Cell Structure And Microscopy Flashcards
Structure of double nuclear envelope
A double membrane which compartmentalises the Nucleus and prevents damage. This protects the DNA.
Structure of nuclear pores
Allows molecules to enter (e.g. nucleotides for DNA replication) and leave the cell (e.g mRNA leaves the cell).
Structure of Nucleolus
Composed of RNA and proteins.
Structure of Chromatin
DNA (with associated histone proteins).
Contains the Genetic Code which controls the activity of the cell.
Function of nucleus
1) Controls all the activity of the cell.
2) The Genetic Code (DNA) of the cell is stored, replicated, and copied into RNA (transcribed).
3) The Nucleus is attached to the Rough ER so the mRNA can easily get to ribosomes.
Function of Nucleolus
Produce and assemble the cells ribosomes- site of ribosome production
Function of nuclear envelope
Membrane that divides the nucleus and prevents damage- protects DNA
Structure of Rough Endoplasmic Reticulum
** Stacks of flattened membranes bound** (fluid filled sacs) which form sheets called cisternae.
Attached to the nucleus and studded with ribosomes.
Structure of smooth Endoplasmic Reticulum
** Stacks of flattened membranes bound** (fluid filed) sacs which form sheets called cisternae.
Attached to the nucleus
Does not have ribosomes ( is a system of interconnecetd tubes)
Function of Rough Endoplasmic Reticulum
Site of protein synthesis and glycoproteins synthesis
Transport proteins that synthesised on the attached ribosomes. Some proteins will be secreted by the cell whilst others will be placed on the surface of the cell membrane.
Function of smooth Endoplasmic Reticulum
It mostly creates lipids which cells need along with carbohydrates and steroid syntheis , and storage
Structure of Golgi Apparatus
** Stacks of flattened , membranes bound** (fluid filed) sacs which form sheets called cisternae.
Continuously formed from the ER at one end and budding off as Golgi vesicles at the other
Function of Golgi Apparatus
• Allows internal transport.
• Receives proteins from the RER
• Modifies and processes molecules (such as new lipids and proteins) and packages them into vesicles.
• These may be secretory vesicles (if the proteins need to leave the cell) or lysosomes (which stay in the cell).
• Makes lysosomes
• Lipid synthesis
Structure of ribosomes
• A 2 subunit organelle (80S in size in eukaryotes)
• Made from RNA and protein.
• Not membrane bound.
• Very small organelles: about 22nm in diameter.
• Found free floating in the cytoplasm or attached to the Rough ER
Function of ribosomes
-The site of translation in protein synthesis
-They assemble amino acids into chains of protein using mRNA
Structure of Mitochondrion
-Oval shape
-surrounded by 2 membranes ( double membrane)
_The inner membrane forms finger-like structure called cristae whic increases the surface area
-The solution , matrix contains enzymes for respiration
-Contains mitochondrial DNA which enable it to reproduce and create enzymes
Function of Mitochondrion
-Site of aerobic respiration
-Release ATP during respiration (energy carrier in cells)
Structure of lysosomes
Spherical sacs surrounded by a single membrane
Function of lysosomes
Contain a powerful hydrolytic digestive enzymes known as lysozymes
Break down worn components of the cell or digest invading cells
Structure of centrioles
Component of cytoskeleton composed of many microtubules
Small hollow cylinder that occur in parts next to the nucleus in animal cells
Each centriole contains a ring of 9 triple microtubules
Function of centrioles
Copies itself during cell division and then helps to form the spindle in cell division
Involved in the organisation of chromosomes in cell division
Structure of cilia
‘Hair like’ extensions that protrude from some animal cell types.
In a cross section has an outer membrane and a ring of 9 pairs of protein microtubules inside with two in the middle (9 = 2 arrangement)
Arrangement allows movement
function of cilia
Sensory function (e.g nose), beat creating a current to move/waft fluid/ mucous/ objects .
For locomotion
Structure of plasma membrane
The membrane found on the surface of animal cells and inside the cell wall of plant and prokaryotic cells
phospholipid bilayer ( proteins and cholesterol within it)
Composed of glycoproteins and glycolipids on the surface
Function of plasma membrane
• Regulates the movement of substances into and out of the cell.
• Contains receptor molecules (glycoproteins and glycolipids) which allow it to respond to chemical like hormones
Cholesterol provides strength and reduces fluidity
proteins are for transport
Structure of cytoskeleton
Made up of three structural component：
Microfilaments
Microtubules
Intermediate fibres
Function of cytoskeleton
Microfilaments- Fibres made from the protein actin. They are responsible for movement of the cell and cytoplasm during cytokinesis
Microtubules- Formed by the globular protein tubulin. They polymerise to form tubes that determine the shape of the cell. They also act as tracks for organelles moving forward.
