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

Endoplasmic Reticulum Rough Endoplasmic Reticulum Spot the difference? Smooth Endoplasmic Reticulum http://images.wellcome.ac.uk/

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

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 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

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.

The Mitochondrion (pl. Mitochondria) The power house of the cell Has a smooth outer membrane and a folded inner membrane Where aerobic respiration occurs Mitochondria in mammalian lung cells

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.

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.

Hormone secreting cell: many vesicles holding the hormones until secretion. 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

Photosynthetic plant cell: chloroplasts for performing photosynthesis Palisade mesophyll cells carry out most of the photosynthesis in plant cells Organelles involved: Chloroplasts Mitochondria Large Vacuole

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.

WHAT IS A SYSTEM? Endomembrane System Inside membrane A system of membranes inside the cell membrane Multiple parts working together with shared function

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.

Like a bubble Phospholipid bilayer MOSAIC Endomembrane System Membranes within the eukaryotic cell that work together to modify, process and ship molecules around and out of the cell. Semipermeable FLUID

Endomembrane System All made of phospholipid bilayer Includes: Nuclear envelope Rough ER Smooth ER Transport vesicles Golgi apparatus Secretory vesicles Lysosomes Vacuole

The Endomembrane System nucleus nuclear pore cell membrane rough ER protein secreted ribosome vesicle proteins smooth ER cytoplasm transport vesicle Golgi apparatus

nuclear membrane DNA Nucleus mrna nuclear pore mrna production of mrna from DNA in nucleus mrna out of nucleus through nuclear pore

Using RNA code, a protein is synthesized on a ribosome and transported in channels of the ER. Protein is packaged into transport vesicles 3. Packaging (protein into a vesicle) 2. Translation (mrna protein) 1. Transcription (DNA RNA)

Endoplasmic Reticulum Function processes proteins manufactures membrane Structure membrane connected to nuclear envelope & extends throughout cell

Types of ER rough smooth

Protein is packaged into transport vesicles and travels to the Golgi along the cytoskeleton track 4. Transport (protein in vesicle moves to Golgi)

Vesicle fuses with the Golgi and protein is modified as it passes through. 5. Modify (Golgi changes or adds to the protein)

Golgi Apparatus 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 secretory vesicles transport vesicles

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

Eukaryotes 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

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 ~2 bya infolding of the plasma membrane plasma membrane endoplasmic reticulum (ER) nuclear envelope *note double membrane nucleus DNA Prokaryotic cell cell wall Prokaryotic ancestor of eukaryotic cells plasma membrane Eukaryotic cell

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 FIRST early eukaryotic cells engulfed aerobic bacteria but did not digest them Led to the origin of mitochondria Mutually beneficial relationship internal membrane system aerobic bacterium mitochondrion Endosymbiosis Ancestral eukaryotic cell Eukaryotic cell with mitochondrion

Endosymbiosis THEN early eukaryotic cells engulfed photosynthetic bacteria but did not digest them Led to origin of chloroplasts mutually beneficial relationship Eukaryotic cell with mitochondrion chloroplast Endosymbiosis mitochondrion Eukaryotic cell with chloroplast & mitochondrion

Endosymbiosis 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

A model of the origin of eukaryotes

Theory of Endosymbiosis How is the word theory in science different than the use of the word theory in every day language? Lynn Margulis

Structural Evidence 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

Genetic Evidence Both mitochondria & chloroplasts have circular naked DNA DNA shares common sequences with modern prokaryotes

Functional Evidence Both mitochondria & chloroplasts move freely within the cell reproduce independently from the cell through binary fission are inhibited by antibiotics

Where Did Organelles Come From? Membranous infoldings Nucleus ER Golgi Lysosomes Vesicles Endosymbiosis Mitochondria Chloroplasts

Endosymbiotic theory Membrane infolding

Bibliography / Acknowledgments Jason de Nys Chris Paine