Transcript Cell Structure and Function


The Cell Theory
› 1500’s – Europeans used lens to look at cloth
quality
› 1600’s – two useful instruments were made with
lens from the 1500’s
 Microscope
 Telescope
 Leeuwenhoek was the first to study nature under a
microscope
› 1665 – Hooke used the first light microscope to
look at plant tissue
 Looked at cork
 Found the cells are the basic unit of life
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Cell Theory
› 1838 – Schelldon found all plants are made of
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cells
1829 – Schwann found that all animals are made
of cells
1855 Virchow found cells come from cells
1931 – Plowe found cells have cell membrane
that is a physical structure between cells
1970 – Maegulis proposes theory of tiny
organelles in the cell once were free living cells
Cell
theory states
› All living things are composed of
cells
› Cells are the basic structure and
function in living things
› New cells are produced from
existing cells
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Cells come in many shape and sizes
› Typical cell 5 to 50 micrometers in diameter
› The tiniest bacteria are only 0.2 micrometer across and
hard to see with the most powerful light microscope
› Chaos chaos a giant bacteria is 1000 micrometers and
can be seen with naked eye
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Common structures in most cells
› Cell membrane
› Cell wall
› Nucleus
› cytoplasm
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2 categories of cells
› Prokaryotes –
 smaller and simpler cells
 No nuclear membrane (genetic material dispersed throughout
cytoplasm)
 Cell membrane
 prokaryotic DNA is circular (it has no ends).
 Cytoplasm
 No membrane-bound organelles
 All bacteria
 Escherichia coli lives in your intestine
 Carries out every activity associated with life
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Grow
Reproduce
Respond to stimulus
Move sometime during their life cycle
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Eukaryotes
› Contain a nucleus, cell membrane, and
cytoplasm
› Most contain organelles
 Specialized structures that perform important
cellular functions
› Some single cell organism
› Most are Multicellular organisms
› Eukaryotic DNA is linear
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Pro vs. Eu
Eukaryotic Cell Structure
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Organelles – little organs
› Structures that are specialized for certain
processes
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2 major parts of a cell
› Nucleus
› Cytoplasm
Eukaryotic Cell Structure
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Cytoplasm –
› Cytoplasm is basically the substance that fills the cell.
› It is a jelly-like material that is eighty percent water
and usually clear in color.
› It is more like a viscous (thick) gel than a watery
substance, but it liquefies when shaken or stirred.
› Cytoplasm, which can also be referred to as cytosol,
means cell substance.
› The cytoplasm is the site where most cellular activities
occur, such as many metabolic pathways like
glycolysis, and processes such as cell division.
Eukaryotic Cell Structure
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Nucleus - also sometimes referred to as the "control
center", is a membrane-enclosed organelle found
in eukaryotic cells.
› It contains most of the cell's genetic material, organized
as multiple long linear DNA molecules in complex with
a large variety of proteins, such as histones, to form
chromosomes.
› Nuclear envelope - a double membrane that encloses the
entire organelle and separates its contents from the
cellular cytoplasm and is dotted with pores which allow
material to flow in and out
› Chromatin – granular material consisting of DNA bound to
a protein.
Eukaryotic Cell Structure
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Nucleus
› Chromosomes – condensed chromatins
 Happens when cells divide
 Distinct threadlike structures containing
genetic information
› Nucleolus – small, dense region where
ribosomes are formed
Eukaryotic Cell Structure
Eukaryotic Cell Structure
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Ribosomes - the components of cells that make
proteins from amino acids.
› Small particles of proteins and RNA found
throughout the cytoplasm
› Considered a small machine in a large
factory producing proteins
› Cells active in producing proteins are often
packed with ribsomes
Eukaryotic Cell Structure
Eukaryotic Cell Structure
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Endoplasmic Reticulum –
› responsible for the production of the protein and
lipid components of most of the cell's organelles.
› The ER contains a great amount of folds - but the
membrane forms a single sheet enclosing a single
closed sac.
› This internal space is called the ER lumen.
› The ER is additionally responsible for moving proteins
and other carbohydrates to the Golgi apparatus, to
the plasma membrane, to the lysosomes, or
wherever else needed.
Eukaryotic Cell Structure
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Endoplasmic Reticulum –
› There are two types of ER - rough, which is coated
with ribosomes, and smooth, which isn't.
