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Outer protectionCell control centerEnergy centerCell processingStorage and WasteCell division
Cell Parts
Organs are specialized structures in the body that perform specific life processes
Organelles are specialized structures inside the cell that perform specific cellular processes
Most organelles are surrounded by a membrane
Organelle
All cells have to perform the same basic activities to stay alive:
Use energy Store materials Absorb materials Transport substances Eliminate waste Reproduce
Cell Processes
Cell Fractionation
A method of separating cell parts to study their function
Homogenization: disruption of cell membrane without damaging organelle
Centrifuge: instrument that spins at high speeds to separate contents by density
http://richmondschoolbiology.files.wordpress.com/2008/09/cell-fractionation-diagram.jpg?w=652&h=450
Cell Fractionation
http://www.freewebs.com/ltaing/chpt7.3Cellfractionation.gif
Steps to Cell Fractionation
1. Homogenize2. Centrifuge
Pellet: larger, more dense components Supernatant: lighter, suspended in
liquid above the pellet3. Decant supernatant 4. Repeat centrifugation at higher
speeds to separate into smaller components
Topics
Membranes & contents Plasma membrane, cell wall, cytoplasm
Nucleus & contents Nucleus, nuclear envelope, nucleolus, ribosome
Endomembrane System ER, Golgi body, lysosome, vacuole, vesicles
Organelles in metabolism Mitochondria, chloroplast, peroxisome
Cytoskeleton Microfilament, intermediate filament,
microtubule
All cells are surrounded by a flexible membrane
Also known as the plasma membrane
Controls exchange of material between interior of the cell and the external environment
Protection
Cell Membrane
Plasma Membrane Structure
Cell membrane made of phospholipid
Phospholipids also form the membrane around organelles
Phospholipid Bilayer
Bilayer = 2 layersEach layer is called a leaflet and
composed of phospholipids
Phospholipid Bilayer
Phospholipid arranged so that hydrophobic tails do not face water
Water is on the intracellular and extracellular side
Hydrophobic tails face inwards forming a hydrophobic core
Hydrophilic heads face outwards
Fluid Mosaic Model
Model developed by Singer and Nicolson (1972) to understand membrane structure
Fluid implies movement on membrane
Mosaic implies that the membrane consists of many different molecules
Membrane Fluidity
Membrane fluidity is affected by:
Saturation of fatty acid Double bonds bends fatty acid
chains preventing phospholipids from tight packing
Hydrophobic restrictions Lateral movement: across
same leaflet Flip-flop movement is rare
Cholesterol and temperature
Properties of Cholesterol
Large molecular size Can interrupt intermolecular forces of
attractionNonpolar
Stabilizes hydrophobic interactions
Properties of Cholesterol
Explain which property of cholesterol plays a more significant role at: Low temperature High temperature
Why is this advantageous for a cell?
Mosaic: Membrane Composition
Membrane Proteins Integral Peripheral
Carbohydrates
Integral Membrane Proteins
Embedded in the membrane and spans the entire width of the bilayer
Function: transport Assist in movement of molecules into
and out of cellClassification
type of transport: active or passive direction of transport: Uniport, symport,
antiport(more about this in the Membrane Transport
lesson)
Peripheral Membrane Proteins
Bound non-covalently to either surface of the membrane
Function Extracellular side: communication Intracellular side: structural support
Extracellular Peripheral Protein
Receptor and recognition proteinsLocated on outer leaflet and surfaceExample: antigens, glycoproteins
Intracellular Peripheral Protein
Cytoskeletal proteinLocated on inner membrane
surfaceAttached to cytoskeleton of cell Immobilized (anchored) on
membrane
Carbohydrates
Glycoprotein = carbohydrate + protein
Glycolipid = carbohydate + lipid (phospholipid)
Extracellular sideFunction of cell surface
carbohydrates: identifies the cell (like a name) helping
other cells recognize it acts as a signal for communication
Asymmetry
Each leaflet has a different composition
Leaflet facing the intracellular side has different components compared to the extracellular side
Restrictions in the flip-flop motion help to maintain this asymmetry
Phospholipid Bilayer
Phospholipid Bilayer
Cell Wall
Found outside of the cell membrane in plant and prokaroytes
Rigid but porous Gives shape and
support Provide
protection from injury
Cell Wall Structure
Basic composition like steel-reinforced concrete: microfibrils made of cellulose embedded in a matrix of other polysaccharides and proteins
Cell Wall Structure
Primary cell wall: in young plants, thin and flexible
Middle lamella: thin layer of pectin (sticky)
Secondary cell wall: in mature plants, between primary cell wall and cell membrane
Plasmodesmata: perforations in the cell wall that connect adjacent cells
