Chapter 3: Cell Structure Flashcards
What is a microscope?
An instrument that produces a magnified image of an objet. The most common types are the light and electron microscopes.
Equation for magnification:
Magnification= size of image/ size of real object
What are the units and orders of magnitude for:
Kilometres
Metres
Millimetres
Micrometres
Nanomoteres
Kilometres: km: 103
Metres: m: 1
Millimetres: mm: 10-3
Micrometres: μm: 10-6
Nanometres: nm: 10-9
Define resolution:
The minimum distance apart that two objects can be in order for them to appear as seperate items. This depends on the wavelength or the form of radiation used in a microscope.
Increasing the magnification _________ increase the resolution, especially if the _____________ has been reached.
Does not always
Limit of resolution
Define cell fractionation:
The process where cels are broken up and the different organelles are separated out.
Why is tissue placed in a cold, isotonic buffer solution before cell fractionation can begin?
Cold: to reduce the effects of enzyme activity that would result in cell digestion
Isotonic: to prevent organelles bursting or shriking due to osmosis
Buffered: so that pH does not fluctuate and denature cell membrane poteins and compromise the cell
Descripe hypertonic, isotonic and hypotonic in terms of concentration and water potential:
Hypertonic: Highly concentrated, low water potential
Isotonic: Same concentration, same water potential
Hypotonic: Low concentation, high water potential
IMPORTANT: these words describe the solution outside a cell/organelle
Define homogenation:
The first stage of cell fractionation. Te breadown of cells into a homogenate fluid using a homogeniser/blender. Large pieces of debis are filtered away.
Define ultracentrifugation:
The second stage of cell fractionation. A process in which cell fragments in the filtered homogenate are separated in a centrifuge.
Briefly explain the method for ultracentrifugation:
1) Filtrate is initially placed in a centrifuge and spun at a slow speed.
2) The heaviest organelles are forced to the bottom and form a thin sediment/pellet.
3) The fluid at the top of the tube (supernatant) is removed so it can be spun at a faster speed than before.
4) This process is repeated until all of the organelles have been separated into different test tubes.
What can scientists find out from the cell fractionation process?
The structure and function of organelles.
Name 4 advantages of the electron mircroscope:
- Very short wavelength
- High resolving power
- Focusing using electromagenets rather than mirrors
- Magnifies over 500 000 times
Name 9 disadvantages of the electron microscope:
- Expensive to buy (over £1 000 000)
- Expensive to produce electron beam
- Large, special room required
- Lengthy and complex sample prep (including heavy metal stain)
- Artifacts are often produced
- Vacuum is required
- All images are in black and white
- Specimens must be dead
- Electron beam can damage specimens
Name 8 advantages of the light microscope:
- Cheap to buy (£100-500)
- Cheap to operate
- Small and portable
- Simple and easy sample preparation
- Material is rarely distorted
- No vaccum required
- Natural colour of sample is maintained
- Specimens can be living or dead
Name 4 disadvantages of the light microscope:
- Only magnifies objects up to 2000 times
- Stains are often needed to make cells visible
- Poor resolution
- Relatively long wavelength
What is a transmission elecron microscope?
A microscope which produces images by photographing a screen containing the sample (photomicrographing). The image is produced as some parts of the sample absorb electrons and others reflect it. The resolution is up to 0.1nm.
What is a scanning electron microsope?
A microscope that produces an image by passing a beam back and forth across a specimen in a reguar patern to produce a 3D image. It has a lower resolving power than the TEM but thicker samples can be used (more convenient).
What is an eyepiece graticle?
A glass disc that is placed in the eyepiece of a microscope with a scale etched on to measuer the size of objects.
How can an eyepiece graticulebe used to measure the dimensions of a cell?
It must be callibrated using a stage micrometer slide.
Define cell ultrastructure:
The internal structure of a cell, specialised to its particular function.
What is the nucleus?
An organelle containing hereditary material belonging to the organism. It controls the cells activities, is ususally spherical and is between 10 and 20 micrometers.
Name all 5 parts of the nucleus:
- Nuclear envelope: a double membrane which surrounds the nucleus, attatching it to the ER, containing all of th reactions and controlling the movement of materials in and out of the cell.
- Chromatin: the materials which chromosomes are composed of.
- Nucleoplasm: a granular and jelly- like material which makes up the bulk of the nucleus.
- Nuclear pores: pores which allow for the passage of large materials out of the nucleus. There are generally around 3000 pores, each 40-100 nm in diameter.
- Nucleolus: the manufacturer of ribosomal RNA. Assembles ribosomes.
What is the mitochondrion?
Mitochondria are rod shaped, 1-10 micrometer long organelle which act as the site of aerobic respiration (so produce ATP). The more active the cell, the more mitochondria it contains.
Name all 3 parts of the mitochondria:
- Double membrane: controls entry and exit of materials.
- Cristae: an extension of the inner embrane which increases the surface area for attatchment of enzymes/ proteins for respiration.
- Matrix: storage site of proteins, lipids, ribosomes, DNA and respiratory enzymes.
What are chloroplasts?
The organelle in which photosynthesis is carried out in. They are disc shaped and 2-10 micrometers long and 1 micrometer in diameter.
Name the 4 parts of the chloroplast:
- Chloroplast envelope: a double plasma membrane for selective material entry and exit.
- Thylakoid: these contain the photosynthetic pigment chlorophyll.
- Granum (pl. grana): stacks of thylakoids which are interconnected by tubular extensions called intergranal lamella. This is the site of the first stage of photosynthesis.
- Stroma: the fluid-filled matrix which is the site of the second stage of photosynthesis.
What is the endoplasmic reticulum?
An elaborate, 3D system of sheet- like membranes which spreads across the cytoplasm.
What are the two types of endoplasmic reticulum and what are their functions?
Rough ER: has ribosomes on its outer surface so provides a large SA for protein synthesis and provides a pathway for the transportation of materials (especially synthesised proteins).
Smooth ER: lacks surface ribosomes so is generally more tubular in appearance. It synthesises, stores and transports lipids and carbohydrates.