Intermediate fibres- Gives strength to cells and helps maintain integrity.
Structure of flagella
similar to cilia but longer.
• They protrude from the cell surface and are surrounded by the plasma membrane.
• Like cilia they have a 9 +2 arrangement.
Function of flagella
• (Whip-like) enables a cells mobility.
• The microtubules contract to make the flagellum move.
• Propel cells forward e.g. sperm cells.
Structure of chloroplast
• Double membrane which encloses the stroma.
• Stroma contains: Starch grains, lipid stores, DNA, RNA, ribosomes.
• Series of membrane-bound flattened sacs called thylakoids in the stroma. Thylakoids stacked together are called grana.
• Grana are linked together by lamellae.
• The grana contain chlorophyll
Function of chloroplast
Photsynthetic reactions
The stroma contains enzymes for the light-independent stage of photosynthesis.
Structure of cell wall
Made of B-cellulose microfibrils (complex carbohydrate) in plants / chitin (fungi) / polysaccharides (prokaryotic)
• Cell wall is fully permeable to substances
• Thin layer called the middle lamella which marks the boundary between adjacent cell walls and ‘cements’ adjacent cells together.
Function of cell wall
Gives the plant mechanical strength
• Gives the plant cell support and it’s shape
• Contents of plant cell can ‘push’ against the cell wall (turgid cell). This gives the cell (and the whole plant) good support.
Structure of Large permanent vacuole
• Single membrane bound (membrane is called a tonoplast).
• Contains a fluid called cell sap (solution of mineral salts, sugars, amino acids, wastes etc).
• Selectively permeable barrier
Function of Large permanent vacuole
• Stores cell cap
• Support herbaceous plants by making cells turgid.
• Helps maintain shape and gives support by maintaining ** turgor pressure** .
• Sugars and amino acids act as a temporary food store.
Explain the Interrelationships of protein production and secretion
1)DNA in the nucleus contains the genetic code to make protein.
2) The particular gene (e.g. insulin) is copied by mRNA, which takes the copy of the gene out of
the nucleus via the nuclear pore to the ribosome (on the rough ER).
3) The protein is synthesized on the ribosome bound to the Rough ER where it then passes into the cisternae of the rough ER and it is packaged into a vesicle.
4) The vesicle moves to the golgi apparatus (via the microtubules of the cytoskeleton), and fuses with the golgi apparatus.
5) The protein enters the golgi apparatus where it processes and structurally modifies the protein e.g. adds a carbohydrate chain.
6) The Golgi Apparatus repackages the protein into a secretory vesicle where it travels along the microtubules and fuses with the cell surface membrane.
7) Contents of the vesicle (i.e. the protein) is released by exocytosis.
Explain magnification
How many time bigger the image produced by the microscope is than the real life object
Explain resolution
The ability to distinguish between two objects that are close together (seeing two structures that are very close as two separate objects)
What is the calculation for total magnification
Eyepiece lens magnification X objective lens = Total magnification
What is the magnification equation
Image size
—————————
Actual size X Magnification
What are microscopes used for
Microscopes are used to analyse the cell components and observe organelles (sub cellular structure)
How do light microscopes form an image
Optical microscopes use light to form an image. This is done through the lamp at the bottom of the microscope which is connected to a power source.
Advantages of a light microscope
inexpensive to buy and operate
Small and portable
simple sample preparation
vacuum not required
Specimen can be living or dead
Disadvantages of a light microscope
Limited resolution- 0.2micrometres or 200nm
Can’t distinguish between two objects that are closer than the wavelength of light 500-650nm
Maximum useful magnification of x1500
Cannot observe ribosomes, ER or lysosomes
How do electron microscopes form an image
Electron microscopes use electrons to form an image. A beam of electrons is fired at the specimen which has a much smaller wavelength than light.
The electron microscope can resolve two objects that are extremely close together and are absorbed by air thus must be in a vacuum.
