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Transcript
THE CELL
Chapter 6
HISTORY OF CYTOLOGY

Initial microscopes

Robert Hooke


Antoni Van Leeuwenhoek


Origin of term cell
First to visualize living cells
Cell Theory developed by Schleiden, Schwann,
and Virchow
Every organism is composed of 1+ cells
 A cell is the simplest unit to demonstrate the
properties of life
 Cells arise only from previously existing cells

Visible light is
refracted (bent)
through glass
lenses
LIGHT MICROSCOPY
Magnification
is ratio of image
size to real size
Resolution is
minimum
distance 2
points can be
separate and
still
distinguishable
ELECTRON MICROSCOPE (EM)
Scanning (SEM)
Transmission (TEM)
Details of cell surfaces, 3D image Details of internal cell structures
•Uses a beam of electrons = higher resolution
•Can’t use on living cells
SIMILARITIES IN ALL LIVING CELLS

Plasma membrane: allows selective passage of
molecules
Double layer of phospholipids
 Variety of proteins spread throughout


Varies with cell location and function
Cytosol or cytoplasm: semisolid substance
enclosed by the plasma membrane
 Chromosome(s): carry genes as DNA
 Ribosomes: tiny complexes that make proteins
(genes direct)

CELLULAR CLASSIFICATION

Prokaryotes- before nucleus






NO nucleus (nucleoid region)
NO organelles
Single, circular DNA
Smaller, less complex
E.g bacteria, archaea
Eukaryotes- true nucleus





Nucleus
Membrane bound organelles
DNA arranged on multiple
chromosomes
Larger
E.g protists, fungi, plants,
animals
THE SIMPLICITY OF CELLS

Many small cells
advantaged over few
large cells
As cells grow, volume
increases faster than
surface area
 Ratio constrains size
b/c limits amount of
nutrients in and
wastes out


Effects shapes and body
plans too
EUKARYOTIC CELL TYPES
Plant
Animal
GENETIC CONTROL OF THE CELL

Nucleus is the control center that directs the cell




Chromosomes are the structures that carry
genetic info


Enclosed by a double membrane called a nuclear
envelope
Nuclear pores allow substances to enter and leave
Nuclear lamina protein filaments that maintain
shape
Consists of chromatin, a protein and DNA structure
that coils before cell division
Nucleolus is where rRNA is synthesized from
DNA instructions

Form small and large subunits that exit the nuclear
pores to form ribosomes in the cyoplasm
RIBOSOMES
Use DNA to make proteins
 Made of rRNA and protein complexes
 Build proteins in 2 locations


Free ribosomes formed in cytosol


Bound ribosomes are attached to endoplasmic
reticulum or nuclear envelope


Proteins will remain/function in cytosol
Make proteins that are shipped out of initial cell
Can change building location/type

Structurally identical
TRAFFICKING AND METABOLISM

Endomembrane system
Multiple responsibilities
 Related through connections or vesicle transport


Endoplasmic reticulum
Separates internal compartment of ER from cytosol
 Smooth ER lacks ribosomes



Synthesis lipids and carbs; detoxes alcohol and poisons
 Detox induces proliferation = increase tolerance to drugs
Rough ER

Site of protein synthesis
 Secrete proteins in vesicles that bud from membrane
 Expands itself (makes own phospholipids)
GOLGI APPARATUS

Modifies, stores, and sends products elsewhere

Cis = closest to Er


Trans = opposite side



Receive vesicles from ER
Ships products in vessels
Modified as move between two sides
Manufactures and
refines products in
stages
LYSOSOMES
Made by rough ER and sent to golgi
 Use hydrolytic enzymes to phagocytize food or
damaged organelles

Best in acidic conditions
 Decreased reaction if they break open



Fuse with phagocytotic cells to break down
polymers


Can lead to cell destruction
E.g WBC’s attack and destroy bacteria
Autophagy recycles cell’s own materials

Continuous renewal of cell
VACUOLES
Used for storage or
transport of substances
made by the ER
 Contractile vacuoles
remove excess water from
cell



Hydrolysis in plants and
fungi b/c no lysosomes
Central vacuole
transports solutes in plant
cells; disposes of byproducts

Pigmented to attract
pollinators and signal
poisonous
EXCHANGING ENERGY

Mitochondria
Convert E to usable forms
 Site of cellular respiration = synthesis of ATP
 Number in a cell is related to membrane activity
 2 membranous layers

Innermost layered is folded to form cristae
 Matrix is enclosed by inner and outer membranes


Chloroplasts

Contain chlorophyll or green pigment


Found in leaves and green plants
2 membrane layers
Innermost is a group of interconnected sacs called thylakoids
 Stacks are grana
 Fluid outside thylakoids is the stroma

PEROXISOMES
Transfer H to O2 = H2O2 (hydrogen peroxide)
 Break down fatty acids
 Detoxify alcohol in liver
 Don’t bud from ER, grow by incorporating
proteins from cytosol and lipids

MICROTUBULES

Thickest fibers, made of
dimers of tublin
(α- and β)

A ring of 9 triplets comprise
a centriole produced in a
centrosome


Provides the mobility of
cilia


Produce spindle fibers
during cell division
Beat like an oar
A ring of 9 doubles and 2
singles produce a flagella
MICROFILAMENTS

Solid rods of double twisted
actin subunits

Sometimes mixed with
myosin
Form structural networks
 Allow dynein, a large motor
protein to ‘walk’
 Interactions allow amoebas
to move pseudopodia

INTERMEDIATE FILAMENTS
Made of different protein subunits including keratin
 Maintain and bear tension
 Remain after death


E.g keratinized skin