the ultrastructure of cells (1.2) - sammons...

The Ultrastructure of Cells (1.2)IB Diploma Biology

Explain why cells with different functions have different structures.• Cells have different organelles depending on

the primary function of the cell type.

– This allows cells to specialize for a specific task which can lead to increased complexity of the entire organism.

Identify Ultrastructures Visible in a micrograph of a eukaryotic cell

Nucleus

Look for nuclear membrane and the nucleolus

http://images.wellcome.ac.uk/

Rough Endoplasmic Reticulum

Smooth Endoplasmic Reticulum

“Spot” the

difference?

Endoplasmic

Reticulum

The ‘spots’ are the

difference!

The Rough

Endoplasmic Reticulum

is peppered with

ribosomes that give it

the rough appearance

Proteins synthesized

here are secreted

Smooth ER is site of lipid

production

Cell Membrane Vs Cell Wall

http://commons.wikimedia.org/wiki/File:C_Golgi.jpg

http://commons.wikimedia.org/wiki/File:Golgi_in_the_cytoplasm_of_a_macrophage_in_the_alveolus_(lung)_-_TEM.jpg

I shall name it………The internal reticular

apparatus!!Pretty catchy… no?*

*Everybody

thought that was

a terrible name,

so they called it

the Golgi

apparatus

instead

Camillo

Golgi Look for stacks of membrane, typically

further from the nucleus

The Golgi Apparatus is a

flattened stack of membranes

responsible for the packaging

and delivery of proteins

Lysosomes are simple, membrane-bound organelles full of

enzymes that digest engulfed bacteria and viruses and

large molecules for recycling.

Small clear-ish sac, hard to

distinguish from vesicles unless

contents are visible.

Mitochondria in mammalian lung cells

The Mitochondrion (pl. Mitochondria)

• The ‘power house’ of the cell

• Has a smooth outer membrane and

a folded inner membrane

• Where aerobic respiration occurs

Free Ribosomes:

• 80s sized in

eukaryotes (v. 70s

size in prokaryotes)

• Proteins

synthesized for

use within the cell

(i.e. enzymes used

in the cytoplasm)

Vacuoles & Vesicles:• Animal cells sometimes have small vacuoles for digestion

• Unicellular organisms have contractile vacuoles for expelling water

• Plant cells have large vacuoles that hold water and food

• Vesicles are small clear lipid sacs used for transport

Chloroplasts

• Site of Photosynthesis in Plant Cells

• Stacks of Thylakoids

Centrioles & Microtubules:

• Centrioles are bundles of

microtubules found in Animal Cells

• Microtubules separate

chromosomes in cell division and

make-up cilia and flagella

S1.2.3 Interpret electron micrographs to identify organelles and deduce the function of

specialized cells.

S1.2.3 Interpret electron micrographs to identify organelles and deduce the function of

specialized cells.

Identify the labeled structures in this liver cell TEM image.

Source: http://www.udel.edu/biology/Wags/histopage/empage/empage.htm

What can you

see?

Given a micrograph of a cell, deduce the function of the cell based on the

structures present.

Cells will have specialized shapes given their function. For example:

• Small intestine villus cell: microvilli increase surface area absorption

• Many mitochondria for

fueling active transport.

• Exocrine gland cells of the

Pancreas secrete digestive

enzymes into small intestine

• Enzymes are proteins, so

these cells must produce

proteins in large quantities

• Organelles involved:• Rough ER

• Vesicles

• Golgi Apparatus

• Plasma membrane

Hormone secreting cell: many vesicles holding

the hormones until secretion.

• Palisade mesophyll cells

carry out most of the

photosynthesis in plant cells

• Organelles involved:• Chloroplasts

• Mitochondria

• Large Vacuole

Photosynthetic plant cell: chloroplasts for

performing photosynthesis

DRAWINGS

● Look at the following three electron micrographs carefully and examine the significant features that will be included in the drawing.

