2.1 Cell Structure Flashcards
What was research like before and after microscopes?
Before- no knowledge of bacteria, cells, etc.
After- power to understand disease, cell division, beginnings of life, etc.
Definition of Magnification
How many times an image appears larger than the actual size of the object being magnified.
Who developed first microscope and when was the first cell observed?
Robert Hooke developed first microscope in the 17th century.
In the 19th century, an individual cell was first observed by Robert Brown.
What are cells?
Cells are basic unit of life and can only develop from existing cells.
Both plant and animal tissue is made up of cells.
Definition of Resolution
Smallest distance between 2 points that can still be seen as 2 points.
Dry Mount
-View small inanimate objects that don’t require water.
-Can be viewed whole or as thin slices.
-Eg. hair, pollen, dust.
Wet Mount
-Suspend specimens in liquid.
-Add cover slips at an angle.
-Allows small aquatic organism to be seen.
Squash Slides
-Wet mount first applied
-Pressure then applied to squash sample, so this is thin enough for light to pass through and removes excess liquid.
-Eg. mitosis in root meristem.
Smear Slides
-Edge of slide used to smear a sample creating thin, even coat.
-Cover slip added at an angle.
-Eg. Observing blood.
What is staining used for?
Used to increase contrast with different cellular components. Different cellular components take up stain to different degrees making them more or less visible.
Positively charged stains
Are attracted to negatively charged materials, staining components.
Eg. Crystal violet, methylene blue.
Negatively charged stains
Are repelled by negative cytosol (aqueous interior in cells). Dyes stay outside of cells, so cells are unstained making them more visible.
Eg. Nigrosin, Congo red.
What is differential staining?
Distinguishing between 2 types of organism that would be hard to identify. Also differentiates between different organelles of an organism within a tissue sample.
Gram positive bacteria
Has thick pepticloglycan layers so absorb surrounding materials.
Gram negative bacteria
Has thin wall so loses any stain. Then stained again with a different stain to differentiated between other types of bacteria.
What is acid-fast technique?
Distinguishes between mycobacterium and other bacteria.
Acid-Fast Technique Method
1) Lipid solvent carry’s carbolfuchsin dye to cells being studied.
2) Cells wash with dilute acid-alcohol solution. Mycobacterium are not affected and retain bright stain.
3) Other bacteria lose stain and are exposed to methylene blue stain.
Bacteria Staining Method
1) Crystal violet is applied to bacterial specimen slide.
2) Iodine is then added, fixing the dye.
3) Slide is washed with alcohol.
4)Gram positive bacteria retain crystal violet stain appearing blue.
5) Gram negative bacteria have thinner cell walls and lose the stain. They are then stained with safranin dye making them appear red.
How do electron microscopes work?
They use beams of electrons instead of light rays.
Why do electron microscopes have a higher resolution?
Electron beams have shorter wavelengths than light microscopes, which results in a higher resolution .
Millimeter to micrometer conversion
x1000 for conversion to smaller unit.
Equation for magnification
Magnification-Image size/ Actual size.
Calibration method
1) Find relationship between eye piece graticule and stage micrometer.
2) Multiply by actual size of object.
Eyepiece graticule
Ruler in the eyepiece lens.
Stage micrometer
Ruler on specimen slide.
Features of electron microscope
-x 500,000 magnification.
-Cells ultra structure is visible.
-Very expensive and hard to use.
-Specimens can be damaged by electrons.
-Complex preparation process, which can lead to artifacts.
Transmission Electron Microscope (TEM)
Beam of electrons transmitted through specimen, which is focused to produce an image.
-Similar to light microscopy.
What is the resolution of transmission electron microscopes?
0.5 nm.
What is resolution of scanning electron microscopes?
3-10 nm.
How does laser scanning con-focal microscopy work?
Single spot of focused light moves across specimen that has been marked with fluorescent dye.
Use of fluorescence in laser scanning con focal microscopy.
Fluorescence is used for absorption and re-radiation of light.
Re-radiated light in laser scanning con focal microscopy.
Re-radiated light has longer wavelength and lower energy.
Filtered through a pinhole aperture and unwanted radiation doesn’t pass through, which reduces resolution.
Application of Laser Con focal Scanning Microscopy.
-Non invasive.
- Can diagnose eye diseases
-Used in development of new drugs.
Magnification of light,TEM, SEM
Light= x 2000
SEM=x 150,000
TEM=x 1,000,000
Resolution of Light, TEM, SEM
Light=200nm
TEM=3-10nm
SEM=0.5nm
2D or 3D of Light, TEM, SEM
Light= 2D
TEM= 3D
SEM=2D
Colour of Light, TEM, SEM
Light= yes(natural colour)
TEM+SEM= no is black and white but can be coloured artificially.
Type of sample of Light, TEM, SEM
Light= Living or dead (not in a vacuum)
TEM+SEM= Dead (has to be in a vacuum)
Cost of Light, TEM, SEM
Light=cheapest
TEM+SEM= Expensive
Ease of use of Light, TEM, SEM
Light= Easy to prepare and highly accessible.
TEM+SEM= Complex preparation process, which can lead to artifacts. Large microscope so hard to move.
What is meant by the term eukaryotic?
Any cell or organism that clearly posses a defined nucleus.
What are membranes?
Membranes cover surface and are known as plasmid or cell surface membranes.
What are the functions are membranes?
-Keep all cellular components inside the cell.
