Studying Cells Flashcards
Contrast the structures of prokaryotic and eukaryotic cells (7)
Where is pili found?
In prokaryotic cells
What is the role of a pili?
-May connect between bacteria allowing horizontal DNA transfer between bacteria
Describe prokaryotic cells/bacterial cells (2)
-prokaryotes do not have a nucleus or other membrane bound organelles
-The DNA of a prokaryotic cell is circular and is not associated with histones
What is the cell wall in prokaryotic/bacterial cells made of?
PEPTIDOGLYCON (NOT CELLULOSE)
What type of ribosomes do a prokaryotic cells have?
70 S
What part of eukaryotic cells have 70s ribosomes?
Chloroplasts and mitochondria
Describe what a virus is
-acellular
-Not alive
-Very small
-Require a living cell to replicate inside
Describe the structure of a virus (4)
-contains DNA or RNA, (which can be single or double stranded)
-Surrounded by a protein coat called a capsid
-Also a virus has attachment proteins which enable it to bind to host cells
-Has enzymes that it uses to replicate genetic information and insert into the host cell DNA
What can viruses not do because they have no organelles?
-They’re unable to replicate independently so they can’t synthesise proteins or DNA to make copies of themselves
-They need to use host cell organelles to do this
Create a table for the features of prokaryotic cells, viruses and eukaryotic cells
Describe the features of a light microscope
-Specimen are illuminated with light (can be living or dead)
-Focus using glass lenses and viewed using the eye
-organelles need to be stained with a dye to make them more visible
-Can magnify by a larger amount (x1500)
-At higher magnification the microscope loses resolution
What is the resolution of light microscope limited by?
The wavelength of light (400-600 nm for visible light)
If the wavelength of the light/electrons is shorter what happens to the resolution?
Resolution is better
Name two structures found within a eukaryotic cell that cannot be identified using an optical microscope
Any two from
Mitochondria/ribosome/endoplasmic reticulum/lysosome/cell surface membrane
What are the two types of electron microscope?
-transmission electron microscope (TEM)
-Scanning electron microscope (SEM)
What is the difference between a transmission electron microscope and a scanning electron microscope?
TEM produce 2D images
SEM produce 3D images
What do both types of electron microscopes use?
-A beam of electrons to illuminate the specimen (rather than light)
-Electrons can be easily produced and focused using electromagnets and detected using a Phosphor screen or photographic film
-Electrons have a very small wavelength so they can produce images with higher resolution
Describe transmission electron microscopes
-electrons passed through the specimen (must be dead & kept in a vacuum )
-less dense areas absorb less electrons and appear lighter, dense areas absorb more electrons so appear darker
-Allow you to view organelles and internal structures
Describe scanning electron microscopes
-specimens are not sliced and electron bounce off the surface of the specimen
-images are always in black-and-white
-They always produce a 3D image
Give a summary table of the comparison of electron and light microscope
Describe the principles and the limitations of using a transmission electron microscope to investigate cell structure (5)
Principles (how it works)
Limitations (drawback/disadvantages)
Give one advantage of using a TEM rather than an SEM
Higher resolution/higher magnification/higher details
OR
Allows internal details or structures to be seen within cells
Give one advantage of using an SEM rather than a TEM
Thin sections do not need to be prepared/show surface of specimen/ can have 3-D images
Scientist use optical microscopes and transmission electron microscopes to investigate cell structure. Explained the advantages and limitations of using a TEM to investigate cell structure
advantages:
-Small objects can be seen
-TEM has higher resolution
-wavelength of electron shorter
Limitations :
-Cannot look at living cells
-Must be in a vacuum
-Must cut section/thin specimen
-Preparation may cause artefacts (false images)
Describe how you could make a temporary mount of a piece of plant tissue to observe the position of starch grains in the cell when using an optical (light) microscope
- add a drop of water to the microscope slide
-Get a thin section of plant tissue and float on the drop of water
-stain with KI solution
-Lower the cover slip using a mounted needle to avoid air bubbles
When using an optical microscope, which two pieces of equipment are required?
Eyepiece lens graticule and stage micrometer
Describe how to convert units and give some examples
What is the equation for magnification?
Why must cell fractionation and differential centrifugation occur
To separate organelles from the cell for electron microscopes
What is the name of the method of separating organelles and describe it?
- homogenising
-Tissue is homogenised and blender to break up the cells releasing and organelles into a solution
-filter to the mixture to remove any large pieces of tissue/cellular debris producing a solution of suspended organelles
When homogenising a solution, what must the solution be and why?
- ice cold-reduces action of enzymes that would digest organelles
-Isotonic (same water potential)- prevents osmosis of water in or out of organelles so organelle don’t burst or shrivel
-Buffered-to stop pH changes which could denature proteins
Describe how differential centrifuge of the supernatant can occur
- centrifuge at a high speed ( dense organelles are forced to the bottom of the tube into a pellet which is removed) the supernatant can be spun again to obtain smaller organelles
- Centrifuge at a higher speed-the next densest organelles are forced to the bottom of the tube into a pellet. This pellet is removed and can be suspended.
