deck_5661096 Flashcards
What is an electron micrograph?
Photograph of an image seen using an electron microscope
What is magnification?
The number of times larger an image appears, compared with the size of the object
What are organelles?
Small structures within cells, each of which has a specific function
What is a photomicrograph?
A photograph of an image seen using an optical microscope
What is resolution?
The clarity of an image; the higher the resolution, the clearer the image
What sort of magnification do microscopes produce?
Linear magnification, which means that if a specimen is seen magnified x100, it appears to be 100 times wider and 100 times longer than it really is
What did optical microscopes play a key role in?
Developing our understanding of cell structure-They were the first sort to be used
Why are optical microscopes still used in schools, colleges, hospitals and research laboratories?
Because they are relatively cheap, easy to use, portable and able to be used in the field as well as in laboratories, and able to be used to study whole living specimens
What do these microscopes rely on?
Lenses to focus a beam of light
What magnification do optical microscopes allow?
Up to x1500, or in some types x2000, which enables us to see clearly some of the larger structures inside cells
What are optical microscopes resolution like?
Limited which is why they cannot magnify any higher while still giving a clear image
How do optical microscopes work?
They use visible light, a part of the electromagnetic spectrum, that has a wavelength of between 400 and 700 nm
What is the wavelength of visible light?
It ranges from 400 to 700 nm so structures closer together than 200 nm will appear as one object
Can ribosomes be examined with an optical microscope?
No because they are very small, non-membrane-bound, cell organelles of about 20nm diamteter
How do you calculate magnification?
Total magnification=magnifying power of the objective lens x magnifying power of the eyepiece lens
What are laser scanning microscopes also called?
Confocal microscopes
How do laser scanning microscopes work?
They use a laser light to scan an object point by point and assemble, by computer, the pixel information into one image, displayed on a computer screen
What are the images like from these microscopes?
High resolution and show high contrast. They have depth selectivity and can focus on structures at different depths within a specimen, Such microscopy can therefore be used to clearly observe whole living specimens, as well as cells
What profession uses these microscopes?
Many branches of biological research and medical professions, eg to observe fungal filaments within the cornea of the eye of a patient with a fungal corneal infection, in order to give a swift diagnosis and earlier so more effective treatment
How do electron microscopes work?
They use a beam of fast-travelling electrons with a wavelength of about 0.004 nm. This means they have much greater resolution than optical microscopes and can be used to give clear and highly magnified images. The electrons are fired from a cathode and focused, by magnets rather than glass lenses, on to a screen or photographic plate
Why do electron microscopes have a much better resolution compared to optical microscopes?
Fast-travelling electrons have a wavelength of about 125,000 times smaller than that of the central part of the visible light spectrum
What do you have to do before using a transmission electron microscope?
The specimen has to be chemically fixed by being dehydrated and stained
How do transmission electron microscopes work?
The beam of electrons passes through the specimen, which is stained with metal salts, Sine electrons pass through and are focused on the screen or photographic plate
What are the images like, when created my a transmission electron microscope?
The electrons form a 2D black and white image, when photographed its called a photomicrograph. They can produce magnification of up to 2 million times and new generations being developed can magnify up to 50 million times
When were scanning electron microscopes developed?
During the 1960s
How do scanning electron microscopes work?
Electrons don’t pass through the specimen, which is whole, but cause secondary electrons to ‘bounce off’ the specimen’s surface and be focused on to a screen
What are the images like when formed from a scanning electron microscope?
A 3D image with a magnification from x15 to up to x200,000 is formed. The image is black and white but computer programmes can add false colour.
What is a disadvantage of scanning electron microscopes?
The specimen has to be placed in a vacuum and is often coated with a fine film of metal
What are the similarities between both types of electron microscopes?
They are both very large, very expensive, need a lot of skill/training to use, specimen have to be dead as they are viewed whilst in a vacuum and the metallic salt stains used for staining specimens may be potentially hazardous to the user
What can be seen by the human eye?
A hen’s egg, amoeba and onion epidermis cell
What can be seen with a light microscope?
Amoeba, onion epidermis cell, human ovum, human cheek cells, mitochondria, chloroplast, bacteria and influenza virus
What can an electron microscope see?
Everything the light microscope can, plus ribosome, protein, lipids and and atom
How do you observed an unstained specimen, eg paramecium which are colourless and transparent?
