Microscopes and cell structure Flashcards
Define magnification
The number of times larger an image appears compared to the original object
Define resolution
The ability of an optical instrument to distinguish between two points that are close together on an object
Optical microscopes allow a magnification of up to?
1500 x
In some cases 2000 x
Give an example of an organelle a light microscope cannot magnify?
Ribosomes as they have a diameter of 20nm
What is a laser scanning/ confocal microscope?
Lasers scan the surface of an object and display it on a computer screen
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
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.
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
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
What stain is commonly used on specimens?
Methylene blue
Why do we stain specimens?
To differentiate between structures
What does Sudan Red stain?
Lipids
What does Iodine stain?
Cellulose
What stains chromosomes?
Acetic Orcein
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.
Describe the structure of the nucleus
Double membrane called the nuclear envelope
Has nuclear pores
Nucleolus containing RNA
Describe the function of the nucleus
Envelope separates contents
Pores allow larger substances like mRNA through
Nucleolus produces ribosomes
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
