Cell structure Flashcards
Define magnification
How much bigger the image appears, compared with the size of the object
What is the effect of increasing the power of an microscope?
More powerful microscope= higher magnification but not necessarily greater resolution
Define Resolution
The clarity of an image: how well a microscope distinguishes between 2 points that are close together.
What is the name of the most common and first microscope?
Optical (light) Microscopes
How do optical (light) microscopes form an image?
They use a beam of light (focused by lenses) to form an image.
What are the advantages of the optical (light) microscope?
- cheap
- easy to use
- simple sample prep
- portable
- specimen can be living or dead
- coloured images formed
What are the disadvantages of the optical (light) microscope?
- low magnification and resolution so they can’t see ribosomes.
- can’t use florescent dyes
What type of radiation does light (optical) microscopes use?
Visible light
Why is the resolution of optical (light) microscopes low?
They have a relatively long wavelength of light.
How do laser scanning microscopes create an image?
They use a high power beam of light or
laser of light) to create an image (computerised image
How does a Laser Scanning Microscope create an image?
The laser passes over each point in the specimen and a computer assembles the pixel information into 1 image.
What are the advantages of the laser scanning microscope?
- specimen can be living or dead
- higher resolution than light microscope.
- have depth selectivity =>so it can focus on structures at depth selectivity
- you can visualise whole, living specimens rather than just cells
How do electron microscopes create an image?
Use a beam of electrons, which is fired from a cathode and focused on the specimen by magnets
How do electron microscopes have high resolution?
The electron beam has a short wavelength.
Why can electron microscopes only view dead specimens?
The specimen has to be coated with a fine metal sheet and placed in a vacuum.
How do scanning electron microscopes form 3D images?
The electron beam hits the specimen and is scattered into a detector
What is the orientation of the detector on a scanning electron microscope?
The detector is on the side forming 3D images.
What’s a disadvantage of a SEM in comparison to a TEM?
It has lower magnification and resolution
Define photograph
Photograph of an image seen using an optical microscope
Define electron micrograph
Photograph of an image seen using an electron microscope
What are the advantages of Electron microscopes?
- High magnification and resolution
- Can use florescent dyes
What are the disadvantages of Electron microscopes?
- expensive to buy and operate
- large and needs to be installed
- complex staining/sample prep
- risk of artefacts
- black and white images
- specimens are dead cuz of prep
What medium do light microscopes use to create an image?
Light beam
What medium do laser scanning electron microscopes use to create an image?
Light beam
What medium do SEM microscopes use to create an image?
Electron beam
What medium do TEM microscopes use to create an image?
Electron beam
What is the sample prep for light microscopes?
Simple preparation
What is the sample prep for laser scanning microscopes?
Simple preparation
What is the sample prep for SEM?
Complex staining Process
What is the sample prep for TEM?
Complex staining process- requires a very thin sample to allow electrons to penetrate.
Dimensions for light microscopes
2D
Dimensions for laser scanning microscopes
3D
Dimensions for SEM
3D
Dimension for TEM
2D
What is the max magnification for light microscopes?
x1500
What is the max magnification for laser scanning microscopes?
x1500
What is the max magnification for SEM?
x200,000
What is the max magnification for TEM?
2,000,000
What is the max resolution for light microscopes?
200nm
What is the max resolution for laser scanning microscopes?
160nm
What is the max resolution for SEM?
20nm
What is the max resolution for TEM?
0.1nm
Do light microscopes use coloured or black and white images?
Coloured
Do laser scanning microscopes use coloured or black and white images?
Coloured
Do SEM use coloured or black and white images?
Black and White
Do TEM use coloured or black and white images?
Black and white but computer software can add false colour
What is the magnification formula?
Magnification=Image size/Actual Size
Why do structures like chlorophyll not require staining?
Some structures, e.g. chlorophyll, naturally modify light as it passes through, making them easy to visualise with a microscope.
What is Staining?
Staining is a technique where dye is used to highlight cells and cell structures, making them easier to visualise in a microscope.
What is differential staining and how does it work?
Stains work by binding to different types types of molecules or cell structures. This allows different components of cells can be identified.
What does Acetic orcein Stain?
Acetic orcein binds to DNA allowing the chromosomes and nucleus to be visualised
What does Eosin stain?
Eosin stains cytoplasm
What does Sudan Red stain?
Sudan Red stains lipids
What does Iodine stain?
Iodine stains starch granules dark purple and plant cell walls yellow
How do some microscopes produce a clear image of a colourless, transparent specimen without staining?