Some microscopes use light interference instead of light absorption to produce a clear image without staining. Some use a dark background against which the illuminated specimen shows up
What are stains?
Coloured chemicals that bind to molecules on or in the specimen, making it easy to see
What is an all-purpose stain?
Methylene blue
What is differential staining?
Some stains bind to specific cell structures, staining each structure differently so the structures can be easily identified within a single preparation
What are examples of differential staining?
Acetic orcein binds to DNA and stains chromosomes dark red, Eosin stains cytoplasm; Sudan red stains lipids, And iodine in potassium iodide solution stains the cellulose in plant cell walls yellow, and starch granules blue/black/violet
How are the prepared, permanently fixed slides made by experts in labs?
By dehydrating the specimen, embedding them in wax to prevent distortion during slicing, and use a special instrument to make very thin slices called sections which are stained and mounted in a special chemical to preserve them
What is the formula for calculations involving magnification?
M=I over A which is magnification=image size over actual size
What is an eyepiece graticule?
A measuring device that is placed in the eyepiece of a microscope and acts as a ruler when you view an object under the microscope
What is a stage graticule?
A precise measuring device that is a small scale that is placed on a microscope stage and used to calibrate the value of eyepiece divisions at different magnifications
What are all animal, plant, fungal and protoctist cells?
Eukaryotic cells
What do all eukaryotic cells have?
Nucleus surrounded by nuclear envelope and containing DNA, a nucleolus containing RNA, cytoplasm which suspends the organelles, a cytoskeleton (network of protein filaments in the cytoplasm that move organelles within the cell), a plasma membrane, membrane bound organelles such as nucleus/mitochondria/Golgi apparatus/endoplasmic reticulum, small vesicles and ribosomes (organelles without membranes) which are where proteins are assembled
What are organelles?
They are inside every cell and each have a specific function, this provides a division of labour so every cell can carry out all its functions efficiently
What are most of the organelles like within eukaryotic cells?
Membrane bound, meaning they are covered by a membrane which keeps each organelle separate from the rest of the cell so it is a discrete compartment
Do prokaryotic cells also have membrane bound organelles?
No
How have scientists been able to see the structure of these organelles?
Electron microscopy by making and examining several sections of an organelle in order to build up a 3D image of it
How have scientists been able to find out the functions of these organelles?
Biochemistry research
What is the nucleus surrounded by?
A double membrane called a nuclear envelope. It also has pores
What is the nucleolus’ structure?
It doesn’t have a membrane around it, and it contains RNA
What is chromatin?
The genetic material made up of DNA wound around histone proteins
How does chromatin change when the cell dividing or not dividing?
When not dividing it is spread out and extended. When it is about to divide it condenses and coils tightly into chromosomes which make up nearly all the organisms genome
What is the function of the nuclear envelope?
It separates the contents of the nucleus from the rest of the cell
What can happen to the outer and inner nuclear membrane in some regions?
They can fuse together. At these points some dissolved substances and ribosomes can pass through
What do the pores in the nuclear envelope allow?
Larger substances such as mRNA to leave the nucleus. Also some substances such as steroid hormones may enter the nucleus from the cytoplasm via these pores
What is the function of the nucleolus?
It is where ribosomes are made
What are the functions of chromosomes?
They contain the organism’s genome
What is the overall function of the nucleus?
It’s the control centre of the cell, stores organism’s genome, transmits genetic information and provides the instructions for protein synthesis
What is the structure of the rough endoplasmic reticulum?
It is a system of membranes, containing fluid filled cavities called cisternae, that are continuous with the nuclear membrane. It is also coated with ribosomes
What is the function of the rough ER?
It is the intracellular transport system because the cisternae form channels for transporting substances from one area of the cell to another. It also provides a large surface area for ribosomes which turn amino acids into proteins which then actively pass through the membrane, into the cisternae and then transported to the Golgi apparatus for modification and packaging
What is the structure of the smooth endoplasmic reticulum?
Its a system of membranes containing fluid filled cavities called cisternae that are continuous with nuclear membrane. There are no ribosomes on its surface
What is the function of the smooth ER?
Contains enzymes that catalyse reactions involving lipid metabolism (eg synthesis of cholesterol, synthesis of lipids/phospholipids and synthesis of steroid hormones) also it is involved with absorption, synthesis and transport of lipids from the gut
What is the structure of the Golgi apparatus?
