Cells Flashcards
What is cell fragmentation?
The process where cells are broken up and the different organelles they contain are separated out.
Why must the solution in cell fragmentation be cold?
To reduce enzyme activity that may break down the organelle.
Why must the solution in cell fragmentation be isotonic?
To prevent organelles bursting or shrinking because of osmotic gain or loss of water.
Why must the solution in cell fragmentation be buffered?
So that the pH doesn’t fluctuate as this could denature the enzymes or alter the structure of the organelles.
What happens during homogenisation?
Cells are broken up by a homogeniser (blender).
This releases organelles from the cell.
The resultant fluid (homogenate) is then filtered to remove any complete cells and large pieces of debris.
What are the two stages to cell fragmentation?
Homogenisation and ultra centrifugation.
What is ultracentrifugation?
The process by which the fragments in the filtered homogenate are separated out in a centrifuge machine.
Define resolution.
The minimum distance apart that two objects must be for them to appear as separate items. (car headlights).
What does the resolving power depend on?
The length of the wavelength,
Or form of radiation used.
What does increasing the magnification do?
Increases the size of the image.
but not always the resolution
What are the advantages of a light microscope?
- living cells can be observed
- natural colour can be seen
- movement can be observed
- specimen rarely distorted during preparation
- specimens may be living or dead
- cheap
- easy to use
- portable
What are the disadvantages of light microscopes?
- limited magnification
* limited resolution
What do the advantages of a scanning electron microscope (SEM) include?
- high magnification (x500,000)
- high resolution (10 times better than light microscope)
- a 3D image is produced
What are the disadvantages of a scanning electron microscope?
- high energy electrons can destroy specimens
- preparation distorts specimen
- vacuum needed - no living cells
- all images in black and white (no colour)
- cells dehydrated
What are the advantages of a transmission electron microscope?
- high magnification (x500,000)
* high resolution (0.1nm) - 2000x better than light microscope
Disadvantages of transmission electron microscope include…
• very thin preparations needed
• high energy electrons can destroy specimens
• preparations distorts specimens
•
What is a specialised cell?
A cell with additional features that allow the cell to carry out a particular function.
In plants, the leaf is…
An organ.
Give three examples of organ systems in humans.
The digestive system, the respiratory system and the circulatory system.
What is the difference between eukaryotic and prokaryotic cells?
Eukaryotic cells are larger, and have a nucleus bounded by nuclear membranes (nuclear envelopes)
Whereas
Prokaryotic cells are smaller and have no nucleus or nuclear envelope.
What is the role of the cell wall?
A physical barrier that excludes certain substances to protect against mechanical damage and osmotic lysis.
What is the role of a capsule?
Protects bacterium from other cells and helps groups of bacteria to stick together for further protection.
What is the role of circular DNA?
It possesses the genetic information for the replication of bacterial cells.
What is the role of a plasmid?
It possesses genes that may aid the survival of bacteria in adverse conditions, e.g, produces enzymes that break down antibiotics.
Define magnification.
How many times larger the image is, compared to the actual size of the object.
What would improve the optical power of an optical microscope?
Using short wave daylight, instead of longer wavelength artificial light.
In a mitochondrion, why is there a folding of the inner membrane?
Because this increases the surface area, and therefore there is more enzymes for aerobic respiration to take place to release ATP.
In a chloroplast, what is a stack of thylakoid membranes called?
A granum.
Which part of the chloroplast contains chlorophyll?
Thylakoid membrane.
Why might mitochondria appear as different shapes under an electron microscope?
All mitochondria share the same shape (sausage shaped). However, under the electron microscope they are sliced to create a 2D image and are in different orientations. This means they appear a different shape.
What covers RER?
Ribosomes.
What is a tissue?
A group of SIMILAR cells with common origin.
Describe how a student could find out where in a potato cell starch was present.
Add iodine and examine under an optical microscope. It will turn blue/back where starch is present.
Give ways in which the structure of chloroplasts area adapted to their functions.
- contain chlorophyll
- lots of grana increase the surface area for light absorption
- different pigments to absorb different wavelengths
- stomata contains enzymes for photosynthesis
- ribosomes for protein synthesis
Evidence that would show that the mitochondria could still function after isolation…
- measure oxygen uptake
- look for the production of ATP
In cell fragmentation, what must the conditions be?
