Microscopes and cell structure Flashcards by Jim Moroney

Define magnification

The number of times larger an image appears compared to the original object

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Define resolution

The ability of an optical instrument to distinguish between two points that are close together on an object

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Optical microscopes allow a magnification of up to?

1500 x

In some cases 2000 x

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Give an example of an organelle a light microscope cannot magnify?

Ribosomes as they have a diameter of 20nm

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What is a laser scanning/ confocal microscope?

Lasers scan the surface of an object and display it on a computer screen

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What are the features of a laser scanning/ confocal microscope?

Can focus on structures at different depths within cells

Can observe live organisms

Show high contrast and high resolution

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What are the types of electron microscope and what electron micrographs do they form?

Transmission electron microscope - forms a 2D, black and white image.

Scanning electron microscope - electrons bounce off the surface of the object, forms a 3D, black and white image.

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Explain the similarities between a scanning and a transmission electron microscope.

Organisms have to be dead

The specimen is chemically fixed and stained with metal salts

Organism has to be in a vacuum

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Explain the differences between a transmission and a scanning electron microscope

Transmission - is a 2D, black and white image.

Scanning - is a 3D image, where colour can be digitally added

Transmission - magnifies up to 50 million times

Scanning - magnifies up to 20 000 times

Transmission - electrons pass through the specimen

Scanning - electrons ‘bounce’ of the surface

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What stain is commonly used on specimens?

Methylene blue

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Why do we stain specimens?

To differentiate between structures

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What does Sudan Red stain?

Lipids

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What does Iodine stain?

Cellulose

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What stains chromosomes?

Acetic Orcein

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What are the limitations of observing structures under microscopes?

Cells are 3D and most photomicrographs show 2D sections

Not all structures are visible depending on where you cut

Structures may appear as different shapes depending on their orientation.

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Describe the structure of the nucleus

Double membrane called the nuclear envelope

Has nuclear pores

Nucleolus containing RNA

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Describe the function of the nucleus

Envelope separates contents

Pores allow larger substances like mRNA through

Nucleolus produces ribosomes

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Describe the structure of the Rough Endoplasmic Reticulum (RER)

A system of membranes containing fluid filled cavities
(cisternae)

Coated in ribosomes

Describe the function of the RER

Cisternae provided channels to transport substances

Provides a large surface area for ribosomes

Assembles amino acids into proteins

Describe the structure of the Smooth Endosplasmic Reticulum

Same as the RER, but no ribosomes on surface

Describe the function of the SER

Contains enzymes to catalyse reactions involved with lipid metabolism

Describe the structure of the Golgi Apparatus

Stacks of membrane bound, flattened sacs

Secretory vessels bring substances to and from the Golgi

Describe the function of the Golgi Apparatus

Modifies proteins:

Can add sugar and lipid molecules to make glycoproteins and lipoproteins

Folds proteins into their 3D shape

Packages proteins into vesicles

Describe the structure of the mitochondria

Double membrane

Inner folded membrane called the Cristae

Fluid filled matrix within

Describe the function of mitochondria

Site of ATP production Abundant where metabolic activity is high

Describe the structure of the chloroplasts

Double membrane Thylakoids are flattened sacs, containing chlorophyll Each stack is a granum Stroma (fluid) Loops of DNA and starch grains

Describe the function of the chloroplasts

Site of photosynthesis Abundant in palisade cells ( 1st stage of photosynthesis - Light energy trapped bay chlorophyll to make ATP, in the grana) (2nd stage of photosynthesis - hydrogen reduced to co2, to make carbs, in the stroma)

Describe the structure of the vacuole

Tonoplast membrane contains fluid

Describe the function of the vacuole

Filled with water and solutes to maintain cell turgidity

Describe the structure of the lysosome

Small 'bags' formed in the Golgi Contain powerful hydrolytic enzymes

Describe the function of the lysosome

Separate enzymes from then rest of the cell Engulf old organelles and foreign/ dead matter

Describe the structure of the cilia and undulipodia

Protrusions from the cell surrounded by the cell surface membrane Formed from centrioles and contain microtubules

Describe the structure of ribosomes

Small and spherical Made of RNA Made in the nucleolus

Describe the function of ribosomes

Synthesise proteins to be exported out of the cell

Describe the structure of centrioles

Two bundles of microtubules at right angles Arranged to form a cyllinder

Describe the function of centrioles

Threads of tubular extend from the centriole during mitosis

Describe the structure of the cytoskeleton

Network of protein structures Rods of microfilaments made from actin Myosins, as well as other proteins, act as motors

Describe the function of the cytoskeleton

Support and mechanical strength Allow cell movement Form the track for motor proteins Intermediate filaments anchor the nucleus in place

Describe the 1st half of the secretion of a protein (up until the RER)

A gene is transcribed onto mRNA mRNA passes out through the nuclear pore At the RER, instructions are translated in the ribosomes and proteins are made Molecules pass through the cisternae

Describe the second half of the secretion of a protein

Vesicles leave the RER to the Golgi, via microtubules Vesicles fuse with the Golgi where the protein is modified Molecules pinch off the Golgi and are transported again to the plasma membrane Vesicle fuses with the plasma membrane and exocytosis occurs

How are prokaryotic and eukaryotic cells similar?

Both have a plasma membrane, cytoplasm, ribosomes, DNA and RNA

How are prokaryotic cells different from eukaryotic cells?

Naked DNA is wrapped around histone proteins No nucleus Much smaller Peptidoglcan wall No membrane bound organelles

What are some additional features of a prokaryotic cell?

Pili Flagella Waxy capsule

What evidence is there that eukaryotic cells, like mitochondria, have evolved from prokaryotic cells?

The endosymbiont theory - both divide by binary fission, have plasmid DNA's and have small ribosomes