● DRAW ONLY WHAT YOU SEE!! Do not include what you think you should see. ● All drawings must be done in pencil ONLY. ● Drawings must be large and clear so that features can be easily distinguished. Use

at least ½ page for each drawing.● No more than two drawings should be on a single page of unlined white paper. ● Always use distinct, single lines when drawing. ● All drawings must have the following indicated:

o Title (give a full, clear and concise title that explains what is being illustrated) o Magnification (indicate the magnification at which the specimen was drawn) o Labels (each label line must be straight and should not overlap with other

label lines; all labels must be to one side and aligned in a vertical column)o Scale (always include a scale bar indicating the length or width of the

specimen drawn)

Drawing sample 1: “Typical Homo sapiens

Pancreas Beta Cell”

1. Observe the cells in the

micrograph image.

2. Draw a single cell on

unlined white paper.

3. Title the drawing.

4. Label structures (note:

darkest circles are secretory vesicles that

will secrete insulin out of the cell and into

the bloodstream).

5. Add a scale bar to

indicate that the cell is

10 um long. (Source)

6. Calculate the drawing

magnification.

Drawing sample 2: “Typical Zea mays Leaf

Cell”

1. Observe the cell in the

micrograph image.

2. Draw a single cell on

unlined white paper.

3. Title the drawing.

4. Label structures

5. Add a scale bar to

indicate the length of

the cell.

6. Calculate the drawing

magnification.

Drawing sample 3: Typical Plant Cell

1. Observe the cells in the

micrograph image.

2. Draw a single cell on

unlined white paper.

3. Title the drawing.

4. Label structures

5. Calculate size if

magnification is 1800x.

Endomembrane System

WHAT IS A SYSTEM?

Inside membraneMultiple

parts working together

with shared function

“A system of membranes inside

the cell membrane”

Endomembrane System

Membranes within the eukaryotic cell that work together to modify, process and ship molecules around and out of the cell.

List adjectives to describe a membrane.

Endomembrane System

Membranes within the eukaryotic cell that work together to modify, process and ship molecules around and out of the cell.

FLUID

MOSAIC

Like a bubble

Phospholipid bilayer

Semipermeable

Endomembrane System

• All made of phospholipid bilayer

• Includes:– Nuclear envelope

– Rough ER

– Smooth ER

– Transport vesicles

– Golgi apparatus

– Secretory vesicles

– Lysosomes

– Vacuole

proteins

transportvesicle

Golgiapparatus

vesicle

smooth ER

rough ER

nuclear porenucleus

ribosome

cellmembrane protein secreted

cytoplasm

The Endomembrane System

production of mRNA

from DNA in nucleus

mRNA out of nucleus

through nuclear pore

DNA

NucleusmRNA

nuclearmembrane

mRNA

nuclear pore

3. Packaging (protein into a

vesicle)

2. Translation (mRNA – protein)

1. Transcription (DNA – RNA)

• Using RNA code, a protein is

synthesized on a ribosome

and transported in channels of

the ER.

• Protein is packaged into

transport vesicles …

Endoplasmic Reticulum

• Function

– processes proteins

– manufactures membrane

• Structure

– membrane connected to nuclear envelope & extends throughout cell

Types of ER

rough smooth

4. Transport (protein in vesicle moves to

Golgi)

Protein is packaged into

transport vesicles and … travels

to the Golgi along the

cytoskeleton “track”

5. Modify (Golgi changes or adds to the

protein)

Vesicle fuses with the Golgi and

protein is modified as it passes

through.

Golgi Apparatus

transport vesicles

secretoryvesicles

• Function

– finishes, sorts, tags & ships products

• like “UPS shipping department”

– ships products in vesicles

• membrane sacs

• “UPS trucks”

Details of cis-trans

cisterna are not

required

6. Secrete (vesicle moves protein towards cell

membrane)

Completed protein is packaged

into secretory vesicles for

release from the cell or stored in

vesicle or lysosome if used

inside the cell.

Vesicle transport

7. Exocytosis (vesicle fuses with the cell

membrane, releases protein)

Vesicle fuses with the cell

membrane and protein is

released

Concept Check:

What has happened to the size of the membrane when a vesicle releases its protein contents to the outside of the cell?