-Allows selected molecules in/out of the cell.
-Isolates organelles from cytoplasm, allowing cellular processes to occur separately.
-Important in cell signalling.
What is the nucleus?
Consists of genetic material, chromatin, bound in nuclear membrane. Contains denser areas called nucleolus.
What is chromatin?
The material of which the chromosomes of organisms other than bacteria (i.e. eukaryotes) are composed, consisting of histone protein and DNA.
What is the nucleolus?
Structure in the nucleus that makes ribosomes and is composed of RNA and proteins.
What are nuclear pores?
Holes in the nuclear membrane. Allows mRNA to leave the nucleus.
What are ribosomes?
Cellular structure made of both RNA and protein. It is the site of protein synthesis.
How are ribosomes formed?
Ribosomal DNA is transcribed in the nucleolus. Forms the template for protein but folds into sub-units that pair together to form ribosomes.
Rough endoplasmic reticulum (RER)
Most ribosomes attach to this and is responsible for synthesis and transport of proteins.
Smooth endoplasmic reticulum (SER)
System of membrane bound sacs that has no ribosomes but is involved in synthesis and storage of lipids.
Transport Vesicle
Membrane sacs of ER bud off to form vesicles. Transport materials inside the cell. ER , transport to Golgi apparatus.
Golgi Apparatus
Form of cisternea with no ribosomes. Modifies proteins and packages them for specific destinations inside and outside the cell. Vesicles fuse with 1 cisternae at one end and new ones bud off at the other.
Mitochondria structure
Double membrane bound organelles. Inner membrane folds to form cristae. Fluid centre is called the matrix that contain 70s ribosomes and DNA. Site of aerobic respiration and ATP production.
Microtubules
Main component of cells cytoskeleton. They connect cells organelles, cause it move or change cell shape. Spindle fibres are a type of microtubule.
Centrioles
Made up of microtubules and occur in pairs to form centrosome. Involved in spindle fibre formation and cell division.
Microfilaments - Actin Filaments
Cytoskeleton is a network of very fine actin filaments. Not made of microtubules, but work with them to maintain or change cell shape/ help cell to move.
Cilia
Hair-like outgrowth on surface of a cell. Cilia beat to power cell movement or to move fluid across cells surface.
Where do plants get their energy from?
Plants gain their energy from the sunlight. Chloroplasts convert this energy.
Do plant cells contain vacuoles?
Plant cells contain 1 or more permanent vacuoles.
Function of the cell wall
Cell wall provides structural strength to the cell and can function as a carbohydrate store by varying amount of cellulose it holds. In plants, microfibrils of cellulose polymer.
In fungi, chitin a polysaccharide.
Cell wall in prokaryotes
Made up of peptidoglycan, but not cellulose or chitin.
What does cell wall contain?
Contains pores within the cell wall called plasmodesmata. These connect 2 cells together by cytoplasm, enabling exchange and transport of substances.
Plasmodesmata
Microscopic channels that cross cell wall of plant cells to allow transport and communication.
Function of the chloroplasts
Use water, carbon dioxide and light to build sugars . Site of photosynthesis.
Chlorplast structure
Double membranes filled with liquid called stroma and contains sacs of thylakoid membrane called grana, which are joined by lamellae. Thylakoid membranes are the site of photosynthesis.
Function of vacuoles
Permanent vacuoles only exist in plant cells. Vacuole keeps cell firm as it creates turgor pressure. Consists of a semi-permeable membrane called tonoplasts filled with cell sap.
Tonoplast
Partially permeable membrane of a vacuole that is filled with cell sap (watery solution of different substances).
Amyloplast
Double membrane bound sac around starch granules.
Prokaryote
Usually single called organism, whose DNA is suspended freely in cytoplasm, so has no nucleus. Eg. bacteria, archaea.
Are prokaryotes more complex than eukaryotes?
No, prokaryotes are simpler than eukaryotes, lacking organelles such as nucleus.
What are the evolutionary domains for prokaryotes?
-Bacteria
-Archaea
Features of prokaryotes
-Only 1 membrane and no membrane bound organelles.
-Peptidoglycan cell wall
-DNA in cytoplasm (nucleoid) -single loop/circular chromosomes.
-ATP production takes place in mesosomes.
What is the nucleoid?
Circular, double stranded DNA not surrounded by nuclear membrane. Contains most of genetic material and controls cell reproduction.
Plasmid
Small circular, double stranded DNA molecule. Can be frequently transmitted.
Mesosomes
Invagination(folded) of membrane and is where ATP is made.
Where does transcription and DNA replication take place?
Nucleoid.
Function of Capsule
Mucus-like protective layer that protects bacteria from viruses or hosts immune system by hiding antigens on cell surface. Made up of polysaccharides and contains water to protect against desiccation(drying out).
Flagella
Long helical tubes extending out of cell wall, which rotate to move the cell.
Pili
Hollow protein structures (hair-like) used during bacterial conjugation(transfer of genetic material from one bacterium to another).
Plasmids
Small continuous loops of DNA that are replicated independently of a bacterium’s chromosomal DNA.
When are plasmids commonly used?
Most commonly used in genetic engineering to make copies of genes or hormones.
What else does pilus do in terms of plasmids?
Pilus draws bacteria together and plasmids can replicate.
Lysosomes
Specialised vesicles that contain hydrolytic enzymes. They break down waste materials and old cells.
