Download Cell organelles

Cell – the basic unit of life
Cells
• Smallest living unit
• Most are microscopic
Discovery of Cells
• Robert Hooke (mid-1600s)
– Observed bark of oak tree
– Saw “row of empty boxes”
– Coined the term cell
Cell theory
• (1839)Theodor Schwann & Matthias Schleiden
“ all living things are made of cells”
• (50 yrs. later) Rudolf Virchow
“all cells come from cells”
Principles of Cell Theory
• All living things are made of cells
• Smallest living unit of structure and
function of all organisms is the cell
• All cells arise from preexisting cells
Cell Size
The origin and evolution of cells
• On the basis of presence of nucleus cells are divided into two
groups:
– Prokaryotic cells: lack a nuclear envelope
– Eukaryotic cells: have a nucleus in which the genetic material is
separated from the cytoplasm.
• Prokaryotic cells are generally smaller and simpler than
eukaryotic cells; their genomes are less complex and they do
not contain cytoplasmic organelles.
Cell Types
• Prokaryotic
• Eukaryotic
Prokaryotic Cells
• First cell type on earth
• Cell type of Bacteria and Archaea
Prokaryotic Cells
• No membrane bound nucleus
• Nucleoid = region of DNA concentration
• Organelles not bound by membranes
Prokaryotic Cells
• Features shared by all prokaryotic cells:
– All have a plasma membrane.
– All have a region called the nucleoid where
the DNA is concentrated.
– The cytoplasm (the plasma-membrane
enclosed region) consists of the nucleoid,
ribosomes, and a liquid portion called the
cytosol.
Prokaryotic Cells
• Specialized features of some prokaryotic
cells:
– A cell wall just outside the plasma membrane.
– Some bacteria have an outermost slimy layer
made of polysaccharides and referred to as a
capsule.
• Some bacteria have flagella, locomotory
structures.
• Some bacteria have cillia, threadlike
structures that help bacteria adhere to one
another during mating or to other cells for
food and protection.
Figure 4.5 A Prokaryotic Cell
Structure of Prokaryotic cell
• Using bacteria as our sample prokaryote, the
following structures can be found in bacterial
cells:
• Capsule - Found in some bacterial cells, this
additional outer covering protects the cell
when it is engulfed by other organisms, assists
in retaining moisture, and helps the cell
adhere to surfaces and nutrients
• Cillia - Hair-like structures on the surface of
the cell that attach to other bacterial cells.
Flagella - Long, whip-like protrusion that aids
in cellular locomotion.
• Ribosomes - Cell structures responsible for
protein production.
Plasmids - Gene carrying, circular DNA
structures that are not involved in
reproduction.
Nucleiod Region - Area of the cytoplasm that
contains the single bacterial DNA molecule.
Cell Wall - Outer covering of most cells that
protects the bacterial cell and gives it shape.
Cytoplasm - A gel-like substance composed
mainly of water that also contains enzymes,
salts, cell components, and various organic
molecules.
Cell Membrane or Plasma Membrane Surrounds the cell's cytoplasm and regulates
the flow of substances in and out of the cell.
Eukaryotic Cells
• Nucleus bound by membrane
• Include fungi,, plant, and animal cells
• Possess many organelles
Protozoan
Eukaryotic Cells
• Eukaryotes, animals, plants, fungi have
a membrane-enclosed nucleus in each
of their cells.
• Eukaryotic cells:
– tend to be larger than prokaryotic cells.
– have a variety of membrane-enclosed
compartments called organelles.
– have a protein scaffolding called the
cytoskeleton.
Eukaryotic Cells
• Compartmentalization is the key to
eukaryotic cell function.
• Each organelle has a specific role
defined by chemical processes.
• Membranes surrounding these
organelles keep away inappropriate
molecules and also act as traffic
regulators for raw materials into and
out of the organelle.
Representative Animal Cell
Structure
cell membrane
nucleus
nucleolus
ribosomes
ER
Golgi
centrioles
cell wall
mitochondria
cholorplasts
One big vacuole
cytoskeleton
Animal cells
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Plant cells
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Cell Structures and Their
Functions
Things in common
Cell membrane
Cytoplasm
Genetic Material
Energy Currency
Enzymes
Plasma Membrane
• Every cell is surrounded by a plasma membrane, a
continuous membrane composed of a lipid bilayer with
proteins floating within it and protruding from it.
Plasma Membrane
• The current model of how membranes are
constructed is known as Fluid-Mosaic Model.
• Proposes that various molecules of
membrane are able to flow and move about.
Phospholipids
• Polar
– Hydrophylic head
– Hydrophobic tail
• Interacts with water
Proteins
• Can be found on the surface of the membrane
or within the membrane among
phospholipids.
• Roles of the plasma membrane:
– Acts as a selectively permeable barrier.
– Is an interface for cells where information is
received from adjacent cells and extracellular
signals.
– Allows cells to maintain a constant internal
environment.
– Has molecules that are responsible for binding
and adhering to adjacent cells.
CELL WALL
• The cell wall is the tough, fairly rigid layer that
surrounds some types of cells.
• It is located outside the cell membrane.
• In bacteria, peptidoglycan forms the cell wall.
• Fungi possess cell walls made of chitin.
• In plants: cellulose
Functions
• provides these cells with structural support
and protection.
• A major function of the cell wall is to act as a
pressure vessel, preventing overexpansion when water enters the cell.
Membranous Organelles
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Endoplasmic Reticulum
Golgi Apparatus
Lysosomes
Chloroplast
Mitochondrion
Peroxisomes
Nucleus
Endoplasmic Reticulum
• Is a set of folded membranes and tubes
throughout the system.