› Rough ER is the site of protein synthesis.
› The smooth ER is where the vesicles carrying newly
synthesized proteins (from the rough ER) are budded
off
› Uses enzymes to in the synthesis of lipid membranes
and detoxification of drugs
 The liver cells play a role in detoxification and contain
large amounts of ER
Eukaryotic Cell Structure
Eukaryotic Cell Structure
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Golgi Apparatus –
› The Golgi complex contains a great number of
vesicles.
 These vesicles are used to send molecules to the cellular
membrane, where they are excreted.
› There are also larger secretory vesicles, which are
used for selective excretion.
› The Golgi is principally responsible for directing
molecular traffic in the cell
› nearly all molecules pass through the Golgi complex
at some point in their existence.
 The sorting is mediated by the vesicles.
 When proteins bind with their appropriate receptor on
the vesicle, they are encoated in the vesicle and
transported away.
Eukaryotic Cell Structure
Eukaryotic Cell Structure
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Lysosome
› The lysosome is a membranous bag which
contains hydrolytic enzymes that are used to
digest macromolecules.
› The lysosome contains over 40 enzymes
Eukaryotic Cell Structure
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Vacuoles –
› used only in plant cells.
› It is responsible for maintaining the shape and
structure of the cell.
› Plant cells don't increase in size by expanding the
cytoplasm, rather they increase the size of their
vacuoles.
› The vacuole is a large vesicle which is also used to
store nutrients, metabolites, and waste products.
› The pressure applied by the vacuole, called turgor, is
necessary to maintain the size of the cell.
Eukaryotic Cell Structure
Eukaryotic Cell Structure
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Chloroplast –
› The chloroplast, basically, is the organelle responsible
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for photosynthesis.
Structurally it is very similar to the mitochondrion.
It contains a permeable outer membrane, a less
permeable inner membrane, a intermembrane
space, and an inner section called the stroma.
However, the chloroplast is larger than the
mitochondria
Unlike other organelles, chloroplast and
mitochondria have their own DNA.
Eukaryotic Cell Structure
Eukaryotic Cell Structure
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Mitochondria –
› Converts chemical energy stored in food
into compounds that are more convenient
for the cell to use
› The powerhouse of the cell
› The mitochondrion consists of four major
sections – the outer membrane, the
intermembrane space, the inner membrane,
and the matrix.
Eukaryotic Cell Structure
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Mitochondria –
› The Outer Membrane -This membrane contains a great
number of large transport proteins, which allows for large
molecules to enter with ease. This membrane includes
proteins that can convert lipid substrates into forms that
can be used by the matrix.
› Inner membrane space - This space contains enzymes
› Inner membrane - This membrane is highly convoluted,
forming many folds called cristae. This serves to greatly
increase the surface area, allowing more work to be done
is a smaller space
› Matrix - The Krebs Cycle takes place here. It also contains
several copies of the mitochondrial DNA genome, special
mitochondrial ribosome's, tRNAs, and various enzymes
required for the expression of the mitochondrial gene
Eukaryotic Cell Structure
Eukaryotic Cell Structure
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Cytoskeleton –
› Eukaryotic cells have a wide variety of distinct
shapes and internal organizations.
› Cells are capable of changing their shape, moving
organelles, and in many cases, move from place to
place. This requires a network a protein filaments
placed in the cytoplasm known as the cytoskeleton.
› The two most important protein filaments are called
the actin filaments and the microtubules.
 The actin is responsible for contraction (like in muscles)
and the microtubules are for structural strength
Eukaryotic Cell Structure
Cell Boundaries
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Cell membrane –
› cell membrane is a flexible lipid bilayer.
› The lipid molecules (mostly phospholipids) that make
up the membrane have a polar, hydrophilic head
and two hydrophobic hydrocarbon tails.
› When the lipids are immersed in an aqueous solution
the lipids spontaneously bury the tails together and
leave the hydrophilic heads exposed.
 Thus this is a handy membrane to use, because it can
automatically fix itself when torn
Cell Boundaries
Cell Boundaries
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Cell Walls –
› It provides the most significant difference between
plant cells and other eukaryotic cells.
