Cell Structure & Function
Source: http://koning.ecsu.ctstateu.edu/cell/cell.html
Definition of Cell
A cell is the smallest unit that is capable of performing life functions.
“Typical” Animal Cell
http://web.jjay.cuny.edu/~acarpi/NSC/images/cell.gif
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Cells
cells
-possess a membrane-bound nucleus
-are more complex than prokaryotic cells
-compartmentalize many cellular functions within organelles and the endomembrane system
-possess a cytoskeleton for support and to maintain cellular structure
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Eukaryotic Cells
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Cells
Nucleus
-stores the genetic material of the cell in the form of multiple, linear chromosomes
-surrounded by a nuclear envelope composed of 2 phospholipid bilayers
-in chromosomes – DNA is organized with proteins to form chromatin
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Cells
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Cells
Ribosomes
-the site of protein synthesis in the cell
-composed of ribosomal RNA and proteins
-found within the cytosol of the cytoplasm and attached to internal membranes
Cell Structure
• All Cells have:
–an outermost plasma membrane
–genetic material in the form of DNA
–cytoplasm with ribosomes
Cell Parts
Organelles
Surrounding the Cell
Cell Membrane
• Outer membrane of cell that controls movement in and out of the cell
• Double layer
http://library.thinkquest.org/12413/structures.html
Cell Wall
• Most commonly found in plant cells & bacteria
• Supports & protects cells
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Inside the Cell
Nucleus
• Directs cell activities
• Separated from cytoplasm by nuclear membrane
• Contains genetic material - DNA
Nuclear Membrane
• Surrounds nucleus
• Made of two layers
• Openings allow material to enter and leave nucleus
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Nucleolus
• Inside nucleus
• Contains RNA to build proteins
http://library.thinkquest.org/12413/structures.html
Cytoplasm
• Gel-like mixture
• Surrounded by cell membrane
• Contains hereditary material
Endoplasmic Reticulum • Moves materials around in
cell
• Smooth type: lacks ribosomes
• Rough type (pictured): ribosomes embedded in surface
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Ribosomes
• Each cell contains thousands
• Make proteins
• Found on ribosomes & floating throughout the cell
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Mitochondria
• Produces energy through chemical reactions – breaking down fats & carbohydrates
• Controls level of water and other materials in cell
• Recycles and decomposes proteins, fats, and carbohydrates
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Golgi Bodies
• Protein 'packaging plant'
• Move materials within the cell
• Move materials out of the cell
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Lysosome • Digestive 'plant' for proteins,
fats, and carbohydrates
• Transports undigested material to cell membrane for removal
• Cell breaks down if lysosome structure
is disrupted.
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Vacuoles
• Membrane-bound sacs for storage, digestion, and waste removal
• Contains water solution
• Help plants maintain shape
http://library.thinkquest.org/12413/structures.html
1. Plasma Membrane
• All membranes are phospholipid bilayers with embedded proteins
• The outer plasma membrane
– isolates cell contents
–controls what gets in and out of the cell
–receives signals
3. Cytoplasm with ribosomes
–Cytoplasm – fluid area inside outer plasma membrane and outside DNA region
–Ribosomes – make proteins
Cell Structure
• All Cells have:
–an outermost plasma membrane
–genetic material in the form of DNA
–cytoplasm with ribosomes
Why Are Cells So Small? (4.2)
• Cells need sufficient surface area to allow adequate transport of nutrients in and wastes out.
• As cell volume increases, so does the need for the transporting of nutrients and wastes.
Why Are Cells So Small?
• However, as cell volume increases the surface area of the cell does not expand as quickly.
– If the cell’s volume gets too large it cannot transport enough wastes out or nutrients in.
• Thus, surface area limits cell volume/size.
Why Are Cells So Small?
• Strategies for increasing surface area, so cell can be larger:
– “Frilly” edged…….
– Long and narrow…..
• Round cells will always be small.
