Download Lecture #8 - Suraj @ LUMS

Lecture 8
Cells
Structure: A Tour of the Cell
The Cell:
A basic unit of living matter separated from
its environment by a plasma membrane.
The smallest structural unit of life.
Discovery
First observations of cells were made with
light microscopes: Robert Hooke (1665):
Used primitive microscope to observe cork
(dead plant cells). Coined the word cell.
Cell Theory
Developed 200 years ago.
1. All living organisms are made up of one
or more cells.
2. The smallest living organisms are single
cells, and cells are the functional units
of multi-cellular organisms.
3. All cells arise from pre-existing cells.
Relative Sizes of Procaryotic and Eucaryotic Cells
and Viruses
Different Classes of Cells
• Prokaryotic
• Eukaryotic
- Animal
- Plant
• All possess a cell membrane. Called the
plasma membrane in bacterial cells and
cytoplasmic membrane in animal/plant
cells.
The Cell Membrane
• Functions as a semi-permeable barrier, allowing a very
few molecules across it while fencing the majority of
organically produced chemicals inside the cell.
• Structure is a lipid bilayer (also referred to as the fluidmosaic model).
• The most common molecule in the model is the
phospholipid, which has a polar (hydrophilic) head and
two nonpolar (hydrophobic) tails. These phospholipids
are aligned tail to tail so the nonpolar areas form a
hydrophobic region between the hydrophilic heads on the
inner and outer surfaces of the membrane.
Lipid Bilayer
Functions of Cell Membranes
• Separate cell from nonliving environment. Form most
organelles and partition cell into discrete compartments
• Regulate passage of materials in and out of the cell and
organelles. Membrane is selectively permeable.
• Receive information that permits cell to sense and respond
to environmental changes. Hormones Growth factors
Neurotransmitters
• Communication with other cells and the organism as a
whole. Surface proteins allow cells to recognize each other,
adhere, and exchange materials.
Prokaryotic Cells
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Bacteria and blue-green algae.
Small size: Range from 1- 10 micrometers in length.
About one tenth the size of a eukaryotic cell.
No nucleus: DNA in cytoplasm or nucleoid region.
Ribosomes are used to make proteins
Cell wall: Hard shell around membrane
Other structures that may be present:
1. Capsule: Protective, outer sticky layer. May be used for
attachment or to evade immune system.
2. Pili: Hair-like projections (attachment)
3. Flagellum: Longer whip-like projection (movement)
Prokaryotic Cells
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Bacteria and blue-green algae.
Small size: Range from 1- 10 micrometers in length.
About one tenth the size of a eukaryotic cell.
No nucleus: DNA in cytoplasm or nucleoid region.
Ribosomes are used to make proteins
Cell wall: Hard shell around membrane
Other structures that may be present:
1. Capsule: Protective, outer sticky layer. May be used for
attachment or to evade immune system.
2. Pili: Hair-like projections (attachment)
3. Flagellum: Longer whip-like projection (movement)
Prokaryotic Cells:
Prokaryotic Cell Wall
• Made up of peptidoglycans, molecules that have a
carbohydrate (polysaccharide) attached to a
polypeptide chain. The polysaccharide chains are
liked by short amino acid chains.
• Forms a net like structure that surrounds the whole
cell.
• Function – support and prevention of lysis
• Use to identify different types of bacteria
• Gram positive and Gram negative
Gram negative and Gram positive
• Gram because of inventor.
• Bacteria with small amounts of peptidoglycan
and, characteristically, lipopolysaccharide, are
Gram-negative. Cells are a pink colour after
staining.
• Bacteria containing relatively large amounts
of peptidoglycan and no lipopolysaccharide
are Gram-positive. Cells are a purple colour
after staining.
Eukaryotic Cells
• E.g protists, fungi, plant, and animal cells.
• Nucleus: Protects and houses DNA
• Membrane-bound Organelles: Internal
structures with specific functions such a:
Separate and store compounds
Store energy
Work surfaces
Maintain concentration gradients
Eukaryotic Cell Surfaces
• Cell wall: Much thicker than cell membrane,
(10 to 100 X thicker).
• Provides support and protects cell from lysis.
• Plant and algae cell wall: Cellulose
• Fungi and bacteria have other polysaccharides.
• Not present in animal cells or protozoa.
