Organelles

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