Some microscopes use light interference, rather than light absorption.
Others use dark background against which the illuminated specimen can be seen.
Are eukaryotic cells simple or complex and give examples?
Complex and include plant, animal and fungal cells.
Are prokaryotic cells smaller/bigger/complex/simpler than eukaryotic cells?
Prokaryotic cells are smaller and simpler.
What is ultrastructure?
The internal structure of a cell.
Define organelles
Components of cells which perform a specific function
Are eukaryotic cells membrane bound?
Yes, they are membrane-bound (covered in a membrane), therefore separated from the rest of the cell.
What is the function of the nucleus?
- store and transmit genetic information
- provide the instruction(mRNA) for protein synthesis
- acts as the control centre of the cell
How is the nucleus separated from the rest of the cell?
By the nuclear membrane
Is the nuclear membrane double or single?
double
What is the importance of the nuclear pores in the nuclear membrane?
Nuclear pores allow mRNA and ribosomes to pass through.
Pores also allow substances (e.g. steroid hormones) to enter the nucleus.
What do the nuclei(nucleolus) contain and what is the function?
- contain densely packed DNA and protein
- this is where rRNA is manufactured and ribosomes are assembled.
What is chromatin and how is it made? How are chromosomes made?
- DNA is tightly packaged through the association with histone proteins forming chromatin.
- chromatin is the genetic material and condenses into tightly coiled chromosomes which contain the organism’s genes.
What is a nucleoplasm?
The cytoplasm within the nucleus
How big are ribosomes and are they membrane bound?
- very small organelles(around 20nm wide)
- they don’t have a membrane
How many subunits do ribosomes have and what are the measurement?
2 subunits.
smaller 40S subunit and larger 60S subunit.
What are the subunits in ribosomes made of?
Each subunit is made up of rRNA and protein.
Where are ribosomes found?
either floating freely in the cytoplasm or associated with the RER
What is the difference between proteins synthesised by ribosomes attached to the RER or ribosomes associated with the RER?
Ribosomes bound to the RER mainly synthesise proteins which will be exported out of the cell, whilst free- floating ribosomes synthesise proteins that will be used inside the cell.
What is the function of the mitochondrion?
site of the aerobic stages of respiration and produces ATP
What is the correlation between level of mitochondria and activity of cells?
The more metabolically active a cell is, the more mitochondria is contains
What is the shape of the mitochondria and is it membrane bound?
-rod shaped and membrane bound organelles(double membrane)
What is the function of the membrane?
controls what enters and exists the mitochondrion
What does the inner membrane contain in mitochondria ?
The inner membrane is packed is packed proteins involved in aerobic respiration and is folded into cristae
What is the benefit of the cristae?
Cristae increase the surface area available for the attachment for these protiens
What is the intermembrane space?
The space between the outer and inner membrane
What is the importance of the gel-like matrix?
Contains enzymes needed for aerobic respiration (thus ATP formation), as well as lipids, ribosomes and DNA
What is the benefit of mitochondrial ribosomes and mitochondrial DNA?
-they are smaller than cytoplasmic ribosomes and allow the mitochondrial to self replicate in response to increased energy demand.
What is the function of the cell surface(plasma) membrane?
- composed of a phospholipid bilayer
- has an essential role in controlling what enters and exists the cell.
- also has receptors on it, allowing it to interact with other proteins and other chemicals like hormones.
What is the cytoplasm and what does it do?
- a jelly-like substance e]which surrounds the organelle in a cell.
- is an aqueous solution and contains dissolved molecules that take part in metabolic reactions.
What is the cytoskeleton and its function?
- a complex network of proteins in a cytoplasm.
- gives the cell mechanical strength, maintains its shape and is also involved with the movement of organelles within the cell.
Microfilaments(size, subunits, functions)
- smallest of the 3 types(7nm diameter)
- polypeptides made up of repeating actin units
- mesh of microfilaments in the cytoplasm is important for maintaining the shape and mechanical strength of the cell
- microfilaments are also important for cell movement in cells like amoebas and lymphocytes
Intermediate filaments(size, subunits, functions)
- 2nd smallest (about 10nm diameter)
- made of interlocking protein fibres
- anchor the nucleus within the cytoplasm
- can extend outside the cell, allowing cells to stick together (stabilising tissues) and communicate with each other.