-This process can be repeated many times at higher speed with each step (this separates organelles according to their densities)
Describe how you could use cell fractionation to isolate chloroplasts from leaf tissue (3)
- Break up the cells in a blender/homogeniser and filter to remove cellular debris
-Place in an ice cold, isotonic, buffered solution
-Use differential centrifugation
-Chloroplasts are in the second pellet
What are eukaryotic cells?
-Cells with the true nucleus that have membrane bound organelles
-Linear DNA molecules called around histone proteins to form chromatin
What are the four eukaryotic kingdoms?
-animalia
-Plantae
-protostica (algae)
-Fungi (unicellular yeast cells)
Give some examples of eukaryotic cells
Plants
Animal
Fungi
Algae
Protozoan
Draw a eukaryotic/animal cell
Draw a eukaryotic/animal cell
What organelles are found within eukaryotic cells?
-Nucleus
-Mitochondria
-Rough endoplasmic reticulum
-Smooth endoplasmic reticulum
-Cytoplasmic ribosome
-Golgi apparatus/body
-lysosome
-Cell surface membrane
-Centrioles
Describe the structure of a nucleus within a eukaryotic cell
-nuclear envelope/double membrane and pores
-Chromosomes/chromatin (DNA associated with histones)
-Nucleolus
Describe the function of a nucleus within a eukaryotic cell
-stores genetic information for polypeptide production
-Site of DNA replication
-Site of production of mRNA (transcription) and TRNA
-Site of production of rRNA/ribosomes (nucleolus)
Describe the structure of mitochondria in eukaryotic cells
-double membrane (between inner and outer membrane /inter-membrane space- filled with fluids )
-Inner membrane highly folded to form (increase surface area)
-Matrix (liquid part) containing mitochondrial DNA, ribosomes, proteins, and lipids
Describe the function of mitochondria in eukaryotic cells
-Site of ATP production by aerobic respiration
-Cells that need a lot of ATP have lots of mitochondria e.g muscle cells (for muscle contraction) and epilethial cells (for active transport of ions)
Describe the structure of the rough endoplasmic reticulum in eukaryotic cells
-Highly folded membranes with 80S ribosomes embedded
-The membrane is folded into flattened sacks called cisternae
-Joined to the nucleus
Describe the function of the rough endoplasmic reticulum in eukaryotic cells
- synthesise and transports proteins throughout the cell
-Cells which make lots of protein e.g antibodies have lots of rough endoplasmic reticulum (antibodies producing plasma cells)
Describe the structure of the smooth endoplasmic reticulum in eukaryotic cells
Highly folded membranes flattened into sacks called cisternae
Describe the function of the smooth endoplasmic reticulum in eukaryotic cell
-recombines glycerol and fatty acids to make triglycerides
-Packages triglycerides into vesicles and transports them to the golgi apparatus
Describe the structure of the cytoplasm ribosome in eukaryotic cells
-made up of two sub units that are made of long strands of RNA and ribosome proteins
-Eukaryotic cells contain 80s cytoplasmic ribosomes
Describe the function of cytoplasmic ribosome in eukaryotic cells
Site of protein synthesis from amino acids
Describe the structure of the Goldie apparatus/body in eukaryotic cells
-flattened sacs made of membrane filled with fluids
-Golgi vesicles pinch off from the main membrane
Describe the function of the Golgi apparatus in eukaryotic cells
- Sorts, modifies and packages proteins and triglycerides into vesicles
-Golgi vesicles may be used to form lysosomes
-Cells with extensive Golgi, packages lots of molecules for export
Describe the structure of lysosomes in eukaryotic cells
- Membrane bound organelle that stores and releases many hydrolytic enzymes
Describe the function of lysosomes in eukaryotic cells
-contains hydrolytic enzymes- phagocytes are a type of white blood cell that contain many lysosomes, as they hydrolyse invading pathogens
Describe the structure of cell surface membranes in eukaryotic cells
-made up of phospholipids, specific transport proteins, and carbohydrates arranged into what is described as fluid mosaic model
Describe the function of cell surface membrane in eukaryotic cells
Controls the passage of molecules in and out of the cell
Describe the structure of centrioles in eukaryotic cells
-microtubules
Describe the functions of centrioles in eukaryotic cells
-from a network of spindle fibres onto which chromosome attach
-Pull chromosomes/chromatids apart during mitosis
-THESE ARE ONLY FOUND IN ANIMAL CELLS (NOT PLANT CELLS)
Draw a plant cell (eukaryotic)
Describe the structure of chloroplasts and the function of each organanelle
-granum- stack of thylakoid membranes
-thylakoid membrane- contains chlorophyll for photosynthesis and ATP synthase enzyme to produce ATP
-Stroma- fluid filled part, some of the photosynthetic reactions occur heee
-starch grains- the energy storage molecule in plants
-DNA and ribosomes- contain their own DNA and 70s ribosomes for synthesis of enzymes needed for photosynthesis
Describe the structure of cellulose cell walls (in plants and algae)
-very strong (many weak hydrogen bonds between cellulose fibrils), this limits the volume of water that can move into the cell and stop osmotic lysis (bursting)
-The wall is permeable to most molecules, unlike the membrane
-Has plasmodesmeta which has gaps in the cell wall that connects cytoplasms together to allow water soluble molecules to move easily
Describe the key differences between plant and animal cells