Cold, isotonic and buffered.
Why do specimens usually need to be stained?
- to increase contrast
- to make structures (eg cells or organelles) visible
- because mist specimen are not coloured
Exactly what happens in ultracentrifugation?
- the tube of filtrate is placed in the centrifuge and spun at a slow speed
- the heaviest organelles, the nuclei, are forced to the bottom of the tube, where they for a thin sediment or a pellet
- the fluid at the top of the tube (supernatent) is removed, leaving just the sediment of nuclei
- the supernatent is transferred to another tube and spun at a faster speed than before
- the next heaviest organelles - the mitochondria - are forced to the bottom of the tube
- the process is continued so that, at each increase in speed, the next heaviest organelles is sedimented and separated out
Which organelle - mitochondria or lysosomes need to be spun at a higher speed before they are separated?
Lysosomes
What is an eyepiece graticule?
A glass piece that is placed in the eyepiece of a microscope.
What are the functions of the nucleus?
- act as the control centre of the cell through the production of mRNA and tRNA and hence protein synthesis
- retain the genetic material of the cell in the form of DNA and chromosomes
- manufacture ribosomal RNA and ribosomes
What are christae?
Extensions of the inner membrane
What is the function of christae?
To provide a large surface area for the attachment of enzymes and other proteins involved in respiration.
What is the function of RER?
Makes and transports proteins
found in animal and plant cells
What is the function of lysosomes?
Destroys (digests) dead organelles, chemicals and toxins
found in animal and plant cells
What is the function of a chloroplast?
To carry out photosynthesis.
What is the function of the golgi apparatus and where is it found?
Makes proteins
Found in animal and plant cells
What is the function of the golgi vesicles? And where are they found?
Transports proteins
Found in animal and plant cells
What is the function of the golgi apparatus and where is it found?
Makes proteins
Found in animal and plant cells
What is the function of the golgi vesicles? And where are tehy found?
Transports proteins
Found in animal and plant cells
What is magnification?
How many times larger the image is compared to the actual size of the object
What modifies proteins for excretion?
The golgi apparatus
What is a colouring process that helps to distinguish between structures?
Staining
One thousandth of a micrometer?
Nanometer
What is a cell wall?
The cellulose outer surface of the plant cell
What is a thousandth of a millimetre?
Micrometer
Largest organelle in a cell?
Nucleus
The site of photosynthesis?
Chloroplasts
The organelle where ATP is produced?
Mitochondria
The site of protein synthesis?
Ribosomes
Describe a vacuole
A water and solute filled sac that pushes the cytoplasm against the wall, keeping the cell turgid
What’s a nuclear envelope?
A double membrane surrounding the nucleus.
What is a cell that doesn’t contain a true nucleus?
A prokaryote
What is a cell that contains a true nucleus?
A eukaryote
Explain what is meant by resolution
The ability to distinguish between 2 separate points that are close together.
What is a specialised cell?
A cell with additional features that allow the cell to carry out a particular function
What is a tissue?
A group of cells with common origin
What is christae?
Extensions of the inner membrane
What are the conditions needed for the solution in cell fragmentation?
- isotonic
- cold
- buffered
A stack of thylakoids membranes is called…
A granum
How do you calculate magnification?
Magnification= size of image / size of real object
Whatever the type of microscope, what does the resolving lower depend on?
The wavelength or form of radiation used.
If the resolution of a microscope is 0.2 ym, what does this mean what you will see?
An objects greater than 0.2ym apart will be seen separately. Any objects closer than this will appear as a single object.
The greater resolution, the image produced is…?
Clearer
Cell fragmentation is the process by which…
Cells are broken up and the different organelles they contain are separated out.
What must happen before cell fragmentation?
The tissue must be placed in a cold, buffered and isotonic solution of the same water potential as the tissue
In cell fragmentation, why must the solution be cold?
To reduce enzyme activity that may break down the cell
In cell fragmentation, why must the solution be of the same water potential as the tissue?
