Chapter 3: Cell Structure Flashcards
What is the resolution of a light microscope? (3.1)
- objects that are 0.2 μm apart, or further
What is the resolution of an electron microscope? (3.1)
- objects that are 0.1 nm apart, or further
What is magnification? (3.1)
- how many times bigger the image is, compared to the object
What is the resolution / resolving power of a microscope? (3.1)
- the minimum distance apart two objects can be for them to appear separate items
- depends on wavelength or form of radiation used
- increasing magnification will not always increase the resolution
What is cell fractionation? (3.1)
- the process in which cells are broken up to obtain separated organelles
- enables the study of structure and function of organelles
What has to occur before cell fractionation? (3.1)
- the tissue must be placed in solution
-> cold to reduce enzyme activity which may break down any organelles
-> same water potential to prevent damage to cells as a result of osmotic gain or loss
-> buffered so that the pH doesn’t fluctuate, which could alter the structure or enzyme function of organelles
What are the two stages of cell fractionation? (3.1)
- homogenation
-> cells broken up by homogeniser
-> homogenate is filtered - ultracentrifugation (for animal cells)
-> filtrate spun at low speeds
-> heaviest organelles (nuclei) are forced to the bottom of the tube, where they form thin sediment or pellet
-> supernatant (the top liquid) gets removed
-> the process continues in another tube (next mitochondria)
What are the principles of an optical microscope? (3.2)
- the magnification of a specimen using the objective lenses and the further magnification with an eyepiece
- it uses waves of light
- it has a resolution of 0.2 μm
What are the principles of a transmission electron microscope? (3.2)
- the identification of a surface by passing a beam of electrons through a thin specimen
- some parts absorb electrons, which appear dark
- some transmit electrons, which appear light
- electrons are focused via a condenser electromagnet
- the image produced can be photographed, called a photomicrograph
- its resolving power is 0.1 nm
What are the principles of a scanning electron microscope? (3.2)
- the identification of a surface by projecting a bean of electrons onto a specimen
- the beam is passed back and forth along the object in a regular pattern
- the electrons become scattered depending on the contours of the surface
- it has a resolving power of 20 nm
What are the positive and negative factors of an optical microscope? (3.2)
POSITIVES
- quite portable
- cheap
- can view live specimens
- image in colour
NEGATIVES
- low resolving power
What are the positive and negative factors of a transmission electron microscope? (3.2)
POSITIVES
- high resolving power
NEGATIVES
- complex staining process required, limiting the resolution
- high energy electron beam required
- expensive
- not very portable
- a vacuum is needed, so cannot view live specimens
- not in colour
- 2D
- may result in artefacts
- object must be thin
What are the positive and negative factors of a scanning electron microscope? (3.2)
POSITIVES
- high resolving power
- image in 3D
- image in colour
NEGATIVES
- must take place in a vacuum, so live specimens cannot be viewed
- expensive
- not very portable
- complex staining process required, so limited resolving power
What is an eyepiece graticule? (3.3)
- used to measure the size of objects under a microscope
- glass disc that is placed in the eyepiece
- usually 10 m long and divided into 100 sub-divisions
- needs to be calibrated as different objective lenses have different magnifications
How do you calibrate an eyepiece graticule? (3.3)
You will need a stage micrometer, a microscope slide with a 2mm scale etched, with the smallest sub-division measuring 0.01 mm (10 μm)
1) line up the graticule to the micrometer
2) find out how many units of the graticule there are to the number of units on the micrometer
3) find how many μm a single graticule unit is worth
Define cell ultrastructure (3.4)
The internal structure of the cell that allows it to carry out functions (such as organelles)
What is the structure and function of the nucleus? (3.4)
The nucleus contains the organisms hereditary material and controls cell activity. It is usually between 10 and 20 μm in diameter. It produces mRNA, tRNA and rRNA.
- the nuclear envelope
-> double membrane that surrounds nucleus (outer membrane continuous with the ER and ribosomes)
-> controls entry and exit of material and contains reaction that are taking place - the nuclear pores
-> allows the passage of large molecules, such as mRNA out of the nucleus (3000 pores) - the nucleoplasm
-> granular, jelly-like material making up the bulk of the nucleus - chromosomes
-> consist of protein-bound, linear DNA and made of chromatin. The protein is called histones - the nucleolus
-> small, spherical region in nucleoplasm, there may be more than one
-> manufactures rRNA and assembles ribosomes
What is the structure and function of the mitochondrion? (3.4)
Are rod-shaped and 1-10 µm in size. Are the site of the aerobic stages (Krebs cycle and oxidative phosphorylation pathway) of respiration, and therefore are responsable for producing the energy carrying molecule ATP from respiratory substrates like glucose.