Microtubules(size, subunits, functions)
- largest type (18-30nm diameter
- repeating subunits of protein tubulin
- movement of substances and organelles within the cell’s cytoplasm using cytoskeletal motor proteins
- help movement of vesicles
- transport of substances through endocytosis and exocytosis
How do microtubules use motor proteins and how do motor proteins work?
- Motor proteins ‘walk’ along the microtubules, carrying organelles with them
- Motor proteins use energy from ATP hydrolysis to carry out their functions
How do microtubules enable chromosomes to be moved within the cell?
-the spindle(formed before a cell divides) is composed of threads of microtubules, which enable chromosomes to be moved within the cell
What are cilia and undulipodia?
-protrusions from cells which are surrounded by a cell membrane
How are cilia and undulipodia formed?
1) centrioles divide and line up at the cell membrane
2) microtubules then grow outwards from the centrioles, deforming the membrane and forming protrusions
What is the function of the cilia in epithelial cells?
-epithelial cells lining the airways have many cilia, which help move mucus along the airways
What is the benefit of receptors on the cilia?
-most cell types have at least 1 cilia which contains receptors, allowing the cell to detect signals in its environment
What is the name of the only human cell that have undulipodia and why?
- sperm cells
- enables them to move
Why are lysosomes highly abundant in secretory cells?
- they perform many roles which aid secretion
What are vesicles?
-Vesicles are organelles enclosed by a lipid bilayer that contain molecules such as enzymes.
What are lysosomes, where are they formed and what do they contain?
- lysosomes= an example of vesicles
- formed from the Golgi apparatus
- Contain digestive enzymes such as proteases, lipases, and lysozymes(which hydrolyse specific bacterial cell walls)
Why are lysosomes abundant in phagocytic cells?
-to keep the hydrolytic enzymes in separate compartment.
What are the roles of lysosomes in cells?
- hydrolysis of material ingested by phagocytic cells
- digestion of old and damages organelles to recycle their useful components
- complete breakdown of cells when they have died(autolysis)
- release of enzymes to digest material outside of cells(exocytosis)
What is the endoplasmic reticulum(ER)?
-is a network of membranes enclosing fluid-filled cavities and cisternae.
What is the RER?
-the RER is the intracellular transport system and has many ribosomes present on its surface
What is the function of the RER?
-provide large surface area for protein synthesis
How do proteins travel from the RER to the Golgi apparatus?
- The synthesised proteins actively pass through the membrane into the RER cisternae.
- Vesicles are pinched off from the cisternal membrane and travel to the Golgi.
What is the difference between the RER and SER?
-SER have no ribosomes on its surface and is often more tubular than the RER.
What’s the function of the SER?
- to synthesise, store and transport lipids and carbohydrates.
- It contains many enzymes which aid its function in lipid metabolism including synthesis of cholesterol and steroid hormones.
What is the Golgi apparatus and its function?
- is a set of fluid-filled, membrane-bound, flattened sacs.
- receives vesicles from the ER containing, proteins, lipids and carbohydrates before modifying and repackaging them.
- 2nd role= sort, package, and transport molecules around the cell.
What happens in the cisternae of the Golgi?
-proteins are modified by folding and joining them together with other molecules:
=lipids–>lipoproteins
=sugars–>glycoproteins
=polypeptides–>full protein
Where do processed molecules such as proteins, carbohydrates and lipids go after the Golgi apparatus?
-they bud off from the Golgi to from a vesicle
Where are vesicles from the Golgi apparatus sent?
- The cell surface for incorporation to the plasma membrane and secretion
- The cell surface to be exported outside the cell
- Other places within the cell for storage
What are the organelles involved with protein synthesis and how are they involved?
1) Nucleus-contains gene(for protein synthesis) and is the site of transcription and produces mRNA
2) Ribosomes/RER- Site of protein synthesis + translation
3) Vesicles- for transport of protein
4) Golgi apparatus- processes/modifies + repackages proteins
5) Vesicles- fuse of cell surface/plasma membrane(exocytosis)
what are some additional features of plants cells that animals don’t have?
- chloroplasts
- cell wall
- plant vacuole
what is the size and shape of chloroplasts and where are they found?
- small(around 4-10um)
- disc shaped
- found in plant cells and some protoctists.
What is the function of chloroplasts?
site of photosynthesis in plant cells
What is the role of the chloroplast envelope?
- its a double membrane that surrounds the organelle, and controls what enters and leaves the chloroplast
What is a granum(grana)?
- stacks of flattened discs
What is a single disc called and what is its role?