• The general structure :membranous network
of cisternae.
• Two types: rough endoplasmic reticulum
smooth endoplasmic reticulum
Functions
• Provides a large surface area on which chemical
reactions can take place.
• It synthesizes lipids, phospholipids and steroid.
• It also carries out the metabolism of
carbohydrates, drug detoxification.
• attachment of receptors on cell membrane
proteins.
• RER involved in protein synthesis
Golgi Bodies
• The Golgi is composed of stacks of membrane-bound
structures known as cisternae.
• Each cisternae comprises a flat, membrane enclosed
disc that includes special Golgi enzymes.
• The cisternae stack has two main functional regions:
the cis-Golgi network and trans-Golgi network.
• Vesicles from the endoplasmic reticulum fuse with the
network and subsequently progress through the stack
to the trans Golgi network, where they are packaged
and sent to their destination
Functions
• Site of synthesis and packaging of molecules
produced in cells.
• Involved in transportation of molecules s/a
carbohydrates, proteins, insulin outside the
cell.
Lysosomes
• Lysosomes are cellular organelles that contain
hydrolase enzymes that break down waste
materials and cellular debris.
Used in four major ways
• Cell damaged- membranes of Lysosomes
break-enzymes release- components of cells
broken- available for surrounding cells.
• Also play part in normal development of an
organism.
• Lysosomes combine with food vacuoles. Eg:
Paramecium
• Used in destruction of engulfed harmful
microbes
Peroxisomes
• Peroxisomes are small membrane bound
vesicles.
• In human cells, peroxisomes produce
hydrogen peroxides that is used to destroy
invading microbes.
• They contain enzymes responsible for
breakdown of fatty acids and cholesterol
synthesis.
How did organelles evolve?
• many scientists theorize that
eukaryotes evolved from
prokaryote ancestors.
• in 1981, Lynn Margulis
popularized the
“endosymbiont theory.”
Endosymbiont theory:
• a prokaryote ancestor
“eats” a smaller prokaryote
• the smaller prokaryote
evolves a way to avoid
being digested, and lives
inside its new “host” cell
kind of like a pet.
• the small prokaryotes that can do
photosynthesis evolve into chloroplasts,
and “pay” their host with glucose.
• The smaller prokaryotes that can do
aerobic respiration evolve into
mitochondria, and convert the glucose into
energy the cell can use.
• Both the host and the symbiont benefit
from the relationship
Mitochondria
• Have their own DNA- semiautonomous
Structure :
1.the outer mitochondrial membrane
2.the intermembrane space
3.the inner mitochondrial membrane
4.the cristae space
5.the matrix
Located on their surface are enzymes
involved involved in respiration
Figure 4.14 A Mitochondrion Converts Energy from Fuel Molecules into ATP (Part 2)
Mitochondria
• Break down fuel molecules (cellular respiration)
– Glucose
– Fatty acids
• Release energy
– ATP
Mitochondria found in both plants and animals are called the power
houses of the cell. They convert the energy in the bonds of glucose and
oxygen to readily available energy in the form of ATP. This process is
called aerobic respiration.
Chloroplasts
Chloroplasts
-organelles present in cells of plants and some
other eukaryotes
-contain chlorophyll for photosynthesis
-surrounded by 2 membranes
-thylakoids are membranous sacs within the
inner membrane
-grana are stacks of thylakoids
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Mitochondria & Chloroplasts
Endosymbiosis
-proposal that eukaryotic organelles evolved
through a symbiotic relationship
-one cell engulfed a second cell and a
symbiotic relationship developed
-mitochondria and chloroplasts are thought to
have evolved this way
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• Mitochondria developed from proteobacteria
• and chloroplasts from cyanobacteria.
Mitochondria & Chloroplasts
Much evidence supports this endosymbiosis
theory.
Mitochondria and chloroplasts:
-have 2 membranes
-possess DNA and ribosomes
-are about the size of a prokaryotic cell
-divide by a process similar to bacteria
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Nucleus
• Known as the “ control centre of the Cell”
– a membrane-bound sac evolved to store the cell’s
chromosomes(DNA)
– stores the genetic material of the cell in the form of
multiple, linear chromosomes
– To control the activity of cell by regulating gene
expression
– surrounded by a nuclear envelope composed of 2
phospholipid bilayers
– in chromosomes – DNA is organized with proteins to
form chromatin
• Nuclear membrane:
• separates the nucleoplasm, liquid material in
the nucleus, from the cytoplasm
• Nuclear pores:
• Exchange of materials
• allows thousands of large molecules such as
RNA to pass into and out of the nucleus each
minute.
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Nucleolus:
Inside nucleus
Location of ribosome factory
Made of RNA
NON MEMBRANEOUS
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Ribosomes
Cytoskeleton
Centrioles
Cillia and Flagella
Ribosomes
• A ribosome is made from complexes of RNAs
and proteins -ribonucleoprotein.
• Each ribosome is divided into two subunits:
the smaller subunit and the larger subunit
Cytoskeleton
Cytoskeleton
-network of protein fibers found in all
eukaryotic cells
-supports the shape of the cell
-keeps organelles in fixed locations
-helps move materials within the cell
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Cytoskeleton
Cytoskeleton fibers include
- microfilaments – responsible for cellular
contractions, crawling, “pinching”
-microtubules – provide organization to the
cell and move materials within the cell
-intermediate filaments – provide structural
stability
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Cytoskeleton
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Cilia and flagella
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both cilia and flagella are constructed from microtubules
• both provide either locomotion for the cell or move fluid pass the cell