To prevent organelles bursting or shrinking sue to osmotic loss or gain of water
In cell fragmentation, why must the solution be buffered?
So that the cell’s pH doesn’t fluctuate.
Ultracentrifugation is the process by which…
The fractions in the filtered homogenate are separated in a centrifuge machine. This spins tubes of homogenate at very high speeds to create a centrifugal force.
Describe what happens in ultracentrifugation in animal cells
- tube of filtrate is placed in the centrifuge and spun at low speed
- heaviest organelles (nuclei) are forced to bottom of tube where they form a pellet
- the fluid at the top of the tube (supernatent) is removed, leaving just the supernatent
- the supernatent is transferred to another tube and spun in centrifuge faster than before
- next heaviest organelle (mitochondria) forced to the bottom of the tube)
- process continues in this way
In ultracentrifugation, which organelle is the last to be separated?
Lysosomes because they’re the lightest
What are the two types of electron microscope?
The transmission and the scanning microscope
Limitations of the transmission electron microscope?
- specimen must be stained
- the whole system must be in a vacuum so no living specimen can be observed
- specimen must be extremely thin
- the image may contain artefacts
In the TEM, why must the specimen be extremely thin?
To allow electrons to penetrate through
Give an example of a prokaryote cell
Bacterium
Describe the general eukaryotic cell
Have a distinct nucleus and possess membrane bound organelles
Give an example of a eukaryotic cell
Epithelial cell
What are the functions of a nucleus?
- act as the control centre of the cell through the production of mRNA and tRNA and hence protein synthesis
- manufacture ribosomal RNA and ribosomes
- retain the genetic material of a cell in the form of DNA and chromosomes
Why does christae have a larger surface area?
For the attachment of enzymes and other proteins involved in respiration
What does the matrix contain?
Proteins, lipids, ribosomes and DNA
Why do mitochondria require a plentiful supply of ATP?
Because they are high in cells that have a high level of metabolic activity
What is a grana?
A stack of thylakoids membranes
What are the functions of the RER?
- to provide a large surface area for the synthesis of proteins and glycoproteins
- provide a pathway for the transport of materials, especially proteins, throughout the cell
What are the functions of the SER?
synthesise, store and transport lipids and carbohydrates
In animals, the stomach is actual of tissues such as…
- muscles to churn and mix the stomach contents
- epithelium to protect stomach wall and produce secretions
What is a prokaryotic cell?
A cell smaller than eukaryotic cells with no nucleus of nuclear envelope
Explain why there might be lots of mitochondria in a pancreatic cell
Because AEROBIC respiration takes place at these mitochondria which releases ATP because these organelles need lots of energy
How does the micro villi structure help in the absorption of substances from the small intestine?
They increase the surface area for diffusion
Under an electron microscope, why might mitochondria appear different?
All mitochondria are sausage shaped - and a e exactly the same shape. However, they are in different orientations, so when sliced to create a 2D image, they appear different.
How could a student could find out if starch was present in a thin section of a potato?
Add iodine and examine under a microscope. It turns blue where starch is present
Why is it important to cut a thin section of tissue for viewing under an optical microscope?
Because it just only be a singer layer of cells thick to allow light to pass through
Give ways in which chloroplasts are adapted to their function.
- contains chlorophyll
- lots of grana increase the surface area for light absorption
- different pigments to absorb different wavelengths
- stomata contains enzymes for photosynthesis
- ribosomes for protein synthesis
What is meant by differentiation?
L
After ultracentrifugation, how could you tell that mitochondria can still function?
Measure oxygen uptake
Look for the production of ATP
What else do plant cells have on top of th contents of animal cells?
- cell membrane
- chloroplasts
- vacuole
How are epithelial cells adapted for their function?
- They have villi which increases the surface area for absorption
- Microvilli - further increase the surface area
- Lots of mitochondria - provides energy for the transport of digested molecules into the cell.
No nucleus
Prokaryotes
No membrane bound organelles
Prokaryotes
Small ribosomes
Prokaryotes
Peptidoglycan cell well
Prokaryotes
Membrane bound organelles
Eukaryotes
Membrane bound nucleus
Eukaryotes
DNA in form of linear molecules wrapped around histones
Eukaryotes
Large ribosomes
Eukaryotes
No cell wall
Eukaryotes
How does a transmission electron microscope work?
