A2.2 Cell Structure Flashcards
Function of Mitochondria
- Site of aerobic respiration (release energy)
Function of ribosome
- Site of protein synthesis
Function of cell membrane
- Controls movement of substances in and out of cell
What is Cytology
Study of cells.
Cell theory statements
- All organisms are made up of one or more cells.
- Cells are the smallest unit of life.
- All cells come from pre-existing cells.
Why are microscopes used?
Microscopes with high magnification and resolution helps make cells visible as they are very small.
Define Magnification
Number of times larger an image is than the object.
Define Resolution
Minimum distance between two points which they can still be distinguished.
Difference between Light microscopes and Electron microscopes
- Light: Inexpensive; specimen prep is simple; magnifies up to 2000; specimens can be dead or alive. Image can be in color.
- Electron: Expensive; preparation of specimens is very complex; magnifies up to 500000; specimens have to be dead. Image is produced in black and white.
Converting units
μm = 1000 x mm
nm = 1000 x μm
Magnification calculation
Total magnification = Ocular x Objective
Magnification = Image size/ specimen size
Example question: Object has been magnified x31000 and measures 43mm in length. What is its actual size in nm?
Object size = image / magnification
43/31000 = 0.001387
0.001387 x 1000 = 1.387μm
Types of electron microscope
Transmission electron microscope (TEM): beam of electron is transmitted through a specimen and focused to produce an image. Similar to light microscopy. Has excellent resolution (resolving power of 0.5nm). Has magnification of up to 500,000.
Scanning electron microscope (SEM): a beam of electrons is sent across the surface of a specimen and the reflected electron are collected. Has good resolution (resolving power of 3-10nm). Has magnification of up to 100,000. Can produce 3D images.
Explain what is meant by an Artefact
- Structures that are produced due to perpetration process, not actually a feature of the specimen.
- Can be found in light microscopy as well. Bubbles trapped under coverslip are artefacts.
- Artefacts are inevitable in electron microscopy. Experience allows scientists to distinguish between artefacts and actual structures.
Explain Freeze-fracture
- A process of preparing a sample for electron microscopy: Specimen is rapidly frozen then physically broken apart.
- This reveals a plane through a sample: vital for understanding the structure of the cell membrane
Explain Cryogenic electron microscopy
- Recent advancement in electron microscopy.
- Revolutionary in understanding structure of viruses and other cellular proteins.
- How it works: specimens are frozen in ice using very low temp and an image formed using computer enhancements that shows the 3D framework of proteins integral to cell functioning.
Microscopy and technique used to study different structures within living organisms’ cells
- Light microscopy.
- Fluorescence: cells are stained with special dyes that bind to specific cellular components. When UV is shone on specimen, the parts that the dye bind to fluoresce.
- Immunofluorescence: antibodies combined with the dye are added to the specimen. The antibodies bind to their target. This allows specific parts of the cell to be visible when UV light is shone.
Structures common to all cells
- DNA: as their genetic information
- Cytoplasm: mainly composed of water
- Plasma membrane: composed of phospholipids which surround the cytoplasm.
Features of Prokaryotes
- Believed to have been among first life forms on earth
- 10-100 microns in size
- single-celled (unicellular) or
- Filamentous (strings of single cells)
