Transcript Resolving power

Structure and Function
of the Cell
Chapter 3
3-1
How we learn about cells.
• Brightfield Microscopy
– visible light passes through the specimen and then
through glass lenses. (magnification up to 1000x)
• Magnification is the ratio of an object’s image to its
real size.
• Resolving power is a measure of image clarity.
– It is the minimum distance two points can be separated
and still viewed as two separate points.
– Resolution is limited by the shortest wavelength of the
source, in this case light.
– Resolution of a light microscope is about 0.2um.
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• The minimum
resolution of a light
microscope is about 2
microns, the size of a
small bacterium
• Light microscopes can
magnify effectively to
about 1,000 times the
size of the actual
specimen.
– At higher
magnifications, the
image blurs.
Fig. 7.1
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• While a light microscope can resolve individual
cells, it cannot resolve much of the internal
anatomy, especially the organelles.
• To resolve smaller structures we use an electron
microscope (EM), which focuses a beam of
electrons through the specimen or onto its
surface.
– Electron microscopes with shorter wavelengths than
visible light have finer resolution.
– The resolution of a modern EM is about 2 nm.
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• Transmission electron microscopes (TEM) are
used mainly to study the internal ultrastructure of
cells.
– A TEM aims an electron beam through a thin
section of the specimen.
– The image is focused
and magnified by
electromagnets.
– To enhance contrast,
the thin sections are
stained with atoms
of heavy metals.
Fig. 7.2a
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• Scanning electron microscopes (SEM) are
useful for studying surface structures.
– The sample surface is covered with a thin film of
gold.
– The beam excites electrons on the surface.
– These secondary electrons are collected and focused
on a screen.
• The SEM has great
depth of field,
resulting in an
image that seems
three-dimensional.
Fig. 7.2b
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Cell Characteristics
• Plasma Membrane
– Outer cell boundary
• Cytoplasm
– Cytosol
– Cytoskeleton
– Cytoplasmic inclusions
• Organelles
– Specialized structures that perform specific
functions
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Plasma Membrane
•
•
•
•
Intracellular versus extracellular
Membrane potential
Glycolipids and glycoproteins
Fluid-mosaic model
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Membrane Lipids
• Phospholipids form a lipid bilayer
– Hydrophilic (water-loving) polar heads
– Hydrophobic (water-fearing) nonpolar heads
• Cholesterol: Determines fluid nature of membrane
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Membrane Proteins
• Integral or intrinsic
– Extend from one
surface to the other
• Peripheral or extrinsic
– Attached to either the
inner or outer surfaces
of the lipid bilayer
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Plasma membrane
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Membrane Proteins
1. Marker Molecules
• Allow cells to identify
on another or other
molecules
• Glycoproteins
– Also Glycolipids
• Examples:
– Immune system
– Recognition of oocyte
by sperm cell
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2. Attachment Sites
Integrins: Proteins
in the plasma
membrane attach
to extracellular
molecules.
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3. Channel Proteins
• Nongated ion channels
– Always open
• Ligand gated ion channel
– Open in response to small
molecules that bind to
proteins or glycoproteins
• Voltage-gated ion channel
– Open when there is a
change in charge across the
plasma membrane
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4. Receptors
• Receptor molecules
– Exposed receptor site
• Linked to channel
proteins
– Acetylcholine
• Linked to G proteins
– Alter activity on inner
surface of plasma
membrane
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5. Enzymes and Carrier Proteins
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Nucleus
• DNA dispersed throughout
• Consists of :
– Nuclear envelope: Separates nucleus from cytoplasm
and regulates movement of materials in and out
– Chromatin: Condenses to form chromosomes during
cell division
– Nucleolus: Assembly site of large and small ribosomal
units
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Nucleus
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Cytoplasm
• Cellular material outside
nucleus but inside plasma
membrane
• Cytosol: Fluid portion
• Cytoskeleton: Supports
the cell
– Microtubules
– Microfilaments
– Intermediate filaments
• Cytoplasmic inclusions
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The Endomembrane System
Nuclear Endoplasmic
Golgi
Envelope Reticulum Apparatus
Secretory
Vesicle
If you stick your finger in the hole of a doughnut
is it inside or outside the doughnut?
