Cells & Organelles

A Dr. Production

Two Basic Types of Cells

• Pro karyotes:– prounounced: pro-carry-oats

• Eu karyotes– Proun: you-carry-oats

A. ProkaryotesSmall, simple cells (relative to eukaryotes)Size: about 1 µm (1 micron)No internal membrane-bounded organellesNo nucleusSimple cell divisionSingle linear chromosome

Contain the domains; 1. True (Eu)bacteria &

2. Archaebacteria

1. True Bacteria = Eubacteria

• Majority of bacteria

• Examples include: E. coli, Lactobacillus (yogurt), Lyme disease

Eubacteria•Peptido glycan cell walls (carbos & AA)

•Separated into Gram + and - forms

Gram negative

Gram positive

Bacteria in the Environment

A) An acid hot spring in Yellowstone is rich in iron and sulfur. B) A black smoker chimney in the deep sea emits iron sulfides at very high temperatures (270 to 380 degrees C).

example: Iron utilizing Baceria

A B

2. Archaebacteria

• Live in extreme environments: high salt, high temps

• Different cell wall• Very different

membrane lipids• Unusual nucleic acid

sequence

Archaea types: Based on their physiology, Archae can be organized into three types:

• Methanogens (prokaryotes that produce methane); • Extreme halophiles (prokaryotes that live at very

high concentrations of salt (NaCl); • Extreme (hyper) thermophiles (prokaryotes that

live at very high temperatures).

All archaea have features that distinguish them from Bacteria (i.e., no murein in cell wall, ether-linked membrane lipids, etc.). And, these prokaryotes exhibit unique structural or biochemical attributes which adapt them to their particular habitats.

B. Eukaryotes• Bigger cells: 10-100 µm• True nucleus• Membrane-bounded

structures inside. Called organelles

• Divide by a complex, well-organized mitotic process

Liver Cell 9,400x

Eukaryotes• Larger more complex

cells that make up most familiar life forms: plants, animals, fungi, protists

• Surrounded by a cell membrane made of lipids

The Cell Theory

• Cells first observed by R. Hooke 1665• Named for the Monk prayer cells• Cell Theory states that;

1. All life is composed of cells2. Cells are the basic units of life

3. Cells arise from already existing cells

Cells are typically Small

Typical cell size

Why are Cells Small?• Cells must exchange gases & other

molecules with environment…• Nutrients in, Wastes out• As size increases, the rate of diffusion

exchange slows down….• This is due to the ratio of surface area to

volume

Surface Area to Volume• Cell surface area is important in taking in

nutrients• Surface area increases as the square of cell

diameter• But… entire cell volume needs to be fed• And, cell volume increases as the cube of cell

diameter

Consider 2 Cells...

Surface Area to Volume Cell Radius (R)

5 µm 50 µm Surface Area

(4πr2) 314 µm2

31,400 µm2

Volume (4/ 3πr3)

524 µm3

524,000 µm3

Surf ace Area to Volume Ratio

0.6

0.06

The Eukaryotic Cell: Components

• Outer cell membrane composed of lipids and proteins

• Cytosol: interior region. Composed of water & dissolved chemicals…a gel

• Numerous organelles….

Organelles• Specialized structures

within eukaryotic cells that perform different functions...

• Analogous to small plastic bags within a larger plastic bag.

• Perform functions such as :– protein production

(insulin, lactase…)– Carbohydrates,

lipids…

Organelles of Note:The Nucleus

• Contains the genetic material (DNA), controls protein synthesis.

DNA --> RNA --> Protein• Surrounded by a double

membrane with pores• Contains the chromosomes =

fibers of coiled DNA & protein in the form of chromatin

Chromosomes

All Chromosomes from a single cell

One chromosome Pulled apart

A single chromosomeShowing the amount of DNA within

Mitochondria• Generate cellular energy in the

form of ATP molecules• ATP is generated by the

systematic breakdown of glucose = cell respiration

• Also, surrounded by 2 membrane layers

• Contain their own DNA!• A typical liver cell may have

1,700 mitoch.• All your mitoch. come from

your mother..

PlastidsSynthesize

carbohydrates• Leucoplasts: white

in roots and tubers• Chromoplasts:

rainbow accessory pigments

• Chloroplasts: green in leaves and stems

Chloroplasts• Found in plants and some

protists. Responsible for capturing sunlight and converting it to food = photosynthesis.

• Surrounded by 2 membranes

• And…contain DNA

Ribosomes• Size ~20nm• Made of two subunits

(large and small)• Composed of RNA and

over 30 proteins• Come in two sizes…80S

(40s + 60s) and 70S (30s + 50s)

• S units = Sedimentation speed

Ribosomes• DNA --> RNA --> Protein• The RNA to Protein step

(termed translation) is done on cytoplasmic protein/RNA particles termed ribosomes.

• Contain the protein synthesis machinery

• Ribosomes bind to RNA and produce protein.