Contains a stack of membrane-bound flattened sacs. Secretory vesicles bring materials to and from the Golgi apparatus
What are the functions of the Golgi apparatus?
Proteins and modified and then packaged into vesicles
What are examples of how the Golgi modifies proteins?
Adding sugar molecules to make glycoproteins, adding lipid molecules to make lipoproteins and being folded into their 3D shape
What happens after the Golgi has packaged proteins into vesicles?
They are pinched off and then stored in the cell, or moved to the plasma membrane, either to be incorporated into the plasma membrane, or exported outside the cell
What shape can mitochondria be?
Spherical, rod-shaped or branched, and they are 2-5 micrometers long
What is the mitochondria surrounded by?
Two membranes with a fluid filled space in-between them, The inner membrane is highly folded into cristae
What is the inner part of the mitochondria like?
It is a fluid filled matrix
What are the functions of mitochondria?
The site of ATP production during aerobic respiration, they are self-replicating so can be made if the cell’s energy needs increase and they are abundant in cells where lots of metabolic activity takes place, eg in liver cells at synapses where neurotransmitter is synthesised and released
What size are chloroplasts?
They are large organelles, 4-10 micrometers long
Where are chloroplasts found?
Only in plant cells and in some protoctists. They are abundant in leaf cells, particularly the palisade mesophyll layer
What is the structure of chloroplasts?
Surrounded by a double membrane (envelope). Inner membrane is continuous with stacks of flattened membrane sacs called thylakoids which contain chlorophyl. Each stack of thylakoids are called a granum, and the fluid filled matrix is called the stoma
What do chloroplasts contain?
Loops of DNA and starch grains
What are the functions of chloroplasts?
Site of photosynthesis, first stage of photosynthesis occurs in the grana (light energy is trapped by chlorophyl to make ATP, and water is split to make hydrogen ions), also the second stage occurs in the stoma (when hydrogen reduces carbon dioxide using ATP, to make carbohydrates
What is the structure of a vacuole?
It is surrounded by a membrane called the tonoplast and contains fluid. They are only found in plant cells as they have a large permanent vacuole
What is the function of a vacuole?
Filled with water and solutes and maintains cell stability because when full it pushes against the cell wall making it turgid. If all plant cells are turgid then it helps to support the plant (especially in non-woody plants)
What is the structure of lysosomes?
Small bags formed from the Golgi apparatus and each is surrounded by a single membrane. They contain powerful hydrolytic (digestive) enzymes, and they are abundant in phagocytic cells such as neutrophils and macrophages that can ingest and digest invading pathogens
What are the functions of lysosomes?
Keep powerful hydrolytic enzymes separate from the rest of the cell, and they can engulf old cell organelles and foreign matter then digest them and return the digested components to the cell for reuse
What is the structure of cilia and undulipodia?
They are protrusions from the cell, surrounded by the cell surface membrane. Each contain microtubules and are formed from centrioles
What are the functions of cilia and unculipodia?
Epithelial cells lining airways have hundreds of cilia that beat and move the band of mucus. Nearly all cell types in the body have a cilium that acts as an antenna (contains receptors and allows cells to detect signals about its immediate environment). The only human cell to have an undilopodium, is a spermatozoon
What are organelles without membranes?
Ribosomes, centrioles, cytoskeleton and cellulose cell wall
What is the structure of ribosomes?
Salle spherical and about 20nm in diameter. Made of ribosomal RNA in the nucleolus as two separate subunits that pass through the nuclear envelope into the cytoplasm and then combine. Some remain free in the cytoplasm and some attach to the endoplasmic reticulum
What are the functions of ribosomes?
Bind to the exterior of RER mainly for synthesising proteins that will be exported outside the cell. The free ribosomes in the cytoplasm, either single or in clusters, are primarily the site of assembly of proteins that will be used inside the cell
What is the structure of centrioles?
Consist of two bundles of microtubules at right angles to each other, which are made of tubulin protein subunits are arranged to form a cylinder
How are centrioles made?
Before a cell divides the spindle, made of threads of tubulin, forms the centrioles. Chromosomes then attach to the middle part of the spindle and motor proteins walk along the tubulin threads pulling the chromosomes to opposite poles
What are the functions of centrioles?
