residual body)  lysosomes fill up interferes
with cell functions
 example: Tay Sachs disease
lipid-digesting enzyme malfunction
affects neurons
Vacuoles
 are large vesicles from ER or Golgi
 solution inside different from cytosol due to
its selectively permeable membrane
 Types:
 food vacuoles
 contractile vacuoles
remove excess water
 in plant cells act like
 lysosomes
storage bins
Large Central Vacuoles in Plant Cells
 develops by coalescence of smaller vacuoles
 solution inside it called cell sap
Endosymbiont Theory
 early ancestor of eukaryotic cells engulfed an
oxygen-using nonphotosynthetic prokaryotic
cell = mitochondrion
 over time prokaryotic cell became an
endosymbiont (a cell living w/in another cell)
 some time later some or 1 of these engulfed a
photosynthetic prokaryotic cell and
developed same relationship = chloroplast
Endosymbiosis Theory
Mitochondria
 in nearly all cells, 1- 10 microns
 # correlates with metabolic activity of cell
 dbl membrane
 inner membrane folded (cristae) & divides
mitochondria into 2 separate inner
compartments (intermembrane space &
matrix)
 matrix contains enzymes for cellular
respiration, DNA, ribosomes
 intermembrane has enzymes that make ATP
Mitochondrion Structure
Chloroplasts
 a plastid
 dbl membrane separates inside  2 parts
 3-6 microns
 in green parts of plants (chlorophyll)
 thylakoids: inner membrane folds in disc-
shapes: 1 stack of discs = granum
 fluid in inner folds = stroma
Plastids
 group of plant organelles
 other examples:
1. amyloplast
colorless
 in roots & tubers
 stores starch
2. Chromoplast
1. pigments that give fruits & flowers their
colors

Peroxisomes
 specialized metabolic compartment with 1
membrane
 contain enzymes that remove H atoms from
various molecules  to O2  H2O2
 H2O2  2 H2O by enzymes in liver
peroxisomes
 functions:
 break down fatty acids
 in hepatocytes detoxify alcohol, poisons
Glyoxysomes
 specialized peroxisomes in fat-storing tissues
of plant seeds
 contain enzymes that start catabolism of fatty
acids  sugars
 seed uses these sugars for energy to  plant
Cytoskeleton
 organizes the structure & activities of a cell
 3 types:
1. Microtubules
2. Microfilaments
3. Intermediate Filaments
Functions of the Cytoskeleton
1. mechanical support
2. maintain cell shape
3. provides anchor for organelles & cytosol
enzymes
4. cell motility
Cytoskeleton & Cell Motility
 involves interaction between cytoskeleton &
motor proteins
 both work with plasma membrane to
move cell
 make flagella or cilia move
 muscle fiber contraction
 migration of neurotransmitter vesicles to
axon tips
Motor Protein Animation
 http://www.sinauer.com/cooper5e/animation1204.
html
Types of Cytoskeleton
Assembly of Microfilaments
 http://www.sinauer.com/cooper5e/animation1201.h
tml
Cell Surface Projections Formed by Cytoskeleton
 http://www.sinauer.com/cooper5e/micrograph1202
.html
Microvilli
 http://www.sinauer.com/cooper5e/micrograph1201.
html
Cytoskeleton Animation
 http://www.bmc.med.utoronto.ca/bmc/images/stori
es/videos/eddy_xuan.mov
Microtubules
 in all eukaryotic cells
 hollow rods 25 nm across, 200 nm – 25
microns long
 made from a globular protein: tubulin, a
dimer (made of 2 subunits)
Microtubules
Assembly of Microtubules
 http://www.sinauer.com/cooper5e/animation1203.
html
Microtubule Functions
 shape & support cell (compression-resistant
role)
 serve as tracks other organelles with motor
proteins can move along
 guide secretory vesicles from Golgi  plasma
membrane
 in mitotic spindle to separate chromosomes
 in animal cells: microtubules made in
centrosome
Centrioles
 pair w/in each centrosome
 each made of 9 sets of triplet microtubules
 only in animal cells
Micrograph of Centrioles
 http://www.sinauer.com/cooper5e/micrograph1206
.html
Cilia
 locomotor appendage on some cells
 move fluid over surface
 are usually many on cell surface
 0.25 microns across & 2 – 20 microns long
 move like oars (alternating power /recovery
strokes)
 generate force perpendicular to cilium’s axis
Cilia & Flagella Structure
 locomotor appendage
 share common structure with cilia: 9
doublets of microtubules in ring with 2 single
microtubules in center then covered with
plasma membrane
Cilia & Flagella Structure
 dyneins: large motor proteins extending
from one microtubule doublet to adjacent
doublet
 ATP hydrolysis drives changes in dynein
shape so cilia or flagella bend
Flagella & Cilia Animation
 http://biology-
animations.blogspot.com/2008/02/flagell-and-ciliaanimation-video.html
Microfilaments
 are really actin: globular protein that links