• Breaks in surface: Channels between adjacent
plant cells form a circulatory and
communication system between cells. Sharing
of nutrients, water, and chemical messages
Membrane-Bound Organelles
of Eukaryotic Cells
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Nucleus
Rough Endoplasmic Reticulum (RER)
Smooth Endoplasmic Reticulum (SER)
Golgi Apparatus
Lysosomes Vacuoles
Chloroplasts
Mitochondria
Membrane Bound Organelles
Nucleus
Processing and transport
Rough ER
Smooth ER
Golgi Body
Completed Protein
Eucaryotic Cells: Typical Animal Cell
Eucaryotic Cells: Typical Plant Cell
Chloroplasts
• Site of photosynthesis in plants and algae.
CO2 + H2O + Sun Light -----> Sugar + O2
• Number may range from 1 to over 100 per cell.
• Disc shaped structure with three different
membrane systems:
– 1. Outer membrane: Covers chloroplast surface
– 2. Inner membrane: Contains enzymes needed to
make glucose during photosynthesis. Encloses
stroma (liquid) and thylakoid membranes.
– 3. Thylakoid membranes: Contain chlorophyll,
green pigment that traps solar energy. Organized in
stacks called grana.
Chloroplasts Trap Solar Energy and
Convert it to Chemical Energy
Chloroplasts
• Contain their own DNA, ribosomes, and make
some proteins.
• Can divide to form daughter chloroplasts.
• Type of plastid: Organelle that produces and
stores food in plant and algae cells.
• Other plastids include: Leukoplasts: Store
starch. Chromoplasts: Store other pigments
that give plants and flowers color.
Mitochondria
• Change chemical energy of molecules into the
useable energy of the ATP molecule.
• Oval or sausage shaped.
• Contain their own DNA, ribosomes, and make
some proteins.
• Can divide to form daughter mitochondria.
• Structure:
Inner and outer membranes.
Intermembrane space.
Cristae (inner membrane extensions),
Matrix (inner liquid)
Mitochondria Harvest Chemical Energy
From Food
The Cytoskeleton
• Complex network of thread-like and tube-like structures.
• Functions: Movement, structure, and structural support.
• Three Cytoskeleton Components:
1. Microfilaments: Smallest cytoskeleton fibres. Important
for: Muscle contraction: Actin & myosin fibres in muscle
cells “Amoeboid motion” of white blood cells .
2. Intermediate filaments: Medium sized fibres Anchor
organelles (nucleus) and hold cytoskeleton in place.
Abundant in cells with high mechanical stress.
3. Microtubules: Largest cytoskeleton fibres. Found in
structures that help move chromosomes during cell division
(mitosis and meiosis). Found in animal cells, but not plant
cells. Movement of flagella and cilia.
Components of the Cytoskeleton are
Important for Structure and Movement
The Cytoskeleton
Cilia and Flagella
• Projections used for locomotion or to move
substances along cell surface.
• Enclosed by plasma membrane and contain
cytoplasm.
• Consist of 9 pairs of microtubules surrounding
two single microtubules (9 + 2 arrangement).
• Flagella: Large whip-like projections. Move in
wavelike manner, used for locomotion.
Example: Sperm cell
• Cilia: Short hair-like projections. Example:
Human respiratory system uses cilia to remove
harmful objects from bronchial tubes and
trachea.
Lysosomes, Aging, and Disease
• As we get older, our lysosomes become
leaky, releasing enzymes which cause
tissue damage and inflammation.
Example: Cartilage damage in arthritis.
• Steroids or cortisone-like antiinflammatory agents stabilize lysosomal
membranes, but have other undesirable
effects (affect immune function).
Important Differences Between
Plant and Animal Cells
Plant cells
Cell wall
Chloroplasts
Large central vacuole
Flagella rare
No Lysosomes
No Centrioles
Animal cells
None
No chloroplasts
No central vacuole
Flagella more usual
Lysosomes present
Centrioles present
Organelles and Function
• Manufacture Nucleus Ribosomes Rough ER
Smooth ER Golgi Apparatus
• Breakdown Lysosomes Vacuoles
• Energy Processing Chloroplasts (Plants and
algae) Mitochondria
• Support, Movement, Communication
Cytoskeleton (Cilia, flagella, and centrioles)
Cell walls (Plants, fungi, bacteria, and some
protists) Extracellular matrix (Animals) Cell
junctions
Viruses are not cells!
• They are referred to as particles.
• They are the smallest living organisms on
the planet.
• They are obligate parasites
• Core of nucleic acids surrounded by a
protein coat (capsid)
• Some viruses have a DNA genome and
others have an RNA genome.