Advantages of electron microscope
Maximum resolution of 0.2nm (1000x greater than optical microscopes)
over x500,000 magnification
Disadvantages of electron microscopes
Expensive to buy and operate
Large and needs to be installed
Complex sample preparation
Sample preparation often distorts material
Vacuum required
Specimens are dead
Black and white images produced
How does scanning electron microscopy work
SEMs scan a beam of electrons across the surface of the specimen
This bounces off the surface and scatters the electrons which are detected, forming an image
SEMs therefore form a 3D image that shows the surface of a specimen
Advantages of scanning electron microscopy
3D images are formed that shows the surface of a specimen
Magnification is x500,000 or less
Can be used on thick or 3d specimens
Allows external 3d structures to be observed
Disadvantages of scanning electron microscopy
Lower resoltuions than TEMs
Cannot be used on live specimens (unlike microscopes)
Do not produce a colour image (unlike optical microscopes)
Note images are often digitally processed (enhanced)
How does transmission electron microscopy work
TEMs use electromagnets to focus a beam of electrons, which is transmitted through the specimen
Denser parts of the specimen absorb more electrons, making them appear darker on the final image (contrast between the different parts being observed)
2D image is produced which shows the detailed internal structure of cells
Advantages of transmission electron microscopy
Higher resolution images = more detail
Internal structure can be seen
Magnification is x1,000,000 or more
Disadvantages of transmission electron microscopy
Only used with very thin specimens or thin sections of an object
Cannot be used to observe live specimens because of the vaccum inside the TEm plus all the water must be removed from the specimen
Lengthy treatement require to prepare specimens. Artefacts could be introduced these look like real structures but are actually the result of preserving or staining.
Do not produce a colour image and 2D
How does laser scanning confocal microscopy work
A thick section of tissue or small living organism is viewed at a high light intensity with fluorescent dyes
The laser beam is reflected by the fluorescent dye
Multiple depths of the tissue section/ organism are scanned to produce an image. As if the laser beam is building the image layer by layer .
A 3D or 2D image can be created in different focal planes
Advantages of laser scanning confocal microscopy
Used on thick or 3d specimens
External 3d structure is observed
Very clear and high resolution because the laser beams can be focused at a very specific depth. Cytoskeletons can be observed
Disadvantages of laser scanning confocal microscopy
Slow process and takes a long time to obtain an image
Laser could cause photodamage to cells
What are the conversion going up from nm km:
nm , μm , mm , cm , m , km
÷ 1000
÷ 1000
÷ 10
÷ 100
÷ 1000
What to do during a microscope calculation question
Step 1: Circle what the question is asking for.
Step 2:Measure the image (if that is required)
Step 3: Write out what you know (I=, A=, M=)
Step 4: Write formula, convert units and sub in the values
What is the formula for magnification using a scale bar
Magnification =
measured length of scale bar
————————————————————-
actual length of scale bar
What is a photo-micrograph
A photo-micrograph is a photo or digital image taken through a microscope to show a magnified image of a specimen.
How does the abundance of various organelles in mitochondria tell us the function of it
Mitochondria– Cells with many mitochondria typically undertake energy-consuming processes (e.g. neurons, muscle cells)
How does the abundance of various organelles in ER tell us the function of it
Cells with extensive ER networks undertake secretory activities (e.g.plasma cells, exocrine gland cells)
How does the abundance of various organelles in lysosomes tell us the function of it
Cells rich in lysosomes tend to undertake digestive processes (e.g. phagocytes)
How does the abundance of various organelles in chloroplast tell us the function of it
Cells with chloroplasts undergo photosynthesis (e.g. plant leaf tissue but not root tissue)
Why are stains used in light microscopy
Many tissues that are used in microscopy are transparent, letting light and electrons through them.
This makes it difficult to see details.
Stains are often used to color the tissues
How does staining work in light microscopy?
Coloured dyes are dropped with a pipette when staining specimens. They absorb specific colors of light whilst reflecting others, making the structure visible.
Certain tissues absorb certain dyes, depending on their chemical nature.
Sometimes specimens are stained with more than one dye to ensure different tissue show up (differential staining)
Most colors are not natural
What stains are used in light microscopy
Toluidine blue , methylene blue , phloroglucinal and eosin are common stains
How does staining work in electron microscopy
When using electron microscope the specimen must be stained to absorb/ scatter the electrons
Electrons have no colour so dyes used cause the tissue to show up black or different shades of grey
What stains are used in electron microscopy?
Heavy metal compounds are commonly used as stains because they provide a good contrast by absorbing/ scattering electrons. For example osmium tetroxide and Ruthenium tetroxide
Any colour present in electron micrograph is unnatural and not as a result of staining
Colour usually added using an image processing software
Explain the eyepiece graticule
- Attached to the eyepiece of the microscope
- Has a scale, but NO UNITS
- It always remains constant therefore it needs to be recalibrated for each objective lens (x4, x10, x40)
Explain the stage micrometer
- this is a microscopic ruler on a special slide with a tiny scale etched on it (in µm)
- The ruler is 1mm long, and divided into 100 divisions.