Cells
• Structures in all cells – Nucleus
– Ribosomes
– Endomembrane System • Endoplasmic reticulum – smooth and rough
• Golgi apparatus
• Vesicles
– Mitochondria
– Cytoskeleton
CYTOSKELETON
MITOCHONDRION
CENTRIOLES
LYSOSOME
GOLGI BODY
SMOOTH ER
ROUGH ER
RIBOSOMES
NUCLEUS
PLASMA MEMBRANE
Fig. 4-15b, p.59
VESICLE
CYTOPLASM
Nucleus (4.5)
• Function – isolates the cell’s genetic material, DNA
– DNA directs/controls the activities of the cell
• DNA determines which types of RNA are made
• The RNA leaves the nucleus and directs the synthesis of proteins in the cytoplasm at a ______________
Nucleus
• Structure
–Nuclear envelope
• Two Phospholipid bilayers with protein lined pores
–Each pore is a ring of 8 proteins with an opening in the center of the ring
–Nucleoplasm – fluid of the nucleus
Nuclear pore bilayer facing cytoplasm Nuclear envelope
bilayer facing nucleoplasm
Fig. 4-17, p.61
Nucleus
• DNA is arranged in chromosomes
–Chromosome – fiber of DNA with proteins attached
–Chromatin – all of the cell’s DNA and the associated proteins
Nucleus
• Structure, continued
–Nucleolus
• Area of condensed DNA
• Where ribosomal subunits are made
– Subunits exit the nucleus via nuclear pores
Structures of the Endomembrane System
• Endoplasmic Reticulum (ER)
–Continuous with the outer membrane of the nuclear envelope
–Two forms - smooth and rough
• Transport vesicles
• Golgi apparatus
Endoplasmic Reticulum (ER)
–The ER is continuous with the outer membrane of the nuclear envelope
–There are 2 types of ER:
• Rough ER – has ribosomes attached
• Smooth ER – no ribosomes attached
Endoplasmic Reticulum
• Rough Endoplasmic Reticulum (RER)
• Network of flattened membrane sacs create a “maze”
– RER contains enzymes that recognize and modify proteins
• Ribosomes are attached to the outside of the RER and make it appear rough
Endoplasmic Reticulum
• Function RER
• Proteins are modified as they move through the RER
• Once modified, the proteins are packaged in transport vesicles for transport to the Golgi body
Endomembrane System
• Smooth ER (SER) – Tubular membrane structure
– Continuous with RER
– No ribosomes attached
• Function SER – Lipids are made inside the SER
• fatty acids, phospholipids, sterols..
– Lipids are packaged in transport vesicles and sent to the Golgi
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Endomembrane System
Vacuoles
-membrane-bound structures with various functions depending on the cell type
There are different types of vacuoles:
-central vacuole in plant cells
-contractile vacuole of some protists
-vacuoles for storage
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Endomembrane System
Endomembrane system
-a series of membranes throughout the cytoplasm
-divides cell into compartments where different cellular functions occur
1. endoplasmic reticulum
2. Golgi apparatus
3. lysosomes
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Endomembrane System
Rough endoplasmic reticulum (RER)
-membranes that create a network of channels throughout the cytoplasm
-attachment of ribosomes to the membrane gives a rough appearance
-synthesis of proteins to be secreted, sent to lysosomes or plasma membrane
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Endomembrane System
Smooth endoplasmic reticulum (SER)
-relatively few ribosomes attached
-functions:
-synthesis of membrane lipids
-calcium storage
-detoxification of foreign substances
Endomembrane System
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Endomembrane System
Golgi apparatus
-flattened stacks of interconnected membranes
-packaging and distribution of materials to different parts of the cell
-synthesis of cell wall components
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Endomembrane System
Lysosomes
-membrane bound vesicles containing digestive enzymes to break down macromolecules
-destroy cells or foreign matter that the cell has engulfed by phagocytosis
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Golgi Apparatus
• Golgi Apparatus
– Stack of flattened membrane sacs
• Function Golgi apparatus
– Completes the processing substances received from the ER
– Sorts, tags and packages fully processed proteins and lipids in vesicles
Golgi Apparatus
• Golgi apparatus receives transport vesicles from the ER on one side of the organelle
– Vesicle binds to the first layer of the Golgi and its contents enter the Golgi
Golgi Apparatus
– The proteins and lipids are modified as they pass through layers of the Golgi
– Molecular tags are added to the fully modified substances
• These tags allow the substances to be sorted and packaged appropriately.
• Tags also indicate where the substance is to be shipped.
Golgi Apparatus
Transport Vesicles
• Transport Vesicles
– Vesicle = small membrane bound sac
– Transport modified proteins and lipids from the ER to the Golgi apparatus (and from Golgi to final destination)
Mitochondria (4.15)
• Function – synthesis of ATP
– 3 major pathways involved in ATP production
1. Glycolysis
2. Krebs Cycle
3. Electron transport system (ETS)
Mitochondria
• Structure:
– ~1-5 microns
– Two membranes
• Outer membrane
• Inner membrane - Highly folded
– Folds called cristae
– Intermembrane space (or outer compartment)
– Matrix
• DNA and ribosomes in matrix
Mitochondria
Mitochondria (4.15)
• Function – synthesis of ATP
– 3 major pathways involved in ATP production
1. Glycolysis - cytoplasm
2. Krebs Cycle - matrix
3. Electron transport system (ETS) - intermembrane space
Mitochondria
TEM
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Mitochondria
Mitochondria
-organelles present in all types of eukaryotic cells
-contain oxidative metabolism enzymes for transferring the energy within macromolecules to ATP
-found in all types of eukaryotic cells
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Mitochondria
-surrounded by 2 membranes
-smooth outer membrane
-folded inner membrane with layers called cristae
-matrix is within the inner membrane
-intermembrane space is located between the two membranes
-contain their own DNA
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Mitochondria