with others into chains, which twist helically
around each other, forming microfilaments
in all eukaryotic cells
function: bears tension
many found just inside plasma membrane
(support cell shape) which gives cytosol gellike consistency just inside plasma
membrane
make up core of microvilli
Microfilaments
 with myosin (another contractile protein)
make
 muscle fibers contract
 Amoeboid movement (pseudopods)
Intermediate Filaments
 8 – 12 nm across
 tension bearing
 not assembled/disassembled like
microtubules & microfilaments
 made of proteins, one is keratin
 line interior of nuclear envelope, axons
 support framework of cell shape
Intermediate Filaments
Extracellular
 materials made by cell but put into
extracellular space:
 Cell Wall
 Extracellular Matrix
 Cell Junctions
Plant Cell Walls
 functions:
 protection
 maintains
shape
 prevents excessive uptake of water
Details
 exact chemical composition varies from
species to species
 all have microfibrils made of cellulose
Plant Cell Wall Basic Design
Plant Cell Walls
 secreted by cell membrane
 young plant cell secretes primary cell wall:
 thin,
flexible
 middle lamella: lies between primary cell
walls of adjacent cells
made
of pectin: glues adjacent cells togeher
Plant Cell Walls
 when cell stops growing either:
1. secrete hardening substances into primary
wall
2. secrete a secondary wall between plasma
membrane & primary cell wall
 has strong & durable matrix
 wood is mostly secondary cell wall
Primary & Secondary Cell Walls
Extracellular Matrix (ECM)
 in animals
 main ingredient: glycoproteins
 collagen
embedded in proteoglycans
(protein with many carbohydrates
attached)
40%
of all the protein in human body is
collagen
ECM
 fibronectin: ECM glycoprotein binds to cell-
surface receptor proteins called integrins
 integrins: span plasma membrane
transmitting signals from ECM 
microfilaments on inner border of plasma
membrane
ECM
Cell Junctions
1. plasmodesmata: perforations in plant cell
walls lined with plasma membrane, filled
with cytoplasm
 cytosol flows from cell to cell

plasma membranes of adjacent cells
contiguous
Plasmodesmata
Cell Junctions in Animal Cells
3 main types
1. Tight Junctions
 plasma membranes of adjacent cells
tightly pressed against each other
 bound together by proteins
 form continuous seal around cell
 example: tight jcts around skin cells
make skin water proof
Tight Junctions
Cell Junctions in Animal Cells
 2. Desmosomes
 function
like rivets
 fastens cells together
 anchored in cytoplasm by intermediate
filaments
 example: attach muscle cells to each other
Desmosomes
Cell Junctions in Animal Cells
 3. Gap Junctions
 cytoplasmic
channels from 1 cell to
another
 made of membrane proteins that
surround a pore open to ions, sugars, a.a.
 necessary for communication between
cells like cardiac muscle and in animal
embryos
Gap Junctions
Cell Animation
 http://vcell.ndsu.nodak.edu/animations/flythrough
/movie-flash.htm

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