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Cell Structure
AND FUNCTION
Cell Theory
 All organisms are composed of one or more cells.
 Cells are the basic unit of structure and function in
organisms.
 All cells come only from other cells.
The Cell

Cells are small so they can exchange materials
with their surroundings.
Sizes of Living Things
Essential Tasks of Living Things
 Obtain food and energy
 Convert energy from an external source into a form that
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works within the cell
Construct and maintain the molecules that make up cell
structures
Carry out chemical reactions
Eliminate wastes
Reproduce
Keep records of how to build structures
Types of Cells
 Eukaryotic
 Prokaryotic
Eukaryotic Cells
 All cells are surrounded by a plasma membrane
made of phospholipids and proteins.
 have membrane bound intracellular organelles.
 The most prominent organelle is the nucleus that
controls the workings of the cell.
Eukaryotic Cells: Membrane
Eukaryotic: Structural Components
 Plasma membrane  regulates what enters and exits
the cell.
 Inside the plasma membrane, the nucleus is
surrounded by cytoplasm.
 Plant cells have a cell wall in addition to the
plasma membrane.
Eukaryotic: Organelles
 Animal and plant cells have organelles.
 Organelles compartmentalize functions within the
cell.
 Animal vs. Plant Cells
 organelles are similar to each other except that centrioles
and lysosomes are present only in animal cells, and
chloroplasts are present only in plant cells.
Eukaryotic: Animal Cell
Eukaryotic: Plant Cell
Cell Organelles
Nucleus
 Structure
 Chromatin: DNA and proteins
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Nucleolus: Chromatin and ribosomal subunits
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Nuclear envelope: Double membrane with pores
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Nucleoplasm: semifluid medium inside the nucleus.
Nucleus and the Nuclear Envelope
Ribosomes
 Protein synthesis occurs at tiny organelles called
ribosomes.
 Ribosomes are composed of a large subunit and a
small subunit.
 Ribosomes can be found alone in the cytoplasm, in
groups called polyribosomes, or attached to the
endoplasmic reticulum.
Ribosomes
Endomembrane System
 Consists of:
 Nuclear envelope (see nucleus slide)
 Endoplasmic reticulum
 Golgi apparatus
 Vesicles
Endomembrane: Endoplasmic Reticulum
 Endoplasmic reticulum (ER)  a system of
membranous channels and sacules.
 Rough ER is studded with ribosomes and is the
site of protein synthesis and processing.
 Smooth ER lacks ribosomes and is the site of
synthesis of phospholipids and the packaging of
proteins into vesicles, among other functions.
Endomembrane: Endoplasmic Reticulum
Endomembrane: Endoplasmic Reticulum
Endomembrane: Golgi Apparatus
 The Golgi apparatus consists of a stack of curved
saccules.
 The Golgi apparatus receives protein and also
lipid-filled vesicles from the ER, packages,
processes, and distributes them within the cell.
 This organelle may also be involved in secretion.
Endomembrane: Golgi Apparatus
Endomembrane: Vesicles
 Lysosomes
 In animal cells only
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vesicles produced by the Golgi apparatus.
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Lysosomes contain hydrolytic enzymes and are involved in
intracellular digestion.
Endomembrane: Vesicles
Endomembrane: Vesicles
 Vacuoles
 Larger in plant than animal cells
 Large membranous sacs in the cell that store substances
(including water)
 Note: vesicles are smaller forms of vacuoles
Endomembrane: Vesicles
Endomembrane: Vesicles
 Peroxisomes
 Peroxisomes are vesicles than contain enzymes.
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The enzymes in these organelles use up oxygen and
produce hydrogen peroxide.
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Peroxisomes are abundant in the liver where they
produce bile salts and cholesterol and break down fats.
Endomembrane: Vesicles
Energy-Related Organelles
 The two energy-related organelles of eukaryotes are
chloroplasts and mitochondria.
 Both organelles house energy in the form of ATP.
Chloroplasts
 In plant cells only
 A chloroplast is bounded by two membranes
enclosing a fluid-filled stroma that contains
enzymes.