- cristae and mitochondria are high in number
- especially in epithelial cells, which absorb nutrients via active transport
- the double membrane
-> controls entry and exit of material, the inner membrane folds to form the cristae - the cristae
-> extensions of the inner membrane
-> large surface area for the attachment of enzymes and other proteins involved in respiration - the matrix
-> contains protein, lipids, ribosomes and DNA (allowing mitochondria to control the production of their own proteins)
What is the structure and function of the chloroplast? (3.4)
Disc shapes organelles, usually 2-10 µm long and 1 µm in diameter, that harvest sunlight and carry out photosynthesis.
- contain both ribosomes and DNA, easily manufacture proteins
- the chloroplast envelope
-> highly selective double plasma membrane - the grana
-> stacks of up to 100 disc-like structures called thylakoids
-> within a thylakoid is chlorophyll
-> some thylakoids have tubular extensions (intergranal lamella) that join onto adjacent grana
-> grana is where light absorption takes place (1st stage)
-> have a large surface area for attachment of chlorophyll, electrons carriers and enzymes - the stroma
-> a fluid-filled matrix where synthesis of sugars takes place (2nd stage)
-> within are other structures, such as starch grains
-> provides all enzymes to make sugars
What is the structure and function of the endoplasmic reticulum? (3.4)
A complex network of sheet-like membranes spreading through the cytoplasm. They enclose a network of tubules and sacs called cisternae
- cells with large quantities of carbohydrates, lipids and proteins, such as liver and secretory cells with have an extensive ER
- rough endoplasmic reticulum
-> provides a large surface area for the synthesis of proteins and glycoproteins
-> provides a pathway for the transport of material, such as proteins - smooth endoplasmic reticulum
-> often have a more tubular appearance
-> synthesises, transports and stores lipids
-> synthesises, transports and stores carbohydrates
What is the structure and function of the Golgi apparatus? (3.4)
It is similar to the SER, but is more compact. Proteins and lipids produced by the ER are passed through the Golgi in sequence. It modifies proteins by adding non-protein elements like carbohydrates. It then ‘labels’ and sorts them. These are then transported in the vesicles, which are often pinched off, where they fuse with the cell membrane. This transportation is called exocytosis.
- form glycoproteins
- produces sectretory enzymes (pancreas)
- form lysosomes
- the Golgi apparatus is especially well developed in secretory cells, such as epithelial cells
- cisternae
-> flattened sacs, like those in the SER - vesicles
-> small rounded hollows structures
What is the structure and function of the lysosome? (3.4)
Formed when vesicles contain up to 50 enzymes like proteases and lipases and are 1 µm in diameter. They also contain lysozymes (hydrolyse bacteria cell walls). Lysosomes isolate the enzymes until diffusion out of the cell or into phagocytise vesicles in the cell.
- hydrolyse material ingested by phagocytic cells (white blood cells and bacteria)
- release enzymes outside cell, to destroy material around the cell
- digests worn out organelles to recycle parts
- autolysis: completely breaks down dead cells
- in epithelial and phagocytic cells
What is the structure and function of the ribosome? (3.4)
Are small, cytoplasmic granules found in cytoplasm or RER. There are two types, 70S and 80S. The ribosome has two subunits, a large and a small, each containing rRNA and protein. They can account for up to 25% of the dry mass of the cell. They are the site of protein synthesis.
- the Svedberg unit refers to the speed of the centrifuge
- 80S
-> found in eukaryotic cells, around 25 nm in diameter - 70S
-> found in prokaryotic cells, mitochondria and chloroplasts, slightly smaller
What is the structure and function of the cell wall? (3.4)
Containing microfibrils of cellulose embedded in a matrix. They provide mechanical strength for the cell, and plant, and prevent osmotic bursting. They also allow water to ass along it, contributing to water transport through the plant.
- the cell walls of algae are made of cellulose, glycoproteins, or both
- the cell walls of fungi contain a nitrogen-containing polysaccharide called chitin, a polysaccharide called glycan and glycoproteins
- the middle lamella
-> marks boundary between cells
-> cements them together