- This scale is very accurate. Each division is 0.01mm or 10 µm
What is differential staining
Differential staining is a technique which involves many chemical stains being used to stain different parts of a cell in different colours.
How does the stains Crystal violet and methylene blue work
They are positively charged, and therefore are attracted to and stain negatively charged materials.
How does the stains Nigrosin and Congo red work
Nigrosin and Congo red are negatively charged, and therefore cannot enter the cells because cytosol repels them. This creates a stained background, and the unstained cells then stand out.
Explain the process of gram staining for gram-positive bacteria
Common use of differential staining. Two different stains are used- crystal violet and safranin
Crystal violet is added, then iodine to fix the stain, and then alcohol is used to wash away any unbound stain.
Gram-positive bacteria appear blue/purple as the stain is retained due to the thicker peptidoglycan cell wall later absorbing the dye.
How can distinguishing between positive and negative bacteria help in the real world
Being able to distinguish between the two types of bacteria helps medics to prescribe an appropriate antibiotic to patients with bacterial infections,
e.g., penicillin can be used to treat gram-positive bacteria but not gram-negative
What is a eukaryotic cell
Most eukaryotic cells are complex multicellular organisms containing a range of specialised cells to perform a variety of functions.
What is an organism
Organisms are made up of organ systems, which contain a range of organs working together to perform a function.
What are organs
Organs are made up of a range of tissues working together to perform a function
What is a tissue
A tissue is a group of cells that work together to perform a particular function.
What is the structure of a nucleus
Surrounded by a double membrane nuclear envelope with nuclear pores.
Contains chromosomes, consisting of protein- bound, linear DNA, and one or more nucleolus.
What are prokaryotic cells
Prokaryotic cells are single-celled organisms that lack a nucleus and other membrane-bound organelles.
Describe a prokaryotic cell
cytoplasm does not contain any membrane-bound organelles
The ribosomes are smaller, (70S in size in prokaryotes).
Bacteria still contain DNA, but it is not stored in a nucleus.
The DNA is found as a single, circular molecule in the cytoplasm and it is not associated with histone proteins.
Prokaryotic cells do have cell walls made up of a glycoprotein called murein.
They can contain plasmids, which are rings of DNA containing genes linked to survival such as antibiotic resistance.
Surrounding the cell wall, some bacteria have a capsule which is to provide protection from other cells and to help bacteria stick together.
Flagella which used for locomotion.
Explain the process for staining gram-negative bacteria
Common use of differential staining. Two different stains are used- crystal violet and safranin
Crystal violet is added, then iodine to fix the stain, and then alcohol is used to wash away any unbound stain.
Gram-negative bacteria cannot absorb crystal violet stain as their peptidoglycan cell wall is thin and so do not retain the stain due to having thinner walls. Therefore, safranin is used as a counterstain, turning them red.
Describe a eukaryotic cell
• Do have a nucleus
• Do have membrane- bound organelles
• Includes all animal and plant cells
Contains Ribosomes (80S)
Contains a cytoskeleton
Contains centrosomes
Biological drawing rules
Use a sharp pencil and ruler
Draw with an underline with annotations
Use smooth continuous lines to draw, no overlapping and no gaps
No shading or coloring in
Be accurate when drawing
Drawing must take 50% of the box
Labels should be straight and parallel to the drawing. Arrows should not be used
Labels should touch the cell that is being labeled
Include scale/ magnification
No cross-hatching
Explain the procedure of calibrating and using an eyepiece graticule
Use a stage micrometer. This is a microscope slide with an accurate scale etched on it and insert the graticule into the eyepiece lens and line up the two scales.
It is then possible to count the number of divisions on the eyepiece graticule equivalent to each division on the stage micrometer and calculate the length that one eyepiece division is equivalent to.
Explain the procedure of using a microscope
Place the slide showing the specimen on the microscope stage.
Looking from the side at eye level , twist the focusing dial until themicroscope stage has moved up so that the slide is just about to touch the lens.
Then use the coarse focusing dial to focus DOWN until you can clearly see the cells in the field of view. (Make sure the cells are in the centre of the field of view)
Use the smallest power objective and focus until you can see the cell . Then rotate to the medium power lens and again focus until you can see the cells clearly. Lastly, switch to the highest power objective lens.
Use the eyepiece graticule to measure the length of cells
Make scientific annotated drawings of the stages of a selection of cells.
What is the resolution of light,SEM,TEM,Laser scanning confocal Microscopy
200nm
2nm
0.2nm
0.2nm>
What is the magnification of light, SEM,TEM,Laser scanning confocal Microscopy
X1500
X500,000
X1,000,000
X1,000,000<
