2.1 Cell Biology Flashcards
What’s the use of Microscopes?
Microscopes can be used to observe and investigate cell structure
Types of Microscopes?
Different types of microscope can be used to study cells at different levels of detail
- Light microscopes
- Electron microscopes
What are light microscopes?
Light microscopes use light to form an image
- Maximum resolution is 0.2 micrometres (µm)
- Maximum useful magnification is ×1500
- used to observe larger structures:
= entire cells
= nuclei
= mitochondria and chloroplasts
Light Microscopes : Positives
- they are small and relatively cheap
- they can be used to produce colour images
- they allow the observation of living specimens
Light Microscope : Negatives
- they’re resolution is lower
- they’re magnification is also lower
- aren’t capable of seeing specific small structure
What are Electron Microscopes?
Electron microscopes use electrons to form an image
- Maximum resolution of 0.2 nm
- Maximum magnification from around ×1,000,000 up
Electron microscopes can be used to observe small structures inside cells:
= cell membranes
= ribosomes
- there are two types:
= transmission electron microscopes (TEMs)
= scanning electron microscopes (SEMs)
Electron Microscopes : Positives
- produces very high resolution therefore the specimen can be well investigated
- also has a very high magnification to identify certain parts
- images can be artificially coloured during processing
- helps validate studies and has 2 different types
Electron Microscope : Negatives
- they are very large and expensive
- specimens must be prepared using a highly complex process
- live specimens cannot be observed
- images are always produced as black and white
EM : Transmission Electron Microscopes
- Use electromagnets to transmit a beam of electrons through a specimen; denser parts appear darker on the final image
- TEMs produce images that:
= are high-resolution
= allow the internal structures within cells
= are two-dimensional
EM : Scanning Electron Microscope
- pass a beam of electrons across the surface of a specimen and then detect the rate at which the electrons bounce back
- SEMs produce images that:
= are three-dimensional
= show the surface of specimens
= lower maximum resolution than TEMs
What’s the Magnification Formula?
Magnification = size of Image ÷ size of Actual object
The magnification formula can be rearranged to allow the calculation of:
- magnification (M)
- size of image (I)
- size of actual size (A)
Describe conversion units in Magnification:
Units of measurement relate to each other as follows:
- 1000 nm = 1 µm
- 1000 µm = 1 mm
- 1000 mm = 1 m
- 10 mm = 1 cm
What is magnification?
Magnification:
The number of times larger an image is than the actual object
The ability of a microscope to magnify an object depends on the type of microscope, and on the features of the microscope itself
What is resolution?
Resolution:
The ability to distinguish separate points on an image as two separate objects
The higher the resolution, the shorter the distance at which the two objects can be clearly distinguished
What’s a Eukaryotic cell?
- Eukaryotic cells are larger than other cells
- their DNA is contained in a nucleus
- are complex multicellular organisms containing a range of specialized cells
EC : Cell Membrane
- cells are surrounded by a cell surface membrane
- it controls the exchange of materials between the internal cell environment and the external environment; involved in osmosis
- membrane is ‘partially permeable’
- in control of what goes inside and outside of the cell
EC : Cell Wall
- found in plant cells but not in animal cells
- cell walls are formed outside of the cell membrane
- provide structural support to the cell
- is thick and also provides protection for the cell
EC : Nucleus
- present in all eukaryotic cells
- is relatively large and separated from the cytoplasm by a double membrane
- the nuclear envelope: which has many pores
- nuclear pores: are important channels for allowing mRNA and ribosomes to travel out of the nucleus
- nucleolus: are the sites of ribosome production
EC : Mitochondria
- the site of aerobic respiration (the powerhouse of the cell)
- are just visible with a light microscope
- surrounded by double-membrane with the inner membrane
EC: Chloroplast
- Chloroplasts are found in plant cells
- Larger than mitochondria, also surrounded by a double-membrane
- Chloroplasts are the site of photosynthesis
- Also contain small circular pieces of DNA and ribosomes used to synthesise proteins needed in chloroplast replication and photosynthesis
- the green colour a result of a pigment, chlorophyll
EC: Ribosomes
- found in all cells
- found freely in the cytoplasm of all cells or as part of the rough endoplasmic reticulum in eukaryotic cells
- each ribosome is a complex of ribosomal RNA (rRNA) and proteins
80S ribosomes are found in eukaryotic cells - Site of translation
EC : Endoplasmic Reticulum (Rough)
- found in plant and animal cells
- their surface is covered in ribosomes
- formed from continuous folds of membrane continuous with the nuclear envelope
- processes proteins made by the ribosomes
- RER - site of protein synthesis and glycoprotein synthesis
- the proteins can then be transported through the RER
EC : Endoplasmic Reticulum (Smooth)
- found in plant and animal cells
- does not have ribosomes on the surface
- involved in the production, processing and storage of lipids, carbohydrates and steroids
- SER – create, store, and transport lipids and carbohydrates.