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Organelles
• Small specialized structures for particular
functions
• Most have membranes that separates interior
of organelles from cytoplasm
• Related to specific structure and function of
the cell
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Ribosomes
• Sites of protein
synthesis
• Composed of a large
and small subunit
• Types
– Free
– Polyribosomes
– Attached to
endoplasmic reticulum
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Endoplasmic Reticulum
• Types
– Rough
• Attached ribosomes
• Proteins produced and
modified
– Smooth
• Not attached ribosomes
• Manufacture lipids
• Cisternae: Interior
spaces isolated from
rest of cytoplasm
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Golgi Apparatus
• Modification,
packaging, distribution
of proteins and lipids
for secretion or
internal use
• Flattened membrane
sacs stacked on each
other
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Function of Golgi Apparatus
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Action of Lysosomes
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Peroxisomes and Proteasomes
• Peroxisomes
– Smaller than lysosomes
– Contain enzymes to break down fatty and amino
acids
– Hydrogen peroxide is a by-product of
breakdown
• Proteasomes
– Consist of large protein complexes
– Include several enzymes that break down and
recycle proteins in cell
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Mitochondria
• Provide energy for cell
• Major site of ATP
synthesis
• Membranes
– Cristae: Infoldings of
inner membrane
– Matrix: Substance
located in space
formed by inner
membrane
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Centrioles
• In specialized zone
near nucleus:
Centrosome
• Each unit consists of
microtubules
• Before cell division,
centrioles divide,
move to ends of cell
and become spindle
fibers
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Cilia
• Appendages projecting
from cell surfaces
• Capable of movement
• Moves materials over
the cell surface
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Flagella
• Similar to cilia but
longer
• Usually only one
exists per cell
• Move the cell itself in
wavelike fashion
• Example: Sperm cell
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Microvilli
• Extension of plasma
membrane
• Increase the cell
surface
• Normally many on
each cell
• One tenth to one
twentieth size of cilia
• Do not move
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Movement through the Plasma
Membrane
•
•
•
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Diffusion
Osmosis
Filtration
Mediated transport mechanisms
– Facilitated diffusion
– Active transport
– Secondary active transport
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Diffusion
• Movement of solutes from an area of higher
concentration to lower concentration in
solution
– Concentration or density gradient
• Difference between two points
– Viscosity
• How easily a liquid flows
– Temperature
– Size of the diffusing molecule
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Diffusion
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Osmosis
• Diffusion of water (solvent) across a
selectively permeable membrane
• Important because large volume changes
caused by water movement disrupt normal
cell function
• Cell shrinkage or swelling
– Isotonic: cell neither shrinks nor swells
– Hypertonic: cell shrinks (crenation)
– Hypotonic: cell swells (lysis)
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Osmosis
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Osmosis
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Filtration
• Works like a sieve
• Depends on pressure difference on either side of
partition
• Moves from side of greater pressure to lower
– Example: In kidneys in urine formation
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Mediated Transport Mechanisms
• Involve carrier
proteins
• Characteristics
– Specificity
• To a single type of
molecule
– Competition
– Saturation
• Rate of transport
limited to number of
available carrier
proteins
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Saturation of a Carrier Protein
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Mediated Transport Mechanisms
• Facilitated diffusion
– Higher to lower
concentration without
metabolic energy
• Active transport
– Requires ATP
• Secondary active
transport
– Ions or molecules move
in same (symport) or
different direction
(antiport)
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Secondary Active Transport
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Endocytosis
• Internalization of
substances by
formation of a vesicle
• Types
– Phagocytosis
– Pinocytosis
– Receptor-mediated
endocytosis
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Pinocytosis and
Receptor-Mediated Endocytosis
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Exocytosis
• Accumulated vesicle secretions expelled from cell
• Examples
– Secretion of digestive enzymes by pancreas
– Secretion of mucus by salivary glands
– Secretion of milk by mammary glands
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Overview of Cell Metabolism
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Chromosome Structure
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Overview of Protein Synthesis
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Overview of Protein Synthesis
• Transcription
– Copies DNA to form
mRNA
– tRNA carries amino
acids to ribosome
• Translation
– Synthesis of a protein
at ribosome
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Translation
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Cell Life Cycle
• Interphase
– Phase between cell
divisions
• Mitosis
–
–
–
–
Prophase
Metaphase
Anaphase
Telophase
• Cytokinesis
– Division of cell
cytoplasm
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RNA primer made by RNA polymerase
3'
Newly synthesized DNA
DNA polymerase adds complimentary
base pairs to 3’ end.
5'
Leading strand
(Continuous replication)
3'
5'
Lagging strand:
(Okazaki fragments )
Helicase unwinds DNA
5'
3'
3'
1. Unwinding
- Helicase
2. Complimentary base pairing
- RNA polymerase makes RNA primer
5'
- DNA polymerase adds nucleotides to 3' end
3. Joining
-DNA polymerase removes RNA sequences.
-Ligase joins DNA fragments
Mitosis
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Mitosis
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Meiosis
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Comparison of Mitosis
and Meiosis
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Cellular Aspects of Aging
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Cellular clock
Death genes
DNA damage
Free radicals
Mitochondrial damage
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