Cells & Viruses Flashcards
What are the two types of cells
Prokaryotic and eukaryotic
Give 3 examples of eukaryotic cells
Animal cells, plant cells, fungal cells
What are the three types of microscopes
Light microscope
Electron microscope
Transmission electron microscope
Define the term resolution
The ability to discriminate fine detail, two neighbouring points are seen as separate
Why does the electron microscope have better resolution?
Electrons have a shorter wavelength than light
What is the main advantage of using a light microscope?
Living processes such as mitosis can be observed
The interior of an electron microscope is a vacuum therefore the specimens have to be dead
Give 3 comparisons of light microscopes and transmission electron microscopes
Light:light reflected by glass lens
TEM:beams refracted by electromagnetic lenses
Light:Low magnification 1500X maximum
TEM: High magnification 1 000 000X maximum
Any others from:
TEM have higher resolution
Image formed on the retina from Light microscopes but imagine is formed on fluorescent screen in TEM
Light microscopes can view living specimens, TEM can’t
What is the difference in the scanning electron microscope (SEM) and transmission electron microscope (TEM)?
TEM specimens are coated in a film of gold so electrons reflect off the surface to create a 3D effect image
Describe the process of homogenisation
Place chopped up specimen into a cold isotonic buffer solution
Blend the tissue to break open cells releasing the organelle
Filter the mixture to remove debris
Describe the process of centrifugation
Mixture is spun so the denser parts are thrown to the bottom, forming a sediment
The supernatant is poured into a tube leaving the sediment ( contains the nucleus )
This is repeated at higher speeds multiple times to retrieve different organelles
Describe a safety precaution of using a centrifuge
Having an equal mass/ counter balance
Why is it a cold isotonic buffer solution?
Cold- to reduce enzyme activity which could break down organelles
Isotonic- to prevent the organelles bursting from osmosis
Buffer- to maintain a constant pH so enzymes/proteins aren’t denatured
Compare the cell walls in eukaryotic cells
Animal- none
Plant- cellulose
Fungal- chitin
Describe the types of granules found in eukaryotic cells
Animal- Glycogen
Plant- Starch
Fungal- Glycogen
Which eukaryotic cells have lysosomes
Animal and fungal
Which eukaryotic cells have vacuoles
Plant
Fungal
Describe the structure of the nucleus
Largest organelle enclosed within a double membrane , contains chromatin and nucleoli
Outline the function of the nucleus
Nuclear pores allow large molecules in and out of the nucleus.
Nucleolus synthesis ribosomal RNA and manufactures ribosomes
Describe the structure of ribosomes
Small bodies of protein and RNA
Either attached to RER or free in cytoplasm
Outline the function of ribosomes
Site of polypeptide synthesis
Free ribosomes will produce proteins that will function within the cytoplasm
Describe the structure of RER
It is a membrane system with flattened sacs, it continues with the outer nuclear membrane, covered with ribosomes
Describe the role of RER
The polypeptides made on the ribosomes accumulate in the rough ER to be passed on,in vesicles, to the Golgi apparatus
Describe the structure of SER
membrane system of interconnecting tubules
Describe the role of SER
synthesis of lipids and their distribution throughout the cell
Describe the structure of the Golgi apparatus
A stack of membrane bound sacs ( called cisternae)
Formining face has vesicles from the rough ER joining it
Mature face has vesicles pinching off
Describe the role of the Golgi apparatus
Polypeptides are combined ( to form quaternary proteins ) or modified ( e.g glycoproteins )
Finished proteins are packaged into vesicles either for secretion by exocytosis or delivery within the cell
Describe the structure of lysosomes
Vesicles produced by the Golgi apparatus that contain hydrolytic enzymes
Describe the role of lysosomes
They combine with membrane-bound degenerate organelles ( or ingested particles )
This forms secondary lysosomes
Hydrolytic enzymes digest the contents
Describe the structure of mitochondria
Sausage shaped surrounded by a double membrane, inner membrane is folded into cristae
It has a fluid-filled matrix
Outline the role of mitochondria ( mitochondrion)
Synthesis of ATP by aerobic respiration
Describe the structure of chloroplasts
Ovoid, surrounded by a double membrane, has a system of lamellae with thylakoids stacked into grana, also contain lipid droplets and starch grains
Outline the role of chloroplasts
Site of photosynthesis
Chlorophyll molecules are attached to the lamellae
Describe the structure of a vacuole
Large permanent structure, membrane of the sap vacuole in plant cells is called the tonoplast
Outline the role of a vacuole
Storage of water and ions
Describe the structure of microtubules
Tubular, formed from the protein Tubulin, Occur within centrioles and throughout the cytoplasm, animal and fungal cells both contain a pair of centrioles.
They occur as nine triplets of microtubules in a circular arrangement
Outline the role of microtubules
Centrioles form the spindle fibres during cell division, microtubules also form part of the cytoskeleton and allow movement of cell organelles
Describe the structure of microvilli
Finger-like folds of the cell surface membrane
Outline the role of microvilli
Increases the surface area for absorption of molecules and ions
Describe the structure of Plasmodesmata
Strands of cytoplasm between neighbouring plant cells that pass through pores in the walls
Outline the role of plasmodesmata
Allow the transport of materials between adjacent plant cells
What are viruses measured in and what is their typical range of size
They are so small they are measured in manometers (10nm-300nm)
Describe the structure of a virus
Encased in a protein coat that surrounds nucleic acid (the nucleic acid can be DNA or RNA)
What is the structure of a phage and what do they do?
Bacteriophages or phages have a DNA core and parasitise bacteria.
Inside their hosts (bacteria), the viral DNA codes for new proteins to make the capsid
The DNA replicates to make lots of new copies that are packaged within these protein coats, forming new viruses.
The bacterial cell ruptures releasing lots of new viruses to continue the cycle. The bacterial cell is destroyed in the process.
Describe the structure and function of a retrovirus e.g HIV
Retroviruses have an RNA core
This RNA is encased in protein coat and surrounded by a lipid bilayer containing glycoprotein.
The RNA is delivered into the host cell by the retrovirus, along with the enzyme reverse transcriptase.
Reverse transcriptase catalyses the formation of DNA from
this RNA.
This DNA is used to synthesise new viruses, by making
protein coats and viral RNA.
Normally, DNA is used to synthesise RNA, however in retroviruses the reverse happens and the RNA is used to make DNA.
Why does HIV cause immunity problems
because it invades a particular lymphocyte called a helper T- cell.
Helper T cells are important in protecting against disease. The more cells that are invaded the less effective the immune system, until it becomes critically compromised, and AIDS may develop.
Describe 3 features of a prokaryotic cell
The earliest formed organisms
They have no “true” nucleus.
Cell or organism’s DNA is not organised into chromosomes and is not surrounded by a nuclear membrane
They possess naked, circular DNA, small ribosomes, possibly plasmids and a cell wall made of peptidoglycan or murein.
There are no membrane bound organelles.
Examples include Bacteria and blue green algae
Describe Fungal cells 7 features
A cell wall made of chitin
Often contain a vacuole
Glycogen as a carbohydrate store
Lysosomes
Often multinucleate (many nuclei within each cell)
They do NOT photosynthesise and do NOT have chloroplasts
Many fungal cell appear long and have elongated threads of hyphae that spread through the substrate