Electrons are fired at a very thin slice of sample.
Electrons that pass through the sample are detected on a screen behind the sample.
What kind of image does a TEM produce?
2D (very high magnification and resolution)
How do scanning electron microscopes work?
Electrons bounce off sample’s surface and hit the detector
What kind of image does a SEM produce?
3D
What is used as the radiation of a light microscope?
Light
What is used as the radiation of an electron microscope?
Electrons.
Benefits of light microscope?
Can view live specimen, in colour, no vacuum. Easy slide preparation which is unlikely to distort specimen or introduce artefacts.
Problems with electron microscope?
Black and white (however colour can be added afterwards), can only view dead specimen, sample must be in a vacuum. Complex slide preparation which is kids likely to distort specimen and introduce artefacts.
What are samples stained with in electron microscopes?
Electron dense heavy metals (eg gold).
In a cell, how is a protein processed?
- Proteins are synthesised in ribosomes in the RER.
- Proteins move to golgi apparatus in vesicles.
- Golgi modifies proteins and packages them into vesicles.
- Vesicles containing modified protein are carried to cell surface membrane.
- Vesicles fuses with cell surface membrane.
- Modified proteins released from cell by exocytosis.
What is a tissue?
A collection of cells of similar types working together to perform a specific function.
What is an organ?
A collection of similar tissues working together to perform a specific function.
Where does the name of the fluid mosaic model come from?
Fluid because of the bilayer and molecules move around.
Mosaic because the molecules of different substances that make up the membrane are arranged in a mosaic.
Functions of membrane protein?
- they may act as enzymes. Enzymes that digest disaccharides are found in the cell surface membranes of the epithelial cells that line the small intestine.
- the many act as channel proteins through the membrane to allow specific ions or molecules through.
- they act as carrier proteins and play an important role in transporting substances into or out of the cell.
- they act as receptors for hormones. A hormone will only act on a cell that has the right protein receptors in its cell surface membrane or cytoplasm.
- they act as molecules that are important in cell recognition, and may act as antigens.
A bacterium (prokaryotic organism) is surrounded by a cell surface membrane. Outside this membrane is a _______ __________
Cell wall.
What’s the difference between plant cell walls and bacterial cell walls?
Plant cell walls are made of cellulose.
Bacterium contains a glycoproteins called murein.
How does a TEM work?
The TEM produces a beam of electrons that is focused onto the specimen by an electromagnet. The beam passes through a thin section of the specimen, with parts of the specimen absorbing electrons (so appearing dark) and other parts allowing light to pass through (so appearing light). A photomicrograph is produced.
Advantages and disadvantages of TEM?
A:
- high resolution (so can see internal structures)
D:
- must be in a vacuum
- staining process
- specimen must be thin
- image may contain artefacts
How does an optical microscope work?
Fire light at an object to form an image.
Advantages and disadvantages of light microscope?
A:
- can view living specimens
- produces colour image
D:
- low resolution because light has a long wavelength
Differences in prokaryotic cells and eukaryotic cells?
- prokaryotes are smaller. Eg ribosomes in prokaryotes are 70S, but in eukaryotes are 80S.
- the cytoplasm of prokaryotes has no membrane bound organelles.
- prokaryotes have no nuclei; instead, a single circular DNA molecule that’s free in the cytoplasm.
- in addition to eukaryotic cells, prokaryotes have 1 or more plasmids, 1 or more flagella, and a capsule surrounding the cell.
In centrifugation, which is the least dense organelle?
Ribosomes
In centrifugation, which is the middle density organelle?
Lysosomes
In centrifugation, which is the most dense organelle?
Nuclei
How are organelles released during homogenisation?
Cells are broken up by a homogeniser. This breaks the plasma membrane, and so releasing the organelles.
Define specialised cells.
A group of cells which have differentiated to carry out a specific function.
Define tissue.
An aggregation of similar cells that perform a specific function.
Define organ.
Tissues are aggregated into organs, that are coordinated to perform a variety of functions.
Define system.