 Membranes inside the stroma are organized into
thylakoids that house chlorophyll.
 Chlorophyll absorbs solar energy and
carbohydrates are made in the stroma.
Chloroplasts
Mitochondria
 Mitochondria are found in plant AND animal cells.
 Mitochondria are bounded by a double membrane
surrounding fluid-filled matrix.
 The inner membranes of mitochondria are cristae.
 The matrix contains enzymes that break down
carbohydrates and the cristae house protein complexes that
produce ATP (usable form of energy in cells).
Mitochondria
The Cytoskeleton
 a network of filaments and tubules that extends from the
nucleus to the plasma membrane.
 The cytoskeleton contains three types of elements
responsible for cell shape, movement within the cell, and
movement of the cell:
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Actin filaments
Microtubules
Intermediate filaments
Cytoskeleton: Actin Filaments
 occur in bundles or mesh-like networks.
 Actin filaments play a structural role in intestinal
microvilli and also interact with motor molecules,
such as myosin.
Cytoskeleton: Microtubules
 small hollow cylinders made of the globular
protein tubulin.
 Microtubules help maintain the shape of the cell
and act as tracks along which organelles can move.
Centrosome
 Assembles and co-ordinates the activity of the
spindle fibres when the cell divides
 Made up of:
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Centrioles
Cilia
flagella
Centrosome: Centrioles
 Centrioles are short cylinders with a 9 + 0 pattern of
microtubule triplets.
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9 sets of microtubule triplets, with no microtubules in the
middle
 Centrioles may be involved in microtubule formation
and disassembly during cell division and in the
organization of cilia and flagella.
Centrosome: Centrioles
Centrosome: Cilia and Flagella
 Cilia (small and numerous) and flagella (large and single)
have a 9 + 2 pattern of microtubules and are involved in cell
movement.
 Cilia and flagella move when the microtubule doublets slide
past one another.
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Cilia moves in wave-like motion (e.g. in trachea)
Flagella produce an undulating, whip-like motion
 Each cilium and flagellum has a basal body at its base.
Centrosome: Cilia and Flagella
Size
 Prokaryotic Cells
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Small (about the size of mitochondria)
Between 1 – 10 micrometres
 Eukaryotic Cells
 Between 10 – 100 micrometres
Kingdoms
 Prokaryotic Kingdoms
 **Bacteria
 Archaea
 Eukaryotic Kingdoms
 Protista
 Fungi
 Animalia
 Plantae
Complexity
 Prokaryotes
 Lack membrane bound organelles
o
Most bacteria have these constant features:
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Outer Boundary: Cell wall
Plasma membrane
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Cytoplasm: Ribosomes (thousands)
Thylakoids (Cyanobacteria)
Innumerable enzymes
Complexity
 Eukaryotic
 Very complex
 Many membrane bound organelles, vesicle and transport
systems
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See yesterdays note
Nucleus
 Prokaryotic Cells
 Nucleoid:
Chromosome (single loop of DNA)
 Bacterial cells may have plasmids
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Self-replicating DNA molecules that contain genes such as
antibiotic resistance
 Often used in genetic engineering
 Eukaryotic Cells
 DNA is contained in the membrane bound nucleus
Reproduction
 Prokaryotes
 binary fission (cells budding off)
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Creates clones of existing cells
Some have pili that help cells attach to surfaces and
exchange plasmids with other prokaryotic cells
 Eukaryotes
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Mitosis (cell division)
Meiosis (formation of sex cells)
Other Important Points
 Prokaryotic Cells
 Bacteria that can carry out photosynthesis have
thylakoids that develop from invaginations of cell
membrane
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Thylakoids work same way as those in chloroplasts do
Many bacteria also have cilia and flagella to help with
locomotion
Prokaryotic Cells
Prokaryotic Cells
Evolution of Eukaryotic Cell
Endosymbiotic hypothesis.
 Eukaryotes arose from a symbiotic relationship between
various prokaryotes.
 Heterotrophic bacteria became mitochondria.
 Cyanobacteria became chloroplasts.
 Host cell was a large eukaryotic cell.
Evolution of the eukaryotic cell