Draw a picture to illustrate.

http://www.stolaf.edu/people/giannini/flashanimat/cellstructures/endomembrane%20protein%20synthesis.swf

Where did it come from?

The hypothesis is that eukaryotes evolved from prokaryotes.

In the early prokaryotic cells, there was an infolding of the plasma membrane into the cytoplasm.

The infolded membrane began to specialize for particular tasks.

This would explain why the endomembrane system is a phospholipid bilayer, just like the cell membrane.

Origin of Eukaryotic Cells

• Earth is 4.6 byo

• Life originated 3.5–4.0 bya

• Prokaryotes dominated earth for about 1by

Cyanobacteria•A type of prokaryote with much infolding of the cell membrane

•Capable of performing photosynthesis, which releases oxygen into the atmosphere

Cyanobacterium heterocyst

Oxygen atmosphere• Oxygen begins to accumulate 2.7 bya

• evidence in banded iron in rocks (rusting)

• makes aerobic respiration possible

• nearly all are aerobic,

–they depend on free oxygen to carry out their metabolic processes

• Accordingly, they could not have evolved before at least some free oxygen was present in the atmosphere

Eukaryotes

Two processes are thought to have led to the origin of eukaryotes….

1. Infoldings of the prokaryotic cell membrane

2. Endosymbiosis

Development of internal membranes• create internal micro-environments

(“compartments”)

• advantage = increase efficiency

infolding of theplasma membrane

DNA

cell wall

plasmamembrane

Prokaryoticcell

Prokaryotic ancestor of eukaryotic cells

Eukaryoticcell

endoplasmicreticulum (ER)

nuclear envelope*note double membrane

nucleus

plasma membrane

~2 bya

Check: Given what you know about infolding and the cell membrane as

a phospholipid bilayer:

• Why is the nuclear membrane a DOUBLE membrane (two layers of bilayer)

REMEMBER: Two processes are thought to have led to the origin of

eukaryotes….

1. Infoldings of the prokaryotic cell membrane

2. Endosymbiosis

Endosymbiosis

Ancestral eukaryotic cell

Eukaryotic cellwith mitochondrion

internal membrane

systemaerobic bacterium mitochondrion

Endosymbiosis

• FIRST early eukaryotic cells engulfed aerobic bacteriabut did not digest them

• Led to the origin of mitochondria

• Mutually beneficial relationship

mitochondrion

chloroplast

Eukaryotic cell with

chloroplast & mitochondrion

Endosymbiosis

Endosymbiosis

• THEN early eukaryotic cells engulfed

photosynthetic bacteria

but did not digest them• Led to origin of chloroplasts

• mutually beneficial relationship

Eukaryoticcell with mitochondrion

• In this relationship one cell lived within the other, which is a special type of symbiosis called endosymbiosis

• in some cases of a symbiotic relationship, one symbiont cannot live independently of the other

• This may have been the case early symbiotic prokaryotes that became increasingly interdependent until the unit could exist only as a whole

Endosymbiosis

A model of the origin of eukaryotes

Theory of Endosymbiosis

Lynn MargulisHow is the word “theory” in science

different than the use of the word theory in

every day language?

Both mitochondria & chloroplasts

– Resemble bacterial structure

–Are found in membranous envelopes (like a cell membrane)

–are the same approximate size as prokaryotes

–have 70s ribosomes

Structural Evidence

Both mitochondria & chloroplasts

–have circular naked DNA

–DNA shares common sequences with modern prokaryotes

Genetic Evidence

Both mitochondria & chloroplasts

–move freely within the cell

–reproduce independently from the cell through binary fission

–are inhibited by antibiotics

Functional Evidence

Where Did Organelles Come From ?

• Membranous infoldings

– Nucleus

– ER

– Golgi

– Lysosomes

– Vesicles

• Endosymbiosis

– Mitochondria

– Chloroplasts

Membrane infolding

Endosymbiotic theory

Bibliography / Acknowledgments

Jason de

Nys

Chris

Paine