Also known as the cytosol
Mostly made of water Can range from a liquid
to a jelly-like substance Contains dissolved
substances Organelles are
suspended in the cytoplasm (but are anchored by cytoskeleton and not freely floating)
Cytoplasm
Nucleus
Control centre of the cell
Contains genetic information (e.g. chromosomes)
Contains nucleolus
Surrounded by a nuclear membrane
Nuclear membrane is double layered and has pores
Nucleolus
Darker area in the nucleus
Synthesis of rRNA (ribosomal RNA)
Assembly of rRNA with protein imported from the cytoplasm to form the large and small ribosomal subunits
Ribosome Structure
RNA protein complex
2/3 RNA (double stranded coils in turquoise, grey, orange, indigo)
1/3 protein (small coiled alpha helices in violet and navy blue)
http://rna.ucsc.edu/rnacenter/images/70s_atrna.jpg
Ribosome Structure
2 subunits: large
(turquoise colour)
small (lime green colour)
http://www.ks.uiuc.edu/Gallery/Science/translation_proteins/tn/ribosome_ao_small_st.jpg.html
Ribosomes
Made in nucleolus
Can be bound to the rough endoplasmic reticulum or float freely in cytoplasm
Function to catalyze the reactions of protein synthesis
Endomembrane System
direct physical contact
transfer of membrane segments as vesicles http://www.science-art.com/gallery/52/52_10202008105023.jpg
Organelles of the endomembrane system are related through:
Endomembrane System Nuclear envelope Rough and Smooth ER Golgi Body Lysosome Vacuole Vesicles
http://bioserv.fiu.edu/~walterm/fallspring/cell_components/cell_talk_files/image010.jpg
Cisternae: network of flattened, interconnected membrane sacs (tubes and pockets)
Continuous with the nuclear envelope
Endoplasmic Reticulum Structure
Endoplasmic Reticulum Types Two types of ER are distinct but
connected: rough and smooth
Rough Endoplasmic Reticulum Contains ribosomes bound to its
membrane surface Produces integral and secretory proteins:
Integral proteins are embedded in the ER membrane and will end up on the plasma membrane
Secretory proteins are housed in the cisternal space of the ER and will be secreted by exocytosis
Both protein types will be delivered to the cell surface via transport vesicles
Note: Free ribosomes produce cytosolic proteins
Smooth Endoplasmic Reticulum No ribosomes on its membrane
surface Site for lipid synthesis
Golgi Body Structure
Also consists of cisternae: flattened, stacked, interconnected membrane sacs (similar to ER)
Located near ER Also known as the
Golgi apparatus
Golgi Body Function
Modifies proteins and lipids
Process materials to be removed from the cell
Directs secretion: Make and secrete
mucus Packages products
into vesicles for transport
Sorts and targets vesicle to various parts of the cell
Golgi Body
Golgi is polar: cis and trans poles
Cis face “receiving” side Located near the
ER Transport vesicles
bud from ER and add its membrane and content of the lumen to Golgihttp://4.bp.blogspot.com/_rBYpndaJ_ak/S-sxGmLUOuI/AAAAAAAAAGM/oKWwbrO41-U/s1600/Golgi+apparatus.gif
Golgi Body
Trans face “shipping” side Vesicles bud from
Golgi to various locations
Targets of vesicles: Other organelles Cytoplasm Plasma
membrane surface
Export - outside cell
http://4.bp.blogspot.com/_rBYpndaJ_ak/S-sxGmLUOuI/AAAAAAAAAGM/oKWwbrO41-U/s1600/Golgi+apparatus.gif
Lysosome
Membrane bound sac of hydrolytic enzymes
Enzyme and lysosomal membrane made by RER and transferred to Golgi http://www.daviddarling.info/images/lysosome.gif
Lysosome
Enzymes work best at pH 5
Maintains acidic pH by pumping H+ into the lumen
Why would a cell want lysosomal enzymes to function at a pH that is different from the cytosol (neutral pH)?
http://www.daviddarling.info/images/lysosome.gif
Lysosome Function
Phagocytosis lysosome fuse with
food vacuole to digest food (acts similarly to stomach in animals)
Mostly in small organisms (e.g. amoeba)
Seen in some human cells: macrophages http://kvhs.nbed.nb.ca/gallant/biology/lysosome.jpg
Lysosome Function
Autophagy: lysosome recycles cell’s own organic material
Important in development of multicellular organisms Tadpole to frog: destroy
cells of tail Human embryos:
destroy webbing between fingers
http://kvhs.nbed.nb.ca/gallant/biology/lysosome.jpg
Fluid-filled membrane bound sac surrounded
Similar to vesicles but tend to be larger
Derived from the ER and Golgi
In animal cells: many small vacuoles
In plant cells: one large central vacuole
Vacuole Structure
Vacuole Function
General: Storage of food,
water, waste Removing
unwanted substances from the cell
Types of Vacuoles
Food vacuole: formed by phagocytosis, fuses with a lysosome to digest food and invaders
Contractile vacuole: in freshwater protists, pump excess water out of the cell
Central vacuole: in plants, maintaining internal fluid pressure (turgor) which helps gives plants structure and strength
Endomembrane System
Can you describe what is happening at each phase?