They’re involved in the formation of cilia and undilopodia by the centrioles multiplying and lining up beneath the cell surface membrane, before the cilia can form. The microtubules sprout outwards from each centriole, forming a cilium or undilopodium
Where are centrioles found?
They are usually absent from cells of plants but may be present in some unicellular green algae such as chlamydomonas
What is a cytoskeleton?
A network of protein structures within the cytoplasm
What does the cytoskeleton consist of?
Rod-like microfilaments made of subunits of the protein actin, intermediate filaments about 10nm in diameter, straight/cylindrical microtubules made of protein subunits called tubulin about 19-30nm in diameter
What are the cytoskeletal motor proteins, myosins, kinesins and dyneins?
Molecular motors. Also they are enzymes and have a site that binds to and allows hydrolysis of ATP as their energy source
What are the functions of cytoskeleton?
Protein microfilaments give support and mechanical strength, keep the cell’s shape stable and allows movement. Microtubules also provide shape and support to cells and help substances and organelles to move through the cytoplasm within a cell. Intermediate filaments anchor the nucleus within the cytoplasm and extend between cells in some tissues to allow cell-cell signalling
What is the structure of a cellulose cell wall?
The cell wall of plants is on the outside of the plasma membrane and is made from bundles of cellulose fibres
Where are cellulose cell walls found?
They are absent from animal cells, fungi have cell walls that contain chitin (not cellulose)
What is the function of a cellulose cell wall?
It is strong so can prevent plant cells from bursting when turgid. They provide strength and support, maintain the cell’s shape, contribute to the strength and support of the whole plant, and are permeable and allow solutions to pass through
What is the first stage of making and secreting a protein?
The gene that has the coded instruction for a proteins such as insulin, housed on chromatin in the nucleus, is transcribed into a length of messenger RNA
What then happens to the mRNA (second stage of making/secreting a protein)?
Many copies of it are made and they pass out of the pores in the nuclear envelope to the ribosomes
What happens at the ribosomes (third stage of making/secreting a protein)?
The instructions are translated and insulin molecules are assembled
What happens to the insulin molecules (fourth stage of making/secreting a protein)?
They pass into the cisternae of the rough ER and along the hollow sacs
What happens to the vesicles, containing insulin (fifth stage of making/secreting a protein)?
They are pinched off from the RER and pass, via microtubules and motor proteins, to the Golgi apparatus
What happens to the vesicles at the Golgi (sixth stage of making/secreting a protein)?
They fuse with the Golgi apparatus, where the insulin protein molecules may be modified for release
What is the seventh stage of making/secreting a protein?
Inside vesicles pinched off from the Golgi apparatus, these molecules pass to the plasma membrane
What is the final stage of making/secreting a protein?
The vesicles and plasma membrane fuse, and the insulin is released to the outside of the cell
What is exocytosis?
A type of bulk transport, an active process for which energy is needed
What are bacteria?
Microorganisms that have prokaryotic cells
How are eukaryotic and prokaryotic cells similar?
They have a plasma membrane, cytoplasm, ribosomes for assembling amino acids into proteins, DNA/RNA
How are eukaryotic and prokaryotic cells different?
Prokaryotic cells are much smaller, have a less well developed cytoskeleton with no centrioles, don’t have a nucleus, don’t have membrane bound organelles, have a wall that is made of peptidoglycan (not cellulose), have smaller ribosomes and have naked DNA that isn’t wound around histone proteins but floats free in the cytoplasm as a loop
What do some prokaryotic cells also have?
A protective waxy capsule surrounding their cell wall, small loops of DNA called plasmids as well as the main large loop of DNA, flagella (projection enabling movement) and pili (smaller projections enabling bacteria to adhere to host cells or to each other, and allow passage of plasmid DNA from one cell to another)
How do prokaryotic cells divide?
By binary fissions (not by mitosis). They don’t have linear chromosomes so don’t carry out mitosis, but before they divide, their DNA is copied so that each new cell receives the large loop of DNA and any smaller plasmids
What organelles do prokaryotes have?
They don’t have any membrane-bound organelles, but they do have organelles that aren’t covered by a membrane, such as ribosomes
Why are bacteria microorganisms and prokaryotic cells?
Because they are very small and have a cell structure of a prokaryote. However not all microorganisms are prokaryotes eg yeast and amoebae are microorganisms that have eukaryotic cells. Viruses are microscopic but they don’t have cells