- thylakoid
- contains the pigment chlorophyll and is where the first stage of photosynthesis takes place
What are grana linked by?
-intergranal lamellae
What is the stroma and what is its role?
- the stoma is a fluid-filled chamber which surrounds the grana.
- this is where the 2nd stage of photosynthesis takes place. It contains enzymes, starch grains, DNA and ribosomes. This allows the chloroplast to quickly and easily manufacture the proteins needed for photosynthesis.
What is a vacuole?
-a fluid- filled sac containing different dissolved solutes
What is a tonoplast?
a single membrane surrounding the vacuole
What are the functions of the vacuole?
- maintain the structure of the plant cell as when its full, it pushes against the cell wall making the cell turgid
- contain sugars and amino acids which may act act temporary energy store for the plant
- contain pigment, which colour petals to attract pollinators
What is the plant cell wall made of?
polysaccharide cellulose
How are bundles of cellulose fibres made?
-multiple cellulose molecules join to form bundles of cellulose fibres
What are the functions of cellulose fibres?
- to provide mechanical strength to the cell to prevent its from bursting due to changes in water potential
- to provide support to the whole plant
- to allow for the passage of water through the plant across multiple cell walls
- maintains the cell’s shape
What is the fungal cell wall made of?
chitin
What are some features which are universal to all prokaryotic cells?
- cell membrane
- no nucleus-DNA is in the form of a loop and isn’t associated with histone proteins
- cytoplasm(lacks membrane- bound organelles)
- 70S ribosomes for translating and assembling(these are smaller than those found in eukaryotes)
What do glycogen granules and oil droplets do in prokaryotic cells?
-acts as an energy store
What is the cell wall in prokaryotes made of an what’s is purpose?
- peptidoglycan
- acts as a physical barrier to protect the prokaryote from mechanical forces and water potential changes
What is the difference between the cytoskeleton in prokaryotes and eukaryotes?
-much less developed cytoskeleton with no centrioles
How are prokaryotic cells divided?
The peptidoglycan wall is broken down by binary fission which is coordinated by the simple prokaryotic cytoskeleton
What are some non universal features of the prokaryotic cells?
- flagellum
- capsule
- pili
What is the flagella and what’s its role?
-the flagellum is a long hair-like structure that rotates allowing the prokaryotic cell to move
What is the capsule an what’s its role?
-the capsule is made up of secreted slime and it helps protect the prokaryote from detection by other cells. It also allows individual bacteria to stick together.
What’s the pili and what’s its role?
-pili are small, hair-like projections made of protein that extend out of the bacteria, enabling them to adhere to host cells or to each other
What’s a nucleoid?
-a region in the cytoplasm containing the main genetic material of the prokaryotic cell
What are plasmids?
small loops of naked DNA that are not part of the main circular DNA molecule
What is a benefit of plasmids?
- they can be replicated an passed on in cell division.
- plasmids can also be transferred from 1 prokaryotic cell to another through the pili, allowing for the transfer of useful genes such as antibiotic resistance
Is there a nucleus present in eukaryotic and prokaryotic cells?
Eukaryotic cells-present
Prokaryotic cells- absent
What is the difference in DNA between eukaryotic and prokaryotic cell?
eukaryotic cells- linear and packaged into chromosomes in the nucleus
prokaryotic cells-circular and freely floating in the cytoplasm
Does the cytoplasm in eukaryotic and prokaryotic cells have membrane bound organelles?
eukaryotic cells- contains membrane bound organelles
prokaryotic cells-lacks membrane bound organelles
Do prokaryotic and eukaryotic cells have a cell membrane?
yes, both of them do
Are the ribosomes in eukaryotic and prokaryotic cells bigger or smaller?
eukaryotic cells-larger
prokaryotic cells-smaller
What is the cell wall in eukaryotic and prokaryotic cells made of?
eukaryotic cells-cellulose or chitin
prokaryotic cells-murein/peptidoglycan
Are chloroplast present in eukaryotic and prokaryotic cells?
eukaryotic-sometimes
prokaryotic-absent
Are there flagellum in eukaryotic and prokaryotic cells?
eukaryotic cells-absent
prokaryotic cells- sometimes
Are there capsules in eukaryotic and prokaryotic cells?
eukaryotic-absent
prokaryotic-sometimes
Are there pili in eukaryotic and prokaryotic cells?
eukaryotic-absent
prokaryotic-sometimes
Are there plasmid in eukaryotic and prokaryotic cells?
eukaryotic- absent
prokaryotic- sometimes