EC : Golgi Apparatus
- found in plant and animal cells
- stacks of membranes creating flattened sacs, surrounded by small round hollow vesicles.
- modifies proteins and lipids before packaging them into Golgi vesicles
- proteins that go through the Golgi apparatus are usually exported put into lysosomes or delivered to membrane-bound organelles
EC : Vesicles
- found in plant and animal cells
- a membrane-bound sac for transport and storage
- proteins and lipids are transported in the Golgi vesicles
EC : Lysosomes
- formed when the Golgi apparatus contains enzymes
- its a specialist forms of vesicles which contain enzymes (enzymes that break biological molecules down)
- break down waste materials such as worn-out organelles
EC : Centriole
- hollow fibres made of microtubules
- two centrioles at right angles to each other form a centrosome, which organises the spindle fibres during cell division
EC : Microtubles
- found in all eukaryotic cells
- makes up the cytoskeleton of the cell
- the cytoskeleton is used to provide support and movement of the cell
EC : Microvilli
- found in specialised animal cells
- cell membrane projections
- used to increase the surface area of the cell surface membrane in order to increase the rate of exchange of substances
What’s a Prokaryotic cell?
- Prokaryotic cells are simple cells that lack a nucleus and other membrane-bound organelles
- they are found in single-celled organisms such as bacteria.
PC : Plasmids
- small loops of DNA that are separate from the main circular molecule
- plasmids contain genes that can be passed between prokaryotes
- not present in all prokaryotes
PC : Capsule
- a final outer layer
- helps protect bacteria from drying out and from attack by cells of the immune system of the host organism
- not present in all prokaryotes
PC : Cilia
- hair-like projections made from microtubules
- allows the movement of substances over the cell surface
PC : Flagella
- a long, hair-like structure that rotates, enabling the Prokaryote to move
- contract to provide cell movement for example in Bacteria
- similar in structure to cilia, made of longer microtubules
PC : Pili
- for attachment to other cells or surfaces
- involved in the cells sexual reproduction
Comparison of PC and EC : Size
PC = 0.5-5 micrometres DIAMETER
EC = can be upto 100 micrometres DIAMETER
Comparison of PC and EC : Genome
PC = DNA is circular with no proteins, free in the cytoplasm
EC = DNA codes for proteins, formed into chromosomes
Comparison of PC and EC : Cell Division
PC = occurs by binary division, no spindles
EC = occurs by mitosis or meiosis and involves spindle fibres to separate chromosomes
Comparison of PC and EC : Ribosomes
PC = 70s ribosomes
EC = 80s ribosomes
Comparison of PC and EC : Organelles
PC = very few
= has no membrane-bound organelles
EC = has numerous types of mem-bound organelles
= single membrane ( Lysosomes, Golgi Complex and Vacuoles)
= double membranes ( Nucleus, Mitochondria, Chloroplast)
= no membrane ( Ribosomes, Centrioles, Microtubules)
Comparison of PC and EC : Cell Wall
PC = made up of Peptidoglycan (Polysaccharide and amino acids)
= as well as Murein
EC = present in plants (made up of cellulose) and fungi (made up of chitin)