Endoplasmic Reticulum = ER

• Cytoplasm is packed w. membrane system which move molecules about the cell and to outside

• Outer surface of ER may be smooth (SER): synthesizes secretes, stores, carbs, lipids and non pps

• Or Rough (RER): synthesizes pp for excretion

• ER functions in lipid and protein synthesis and transport

Golgi Complex• Stacks of

membranes…• Involved in modifying

proteins and lipids into final form…– Adds the sugars to

make glyco-proteins and glyco-lipids

• Also, makes vesicles to release stuff from cell

ER to Golgi network/Endo membrane system

Membrane Flow through Golgi

Lysosomes • important in breaking down

bacteria and old cell components• contains many digestive

enzymes• The ‘garbage disposal’ or

‘recycling unit’ of a cell• Malfunctioning lysosomes result

in some diseases (Tay-Sachs disease)

• Or may self-destruct cell such as in apoptosis

Vacuoles

• Formed by the pinching of the cell membrane

• Very little or no inner structure

• Stores various items

Peroxisomes/Microbodies

• Large vesicles containing oxidative enzymes which transfer H from substrates to O

• Contains catalase that changes H2O2 to H2O

• In plants responsible for photorespiration and converting fat to sugar during germination

Cytoskeleton• Composed of 3 filamentous

proteins:Microtubules

MicrofilamentsIntermediate filaments

• All produce a complex network of structural fibers within cell

The specimen is human lung cell double-stained to expose microtubules and actin microfilaments using a mixture of FITC and rhodamine-phalloidin. Photo taken with an Olympus microscope.

Microtubules

Function in:Function in:- division of cells - division of cells (formation of spindle (formation of spindle fibers)fibers)- some aspects of shape - some aspects of shape - many cell movements - many cell movements (flagella and cilia)(flagella and cilia)- “transport” system - “transport” system within cellwithin cell

Microtubules• Universal in eukaryotes• Involved in cell shape,

mitosis, flagellar movement, organelle movement

• Long, rigid, hollow tubes ~25nm wide

• Composed of and ß tubulin (small globular proteins)

• 9+2 vs 9x3 arrangement

Protist Movement Protist Movement

Microfilaments• Thin filaments (7nm

diam.) made of the globular protein actin.

• Actin filaments form a helical structure

• Involved in cell movement (contraction, crawling, cell extensions)

Intermediate filaments• Fibers ~10nm diam.• Very stable,

heterogeneous group• Examples:Lamins: hold nucleus shapeKeratin: in epithelial cells Vimentin: gives structure to

connective tissueNeurofilaments: in nerve

cells

Image of Lamins which reside in the nucleus just under the nuclear envelope

Cell Motility:Flagella & Cilia

• Both cilia & flagella are constructed the same

• In cross section: 9+2 arrangement of microtubules (MT)

• MTs slide against each other to produce movement

Flagella (flagellum)• Motile structure of many eukaryotic cells; Motile structure of many eukaryotic cells; long, long,

hair-like projectionhair-like projection- e.g., tail of sperm- e.g., tail of sperm

• Core composed of 9 + 2 array of microtubules Core composed of 9 + 2 array of microtubules that arise from a basal body apparatusthat arise from a basal body apparatus– Flagellated Flagellated E. coliE. coli

Cilia (cilium)• Motile or sensory structure in Motile or sensory structure in

eukaryotes composed of 9 + 2 eukaryotes composed of 9 + 2 array of microtubulesarray of microtubules

• Usually numerous short, hair-Usually numerous short, hair-like projections along outside like projections along outside of cellof cell

• Found in many Protista and in Found in many Protista and in lining of lungslining of lungs– StentorStentor feeding feeding– ParameciumParamecium rotating rotating

Possible Origins of Eukaryotic Cells

Endosymbiosis• Theory that eukaryotic

cells arose from an early prokaryote (1) engulfing a second, smaller prokaryote (2)

• The internalized #2 was not digested but became a symbiote.

• Today’s mitochondria & chloroplasts may have arisen this way

Support for this Theory:• Eg. of this type of symbiosis are found today. Sponges harbor photosyn.

algae within their tissues, allowing them to photosynthesize.• The organelles (chloroplasts and mitochondria) resemble bacteria in size

and structure.• These organelles each contain a small amount of DNA but lack a nuclear

membrane.• Each has the capability of self-replication. They reproduce by binary

fission.• They make their own proteins.• During protein synthesis, these organelles use the same control codes and

initial amino acid as prokaryotes.• They contain and make their own ribosomes, which resemble prokaryote’s. • The enzymes that replicate DNA and RNA (polymerases) of the organelles

are similar to those in prokaryotes but different from those of eukaryotes. • The organelles have a double membrane that might be derived from a

prokaryote’s plasma membrane and the membrane of a vesicle.

Resources • Rediscovering Biology Animation Guide• Cell Signaling and Cell Cycle Animations