› The cell wall is rigid (up to many micrometers in
thickness) and gives plant cells a very defined shape.
› The cell wall is composed of cellulose fiber,
polysaccharides, and proteins.
› In new cells the cell wall is thin and not very rigid. This
allows the young cell to grow.
 This first cell wall of these growing cells is called the
primary cell wall. When the cell is fully grown, it may
retain its primary wall, sometimes thickening it, or it may
deposit new layers of a different material, called the
secondary cell wall.
Cell Boundaries
Cell Boundaries
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Diffusion - the process by which molecules
spread from areas of high concentration, to
areas of low concentration.
› When the molecules are even throughout a space -
it is called EQUILIBRIUM
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Concentration gradient - a difference
between concentrations in a space.
Equilibrium – concentration throughout a
solution is the same
Diffusion depends upon random particle
movements, substances diffuse across
membranes without requiring the cell to use
energy
Cell Boundaries
Cell Boundaries
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Osmosis –
› The diffusion of water (across a membrane)
through a selectively permeable membrane
› Water will move in the direction where there
is a high concentration of solute and hence
a lower concentration of water.
Cell Boundaries
Cell Boundaries
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Isotonic –
› A solution that contains the same concentration of solute
as an another solution (e.g. the cell's cytoplasm).
› When a cell is placed in an isotonic solution, the water
diffuses into and out of the cell at the same rate. The fluid
that surrounds the body cells is isotonic.
Cell Boundaries
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Hypertonic solution –
› contain a high
concentration of solute
relative to another
solution (e.g. the cell's
cytoplasm).
› When a cell is placed in
a hypertonic solution,
the water diffuses out of
the cell, causing the cell
to shrivel
Cell Boundaries
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Hypotonic solution –
› contain a low
concentration of
solute relative to
another solution (e.g.
the cell's cytoplasm).
› When a cell is placed
in a hypotonic
solution, the water
diffuses into the cell,
causing the cell to
swell and possibly
explode.
Cell Boundaries
Cell Boundaries
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Osmotic pressure –
› The pressure that must be applied to a
solution to prevent the inward flow of water
across a semi permeable membrane
Cell Boundaries
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Facilitated Diffusion –
› Glucose, sodium ions and chloride ions are
just a few examples of molecules and ions
that must get across the plasma membrane
but to which the lipid bilayer of the
membrane is virtually impermeable.
› Their transport must therefore be "facilitated"
by proteins that span the membrane and
provide an alternative route or bypass.
› Facilitated diffusion
Cell Boundaries
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Active Transport –
› Active Transport - When cells must move
materials in an opposite direction - against a
concentration gradient. It requires Energy.
› Proteins or Pumps are found in the cell
membrane transport molecules across the
membrane.
Cell Boundaries
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Molecular transport –
› Proteins are used to move small molecules such as
calcium, potassium, and sodium ions across the
membrane
 Endocytosis - cell takes in large particles by engulfing
them
 Phagocytosis - "cell eating" - extensions off cytoplasm
surround a particle and package it within a food vacuole
and then the cell engulfs it. Ex. Amoebas use this process.
 Pinocytosis - the process of taking up liquid from the
surrounding environment. Tiny pockets form along the
membrane, fill with liquid, and pinch off.
 Exocytosis - cell gets rid of particles, opposite of
endocytosis
Cell Boundaries
Cell Boundaries
Cell Boundaries
The Diversity of Cellular Life
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Unicellular organisms –
› Single cell organism
› Do all things that you expect living things to
do
 Grow, respond to surrounding, transform
energy and reproduce
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Multicellular organisms –
› Organisms made of many cells
› Organism can develop different ways to
perform tasks.
The Diversity of Cellular Life
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Specialized cells –
› Red blood cells – transport oxygen by
binding oxygen to a specific protein
› Pancreas produces special enzymes to
make it possible to digest food
› Muscle cells give use the ability to move.
› Guard cells in a plant open and close to the
outside depending on the condition of the
plant.
 Example – gas exchange or transpiration
The Diversity of Cellular Life
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Level of organization
› Cells
 basic structural and functional unit of all
known living organisms.
 It is the smallest unit of life that is classified as a
living thing
› Tissue – similar cells grouped together
› Organs – groups of tissues that work together
› Organ System – a group of organs that work
together for a specific propose