http://www.yellowtang.org/images/how_endomembrane_sy_c_la_784.jpg
Organelles in Metabolic Function
MitochondriaChloroplastPeroxisome
Mitochondria Structure
Surrounded by a double membrane
Inner membrane is folded to increase the surface area
Reactions occur on the inner membrane surface
Produces energy through a process called cellular respiration
Reaction involves converting energy from food (e.g. sugars) to cellular energy
Process that occurs inside the mitochondria is aerobic (requires oxygen)
glucose + O2 CO2 + H2O + energy
Mitochondria Function
Cells that are very active (e.g. muscle cells) contain many mitochondria
Cells that are fairly inactive (e.g. fat cells) only have a few mitochondria
Mitochondria
Chloroplast Structure
Surrounded by a double membrane
Contain chlorophyll, a pigment that gives plants their green colour
Chloroplast Structure
Thyakoid: flattened discs (some are interconnected) containing chlorophyll; where light reactions of photosynthesis take place
Granum (grana): Stack(s) of thylakoid
Stroma: Space inside chloroplast
X
Site for starch (a type of sugar) storage
Site for photosynthesis
Reaction involves trapping light energy to create food in the form of sugars
Starting substances are carbon dioxide and water
CO2 + H2O + energy O2 + glucose
Chloroplast Function
Perioxisome Function
Contain enzymes that oxidize organic molecules by transferring hydrogen from substrate to oxygen
Process is useful for: breaking down fatty acids detoxifying alcohol and other harmful
compounds Produces hydrogen peroxide (H2O2) as a
byproduct Hydrogen peroxide is toxic to the cell Contains another enzyme (catalase) that
decomposes hydrogen peroxide to water
Peroxisome Structure
Bound by a single membrane
Spherical with a distinct crystalline core that is a dense collection of enzymes
Often located near mitochondria and chloroplast
http://www.daviddarling.info/images/peroxisome.jpg
Cytoskeleton
A network of fibers extending throughout the cytoplasm
Dynamic: can be quickly dismantled and reassembled in a new location
Cytoskeleton ComponentMicrofilament:
actin Intermediate
filamentMicrotubules:
tubulin
http://www.sciencephoto.com/image/395086/530wm/C0097404-Cytoskeleton_components,_artwork-SPL.jpg
Cytoskeleton Component
http://www.sciencephoto.com/image/395087/530wm/C0097406-Cytoskeleton_components,_diagram-SPL.jpg
Type Microfilament
Intermediate Filament
Microtubule
Structure
DiameterIntracellular FunctionOther Function
Cytoskeleton Component
http://www.sciencephoto.com/image/395087/530wm/C0097406-Cytoskeleton_components,_diagram-SPL.jpg
Type Microfilament
Intermediate Filament
Microtubule
Structure 2 intertwined strands of actin
Fibrous protein supercoiled
Hollow tube of 13 tubulin columns
Diameter 7 nm 8-12 nm 25 nmIntracellular Function
Changes in cell shape (e.g. furrow)
Anchorage of organelles
Organelle & chromosome movement
Other Function
Muscle contraction
Cell motility (e.g. cilia)
Cytoskeleton Component
http://www.sciencephoto.com/image/395087/530wm/C0097406-Cytoskeleton_components,_diagram-SPL.jpg
Cytoskeleton
http://www.sciencephoto.com/media/316728/enlarge
Fluorescent light micrograph of fibroblast cells
Nuclei (green)
Cytoskeleton: actin
filaments (purple)
microtubules (yellow)
Cytoskeleton Cellular Function Summary
Microfilament: mechanical support to maintain cell shape
Intermediate filament: anchorage for organelles and cytosolic enzymes
Microtubule: path for organelle, vesicles & chromosomes to travel; originate from centrosome
A region near the nucleus where microtubules grow out from
Involved in organizing spindle fibers during cell division
In animal cells, a pair of centrioles exist within this region
Centrosome
Centrioles
Exists as pairs in animal cells onlyComposed of 9 sets of triplet
microtubules arranged in a ringHelp organize spindle fibers during cell
division
HW Question
1. Give 2 reasons why it is better for an animal cell to have organelles rather than to perform all its cellular functions in the cytoplasm. Provide a specific example for your reasons. [3 marks]
2. If you were given an illustration of a cross-section of a cell membrane, describe two things that would help you identify the side that faces the outside environment. [2 marks]
3. Describe the flow of molecules through the endomembrane system. [5 marks]
Summary of Differences
Function Animal Plant
Outer protection
Energy centre
Storage
Centrioles
Summary by Cellular Processes
Function Organelle & cell partsOuter protectionCell control centre
Energy centre
Cell processing
Storage and waste
Cell division