Organs that are grouped together to perform particular functions more efficiently.
Function of cell surface membrane?
Regulates the movement of substances in and out of the cell.
Also has receptor molecules, which allows if to respond to chemicals e.g. hormones.
Function of the nucleus?
Controls cells activities (by controlling the transcription of DNA).
Its pores allow substances (e.g. RNA) to move between nucleus and cytoplasm.
Function of nucleolus?
Makes ribosomes.
Function of mitochondria?
Sure of aerobic respiration, where ATP is produced.
Found in large numbers in active cells and require lots of energy.
Function of chloroplast?
Site of photosynthesis.
Some parts occur in Granada, other in the stroma.
Function of Golgi apparatus?
Processes and packages new lipids and proteins.
Also makes lysosomes.
Function of golgi vesicles?
Stores lipids and proteins (that were made by Golgi apparatus), and transports them out of the cell via CS membrane.
Function of lysosomes?
Contains lysozymes (digestive enzymes).
These can be used to digest invading cells of break down worn out components of the cell.
Function of ribosomes?
Site where proteins are made
Function of RER?
Folds and processes proteins that have been made at the ribosomes.
Function of SER?
Synthesises and processes lipids.
Function of cell wall?
Supports cells and prevents them from changing shape.
Function of cell vacuole?
Helps to maintain pressure inside the cell and keep it rigid. This stops plants wilting.
Also involved in the isolation of unwanted chemicals inside the cell.
What is a tissue?
A collection of specialised similar cells that perform a similar function.
What is an organ?
Different tissues aggregated together, coordinated to perform a particular function.
Structure of nucleus?
Surrounded by nuclear envelope which contains many pores.
Nucleus contains chromosomes.
Structure of mitochondria?
Oval shaped.
Double membrane.
Inner membrane is folded into christae.
Inside is the matrix (which contained enzymes involved in respiration).
Structure of chloroplast?
Surrounded by double membrane.
Contains thalakoid membranes, which are stacked up in some parts to form grana - linked together by lamallae (thin, flat pieces of thalakoid membrane).
Structure of Golgi apparatus?
Group of fluid filled, membrane bound flattened sacs.
Vesicles often seen at the edge.
Structure of ribosomes?
Made of proteins and RNA.
No membrane.
Difference between RER and SER?
RER has ribosomes attached (SER doesn’t).
RER folds and processes proteins that’ve been made at ribosomes, but SER synthesises and produces lipids.
Structure of cell wall?
Rigid structure that surrounds cells in plants, algae, fungi.
Made of cellulose.
Structure of cell vacuole?
Found in the cytoplasm of plant cells.
Contains cell sap.
Main difference between prokaryotes and eukaryotes?
Eukaryotes are larger and have a nuclear envelope.
Prokaryotes are smaller and have no nucleus or nuclear envelope.
How do prokaryotes replicate?
By binary fission
Outline binary fission
- The circular DNA and plasmids replicate.
- The cell gets bigger and DNA loops move to opposite piles of the cell.
- The cytoplasm begins to divide.
- Two daughter cells are produced. Each one has a copy of the circular DNA but can have a variable number of plasmids.
Why can some viruses only infect one type of cell?
Because they have diff receptor proteins, therefore require diff receptor proteins on host cells.
How do viruses use host cells?
Viruses use their attachment proteins to bind to complementary receptors on the surface of host cells. Then they inject their DNA or RNA into it.
Outline how ATP is converted into ADP.
When energy is needed, ATP is hydrolysed into ADP and Pi.
A phosphate bond is broken and energy released. This is catalysed by ATP hydrolase.
Outline how ADP is converted into ATP.
A condensation reaction between ADP and Pi (using ATP synthase) re-synthesises it into ATP.
What is an ion?
An atom with an electrical charge.
What is a cation?
Ion with positive charge.
What is an anion?
Ion with negative charge.
What is an inorganic ion?
One which doesn’t contain carbon.
Give an inorganic ion and its use.
Iron ion. This binds to the oxygen in haemoglobin. When oxygen is bound, the Fe2+ ions becomes Fe3+.
Hydrogen ions. The more H+ present, the lower the pH (more acidic).
